Program Information
Optimizing MR Imaging for Minimizing Artifacts That Have Impacts On Radiation Therapy
Y Wu1*, M Chan2 , G Li3 , J Fan4 , Y Rong5 , R Garg1 , (1) Rutgers University, New Brunswick, NJ, (2) Memorial Sloan-Kettering Cancer Center, Basking Ridge, NJ, (3) Memorial Sloan Kettering Cancer Center, New York, NY, (4) Fox Chase Cancer Center, Philadelphia, PA, (5) University of California-Davis, Sacramento, CA
Presentations
MO-L-GePD-IT-3 (Monday, July 31, 2017) 1:15 PM - 1:45 PM Room: Imaging ePoster Theater
Purpose: As the use of MRI in radiation therapy is expanding, it is of clinical significance to investigate MRI artifacts that have impacts on MR-based treatment planning, mainly including distortion artifacts and motion artifacts.
Methods: Distortion artifacts may be caused by MRI system imperfection (nonlinear magnetic field gradient, inhomogeneous magnetic field) or patient specific susceptibility. Distortion was measured at various locations. Correction for nonlinear magnetic field gradient distortion (provided by scanner software) was validated via QA phantom (JM Special Parts, model # J8316) study. Distortion caused by susceptibility or magnetic field inhomogeneity was evaluated by comparing Spoiled Gradient Echo (SPGR) with Fast Spin Echo (FSE) images. Motion artifacts could be ameliorated by reducing scan time, using motion robust sequence, or suppressing bright signal that significantly contributes to motion artifacts. To reduce scan time, fast imaging sequences were used (Single Shot FSE, Fast Recovery FSE), parallel imaging was enabled, parameters were optimized (RBW, Partial Phase Encoding, Zero Interpolation). Alternatively, motion robust sequence (PROPELLER) was employed with slightly prolonged scan time. Additionally, fat/spatial saturation, STIR/FLAIR was used to reduce bright signal from fat or CSF.
Results: Phantom study shows system related distortion was lower than 1mm, and was more severe at locations far from the isocenter. To avoid scanning far from the isocenter, dual prescription (two scans with different isocenters) could be used instead of single prescription for large planning target volumes. Meanwhile, susceptibility related distortion was less apparent in FSE than in SPGR images. By using fast imaging sequences and optimized parameters, motion artifacts were reduced because of decreased scan time. Similarly, utilizing motion robust sequences or fat/CSF suppression techniques ameliorated motion artifacts.
Conclusion: Utilizing appropriate MRI sequences and parameters helps reduce distortion and motion artifacts that could have impacts on radiation therapy.
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