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Fast correction of B 0 field inhomogeneity for pH‐specific magnetization transfer and relaxation normalized amide proton transfer imaging of acute ischemic stroke without Z‐spectrum
Author(s) -
Sun Phillip Zhe
Publication year - 2020
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.28040
Subject(s) - magnetization transfer , imaging phantom , nuclear magnetic resonance , proton , magnetization , relaxation (psychology) , interpolation (computer graphics) , chemistry , materials science , linear interpolation , magnetic resonance imaging , nuclear medicine , physics , magnetic field , computer science , radiology , medicine , artificial intelligence , quantum mechanics , motion (physics) , classical mechanics , pattern recognition (psychology)
Purpose The magnetization transfer and relaxation normalized amide proton transfer (MRAPT) analysis is promising to provide a highly pH‐specific mapping of tissue acidosis, complementing commonly used CEST asymmetry analysis. We aimed to develop a fast B 0 inhomogeneity correction algorithm for acute stroke magnetization transfer and relaxation normalized amide proton transfer imaging without Z‐spectral interpolation. Methods The proposed fast field inhomogeneity correction describes B 0 artifacts with linear regression. We compared the new algorithm with the routine interpolation correction approach in CEST imaging of a dual‐pH phantom. The fast B 0 correction was further evaluated in amide proton transfer imaging of normal and acute stroke rats. Results Our phantom data showed that the proposed fast B 0 inhomogeneity correction significantly improved pH MRI contrast, recovering over 80% of the pH MRI contrast‐to‐noise‐ratio difference between the raw magnetization transfer ratio asymmetry and that using the routine interpolation‐based B 0 correction approach. In normal rat brains, the proposed fast B 0 correction improved pH‐specific MRI uniformity across the intact tissue, with the ratio of magnetization transfer and relaxation normalized amide proton transfer ratio being 10% of that without B 0 inhomogeneity correction. In acute stroke rats, fast B 0 inhomogeneity–corrected pH MRI reveals substantially improved pH lesion conspicuity, particularly in regions with nonnegligible B 0 inhomogeneity. The pH MRI contrast‐to‐noise ratio between the ipsilateral diffusion lesion and contralateral normal tissue improved significantly with fast B 0 correction (from 1.88 ± 0.48 to 2.20 ± 0.44, P < .01). Conclusions Our study established an expedient B 0 inhomogeneity correction algorithm for fast pH imaging of acute ischemia.