Objectives: The aim of this study was to evaluate an influence of post-processing scatter correction in portable abdominal radiography using a low ratio anti-scatter grid (grid). Methods: To assess tube voltage on portable abdominal radiography, a burger phantom was used to measure for inverse of image quality figure (IQFinv). For evaluation of the influence on using or not the grid, IQFinv were measured. Abdominal phantom radiographies were assessed subjectively, in random order, by six radiologic technologists. The radiographies were performed without scatter correction [IG (−)] and with scatter correction at equivalent for grid ratio 6 [IG (6)] and 8 [IG (8)]. Results: There was no significant decrease in IQFinv with 75 and 80 kV in comparison of 70 kV. Even processing scatter correction, IQFinv with using the grid was significantly higher than that without using the grid. The ability to detect nasogastric tube and stomach gas were significantly better in the scatter correction. Deviation index for IG (6) and IG (8) were significantly lower than that of IG (−). Discussion: Portable abdominal radiographies will be improved image quality by utilizing scatter correction, although, it is necessary to consider the scatter correction processing as this may significant decrease deviation index in the practical situation. Conclusion: The post-processing scatter correction should be useful for detection nasogastric tube and stomach gas in portable abdominal radiography.
Purpose: Computed tomography (CT) attenuation correction of myocardial perfusion in single-photon emission computed tomography (SPECT) /CT systems is possibility of misregistration between emission and transmission scans. This study aimed to evaluate the influence of misregistration using a polar map of 17 segments model. Methods: Using the fusion software, we assessed the magnitude and direction of misregistration in 200 consecutive myocardial perfusion SPECT images with 99mTechnetium (99mTc) tetrofosmin. After registration, CT data was shifted by ±1, ±2, and ±3 pixels along the cephalad/caudal, dorsal/ventral, and left/right axes, respectively. The registered image was compared with the shifted image. Results: Misregistration between the SPECT and CT images occurred by 1–2 pixels in 127 cases (63.5%) and by 2 or more pixels in four cases (2%); the maximum misregistration was 1.2±0.4 pixels on average. The polar map scoring was most significantly affected by 3 pixel ventral shift. A ventral shift of 1 pixel affected the scores for the anterolateral and inferolateral segments, whereas a caudal shift of 1 pixel affected the scores for the anterior segment. Conclusion: Since the 17 segments model can evaluate the position more precisely than the five segments model, it is possible to evaluate up to 1 pixel misregistration.
Purpose: Intensity modulated radiation therapy (IMRT) has become a widely accepted and efficient treatment technique for many types of cancers. Patient’s specific quality assurance (QA) should be performed with QA devices. Stability and sensitivity tests conducted on the ArcCHECK (AC) 3D diode array were performed. Methods: Set-up error test with AC was performed. The set-up position moved to lateral (mm), longitudinal (mm) and rotational (°) were 0.5, 1.0, 2.0 and 3.0, respectively. Sensitivity change test of diode array with AC through 230 days was also performed. Same array calibration data was applied to all measurements of volumetric-modulated arc therapy benchmark test through 230 days. Gamma method (2 mm/2% criteria) was performed to analyze the result of all measurements. Results: In the results of positional error, gamma pass rate become degenerate according to positional error became larger. With 0.5 mm or 0.5° positional error, decreasing rate of the pass rate of lateral, longitudinal and rotational were 1.0%, 2.5% and 4.2%, respectively. In the sensitivity change test, the gamma pass rate decreased 2.2%/100 days with same calibration data. Conclusion: AC has highly sensitivity against positional error. Sensitivity of AC has been changed and pass rate was decreased 2.2%/100 days through 230 days. Array calibration should be performed in consideration of change of sensitivity.