Residual gradient non-linearity (GNL) distortions persist after vendor-supplied correction. This work describes and evaluates the performance of a method entitled Phantom-based Residual Error Correction using Individualized System Estimates (PRECISE) to correct these residual distortions. Approach: PRECISE correction maps were created using a commercial distortion phantom on a 0.5T head-specific MR system and added to existing gradient unwarping. The performance of the PRECISE method was then evaluated using the commercial distortion phantom acquired 3D gradient recalled echo acquisitions along each cardinal axis and various other clinical protocols. Residual distortions were decomposed into main magnetic field and gradient non-linearity (GNL) induced components. Main Results: The PRECISE method removed the GNL component of distortions with 95th percentile GNL distortions being reduced from 0.36mm to 0.07mm. Average distortions across various clinical protocols were reduced from 0.193 ± 0.003 mm to mean = 0.055 ± 0.004 mm. 95th percentile distortions across various clinical protocols were reduced from 0.34 ± 0.01 mm to 0.11 ± 0.01 mm. Significance: The phantom-based distortion method in the absence of significant B0 induced distortions results in dramatically improved geometric fidelity. .
Harris et al. (Fri,) studied this question.