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Background and Purpose: Evaluation of cerebral blood flow (CBF) after carotid and cerebral revascularization is essential for early detection of hyperperfusion phenomenon. Single photon emission computed tomography (SPECT) is considered to be a standard modality for evaluation of CBF. It has, however, difficulty in real-time and repetitive evaluation. Recently, arterial spin labeling MRI (ASL-MRI) has evolved with advantages of its immediacy and repetitivity. The purpose of this study is to elucidate the usefulness of ASL-MRI for evaluation of CBF after carotid and cerebral revascularization.Methods: We screened the adult patients who underwent ASL-MRI and SPECT within 24 hours of interval after carotid endarterectomy (CEA), carotid stenting (CAS), or extracranial-intracranial bypass (EC-IC bypass). After excluding the cases of poor image quality, 63 cases (23 CEA, 22 CAS, 18 EC-IC bypass) were enrolled into the study. ASL-MRI (Siemens 3.0T Magnetom Prisma; 2D-PICORE, Voxel size 1.5x1.5x4mm, TR/TE/TI=4000/15.66/1800-2500) were obtained within 24 hours after surgery. SPECT were obtained using N-isopropyl-p-[123I]iodoamphetamine with autoradiography technique. If abnormal CBF increase (≧20%) were detected, patients were treated with anti-hypertensive therapy, and underwent repeated ASL-MRI and SPECT for therapeutic evaluation.Results: Abnormal CBF increase were observed in 6 cases (2 CEA, 2 CAS, and 2 EC-IC bypass) in SPECT, and 4 (2 CEA, 2 EC-IC bypass) in ASL-MRI. In CEA, 2 cases of CBF increase detected in SPECT were also detected in ASL-MRI. In CAS, ASL-MRI did not visualize CBF increase as clearly as in SPECT. In EC-IC bypass, 2 cases of CBF increase detected in SPECT were also detected in ASL-MRI. The patient with increased CBF after revascularization surgery were treated with anti-hypertensive drugs and remained asymptomatic.Conclusion: ASL-MRI was useful for evaluation and early detection of abnormal CBF in CEA and EC-IC bypass, although not in CAS. Decay of radiofrequency pulse due to metallic material is supposed to be the reason. In cases of CEA and EC-IC bypass, ASL-MRI is expected to be an alternative to SPECT with its advantage of immediacy and repetitivity.