An Eight-Channel Phased Array RF Coil for Spine MR Imaging at 7 T

Abstract

To develop a transmit/receive radiofrequency (RF) array for MR imaging of the human spine at 7 T. The prototype is characterized in simulations and bench measurements, and the feasibility of high-resolution spinal cord imaging at 7 T is demonstrated in in vivo images of volunteers. The RF phased array consists of 8 overlapping surface loop coils with a dimension of 12 cm x 12 cm each. Bench measurements were obtained with a phantom made of body-simulating liquid and assessed with a network analyzer. For safety validation, numerical computations of the RF field distribution and the corresponding specific absorption rate were performed on the basis of 3 different human body models. In vivo images of 3 volunteers (2 with a documented scoliosis) were acquired using a 3D-FLASH sequence with a high spatial resolution of 0.57 mm isotropic. The 7 T transmit/receive RF coil could be easily integrated into the patient table for examinations of the cervicothoracic or thoracolumbosacral spine. Comparable results were found for all 3 numerical calculations using different human body models. Measurements of the g-factor indicated good image quality for parallel imaging acceleration factors up to 2.7 along the head-feet direction, which could be validated in the in vivo images. The in vivo images demonstrated very fine anatomic features such as the longitudinal ligaments or the venous drainage through the vertebral bodies. A largely homogeneous excitation over an extensive field-of-view of 40 cm could be obtained. These early results indicate that a multichannel transmit/receive phased array RF coil can be used for in vivo spine imaging at 7 T, thereby rendering high-resolution spine imaging a promising new application in 7 T clinical research.