Fast and accurate multi‐channel B1+ mapping based on the TIAMO technique for 7T UHF body MRI. Issue 5 (9th October 2017)

• Record Type: Journal Article
• Authors: Brunheim, Sascha; Gratz, Marcel; Johst, Sören; Bitz, Andreas K.; Fiedler, Thomas M.; Ladd, Mark E.; Quick, Harald H.; Orzada, Stephan
• Is Part Of: Magnetic resonance in medicine. Volume 79:Issue 5(2018)
• Page Start: 2652
• Page End: 2664
• Publication Date: 2017-10-09
• Subjects: B1+ field -- flip angle mapping -- RF shimming -- 7T ultrahigh field MRI -- 32‐channel transmit/receive RF coil -- 7T body imaging; Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.26925
• Languages: English
• ISSNs: 0740-3194

Abstract

Abstract : Purpose: Current methods for mitigation of transmit field B 1 + inhomogeneities at ultrahigh field (UHF) MRI by multi‐channel radiofrequency (RF) shimming rely on accurate B 1 + mapping. This can be time consuming when many RF channels have to be mapped for in vivo body MRI, where the B1 maps should ideally be acquired within a single breath‐hold. Therefore, a new B 1 + mapping technique (B1TIAMO) is proposed. Methods: The performance of this technique is validated against an established method (DREAM) in phantom measurements for a cylindrical head phantom with an 8‐channel transmit/receive (Tx/Rx) array. Furthermore, measurements for a 32‐channel Tx/Rx remote array are conducted in a large body phantom and the | B 1 + | map reliability is validated against simulations of the transmit RF field distribution. Finally, in vivo results of this new mapping technique for human abdomen are presented. Results: For the head phantom (8‐channel Tx/Rx coil), the single | B 1 + | comparison between B1 TIAMO, the direct DREAM measurements, and simulation data showed good agreement with 10–19% difference. For the large body phantom (32‐channel Tx/Rx coil), B1TIAMO matched the RF field simulations well. Conclusion: The results demonstrate the potential to acquire 32 accurate single‐channel B 1 + maps for large field‐of‐view body imaging within only a single breath‐hold of 16 s at 7T UHF MRI. Magn Reson Med 79:2652–2664, 2018. © 2017 International Society for Magnetic Resonance in Medicine.