title: Early experience of translating pH-weighted MRI to image human subjects at 3 Tesla.
abstract: OBJECTIVE
  In acute stroke, mismatch between lesions seen on diffusion- (DWI) and perfusion-weighted (PWI) MRI has been used to identify ischemic tissue before irreversible damage. Nevertheless, the concept of PWI/DWI mismatch is oversimplified and the ischemic tissue metabolic status and outcome are often heterogeneous. Tissue pH, a well-regulated physiological index that alters on disrupted tissue metabolism, may provide a surrogate metabolic imaging marker that augments the DWI and PWI for penumbra imaging.
  
  
  METHODS
  pH-weighted MRI was obtained by probing the pH-dependent amide proton transfer between endogenous mobile proteins/peptides and tissue water. The technique was validated using animal stroke models, optimized for human use, and preliminarily tested for imaging healthy volunteers.
  
  
  RESULTS
  pH-weighted MRI is sensitive and specific to ischemic tissue acidosis. pH MRI can be optimized for clinical use, and a pilot human study showed it is feasible using a standard 3 Tesla MRI scanner.
  
  
  CONCLUSIONS
  Ischemic acidosis can be imaged via an endogenous pH-weighted MRI technique, which complements conventional PWI and DWI for penumbra imaging. pH-weighted MRI has been optimized and appears feasible and practical in imaging human subjects. Additional study is necessary to elucidate the diagnostic use of pH MRI in stroke patients.
authors.affiliation: Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Athinoula A Martinos Center for Biomedical Imaging, Charlestown, Mass 02129, USA. pzhesun@nmr.mgh.harvard.edu
authors.forename: Phillip Zhe
authors.initials: PZ
authors.lastname: Sun
authors.forename: Thomas
authors.initials: T
authors.lastname: Benner
authors.forename: William A
authors.initials: WA
authors.lastname: Copen
authors.forename: A Gregory
authors.initials: AG
authors.lastname: Sorensen
mesh_terms: D000138:Acidosis / Q000473:pathology*; D000328:Adult; D000818:Animals; D001921:Brain / Q000473:pathology*; D002545:Brain Ischemia / Q000473:pathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D020521:Stroke / Q000473:pathology*