Imaging Early Experience of Translating pH-Weighted MRI to Image Human Subjects at 3 Tesla

Background and Purpose—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. (Stroke. 2010;41[suppl 1]:S147-S151.)