BackgroundFractional flow reserve is widely used in coronary disease management, with a threshold of 0.80. However, similar thresholds are unclear in functional assessment of intracranial atherosclerotic stenosis (ICAS). ObjectiveTo investigate the potential threshold values in functional assessment of ICAS by studying the relation between pressure-derived indexes and perfusion parameters derived from arterial spin labeling (ASL). MethodsPatients were consecutively screened between June 2019 and December 2020. The translesional gradient indices were measured by pressure guidewire under resting-state conditions and recorded as mean distal/proximal pressure ratios (Pd/Pa) and translesional pressure difference (Pa-Pd). Preoperative and postoperative cerebral blood flow (CBF) bilaterally and the relative cerebral blood flow ratio (rCBF) were measured and recorded by ASL imaging. Patients were defined as having reversible hemodynamic insufficiency only if the preoperative rCBF was ResultsTwenty-five patients (19 men, 6 women) with a mean age of 56.7 & PLUSMN;9.4 years were analyzed. Seventeen patients (68%) had lesions at the M1 segment of the middle cerebral artery, eight patients (32%) had lesions in the intracranial internal carotid artery. In 14 of the 25 patients, the preoperative rCBF was ConclusionsIn a highly selected subgroup with ICAS, cut-off values of translesional pressure gradients (Pd/Pa=0.81 or Pa-Pd=8 mm Hg) were preliminarily established, which may facilitate clinical decision-making in the management of ICAS.