Ultrafast Volumetric B-1(+) Mapping for Improved Radiofrequency Shimming in 3 Tesla Body MRI

作者：Sprinkart Alois M^*; Nehrke Kay; Traeber Frank; Block Wolfgang; Gieseke Juergen; Schmitz Georg; Willinek Winfried A; Schild Hans; Bornert Peter

来源：Journal of Magnetic Resonance Imaging, 2014, 40(4): 857-863.

DOI：10.1002/jmri.24438

• B1 mapping
• parallel transmit
• RF shimming
• 3T
• body MRI

Purpose: 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.
Materials and Methods: 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.
Results: 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.
Conclusion: 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.

• 出版日期2014-10
• 单位河北医科大学