An efficient reconstruction algorithm based on the alternating direction method of multipliers for joint estimation of R2* and off-resonance in fMRI.

IEEE Trans Med Imaging. 2017 Feb 13;:

Authors: Hu C, Reeves S, Peters D, Twieg D

Abstract
R 2 mapping is a useful tool in blood-oxygen-level dependent (BOLD) fMRI due to its quantitative nature. However, like T 2 -weighted imaging, standard R 2 mapping based on multiecho EPI suffers from geometric distortion, due to strong offresonance near the air-tissue interface. Joint mapping of R 2 and off-resonance can correct the geometric distortion and is less susceptible to motion artifacts. Single-shot joint mapping of R 2 and off-resonance is possible with a rosette trajectory due to its frequent sampling of the k-space center. However, the corresponding reconstruction is nonlinear, ill-conditioned, largescale, and computationally inefficient with current algorithms. In this work, we propose a novel algorithm for joint mapping of R 2 and off-resonance, using rosette k-space trajectories. The new algorithm, based on the alternating direction method of multipliers (ADMM), improves the reconstruction efficiency by simplifying the original complicated cost function into a composition of simpler optimization steps. Compared to a recently developed trust region algorithm, the new algorithm achieves the same accuracy and an acceleration of 3-6 fold in reconstruction time. Based on the new algorithm, we present simulation and in vivo data from single-shot, double-shot, and quadruple-shot rosettes and demonstrate the improved image quality and reduction of distortions in the reconstructed R 2 map.

PMID: 28207389 [PubMed - as supplied by publisher]