PURPOSE:This study aimed to quantify residual radioactivity in medical devices used during 18F-florbetapir administration with the UG-02 automated infusion device and to identify the optimal residual setting for accurate dose calculation. METHODS:We analyzed 52 amyloid positron emission tomography (PET) examinations performed at our institution. After radiotracer administration, residual radioactivity was measured in the drug vial, infusion circuit, route, residual solution, and individual circuit components. Administration rates and residual ratios were calculated after decay correction to the injection time. Residual ratios estimated by the UG-02 system were compared with measured values, and the optimal residual setting was determined using least-squares optimization. Statistical analyses were performed using paired t-tests, with statistical significance set at P<0.05. RESULTS:The mean administered dose was 348.0±33.3 MBq, whereas the mean residual activity was 93.1±12.6 MBq, corresponding to an administration rate of 77.8% and a residual ratio of 22.2%. The infusion circuit exhibited the highest residual ratio (18.0%), primarily attributable to the air vent filter (13.5%) and infusion set (4.0%). The UG-02 system significantly overestimated the residual ratio in the drug vial compared with the measured value (1.5% vs. 0.9%, P<0.01). The optimal residual setting was 16.1%, reducing the relative error of the displayed dose from 17.1% to 0.08%. CONCLUSION:This study characterized residual distribution within the UG-02 automated infusion system and identified an optimal residual setting for 18F-florbetapir administration. Implementing this setting improves dose calculation accuracy, reduces underdosing risk, and may contribute to improving the quantitative reliability of amyloid PET imaging.
PURPOSE:We investigated the effects of matrix size and magnification ratio on positron emission tomography (PET) image quantitative characteristics using a semiconductor detector PET/CT. METHODS:Three types of phantom were filled with 18F-fluorodeoxyglucose solution and scanned. Images were reconstructed using the ordered-subsets expectation-maximization method, with matrix sizes of 128, 220, 256, 440, 512, and 880, and magnification ratios of 1.0, 1.5, 2.0, 2.5, and 3.0. We evaluated the maximum standardized uptake value (SUVmax), percentage coefficient of variation (%CV), and full width at half maximum (FWHM). RESULTS:Minimal differences in the SUVmax, %CV, and FWHM were observed between the matrix sizes of 128 and 220, and between 440, 512 and 880. However, significant differences were observed between the matrix sizes of 220 and 256, as the largest difference, and between 256 and 440. The influence of the magnification ratio on the image quality was small. CONCLUSION:The magnification ratio has a minor effect on quantitative values and image quality, whereas the impact of matrix size is significant. A noticeable difference in evaluation was observed between matrix sizes of 220 and 256. This was considered an important factor in determining the matrix size for this device.
PURPOSE:Radiochromic film is widely used for patient-specific intensity-modulated radiation therapy quality assurance (IMRT QA) because of its high spatial resolution. However, calibration for converting pixel values to dose requires irradiation at multiple known dose levels, resulting in a substantial workload. Consequently, in some institutions, calibration is performed only under limited circumstances, such as when the film lot changes. This study aimed to develop and validate a Bayesian inference model that estimates the calibration curve using previously acquired calibration datasets together with the unirradiated pixel value of the target film, thereby improving the efficiency of the calibration process. METHODS:A total of 93 calibration datasets acquired using TomoHD were analyzed. A quadratic polynomial regression model was constructed with dose and elapsed time from irradiation to scanning as explanatory variables. Separate models were developed for each scanner orientation (portrait and landscape), and the intercept was estimated using the unirradiated pixel value of the target film. Bayesian inference was performed using Stan, and model convergence was evaluated by trace plots and the Rhat statistic. Model performance was validated using 10 EBT4 films from a different lot by comparing predicted and measured pixel values and evaluating dose errors. RESULTS:All models showed good convergence, with Rhat values below 1.01. For the validation films, the pixel value error was less than 3.6%, and the coefficient of determination (R2) exceeded 0.99. The mean dose error was 2.7±1.3 cGy at 24.0 cGy and 37.5±12.8 cGy at 868.2 cGy. The maximum dose error was 66.6 cGy at 710.6 cGy. CONCLUSION:The proposed method demonstrated the feasibility of estimating the calibration curve using previously acquired calibration datasets and the unirradiated pixel value of the target film. This approach has the potential to improve the efficiency of radiochromic film calibration. Future studies should apply this method to patient-specific IMRT QA and investigate its impact on dose distribution evaluation.
PURPOSE:The purpose of this study is to evaluate the effects of task shifting/sharing, in which radiological technologists assist physicians during vascular access interventional therapy (VAIVT) procedures, on radiation exposure and procedure time for both physicians and radiological technologists. METHODS:We retrospectively compared cases in which radiological technologists assisted with VAIVT procedures and those performed by physicians alone. Radiation exposure was evaluated using the estimated lens radiation dose, air kerma, and dose-area product values. Subsequently, the procedural difficulty and procedure time were assessed. RESULTS:Estimated lens radiation doses were highest in physicians, followed by assisting radiological technologists, and then radiological technologists in their conventional positions. Air kerma at the patient entrance reference point and air kerma area product were significantly lower in the group where radiological technologists aided, whereas no significant differences were observed. CONCLUSION:The results suggest that introducing a rotational system in which physicians and radiological technologists alternate performing assisted VAIVT procedures may reduce physicians' working hours and radiation exposure.
PURPOSE:This study aimed to evaluate the relationship between computed tomography (CT) attenuation values obtained from virtual monochromatic images (VMI) and virtual non-contrast (VNC) images generated by dual-energy CT (DECT) and hemoglobin concentration (Hb), and to investigate the feasibility of anemia assessment using DECT. METHODS:A total of 400 patients (200 males and 200 females) who underwent abdominal contrast-enhanced CT with dual-energy mode were included. Non-contrast VMIs at 70 keV (diaphragmatic dome and celiac artery levels) and equilibrium-phase VNC images (celiac artery level) were generated, and CT attenuation values were measured in the aortic lumen. Correlations between CT values and Hb levels, as well as receiver operating characteristic (ROC) analyses, were performed. RESULTS:For non-contrast VMI, correlation coefficients at the diaphragmatic dome were 0.582 in males and 0.562 in females, and at the celiac artery level were 0.829 in males and 0.860 in females. For VNC images, the coefficients were 0.628 in males and 0.545 in females. ROC analysis of non-contrast VMI at the celiac artery level showed the highest diagnostic performance, with area under the curve values of 0.914 in males and 0.920 in females. CONCLUSION:CT attenuation values on non-contrast VMI at the celiac artery level demonstrated strong correlations with Hb and support the clinical utility of DECT for noninvasive anemia assessment.
