Winkler Simone A, Rutt Brian K
Department of Radiology, Stanford University, Stanford, California, USA.
J Magn Reson Imaging. 2015 Apr;41(4):992-9. doi: 10.1002/jmri.24635. Epub 2014 Apr 10.
To improve image contrast and B1+ field homogeneity in 3 Tesla (T) breast MR.
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.
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.
Both RF shimming and dielectric shimming were shown to improve inhomogeneity in the B1+ field in 3T breast MR.
提高3特斯拉（T）乳腺磁共振成像（MR）中的图像对比度和B1 +场均匀性。
介绍了两种用于3T乳腺MR的实用B1 +匀场方法；使用高介电常数（εr从0到100）的局部垫进行低成本被动匀场，以及双通道射频（RF）匀场（调整Q - I幅度比和0至 - 4 dB以及90至45度的相位差），以及两种方法的组合。该技术已在使用添加乳腺组织的数字人体模型的模拟中以及在六名受试者体内进行了研究。
两种方法均观察到了显著改善，导致左右B1 +不对称率从1.24降至1.00（模拟），从1.26降至1.01（体内）。射频安全性未受到不利影响。
射频匀场和介电匀场均显示可改善3T乳腺MR中B1 +场的不均匀性。
