Purpose To quantify APT effects in acidic ischemic lesions and assess the spatial-temporal relationship between diffusion, perfusion, and pH deficits in acute stroke patients. Methods Thirty acute stroke patients were scanned at 3 T. Quantitative APT (APT#) effects in acidic ischemic lesions were measured using an extrapolated semisolid magnetization transfer reference signal (EMR) technique and compared with commonly used MTRasym(3.5ppm) or APT-weighted parameters. Results APT# images showed clear pH deficits in the ischemic lesion, whereas MTRasym(3.5ppm) signals were slightly hypointense. The APT# contrast between acidic ischemic lesions and normal tissue in acute stroke patients was more than 3 times larger than MTRasym(3.5ppm) contrast (−1.45 ± 0.40 % for APT# vs. −0.39 ± 0.52 % for MTRasym(3.5ppm), p < 4.6 × 10-4). Hypoperfused and acidic areas without an apparent diffusion coefficient abnormality were observed and assigned to an ischemic acidosis penumbra. Hypoperfused areas at normal pH were also observed and assigned to benign oligemia. Hyperintense APT signals were observed in a hemorrhage area in one case. Conclusion The quantitative APT study using the EMR approach enhances APT MRI sensitivity to pH compared to conventional APT-weighted MRI, allowing more reliable delineation of an ischemic acidosis in the penumbra.

INTRODUCTION ADNI is now in its 10th year. The primary objective of the MRI core of ADNI has been to improve methods for clinical trials in Alzheimer’s disease and related disorders. METHODS We review the contributions of the MRI core from present and past cycles of ADNI (ADNI 1, GO and 2). We also review plans for the future – ADNI 3. RESULTS Contributions of the MRI core include creating standardized acquisition protocols and quality control methods; examining the effect of technical features of image acquisition and analysis on outcome metrics; deriving sample size estimates for future trials based on those outcomes; and piloting the potential utility of MR perfusion, diffusion, and functional connectivity measures in multicenter clinical trials. DISCUSSION Over the past decade the MRI core of ADNI has fulfilled its mandate of improving methods for clinical trials in Alzheimer’s disease and will continue to do so in the future.

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