A Novel Method to Decrease Electric Field and SAR Using an External High Dielectric Sleeve at 3T Head MRI: Numerical and Experimental Results

Abstract

Materials with high dielectric constant (HDC) have been used in high field MRI to decrease specific absorption rate (SAR), increase magnetic field intensity, and increase signal-to-noise ratio. In previous studies, the HDC materials were placed inside the RF coil decreasing the space available. This study describes an alternative approach that considers an HDC-based sleeve placed outside the RF coil. The effects of an HDC on the electromagnetic (EM) field were studied using numerical simulations with a coil unloaded and loaded with a human head model. In addition, experimental EM measurements at 128 MHz were performed inside a custom-made head coil, fitted with a distilled water sleeve. The numerical simulations showed up to 40% decrease in maximum 10 g-avg. SAR on the surface of the head model with an HDC material of barium titanate. Experimental measurements also showed up to 20% decrease of maximum electric field using an HDC material of distilled water. The proposed method can be incorporated in the design of high field transmit RF coils.

RF Safety Evaluation of a Breast Tissue Expander Device for MRI: Numerical Simulation and Experiment

“…Even though the dielectric compartment, i.e., saline, does not significantly affect the $\mid {\mathrm{boldB}}_{\mathrm{bold1}}^{+}\mid$ variation in this study, it can significantly affect the E and SAR distribution through the partial shielding effect by generating an additional E which destructively interfere with the incident E generated by the RF coil [8], [31] (see Figs. 3–4 and 7).…”