High permittivity ceramics improve the transmit field and receive efficiency of a commercial extremity coil at 1.5 Tesla.

OBJECTIVE: The purpose of this work is to investigate the use of ceramic materials (based on BaTiO3 with ZrO2 and CeO2 -additives) with very high relative permittivity (εr  ∼ 4500) to increase the local transmit field and signal-to-noise ratio (SNR) for commercial extremity coils on a clinical 1.5 T MRI system.

METHODS: Electromagnetic simulations of transmit efficiency and specific absorption rate (SAR) were performed using four ferroelectric ceramic blocks placed around a cylindrical phantom, as well as placing these ceramics around the wrist of a human body model. Results were compared with experimental scans using the transmit body coil of the 1.5 T MRI system and an eight-element extremity receive array designed for the wrist. SNR measurements were also performed for both phantom and in vivo scans.

RESULTS: Electromagnetic simulations and phantom/in vivo experiments showed an increased in the local transmit efficiency from the body coil of ∼20-30%, resulting in an ∼50% lower transmit power level and a significant reduction in local and global SAR throughout the body. For in vivo wrist experiments, the SNR of a commercial eight-channel receive array, integrated over the entire volume, was improved by ∼45% with the ceramic.

CONCLUSION: The local transmit efficiency as well as the SNR can be increased for 1.5 T extremity MRI with commercial array coils by using materials with very high permittivity.