Technical developments are ongoing in CT, and there has been a continually increasing trend in patient prescription, resulting in increased exposure. Currently, doses delivered during CT are generally evaluated using ...Technical developments are ongoing in CT, and there has been a continually increasing trend in patient prescription, resulting in increased exposure. Currently, doses delivered during CT are generally evaluated using computed tomography dose index (CTDI), which is measured with a 10 cm pencil ionization chamber placed in a 14 cm PMMA phantom. However, shortfalls in CTDI have been identified by the American Association of Physicists in Medicine (AAPM) who have proposed a new method, dose equilibrium (DEq). In this paper, the dose equilibrium was used to estimate the dose in two protocols (thoracic and abdominopelvic) and compared to CTDI values. In addition, a retrospective correction was applied to 20 patient CTDI’s by characterizing the specific DEq profile of the system scans. The results indicated the dose equilibrium estimations of two protocols, thoracic and abdominopelvic, were 29% and 30% respectively, higher than those informed by the CT scanner. In addition, a retrospective dose correction estimation of a random sample of twenty patients demonstrated an annual underestimation in absorbed dose by between 26% and 28%. Continued use of the CTDI method in quality assurance of modern CT could result in greater patient risk. AAPM Task Group 111 presents a more accurate, safer method to estimate dose and its adoption is paramount.展开更多
Branchial arch anomalies can arise from the four first branchial arches, but the most encountered cases are from the second one. Second branchial arch cysts and abscesses occur mainly in older children or young adults...Branchial arch anomalies can arise from the four first branchial arches, but the most encountered cases are from the second one. Second branchial arch cysts and abscesses occur mainly in older children or young adults while fistulae are discovered in young children. We report a case of complete second branchial arch fistula of Bailey III type with adult complaints of painful swelling and local reddishness followed by spontaneous discharge and disappearance of complaints. Diagnosis was based on ultrasound and confirmed by CT scan, with the classic “beak sign” visible on both exams. Three cases were encountered in the family, with no otologic or kidney symptoms, which is quite different from the classical branchiootorenal syndrome which associates severe inner ear and kidney congenital anomalies.展开更多
Objective:To develop a computational model of a multi-detector CT scanner(MDCT),which could be used to simulate the signal of each detector element in the MDCT by using the Monte Carlo method.Methods:The CT scanner wa...Objective:To develop a computational model of a multi-detector CT scanner(MDCT),which could be used to simulate the signal of each detector element in the MDCT by using the Monte Carlo method.Methods:The CT scanner was modelled,including the X-ray source,the bowtie filter,the collimator,the couch and the detector panel.Under a general scanning condition,the signal in each detector element was simulated based on the model by using the MCNPX code.Both the energy spectra at different tube voltages and energy deposition in the detector panel at different collimations were simulated to test the robustness of the MDCT model built in this study.Furthermore,the simulated signals in each detector element were compared with their recorded signals.The accuracies were evaluated by the relative root mean square error(RRMSE)and the structural similarity(SSIM)for each detector element and the whole detector panel,respectively.Results:The simulated energy spectra before and after passing through the phantom and simulated energy deposition in the detector panel were rational.In the scan range from the apex of lung to pubic symphysis,the RRMSE of the 18 axial projections ranged from 0.02 to 0.17,with an average of 0.08.And the SSIMs were calculated to be 0.979 and 0.976 for projections with the largest peak signal and the smallest peak signal,respectively.Conclusions:The computational model of the MDCT developed in this study is accurate and successful,it is helpful for further accurate simulations of the radiation dose and image quality of the MDCT.展开更多
文摘Technical developments are ongoing in CT, and there has been a continually increasing trend in patient prescription, resulting in increased exposure. Currently, doses delivered during CT are generally evaluated using computed tomography dose index (CTDI), which is measured with a 10 cm pencil ionization chamber placed in a 14 cm PMMA phantom. However, shortfalls in CTDI have been identified by the American Association of Physicists in Medicine (AAPM) who have proposed a new method, dose equilibrium (DEq). In this paper, the dose equilibrium was used to estimate the dose in two protocols (thoracic and abdominopelvic) and compared to CTDI values. In addition, a retrospective correction was applied to 20 patient CTDI’s by characterizing the specific DEq profile of the system scans. The results indicated the dose equilibrium estimations of two protocols, thoracic and abdominopelvic, were 29% and 30% respectively, higher than those informed by the CT scanner. In addition, a retrospective dose correction estimation of a random sample of twenty patients demonstrated an annual underestimation in absorbed dose by between 26% and 28%. Continued use of the CTDI method in quality assurance of modern CT could result in greater patient risk. AAPM Task Group 111 presents a more accurate, safer method to estimate dose and its adoption is paramount.
文摘Branchial arch anomalies can arise from the four first branchial arches, but the most encountered cases are from the second one. Second branchial arch cysts and abscesses occur mainly in older children or young adults while fistulae are discovered in young children. We report a case of complete second branchial arch fistula of Bailey III type with adult complaints of painful swelling and local reddishness followed by spontaneous discharge and disappearance of complaints. Diagnosis was based on ultrasound and confirmed by CT scan, with the classic “beak sign” visible on both exams. Three cases were encountered in the family, with no otologic or kidney symptoms, which is quite different from the classical branchiootorenal syndrome which associates severe inner ear and kidney congenital anomalies.
基金National Key R&D Program of China(2019YFC0117304)National Natural Science Foundation of China(12175043,12075064).
文摘Objective:To develop a computational model of a multi-detector CT scanner(MDCT),which could be used to simulate the signal of each detector element in the MDCT by using the Monte Carlo method.Methods:The CT scanner was modelled,including the X-ray source,the bowtie filter,the collimator,the couch and the detector panel.Under a general scanning condition,the signal in each detector element was simulated based on the model by using the MCNPX code.Both the energy spectra at different tube voltages and energy deposition in the detector panel at different collimations were simulated to test the robustness of the MDCT model built in this study.Furthermore,the simulated signals in each detector element were compared with their recorded signals.The accuracies were evaluated by the relative root mean square error(RRMSE)and the structural similarity(SSIM)for each detector element and the whole detector panel,respectively.Results:The simulated energy spectra before and after passing through the phantom and simulated energy deposition in the detector panel were rational.In the scan range from the apex of lung to pubic symphysis,the RRMSE of the 18 axial projections ranged from 0.02 to 0.17,with an average of 0.08.And the SSIMs were calculated to be 0.979 and 0.976 for projections with the largest peak signal and the smallest peak signal,respectively.Conclusions:The computational model of the MDCT developed in this study is accurate and successful,it is helpful for further accurate simulations of the radiation dose and image quality of the MDCT.
