How the phased array coil elements placement influences the image quality in cardiac magnetic resonance

Abstract

Phased array coils are used for signal reception in cardiac magnetic resonance (CMR) for their large spatial coverage and for their high signal-to-noise ratio (SNR). However, SNR loss and image quality degradation may arise in cases of incorrect placement of coil arrays, due to sub-optimal combination of the individual coil signals. Analytical simulation of the magnetic fields produced by each individual receiver of a commercial 8-elements cardiac array is proposed. A 2D cross-correlation between array elements magnetic field maps is also proposed to evaluate coil shift. Phantom and in vivo experiments were performed at 1.5 T to evaluate the effect of array coil misalignment in terms of SNR losses and image degradation. Results obtained from phantom and in vivo experiments with different coil shifting are presented. A SNR reduction up to 70% was observed in the cardiac region in case of misalignment between the anterior and the posterior coil portions. Providing tools to prevent coil misalignment could be beneficial to minimize image degradation in MRI exams. In this paper, we proposed a straightforward method based on 2D cross-correlation to estimate the coil shift from images collected from a homogeneous phantom. Providing knowledge of the B1 field in a region of interest would help technologists to have information on the expected image quality and to potentially give indication whether a coil repositioning is needed.