Characterization and 3D correction of geometric distortion in low-field open-magnet MRI

In this paper, we present a method to characterize and correct geometric image distortion in 0.2 T MR images. A large 3D phantom with spherical balls was used to characterize geometric distortion on an AIRIS Mate 0.2 T MR Scanner (Hitachi). MR images of the phantom were acquired in axial, sagittal and coronal planes using 2D Fast Spin Echo (FSE) sequence and distortions were measured at each control point. Two piecewise interpolation methods were then applied to correct geometric distortion. Distortion was characterized and corrected in any axial, sagittal or coronal slice within an effective FOV of 330(LR) x 180(AP) x 210(HF) mm³. The distortion was reduced from 16 mm to 1.2 mm at 180 mm from the magnet center. A fast and accurate method for correction of geometric distortion was performed within large distances from the magnet isocenter.