Correction of images in an open-configuration MR imaging system for radiation therapy planning and Interventional MRI

Abstract

Purpose In this paper, we present a method to remove system induced geometric distortions in MR images. Methods 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 planes. Using 2D Fast Spin Echo (FSE) sequence, distortions were measured at each control point. Two piecewise interpolation methods were then applied to correct distortions and greyvalues. Results The distortion was reduced from 16 to 1.2 mm at 180 mm from the magnet center. Conclusion Distortions were characterized and corrected in any axial, sagittal or coronal slice within an effective FOV of 330(LR) × 180(AP) × 210(HF) mm 3 . A fast and accurate method for correction of geometric distortion was performed within large distances from the magnet isocenter.

A new phantom to assess and correct geometrical distortions for Magnetic Resonance Imaging: Design and preliminary experiments

“…Images acquired from phantom are post-processed in order to build up distortion maps according to control points detected on the phantom images. This approach offers the advantage of correcting most of the field heterogeneities and gradient non-linearities [6,7,9,[18][19][20][21][22][23].…”

“…2 shows the image acquired in a large FOV configuration with this device. This device was also applied by Viard et al [19] to characterize the distortions of a 0.2 T open magnet MRI. For instance, Fig.…”

“…3. Distortions characterization, curves indicate the iso-value radial error in mm before (a) and after (b) correction (images from [19]). …”