Mehran Shaghaghi1, Weiwei Chen2, Alessandro Scotti1,3, Haiqi Ye2, Yan Zhang2, Wenzhen Zhu2, Kejia Cai1,3,4. 1. Department of Radiology, University of Illinois at Chicago, Chicago, IL, USA. 2. Department of Radiology, Tongji Hospital, Tongji Medical College, Huazhong University of Science & Technology, Wuhan 430030, China. 3. Bioengieering, University of Illinois at Chicago, Chicago, IL, USA. 4. Center for MR Research, University of Illinois at Chicago, Chicago, IL, USA.
Abstract
BACKGROUND: To implement omega plot method for in vivo mapping of proton exchange rates in human brain by taking into account the water direct saturation (DS) effect and multiple saturation transfer exchanging species in vivo. METHODS: Four Z-spectra were collected with chemical exchange saturation transfer (CEST) saturation power =1, 2, 3 & 4 µT. Water DS was estimated by fitting the Z-spectrum to a linear combination of multiple Lorentzian components and its contribution to the signal was subsequently removed. Exchange rate maps were derived by the omega plot, consisting of fitting the inverse of the signal intensity, Mz /(M 0-Mz ), as a function of 1/(γB1)2. RESULTS: The exchange rate values quantified with the DS removed omega plot were significantly higher in the GM region than in the WM region (616±29 vs. 575±20 s-1, P<0.001). Phantom studies confirmed that the exchange rates from DS-removed plots varied linearly with pH (R2=0.998) for the pH range of 6.2 to 7.4, whereas exchange rates from conventional omega plots failed to show such linearity in the entire physiological pH range. CONCLUSIONS: The calculated exchange rate with DS-corrected omega plot is a weighted average for all saturation transfer exchanging proton species which contribute to Z-spectral signal. The healthy brain exchange rate map provided by DS-removed omega plots may serve as a baseline for detecting any pathological changes. 2019 Quantitative Imaging in Medicine and Surgery. All rights reserved.
BACKGROUND: To implement omega plot method for in vivo mapping of proton exchange rates in human brain by taking into account the water direct saturation (DS) effect and multiple saturation transfer exchanging species in vivo. METHODS: Four Z-spectra were collected with chemical exchange saturation transfer (CEST) saturation power =1, 2, 3 & 4 µT. Water DS was estimated by fitting the Z-spectrum to a linear combination of multiple Lorentzian components and its contribution to the signal was subsequently removed. Exchange rate maps were derived by the omega plot, consisting of fitting the inverse of the signal intensity, Mz /(M 0-Mz ), as a function of 1/(γB1)2. RESULTS: The exchange rate values quantified with the DS removed omega plot were significantly higher in the GM region than in the WM region (616±29 vs. 575±20 s-1, P<0.001). Phantom studies confirmed that the exchange rates from DS-removed plots varied linearly with pH (R2=0.998) for the pH range of 6.2 to 7.4, whereas exchange rates from conventional omega plots failed to show such linearity in the entire physiological pH range. CONCLUSIONS: The calculated exchange rate with DS-corrected omega plot is a weighted average for all saturation transfer exchanging proton species which contribute to Z-spectral signal. The healthy brain exchange rate map provided by DS-removed omega plots may serve as a baseline for detecting any pathological changes. 2019 Quantitative Imaging in Medicine and Surgery. All rights reserved.
Entities:
Keywords:
Chemical exchange saturation transfer (CEST); Omega plot; human brain; proton exchange rate
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