The effects of RF coils and SAR supervision strategies for clinically applicable nonselective parallel-transmit pulses at 7 T.

Autor: Herrler J; Department of Neuroradiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany.; Siemens Healthcare, Erlangen, Germany., Williams SN; Imaging Center of Excellence, University of Glasgow, Glasgow, UK., Liebig P; Siemens Healthcare, Erlangen, Germany., Ding B; Siemens Healthcare, Frimley, UK., McElhinney P; Imaging Center of Excellence, University of Glasgow, Glasgow, UK., Allwood-Spiers S; National Health Service Greater Glasgow & Clyde, Glasgow, UK., Meixner CR; Siemens Healthcare, Erlangen, Germany.; Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany., Gunamony S; Imaging Center of Excellence, University of Glasgow, Glasgow, UK.; MR CoilTech, Glasgow, UK., Maier A; Department of Computer Science, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany., Dörfler A; Department of Neuroradiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany., Gumbrecht R; Siemens Healthcare, Erlangen, Germany., Porter DA; Imaging Center of Excellence, University of Glasgow, Glasgow, UK., Nagel AM; Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany.; Division of Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany.
Jazyk: angličtina
Zdroj: Magnetic resonance in medicine [Magn Reson Med] 2023 May; Vol. 89 (5), pp. 1888-1900. Date of Electronic Publication: 2023 Jan 09.
DOI: 10.1002/mrm.29569
Abstrakt: Purpose: To investigate the effects of using different parallel-transmit (pTx) head coils and specific absorption rate (SAR) supervision strategies on pTx pulse design for ultrahigh-field MRI using a 3D-MPRAGE sequence.
Methods: The PTx universal pulses (UPs) and fast online-customized (FOCUS) pulses were designed with pre-acquired data sets (B 0 , B 1 + maps, specific absorption rate [SAR] supervision data) from two different 8 transmit/32 receive head coils on two 7T whole-body MR systems. For one coil, the SAR supervision model consisted of per-channel RF power limits. In the other coil, SAR estimations were done with both per-channel RF power limits as well as virtual observation points (VOPs) derived from electromagnetic field (EMF) simulations using three virtual human body models at three different positions. All pulses were made for nonselective excitation and inversion and evaluated on 132 B 0 , B 1 + , and SAR supervision datasets obtained with one coil and 12 from the other. At both sites, 3 subjects were examined using MPRAGE sequences that used UP/FOCUS pulses generated for both coils.
Results: For some subjects, the UPs underperformed when simulated on a different coil from which they were derived, whereas FOCUS pulses still showed acceptable performance in that case. FOCUS inversion pulses outperformed adiabatic pulses when scaled to the same local SAR level. For the self-built coil, the use of VOPs showed reliable overestimation compared with the ground-truth EMF simulations, predicting about 52% lower local SAR for inversion pulses compared with per-channel power limits.
Conclusion: FOCUS inversion pulses offer a low-SAR alternative to adiabatic pulses and benefit from using EMF-based VOPs for SAR estimation.
(© 2023 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)
Databáze: MEDLINE
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