Improving the detection sensitivity of pH‐weighted amide proton transfer MRI in acute stroke patients using extrapolated semisolid magnetization transfer reference signals

Purpose To quantify amide protein transfer (APT) effects in acidic ischemic lesions and assess the spatial‐temporal relationship among 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 technique and compared with commonly used MTRasym(3.5ppm) or APT‐weighted parameters. Results The APT# images showed clear pH deficits in the ischemic lesion, whereas the MTRasym(3.5ppm) signals were slightly hypointense. The APT# contrast between acidic ischemic lesions and normal tissue in acute stroke patients was more than three times larger than MTRasym(3.5ppm) contrast (−1.45 ± 0.40% for APT# versus −0.39 ± 0.52% for MTRasym(3.5ppm), P