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
in En
| MEDLINE
| ID: mdl-21413081
ABSTRACT
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.
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Algorithms
/
Magnetic Resonance Imaging
/
Image Interpretation, Computer-Assisted
/
Image Enhancement
/
Helium
/
Lung
Type of study:
Diagnostic_studies
Limits:
Humans
Language:
En
Journal:
Magn Reson Med
Journal subject:
DIAGNOSTICO POR IMAGEM
Year:
2011
Document type:
Article
Affiliation country:
Germany