期刊
MAGNETIC RESONANCE IN MEDICINE
卷 83, 期 3, 页码 935-949出版社
WILEY
DOI: 10.1002/mrm.27984
关键词
dipolar order; ihMT; inhomogeneous MT; magnetization transfer; myelin imaging
资金
- Wellcome/EPSRC Centre for Medical Engineering [WT 203148/Z/16/Z]
- King's College London and Imperial College London EPSRC Centre for Doctoral Training in Medical Imaging [EP/L015226/1]
- National Institute for Health Research (NIHR) Biomedical Research Centre based at Guy's and St Thomas' NHS Foundation Trust and King's College London
- EPSRC [EP/L00531X/1] Funding Source: UKRI
Purpose: Inhomogeneous magnetization transfer (ihMT) is an emerging form of MRI contrast that may offer high specificity for myelinated tissue. Existing ihMT and pulsed MT sequences often use separate radiofrequency pulses for saturation and signal excitation. This study investigates the use of nonselective multiband radiofrequency pulses for simultaneous off-resonance saturation and on-resonance excitation specifically for generation of ihMT contrast within rapid steady-state pulse sequences. Theory and Methods: A matrix-based signal modeling approach was developed and applied for both balanced steady state free precession and spoiled gradient echo sequences, accounting specifically for multiband pulses. Phantom experiments were performed using a combination of balanced steady state free precession and spoiled gradient echo sequences, and compared with model fits. A human brain imaging exam was performed using balanced steady state free precession sequences to demonstrate the achieved contrast. Results: A simple signal model derived assuming instantaneous radiofrequency pulses was shown to agree well with full integration of the governing equations and provided fits to phantom data for materials with strong ihMT contrast (PL161 root mean square error = 0.9%, and hair conditioner root mean square error = 2.4%). In vivo ihMT ratio images showed the expected white matter contrast that has been seen by other ihMT investigations, and the observed ihMT ratios corresponded well with predictions. Conclusions: ihMT contrast can be generated by integrating multiband radiofrequency pulses directly into both spoiled gradient echo and balanced steady state free precession sequences, and the presented signal modeling approach can be used to understand the acquired signals.
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