Ultrafast volumetric B1+ mapping for improved radiofrequency shimming in 3 tesla body MRI. Issue 4 (4th November 2013)

• Record Type: Journal Article
• Authors: Sprinkart, Alois M.; Nehrke, Kay; Träber, Frank; Block, Wolfgang; Gieseke, Jürgen; Schmitz, Georg; Willinek, Winfried A.; Schild, Hans; Börnert, Peter
• Is Part Of: Journal of magnetic resonance imaging. Volume 40:Issue 4(2014)
• Page Start: 857
• Page End: 863
• Publication Date: 2013-11-04
• Subjects: Magnetic resonance imaging -- Periodicals; 616
• DOI: 10.1002/jmri.24438
• Languages: English
• ISSNs: 1053-1807

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="jmri24438-sec-0001" sec-type="section"> <title>Purpose</title> <p>To evaluate the use of the recently proposed ultrafast B<sub>1</sub><sup>+</sup> mapping approach DREAM (Dual Refocusing Echo Acquisition Mode) for a refinement of patient adaptive radiofrequency (RF) shimming.</p> </sec> <sec id="jmri24438-sec-0002" sec-type="section"> <title>Materials and Methods</title> <p>Volumetric DREAM B<sub>1</sub><sup>+</sup> 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 B<sub>1</sub><sup>+</sup> 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.</p> </sec> <sec id="jmri24438-sec-0003" sec-type="section"> <title>Results</title> <p>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 B<sub>1</sub><sup>+</sup> cv (MS‐RF shim versus CS‐RF) were up to 14%/39%/47% in transversal slices/coronal slices/ spine area.</p> </sec> <sec id="jmri24438-sec-0004" sec-type="section"> <title>Conclusion</title> <p>Volumetric information about B<sub>1</sub><sup>+</sup> can be used to further improve the accuracy and homogeneity of the B<sub>1</sub><sup>+</sup> field yielding higher diagnostic confidence, and will also be of value for various quantitative methods which are sensitive to flip angle imperfections. <bold>J. Magn. Reson. Imaging 2014;40:857–863</bold>. © <bold>2013 Wiley Periodicals, Inc</bold>.</p> </sec> </abstract>