Accuracy of iodine density thresholds for the separation of vertebral bone metastases from healthy-appearing trabecular bone in spectral detector computed tomography.
PURPOSE
To evaluate quantitative iodine density mapping (IDM) with spectral detector computed tomography (SDCT) as a quantitative biomarker for separation of vertebral trabecular bone metastases (BM) from healthy-appearing trabecular bone (HTB).


MATERIALS AND METHODS
IRB-approved retrospective single-center-study of portal venous SDCT datasets acquired between June 2016 and March 2017. Inclusion of 43 consecutive cancer patients with BM and 40 without. Target lesions and non-affected control vertebrae were defined using follow-up imaging, MRI, and/or bone scintigraphy. ID and standard deviation were determined with ROI measures by two readers in (a) bone metastases, (b) HTB of BM patients and controls, and (c) ID of various vessels. Volumetric bone mineral density (vBMD) of the lumbar spine and age were recorded. Multivariate ROC analyses und Wilcoxon test were used to determine thresholds for separation of BM and HTB. p < 0.05 was considered significant.


RESULTS
ID measurements of 40 target lesions and 83 reference measurements of HTB were acquired. Age (p < 0.0001) and vBMD (p < 0.05) affected ID measurements independently in multivariate models. There were significant differences of ID between metastases (n = 43) and HTB ID (n = 124; mean 5.5 ± 0.9 vs. 3.5 ± 0.9; p < 0.0001), however, with considerable overlap. In univariate analysis, increased ID discriminated bone lesions (AUC 0.90) with a maximum combined specificity/sensitivity of 77.5%/90.7% when applying a threshold of 4.5 mg/ml. Multivariate regression models improved significantly when considering vBMD, the noise of ID, and vertebral venous ID (AUC 0.98).


CONCLUSION
IDM of SDCT yielded a statistical separation of vertebral bone lesions and HTB. Adjustment for confounders such as age and lumbar vBMD as well as for vertebral venous ID and lesion heterogeneity improved discrimination of trabecular lesions.


KEY POINTS
• SDCT iodine density mapping provides the possibility for quantitative analysis of iodine uptake in tissue, which allows to differentiate bone lesions from healthy bone marrow. • Age and vBMD have a significant impact on iodine density measurements. • Iodine density measured in SDCT yielded highest sensitivity and specificity for the statistical differentiation of vertebral trabecular metastases and healthy trabecular bone using an iodine density threshold of 4.5 mg/ml (most performant)-5.0 mg/ml (optimized for specificity).
['Borggrefe|Jan|J|http://orcid.org/0000-0003-2908-7560', 'Neuhaus|Victor-Frederic|VF|', 'Le Blanc|Markus|M|', 'Grosse Hokamp|Nils|N|', 'Maus|Volker|V|', 'Mpotsaris|Anastasios|A|', 'Lennartz|Simon|S|', 'Pinto Dos Santos|Daniel|D|', 'Maintz|David|D|', 'Abdullayev|Nuran|N|']
D000328:Adult D000368:Aged D015519:Bone Density D000071556:Cancellous Bone D005260:Female D006801:Humans D007455:Iodine D007457:Iodine Radioisotopes D008159:Lumbar Vertebrae D008297:Male D008875:Middle Aged D015999:Multivariate Analysis D011857:Radiographic Image Interpretation, Computer-Assisted D012189:Retrospective Studies D013125:Spinal Neoplasms D014057:Tomography, X-Ray Computed
Iodine Bone Tomography Diagnosis Neoplasm metastasis