Background: X-ray angiography perfusion (XAP) is a perfusion imaging technique based on conventional DSA. Objective: In this study, we aimed to validate parameters derived from XAP by comparing them with 15O-gas/water positron emission tomography (PET), using data from patients with chronic ischemic cerebrovascular disease. Methods: 18 consecutive patients were included. XAP was performed with intra-arterial infusion of contrast media, and a time-density curve was constructed for each cerebral hemisphere. From the curves, the relative values of mean transit time (rMTT) and wash-in rate (rWiR) were obtained by dividing the values of the right hemisphere by those of the left hemisphere. These were then compared with the relative values of cerebral blood flow (rCBF) and rMTT calculated from the PET data. Results: XAP rWiR correlated strongly with PET rCBF (r=0.86, P&lt
0.0001). rMTT measurements from the two modalities were also strongly correlated (r=0.85, P&lt
0.0001). Bland-Altman analysis revealed a bias of 0.14±0.18 (95% limits of agreement '0.22 to 0.51) for PET rCBF versus XAP rWiR, and 0.016±0.093 (95% limits of agreement '0.17 to 0.20) for rMTT between the two modalities. Conclusions: The relative values obtained from XAP were validated across a population of patients with chronic ischemic cerebrovascular disease.