Fisiopatologia e Diagnóstico Clínico e Laboratorial do Trombembolismo Venoso 8021.1. Introdução 8021.2. Fisiopatologia 8021.3. Diagnóstico Clínico e Laboratorial 8031.3.1. Dosagem do D-dímero8032. Alterações Ecocardiográficas no Trombembolismo Pulmonar 8052.1. Introdução 8052.2. Ecocardiograma em Trombembolismo Pulmonar (TEP) de Baixo Risco 8052.3. Ecocardiograma em Trombembolismo Pulmonar de Alto Risco 8072.4. Recomendações 8133. Ultrassonografia Vascular no Diagnóstico da Trombose Venosa Profunda 813Doppler8133.1. Sinais Ultrassonográficos da Trombose Venosa: Modo B e3.1.1. Metodologia de Realização do Exame – Aspectos Técnicos8133.2. Protocolos de Realização de USV na TVP 8223.3. Protocolos de Exame 8233.3.1. Exame Completo de USV8233.3.2. Exame de Ultrassom de Compressão Completo das Veias dos Membros Inferiores8263.3.3. Exame de ultrassom de compressão estendido (3 pontos)8263.3.4. Exame de Ultrassom de Compressão de 2 Pontos8263.4. Diagnóstico Diferencial 8273.5. Recomendações 8273.6. Como Descrever o Laudo do Exame 8274. Ultrassonografia Vascular no Diagnóstico da recorrência de trombose venosa profunda e “síndrome pós-trombótica” 8294.1. Recorrência de trombose venosa (RTV) 8294.2. Diagnóstico Ultrassonográfico da Recorrência de Trombose 8304.3. Síndrome Pós-trombótica 8314.3.1. Fisiopatologia8314.3.2. Quadro Clínico8314.3.3. Diagnóstico8315. Protocolos de Seguimento com a Ultrassonografia Vascular após a Trombose Venosa Profunda 8345.1. Introdução 8345.2. Recanalização 8345.3. Recorrência da Trombose 8345.4. Insuficiência Valvular 8345.5. Discussão 8345.5.1. Primeiro USV Negativo8345.5.2. Trombose Proximal x Distal8345.5.3. Recorrência de Trombose Venosa Profunda8365.4. Recomendações 8366. Diagnóstico do Trombembolismo Pulmonar por Angiotomografia, Angio-RM e Angiografia Pulmonar 8376.1. Angiotomografia de Tórax (Angio-TC) 8376.1.1. Técnica e Protocolos de Exames8376.3. Gerações Antigas de Tomógrafos 8386.4. Critérios Diagnósticos 8386.5. Critérios Prognósticos 8406.6. Contraindicação e Situações Especiais 8406.7. Angiorressonância Magnética (Angio-RM) 8416.8. Angiografia Digital com Subtração 8426.9. Recomendações 8427. Cintilografia Pulmonar 8427.1. Evidências 8427.1.1. Introdução8427.1.2. Evidências Relacionadas aos Critérios de Interpretação dos Exames8437.1.3. Acurácia Diagnóstica8437.1.4. Indicações da Cintilografia Pulmonar por Limitações da Angiotomografia Pulmonar8457.1.5. Protocolo8457.1.6. Reconstrução de imagens8467.1.7. Interpretação8467.1.8. Trombembolismo Pulmonar Crônico8467.1.9. Achados Diagnósticos Adicionais8477.1.10. Pitfalls na Interpretação de Estudos V/Q8477.1.11. O Futuro da Avaliação de EP por Técnicas de Medicina Nuclear8477.1.12. Algoritmo Clínico para Investigação de Pacientes com Suspeita de TEP8487.1.13. Algoritmo Diagnóstico8497.1.14. Conclusões850Referências 850O trombembolismo venoso (TEV) manifesta-se como trombembolismo pulmonar (TEP) e/ou trombose venosa profunda (TVP), fazendo parte de um mesmo espectro de doença e apresentando os mesmos fatores de risco. É a terceira causa mais frequente de síndrome cardiovascular aguda no mundo, com potencial risco de vida. No Brasil, segundo dados do Ministério da Saúde coletados entre os anos de 2010 e 2021, o número de internações relacionadas ao TEV ultrapassou 520 mil, com um total de mais de 67.000 óbitos entre 2010 e 2019. Apresenta um alto índice de mortalidade, sendo que aproximadamente 34% dos pacientes acometidos morrem subitamente ou em poucas horas após a primeira manifestação, ou seja, antes mesmo de receberem qualquer tipo de tratamento.Quase 2/3 dos casos de TEV manifestam-se por TVP isolada, sendo a maioria trombose das veias proximais do membro inferior e um terço por TEP.  relataram maior incidência de TEV nos estados do Sul, onde as temperaturas são mais baixas. A incidência de casos de TEV nesses locais apresentou uma média de 2,86 para cada 100.000 habitantes. Na literatura, diversos estudos relacionam a presença de TEV com a variação climática. No Brasil, Ohki et al.  A mulheres são mais comumente afetadas na juventude, sobretudo no puerpério. Durante a gestação, o uso do tabaco, a trombofilia e/ou a história prévia de TEV aumentam o risco nesse grupo de pacientes. Outras situações, como imobilidade prolongada, obesidade, neoplasias, cirurgias de grande porte com tempo anestésico prolongado, politraumatismos, varizes de membros inferiores, terapia de reposição hormonal e doenças cardiovasculares, são consideradas de risco para TEV, reconhecendo-se que há variação na predição do risco entre essas causas. Tal síndrome clínica aumenta exponencialmente com a idade, mesmo com a aplicação de estratégias de prevenção. A etnia é considerada um fator de risco para TEV, com uma incidência significativamente maior entre caucasianos e afro-americanos e menor entre hispânicos e asiáticos. De modo geral, aproximadamente 25-50% dos pacientes que apresentam o primeiro episódio de TEV têm condição idiopática, sem um fator de risco facilmente identificável. A mortalidade precoce no TEV está fortemente associada ao acometimento pulmonar, na forma de TEP, além de idade avançada, neoplasias e doença cardiovascular subjacente. O índice de recorrência é relevante, e os casos não fatais podem cursar com sequelas como hipertensão pulmonar nos casos de TEP crônico ou síndrome pós-trombótica na TVP. Notadamente, houve uma redução dos óbitos por conta da melhor condução diagnóstica e terapêutica após a publicação de posicionamentos e diretrizes internacionais sobre o tema. O diagnóstico de TEV pode não ser tão objetivo; portanto, é necessário foco na abordagem diagnóstica de TEP e TVP, visto que a falha no diagnóstico correto pode ser fatal ou levar a comorbidades permanentes.Nesse contexto, o Departamento de Imagem Cardiovascular (DIC/SBC), o Colégio Brasileiro de Radiologia (CBR), a Sociedade Brasileira de Angiologia e Cirurgia Vascular (SBACV) e a Sociedade Brasileira de Medicina Nuclear (SBMN) desenvolveram em conjunto este documento. O objetivo é abordar aspectos clínicos e diagnósticos, visando a criar uma recomendação única entre as quatro sociedades, que sirva como fonte de informação para os médicos brasileiros, assim como padronização do diagnóstico clínico, laboratorial e por imagem do TEV. A abordagem profilática e terapêutica do TEV não está no escopo desse documento.expertisedos participantes. Cada grupo de trabalho compilou os dados, redigiu os escritos e posteriormente apresentou o texto revisado para os ajustes finais. Os temas mais polêmicos foram discutidos em reunião com a participação da maioria. Quando necessário, foram realizadas correções no texto original.A criação dessa recomendação teve como base diretrizes e estudos populacionais e de caso existentes na literatura, assim como aEssa recomendação é direcionada a médicos clínicos ou cirurgiões, visando a melhor informação a respeito da abordagem diagnóstica do TEV, fornecendo dados sobre a acurácia das ferramentas diagnósticas utilizadas na prática diária. Para os médicos imaginologistas, a descrição detalhada dos protocolos de exames poderá auxiliar na realização de diagnósticos mais precisos, contribuindo para a melhor condução clínica dos casos suspeitos ou confirmados. Cerca de um terço de todos os casos de TEP é fatal, e o câncer mostra-se um dos muitos estados de doença associados a um maior risco de doença trombembólica. Aproximadamente dois terços dos casos de TEV são constituídos por TVP, 85-90% em membros inferiores e um terço por TEP.  Nesse contexto, devemos sempre lembrar que o TEV é doença grave e passível de prevenção.O espectro do trombembolismo venoso (TEV) compreende a trombose venosa profunda (TVP) e a embolia pulmonar (TEP). A doença trombembólica é a terceira doença cardiovascular aguda mais comum depois das síndromes isquêmicas cardíacas e do acidente vascular encefálico. A manifestação clínica dessas doenças abrange um amplo espectro, desde clinicamente silenciosa à embolia maciça, levando ao óbito. A TVP é uma afecção frequente e potencialmente fatal, tendo como principal complicação a embolia pulmonar, que pode ser considerada a primeira causa de morbimortalidade evitável no ambiente intra-hospitalar. Além disso, também pode levar, como complicação crônica, a síndrome pós-trombótica (SPT), o que acarreta importante impacto socioeconômico. Tais complicações podem ocorrer, apesar do diagnóstico e da terapêutica adequados, tendo seu potencial deletério diminuído quão mais cedo for realizado o diagnóstico e instituído o tratamento correto.phlegmasia cerulea dolens(PCD). A PCD caracteriza-se pela oclusão total ou suboclusão maciça das veias de drenagem do membro (segmento femoroilíaco) e colaterais, podendo se estender à microcirculação. A hipertensão venosa chega a tal nível que impede o fluxo arterial.  Com a elevada pressão hidrostática e sequestro de fluidos para o interstício, há formação de edema endurecido de todo o membro, que pode acumular de 3 a 5 litros em volume e levar ao colapso das arteríolas, flictenas pela isquemia tecidual, equimose púrpura, cianose, perda dos pulsos distais, colapso circulatório e choque hipovolêmico. A TVP pode ocorrer tanto em pacientes internados quanto ambulatoriais, tendo sintomatologia inespecífica, podendo variar desde completamente assintomática até um Quadro catastrófico, como naÉ importante ressaltar que o diagnóstico da TVP tem início com a história clínica. Deve-se atentar para antecedentes que potencializem ou predisponham ao risco aumentado de desenvolver fenômenos trombembólicos venosos, conforme postulado por Virchow:- ALTERAÇÕES DO FLUXO (estase):idade, imobilização ≥3 dias ou inatividade física como em pós-operatório, acidente vascular encefálico, fratura de quadril ou joelho, cirurgia geral de grande porte , traumatismo grave, lesão da medula espinal com paresia de membro, imobilização de extremidades com aparelhos gessados ou órteses, viagem prolongada em área confinada, gravidez, insuficiência cardíaca congestiva, varizes, DPOC e queimaduras, entre outras. - LESÃO DE ENDOTÉLIO (traumatismo):idade avançada , tabagismo, antecedente trombembólico conhecido, traumatismos, cirurgias e cateteres venosos, entre outras. - HIPERCOAGULABILIDADE:neoplasias e/ou seus tratamentos, trombofilias hereditárias ou adquiridas, obesidade, uso de contraceptivos orais contendo estrogênio e reposição hormonal, gravidez, tabagismo, doenças infecciosas agudas, síndrome nefrótica e doença inflamatória intestinal, entre outras. Identificado o risco epidemiológico para TVP, que deve ser obrigatório, proceder ao exame físico do paciente. O diagnóstico clínico da TVP apresenta baixa sensibilidade e especificidade, visto que apenas 20-40% dos pacientes com Quadro clínico sugestivo têm a doença confirmada. Os sinais e sintomas mais comuns apresentados pelos pacientes com TVP são dor e edema. Apesar da baixa acurácia do diagnóstico clínico, é importante ressaltar que, a princípio, todo edema assimétrico em extremidades inferiores deve ser valorizado até a completa avaliação diagnóstica finalizada.Doppleré o método de escolha por sua alta acurácia, sendo de fácil execução, boa reprodutibilidade e inócuo. Entretanto, a disponibilidade dessa modalidade de diagnóstico é limitada em centros médicos menores e ambulatórios e durante os turnos noturnos e de fins de semana. Por outro lado, deve-se levar em conta que em uma parcela considerável dos casos (20-50%) o paciente pode apresentar Quadro de TVP extensa , sem ter qualquer sintomatologia sugestiva. A suspeição clínica é essencial para o diagnóstico nesses casos, mas convém ter por base que o diagnóstico clínico não mostra sensibilidade/especificidade satisfatórios, e sua confirmação deve ser feita por meio de exames complementares. Entre esses métodos, a ultrassonografia vascular com A TVP proximal é a de maior potencial emboligênico. Outras classificações, que podem determinar a gravidade da TVP, são aquelas baseadas no grau de extensão do trombo; os mais extensos costumam gerar consequências maiores por carregarem a hipertensão venosa e o grau de obstrução da luz parcial e total. O grau de ocupação da luz, bem como sua localização e extensão determinará a gravidade e o prognóstico do Quadro clínico da trombose venosa.A TVP é classificada como proximal quando envolve as veias femorais e/ou poplítea, com ou sem o envolvimento de outras veias da perna; e distal quando envolve as veias profundas infrapatelares.  desenvolveram um modelo de predição clínica para classificar os pacientes quanto ao risco de TVP. O método, quando associado a exames complementares não invasivos, mostrou-se factível e útil em diversos estudos. O mesmo grupo implementou modificações em 2003, tornando mais fácil o entendimento dos clínicos.  Várias sociedades de especialidade e consensos recomendam a utilização de modelos de predição clínica para estimar a probabilidade do diagnóstico de TVP, antes da realização da USV.  Entre as ferramentas, a mais utilizada é o escore de Wells associado aos valores séricos do D-dímero.  , da extensão da TVP  e do grau de probabilidade , sendo melhor nos pacientes ambulatoriais com TVP proximal e que apresentam escore de alta probabilidade (>2). De modo geral, Silveira et al., em estudo populacional, obtiveram uma acurácia diagnóstica de 0,56 (AUC – área sobre a curva) para pacientes internados. Em pacientes ambulatoriais, a eficácia do escore pode variar de 11,9% a 79,5%.  O ensaio quantitativo do D-dímero, com base no método rápido de Elisa, apresenta alta sensibilidade (próximo de 95%) para o diagnóstico. No entanto, o teste revela baixa especificidade (40%), visto que o D-dímero pode estar aumentado em várias condições além do trombembolismo venoso, como nos casos de infarto agudo do miocárdio, acidente vascular encefálico, inflamações, câncer ativo e gravidez. A especificidade também cai com a idade, e em idosos pode alcançar apenas 10%. Em uma revisão sistemática, apurou-se que o uso de um ponto de corte ajustado para pacientes acima de 50 anos visando a afastar a presença de TVP (idade do paciente em anos [acima de 50] x 10 µg/L) parece tão seguro quanto o ponto de corte padrão, o que foi apontado como uma recomendação na última diretriz europeia de 2019. A medição do D-dímero (um produto de degradação do coágulo de fibrina reticulado) é amplamente utilizada na investigação de pacientes com suspeita de trombembolismo venoso. Consequentemente, um teste quantitativo negativo do D-dímero tem um alto valor preditivo negativo para TEV. Os resultados dos estudos revelam que o risco de desenvolvimento de TEP em pacientes com baixa probabilidade clínica, que não são tratados após um teste de D-dímero negativo, é <1% em três meses após a avaliação inicial. Por outro lado, por conta de seu baixo valor preditivo, um teste D-dímero quantitativo positivo não modifica a probabilidade pré-teste (clínica) e, portanto, é clinicamente inútil. Um teste de D-dímero negativo de alta sensibilidade em combinação com uma baixa probabilidade pré-teste pode excluir a TVP.  Evidências recentes também sugerem que níveis muito altos do D-dímero estão associados a um aumento de quatro vezes na probabilidade de TEP.  Entretanto, quando a probabilidade clínica é alta, independente dos níveis do D-dímero, é obrigatória a realização de um exame de USV para confirmar ou descartar a presença de TVP   de 0,778. Por outro lado, no escore de Genebra a sensibilidade variou de 55,3% a 73,6%; e especificidade, de 48,8% a 90,0%, com área sobre a curva (AUC) de 0,693. Tais escores, quando combinados com a dosagem do D-dímero, como descrito anteriormente, apresentam implicação importante na condução diagnóstica e na indicação de testes de imagem e4.Na avaliação da probabilidade clínica de TEP, as estratégias diagnósticas dependerão da estabilidade hemodinâmica do paciente. Além do Quadro clínico e do D-dímero, as técnicas complementares recomendadas para diagnóstico de TEP são a angiotomografia pulmonar (angio-TC), a cintilografia com V/Q Spect e o ecocardiograma e6. CaA utilidade do ecocardiograma (transtorácico e/ou transesofágico) no trombembolismo pulmonar agudo (TEP) reside na investigação de sobrecarga pressórica de ventrículo direito  e na avaliação funcional dessa cavidade. Pacientes com episódio trombembólico sem repercussão hemodinâmica cursam, na maioria das vezes, com exames normais. Em pacientes com instabilidade hemodinâmica, o ecocardiograma desempenha importante papel de apoio nas etapas de diagnóstico e acompanhamento não invasivo da resposta ao tratamento. O valor preditivo negativo da ecocardiografia varia entre 40-50%; e o resultado normal não exclui TEP.  Ainda que não contribua para o diagnóstico, representa importante ferramenta para discriminação prognóstica: a ausência de alterações de tamanho ou função do VD indicam bom prognóstico.  O exame é também importante para definir diagnósticos diferenciais de dispneia aguda.O ecocardiograma não é um exame obrigatório na rotina diagnóstica em pacientes com suspeita de TEP com estabilidade hemodinâmica nos algoritmos de investigação.  As recomendações gerais definem janelas e cortes essenciais que fornecem as imagens exigidas na obtenção de todos os dados necessários para a quantificação:O estudo do ventrículo direito, com seu formato único em crescente, apresenta dificuldade técnica inerente à geometria assimétrica da cavidade. Entretanto, a padronização da técnica para um exame completo foi estabelecida em 2015 em documento conjunto atualizado das sociedades de ecocardiografia norte-americana e europeia. Paraesternal esquerda, eixo longo e curto;Apical de 4 câmaras;Apical de 4 câmaras focando cavidade ventricular direita;Paraesternal esquerda demonstrando a via de entrada de VD;Subcostal.O Por outro lado, a detecção de alterações correspondentes à sobrecarga de pressão e à disfunção ventricular direita  permite o diagnóstico de TEP maciço e a terapia de reperfusão de emergência, mesmo na impossibilidade de realização de angiotomografia de tórax ou cintilografia de ventilação e perfusão. Em todos os pacientes com suspeita clínica de TEP e instabilidade hemodinâmica, o ecocardiograma é exame obrigatório, pois consegue detectar com segurança alterações em cavidades direitas tradutoras do aumento súbito e grave da resistência vascular pulmonar (pós-carga de VD), responsáveis por disfunção e hipotensão. Nesses pacientes, o registro de um exame normal elimina em definitivo a hipótese de embolia pulmonar maciça.  e ocorre em apenas 4% dos casos de embolia pulmonar em geral, podendo alcançar 18% de prevalência nos pacientes com TEP em unidades de terapia intensiva. O único achado ecocardiográfico patognomônico de TEP é a presença de trombos móveis em cavidades direitas, tronco e/ou ramos de artéria pulmonar . Tal ac são:a) As alterações fundamentais relativas ao trombembolismo agudo grave b) Dilatação de VD;c) Disfunção de VD;Sobrecarga pressórica pulmonar. Ocorre em 30-40% dos pacientes com TEP e indica pior prognóstico.  No entanto, o sinal 60/60 está presente em apenas 12%; e o sinal de McConell em 20% dos pacientes não selecionados. Outro sinal de aumento da pós-carga do VD é redução do tempo de aceleração pulmonar e a presença de desaceleração mesossistólica  reduzido. O ecocardiograma 3D pode ser utilizado em laboratórios com experiência na técnica, para a avaliação da análise evolutiva dos pacientes com TEP maciço e submetidos a trombólise. Nasstrainda parede livre do VD foi um marcador prognóstico independente de mortalidade sem a análise de outros parâmetros como Tapse e S’ do anel tricúspide.  Além dostraindo VD, a dilatação dele foi um marcador prognóstico de pacientes com a forma grave da doença.  Concluindo, o papel da ecocardiografia nesse cenário é fundamental, não só do exame completo como também do ecocardiograma focado (point of care), recentemente abordado pelo posicionamento do DIC/SBC. No início de 2020, a pandemia do novo coronavírus (covid-19) acrescentou um novo e crucial papel para a ecocardiografia. Até o momento, os achados registrados em publicações indicam que o vírus causa aumento significativo no risco de trombose venosa (traduzida por elevação do D-dímero) e, consequentemente, da ocorrência de TEP. Por outro lado, parece provocar trombose local em vasos da microcirculação pulmonar, gerando sobrecarga pressórica sobre o ventrículo direito. Ambos os fatores podem resultar em dilatação e disfunção de VD, mensurados por vários parâmetros, como citado no (classe I/nível de evidência C).O ecocardiograma a beira do leito é exame obrigatório em todo paciente com suspeita clínica de TEP e instabilidade hemodinâmica.  No entanto, representa uma importante ferramenta para discriminação e definição do diagnóstico diferencial.  (classe IIa/nível de evidência B).O ecocardiograma não é exame obrigatório na rotina diagnóstica em paciente com suspeita de TEP e hemodinamicamente estável, nos algoritmos de investigação.  Os trombos originam-se dentro do sistema venoso, muitas vezes em uma área de fluxo mais lento, como a cúspide de uma válvula, propagando-se ao longo do lúmen da veia, que é preenchido do modo parcial ou total pelo trombo. Na fase aguda, os trombos induzem uma resposta inflamatória na parede venosa adjacente; dessa maneira, o termo tromboflebite é aplicado, com sintomas de câimbras e dor local.  Muitos fatores podem iniciar a trombose venosa: no caso de cateteres venosos, o traumatismo da parede inicia a resposta inflamatória que leva a trombose dentro do lúmen venoso.  Entretanto, os sinais clínicos da TVP muitas vezes podem ser inespecíficos; portanto, a anamnese, o exame físico e o conhecimento dos principais fatores que se relacionam com o processo trombótico são fundamentais. A trombose venosa profunda (TVP) é uma condição que deve ser diagnosticada e tratada adequadamente, podendo levar ao tromboembolismo pulmonar (TEP), situação potencialmente fatal.  De modo geral, a avaliação dos pacientes com suspeita de TVP passa por estratificação, escore clínico, dosagem do D-dímero e realização da ultrassonografia vascular (USV). Os fatores de risco para trombose venosa podem ser agrupados em modelos de predição clínica, sendo o escore de Wells um método bem estabelecido pelo qual se pode acessar a probabilidade clínica do diagnóstico da TVP. Uma vez que o diagnóstico clínico da TVP possa estar correto em apenas 50% dos casos, exames complementares são necessários para confirmar ou excluir o diagnóstico.  Dessa forma, analisamos as imagens da parede e do lúmen venoso em tempo real no modo bidimensional (modo B), realizando as manobras de compressão com o transdutor e o estudo do mapeamento de fluxo em cores (MFC),Dopplerpulsado ePower Doppler. A USV é o exame de escolha na suspeita de TVP, e fornece informações da anatomia e funcionalidade venosa. Não é um procedimento invasivo, não usa contraste nefrotóxico e é reprodutível e de baixo custo, mas é examinador e depende de equipamento.  a técnica para realização do exame de pesquisa de TVP inclui os seguintes itens.Como publicado recentemente pelo Departamento de Imagem Cardiovascular,  Para o exame das tibiais posteriores, fibulares e musculares da panturrilha, eventualmente podemos manter o paciente em decúbito dorsal e a perna dobrada com o pé apoiado na cama. Por outro lado, o estudo das veias cavas e ilíacas é realizado com o paciente em decúbito dorsal, lembrando-se da necessidade de preparo prévio para diminuição dos gases intestinais. Na suspeita de síndrome pós-trombótica, o paciente, quando possível, deve ser examinado também em posição ortostática, e para membros superiores, deve ser posicionado em decúbito dorsal, com o membro estendido paralelamente ao corpo e discretamente afastado dele.Para membros inferiores, o paciente deve ser posicionado em decúbito dorsal, com o tronco e cabeça elevados até 30°, posição confortável, próximo da borda do leito, do mesmo lado do examinador e fazendo uma leve rotação lateral da articulação coxofemoral e flexão do joelho. Para o exame das veias femorais comum e femoral superficial, e tibiais posteriores, o paciente deve manter a perna em rotação externa e o joelho levemente fletido. Para o exame da veia poplítea e das veias fibulares (peroneiras), o paciente pode ficar em decúbito ventral ou lateral, apoiado no membro contralateral e com o joelho levemente fletido. Neste último caso, se houver condições clínicas, o paciente pode permanecer sentado, com as pernas pendentes ao lado da cama. Dopplersespectral e colorido. A escolha do transdutor baseia-se primordialmente na relação frequência do transdutor e da localização do objeto a ser estudado. Transdutores de maior frequência fornecem melhor qualidade de imagem, porém têm menor penetração nos tecidos. Em contrapartida, os transdutores de menor frequência permitem uma maior penetração, ainda que ocorra perda de qualidade da imagem. Habitualmente, são utilizados transdutores lineares com frequência entre 4 a 10 MHz para estudo das veias profundas dos membros inferiores ou superiores, e transdutores lineares com frequência entre 7 a 13 MHz para estudo das veias superficiais dos membros inferiores ou superiores. Nos casos de membros inferiores edemaciados e em pacientes obesos, ou seja, com diâmetros muito aumentados e, também, para a avaliação das veias ilíacas e da veia cava inferior, por vezes torna-se necessário a utilização de transdutores convexos multifrequenciais (entre 1 a 5 Mhz), os quais exibem frequências de onda menores e maior penetração das ondas de ultrassom. Ospresetsdevem ser adequadamente calibrados para o exame do sistema profundo e superficial, com zona focal ajustada e escala de cinza, de modo que o lúmen seja escuro na ausência de estase ou trombose. O ganho doDoppler, seja colorido ou espectral, deve ser ajustado para uma escala de velocidades baixas e adequada na avaliação do fluxo venoso. Quando o exame se direciona à avaliação das veias profundas, os equipamentos de USV devem ser ajustados com foco e densidade de linha adequados para o exame bidimensional e as estruturas são avaliadas em cortes transversos e longitudinais.  Em geral, as veias são facilmente compressíveis pelo transdutor. Deve-se trabalhar com equipamentos capazes de fornecer uma boa qualidade de imagem em modo B e que sejam dotados deModo B:inicialmente, o transdutor é posicionado abaixo do ligamento inguinal, visualizando-se a junção safenofemoral. Faz-se, então, uma varredura transversa e longitudinal de todo o sistema venoso do membro inferior. No corte transverso, deve ser realizada a compressão com o transdutor, em especial ao longo da veia femoral comum, da veia femoral e da veia poplítea, com distâncias entre cada compressão em torno de 2 a 3 cm. A técnica de uso da USV para diagnóstico da TVP foi inicialmente descrita por Talbot em 1982, e vem sendo aprimorada ao longo dos anos.  Uma veia normal e sem trombose demonstra completo colabamento luminal pela compressão de suas paredes pelo transdutor  e com mapeamento de fluxo em cores (inferiores). A = artéria, V = veia.Doppler:Objetiva-se registrar as velocidades do fluxo venoso, que são baixas em condições normais aoDopplerpulsado. Na presença de trombose venosa, as velocidades podem estar ainda mais reduzidas, necessitando de ajustes em suas escalas. O fluxo venoso nos membros inferiores é espontâneo e apresenta-se fásico com a respiração e as variações da pressão intra-abdominal , o paciente deverá estar em posição de Trendelenburg reverso.  Muitos dos protocolos realizados por não especialistas em imagens vasculares foram desenvolvidos para locais em que não há disponibilidade de profissional especializado ou mesmo para reduzir o número de chamadas fora do horário de funcionamento habitual do laboratório de USV. Assim, apenas um protocolo de simples realização não é suficiente para afastar definitivamente a TVP. Além do adequado treinamento sob supervisão, mostra-se fundamental a análise da probabilidade pré-teste associada, ou seja, o uso de escores clínicos de probabilidade de TEP/TVP e o conhecimento da menor acurácia da USV no diagnóstico da TVP infragenicular e na TVP assintomática. Nas publicações que avaliaram esse tema, não houve prejuízo maior para o paciente, e o seguimento de protocolos bem estruturados, contemplando os critérios de probabilidade clínica de Wells, ajudou na melhora da acurácia do exame e no encaminhamento adequado dos pacientes com difícil acesso ao especialista. Com a maior disponibilidade de aparelhos de USV, que habitualmente apresentam ótima resolução, o treinamento de profissionais não especialistas em imagem vem se tornando muito frequente e ganhando aceitação, sobretudo nos setores de emergência e urgência ou ainda em locais distantes. Assim, a realização de exames para pesquisa de TVP por intensivistas, emergencistas e residentes do último ano de radiologia/US/ecografistas vasculares é uma realidade atual. A acurácia do exame de US realizado por emergencistas foi testada em uma metanálise e revisão sistemática que incluiu 16 estudos com 2.379 pacientes. Os autores encontraram uma prevalência em TVP de 23% , com sensibilidade média dos exames realizados por emergencistas de 96,1 %  e uma especificidade de 96,8 % . Entretanto, os estudos incluídos eram muito heterogêneos, os treinamentos dos emergencistas foram mal descritos e não havia, na maioria deles, um seguimento maior. Um estudo prospectivo publicado no mesmo ano e com um número muito menor de pacientes não reproduziu esses dados, o que refletiu a necessidade de protocolos de treinamento rigorosos desses profissionais, visto que, nesse estudo, apenas os três primeiros exames realizados por não especialistas foram supervisionados. Dopplerespectral. Os protocolos de exames vão usar esses parâmetros para chegar ao diagnóstico: compressibilidade da veia (o mais importante); calibre (diâmetro) da veia, aspecto ecográfico das paredes e do lúmen venoso, e a análise do mapeamento de fluxo em cores e doDopplerespectral.Para a pesquisa de trombose venosa pelo USV, convém analisar os parâmetros descritos, ou seja, a combinação de componentes da escala de cinza (modo B) com manobras de compressão pelo transdutor e avaliação pelo mapeamento de fluxo em cores ePoint of Care). Eles são escolhidos conforme a disponibilidade de aparelho de US no local em que o paciente é atendido, do horário do atendimento e da presença de médico especialista ou não para realizar o exame de USV.Existem alguns protocolos de pesquisa de TVP bastante estabelecidos, que podem ser completos ou não (Protocolos para pesquisa de TVP e15:Exame completo de ultrassonografia vascular –Exame de ultrassom de compressão completo das veias dos membros inferiores –Exame de ultrassom de compressão estendido (3 pontos) –Exame de ultrassom de compressão de 2 pontos – O protocolo completo constitui na utilização de todos os recursos do US para definir o diagnóstico da trombose, ou seja, avaliação da compressibilidade, calibre, aspecto ecográfico da parede e lúmen eDopplercolorido e espectral de todas as veias infrainguinais até o tornozelo, em todos os segmentos: veias femorais, poplítea, tibiais posteriores e fibulares  a realização do exame completo de ecografia vascular para o diagnóstico de TVP aguda. Além de ser uma abordagem mais completa do paciente, a inclusão do exame do segmento infrapoplíteo permite o diagnóstico de outras doenças musculosqueléticas, que fazem parte do diagnóstico diferencial da TVP, como cisto de Baker, hematomas ou doenças musculares. bulares . De modDopplercolorido , observação da fasicidade do fluxo e análise da morfologia doDopplerespectral em veias femorais e poplíteas. Ainda que seja realizado de forma completa apenas o exame do membro sintomático, é relevante lembrar que a análise doDopplerespectral deverá ser feita em ambas as veias femorais comuns para avaliar a simetria. Quando houver assimetria no padrão do fluxo, há a necessidade de estudar as veias intrabdominais (classe I/nível de evidência A). Realiza-se o exame com compressões a cada 2 cm de intervalo, análise do preenchimento do vaso pelo Esse protocolo utiliza apenas a avaliação da compressibilidade de todas as veias infrainguinais até o tornozelo, em todos os segmentos  com a mesma especificidade .  Um resultado bastante semelhante foi obtido em um estudo de acurácia do protocolo de 3 pontos realizado por médicos emergencistas .  Uma metanálise recente, que incluiu 17 estudos de 16 artigos originais, comparou o protocolo de Pocus (Point of Care UltraSound) de 3 pontos com o de 2 pontos. No geral, o Pocus de 2 pontos apresentou sensibilidade combinada  x 10 in µg/L) appeared to be as safe as the standard cutoff value, which was pointed out as a recommendation in the latest 2019 European guideline.Measurement of D-dimer (a degradation product of cross-linked fibrin clot) is widely used in the investigation of patients with suspected VTE.Consequently, a negative quantitative D-dimer test has a high negative predictive value for VTE. The results of the studies reveal that the risk of development of PE in patients with low clinical probability who are not treated after a negative D-dimer test is <1% within 3 months of the initial evaluation. However, because of its low predictive value, a positive quantitative D-dimer test does not modify the pretest  probability and is therefore clinically useless. A highly sensitive negative D-dimer test combined with a low pretest probability can exclude DVT.Recent evidence also suggests that very high D-dimer levels are associated with a 4-fold increase in the probability of PE.However, when the clinical probability is high, regardless of D-dimer levels, VUS is mandatory to confirm or rule out the presence of DVT pulmonary angiography, V/Q SPECT scintigraphy, and echocardiography and6. The usefulness of echocardiography  in acute pulmonary embolism (PE) lies in the investigation of right ventricular (RV) pressure overload  and in functional assessment of the RV. In most cases, patients with thromboembolic episodes without hemodynamic repercussions have normal test results. In hemodynamically unstable patients, echocardiography plays an important supporting role in the stages of diagnosis and noninvasive monitoring of treatment response.The negative predictive value of echocardiography ranges from 40%-50%, and a normal result does not exclude PE.Despite not contributing to the diagnosis, it represents an important tool for prognostic discrimination: the absence of changes in RV size or function indicate a good prognosis.The test is also important to define differential diagnoses of acute dyspnea.Echocardiography is not a mandatory test in the diagnostic routine for hemodynamically stable patients with suspected PE in diagnostic algorithms.The general recommendations define the essential windows and views that provide the images required to obtain all the necessary data for quantification:In the study of the RV, with its unique crescent shape, there are technical difficulties inherent in the asymmetric geometry of the cavity. However, the technique for a comprehensive examination was standardized in 2015 in an updated joint document from the American Society of Echocardiography and the European Association of Cardiovascular Imaging.Left parasternal, long- and short-axis;Apical 4-chamber;RV-focused apical 4-chamber;Left parasternal RV inflow;Subcostal.Conversely, the detection of changes corresponding to RV pressure overload and dysfunction  allows the diagnosis of massive PE and emergency reperfusion therapy, even if chest CT angiography or ventilation and perfusion scintigraphy cannot be performed.Echocardiography is mandatory for all hemodynamically unstable patients with clinically suspected PE, as it can reliably detect changes in the right cavities that reflect a sudden and severe increase in pulmonary vascular resistance (RV afterload), responsible for dysfunction and hypotension. In these patients, normal test results definitively rule out the hypothesis of massive PE.and occurs in only 4% of overall cases of PE, reaching an 18% prevalence in patients with PE in intensive care units.The only pathognomonic echocardiographic finding of PE is the presence of mobile thrombi in the right cavities and/or pulmonary trunk or branch arteries . This fare:Key changes related to severe acute PERV dilatation;RV dysfunction;Pulmonary pressure overload. It occurs in 30%-40% of patients with PE and indicates worse prognosis.However, the 60/60 sign is present in only 12%, and McConnell sign in 20% of unselected patients. Another sign of increased RV afterload is reduced pulmonary acceleration time and the presence of mid-systolic deceleration .The 3D echocardiography can be used in laboratories with experience in the technique for an evolutionary analysis of patients with massive PE treated with thrombolysis.In addition to RV strain, RV dilatation was a prognostic marker of patients with the severe form of the disease.In conclusion, echocardiography plays a key role in this scenario, not only the comprehensive but also the problem-focused echocardiogram (point of care), as recently addressed by the position statement of the Department of Cardiovascular Imaging of the Brazilian Society of Cardiology (DIC/SBC).In the beginning of 2020, the new coronavirus pandemic (COVID-19) added a crucial new role for echocardiography. So far, findings reported in the literature indicate that the virus causes a significant increase in the risk of venous thrombosis (translated by increased D-dimer) and, consequently, in the occurrence of PE. Conversely, it seems to cause local thrombosis in pulmonary microcirculation vessels, leading to RV pressure overload. Both factors can result in RV dilatation and dysfunction, measured by various parameters, as described in(grade of recommendation: I/level of evidence: C).Bedside echocardiography is a mandatory test for all hemodynamically unstable patients with clinically suspected PE.However, it represents an important tool for discriminating and defining differential diagnoses.(grade of recommendation: IIa/level of evidence: B).Echocardiography is not mandatory in the diagnostic routine for hemodynamically stable patients with suspected PE in diagnostic algorithms.Thrombus formation often occurs in regions of slow flow within the venous system, such as the cusp of a valve, spreading along the vein lumen, which is completely or partially filled by the thrombus. During the acute phase, the thrombi induce an inflammatory response on the adjacent venous wall. This is known as thrombophlebitis, and symptoms include cramp and local pain.Many factors can trigger venous thrombosis. In the case of venous catheters, wall trauma induces the inflammatory response that leads to thrombosis within the vein lumen.However, clinical signs of DVT can often be nonspecific; therefore, medical history, physical examination, and awareness of the main factors associated with the thrombotic process are essential.If not properly diagnosed and treated, deep vein thrombosis (DVT) can lead to pulmonary embolism (PE), a potentially fatal condition.The evaluation of patients with suspected DVT usually involves stratification, clinical score, D-dimer measurement, and intravascular ultrasound (VUS).Risk factors for venous thrombosis can be grouped in clinical prediction models. The Wells score is a well-established method used to assess the clinical probability of a DVT diagnosis. Considering that only 50% of clinical DVT diagnoses may be correct, supplementary imaging is required to confirm or rule out diagnosis.Therefore, real-time B-mode ultrasound (US) images of the vein wall and lumen are obtained with transducer compression maneuvers and color flow Doppler (CFD), pulsed Doppler, or power Doppler.VUS is the method of choice for suspected DVT, providing information on venous anatomy and function. In addition, it is noninvasive, does not use nephrotoxic contrast, and is reproducible and inexpensive, although it is operator- and device-dependent.the imaging technique to study DVT includes the following items:As recently stated by the Department of Cardiovascular Imaging,For the peroneal, muscular, and posterior tibial veins of the calf, the patient may sometimes be placed in the supine position, with the leg bent and the foot resting on the bed. Conversely, imaging study of iliac veins and the vena cava is conducted with the patient in the supine position. Prior preparation is required to reduce intestinal gases. In case of suspected post-thrombotic syndrome, if possible, the patient should also be examined in the upright position. For imaging of the upper extremities, the patient should be placed in the supine position, with the limb stretched alongside and slightly away from the body.For imaging of the lower extremities, the patient should be placed in a comfortable supine position with the torso and head elevated up to 30°, lying close to the edge of the bed, on the same side of the operator, with the hip slightly abducted and the knee slightly flexed. For the common and superficial femoral veins and the posterior tibial vein, the patient should keep the leg externally rotated and the knee slightly flexed. For the popliteal vein and peroneal veins, the patient should be placed in a prone or lateral decubitus position, resting on the contralateral limb with the knee slightly flexed. In case of any clinical condition, the patient may remain seated at the edge of the bed with the legs hanging down.In general, veins are easily compressible by the transducer.Devices that produce high-quality images in B-mode and that are equipped with spectral Doppler and color Doppler should be used. The choice of transducer is primarily based on the relationship between the transducer’s frequency and the location of the object to be studied. High-frequency transducers produce high-quality images but have low tissue penetration. On the other hand, low-frequency transducers penetrate deeper, but produce lower quality images. Linear transducers with frequencies between 4 and 10 MHz are often used to investigate upper- or lower-extremity deep veins, whereas linear transducers with frequencies between 7 and 13 MHz are used to investigate upper- or lower-extremity superficial veins. For evaluation of swollen lower limbs and patients with obesity , iliac veins, and the inferior vena cava, a multi-frequency convex transducer (between 1 and 5 MHz) may be necessary, as it has lower wave frequencies and deeper US wave penetration. Presets should be properly calibrated for imaging of the deep and superficial venous systems, with adjusted focal zone and gray scale, so that the lumen is dark in the absence of stasis or thrombosis. Spectral or color Doppler gain should be adjusted to a low velocity scale suitable for evaluating venous flow. For deep vein evaluation, VUS devices must be adjusted with proper focus and line density for two-dimensional imaging. The structures are evaluated in cross-sectional and longitudinal views.B-mode:the transducer is initially positioned below the inguinal ligament, allowing visualization of the saphenofemoral junction. Longitudinal and cross-sectional scanning of the entire lower-extremity venous system is then performed. In the cross-sectional view, transducer compression must be applied especially along the common femoral, femoral, and popliteal veins with a distance of approximately 2 to 3 cm between each compression. The use ofVUS as a diagnostic technique for DVT was first described by Talbot in 1982, and the method has been improved over the years.A normal vein without thrombosis shows complete lumen collapse during transducer compression of the walls  and color flow Doppler (bottom). A = artery, V = vein.Doppler:This technique is intended for recording venous flow velocities, which are low under normal pulsed Doppler conditions. In the presence of venous thrombosis, velocities may be further reduced, requiring scale adjustment. Lower-extremity venous flow is spontaneous and phasic in response to breathing and variations in intra-abdominal pressure , but the sensitivity is reduced to approximately 65%. Conversely, duplex US  is the first-line imaging test for DVT diagnosis, with a sensitivity of 96% and a specificity of 98% to 100%. However, duplex US is time-consuming, requires patient transport to a diagnostic imaging center, and the immediate availability of an imaging specialist.In addition, to obtain an accurate diagnosis, the operator must be familiar with the method’s indications and limitations. Only 20% to 30% of imaging tests of suspected DVT show abnormal findings, and 90% of patients with fatal PE are asymptomatic for DVT.Test limitations and, therefore, accuracy are associated with obesity, mobility restrictions, major edema, and/or presence of wounds, orthopedic devices, bandages/plasters, etc. Relevant clinical information and focused physical examination are essential to assist in the interpretation of IVUS results during DVT investigation, and adequate protocol training is imperative. Despite these limitations, the easy handling, harmless nature, and wide availability of portable devices make this tool extremely applicable in daily practice. In addition, advances in electronic miniaturization have resulted in the creation of pocket-sized US scanning devices equipped with linear array transducers, further disseminating the use of compression VUS for DVT diagnosis.IVUS has been the reference method for diagnosis since the first accuracy studies of symptomatic and asymptomatic patients with suspected above- and below-knee DVT.The Society for Vascular Ultrasound recommends an examination time of approximately 75 minutes for a complete bilateral examination: 40 to 60 minutes for the actual imaging test and 15 minutes for clinical data analysis, consultation of previous imaging tests, and patient and room preparation.Regardless of the test protocol of choice, the examination room should be comfortably warm to prevent venospasm. To evaluate the inferior vena cava (IVC), the patient should be placed in a reverse Trendelenburg position.Many of the protocols performed by nonexperts have been developed for settings where experts are not available or to reduce the number of VUS performed after normal laboratory working hours. Thus, a single simple imaging protocol is not enough to definitively rule out DVT. In addition to proper supervised training, pretest DVT probability analysis is essential, that is, the use of clinical PE/DVT probability scores and awareness of the lower accuracy of VUS in the diagnosis of asymptomatic below-knee DVT. Studies on the topic did not report any major disadvantage for patients, and well-structured protocols with Wells’ clinical probability criteria helped improve test accuracy and proper referral of patients without easy access to imaging experts.With increased availability of VUS devices, which usually have excellent resolution, the training of nonexperts has become very frequent and gained increased acceptance, especially in the emergency and urgent care departments and in distant locations. Thus, imaging tests for suspected DVT performed by critical care and emergency physicians and last-year radiology/US/VUS residents is a current reality. The accuracy of emergency physician-performed US was assessed in a systematic review and meta-analysis of 16 studies with 2,379 patients. The prevalence of DVT was 23% (7.4%-47.3%), with a mean sensitivity of 96.1% (95%CI: 90.6%-98.5%) and a specificity of 96.8% (95%CI: 94.6%-98.1%). However, the studies included were very heterogeneous, the training process of emergency physicians was poorly described, and most of the studies had short follow-up periods. These data were not reproduced in a prospective study published in same year with a much smaller sample size, indicating the need for strict training protocols for these professionals, given that only the first three tests performed by nonexperts were supervised.During VUS investigation of venous thrombosis, the parameters previously described should be analyzed, ie, the combination of grayscale components (B-mode) with compression transducer maneuvers and CFD and spectral Doppler evaluation. Imaging test protocols use the following parameters to reach diagnosis: vein compressibility (the most important), vein caliber (diameter), US features of vein wall and lumen, and CFD and spectral Doppler evaluation.There are some well-established complete and focused (point-of-care) DVT imaging protocols. They are chosen according to device availability at the facility where the patient is being examined, time of patient arrival, and whether there is an expert available to perform VUS.DVT imaging protocols and15:Whole-leg VUS –Complete lower extremity venous compression US –Three-point extended compression US –Two-point extended compression US –The complete protocol involves using all US resources to diagnose thrombosis: evaluation of compressibility, caliber, vein wall and lumen appearance on US, and color and spectral Doppler of all veins from below the inguinal ligament to ankle in all segments   complete duplex US for the diagnosis of acute DVT. In addition to being a more complete patient approach, examining the infrapopliteal segment allows the diagnosis of other musculoskeletal diseases that are part of the differential diagnosis of DVT, such as Baker’s cyst, hematomas, and muscle diseases. veins) . In genDuplex ultrasound includes compression at 2-cm intervals, CFD analysis of vessel filling , observation of flow phasicity, and spectral Doppler analysis of femoral and popliteal veins morphology. If complete testing is performed only in the symptomatic limb, spectral Doppler evaluation should be performed in both common femoral veins to assess symmetry. In case of asymmetric flow pattern, the intra-abdominal veins should be investigated .This protocol involves only the evaluation of compressibility in all veins below the inguinal segment to the ankle in all segments .A recent meta-analysis of 17 studies from 16 original articles compared three-point vs. two-point point-of-care US (POCUS) protocols. Overall, the two-point POCUS had similar pooled sensitivity  and specificity  to the three-point POCUS . The false-negative rates of two-point (4.0%) and three-point POCUS (4.1%) were almost similar. Meta-regression analysis showed that high sensitivity and specificity tended to be associated with the initial POCUS performer and separate POCUS training for DVT.This protocol involves only the evaluation of compressibility from the common femoral vein to the popliteal vein, where all leg veins converge. It is also called the three-point protocol, as it assesses the compressibility of all proximal veins of the investigated lower extremity . The seIn this protocol, compressibility is evaluated at only two sites: the common femoral vein, 1-2 cm above and below the saphenofemoral junction (groin); and the popliteal vein, up to where the leg veins converge .Emergency physicians can achieve a level of competence equivalent to that of experts, but substantial training and practice are required to achieve and maintain this performance. To reach this level of excellence, they need regular training in US imaging.In general, emergency physicians are able to perform this protocol after training, with good reproducibility. There are several methods for performing this imaging protocol in the emergency setting. Most training programs include theoretical lectures on imaging technique, mock training, and observation of a number of different tests. However, some studies mention training programs that last only 10 minutes or less than 2 hours. This significant difference between protocols hinders comparisons between studies and, consequently, affects accuracy.A randomized controlled trial with more than 2,000 patients comparing whole-leg vs. serial two-point US plus D-dimer measurement showed that the two strategies are equivalent for the management of symptomatic outpatients with DVT. However, in the latter, the physicians were VUS experts, which indicates that this testing protocol should be performed by well-trained physicians and follow clinical probability scores to be accurate. In most cases, if symptoms persist or if D-dimer is elevated, compression US must be repeated.A study comparing complete two-point procedures performed by experienced emergency physicians showed that 362 of 2,451 patients had DVT. Two-point US would not have been able to diagnose 23 patients with proximal DVT (6.2%).Finally, the recommended complete imaging protocol is the one intended for DVT investigation because it scans the entire deep vein leg system, and it should be performed by experts. In addition, it requires dedicated high-grade devices and patient transport from the emergency department/ward to the imaging center.Conversely, two- and three-point compression US protocols are simple, fast, do not require experts or sophisticated devices, and can be performed at the bedside. These protocols are suitable for emergency departments and hospital wards, especially after working hours and on weekends. Together with pretest probability evaluation, they should be able to provide an initial assessment of patients with suspected DVT.Two-point compression US protocols are an extremely important tool for critically ill patients in certain settings, such as the current coronavirus disease 2019 (COVID-19) pandemic. There is a relationship between COVID-19 and a prothrombotic state, which favors the occurrence of thromboembolic phenomena. Thus, in case of a clinical possibility of DVT, performing a quick, focused US of the suspected limb should be considered when the diagnosis has an impact on patient management.In other cases, venous thrombosis may occur due to extrinsic compression by vascular abnormalities, such as aneurysms and pseudoaneurysms, or extravascular conditions, such as hematomas, abscesses, synovial cysts, lymphadenomegaly, and neural and hematological tumors.Complete US imaging of the limb provides the ability to identify associated clinical conditions and differentiate them from nonthrombotic abnormalities. Conversely, a swollen limb associated with stasis or decreased respiratory variability in the femoral vein may indicate extrinsic compression in the pelvic region. Lymphadenomegaly, uterine fibroids, retroperitoneal tumors, and May-Thurner syndrome are among possible causes.In this case, the sonographer should draw attention to these findings and suggest them as possible causes on the report.The symptoms triggered by a thrombotic event are common to several other acute or chronic conditions, such as ruptured synovial cysts, chronic venous insufficiency, hematomas, and muscle tears.Lymphadenomegaly, especially in the inguinal region due to lymphoproliferative disease, may lead to clinical manifestations of marked limb edema due to a possible compressive venous component or insufficient regional lymphatic drainage. Although easy to identify, occasionally the tumor mass can be so large that it hides the vein, making it difficult to characterize the flow or even the presence or absence of thrombus.Pseudoaneurysms, despite having well-defined color VUS features, can develop variable echogenicity in B-mode when thrombosed, depending on the volume and time of occlusion. When massive, they can also lead to venous compression and be associated with other conditions, such as blunt trauma or bone tumors, hindering vein identification.have described features suggestive of hematoma: mixed echogenicity, absence of anechoic regions, perilesional hyperechogenicity , and a relationship between the longitudinal and transverse axis of lesions > 2.A common differential diagnosis of DVT on US is muscle hematoma, especially when located in the calf muscles. Clinical presentation is very similar to venous occlusion and is not always clear. Trauma or sudden pain are often mentioned in medical history. Su et al.One of the most common additional nonvascular findings on venous imaging is the popliteal synovial cyst, or Baker’s cyst. It is most commonly located in the posteromedial surface of the popliteal fossa and most often does not trigger symptoms in the vascular system. However, in rare conditions, an intact cyst can present posterolaterally, with varying degrees of venous, arterial, and nervous compression, thus triggering neurovascular symptoms in the affected limb. In case of rupture towards the calf, Baker’s cyst may mimic the main features of acute venous thrombosis. Despite clinical similarity, differentiation between articular and vascular cysts must be made because each condition requires a completely different treatment approach. Some cyst features may help differentiate it from thrombotic events. Baker’s cyst communicates with the joint cavity close to the medial head of the gastrocnemius muscle, which is a key diagnostic feature . DespitSoft tissue tumors, benign tumors , or malignancies  may mimic the clinical features of venous thrombosis or present as a compressive condition .110VUS is a very accessible and widely available tool for the initial investigation of venous thrombosis; however, nonthrombotic conditions should be considered in the differential diagnosis. In experienced hands, IVUS allows alternative diagnoses of conditions that often occur in cases of suspected venous obstruction.Complete duplex US should be used for the diagnosis of acute DVT ..Spectral Doppler of both common femoral veins should be performed to evaluate symmetry. In case of asymmetric flow pattern, the intra-abdominal veins should be investigatedAcute/recent;Chronic/old;Predominance of acute changes;Predominance of chronic changes.Based on the consensus, the following terminology should be used to describe US abnormalities associated with DVT:The term “indeterminate” might be used only in the few occasions that the time of the event cannot be determined.Findings:first, it is fundamental to describe technical quality, the conditions in which the test was performed (if urgent or not), whether the patient was able to stay in the proper position, and if any major edema or other factors that could prevent proper technical quality were detected.Vein evaluation should be described separately, especially if there is venous thrombosis. All imaging features must be described: B-mode and Doppler (which can lead to the conclusion on the presence or absence of thrombosis), time of clinical onset, and whether the thrombus is acute, indeterminate, or has chronic post-thrombotic changes.Vein features to be included in the findings:Vein caliber  and wall appearance in all evaluated segments;Total or partial compressibility and specification of the affected segment;Presence or absence of intraluminal material. If present, evaluate echogenicity, complete or partial luminal obstruction, and presence or absence of a mobile component;Regarding flow:- Color Doppler: describe if present or absent and if it causes partial or complete luminal obstruction;- Spectral imaging: flow may be absent. If present, describe whether the flow is continuous or phasic in response to breathing and whether it increases (or not) distal compression and/or associated reflux.Presence or absence of collaterals;If applicable, include possible differential diagnoses: Baker’s cyst, tumors, signs suggestive of lymphedema, and images suggestive of hematoma.Conclusions:Report if there are signs of thrombosis or not. If so, specify whether it is totally or partially occlusive and whether the vein(s) and venous segments are affected. Specify whether it is acute/recent or there are chronic/old post-thrombotic changes. In cases of clinically subacute thrombosis (between 2 weeks and 6 months), the following terminology should be used: predominant signs of acute thrombosis or predominant signs of chronic thrombosis. In cases of nonocclusive thrombosis, specify whether there is associated flow or not. Features that should be reported to support the conclusions are summarized inIn current medical practice, the recommendation is that a patient diagnosed with a first episode of DVT be treated with an anticoagulant for 3 to 6 months,which most often results in resolution of symptoms due to recanalization of the vein or emergence of collateral circulation.This refers to a new episode of venous thromboembolism (VTE) in an individual with a previous history of this type of event. In cases of lower-extremity thrombosis, recurrence may manifest as a thrombus in a new location  or in a previously affected segment.Recurrent thrombosis is a common event. After anticoagulant discontinuation, the recurrence rate is estimated to progressively increase over time, reaching 40% among all patients within 10 years .When there is no identifiable main causal factor, or when there is only a transient minimal cause (“unprovoked”/idiopathic thrombosis), which occurs in approximately half of DVT cases, the prevalence of recurrence increases to 5%-10% at 1 year and up to 30% at 5 years,which warrants treatment continuation with vitamin K antagonists (VKAs) or non-vitamin K oral anticoagulants (NOACS) for 6 months or over, as these significantly reduce the risk of recurrence by 80%-90%.The most important risk factor for recurrence is the cause of the first episode of DVT. In patients with DVT caused by a transient risk factor , the annual risk is only 1%, and a 3-month treatment may be considered depending on other risk factors.Optimal duration of anticoagulant treatment remains under discussion and is based on the extent of thrombosis  and on the cause of the thrombotic event, when related to a main predisposing factor. We follow the recommendations of the American College of Chest Physicians (ACCP).Recurrence after stopping anticoagulation primarily depends on two factors: first, whether acute DVT has been effectively treated, including minimum duration of anticoagulant treatment; and second, the presence of intrinsic risk factors that increase recurrence, notably malignant disease and thrombophilias.In addition to the precipitating cause of DVT, other factors should be considered to determine the risk of recurrence. The sonographer should be attentive to clinical factors that are associated with recurrent thrombosis, such as: unprovoked DVT , obesity , male sex , positive D-dimer test , residual thrombosis , hereditary thrombophilia , inflammatory bowel disease , antiphospholipid antibody , and malignancy.This treatment affects the vascular endothelium and the coagulation cascade, thereby releasing prothrombotic substances during tumor lysis.Malignant disease is a major risk factor for both thrombosis and recurrent DVT. The risk for recurrent DVT is 2- to 4-fold higher in patients with cancer, reaching 4.2-fold in those undergoing chemotherapy.Complete resolution has been demonstrated in 56% of patients undergoing ultrasound scanning during follow-up,and this rate is different for proximal and distal thromboses. In distal thrombosis, complete recanalization is more frequent and there are no sequelae such as significant reflux or obstruction. Conversely, the prevalence of reflux or obstruction in proximal thrombosis or thrombosis involving the two segments is much more significant.Knowing the natural history of DVT is important to choose the appropriate therapy and, in the case of vascular ultrasound, to conduct patient follow-up. Recanalization is a dynamic process that depends on lytic or procoagulant forces; it starts in the first week after an episode of DVT and continues for months, with most of the thrombotic mass being reduced in the first 3 months.Reflux, associated or not with venous obstruction due to incomplete recanalization, may cause persistent venous hypertension, leading to the appearance of signs of chronic venous hypertension. These are known as post-thrombotic syndrome (PTS).The recanalization rate is related to the prevalence of reflux in the venous system. The faster the recanalization, the greater the association with competent valves.a recent meta-analysis of 14 studies showed only a mild increase in the risk of recurrence  in patients with residual venous thrombosis.Although several studies have highlighted the importance of residual venous thrombosis, which is usually diagnosed by VUS examinations in the follow-up of patients with DVT,There are no isolated VUS parameters that characterize recurrent thrombosis, or validated clinical models that allow its diagnosis. The diagnosis is based on reappearance of symptoms and clinical findings of DVT, considering the probability associated with risk factors and the presence of ultrasound findings suggestive of recurrent thrombosis.Comparative findings of an examination of currently suspected recurrence versus a baseline examination at the end of treatment are the only validated method for the diagnosis of recurrent DVT. Therefore, the existence of previous examinations that clearly and accurately describe the extent of involvement and the degree of recanalization of the previous thrombosis is key.Ultrasound findings are similar to those described for the diagnosis of the first thrombosis, and the presence of an old thrombotic mass may hinder the diagnosis of recurrence. Such findings are listed inBecause an increase of 2 mm at maximum compression has a low positive predictive value, other authors have proposed the use of an increase in vein diameter ≥4 mm for the diagnosis of recurrent DVT.A recent study that reviewed 36 published articles demonstrated that a new noncompressible vein or an increase in the diameter of a previously thrombosed vein segment ≥4 mm is sufficient to confirm the diagnosis of recurrent DVT. An increase in vein diameter of less than 2 mm allows recurrence to be ruled out, and an increase between 2 and 4 mm is considered unclear.The diagnosis may be easier when recurrent thrombosis occurs in the contralateral extremity or in a new segment that was clearly not involved in the previous venous thrombosis. When it occurs in a previously involved segment, an increase in vein diameter by 2 mm under compression of the previously thrombosed segment has been reported as a criterion for the diagnosis of recurrent DVT.Thrombus echogenicity, even when correlated with in vitro thrombus organization, makes the in vivo evaluation subjective. Importantly, even acute thrombi may have different stages of organization.demonstrated that a diagnostic strategy comparing an examination of currently suspected recurrence with a baseline examination at the end of treatment can be safely used to rule out recurrent DVT.La Gal et al.Such considerations reinforce the need for a thorough examination at the end of treatment to be used for comparison with subsequent procedures. All findings should be described, including residual diameter after maximum compression and site of measurement .Post-thrombotic syndrome (PTS) is a chronic condition characterized by signs and symptoms that develop as a consequence of previous DVT. The most common complication appears in the long term and affects 20%-40% of cases of lower-extremity DVT, even in the presence of adequate anticoagulation.PTS has a significant impact on the quality of life of patients, compromising and limiting their daily activities and productivity. This impact can be compared to that of cancer and heart disease, in addition to causing a significant cost increase to the health care system. Data from Swedish studies showed costs about 75% higher than those of primary DVT.The pathophysiology of PTS is a combination of obstructive phenomena and venous reflux due to valve insufficiency, which result in venous hypertension. Increased venous pressure in subcutaneous capillaries and microcirculation culminates in valve incompetence in perforating veins. In most cases, the obstructive process is characterized by recanalization occurring within 6-12 months of the acute event, which leads to a combination of partial obstruction and varying degrees of reflux in the affected segments. All changes ultimately result in destruction of venous valves, development of collateral valves in sites where a greater degree of obstruction persists, and a greater tendency to recurrence of acute episodes.A system of competent saphenous veins may act favorably in venous drainage when there is a significant obstructive component. Conversely, when there is insufficiency of preexisting saphenous veins, venous return will be even more compromised, and the clinical status of these patients may deteriorate more quickly.The inflammatory process is the main factor in PTS, being present in the resolution of thrombosis. Fibrinolysis, thrombus organization, and neovascularization involve interleukin-6 and intercellular adhesion molecule-1, which causes valve damage within the first months of the acute phase of DVT. Prandoni and Kahn suggest that the absence of recanalization in this period is an important predictor of PTS.PTS includes a wide spectrum of manifestations ranging from mild clinical signs to severe symptoms such as chronic pain in the affected limb (limiting daily activities), intractable edema, and ulcers. Other signs may appear, such as hyperemia, hyperpigmentation, venous dilations, and lipodermatosclerosis, in addition to symptoms such as pain, heaviness, paresthesia, pruritus, and cramps. In more advanced cases, cutaneous, subcutaneous, and lymphatic infections may occur.The degree of residual luminal obstruction is directly related to the severity of repercussion of these clinical manifestations, leading to severe pain and venous claudication.The following risk factors may contribute to the development of PTS:- Obesity;- Varicose veins;- Proximal thrombosis and recurrence;- Inadequate use of oral anticoagulant;- Time: the slower the resolution of DVT, the greater the probability of PTS;- Age and gender (there are contradictory studies);- Other potential but not yet proven factors: malignancy, immobilization, surgery, pregnancy, and thrombophilia.This condition should be diagnosed after the end of treatment of the DVT episode, ie, PTS cannot be characterized before the first three months.The diagnostic strategy for PTS should consist of clinical examination, laboratory tests, imaging studies, and air plethysmography. There is no reference laboratory, imaging, or functional test for the diagnosis of PTS. However, the presence of venous obstruction and reflux must be recorded by an imaging test, and an attempt should be made to inform which of the two pathophysiological components predominates, even if nonquantitatively.The clinical, etiological, anatomical, and pathological (CEAP) classification and the venous clinical severity score (VCSS) used for chronic venous insufficiency (CVI) can be appropriately applied to quantify PTS with different measures.The Brandjes scale, the Ginsberg measure, and the Villalta scale were specifically developed to assist in the diagnosis of PTS, but unfortunately they have not been adopted comparatively in other studies. At the 2008 meeting of the International Society on Thrombosis and Haemostasis, held in Vienna, the Villalta scale was recommended for defining the presence of PTS, with a score >5 indicating the diagnosis. The presence of ulcer makes the score even more severe .140,VUS is the imaging method of choice because of its low cost, availability in small centers, and high accuracy. In patients with a clinical presentation suggestive of PTS but no history of DVT, ultrasound is indicated to screen for evidence of previous DVT.VUS provides the location, the measurement of vein diameters after the compression maneuver , and, mIn addition to defining the diagnosis,VUS can be used for therapeutic planning. The test is important in the evaluation of the involvement of the iliocaval segment for endovascular approach and restoration of patency as well as in post-treatment follow-up, having a key role in the diagnosis of recurrent thrombosis.When there are barriers to the use of VUS, such as the presence of severe edema and lipodermatosclerosis, which often includes focal fibrocalcific nodules, some strategies should be adopted for improving image acquisition.Modification of transducer position and angle of insonation of the ultrasound beam, reduction in transducer frequency, and use of trapezoid mode with linear transducers are recommended; if necessary, the transducer should be replaced with lower-frequency devices that enable greater penetration, such as convex, sector, and endocavitary transducers.Patients with PTS should be examined in the supine and upright positions, which allows a better visualization of luminal changes, such as thickening and trabeculae, and promotes a more effective investigation of reflux and20.In the iliocaval segment, not only should the physician assess patency but also look for signs of extrinsic compression, especially compression of the left common iliac vein between the direct common iliac artery and the adjacent vertebral body, usually L5.The main ultrasound findings are reduced vein diameters and chronic luminal changes, such as parietal thickening and hyperechoic trabeculae, in addition to valve insufficiency. A less frequent finding is the presence of flow with an arteriovenous fistula pattern in focal points of venous segments affected by thrombosis, without repercussions in adjacent axial veins and arteries and of unknown clinical significance.DVT is a dynamic process with periods of recanalization, progression, and recurrence, and VUS is an important tool for the diagnosis and follow-up of DVT. Ultrasound findings play an important role in the outcome of this disease and are useful at different stages, which will be described below.Such data have been confirmed by studies using VUS, which demonstrated thrombus regression within the first three months and complete recanalization in approximately half of patients within 6 to 9 months of the episode of DVT.Partial recanalization and persistently occluded segments occur in approximately 20% and 5% of cases, respectively and femoral vein (blue). Presence of partial recanalization of the venous segment surrounding residual fibrosis. B: longitudinal view of the femoral vein. Normal ascending venous flow is detected in blue by color flow Doppler, and reflux is shown in red after distal compression maneuver. C: cross-sectional view of the calf muscle vein, with increased diameters and reduced compressibility. In 1, an echogenic image refers to a previous DVT, and in 2, a hypoechoic image refers to a current recurrence.Some factors associated with persistent post-thrombotic changes, such as the presence of residual thrombi and/or post-phlebitic valve insufficiency, were considered predictors of PTS. However, whether such findings can be used to change a therapeutic plan remains a controversial topic in the literature.They also recommend that a comprehensive ultrasound examination be performed within 5 days to 1 week of an initial negative comprehensive or point-of-care ultrasound in the following situations:The US Society of Radiologists in Ultrasound has recently recommended full compliance with the VUS protocol for diagnosing DVT.Persistent or worsening symptoms;Patients at high risk for DVT whose etiology of symptoms has not been elucidated;Technically compromised previous examinations.There has been a debate regarding follow-up protocols with VUS for patients undergoing treatment for proximal DVT, ie, in the iliac, femoral, and popliteal territories. It is not clear whether patients on adequate anticoagulant medication would benefit from VUS during treatment, or whether the conclusions of a repeated examination would change the established treatment strategy. However, VUS performed at the end of treatment has been shown to be an important basis for future evaluations, being crucial for detecting which veins were recanalized and which veins still have post-thrombotic changes.Regarding isolated leg vein thrombosis, classified as axial when it involves the tibial and/or peroneal veins, and as muscular when it involves the muscular veins only, some centers do not include its study in the investigation of DVT with VUS. With this initial approach, patients should undergo a second examination on the seventh day after the onset of symptoms. The second procedure is indicated for assessing the possibility of involvement of the proximal segment, if there has been propagation of distal DVT not diagnosed in the acute phase. When the results of the second examination are normal, the possibility of thrombosis is ruled out and the patient is not anticoagulated. In such centers, the estimated risk of pulmonary embolism (PE) at the end of 3 months is 0.5% .with limited benefits from anticoagulation. A meta-analysis conducted by Masuda et al.reinforced the low rate of propagation. In a randomized study, Schwartz et al.demonstrated no statistically significant differences between patients treated with anticoagulation for 10 days and individuals without treatment (3.7% vs. 3.8%). The propagation rate described by the authors for the popliteal vein was 1.9%.A serial follow-up protocol with VUS is recommended given the low rate of proximal propagation of popliteal vein thrombosis, which ranges from 3 to 15%,found no robust publications to compare patients treated with anticoagulation or followed-up with VUS. Lagerstedt et al.studied patients with symptomatic distal DVT and treated with warfarin for 5 days. Patients were then allocated to warfarin maintenance for 3 months or treatment discontinuation. After 3 months, the recurrence rate of DVT was 29% and 0% in the “treated” versus “untreated” groups, respectively.Few studies have addressed recurrence in distal DVT. Masuda et al.In high-risk cases , they recommend a 12-week treatment.Anticoagulation treatment is chosen for cases of symptomatic distal DVT. Most authors suggest a short duration, up to 6 weeks, in low-risk patients.Centers using a comprehensive VUS protocol choose to treat patients regardless of venous thrombosis being proximal or distal. The estimated risk of PE with this approach, at the end of 3 months, is also low .Evidence regarding post-thrombotic changes used as a parameter to guide the duration of anticoagulation is not robust. Additional research is needed in this field.Other authorshave highlighted the link between the presence of reflux in the popliteal vein, the permanence of fibrotic tissue, and the development of PTS. Sartori et al.followed-up 172 patients with isolated leg vein thrombosis treated with enoxaparin for 6 weeks and assessed the degree of recanalization with IVUS. The examination was performed during diagnosis and at the end of treatment. Approximately half of patients (49.5%) had recanalized veins, and there was no statistical significance between recanalization and thrombus size or anatomical site involved .A study on patients with proximal DVT treated with rivaroxaban evaluated ultrasound changes found at 1, 3, 6, and 12 months as well as recanalization rates in the affected veins.The diagnosis of recurrent DVT is more complex because, different from the approach to the initial episode of DVT, which includes validated algorithms of pretest probability combined with the use of D-dimer and VUS,such criteria are not validated for recurrence.An VUS finding of non-compressibility of a previously unaffected segment can be considered diagnostic.After an initial episode of DVT, recurrence may occur in approximately 25% of patients within 5 years and account for an increased risk of PE and PTS.and the diagnosis depends on a previous good-quality examination with an adequate number of images for comparison, together with caliber measurements in the different affected venous segments; however, this is not observed in daily clinical practice. Also, this criterion is not used in previous episodes of calf vein thrombosis, which makes patient approach even more difficult.At times, an initial thrombus will not resolve completely, which results in chronic post-thrombotic changes and may hamper the diagnosis. In this case, the diagnosis of recurrent DVT in a previously affected venous segment can be made by detecting an increase in thrombus diameter of at least 4 mm compared with a previous study. However, the accuracy of this finding is controversial,The follow-up of patients with recurrent DVT should follow the criteria used during the initial episode, as there is a lack of studies addressing the follow-up of this specific group. We also highlight the importance of a comprehensive study at the end of treatment, or a follow-up examination after 6 months in cases of prolonged anticoagulation, including the investigation of chronic post-thrombotic changes with an assessment of venous insufficiency with the patient in the upright position.Based on medical literature data and guideline expert discussions, we suggest the following:Negative initial VUS:perform a comprehensive ultrasound examination within 5 days to 1 week of an initial negative comprehensive or point-of-care ultrasound in the following situations: (a) persistent or worsening symptoms, (b) patients at high risk for DVT whose etiology of symptoms has not been elucidated, and (c) technically compromised previous examinations.Initial VUS with diagnosis of proximal DVT :repeat comprehensive ultrasound examination towards the end of treatment to assess the degree of recanalization and presence of post-thrombotic changes. Or, at any time the patient presents with symptoms during treatment, for evaluation of recurrence or extent of the initial thrombosis.Initial VUS with diagnosis of distal DVT :repeat ultrasound examination within 6 weeks or 12 weeks of the onset of clinical manifestations, according to the established therapeutic plan.Patients with recurrent DVT:repeat ultrasound examination at the end of treatment, or a follow-up examination after 6 months in cases of prolonged anticoagulation, or at any time in the presence of symptoms.evaluated the role of CT pulmonary angiography combined with lower-extremity CT venography in the diagnosis of PE. Patients were clinically classified according to the probability of PE using the Wells score,and pretest results were compared with posttest results. The authors demonstrated that CT angiography combined with CT venography has a positive predictive value (PPV) of 96% in patients with high clinical probability of PE, and a negative predictive value (NPV) of 97% in patients with low clinical probability. In patients with moderate clinical probability, both NPV and PPV were 92%, demonstrating an excellent case-solving capacity.The PIOPED II studyCT angiography also allows the assessment of the aorta, lung parenchyma, chest wall, and pleural space, with excellent spatial resolution, and the making of alternative diagnoses in cases of suspected PE, which may occur in up to 2/3, such as aortic dissection, pneumothorax, pneumonia, and lung cancer. Thus, the treatment for each of these conditions can be properly initiated.CT angiography is currently the method of choice for evaluating patients with suspected PE after clinical risk stratification. A negative CT angiogram in patients with low clinical probability is sufficient to rule out this diagnosis. A positive CT angiogram in patients with high clinical probability confirms the diagnosis of PE.As CT angiography is the gold standard for the diagnosis of PE, studies that attempt to characterize prognostic factors using CT for evaluation of the RV have emerged.demonstrated that an increased RV, assessed by CT angiography using the ratio between the dimensions of the RV and the LV , is an independent mortality factor ,which confirms the potential use of this tool in the risk stratification of patients with acute PE.In a retrospective study, Schoepf et al.selected three types of CT angiography findings  to assess the risk of short-term death, defined as in-hospital death or death within 30 days of CT angiography due to PE  Imaging protocols:depend on available equipment and information such as patient’s height and weight. Ideally, they should include:- Acquisition performed with the patient holding the breath (apnea) without exercising a Valsalva maneuver or respiratory pause;- Use of test bolus or bolus tracking with an ROI on the pulmonary trunk to monitor the arrival of the contrast material in the pulmonary arterial circulation and to perform the examination at the appropriate time;- Imaging from the lung base to the apex, which minimizes motion artifacts in the most important regions and reduces the artifact resulting from concentrated contrast in the superior vena cava;- Acquisition and reconstruction of images with thin slice thickness (1 mm or less) and without gaps between images to allow multiplanar reconstructions with no loss of spatial resolution;- Comprehensive study of all thoracic structures, which allows the assessment of possible differential diagnoses for the patient’s complaint;- Use of lower kV, which significantly attenuates iodine and substantially reduces the radiation dose. This reduction causes an increase in image noise: the use of 100 kV instead of traditional 120 kV should be preferred, as long as the signal-to-noise ratio is kept at acceptable levels. Obese patients may need higher kV;- Use of iterative reconstruction, which reduces radiation doses and keeps image noise at acceptable levels.b) Contrast material injection protocols:depend on the available type of contrast material and venous access. Ideally, they should include:- Large-bore antecubital vein access that allows the injection of contrast material with an injection pump at a minimum speed of 4 mL/s;- Use of more concentrated contrast materials, such as 350 mg I/mL.The main advantages of this method for evaluation of PE are the following  at two different energy levels.llowing :allowing monoenergetic reconstructions.It generates an iodine-enhanced map as a by-product, which reflects at that time the distribution of contrast material across the lung parenchyma. A joint evaluation of the iodine-enhanced map with angiographic images can sensitize the detection of small thrombi in distal pulmonary branch arteries,Conversely, monoenergetic reconstructions at low energy levels  increase iodine attenuation, but they also increase image noise. This type of reconstruction improves angiographic images in cases of suboptimal vascular opacification or allows reductions in contrast dose, eg, in patients with renal dysfunction.Performing CT pulmonary angiography using older scanners can be a major challenge. However, after adjustments to imaging parameters and optimization of contrast use, using larger volumes or adjusting the injection rate may be required to compensate for a slower acquisition and to obtain good-quality diagnostic images.:The diagnosis of acute PE with CT angiography is based on the identification of occlusive or nonocclusive thrombi within the pulmonary branch arteries. The diagnostic criteria for acute PE on CT angiography areOcclusive filling defect causing an increase in caliber of the affected vessel ;Contrast-edged, central, nonocclusive filling defect ;Nonocclusive filling defect adhering to the vessel wall and forming an acute angle with it .Acute PE is the main cause of filling defects in pulmonary branch arteries. Possible pitfalls and differential diagnoses include:- Flow and/or motion artifacts;- Incorrect anatomical interpretation;- Reflex vasoconstriction;- Chronic PE;- Nonthrombotic emboli;- Congenital anomalies (pulmonary artery agenesis and/or hypoplasia);- Inflammatory diseases ;- Neoplasms (thrombi and/or tumor invasion or primary neoplasms of the pulmonary arteries).An indirect sign of acute PE on CT is pulmonary infarction , which The changes with prognostic value that can be characterized on CT angiography are related to an acute overload of the right heart chambers. Although dilations in the superior vena cava and azygos veins and in the pulmonary trunk as well as objective measurements of RV function have been cited as prognostic markers, the most important sign of RV dysfunction is an increase in RV dimensions with an RV/LV ratio greater than 1.0 in an axial CT plane .181As CT angiography is an important tool in the diagnosis of acute PE, the only absolute contraindication is a history of severe allergy to iodinated contrast material. In such cases, alternative diagnostic methods include V/Q scintigraphy, MR angiography, gadolinium-enhanced CT angiography, or serial Doppler ultrasound of the lower extremities. A history of mild-to-moderate allergic reactions can be approached with the use of premedication for desensitization.There are other special situations that may require adaptation of the protocol or replacement of CT angiography with other diagnostic methods:To avoid exposing the breast tissue to ionizing radiation, especially in patients with a normal chest radiograph, V/Q scintigraphy (or the perfusion-only study) or serial Doppler ultrasound of the lower extremities can be alternatives.When CT angiography is used, the protocol should be optimized by ensuring adequate venous access and injection rates to achieve high diagnostic quality and avoid repetitions.This is not an absolute contraindication. The patient should preferably be hydrated before the examination, but cautiously to avoid congestion. In urgent cases, CT angiography can be performed even without prior preparation. V/Q scintigraphy and serial Doppler ultrasound of the lower extremities remain as alternatives.If available, dual-energy CT scanners and monoenergetic reconstructions can be used to reduce the dose of iodinated contrast material and still ensure adequate vascular opacification.This case requires examinations that can be performed at the bedside, such as echocardiography and Doppler ultrasound of the lower extremities.This diagnostic method was evaluated in the PIOPED III study,which combined MR pulmonary angiography with lower-extremity MR venography for diagnosis.MR angiography is an alternative to CT angiography, allowing a direct study of the pulmonary arteries.Also, MR angiography allows the performance of other techniques, such as lung perfusion, great vessel flow quantification, and cardiac function assessment.MR angiography has some advantages over CT angiography. The main benefits are the absence of radiation and the employment of a contrast material (gadolinium) that can be used in patients with iodinated contrast allergy.Currently, the indication of MR imaging for patients with renal insufficiency, especially those receiving dialysis, has been revised because of the occurrence of progressive systemic fibrosis related to the use of gadolinium.The main disadvantages of MR angiography are lower spatial resolution, higher cost, greater complexity, longer examination, reduced availability, and difficulty monitoring critically ill patients inside the machine due to the high magnetic field.The results of the PIOPED III study(183) showed that MR angiography was technically inadequate in 25% of patients. With these technically inadequate tests included, the method diagnosed PE in 57% of patients. When the technically adequate tests were analyzed separately, MR angiography had a sensitivity of 78% and a specificity of 99% for the diagnosis of PE. When MR angiography was combined with MR venography, the combination showed a sensitivity of 92%, superior to MR angiography alone, and a specificity of 96% for the diagnosis. However, the tests were technically inadequate in 52% of patients, which caused a major problem.concluded that MR angiography should only be used for the diagnosis of PE at centers of excellence in MR imaging and when other methods are contraindicated. Currently, the main indication for MR imaging is as an alternative method to CT scanning in patients with iodinated contrast allergy.The PIOPED III studytogether with the advances of CT angiography (similar accuracy with a less invasive procedure), are determining factors for digital subtraction angiography to have virtually fallen into disuse for the diagnosis of acute PE. However, the method remains an important diagnostic tool in the evaluation of chronic PE, especially in candidates for balloon angioplasty.For a long time, digital angiography was considered the gold standard for the diagnosis of PE. Invasive nature, greater exposure to ionizing radiation, and complications of up to 0.5% of mortality, 1% of severe complications, and 5% of minor complications,The indication of imaging methods for the diagnosis of acute PE should be based on hemodynamic status and clinical assessment of pretest probability, with the application of validated rules  combined with D-dimer. The aim is to avoid unnecessary use of imaging methods ;CT angiography is the imaging method of choice for diagnosing acute PE. It can be replaced with V/Q scintigraphy in cases of severe iodine allergy or in special situations such as pregnant women or patients with severe renal insufficiency. MR angiography is reserved for centers of excellence in the method or for when CT angiography and V/Q scintigraphy are inappropriate or unavailable;The diagnosis of acute PE should be rejected in patients with low or moderate probability and negative CT angiography ;The diagnosis of acute PE should be accepted in patients with moderate or high probability and CT angiography demonstrating thrombi in segmental or proximal branches ;Lower-extremity CT venography is not recommended because of high exposure to ionizing radiation and should be replaced with IVUS for the evaluation of DVT ;In normal radiograph cases, both CT angiography and V/Q scintigraphy can be used; however, in abnormal radiograph cases, the recommendation is to proceed with CT angiography ;In pregnant patients, both CT angiography and V/Q scintigraphy can be used. With modern techniques, both tests cause little maternal and fetal exposure to ionizing radiation.This should be considered a tomographic criterion of RV dysfunction and a marker of poor prognosis, even in patients at clinically low risk .Increased dimensions of the right heart chambers, with RV/LV ratio > 1.0, are linked to 5-fold higher mortality rates due to acute PE.Diagnostic flowcharts in hemodynamically stable and unstable patients, according to the clinical probability of PE, are shown inFor practical purposes, “lung scintigraphy” is defined in this section as a single test containing different combinations of lung ventilation/perfusion scans, or even a perfusion-only study. Based on international guidelines proposed by the US Society of Nuclear Medicine and Molecular Imaging (SNMMI), the European Association of Nuclear Medicine (EANM), and the European Society of Cardiology (ESC), the main indications for lung scintigraphy are listed and discussed below.Primary indication:determine the probability of PE.Secondary indications:Record the degree of PE resolution in the follow-up of chronic PE;Quantify differential lung function before surgical resection of lung cancer;Assess lung transplants;Assess congenital heart or lung disease, or conditions such as cardiac shunting, pulmonary artery stenosis, and arteriovenous fistula, including their treatment.Confirm the presence of a bronchopleural fistula.Assess chronic parenchymal lung disorders such as cystic fibrosis;Assess PE as a cause of pulmonary hypertension.The following findings are considered positive for PE:Disagreement between ventilation and perfusion studies in at least one segment or two subsegments, with hypouptake present only or more extensively in perfusion compared with normal ventilation (known as a mismatch), conforming to the pulmonary vascular anatomy (wedge-shaped hypoperfusion areas with the base projecting to the lung periphery).The following findings are considered negative for PE:Normal perfusion pattern conforming to the anatomic boundaries of the lungs;Matched pattern between ventilation and perfusion studies ;Mismatch between ventilation and perfusion that does not follow a lobar, segmental, or subsegmental pattern.The following findings are considered nondiagnostic for PE:Widespread ventilation/perfusion abnormalities not typical of specific diseases.In scintigraphic evaluation for the detection of PE, there is sufficient scientific evidence for the use of well-defined interpretive criteria, as proposed by the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED), PIOPED II, and PISAPED studies, as well as for interpretation based on the clinical experience of the nuclear medicine or imaging physician .while the PIOPED II (which uses fewer scan categories) and PISAPED criteria resulted in a smaller number of indeterminate or inconclusive studies.Both PIOPED II and PISAPED criteria had equivalent performances in terms of interpretation when chest radiography was combined with lung ventilation scintigraphy.There are, however, insufficient studies replicating these results, with no double-blind multicenter comparisons between the two strategies, which jeopardizes the finding that the methods have equivalent accuracy.The revised PIOPED criteria proved to be more accurate than the original PIOPED criteria,Therefore, the combination of ventilation studies is recommended whenever possible, mainly because of the increased specificity of the combined study compared with radiography alone. In older adults, up to 60% of false-positive tests may result from absent ventilation, given the high prevalence of respiratory diseases.An analysis based on the experience of the nuclear medicine physician  may provide a more accurate interpretation than studies using well-defined criteria alone. For the interpretation to be the best possible, the physician should provide an opinion based on detailed knowledge of the different objective criteria listed above.The most recent EANM consensus (2019) suggests that tomographic imaging (SPECT or SPECT/CT) should always be performed routinely, leaving planar imaging for when the former is no longer possible.With regard to the imaging method of single-photon emission tomography (SPECT), there is a considerable body of literature supporting its use, including evidence regarding SPECT studies combined with low-dose CT, which seems to increase diagnostic accuracy.or robust prospective studies evaluating patient outcomes with SPECT versus planar scintigraphy and CT angiography,some reports have showed an increased diagnostic accuracy of SPECT and SPECT/CT. There remains some uncertainties about the interpretation of SPECT and SPECT/CT with the PIOPED and similar criteria, the best SPECT protocol for ventilation imaging, and the optimal imaging protocol .However, findings of a segmental ventilation/perfusion mismatch should be regarded as positive. Findings of a single subsegmental mismatch should not be regarded as suspects for PE.Although there are no robust multicenter studies comparing SPECT with planar scintigraphic imaging or even CT angiography,and that a normal perfusion study virtually excludes PE.Additionally, it is worth noting that, regardless of the criteria adopted for interpretation, there is a consensus that patients with low probability of PE on lung scintigraphy have a favorable prognosisOlder studies had a significantly lower accuracy, in addition to a rate of nondiagnostic studies nearing 65% in the original PIOPED study. The rate currently ranges from 1% to 4%, which is significantly lower than that of other imaging methods.There is a marked difference in the diagnostic accuracy of lung scintigraphy between older studies, performed in the 1980s and 1990s, and more recent studies using updated machines and tomographic methods.Overall, the diagnostic accuracy of more recent studies, especially those of SPECT, is equal to or greater than those of CT angiography; in some studies, such as the PIOPED II, scintigraphy had a greater capacity to detect subsegmental PE. Therefore, there are no robust scientific data to support the superiority of CT angiography over scintigraphy.However, in practice, CT angiography remains the method of choice, mainly because of its quick procedural time and greater availability (24 hours) compared with nuclear medicine tests.Lung scintigraphy performed as SPECT is the imaging test with the lowest rate of inconclusive results (<3%).There was an important variability in sensitivity (Se) and specificity (Sp) values in the initial studies: Se = 67% for planar imaging and Se = 93% for SPECT in an animal model (pigs);Se = 80% and Sp = 78% for planar imaging; Se = 80% and Sp = 96% for SPECT;and Se = 76% and Sp = 85% for planar imaging vs. Se = 97% and Sp = 91% for SPECT.Therefore, diagnostic accuracy in the initial studies generally rose from 70%-80% with planar imaging to more than 90% with SPECT.The main differences in diagnostic accuracy between planar and SPECT studies are due to the greater detection of changes in subsegments and in medial segments close to the mediastinum; in the latter, SPECT can detect up to 53% more areas suggestive of PE than planar studies.Combining SPECT with low-dose CT improves the method even further by increasing its specificity and adding the capacity of low-dose CT. This is useful in the differential diagnosis for identifying emphysema, pneumonia, and/or other parenchymal changes that cause vascular compression and may therefore explain perfusion defects. should be recommended, as it has no contraindications, a lower rate of indeterminate test results, and reduced exposure of the female breast to radiation (see below).In conclusion, both tests have advantages and disadvantages, with scintigraphy being superior to CT angiography in cases of concomitant diseases, chronic PE, and indeterminate CT angiography results.Perfusion-only studies are recommended in patients suspected of massive PE and pregnant patients, as discussed below. Using low-dose CT instead of a ventilation study increases sensitivity compared with perfusion-only studies; however, this strategy leads to a higher rate of false-positivesand increased radiation exposure in pregnant women.Comparisons of perfusion-only scintigraphy with CT pulmonary angiography as the gold standard demonstrated a sensitivity of 86% and a specificity of 93% for perfusion imaging. When the PISAPED criteria were applied to the PIOPED II study population, perfusion-only scintigraphy had a weighted sensitivity of 82% and a weighted specificity of 96%.In addition to the previously discussed items, lung scintigraphy has been the preferred choice over other imaging methods in pregnant women because of reduced breast exposure to radiation and in some cases of limitation of contrast use on CT angiography. Such indications will be detailed below.a) Exposure to radiation and use during pregnancy:Since ventilation studies and chest radiographs are commonly normal in young individuals, a usual recommendation is skipping this portion of the study in those known to be at risk for the effects of radiation, such as women in the first trimester of pregnancy, because of the likely greater vulnerability of the fetus to the effects of radiation.This ensures reduced radiation exposure compared with CT angiography and no exposure to iodinated contrast material.In pregnant women, a protocol including a perfusion-only study and reduced radioactivity is initially recommended (see section on imaging techniques). A normal perfusion study excludes PE, and the ventilation study should only be performed in exceptional cases or cases of uncertainty about a positive result the day after the perfusion scan.and less than 1 mSv on perfusion-only scintigraphy when not combined with tomography or ventilation studies.Fetal doses seem to be low and similar in both methods.The critical maternal organ to be protected in this case is the breast, which absorbs radiation doses between 8.6 to 44 mSv on CT angiographyb) Other clinical limitations of CT angiography:Because of the intravenous use of iodinated contrast material, CT angiography might not be performed in a large number of critically ill patients, such as those with renal insufficiency, those who have recently had a myocardial infarction, those requiring ventilatory support, and those with a history of iodinated contrast allergy/anaphylaxis. In such cases (in addition to those mentioned in item A and in the section on diagnostic accuracy) and in rare cases of inability to perform the test, lung scintigraphy should always be indicated, as it has no contraindications, no related complications, and a low rate of inconclusive test results.1. Ventilation studya. Radiopharmaceuticals:i. Inert gases:1.Xe:This is historically the agent used in ventilation studies.It has a half-life of 5 days and a (low) energy of 81 keV.In the PIOPED I study, the single-breath technique was the most used.Xe is inhaled during the first 20 seconds, and one image should be obtained from the posterior view.This gas is not available in Brazil.2.81mKr:81Ru).This is produced from a high-cost generator of rubidium  and a half-life of 13 seconds.81mKr is a true gas that does not cause artifacts due to central airway deposition. An advantage is that ventilation and perfusion can be imaged simultaneously, as the gamma energy of81mKr is greater than that of99mTc (used as a perfusion marker).81mKr the best choice for children.Low radiation exposure makesThis gas is not available in Brazil.ii. Radiolabeled aerosols:Xe and81mKr in Brazil for ventilation studies, radioaerosols are generally used.Given the unavailability of2. An aerosol is a relatively time-stable, two-phase system consisting of particles suspended in air. The radiolabeled particles may be liquid, solid, or a combination of the two. The percentage of particles remaining in the lung after inhalation (deposition fraction) depends on the aerodynamic properties of the particles, particularly on their size. The deposition fraction is up to 50%, with ultrafine nanoparticles , which are deposited predominantly in the alveolar region by diffusion.99mTc-DTPA, which is cleared from the alveolar region by transepithelial diffusion. It has a biological half-life of 80 minutes in healthy nonsmokers, 45 minutes in healthy passive smokers, and 24 minutes in healthy active smokers.The most commonly used radiolabeled aerosol is99mTc-labeled solid graphite particles generated at high temperatures.These particles have a diameter of about 0.005 to 0.2 micrometers,are hydrophobic, and tend to aggregate, which is why they should be used within 10 minutes of being generated. They are suspended in argon gas (therefore having the property of gas). Studies using99mTc-Technegas and81mKr have provided comparable results.However, the availability of Technegas equipment in Brazil is low, especially because of its high cost.Another radiolabeled aerosol available is Technegas, which consists of extremely smallb. Imaging protocols:i. As PE is a life-threatening condition, the recommendation is that the diagnosis be made as soon as possible, usually with 1-day ventilation/perfusion protocols. Lung ventilation studies, which will be used for comparison with the corresponding perfusion study, should be performed before perfusion imaging, requiring very low radioactivity. Sequential perfusion imaging with low-to-moderate radioactivity produces high-quality comparative images, with the diagnosis being made in a short time.ii. Whenever possible, tomographic imaging should be performed as follows:Ventilation with the appropriate radiolabeled aerosol, patient in the supine position, using a 1 to 4 dose ratio between ventilation and perfusion, respectively .A large field-of-view, dual- or triple-head gamma camera and a general-purpose collimator should be used. At least 128 images will be obtained in a 64 x 64 matrix and 10 seconds per image.Perfusion images should be obtained immediately after ventilation images. To avoid patient movement, peripheral venous access for perfusion imaging should be placed before the start of the ventilation study.2. Perfusion studya. Radiopharmaceutical:99mTc-labeled macroaggregated albumin (99mTc-MAA) is used in perfusion studies.i.b. Imaging protocols:Patient should be in the supine position, and venous access should have been previously obtained ;99mTc-MAA .Venous access is used to administer activity between 100 and 120 MBqIn the same gamma camera used for ventilation imaging, without any patient movement, perfusion images should be obtained as follows:128 tomographic images (SPECT) in a 64 x 64 matrix and 5 seconds per image.3. Perfusion-only study:in pregnant patients and those suspected of massive PE, a perfusion-only study is indicated.Images should be iteratively reconstructed with ordered-subsets expectation maximization (OSEM), according to a suggested protocol with 8 subsets and 2 iterations.a)In V/Q SPECT and planar V/Q scintigraphy, images should be interpreted based on:Basic criteria for evaluating imaging studies;Knowledge and experience of the interpreting physician ;Pretest probability according to holistic interpretation principles.b)For them to be clinically relevant, lung scintigrams should be described as positive or negative for the presence of PE (PE: YES or NO), not based on probability categories.c) Basic criteria for interpreting V/Q scintigrams:i. Reports of absence of PE are based on:i.1. Normal lung perfusion;i.2.Matched or reversed-mismatched V/Q defects  of any size, shape, or number, in the absence of true mismatch;i.3. Mismatch with no lobar, segmental, or subsegmental pattern.ii. Reports of presence of PE are based on:ii.1. V/P mismatch of at least 1 segment or 1 subsegment conforming to the lung perfusion anatomy.iii. A study is nondiagnostic when:iii.1.Multiple V/P abnormalities not typical of specific diseases are observed.Mortality results from pulmonary hypertension, right heart failure, and arrhythmias. V/Q scintigraphy is generally used as an auxiliary tool in the diagnosis of chronic thromboembolic pulmonary hypertension,with greater sensitivity and specificity than multidetector CT.Chronic PE is a medical condition different from acute PE. It is an insidious, progressive disease that has no treatment and a poor prognosis.Ventilation and perfusion scintigraphy with tomographic imaging (V/Q SPECT) has been able to demonstrate the presence of clinical situations other than PE, such as COPD, left heart failure, and pneumonia. In 39% of patients who undergo the diagnostic procedure and do not have PE, and in 22% of those with PE, some of the following additional findings will be present.a) COPD:characterized by matched ventilation/perfusion defects. Ventilation defects are frequently more pronounced than perfusion defects, a phenomenon known as reverse mismatch.A significant correlation between the degree of ventilation abnormalities detected on scintigraphic studies and the results of pulmonary function tests has been described.PE is frequent in patients with COPD,accounting for about 10% of deaths in those with stable COPD.b) Left heart failure:perfusion is redistributed to the upper lung regions.Ventilation redistribution is less extensive than perfusion redistribution. A mismatch can be observed in the dorsal regions, with a diffuse nonsegmental pattern, and should not be interpreted as PE.c) Pneumonia:matched ventilation/perfusion defects are observed, and the former are usually larger, causing a reverse mismatch.A finding suggestive of pneumonia is the stripe sign, which refers to the maintenance of perfusion in the pleural surface adjacent to a central area of matched defect.The stripe sign pattern is best detected on tomographic studies.As is the case with any diagnostic method, V/Q scintigraphy requires the nuclear medicine physician reporting the study to be aware of possible errors inherent to the test, such as the following:99mTc-MAA. Drawing blood from a patient into a syringe containing the99mTc-MAA solution may cause aggregation of particles, creating the so-called hot spots. A similar defect may arise from failure to resuspend99mTc-MAA particles prior to intravenous administration.a) Technical artifacts may arise from preinjection handling ofb) Planar imaging may underestimate the presence and/or extent of perfusion abnormalities due to superposition of normally perfused areas. This artifact is eliminated by scintigraphic imaging with tomographic views (SPECT).c) Whenever possible, the use of Technegas is preferred over liquid aerosols in patients with COPD. In rare patients with emphysema, Technegas particles are trapped in bullae, leading to a pattern that may be mistaken for a mismatch.d) Mismatched perfusion defects with no clear segmental pattern may be seen in older patients in cases of partially resolved PE, but not in cases of acute PE. Also, mismatched perfusion defects are observed in other lung conditions, such as lung cancer, mediastinal lymphadenopathy, actinic sequelae, pneumonitis, fibrosis, and heart failure.e) Ventilation and perfusion scintigraphy may fail to detect thromboembolism that causes only partial vascular obstruction with few hemodynamic effects. This problem has low clinical significance. A possible explanation is that nonocclusive emboli are usually associated with other signs of PE in other regions, leading to a correct diagnosis. Nonetheless, when the presence of partial occlusion is identified , the study should be reported as positive for PE.In such cases, chest CT scans usually reveal the presence of other conditions, such as tumors or other mediastinal processes, congenital pulmonary vascular abnormalities, or aortic aneurysm.f) Overall, the complete absence of unilateral perfusion in the presence of normal ipsilateral ventilation and without any other mismatch in the contralateral lung is not due to PE.68Ga, one of the first isotopes used in lung perfusion imaging, was introduced as the future of nuclear medicine pulmonary evaluation. As it is a positron-emitting isotope,68Ga requires a PET system and is used as68Ga-labeled microspheres to assess perfusion. Ventilation, in turn, is assessed with a similar technique to that of Technegas, using68Ga-labeled particles called Galligas. At the technical level, the transition does not imply major difficulties or investments because the radiopharmacy requirements remain relatively simple with the use of existing Technegas equipment. The only difference is the modified MAA synthesis and its consequent labeling with68Ga  instead of99mTc, with a radiation dose very similar to that of conventional V/Q SPECT/CT scans, better count statistics, higher spatial and temporal resolution, and reduced acquisition time . Other advantages are the commercial availability of respiratory-gated acquisition systems that reduce artifacts, especially at lung bases; the possibility of multiple ventilation studies with or without bronchodilator on the same day owing to the short half-life ofT scans.proposed a protocol for systematic review and meta-analysis of diagnostic accuracy and clinical outcome of patients evaluated with V/Q SPECT, whose results are still to be published and will certainly provide more evidence for the adoption of this technique.In 2018, Le Roux et al.However, the assay has low specificity (40%) because D-dimer levels may be increased in several conditions other than VTE, such as in acute myocardial infarction, stroke, inflammation, active cancer, and pregnancy. Specificity also decreases with age, and it can be as low as 10% in older adults.Consequently, a negative quantitative D-dimer test has a high negative predictive value for VTE. The results of the studies reveal that the risk of development of PE in patients with low clinical probability who are not treated after a negative D-dimer test is <1% within three months of the initial evaluation.Conversely, because of its low predictive value, a positive quantitative D-dimer test does not modify the pretest  probability and is therefore clinically useless. Recent evidence, however, suggests that very high D-dimer levels are associated with a 4-fold increase in the probability of PE,which is important for assessing the burden of thromboembolic disease and may have prognostic significance.Assessing the clinical probability of PE helps physicians choose the most appropriate objective test to diagnose or exclude the diagnosis . MeasurDiagnostic strategies will depend on the patient’s hemodynamic stability, as follows:a) Stable patients:Based on these considerations, when the clinical probability of PE is low and the quantitative D-dimer test is negative, the diagnosis is unlikely and additional investigations are not needed . When tb) Hemodynamically unstable patients:When acute thoracic aortic dissection is suspected due to chest pain, CT angiography allows this differential diagnosis to be evaluated.When the patient presents with severe hypotension or cardiogenic shock , transtGiven the need for expediting the diagnosis and treatment of these patients, the strategy employed in a specific health facility should be adapted to each clinical situation and local context. When the initial examination suggests a massive PE, other actions should be adapted to the clinical situation, and antithrombotic therapy may be administered.Although CT angiography is more readily available, it is contraindicated in a substantial number of patients, as shown in the PIOPED II study.Currently, V/Q SPECT is rarely available 24 hours a day, 7 days a week. Consequently, the two tests should be ready for use at least in tertiary care centers, as both are crucial for appropriate diagnostic algorithms of PE. In each center, the diagnostic algorithm used for PE should be based on local conditions and particularly on the availability of V/Q SPECT and CT angiography.When suspected, PE should be confirmed or refuted to avoid the risk of over- and undertreatment, which requires imaging tests. Only the optimal techniques, ie, CT angiography and V/Q SPECT, are recommended. The choice of imaging modality will depend on availability.V/Q SPECT, when available, has considerable advantages over other imaging techniques for the diagnosis of PE, such as high sensitivity and specificity, lower predictable radiation burden, and suitability to the follow-up of patients with PE and its natural history.Diagnostic flowcharts for hemodynamically stable and unstable patients, according to the clinical probability of PE, are shown inV/Q scintigraphy is strongly recommended for the diagnosis of PE, with high accuracy even in the presence of COPD and pneumonia;Technegas is superior to DTPA in patients with COPD;81mKr is advantageous;When available,99mTc-labeled aerosol should be used for ventilation and 100-120 MBq99mTc-labeled MAA for perfusion;The radiation dose should be reduced as much as possible, not affecting image quality (ALARA principle). Overall, 30 MBqIn pregnant patients, the perfusion-only study is recommended;The interpretation should be holistic; the probabilistic interpretation is obsolete;A key criterion for the diagnosis of PE is the presence of mismatch in more than 1 subsegment.