Practical Methods for ImprovingB+1Homogeneity in 3 Tesla Breast Imaging

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Abstract

Purpose:

To improve image contrast and Symbol field homogeneity in 3 Tesla (T) breast MR.

Materials and Methods:

Two practical Symbol 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 Symbol 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 Symbol field in 3T breast MR.

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