(Sunday, 7/14/2019) 4:00 PM - 5:00 PM
Room: Stars at Night Ballroom 2-3
Purpose: MR system distortion is a major concern in MR simulation for treatment planning. However, large phantoms for distortion determination are costly and unwieldy to handle. Here we propose an easily implementable methodology for MR distortion determination of the entire imaging space of the scanner through the use of a compact commercially available distortion phantom.
Methods: The MagphanRT phantom consists of solid fiducial spheres surrounded by a background fluid. The phantom is scanned at several locations within the scanner. From each scan, an approximate location of the phantom is determined from a subset of these spheres. A displacement field is then fit to the individual fiducial displacements of the entire multi-scan data set. The fitting function is an orthogonal polynomial expansion that has been augmented to include independent rigid-body transformations for each scan. The rigid-body portions of the displacement field are then discarded from the overall distortion fit, as they represent the uncertainty in absolute positioning of the phantom in each scan rather than an actual distortion.
Results: Multi-positional scans of the phantom were used successfully to determine the distortion field with extended coverage. A single scan of the phantom covered 20 cm in its smallest dimension. By stitching together three overlapping scans we extended the distortion measurements to 30 cm. No information about the absolute location or orientation of each scan was required. The method can be easily applied for larger FOVs by using a combination of larger displacements and more scans.
Conclusion: The implementation of the described method allows for determining distortions throughout the entire scanner imaging volume using a standard compact distortion phantom. This eliminates the need for bulky phantoms covering the entire MR bore as these are cumbersome to handle and not readily available at most institutions.
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