Parallel transmit capability of various RF transmit elements and arrays at 7T MRI. Issue 2 (10th April 2017)

• Record Type: Journal Article
• Authors: Rietsch, Stefan H. G.; Orzada, Stephan; Bitz, Andreas K.; Gratz, Marcel; Ladd, Mark E.; Quick, Harald H.
• Is Part Of: Magnetic resonance in medicine. Volume 79:Issue 2(2018)
• Page Start: 1116
• Page End: 1126
• Publication Date: 2017-04-10
• Subjects: ultrahigh field -- 7 T -- radio frequency (RF) -- RF antenna array -- parallel transmit (pTx); Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.26704
• Languages: English
• ISSNs: 0740-3194

Abstract

Abstract : Purpose: In this work, 22 configurations for remote radiofrequency (RF) coil arrays consisting of different transmit element designs for 7 Tesla (T) ultrahigh‐field MRI are compared by numerical simulations. Methods: Investigated transmit RF element types are rectangular loops, micro striplines, micro striplines with meanders, 250‐mm shielded dipoles with meanders, and lambda over two dipoles with and without shield. These elements are combined in four different configurations of circumferential RF body arrays with four or eight transmit elements each. Comparisons included coupling behavior, degrees of freedom offered by the individual transmit patterns, and metrics like power and specific absorption rate efficiency. Results: Coupling between neighboring RF elements is elevated (up to –7 dB) for all arrays with eight elements, whereas it is below –25 dB for arrays with only four elements. The cumulative sum of singular values points out highest degrees of freedom for the central transversal, reduced values in the central coronal, and minimum values in the sagittal slice. Concerning power and SAR efficiency, eight lambda over two dipoles are most advantageous. Conclusions: Among the investigated remote arrays and parameters, a combination of eight dipoles appears to be most favorable for potential use in 7T body MRI. Magn Reson Med 79:1116–1126, 2018. © 2017 International Society for Magnetic Resonance in Medicine.