Homogeneous RF Field Distribution Optimization in 3T Abdominal Imaging

Abstract

The appearance of severe signal drop-outs in abdominal Magnetic Resonance Imaging at 3 Tesla arises primarily from areas of very low magnetic flux density B1 of the transmit field in the body, and is problematic in both obese as well as very thin subjects. In this study, we show how thin patient-friendly pads containing new high permittivity materials can be designed and optimized, and when placed around the subject increase substantially the B1 uniformity and the image quality. Results from nine healthy volunteers show that inclusion of these dielectric pads results in statistically significant decreases in the coefficient of variance of the B1 field, with stronger and more uniform fields being produced. In addition there are statistically significant decreases in time-averaged power required for scanning. These differences are present in both quadrature-mode operation (coefficient of variance decrease, P < 0.0001, mean 25.4 ± 10%: power decrease, P = 0.005, mean 14 ± 14%) and also for the RF-shimmed case (coefficient of variance decrease, P = 0.01, mean 16 ± 13%: power decrease, P = 0.005, mean 22 ± 11%) of a dual-transmit system.