Fast three-dimensional inner volume excitations using parallel transmission and optimized k-space trajectories

• Verfasst von: Davids, Mathias [VerfasserIn]
• Verfasst von: Schad, Lothar R. [VerfasserIn]
• Titel: Fast three-dimensional inner volume excitations using parallel transmission and optimized k-space trajectories
• Verf.angabe: Mathias Davids, Lothar R. Schad, Lawrence L. Wald, and Bastien Guérin
• Jahr: 2016
• Jahr des Originals: 2015
• Umfang: 13 S.
• Fussnoten: Gesehen am 04.07.2019 ; Published online 3 November 2015 in Wiley Online Library
• Titel Quelle: Enthalten in: Magnetic resonance in medicine
• Ort Quelle: New York, NY [u.a.] : Wiley-Liss, 1984
• Jahr Quelle: 2016
• Band/Heft Quelle: 76(2016), 4, Seite 1170-1182
• ISSN Quelle: 1522-2594
• DOI: doi:10.1002/mrm.26021
• Datenträger: Online-Ressource
• Sprache: eng
• Sach-SW: B0 robustness
• Sach-SW: inner volume excitation
• Sach-SW: k-space trajectory optimization
• Sach-SW: Parallel transmit
• Sach-SW: spatially selective excitation
• K10plus-PPN: 166861023X

Abstract

Purpose To design short parallel transmission (pTx) pulses for excitation of arbitrary three-dimensional (3D) magnetization patterns. Methods We propose a joint optimization of the pTx radiofrequency (RF) and gradient waveforms for excitation of arbitrary 3D magnetization patterns. Our optimization of the gradient waveforms is based on the parameterization of k-space trajectories (3D shells, stack-of-spirals, and cross) using a small number of shape parameters that are well-suited for optimization. The resulting trajectories are smooth and sample k-space efficiently with few turns while using the gradient system at maximum performance. Within each iteration of the k-space trajectory optimization, we solve a small tip angle least-squares RF pulse design problem. Our RF pulse optimization framework was evaluated both in Bloch simulations and experiments on a 7T scanner with eight transmit channels. Results Using an optimized 3D cross (shells) trajectory, we were able to excite a cube shape (brain shape) with 3.4% (6.2%) normalized root-mean-square error in less than 5 ms using eight pTx channels and a clinical gradient system (Gmax?=?40 mT/m, Smax?=?150 T/m/s). This compared with 4.7% (41.2%) error for the unoptimized 3D cross (shells) trajectory. Incorporation of B0 robustness in the pulse design significantly altered the k-space trajectory solutions. Conclusion Our joint gradient and RF optimization approach yields excellent excitation of 3D cube and brain shapes in less than 5 ms, which can be used for reduced field of view imaging and fat suppression in spectroscopy by excitation of the brain only. Magn Reson Med 76:1170?1182, 2016. ? 2015 Wiley Periodicals, Inc.