Three-dimensional mapping of the B1 field using an optimized phase-based method: application to hyperpolarized 3He in lungs.
Magn Reson Med
; 65(4): 1166-72, 2011 Apr.
Article
en En
| MEDLINE
| ID: mdl-21413081
A novel method is presented for the three-dimensional mapping of the B(1) -field of a transmit radio-frequency MR coil. The method is based on the acquisition of phase images, where the effective flip angle is encoded in the phase of the nonselective hard pulse excitation. The method involves the application of a rectangular composite pulse as excitation in a three-dimensional gradient recall echo to produce measurable phase angle variation. However, such a pulse may significantly increase the radio-frequency power deposition in excess of the standard acceptable SAR limits, imposing extremely long TRs (>100 msec), which would result in acquisition times significantly greater than a single breath-hold. In this study, the phases of the radio-frequency excitation are modified, resulting in a different pulse sequence scheme. It is shown that the new method increases sensitivity with respect to radio-frequency inhomogeneities by up to 10 times, and reduces the total duration of the pulse so that three-dimensional B(1) mapping is possible with (3) He in lungs within a single breath-hold. Computer simulations demonstrate the increase in sensitivity. Phantom results with (1) H MRI are used for validation. In vivo results are presented with hyperpolarized (3) He in human lungs at 1.5T.
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Algoritmos
/
Imagen por Resonancia Magnética
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Interpretación de Imagen Asistida por Computador
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Aumento de la Imagen
/
Helio
/
Pulmón
Tipo de estudio:
Diagnostic_studies
Límite:
Humans
Idioma:
En
Revista:
Magn Reson Med
Asunto de la revista:
DIAGNOSTICO POR IMAGEM
Año:
2011
Tipo del documento:
Article
País de afiliación:
Alemania
Pais de publicación:
Estados Unidos