title: Imaging of amide proton transfer and nuclear Overhauser enhancement in ischemic stroke with corrections for competing effects.
abstract: Chemical exchange saturation transfer (CEST) potentially provides the ability to detect small solute pools through indirect measurements of attenuated water signals. However, CEST effects may be diluted by various competing effects, such as non-specific magnetization transfer (MT) and asymmetric MT effects, water longitudinal relaxation (T1 ) and direct water saturation (radiofrequency spillover). In the current study, CEST images were acquired in rats following ischemic stroke and analyzed by comparing the reciprocals of the CEST signals at three different saturation offsets. This combined approach corrects the above competing effects and provides a more robust signal metric sensitive specifically to the proton exchange rate constant. The corrected amide proton transfer (APT) data show greater differences between the ischemic and contralateral (non-ischemic) hemispheres. By contrast, corrected nuclear Overhauser enhancements (NOEs) around -3.5 ppm from water change over time in both hemispheres, indicating whole-brain changes that have not been reported previously. This study may help us to better understand the contrast mechanisms of APT and NOE imaging in ischemic stroke, and may also establish a framework for future stroke measurements using CEST imaging with spillover, MT and T1 corrections.
authors.affiliation: Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA; Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, USA.
authors.forename: Hua
authors.initials: H
authors.lastname: Li
authors.forename: Zhongliang
authors.initials: Z
authors.lastname: Zu
authors.forename: Moritz
authors.initials: M
authors.lastname: Zaiss
authors.forename: Imad S
authors.initials: IS
authors.lastname: Khan
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Singer
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Gochberg
authors.forename: Peter
authors.initials: P
authors.lastname: Bachert
authors.forename: John C
authors.initials: JC
authors.lastname: Gore
authors.forename: Junzhong
authors.initials: J
authors.lastname: Xu
mesh_terms: D000577:Amides / Q000378:metabolism*; D000818:Animals; D002545:Brain Ischemia / Q000150:complications* / Q000175:diagnosis*; D004058:Diffusion; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011522:Protons; D011918:Rats, Inbred SHR; D020521:Stroke / Q000150:complications* / Q000175:diagnosis*; D013997:Time Factors
chemical_list: D000577:Amides; D011522:Protons
keywords: amide proton transfer (APT); apparent exchange-dependent relaxation (AREX); chemical exchange saturation transfer (CEST); ischemia; nuclear Overhauser enhancement (NOE); stroke