Quantifying Radiation Doses in Common Endoscopic Retrograde Cholangiopancreatography Scenarios: An Evaluation of Radiation Safety Measures in a Real-World Environment.

Introduction Radiation safety training remains variable among gastroenterologists performing endoscopic retrograde cholangiopancreatography (ERCP). This study sought to ascribe dosimeter readings to various real-world ERCP scenarios to provide data supporting the 3 pillars of radiation safety: distance, time, and shielding. Methods An ERCP fluoroscopy unit was used to generate radiation scatter from 2 differently sized anthropomorphic phantoms. Radiation scatter was measured at various distances from the emitter, with and without a lead apron, and at various frame rates (measured in frames per second, fps) and degrees of fluoroscopy pedal actuation. An image quality phantom was used to assess resolution at various frame rates and air gaps. Results Increasing the distance resulted in a decrease in measured scatter (from 0.75 mR/h at 1.5 ft to 0.15 mR/h at 9 ft with the average phantom and from 50 mR/h at 1.5 ft to 3.06 mR/h at 9 ft with the large phantom). Depressing the fluoroscopy pedal less frequently, or decreasing the frame rate (ie, increasing the time per frame), resulted in a linear decrease in scatter (from 55 mR/h at 8 fps to 24.5 mR/h at 4 fps and 13.60 mR/h at 2 fps). Providing shielding through the presence of a 0.5-mm lead apron reduced scatter (from 4.10 to 0.11 mR/h with the average phantom; from 15.30 mR/h to 0.43 mR/h with the large phantom). However, decreasing the frame rate from 8 fps to 2 fps did not change the number of line pairs identified on the image phantom. A greater air gap increased the number of line pairs resolved. Conclusions Implementing the 3 pillars of radiation safety led to a quantifiable, clinically significant decrease in radiation scatter. The authors hope that these findings spark greater implementation of radiation safety measures among practitioners utilizing fluoroscopy.

Multi-institution consensus paper for acquisition of portable chest radiographs through glass barriers.

BACKGROUND: To conserve personal protective equipment (PPE) and reduce exposure to potentially infected COVID-19 patients, several Californian facilities independently implemented a method of acquiring portable chest radiographs through glass barriers that was originally developed by the University of Washington. METHODS: This work quantifies the transmission of radiation through a glass barrier using six radiographic systems at five facilities. Patient entrance air kerma (EAK) and effective dose were estimated both with and without the glass barrier. Beam penetrability and resulting exposure index (EI) and deviation index (DI) were measured and used to adjust the tube current-time product (mAs) for glass barriers. Because of beam hardening, the contrast-to-noise ratio (CNR) was measured with image quality phantoms to ensure diagnostic integrity. Finally, scatter surveys were performed to assess staff radiation exposure both inside and outside the exam room. RESULTS: The glass barriers attenuated a mean of 61% of the normal X-ray beams. When the mAs was increased to match EI values, there was no discernible degradation of image quality as determined by the CNR. This was corroborated with subjective assessments of image quality by chest radiologists. The glass-hardened beams acted as a filter for low energy X-rays, and some facilities observed slight changes in patient effective doses. There was scattering from both the phantoms and the glass barriers within the room. CONCLUSIONS: Glass barriers require an approximate 2.5 times increase in beam intensity, with all other technique factors held constant. Further refinements are necessary for increased source-to-image distance and beam quality in order to adequately match EI values. This does not result in a significant increase in the radiation dose delivered to the patient. The use of lead aprons, mobile shields, and increased distance from scattering sources should be employed where practicable in order to keep staff radiation doses as low as reasonably achievable.

Performance Evaluation of Material Decomposition With Rapid-Kilovoltage-Switching Dual-Energy CT and Implications for Assessing Bone Mineral Density.

OBJECTIVE: The purpose of this article is to quantitatively investigate the accuracy and performance of dual-energy CT (DECT) material density images and to calculate the areal bone mineral density (aBMD) for comparison with dual-energy x-ray absorptiometry (DEXA). MATERIALS AND METHODS: A rapid-kilovoltage-switching DECT scanner was used to create material density images of various two-material phantoms of known concentrations under different experimental conditions. They were subsequently also scanned by single-energy CT and DEXA. The total uncertainty and accuracy of the DECT concentration measurements was quantified by the root-mean-square (RMS) error, and linear regression was performed to evaluate measurement changes under varying scanning conditions. Alterations to accuracy with concentric (anthropomorphic) phantom geometry were explored. The sensitivity of DECT and DEXA to changes in material density was evaluated. Correlations between DEXA and DECT-derived aBMD values were assessed. RESULTS: The RMS error of DECT concentration measurements in air ranged from 9% to 244% depending on the materials. Concentration measurements made off-isocenter or with a different DECT protocol were slightly lower (≈ 5%), whereas measurement in scattering conditions resulted in a reduction of 8-27%. In concentric phantoms, higher-attenuating material in the outer chamber increased measured values of the inner material for all methods. DECT was more sensitive than DEXA to changes in BMD at 2 mg/mL K2HPO4. Measurements of aBMD using DECT and DEXA were highly correlated (R(2) = 0.98). CONCLUSION: DECT material density images were linear in response but prone to poor accuracy and biases. DECT-based aBMD could be used to monitor relative change in bone density.

Detection of aortic arch calcification in apolipoprotein E-null mice using carbon nanotube-based micro-CT system.

BACKGROUND: We performed in vivo micro-computed tomography (micro-CT) imaging using a novel carbon nanotube (CNT)-based x-ray source to detect calcification in the aortic arch of apolipoprotein E (apoE)-null mice. METHODS AND RESULTS: We measured calcification volume of aortic arch plaques using CNT-based micro-CT in 16- to 18-month-old males on 129S6/SvEvTac and C57BL/6J genetic backgrounds (129-apoE KO and B6-apoE KO). Cardiac and respiratory gated images were acquired in each mouse under anesthesia. Images obtained using a CNT micro-CT had less motion blur and better spatial resolution for aortic calcification than those using conventional micro-CT, evaluated by edge sharpness (slope of the normalized attenuation units, 1.6±0.3 versus 0.8±0.2) and contrast-to-noise ratio of the calcifications (118±34 versus 10±2); both P<0.05, n=6. Calcification volume in the arch inner curvature was 4 times bigger in the 129-apoE KO than in the B6-apoE KO mice (0.90±0.18 versus 0.22±0.10 mm(3), P<0.01, n=7 and 5, respectively), whereas plaque areas in the inner curvature measured in dissected aorta were only twice as great in the 129-apoE KO than in the B6-apoE KO mice (6.1±0.6 versus 3.7±0.4 mm(2), P<0.05). Consistent with this, histological calcification area in the plaques was significantly higher in the 129-apoE KO than in the B6-apoE KO mice (16.9±2.0 versus 9.6±0.8%, P<0.05, 3 animals for each). CONCLUSIONS: A novel CNT-based micro-CT is a useful tool to evaluate vascular calcifications in living mice. Quantification from acquired images suggests higher susceptibility to calcification of the aortic arch plaques in 129-apoE KO than in B6-apoE KO mice.