Improved Accuracy of Accelerated 3D T2* Mapping with Coherent Parallel Maximum Likelihood Estimation

Abstract

The purpose of this study is to investigate the importance of coherent phase information in improving the accuracy of the accelerated T2* mapping as compared to the magnitude-only fitting. Our approach extends the acceleration attained in Parallel Imaging (PI) to Maximum Likelihood Estimation (MLE) approach based on complex exponential model fitting which avoids phase information loss in recovering T2* relaxation times. The method was tested on a Multiecho Gradient Echo (MEGE) T2* mapping experiment in a numerical phantom and a healthy human brain data with retrospective and prospective (real time) undersampling. Compared with fully sampled reference scans, the use of phase information reduces the error of the accelerated T2* maps up to 20% as compared to baseline magnitude-only method. Coherent fitting results in better denoising and additionally provides valuable information about magnetic field inhomogeneity. The total scan time is clinically acceptable.