Local SAR, global SAR, and power-constrained large-flip-angle pulses with optimal control and virtual observation points.
Magn Reson Med
; 77(1): 374-384, 2017 01.
Article
en En
| MEDLINE
| ID: mdl-26715084
ABSTRACT
PURPOSE:
To present a constrained optimal-control (OC) framework for designing large-flip-angle parallel-transmit (pTx) pulses satisfying hardware peak-power as well as regulatory local and global specific-absorption-rate (SAR) limits. The application is 2D and 3D spatial-selective 90° and 180° pulses. THEORY ANDMETHODS:
The OC gradient-ascent-pulse-engineering method with exact gradients and the limited-memory Broyden-Fletcher-Goldfarb-Shanno method is proposed. Local SAR is constrained by the virtual-observation-points method. Two numerical models facilitated the optimizations, a torso at 3 T and a head at 7 T, both in eight-channel pTx coils and acceleration-factors up to 4.RESULTS:
The proposed approach yielded excellent flip-angle distributions. Enforcing the local-SAR constraint, as opposed to peak power alone, reduced the local SAR 7 and 5-fold with the 2D torso excitation and inversion pulse, respectively. The root-mean-square errors of the magnetization profiles increased less than 5% with the acceleration factor of 4.CONCLUSION:
A local and global SAR, and peak-power constrained OC large-flip-angle pTx pulse design was presented, and numerically validated for 2D and 3D spatial-selective 90° and 180° pulses at 3 T and 7 T. Magn Reson Med 77374-384, 2017. © 2015 Wiley Periodicals, Inc.Palabras clave
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Bases de datos:
MEDLINE
Asunto principal:
Imagen por Resonancia Magnética
Tipo de estudio:
Prognostic_studies
Límite:
Adult
/
Humans
/
Male
Idioma:
En
Revista:
Magn Reson Med
Asunto de la revista:
DIAGNOSTICO POR IMAGEM
Año:
2017
Tipo del documento:
Article
País de afiliación:
Dinamarca