Purpose: To improve image contrast and B1+ field homogeneity in 3 Tesla (T) breast MR.
Materials and methods: Two practical B1+ shimming methods for 3T breast MR are presented; low-cost passive shimming using local pads of high dielectric permittivity (εr from 0 to 100), and two-channel radiofrequency (RF) shimming (adjusting Q-I amplitude ratios and phase differences of 0 to -4 dB and 90 to 45 degrees), as well as a combination of both methods. The technique has been studied both in simulation using a numerical body model with added mammary tissue and in vivo in six subjects.
Results: Large improvements are observed with both methods, leading to a decrease in left-right B1+ asymmetry ratio of 1.24 to 1.00 (simulation) and from 1.26 to 1.01 (in vivo). RF safety was not adversely affected.
Conclusion: Both RF shimming and dielectric shimming were shown to improve inhomogeneity in the B1+ field in 3T breast MR.
Keywords: B+1 inhomogeneity; B1 mapping; RF shimming; breast cancer; dielectric shimming.
© 2014 Wiley Periodicals, Inc.