Journal
JOURNAL OF MAGNETIC RESONANCE
Volume 263, Issue -, Pages 92-100Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jmr.2015.12.022
Keywords
Hyperpolarized MRI; Constant flip angles; Constant-variable flip angles; Variable flip angles
Funding
- Natural Science Foundation of China [81227902, 61471355]
- China Postdoctoral Science Foundation [2014M560636, 2015T80856]
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The longitudinal magnetization of hyperpolarized media, such as hyperpolarized Xe-129, He-3, etc., is nonrenewable. When the MRI data acquisition begins at the k-domain center, a constant flip angle (CFA) results in an image of high signal-to-noise ratio (SNR) but sacrifices the accuracy of spatial information. On the other hand, a variable flip angle (VFA) strategy results in high accuracy but suffers from a low SNR. In this paper, we propose a novel scheme to optimize both the SNR and accuracy, called constant-variable flip angles (CVFA). The proposed scheme suggests that hyperpolarized magnetic resonance signals are firstly acquired through a train of n* CFA excitation pulses, followed by a train of N-n* VFA excitation pulses. We simulate and optimize the flip angle used in the CFA section, the number of CFA excitation pulses, the number of VFA excitation pulses, and the initial and final variable flip angles adopted in the VFA section. Phantom and in vivo experiments demonstrate the good performance of the CVFA designs and their ability to maintain both high SNR and spatial resolution. (C) 2016 Elsevier Inc. All rights reserved.
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