Improvement of a 4-Channel Spiral-Loop RF Coil Array for TMJ MR Imaging at 7T

ABSTRACT

PURPOSE: In an attempt to further improve the radiofrequency (RF) magnetic (B1) field strength in temporomandibular joint (TMJ) imaging, a 4-channel spiral-loop coil array with RF circuitry was designed and compared with a 4-channel single-loop coil array in terms of B1 field, RF transmit (B1+), signal-to-noise ratio (SNR), and applicability to TMJ imaging in 7T MRI. MATERIALS AND METHODS: The single- and 4-channel spiral-loop coil arrays were constructed based on the electromagnetic (EM) simulation for the investigation of B1 field. To evaluate the computer simulation results, the B1 field and B1 + maps were measured in 7T. RESULTS: In the EM simulation result and MRI study at 7T, the 4-channel spiral-loop coil array found a superior B1 performance and a higher B1 + profile inside the human head as well as a slightly better SNR than the 4-channel single-loop coil array. CONCLUSION: Although B1 fields are produced under the influence of the dielectric properties of the subject rather than the coil configuration alone at 7T, each RF coil exhibited not only special but also specific characteristics that could make it suited for specific application such as TMJ imaging.