Software Development for Correction of Gradient-nonlinearity Distortions in Mr Images

A new system for functional proton radiosurgery has been proposed. The goal of the system is to target specific brain areas with high doses of proton beams with submillimeter accuracy. High-energy proton beams have exquisitely sharp lateral penumbra and are, therefore, ideal for functional radiosurgery. Localizing the anatomical target with an MRI-based fiducial system requires correction of gradient nonlinearity distortions inherent in the scanner images. Modern MR scanners are particularly prone to such distortions due to wider bores and stronger gradient fields. The gradient nonlinearity correction described in this work is based on a high-resolution 3D MR scan of a cube phantom. Using a least-squares fitting procedure correction parameters are found that convert the geometrically warped planes of the cube into the ideal planes. In this paper, we describe the initial data processing and quality checks performed before the data is used for estimation of correction parameters.