Image Quality Verification for Off-Center Variation Using ACR Phantom in Open MRI
C P Hong*, D H Lee, B Han, Yonsei University, Wounju-si, Gangwon-doSU-E-I-72 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Image quality assurance of the MR image is rigorously required for MRI-based treatment planning, simulation in radiation oncology. In this work, we investigated image quality for off-center variation using ACR phantom laterally shifting in open MRI.
MR data acquisitions were performed using an open 0.32T MRI (Magfinder II, SciMedix Co., Ltd., Korea) with a permanent magnet. The MR configuration has a patient aperture of 1370 mm and an effective field of view (FOV) of 400 mm. The patient table can be laterally moved up to 120 mm relative to the magnets center. The 2D T1 weighted axial images of the ACR standard phantom were acquired with the following imaging parameters: TR = 400 ms, TE = 15 ms, matrix = 256 256, FOV = 320 mm, slice thickness = 5 mm, bandwidth = 52.6 kHz. The conventional axial image was acquired with the phantom placed at the isocenter, the phantom shifted images were positioned 30 mm, 60 mm, 90mm and 120 mm off-center to the left, and the phantom shifted images were positioned 30 mm, 60 mm, 90mm and 120 mm off-center to the right.
For uniformity of image intensity from isocenter to off-center, integral uniformity in the right off-center direction was 93%, 92%, 91%, 80%, and 47%, respectively. Non-uniformity and geometrical distortion were severely generated by off-center area compared to the isocentric region in open MRI.
Because open MRI can be easily adapted to move laterally, wide-range mapping can be easily achieved to shift the patient table. We developed image quality verification for off-center variation through a phantom moving laterally to cover the entire FOV without specially designed heavy phantom.
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