Practical methods for improving B1+ homogeneity in 3 tesla breast imaging

• Published in: Journal of magnetic resonance imaging 2015-04, Vol.41 (4), p.992-999
• Main Authors: Winkler, Simone A., Rutt, Brian K.
• Format: Article
• Language: English
• Subjects: Adult; Algorithms; B+1 inhomogeneity; B1 mapping; Breast - anatomy & histology; breast cancer; dielectric shimming; Female; Humans; Image Enhancement - methods; Image Interpretation, Computer-Assisted - methods; Magnetic Resonance Imaging - methods; Reproducibility of Results; RF shimming; Sensitivity and Specificity; Young Adult
• ISSN: 1053-1807; 1522-2586
• DOI: 10.1002/jmri.24635

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. J. Magn. Reson. Imaging 2015;41:992–999. © 2014 Wiley Periodicals, Inc.