Sprinkart Alois M, Nehrke Kay, Träber Frank, Block Wolfgang, Gieseke Jürgen, Schmitz Georg, Willinek Winfried A, Schild Hans, Börnert Peter
Department of Radiology, University of Bonn, Germany; Institute of Medical Engineering, Ruhr-University Bochum, Germany.
J Magn Reson Imaging. 2014 Oct;40(4):857-63. doi: 10.1002/jmri.24438. Epub 2013 Nov 4.
To evaluate the use of the recently proposed ultrafast B1 (+) mapping approach DREAM (Dual Refocusing Echo Acquisition Mode) for a refinement of patient adaptive radiofrequency (RF) shimming.
Volumetric DREAM B1 (+) calibration scans centered in the upper abdomen were acquired in 20 patients and three volunteers with written informed consent at a clinical dual source 3 Tesla (T) MR system. Based on these data, RF transmit settings were optimized by central-slice based RF-shimming (CS-RF shim) and by a refined, multi-slice adaptive approach (MS-RF shim). Simulations were performed to compare flip angle accuracy and B1 (+) homogeneity (cv = stddev/mean) achieved by CS-RF shim versus MS-RF shim for transversal and coronal slices, and for volume shimming on the spine.
By MS-RF shim, mean deviation from nominal flip angle was reduced to less than 11% in all slices, all targets, and all subjects. Relative improvements in B1 (+) cv (MS-RF shim versus CS-RF) were up to 14%/39%/47% in transversal slices/coronal slices/ spine area.
Volumetric information about B1 (+) can be used to further improve the accuracy and homogeneity of the B1 (+) field yielding higher diagnostic confidence, and will also be of value for various quantitative methods which are sensitive to flip angle imperfections.
评估最近提出的超快B1(+)映射方法DREAM（双重聚焦回波采集模式）在优化患者自适应射频（RF）匀场中的应用。
在一台临床双源3特斯拉（T）磁共振系统上，对20例患者和3名志愿者进行了以上腹部为中心的容积式DREAM B1(+)校准扫描，所有受试者均签署了书面知情同意书。基于这些数据，通过基于中心切片的RF匀场（CS-RF匀场）和改进的多切片自适应方法（MS-RF匀场）对RF发射设置进行了优化。进行模拟以比较CS-RF匀场与MS-RF匀场在横向和冠状切片以及脊柱容积匀场中实现的翻转角精度和B1(+)均匀性（cv =标准差/平均值）。
通过MS-RF匀场，在所有切片、所有目标和所有受试者中，与标称翻转角的平均偏差降低到小于11%。在横向切片/冠状切片/脊柱区域，B1(+) cv（MS-RF匀场与CS-RF匀场相比）的相对改善分别高达14%/39%/47%。
关于B1(+)的容积信息可用于进一步提高B1(+)场的精度和均匀性，从而产生更高的诊断置信度，并且对于对翻转角缺陷敏感的各种定量方法也具有价值。
