High‐resolution gradient‐recalled echo imaging at 9.4T using 16‐channel parallel transmit simultaneous multislice spokes excitations with slice‐by‐slice flip angle homogenization. Issue 3 (23rd October 2016)

• Record Type: Journal Article
• Authors: Tse, Desmond H. Y.; Wiggins, Christopher J.; Poser, Benedikt A.
• Is Part Of: Magnetic resonance in medicine. Volume 78:Issue 3(2017)
• Page Start: 1050
• Page End: 1058
• Publication Date: 2016-10-23
• Subjects: ultrahigh‐field MR -- parallel transmission -- magnitude least‐squares -- spokes pulses -- simultaneous multislice -- high‐resolution GRE SMS‐pTX; Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.26501
• Languages: English
• ISSNs: 0740-3194

Abstract

Abstract : Purpose: In order to fully benefit from the improved signal‐to‐noise and contrast‐to‐noise ratios at 9.4T, the challenges of B 1 + inhomogeneity and the long acquisition time of high‐resolution 2D gradient‐recalled echo (GRE) imaging were addressed. Theory and Methods: Flip angle homogenized excitations were achieved by parallel transmission (pTx) of 3‐spoke pulses, designed by magnitude least‐squares optimization in a slice‐by‐slice fashion; the acquisition time reduction was achieved by simultaneous multislice (SMS) pulses. The slice‐specific spokes complex radiofrequency scaling factors were applied to sinc waveforms on a per‐channel basis and combined with the other pulses in an SMS slice group to form the final SMS‐pTX pulse. Optimal spokes locations were derived from simulations. Results: Flip angle maps from presaturation TurboFLASH showed improvement of flip angle homogenization with 3‐spoke pulses over CP‐mode excitation (normalized root‐mean‐square error [NRMSE] 0.357) as well as comparable excitation homogeneity across the single‐band (NRMSE 0.119), SMS‐2 (NRMSE 0.137), and SMS‐3 (NRMSE 0.132) 3‐spoke pulses. The application of the 3‐spoke SMS‐3 pulses in a 48‐slice GRE protocol, which has an in‐plane resolution of 0.28 × 0.28 mm, resulted in a 50% reduction of scan duration (total acquisition time 6:52 min including reference scans). Conclusion: Time‐efficient flip angle homogenized high‐resolution GRE imaging at 9.4T was accomplished by using slice‐specific SMS‐pTx spokes excitations. Magn Reson Med 78:1050–1058, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.