On the basis of their visual mismatch negativity (vMMN) results, Liu et al.  claim thIn short, they applied a modified three-stimulus oddball task, with circles as target stimuli and faces as non-target stimuli. There were photographs among the faces showing a frequent emotion category (standard) and a rare one (deviant). Such sequences were presented to Chinese and Canadian participants; same race photographs were used for each group. In the first condition, only visual stimuli were presented; in the second, the photographs were accompanied by meaningless emotional speech (congruent or incongruent with the photographs); and in the third, the auditory stimuli were tones. As for the details of stimulus presentation, EEG recording, etc., this study corresponds to the professional standard. The problematic issues are (1) the relationship between the present findings and the specific requirements of vMMN research; (2) the connection between the data and the interpretation.VMMN is considered as an index of an automatic process, elicited by the violation of regular stimulation. This is why in vMMN studies a primary task is introduced in order to distract attention from the vMMN-related stimuli  congruency was considered to be an important factor (as it was entered into the ANOVAs) but this factor had no effects on the ERPs. Thus, emotional content did not help Chinese participants to identify emotional contents, which directly contradicts the main hypothesis of the study.ad hoc hypotheses can be constructed. For example, participants might search for the meaning of the utterances, and this strategy may have been different in the two samples; utterances in the two languages may have had different arousing capacity, etc.Despite measurable group differences in this study, and even though “Eastern-Western” differences most likely exist in the perception of facial emotions, the ERP effect reported cannot be unequivocally interpreted as culture-related differences in the processing of facial expressions. In a convincing study, as the first step, it is important to disclose how the two groups perceived the experimental situation . As for the source of differences numerous It remains that mismatch-related ERP effects  are exceptional tools in the investigation of automatic processing. Furthermore, learned processing strategies probably influence the acquisition of the memory system underlying mismatch responses, as has been shown in several studies  104462.The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


The demountable disk-drum aero-engine rotor is an important piece of equipment that greatly impacts the safe operation of aircraft. However, assembly looseness or crack fault has led to several unscheduled breakdowns and serious accidents. Thus, condition monitoring and fault diagnosis technique are required for identifying abnormal conditions. Customized ensemble multiwavelet method for aero-engine rotor condition identification, using measured vibration data, is developed in this paper. First, customized multiwavelet basis function with strong adaptivity is constructed via symmetric multiwavelet lifting scheme. Then vibration signal is processed by customized ensemble multiwavelet transform. Next, normalized information entropy of multiwavelet decomposition coefficients is computed to directly reflect and evaluate the condition. The proposed approach is first applied to fault detection of an experimental aero-engine rotor. Finally, the proposed approach is used in an engineering application, where it successfully identified the crack fault of a demountable disk-drum aero-engine rotor. The results show that the proposed method possesses excellent performance in fault detection of aero-engine rotor. Moreover, the robustness of the multiwavelet method against noise is also tested and verified by simulation and field experiments. We can find that if every frequency band has the same relative energy Ent = 1; if only one of the Ent = 0. Thus, we can regard Ent as normalized information entropy. In this paper, the normalized ensemble multiwavelet transform information entropy is developed and introduced for assembly looseness fault detection in aero-engine rotors.In Equation (19), the base of logarithm is Choose the original multiwavelet with the vanishing moment Initialize the free parameters Select the optimal free parameters on the basis of vibration signal by the genetic algorithm and the rule of the minimum information entropy principle;Determine the transform level and conduct the ensemble multiwavelet transform. Obtain the corresponding ensemble multiwavelet transform coefficients;Compute the total energy and the relative energies in each decomposed frequency band. Calculate the normalized information entropy for assembly looseness fault detection in aero-engine rotors.The procedure of the developed method, called normalized ensemble multiwavelet transform information entropy, can be concluded in the following flow chart, as displayed in In this section, the proposed method is firstly applied to the fault detection of an experimental dismountable disk-drum aero-engine rotor for verifying the performance in this task. Then, the proposed method is used for an engineering application. Further verification is performed by monitoring an aero-engine rotor of the same type, but from the engineering field.The photograph of the experimental dismountable disk-drum aero-engine rotor is displayed in The measured dynamic response data are collected from the experimental system under three different assembled quality conditions: looseness condition 1 (tighten up the dismountable disk-drum aero-engine rotor with force moment M1); looseness condition 2 (tighten up the dismountable disk-drum aero-engine rotor with force moment M2 after condition 1); qualified condition 3 (tighten up the dismountable disk-drum aero-engine rotor with force moment M3 after condition 2), such that M1 < M2 < M3. Four vibration signals are measured by the sensors described above for each condition. Therefore, twelve vibration data are measured under all the three states. The sample frequency is set at 6400 Hz. The measured dynamic response data under each assembled quality state from the same sensor in time domain and the corresponding frequency spectrum are displayed in et al. 1994 [The proposed method in this paper is used to process the measured vibration signal. First, generate the customized multiwavelet basis function, which is lifted from cubic Hermite splines , as theSince the ensemble multiwavelet analysis method is applied to analyze the measured vibration data of an assembled quality condition to the extent of level 3 by the research experience, there are eight frequency bands attained. Each frequency band has the same bandwidth. According to Equation (18), the frequency band energy of the ensemble multiwavelet transform coefficients from three assembled quality states is calculated and the corresponding distributions are displayed in Maintenance is indispensable in making sure that the components continue to perform the functions for which they are designed. The basic objectives of the maintenance activity are to deploy the minimum resources to ensure system reliability and to ensure that components perform their intended functions properly. At present, the scheduled maintenance, known as time based (or planned) maintenance, and involving repair at regular time intervals, is still widely adopted on most of the aero-engine in service in China. Due to vibrations exceeding limits, the aero-engine of military aircraft in this case cannot be used normally after working for 446 h. However, the first scheduled repair time interval is 500 h. Thus, the reason for the overweight vibration, and reasonable maintenance are needed. According to engineering experience, the fault called rupture accident of the labyrinth seal toothed disk in the high pressure compressor rotor of an aero-engine emerges frequently. In order to solve this problem, our group carried out the related study on the assembly looseness and crack fault condition monitoring of this dismountable disk-drum aero-engine rotor.The dynamic response signal is acquired from the experimental system, as shown in The proposed method in this paper is applied to the condition monitoring of this aero-engine rotor. The ensemble multiwavelet functions constructed from cubic Hermite splines for the vibration signal in In order to reflect and evaluate the state of this aero-engine rotor, the normalized wavelet information entropy of the acquired signal is computed according to Equation (19), which is shown in The effectiveness of the proposed method on fault diagnosis of demountable disk-drum aero-engine rotor has been verified by the two cases in To verify the feasibility of the proposed method for noisy signal analysis, a simulation experiment is designed and carried out. First, 100 simulated signals with White Gaussian noise are generated to simulate the actual case without fault and a sample is shown in The proposed multiwavelet method is adopted for analyzing all the simulated signal samples. Since the multiwavelet transform is applied to process the signals of all the simulated condition to the extent of level 3, by research experience, there are eight frequency bands attained. The normalized multiwavelet transform information entropy of the simulated signal is computed according to Equation (19), which is shown in The planetary gearbox test rig shown in In this test rig, accelerometer sensors are installed on the casing of the second stage planetary gearbox. The sampling frequency is 10 KHz. A planetary gearbox dataset containing two subsets is obtained from the experimental system under the two different operating conditions. The two conditions include faulty and normal conditions on planetary gearbox. Planet gear in experimental planetary gearbox with tooth breakage fault is shown in The proposed method is adopted for this task. The normalized multiwavelet transform information entropy of the condition vibration signals is computed according to Equation (19), which is shown in A fault diagnosis method based on ensemble multiwavelet analysis is proposed for the condition identification of aero-engine rotor. Multiwavelet has been proven to be a powerful tool to describe the non-stationary vibration signal due to the property of multi-resolution analysis and the multiple wavelet basis functions. To overcome some mentioned limitations, ensemble multiwavelet basis function is constructed via a symmetric multiwavelet lifting scheme. Then, the ensemble multiwavelet transform is performed on the vibration signal of aero-engine rotors. The relative energy in each frequency band of the ensemble multiwavelet transform coefficients, which is equivalent to a percentage of the whole signal energy, is taken as the probability. Normalized information entropy is computed based on the relative energy to reflect and evaluate the state of aero-engine rotor. The proposed method is first applied to the fault detection of an experimental aero-engine rotor. Then the proposed method is used for an engineering application and the results shows that the proposed method performed excellently in this task. Finally, the robustness of the multiwavelet method against noise is also tested and verified by simulation and field experiments.Moreover, it must be said that although a similar multiwavelet method is also be used for equipment condition identification in reference , the sevIn addition, the authors have attracted some interesting results and will carry out a related study in the future. First, the authors have checked the noise attenuation performance in simulation and experiments. However, it is also of significance to study the noise attenuation ability from the technical/methodological viewpoint by referring to the known model-based and signal-based methods . Second,


Upper body movements during walking provide information about balance control and gait stability. Typically developing (TD) children normally present a progressive decrease of accelerations from the pelvis to the head, whereas children with cerebral palsy (CP) exhibit a general increase of upper body accelerations. However, the literature describing how they are transmitted from the pelvis to the head is lacking. This study proposes a multilevel motion sensor approach to characterize upper body accelerations and how they propagate from pelvis to head in children with CP, comparing with their TD peers. Two age- and gender-matched groups of 20 children performed a 10m walking test at self-selected speed while wearing three magneto-inertial sensors located at pelvis, sternum, and head levels. The root mean square value of the accelerations at each level was computed in a local anatomical frame and its variation from lower to upper levels was described using attenuation coefficients. Between-group differences were assessed performing an ANCOVA, while the mutual dependence between acceleration components and the relationship between biomechanical parameters and typical clinical scores were investigated using Regression Analysis and Spearman’s Correlation, respectively (α = 0.05). New insights were obtained on how the CP group managed the transmission of accelerations through the upper body. Despite a significant reduction of the acceleration from pelvis to sternum, children with CP do not compensate for large accelerations, which are greater than in TD children. Furthermore, those with CP showed negative sternum-to-head attenuations, in agreement with the documented rigidity of the head-trunk system observed in this population. In addition, the estimated parameters proved to correlate with the scores used in daily clinical practice. The proposed multilevel approach was fruitful in highlighting CP-TD gait differences, supported the in-field quantitative gait assessment in children with CP and might prove beneficial to designing innovative intervention protocols based on pelvis stabilization. Locomotion is the result of a number of complex interactions involving neuromuscular activity, joint movements, bone alignment, and the rules that govern bodies in motion . TypicalGait stability has been referred to as the capacity to minimize oscillations during walking from the lower to the upper levels of the human body . AccelerCerebral palsy (CP) encompasses two-thirds of all childhood disabilities and refers to a group of permanent disorders, mainly related to movement and posture, attributed to non-progressive disturbances that occurred in the developing fetus or the neonatal brain . The disOnly recently, adopting a single inertial sensing unit attached to the lower back was proposed to carry out global assessments in children with CP ,21. The ad hoc rehabilitation programs aimed at the proper development and maintenance of walking ability in children.The purpose of this work is to characterize how children with CP attenuate upper body accelerations from the pelvis to the sternum and the head, in comparison with a group of TD children. To this aim acceleration data were collected at the three anatomical levels with a multilevel approach based on the use of magneto-inertial sensors. The characterization of the upper body accelerations, and how they are transmitted through the trunk, may allow to gain specific insights about gait strategy and locomotor patterns in children with CP, thus supporting therapists in defining All participants gave their assent and either their parents or legal guardians provided written informed consent according to the declaration of Helsinki. The experimental protocols were approved by the Ethics Committee of the Santa Lucia Foundation.Twenty children with clinical diagnosis of CP and twenty TD children were recruited. Both groups were matched for gender  and age , and were characterized by similar stature . To take into account for the effect of knee flexion contractures during gait , effectig = 9.81 m/s2), ± 1500°/s and ± 600 μT, for the three sensors, respectively. Children were dressed with adjustable supports including swim caps, stretch tops and stretch shorts, with pockets tailored to house the MIMUs. The three units were positioned at head level (H), on the occipital cranium bone close to the lamboid suture, at sternum level (S), in correspondence to the center of the sternum body, and on the pelvis (P), at sacrum-L5 level   were used to collect 3D acceleration, angular velocity and magnetic field vector components using the Motion Studio software. Using the MIMU proprietary algorithm, the orientation of each unit was also obtained. Sample rate was set to 128 samples/s, and full-range scale was set to ± 2g  to control trial performance during data post-processing.® . The inclination of each MIMU with respect to gravity was first computed during the initial part of each test, when each participant was stationary in a standing position. Each MIMU reference frame was then rotated, through a rigid transformation, following the pitch-roll-yaw rotation sequence so as to have one axis aligned with gravity during the above-mentioned stationary phase. Then, for each body segment, a local anatomical frame was defined to match the rotated MIMU reference frame and was characterized by the CC, AP and ML axes. The gravitational acceleration component was removed from the measured acceleration signals using the orientation data provided by the MIMUs’ proprietary algorithm. The acceleration components, recorded during walking, were low-pass filtered using a 4th order Butterworth filter. The cut-off frequency was determined by performing a residual analysis [Data were processed using custom algorithms implemented in Matlabanalysis  on each -1]) and average step length  were estimated.The time taken to complete the 10-meter walking test and the foot striking events were obtained by identifying consistent features (maxima) on pelvis acceleration time histories using the methodology described in  and by c-1]) was computed as the ratio between the average length of the two analysed strides and the relevant duration. To account for the influence of the participants’ stature on average step length, step frequency and walking speed, the corresponding dimensionless normalized parameters were computed as described in [Only the central part of the pathway was considered for further data processing. In particular, steady state walking phases were identified as in  and, forribed in . The avea) were then computed at the three levels of the upper body for each stride, using both the magnitude (Euclidean norm) of the acceleration as well as each component as expressed in the corresponding anatomical frame. The variation of the RMSa from a level i to an upper level j of the upper body was assessed by computing attenuation coefficients  defined as follows:The Root Mean Square of accelerations  adjusted for age was performed on normally distributed parameters to analyse between-group differences in both RMSa values and attenuation coefficients, for each anatomical axis. Similarly, a rank analysis of covariance was performed using the Quade’s test in order to investigate the same aspect in non-normally distributed parameters.The statistical analysis was performed using the IBM SPSS Statistics software package . The alpha level of significance was set to 0.05 for all statistical tests described hereafter. The D'Agostino & Pearson omnibus normality test was performed on all estimated parameters. Descriptive statistics and box plot analysis were performed on both RMSa inter-component relationship at the pelvis, sternum and head levels: RMSaML vs RMSaCC, RMSaAP vs RMSaCC and RMSaAP vs RMSaML. The quality of the regression fitting was quantified in terms of coefficients of determination (R2). To evaluate whether there was an interaction between groups and each covariate (one of the RMSa components at a time), regression coefficients were compared using covariance analysis [Regression lines were obtained to investigate the following RMSanalysis . The anaa values.Finally, the Spearman’s rank correlation coefficient (ρ) was used to assess the relationship between each estimated parameter and the GMFM values. The same analysis was conducted to verify the presence of possible relationships between attenuation coefficients and the observed RMSa parameter was thus used for between-group comparisons [No significant differences was found between the TD and CP groups in either walking speed or normalized walking speed values. The RMSparisons . The ageparisons , whereasThe results of the 2w-ANCOVA and of the Quade’s test for the main effect are presented in a values were significantly larger in the CP than in the TD group. RMSa values were attenuated from pelvis to sternum and from sternum to head in the TD group, whereas in the CP group RMSa values were attenuated from pelvis to sternum and amplified from sternum to head, indicating that attenuation between contiguous levels was different between groups. Specifically, CPS was larger and CSH was smaller in the CP than in the TD group, whereas CPH was not statistically different between the two groups. In order to investigate if the larger CPS observed in children with CP was associated with the larger pelvis RMSa, the correlation between these two parameters was computed, but it did not result statistically significant .The same analysis was initially performed on the magnitude of accelerations at pelvis, sternum and head levels. Again, only group-dependent differences were found see . All thea parameters along CC, ML and AP directions are shown in a were significantly smaller in the TD than in the CP group , whereas CSH in the CC and ML directions were found to be smaller  in the CP than in the TD group . On the other hand, differences in the combined group X gender analysis were found for CPS in the ML direction .Furthermore, RMSaAP vs RMSaML  for the head, RMSaML vs RMSaCC  for the sternum, and RMSaAP vs RMSaCC  for the pelvis.Looking at the inter-component relationships at the different body levels, only three out of nine regression line pairs were significantly different between the two groups  and RMSaAP  at head level and positively correlated with CPHAP .For what concerns the correlation analysis performed between the estimated parameters and the patients’ clinical classification (GMFM), no significant correlation was identified either with the walking speed or with the normalized walking speed. Similarly, for the magnitude of the accelerations in the CP group, no significant correlation was found between the GMFM and RMSIn the present study, a multilevel inertial sensor set-up was proposed to characterize segmental accelerations of pelvis, sternum and head during gait, and to investigate how these accelerations are attenuated from the bottom to the top in children with cerebral palsy (CP), when compared to age-matched children with typical development. Investigating accelerations and how they propagate through the upper body has a valuable physiological meaning and quantifies the role of upper body structures in reducing head accelerations: as a matter of facts, this role can be active, when looking at both trunk and arms movements during gait, as well as passive, when taking into account the contribution of the underlying anatomical structures .The results about absolute and normalized gait velocities showed no statistical differences between the TD and CP groups, as already reported in previous studies ,21. It iThe main contribution of the present study consists in the analysis of the the cranio-caudal (CC), medio-lateral (ML) and antero-posterior (AP) components of acceleration measured at pelvis, sternum, and head levels, which strongly confirmed the presence of greater acceleration values in the CP group at all three anatomical levels. These large accelerations may interfere with the normal processing of visual, vestibular, and somatosensory information regarding body position, thus inducing a vicious circle that potentially weakens the control of the upper body movement during gait, due to the altered sensory feedback. Consistently, it has recently been suggested that visuospatial deficits are crucial components of the disorder in spatial orientation, manipulation, locomotion, navigation, and even social interactions . This ima values obtained at the lower trunk level were slightly higher than those previously reported [a values at each level than in the TD group, despite the comparable walking speed. This observation extends the previously known results about the pelvis. Higher RMSa values at all upper body levels in the CP group are paralleled by increased dynamic ranges of motion in different planes observed in this population [In the CP group, RMSreported ,21, probpulation ,19. Prevpulation , highliga at pelvis level is an important clinical parameter justifying the reduced gait stability in the pathological group. It is revealed that even if patients affected by CP apply an increased pelvis-to-sternum attenuation, this does not adequately reduce high acceleration values at the pelvis level, exhibiting an RMSa at sternum level that is still higher than in the TD counterpart. Specifically, in children with CP, CPS is positive and significantly larger than in the TD group, thus indicating that children with CP attenuate more than TD children from pelvis to sternum. This circumstance could not be attributed to a deficit of the TD group, but potentially to the fact that for TD children, large attenuations are not strictly required to guarantee safe walking and an adequate dynamic stability of the trunk. Looking at the increased pelvis acceleration observed in children with CP, it is conceivable that a physiotherapeutic intervention to stabilize the pelvis may also reduce accelerations at higher body levels. However, the absence of a significant correlation between CPS and RMSa measured at the pelvis, probably due to the heterogeneity of the CP group that include both hemiplegic and diplegic patients, implies that the same percentage of reduction would be maintained also after that intervention. Regardless, the result will be a reduction of instabilities at sternum level.This study confirms that the high RMSSH) presented a behaviour in the CP group that was the opposite to that of the TD group. While the latter group reduced accelerations from the sternum to the head, guaranteeing protection of the head, the former presented a negative CSH, meaning that acceleration increases from the sternum to the head. This inefficiency in attenuating these accelerations could be related to the documented rigidity of the head-trunk system in this pathology [a at sternum and head level maintain similar acceleration values, is consistent with the en bloc locomotion strategy adopted by children with CP to compensate for gait asymmetries that are typical of this population. In this respect, further research is needed to verify this interpretation, looking at similar patterns in other neuromuscular diseases or in amputee gait, as well as in a larger or more homogenous group of children with CP.Going upwards, the analysis of the sternum-to-head attenuation , RMSIn summary, children with CP did not show an adequate upper body stabilization as occurs in TD children, despite good attenuations from the pelvis to the sternum level. The existing thorax movements in children with CP during gait are the result of intertwining trunk control deficits and compensatory strategies due to lower limb impairments . It is wad hoc orthopaedic devices, and to monitor their efficacy in terms of gait stability.The present work focused on the quantitative assessment of upper body accelerations during gait and of their attenuation from the pelvis to the head, in children affected by cerebral palsy using wearable magneto-inertial sensors. The availability and accessibility of the inertial measurement equipment, in fact, does not limit its everyday use by clinicians. Moreover, characterizing how head stabilization is managed during gait in children with CP can be potentially useful to study gait patterns, including compensatory ones. In this respect, the potential role of trunk movements for compensating asymmetries in lower limb patterns was highlighted, specifically involving decreasing/increasing accelerations at the different body levels. The adopted biomechanical parameters were fruitful in highlighting gait differences between children with CP and their TD peers and can be used to support therapists and physicians either to drive the design of innovative intervention protocols or to prescribe S1 Fig2 = 0.5927. panel B) Scattered plot for the age-dependence of normalized walking speed in children with Cerebral Palsy (CP). It is observed that the aforementioned neuromaturation curve disappears, having no trends that can fit the scattered CP group data.panel A) The age-dependence of normalized walking speed in children with typical development (TD). The normalized walking speed was defined as the product of the dimensionless step length and the dimensionless step frequency. According to the literature , an expo(TIF)Click here for additional data file.


Data aggregation processes aim to reduce the amount of exchanged data in wireless sensor networks and consequently minimize the packet overhead and optimize energy efficiency. Securing the data aggregation process is a real challenge since the aggregation nodes must access the relayed data to apply the aggregation functions. The data aggregation security problem has been widely addressed in classical homogeneous wireless sensor networks, however, most of the proposed security protocols cannot guarantee a high level of security since the sensor node resources are limited. Heterogeneous wireless sensor networks have recently emerged as a new wireless sensor network category which expands the sensor nodes’ resources and capabilities. These new kinds of WSNs have opened new research opportunities where security represents a most attractive area. Indeed, robust and high security level algorithms can be used to secure the data aggregation at the heterogeneous aggregation nodes which is impossible in classical homogeneous WSNs. Contrary to the homogeneous sensor networks, the data aggregation security problem is still not sufficiently covered and the proposed data aggregation security protocols are numberless. To address this recent research area, this paper describes the data aggregation security problem in heterogeneous wireless sensor networks and surveys a few proposed security protocols. A classification and evaluation of the existing protocols is also introduced based on the adopted data aggregation security approach. Data aggregation is an important basic concept in wireless sensor networks (WSNs), which has been proposed to optimize the data collection process and the sensor nodes’ energy reserves. Indeed and due to the network density, the data collection process suffers from redundancy and data interrelation which may drain the sensor node batteries and affect the network performance . Thus, it is necessary to use methods for merging data at the intermediate nodes in order to reduce the number of packets transmitted to the base station, thus allowing energy and bandwidth savings. This can be accomplished through a data aggregation mechanism.Despite data aggregation advantages it can lead to some security failings: Usurpation of identity, deliberate removal of the packets, alteration of sensory readings and aggregation results. Many security solutions have been proposed to secure the data aggregation process. These solutions are mainly proposed for homogeneous WSNs where nodes are identical in capacity, energy consumption and hardware complexity. The proposed solutions aim to guarantee secure data aggregation and an authenticated broadcast based on a variety of security mechanisms like symmetric encryption  and authHeterogeneous WSNs represent a new class of technology and a recent research area that overcomes the limits of WSNs, especially in the security field. The continued progress in wireless sensor networks, especially in the miniaturization of the processors has enabled the development of several varieties of nodes. When more than one type of nodes is used in a WSN, it is called heterogeneous . A typicExploitation of the high capacities of the heterogeneous sensor nodes.Respect of the resources constraints of the simple homogeneous sensor nodes.Optimization of the data aggregation process while ensuring high data accuracy.The resource capacities of the heterogeneous sensor nodes have opened new security research directions since complex and high security level algorithms can be used to secure the data aggregation process. Several security techniques are used to secure the data aggregation process in heterogeneous WSNs, the base of which is represented by the privacy homomorphism algorithm . The maiThe main contribution of this paper is to survey the existing security aggregation protocols dedicated to the heterogeneous WSNs. In our opinion, the heterogeneous data aggregation security protocols should be identified and differentiated from those dedicated to the homogeneous WSNs, since they cannot be applied to this classical type of networks. On the other hand, adopting homogeneous data aggregation security protocols in heterogeneous WSNs may underexploit the network resources capacities. To the best of our knowledge, only eight protocols have been proposed and we think that it is interesting to shed light on these protocols and discuss their security strategies. The rest of the paper is organized as follows: Secure data aggregation protocols for heterogeneous WSNs can be classified into two types: End to end and hop by hop data aggregation protocols ,6. In enEnd to end secure data aggregation protocols aim to insure data privacy and confidentiality from the sensor nodes to the base station . To offeOzdemir  has propThe public key of the base station is assigned to the AGGNODEs and the network is deployed.Pair-wise keys are shared between the AGGNODEs and their neighbouring nodes.Each node encrypts data using the symmetric encryption algorithm (RC5)  and sendE be the encryption function and D the decryption function. + and * indicate the addition and the multiplication functions applied on the data set Q. Assuming that the private and the public keys of the base station are respectively a, b belong to Q. This transformation is multiplicatively homomorphic if:Each AGGNODE decrypts the received data, applies the aggregation function and encrypts the result using the privacy homomorphism encryption algorithm described as follows: Let The encrypted data are transmitted and the AGGNODEs aggregate hierarchically the encrypted data during the transmission.Only the base station can decrypt the aggregated data using its private key.CDAP exploits privacy homomorphism  to insurCDAP is dedicated to heterogeneous WSNs. CDAP increases the capacity of securing the data aggregation mechanism when compromised nodes are detected. The network performance using AGGNODEs is evaluated compared to the homogeneous WSNs, where only the base station has higher calculation capacities and larger storage space. Thus, through the AGGNODEs and data aggregation, energy efficiency and the bandwidth are improved while ensuring secure communication. The performance evaluation shows that the protocol could be applied to large heterogeneous WSNs.However, in spite of the increased degree of security, the use of the privacy homomorphism faces limits, including the restricted number of allowed aggregation functions. In addition, the author did not give any indications about the key generation and distribution mechanisms.We assume that since privacy homomorphism is applied on the AGGNODEs, their high capacities are largely exploited. However, due to the use of symmetric encryption at the homogeneous nodes, the data aggregation accuracy can be affected by the latency introduced during the encryption phase. Also, the homogeneous simple sensor nodes have limited capacities and the use of symmetric encryption may not be tolerable by these nodes.et al. [Taban et al.  have addThe first solution uses the privacy homomorphism encryption to conceal data. The homomorphism combined with authentication message MAC are used to construct an authenticated encryption protocol for the aggregation model . HoweverThe second solution uses the Order Preserving Encryption Scheme or OPES  which maN is the total number of the nodes in the network.The third solution uses the Secure Hierarchical In-networking Aggregation (SHIA) protocol , which sTo insure data confidentiality and integrity, the third solution is improved by introducing a logical aggregation tree in the aggregation node. This solution is the latest one in which the communication cost is and OPES (Order Preserving Encryption Scheme)) may reduce the data aggregation accuracy due to the introduced computation delay and may drain the resource capacities of the homogeneous simple sensor nodes.The PIA protocol ensures end to end security and exploits the high capacity of heterogeneous sensor nodes, however, the authors did not indicate how the heterogeneous nodes are deployed. In addition, the heterogeneity exploitation is not sufficiently detailed. The use of homomorphic encryption on aggregation nodes affects significantly the data aggregation process as complex data aggregation functions cannot be applied. The proposed solutions to overcome the restriction of the data aggregation functions  operator and a hash function. The encryption key, and consequently the sensed data, are hidden from the aggregation nodes. With the use of random keys to encrypt the sensed data, the protocol becomes more robust against attacks. Also, the random generation of the new keys by each node offers more privacy.Due to the use of more powerful aggregation nodes, we suppose that this protocol is dedicated to heterogeneous WSNs. In this protocol, the aggregation nodes do not decrypt the received data before applying the aggregation function, thus saving more energy. Data is encrypted using a XOR According to the heterogeneity requirements, we consider that the use of heterogeneous nodes is not optimal and that the higher capacities of the aggregation nodes are not exploited through the use of powerful and complex security primitives. Indeed, the encryption is not performed by the heterogeneous nodes. Also, the homogeneous simple sensor nodes encrypt data and generate new keys periodically, thus exceeding their limited capacities. In another other side, data aggregation accuracy can be significately reduced through the use of the symmetric encryption on the simple sensor nodes (high computation delay).SDKAM was proposed by Sandhya and Murugan . Its mai(1)Encryption MechanismIHC encryption and decryption mechanisms are organized as follows:A Є Ml × l and an initialization vector u Є Vl are chosen.A random encryption matrix m is the vector Vl Є unencrypted data.Set 0 ≤ i <k, calculate For The encrypted data is represented by: The encryption function is given by: (2)Decryption Mechanismk times the following to return to A.Effective key management system: The authors propose an efficient key management in heterogeneous WSNs. This system is based on a decentralized algorithm for key pre-distribution and revocation, which includes the following phases:Key Pre-distribution: In this phase, the keys are chosen from pools of keys and then pre-distributed.Shared key discovery phase: A common key between the neighboring nodes is chosen among the pre-distributed keys.Key path establishment phase: After the secret key is revealed, a secure data transmission path, including encryption and decryption, is established.Key revocation phase: If a node is compromised, the shared keys are revoked through a voting algorithm. Compromised nodes are identified according to their behavior, and are isolated.With A of secret keys and the number of iterations k must be known.The SDAKM protocol is dedicated to heterogeneous WSNs. SDAKM ensures a secure data aggregation and can significantly increase the security degree of the network by providing a secure path through the data encryption process, and an efficient and decentralized key management protocol. Indeed, to decrypt an IHC encrypted text, the matrix A, he cannot decrypt any given cipher text without having a knowledge about k. Therefore, if the number of iterations k is kept secret as a part of the private key, IHC security is increased. In addition, if another vector u is used to encrypt each pure data vector, IHC security could be significantly improved.Therefore, even if an intruder knows the matrix of the keys The main requirement expected while deploying heterogeneous nodes is to exploit their high capacities of computation. SDKAM is based on the use of the privacy homomorphism and the symmetric keys, thus reinforcing security while efficiently exploiting the high capacities of the heterogeneous nodes. However, the protocol faces the limited number of allowed aggregation functions which reduce the degree of data aggregation. We assume that the accuracy requirement is not satisfied due to the use of the symmetric encryption which also affects the limited capacities of the homogeneous simple sensor nodes.et al. [RCDA was proposed by Chen et al. . To confRCDA-HETE is divided into five procedures: installation, intra-group encryption, intergroup encryption, aggregation and verification. During the installation procedure, necessary keys are loaded in the L-nodes and the H-nodes. Each L-node must share a key with the group leader. If the base station knows the information about the group before the deployment, the keys can be pre-loaded in all the L-nodes and the H-nodes. However, in the majority of WSNs, the nodes are deployed randomly.The encryption process begins when the L-nodes of the intra-group want to send their collected data to the corresponding H-node. The objective of this process is to establish a secure channel between the nodes. For example, a node In the intergroup encryption procedure, each H-node aggregates the received data. Then, the H-node encrypts and signs the obtained result. In addition, if the H-node receives the encrypted data and the signatures from the other nodes in the routing path, it will activate the aggregation function.Finally, the verification procedure realized by the base station insures the integrity and the authentication of the aggregation results.RCDA-HETE is a heterogeneous protocol which insures data integrity and authentication. Indeed, RCDA-HETE allows the verification of each sensed data using the H-nodes. The intergroup encryption allows the L-nodes to send encrypted collected data and an authentication message MAC to their leader to verify the data integrity. RCDA-HETE can also use diverse aggregation functions pre-loaded in the H-nodes before the deployment of the network. Thus, the nodes can execute the aggregation functions according to the application needs.RCDA-HETE is secured against malicious attacks. Indeed, the intra-group traffic is encrypted using a pair-wise key and the protocol generates a signature corresponding to each received data. Therefore, the attacker nodes cannot modify the messages or inject false data without the private key. If a malicious node compromises the sensor nodes, the following situations are considered: The adversary can compromise a sensor node and use it as a legal node. Additionally, if the value of a message is altered within a reasonable range, its detection becomes difficult. A malicious node can also try to alter the aggregation result. It can also impersonate the other nodes. The proposed protocol provides security against these attacks using a signature for each generated message. However, we consider that due to the key pre-distribution, the network becomes not scalable. Also, the key management system was not given by the authors.As RCDA-HETE is only based on the use of the simple symmetric encryption between the sensor nodes and the aggregation nodes, we assume that the first data aggregation security requirement in the heterogeneous WSN which is the high exploitation of the heterogeneous nodes capacities is not satisfied.+, an identity based signature scheme (IBS), and a batch verification technique with binary quick search (BQS) for finding invalid signatures. The used cryptographic primitives are adapted to heterogeneous clustered WSNs. Additive HE scheme is used to reduce the total length of the ciphertexts and to achieve end-to-end confidentiality. Due to the (IBS) scheme, hop-by-hop authentication is insured by verifying all the transmitted encrypted data. The batch verification technique is used to reduce the verification costs for multiple signatures. The invalid signatures in the batch verification are identified through the BQS using efficient methods [Sen-SDA was proposed by Shim . Sen-SDA methods .In their network model, the authors have assumed a WSN consisting of one stationary fixed BS which serves as a private key generator (PKG). The BS is responsible for the generation of the private keys for all the nodes. The network consists also of a large number of stationary heterogeneous sensor nodes with unique identifiers (IDs). Each node in the network is mapped to exactly one cluster and can directly communicate with its CH which verifies all the signatures received from its member nodes, applies the aggregation function to the ciphertexts, signs the aggregated ciphertext and sends the result directly to the BS.-The BS generates the system parameter which is preloaded in each sensor node.-The BS keeps a master secret key for the extraction of the private key and a secret key for the decryption of the ciphertexts.-+.Each sensor node encrypts a message using the public key of the BS and obtains a ciphertext through EC-ElGamal-The node uses then the private key to generate a signature.To send a ciphertext-signature pair, each sensor node performs the following steps:-The CH uses the batch verification technique to find and reject the invalid signatures.-The CH then aggregates the received messages with the private key, generates a new signature and sends the signed messages to the BS.After receiving the signed messages from its member nodes, each CH verifies the validity of the timestamps before performing the following steps:-The BS uses the batch verification technique with BQS until the batch verification is completed successfully.-If the batch verification is completed successfully, the BS recovers the message using the secret key corresponding to the public key.The BS verifies the validity of the timestamps before performing the following steps:Due to the use of homomorphic encryption, Sen-SDA is a secure protocol and ensures end-to-end confidentiality since the data is encrypted from the source to the destination using asymmetric encryption. To insure a higher degree of security and to overcome the insecurity of the homomorphic schemes against message modification attacks and injection attacks, the proposed homomorphic encryption is combined to a signature scheme.Sen-SDA also guarantees hop by hop authentication. Indeed, in Sen-SDA, all the intermediate CHs sign their aggregated data after verifying the signatures received from member nodes, and during the signatures verification, the CHs can filter the invalid signatures.To overcome the computational cost of public-key certificate distributions, verifications and storage Sen-SDA is based on the use of an efficient pairing free identity-based signature scheme.+, an identity based signature scheme (IBS), and a batch verification technique with binary quick search (BQS) for finding invalid signatures is a good way to exploit the heterogeneous nodes’ high capacities. However, the use of asymmetric encryption on simple heterogeneous nodes is not optimal due to the limited capacities of the sensor nodes. Also, homomorphic encryption significantly reduces the use of the aggregation functions which affects the data aggregation process and reduces the data aggregation accuracy.We assume that the combination of the homomorphic encryption scheme (HE), EC-El GamalHop by hop secure data aggregation protocols aim to provide strong data aggregation while ensuring data integrity . Neverthet al. [Sanli et al.  have proN readings.The basic idea of SRDA is that the nodes will transmit reference data instead of pure sensed data and only the difference between them is used. SRDA first provides a key distribution protocol with low memory overhead to secure the communication links, and then, to save energy, it uses a security mechanism with a variant strength. In this protocol, differential encrypted data representing the difference between the reference value and the sensed data are transmitted to the aggregation nodes instead of the pure sensed data, to reduce the number of transmitted bits. The reference value is the average of t for the first packet in the session.A node, which can be a sensor node or an aggregation node, transmits the results to a higher level, forwards the packet containing the pure sensed data The group leader creates a reference input j > 1, the sensor node sends differential data For subsequent readings When the session is finished, the group leader removes the reference input of the node.To guarantee security, secret keys are shared between the communicating nodes. To reduce the overload in the key distribution system, additional information such as the location of the sensor nodes can be used. After the network is deployed, the nodes begin an installation key phase or a shared key discovery phase. The aggregation protocol SRDA starts next. Its main steps are summarized as follows:Decrypt data and calculate the number of hops to the base station.NS is calculated as follows: Execute the aggregation function, and then encrypt the obtained result using RC6 algorithm (block cipher) . The numTransmit the encrypted result to the base station.The base station decrypts the received data using the corresponding decryption key.After receiving the sensed data, the aggregation nodes proceed as follows:SRDA protocol is proposed to guarantee data confidentiality using RC6 encryption algorithm. It also ensures data freshness by combining the key and the data aggregation updating. SRDA reduces the number of transmitted bits and increases the network security. It also reduces the energy consumption and bandwidth by sending differential data instead of the pure sensed data.However, due to the frequent changes in the positions of the nodes, which may imply false data transmissions and alter the encryption result, we assume that SRDA is not recommended for mobile WSNs. In addition, SRDA underexploits the high resource capacity of the heterogeneous sensor nodes as the used security mechanism is simple and does not guarantee a high security level. The introduced computation delay generated by the symmetric encryption may also reduce the data aggregation accuracy and compromise the data aggregation process.In the two levels data aggregation security protocols, the network is divided into two parts based on the sensor nodes resource capacities. As shown in In ,23 the aMost of the security protocols, used in data aggregation, aim to secure the network at the level of the aggregation nodes and to establish a secure channel between the aggregation nodes and the base station. However, the collected data, which represent an essential part of the aggregation process, come from a lower level; namely the homogeneous simple sensor nodes. Therefore, securing this level and the collected data becomes a good research option. Most of the studied protocols are interested in securing the higher levels. They also propose encryption mechanisms, which are mostly symmetrical, to secure the low level. This option certainly provides some degree of security, but imposes the computation overhead due to the keys’ distribution mechanisms. Indeed, the sensor nodes have very limited capacities. Therefore, they cannot tolerate the keys’ generation and storage mechanisms. In addition, the key distribution mechanism used between these nodes and the heterogeneous nodes implies additional security problems.In this context, we have proposed in a previous work a new secure data aggregation protocol named Secure Data Aggregation Watermarking-based Scheme in Homogeneous WSNs (SDAW) , which rWhen the data packet is received, the receiver node will extract the watermark. Then the node will use the original data contained in the data packet to generate a new watermark. The values of the extracted and the newly generated watermarks are compared. If they are identical, the node will accept the data and if they are not identical, the node will suppose that the data has been altered and will reject it. The proposed detection and verification mechanism is represented in Compared to the other proposed mechanisms, SDAW offers a good security level while respecting the limited capacities of the sensor nodes. Indeed, SDAW uses a lightweight but reliable security primitive. In addition, contrary to the proposed solutions based on symmetric encryption, which involves additional computation to generate and distribute the keys, and which requires more memory to store the keys, our proposed mechanism SDAW does not encrypt data but is based on the watermark dissimilation which makes it difficult to differentiate the watermark from the original data. Thus, the energy and the memory of the sensor nodes are conserved.To demonstrate the performance of SDAW, it was compared to another hop by hop security mechanism named SecureDAV . SecureDAt the high level of the network CLDWA was proposed to secure the data aggregation process based on a cross-layer reinforced watermarking algorithm . The fraLike the SDAW algorithm, the watermark generation in CLWDA is simple and uses a XOR function to combine the sensed data and the MAC address of the sensor. MD5 message digest algorithm is then used to hash the obtained result. The fragile watermark generation mechanism is enhanced with asymmetric encryption. Thus, the base station and the heterogeneous nodes generate and exchange the encryption keys, using an Elliptic Curve Diffie-Hellman algorithm (ECDH) , to encrThe integration of the watermark into the data packet is based on a Cross-layer watermark embedding mechanism through which the watermark position is dynamically attributed and varies frequently. For this, CLWDA uses the wake-up time of the sensor nodes to compute the watermark position on the data packets. Therefore, each sensor node uses the wake-up time of the neighbour nodes to calculate and identify the watermark position in the data packet. The detection and verification mechanism of CLWDA algorithm operates practically like the SDAW algorithm. When the data packet is received, the heterogeneous node or the base station will extract the watermark and decrypt it according to the cross-layer watermark extraction mechanism. Then, the node will use the original data contained in the data packet to generate a new watermark. The values of the extracted and the newly generated watermarks are compared. If they are identical, the node will accept the data and will reject it otherwise. The proposed detection and verification mechanism in the high level of the network is represented in The performances of CLWDA have been analyzed and compared to another heterogeneous and end to end based security mechanism named CDAP . The obtTo demonstrate the performance of CLWDA protocol compared to CDAP protocol in terms of data aggregation, several simulation experiments have been conducted where four different aggregation functions are used. The first aggregation function (F1) is simple and computes the average of the received data. The second aggregation function (F2) is more complex and computes the average of the collected data only if the value of all received data packets is different from a fixed threshold such as temperature. The third aggregation function (F3) is also complex and computes the difference between the received sensed values if they are greater than a fixed threshold. The last aggregation function (F4) computes the variance value of the received data on the aggregation nodes. The simulation results demonstrated that CDAP, like most of the homomorphism based encryption algorithms, can only use addition and multiplication functions to aggregate the encrypted data. Therefore, the use of complex data aggregation functions is not allowed, which may affect the data aggregation process and reduce the data aggregation accuracy. On the other hand, the watermarking concept does not restrict the use of the aggregation functions, which optimizes the data aggregation.Based on the experimental simulation results we can assume that the proposed two levels based data aggregation security protocol offers better performances compared to privacy homomorphism based protocols. Indeed, the watermarking based security scheme dose not restrict the use of the data aggregation function which optimizes the data aggregation degree. Also the reinforced watermarking algorithm exploits the high capacity of the heterogeneous sensor nodes and offers a good security level. The use of the lightweight fragile watermark at the level of the limited sensor node capacity optimizes data aggregation accuracy and the energy efficiency of the network. However, the watermarking based security scheme does not provide all the security properties  and was designed only to guarantee data integrity and authentication, which represents a security breach.Heterogeneous WSNs have opened a new research direction for several research problems, especially in the security domain. Securing the data aggregation process is one of the security problems which have been widely addressed in homogeneous WSNs, contrary to the heterogeneous WSNs where only a few works have addressed the issue. Based on the used data aggregation security approach, we have classified the existing heterogeneous data aggregation security protocols into three categories: End to end, hop by hop and two levels data aggregation security protocols. The end to end data aggregation security is the most popular approach since it was adopted by the majority of the proposed data aggregation security protocols. The main idea is to use the privacy homomorphism algorithms through which the aggregation functions can be applied directly to the encrypted data, thus protecting the integrity of the data while transmitting it from the aggregation nodes to the base station.The end to end data aggregation security protocols offer a high security level and exploit the high resource capacities of the sensor nodes. However, the use of the homomorphism based algorithms introduces several drawbacks. Indeed, the use of data aggregation functions is restricted to only multiplication and addition functions. In addition, privacy homomorphism based protocols suppose that non heterogeneous nodes  are charged to encrypt the sensed data based on symmetric key and send them to the aggregation nodes (heterogeneous nodes), which are charged to aggregate the received data using the privacy homomorphism algorithm. However, the encryption mechanism can bring extra charges for resource limited non heterogeneous sensor nodes. The good security level offered by the end to end data aggregation security protocols does not mean that all main security issues have been ensured . Indeed, authentication is ensured only by PIA and RCDA protocols where data freshness is ensured by SDKAM and Sen-SDA protocols. On the other hand, data integrity is not ensured by CDAP protocol. Contrary to the end to end data aggregation security approaches, the hop by hop data aggregation security approach encrypts and decrypts data at each aggregation node to provide strong data aggregation (no restriction on the use of the data aggregation functions) while ensuring data integrity and authentication. However, the data confidentiality cannot be ensured and the relayed data is thus more vulnerable to malicious attacks. Also, the hop by hop data aggregation security approach supposes that all the network nodes apply high computation cryptographic algorithms which is inefficient for the resource limited homogeneous sensor nodes deployed in the network. For these reasons, the hop by hop based data aggregation security protocols are not largely used, particularly when security is related to sensitive application areas.The third data aggregation security approach tries to overcome the limits of the two previous approaches by optimizing the data aggregation process, exploiting the high capacity of the heterogeneous aggregation nodes and respecting the limitation of the simple homogeneous sensor nodes. The main idea is to divide the network based on the sensor nodes’ capacities to efficiently balance the work load through the network. Consequently, the high computational data aggregation security algorithms are applied to the heterogeneous aggregation nodes to secure the data aggregation process while simple and lightweight security mechanisms are applied to resource constrained nodes to guarantee a secure data collection. The two levels data aggregation security approach remains a fresh research area and was recently introduced in ,25 whereIn this paper, we have addressed the problem of data aggregation security in heterogeneous wireless sensor networks, pointing out the needs, the constraints and various defense mechanisms used to solve the security problems. Indeed, heterogeneous WSNs are basically designed to address the limitations of conventional homogeneous WSNs. Heterogeneous nodes are supposed to have large capabilities which widely exceed those of the conventional nodes. Hence, introducing high data aggregation security algorithms which are cannot be used by classic nodes, and which offer the possibility of using many aggregation functions, is beneficial. Several complex security primitives can also be combined. The large storage space of the heterogeneous nodes can also be exploited to contain a large number of keys (for random key generation), increasing the security degree. The data aggregation security problem in heterogeneous WSNs remains a new research area and we have tried in this paper to shed light on it by presenting a survey of the few proposed protocols. We have also proposed a new classification of the surveyed protocols, based on the adopted data aggregation security strategy. Finally, an evaluative discussion is given at the end of the paper to analyze the advantages and the disadvantages of each heterogeneous data aggregation security category.


Today, while many researchers focus on the improvement of the regularization term in IR algorithms, they pay less concern to the improvement of the fidelity term. In this paper, we hypothesize that improving the fidelity term will further improve IR image quality in low-dose scanning, which typically causes more noise. The purpose of this paper is to systematically test and examine the role of high-fidelity system models using raw data in the performance of iterative image reconstruction approach minimizing energy functional. We first isolated the fidelity term and analyzed the importance of using focal spot area modeling, flying focal spot location modeling, and active detector area modeling as opposed to just flying focal spot motion. We then compared images using different permutations of all three factors. Next, we tested the ability of the fidelity terms to retain signals upon application of the regularization term with all three factors. We then compared the differences between images generated by the proposed method and Filtered-Back-Projection. Lastly, we compared images of low-dose in vivo data using Filtered-Back-Projection, Iterative Reconstruction in Image Space, and the proposed method using raw data. The initial comparison of difference maps of images constructed showed that the focal spot area model and the active detector area model also have significant impacts on the quality of images produced. Upon application of the regularization term, images generated using all three factors were able to substantially decrease model mismatch error, artifacts, and noise. When the images generated by the proposed method were tested, conspicuity greatly increased, noise standard deviation decreased by 90% in homogeneous regions, and resolution also greatly improved. In conclusion, the improvement of the fidelity term to model clinical scanners is essential to generating higher quality images in low-dose imaging. Computed tomography (CT) is one of the most commonly used diagnostic imaging modalities in modern medicine. CT enables rapid, non-invasive image acquisition at high resolutions. However, CT also exposes the patient to radiation The drive towards lower dose CT imaging  has been an area of focus for the entire CT community Through recent studies, iterative reconstruction (IR) algorithms have been shown to be more robust than FBP algorithms in regards to the presence of noise and artifacts A critical component of tomographic IR algorithms is the accuracy of the forward system model. In positron emission tomography (PET), the forward system model consists of a geometric projection matrix and a sinogram blurring matrix, which can be either measured or simulated In this paper, we show the systematic implementation of accurate system modeling for an IRT in clinical CT. A similar approach for PET Also, there are algorithms  implemented in clinical scanners by vendors, but the technical description and detailed methods are not available to the research community. In this paper, we systematically demonstrate the necessity of implementing focal spot area, flying focal spot, and detector area in the forward system model to generate higher quality images. We also compare our raw-data-domain IRT with a mathematical formulation of image domain iteration called Iterative Reconstruction in Image Space (IRIS). The purpose of this paper is to examine the role of high-fidelity system models in the performance of the iterative image reconstruction approach minimizing energy functional. This paper is organized as follows. In section 2, we mathematically describe iterative image reconstruction and the components of proposed system models. In section 3, we present some initial results on phantom and in vivo data. In section 4, we summarize our findings and conclusions.In this section, we describe the mathematical formulation of IRT and a detailed forward system modeling method. The forward system modeling method can be decomposed into a series of components to increase modeling accuracy. We structure a three-component model that incorporates the most important elements of the system model. Each component can be replaced by a specific scanner parameter or vendor-specific model. The accuracy of this system model is critical in the improvement of image quality of a reconstructed image.We assume a transmission CT system with a field of x-ray attenuation coefficients When The models include a geometric projector  solution without the regularization term and TV solution in A focal spot is the region where electrons transfer their energy to target atoms in order to generate X-rays. In many cases, the focal spot is approximated as a point model, but in reality, the focal spot consists of a finite area  with respect to conspicuity improvement, noise statistics, and resolution. In an in vivo study, we show clinical evidence that supports the proposed approach with subjective assessment. The proposed method is compared with conventional FBP and image domain IR (IRIS) algorithms in a low dose scan. In this case, we used the same raw data for image reconstructions.A cone beam phantom with a spatial resolution section with In the following sections we demonstrate the impact of our various system modules. We will use the following notation: the triplet In To compare artifact propagation, we compare the LS and TV images with a soft contrast section of the phantom. The three cross-sections of the soft contrast region are displayed in To observe the effects of iterations, we simulated a Siddon-type projector with proper Note that the proposed method exhibits significant modeling error reduction in terms of visual evaluation and NRMSE taking into account the nonlinear scaling of log-log plot.In We found that it is difficult to detect low contrast circles  in a low dose scan. In this case, we used the same raw data for image reconstructions. This study was conducted in compliance with the Health Insurance Portability and Accountability Act (HIPAA) and used a scan protocol approved by the Massachusetts General Hospital Institutional Review Board (IRB). We obtained written informed consent as per Federal U.S. guidelines. All procedures in this study were performed in accordance with the approved protocol.A patient was scanned on a dual source For this case, images with the volume In this experiment, we compare three different reconstruction approaches: the conventional FBP method, image domain iterative IRIS, and raw data domain IRT with the proposed methods. We have used To compare images, we defined a priori the regions of comparison. For SNR, the signal is defined over the region containing the hepatic artery, while the background standard deviation is chosen from patches . We have introduced a modular system modeling framework for a sophisticated clinical CT scanner. Even within the same system, some functions can be turned off or manipulated for clinical purposes. The advanced functions of state-of-art CT scanners need to be modeled accordingly for high quality image reconstruction. These parameter changes are meticulously recorded in the header files of raw data. None of these functions can be ignored for accurate system modeling to develop high-fidelity characteristics of an iterative algorithm.As shown in At 50% dose, both IRIS and the proposed TV with advanced system modeling were found to be diagnostically acceptable. Although the proposed TV provided objectively superior images in terms of SNR and CNR, this image quality was achieved through a significant amount of processing. As a technique that achieves fast computations while maintaining good image quality, a hybrid method (such as IRIS) may potentially be a promising approach.Future work will also address a variety of dose reductions on cadavers, and we anticipate being able to reduce computation time for the proposed advanced system modeling by implementing it on parallel computing architectures.


Lung cancer is ranked first worldwide as one of the main cancers in terms of prevalence and mortality rate. The development of effective treatment strategies against lung cancer is therefore of paramount importance. Traditionally, chemotherapy was employed in the treatment of various cancers. However, the non-specific nature of the actions of chemotherapeutic drugs and the potential for tumors to develop resistance to these drugs may render chemotherapy a less favorable option for cancer treatment. Immunotherapy provides an alternative strategy for this purpose. It involves the utilization of the immune system and the immune effector cells to elicit an immune response to the tumors, thereby eliminating them. Strategies include the administration of pro-inflammatory cytokines for immune stimulation, the removal of immunological checkpoints using monoclonal antibodies, and the use of cancer vaccines to enhance immunity against tumors. This article summarizes the above strategies, highlights the reasons why immunotherapy is superior to chemotherapy for the purpose of tumor removal, and reviews the recent clinical studies comparing the clinical outcomes of patients undergoing immunotherapy and chemotherapy. The article also describes advances in immunotherapeutic strategies for the treatment of lung cancer. Lung cancer has long been considered one of the most prevalent cancers in the world. It has become an increasing burden on human health since the 1930s, when both the incidence and mortality rates of lung cancer began rising steadily . TherefoThrough years of research, we have been able to gain a better understanding of the molecular mechanisms and pathways responsible for tumor formation and development. All these endeavors have contributed to the development of chemotherapy where these molecular pathways are targeted to halt tumor growth with the use of anti-cancer drugs. In addition, immunotherapy, the exploitation of the human immune system in the fight against tumors, has also emerged as an effective strategy in cancer treatment, resulting in an increased interest expressed by pharmaceutical companies in the development of immunotherapy drugs. Therefore, one may wonder why the research journey for cancer treatment should go beyond the development of chemotherapy, and why immunotherapy is seen as a milestone for cancer treatment so that it is able to attract the attention of pharmaceutical companies. This article will highlight the rationale and advantages of immunotherapy and will briefly describe the advances in immunotherapy that contribute to its success in lung cancer treatment.Chemotherapy can be regarded as one of a series of traditional methods for cancer treatment, with its first trial dating back to 1942, when nitrogen mustard was used to treat a patient with lymphoma . It invoDespite the potential of chemotherapeutic drugs in tumor removal, it is the way in which they help remove tumors that creates problems with their use, leading to the development of adverse side effects. After a chemotherapeutic drug is administered to the body, the drug travels around the body in the bloodstream, conferring toxicity to actively proliferating cells. However, this non-specific removal of proliferating cells would also make healthy cells that are dividing be the target of the chemotherapeutic drug. Such non-specific cytotoxicity of the drugs could lead to massive cell death. This would warrant an extensive repair mechanism, causing a significant depletion of energy for individuals using the drugs. This is likely the reason why patients receiving chemotherapy experience severe fatigue. In addition, cancer patients receiving chemotherapy are also vulnerable to the damage of their vital organs. Cisplatin, a drug used in non-small cell lung cancer (NSCLC) treatment, was found to lead to kidney damage, an effect partly attributed to the production of pro-inflammatory cytokines . ChemothIn light of such drawback, molecular oncologists had developed a more effective way of chemotherapeutic drug delivery to the tumors, so that the drug can be targeted to the tumors more specifically. The rationale of such drug delivery method is based on the phenomenon that cancer cells normally display specific antigens on their cell surface which are not present on healthy cells. Therefore, certain monoclonal antibodies that possess the ability to bind specifically to these tumor antigens can be utilized to direct the chemotherapeutic drugs specifically to the tumors. These antibodies can be conjugated to the drug to form an immuno-conjugate. It can then be administered to the body of the patients, and the antibodies would direct the drug towards the tumor, where the drug can exert its effects. Such techniques, often called targeted chemotherapy, would ensure that only tumor cells would be targeted for removal, thereby limiting the side effects caused by inappropriate removal of healthy cells.Another major drawback of chemotherapy is the tendency of tumors to develop a resistance to chemotherapeutic drugs, increasing the potential of tumors to reappear after patients receive chemotherapy . Tumor rAs discussed, chemotherapy suffers from drawbacks such as non-specificity and tumor resistance, leading to unwanted side effects and ineffectiveness in halting tumor growth respectively. In response to this, the utilization of the natural body defense system—a system that would ensure that only specific cells would be targeted for removal and that unhealthy cells would be effectively eliminated—should therefore be considered to increase the effectiveness of halting tumor progression. Such consideration has led to the development of immunotherapy, a type of cancer therapy involving the boosting of the ability of the body’s immune system in tumor removal, as an alternative strategy in cancer treatment.In fact, the first trial concerning the use of the immune system in tumor control dates back to 1891, when William Coley discovered that an immune response against a tumor was generated following the injection of streptococcal bacteria into the tumor, thereby causing a reduction of its size . This phAs discussed above, cytokines are one of the first components to be involved in an immune response against tumors, through the induction of the cytotoxic function of T cells. Therefore, cytokines are widely used in current immunotherapies. For example, combinatorial treatment of low doses of interleukin-2 (IL-2) and TNF-α in NSCLC patients has resulted in enhanced tumor regression , making However, there are occasions when the immune system may fail to detect the tumor and destine it for elimination, as tumors themselves may employ defense mechanisms so that they are able to escape immune surveillance. In fact, the immune system would impose certain so called “immunological checkpoints” for itself, so that it would not be able to eliminate the “self” and healthy cells during an immune response to a pathogen or tumor. For example, cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) expressed on T cells, once bound to B7/cluster of differentiation 80 (CD80) molecule on the antigen-presenting cells, would elicit an inhibitory signal to compete with the immune co-stimulatory signal exhibited by the activated co-stimulatory receptor known as CD28. This keeps the activation of T cells in check, and thereby induces immune tolerance. Tumors exploit this immunological checkpoint pathway in order to prevent themselves from being detected and eliminated by the immune system. They express a constitutively low level of B7/CD80 molecule , resultiet al. [et al. [The effectiveness of immune checkpoint inhibitors in the treatment of NSCLC was previously documented. Indeed, Borghaei et al.  and Brah [et al.  comparedDespite the apparent superiority of immunotherapy over traditional chemotherapy in terms of effectiveness in resisting tumor growth, the toxicity profiles of certain immunotherapeutic agents did raise concerns over their utilization in cancer treatment. These concerns are largely caused by the occurrence of immune-related adverse events, which were reported in previous immunotherapeutic clinical trials. For example, the use of BMS-936558, an anti-PD-1 antibody, in a clinical trial resulted in 14% of patients suffering from grade 3 or 4 adverse events. These events include rashes, fatigue and diarrhea . PembrolOverall, to enhance the effectiveness of tumor removal, immunotherapy agents target both the pathways of immune system activation (use of cytokines) and immune system inhibition . However, the likelihood of the development of immune-related adverse events following the utilization of certain immunotherapeutic agents prompts that immunosuppressive therapies may become necessary during the course of immunotherapy.In addition to the aforementioned immunotherapy agents, cancer vaccines have also received considerable attention in research on cancer treatment. They normally contain a certain tumor-specific antigen, such as that in the form of peptides derived from a tumor antigen. Therefore, once administered, an immune response can be mounted against the antigen that is only found in tumors. In this way, the immune system would be “trained” to act against the tumors expressing that antigen, thereby enhancing anti-tumor immune responses.Recently, a number of lung cancer vaccine products have been developed in the form of peptides derived from telomerase and MUC-1, two proteins found to be highly expressed in lung tumors. For example, the administration of GV-1001, a peptide-based vaccine against telomerase, to NSCLC patients was found to immunize these patients against lung tumors by enhancing the immunological memory exhibited by T cells, with minimal adverse side effects . LikewisIt is clearly evident that immunotherapy has significant advantages over the traditional chemotherapeutic strategies in cancer treatment. Immunotherapy allows a bypass of the problem of tumor resistance to chemotherapeutic drugs. It also offers an opportunity to resolve the problem of immune tolerance of tumors through the use of monoclonal antibodies that block the inhibitory signals for the activation of immune effector cells to eliminate tumors. All these factors contribute to the fact that lung cancer patients receiving immunotherapy can live on average 3.2 months longer than those on a chemotherapy course . Despite