B1− non-uniformity correction of phased-array coils without measuring coil sensitivity

Publication date: September 2018
Source:Magnetic Resonance Imaging, Volume 51
Author(s): Frederick C. Damen, Kejia Cai
Parallel imaging can be used to increase SNR and shorten acquisition times, albeit, at the cost of image non-uniformity. B1− non-uniformity correction techniques are confounded by signal that varies not only due to coil induced B1− sensitivity variation, but also the object’s own intrinsic signal. Herein, we propose a method that makes minimal assumptions and uses only the coil images themselves to produce a single combined B1− non-uniformity-corrected complex image with the highest available SNR. A novel background noise classifier is used to select voxels of sufficient quality to avoid the need for regularization. Unique properties of the magnitude and phase were used to reduce the B1− sensitivity to two joint additive models for estimation of the B1− inhomogeneity. The complementary corruption of the imaged object across the coil images is used to abate individual coil correction imperfections. Results are presented from two anatomical cases: (a) an abdominal image that is challenging in both extreme B1− sensitivity and intrinsic tissue signal variation, and (b) a brain image with moderate B1− sensitivity and intrinsic tissue signal variation. A new relative Signal-to-Noise Ratio (rSNR) quality metric is proposed to evaluate the performance of the proposed method and the RF receiving coil array. The proposed method has been shown to be robust to imaged objects with widely inhomogeneous intrinsic signal, and resilient to poorly performing coil elements.