7 T Human in vivo Cardiac Imaging with an 8-Channel Transmit / Receive Array

Introduction: There are numerous reasons why cardiac MRI at high field strengths is a potentially challenging endeavor: the heart is subject to cardiac and breathing motion, necessitating peripheral pulse or preferably ECG-triggered sequences with breath holds or navigator sequences to capture the beating heart. Moreover, MRI signal generation is difficult due to inhomogeneous RF signal transmission [1] caused firstly by the heart’s position deep within the body and the surrounding lung tissue, and secondly due to the reduced Larmor wavelength at 7 T of approximately 12 cm, which is shorter than the dimensions of the human body. This reduced wavelength causes B1 inhomogeneities that can lead to destructive B1 interference (signal voids). Another issue is the specific absorption rate (SAR): the maximum applicable energy often constrains the choice of imaging sequence parameters [2]. The purpose of this study was to transfer experiences in animal cardiac MRI at 7T [3] to human in vivo cardiac imaging using a flexible 8-channel transmit/receive body radiofrequency (RF) coil and to report on the potential benefits and limitations of high-field cardiac MRI.