Coil Combination Method for Multiple-Echo Sequences and PSF Mapping

INTRODUCTION: Phased array coils are increasingly used in MRI for improving the signal-to-noise ratio (SNR) or accelerating MRI acquisitions. Most image reconstruction approaches require a separate step to combine the data from the individual channels into a single composite image. Sum-ofsquares technique is widely used, but it is unsuitable when the phase information needs to be preserved. Optimal combination approaches like phase alignment [3] or SENSE [4] have been proposed, which require additional calibration data. Adaptive reconstruction by Walsh et al.[1] offers several advantages over both sum-of-squares and calibration data based methods, but is computation intensive and prone to errors for strongly T2*-weighted data due to the requirement of spatial smoothness of image phases. In this work a new method for coil combination is proposed, which is particularly suited for multi-echo, multi-reference or spectroscopic acquisitions, which intrinsically contain information on the temporal phase evolution. The performance of the method is demonstrated on the PSF mapping [4] application, widely used for distortion correction in EPI and BOLD fMRI in particular.