coil settings for abdominal MR-simulation at 1.5T ... body array (Body6x1) on a dedicated 1.5T MR-simulator. (Aera .... points (CPs) for distortion detection.
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Results The optimisation process resulted in better image quality in relation to the original presets and “standard images”. Dose was reduced by a factor ranging from 2-4 times. For a given mAs, superior image quality was seen for a higher mA and lower ms, indicating that the detector response was better for a higher dose rate. Saturation artefacts (Fig.2) were visible for 64mA and 10ms when the images included the intersection between the test object and air. The worse UN was seen for LFOV. This was affected by “cutting” from the reconstruction 40 pixel rows at the edge of the panel. It was done because the bad pixel map correction algorithm could not effectively correct the bad pixels. Additionally, for 2D kV images, bad pixel artefacts were visible using the TOR18FDG phantom. The kV detector panel was replaced and the new one was calibrated to get similar gains so the optimisation process was still valid.
Conclusion The performed optimisation process allowed us to manage the image quality which met expected quality criteria with significant reduction in dose. EP-1724 Phantom image quality evaluation under 3 coil settings for abdominal MR-simulation at 1.5T O.L. Wong1, J. Yuan1, S. Yu1, K. Cheung1 1 Hong Kong Sanatoirum & Hospital, Medical Physics and Research Department, Hong Kong, Hong Kong SAR China Purpose or Objective MR-simulation for abdominal radiotherapy often involves the use of customized immobilization vacuum bags and radiofrequency (RF) coil holders. Although several types of RF coils are available for abdominal MR scans, the influence of different RF coils and settings on image quality has rarely been studied. In this study, we aimed to quantitatively compare the quality of image acquired by three different coil settings for abdominal MR-simulation scan on a 1.5T MR-simulator. Material and Methods A homogeneous cylindrical water phantom (diameter~21cm, length~35cm, volume~15L) was positioned on a flat couch top with a vacuum-bag. In combination with a spine coil, three sets of scans, with 4 repeats each, were performed under the coil settings
(Fig1) with either a 18-channel body array (Body18x1), two 6-channel body arrays (Body6x2) or a single 6-channel body array (Body6x1) on a dedicated 1.5T MR-simulator (Aera, Siemens Healthineers, Erlangen, Germany). All images were acquired using a 2D spin-echo T1-weighted (TR/TE=500/20ms) and T2-weighted (TR/TE1/TE2=2000/20/80ms) sequences (FOV=448mm, matrix=448x448, slice thickness=5mm, geometric distortion correction and prescan normalization=ON, 11 slices). For all scans, the coil-to-phantom distance remained constant by fixing the coil holder height. SNR was calculated based on AAPM Report 100 using the central slice from each image set. For image uniformity assessment, the percent of pixels with intensity within 10% of the mean signal was calculated as uniformity index (UI). A rank-sum test was performed to compare SNR and UI differences between three coil settings.
Results As illustrated in Fig2, the SNR of Body6x1 (T1:51.2±1.3, T2:103.8±26.3) was significantly larger than that of Body18x1 (T1:47.7±1.1, T2:81.9±6.7) for both T1 (P
