CT-derived fractional flow reserve in intracranial arterial stenosis: A pilot study based on computational fluid dynamics

Background: CT -derived fractional flow reserve (CT-FFR) has been widely applied in coronary hemodynamic assessment. However, the feasieablity and standardization measurement in intracranial artery stenosis (ICAS) remains to be defined. Purpose: To demonstrate the feasibility of CT-FFR in ICAS functional assessment and explore the optimal CT-FFR measurement position with invasive FFR as reference standard. Materials and methods: Nineteen patients (mean age, 58.6 years +/- 1.9 [SD]; 13 men) with moderate to severe (>= 50 %) ICAS undergoing guidewire-based pressure measurement and preoperative head CT angiography (CTA) were retrospectively enrolled. CT-FFR was measured in the following standard measurement positions, including the end of stenosis (D0), 1 cm distal to the stenosis (D1) and 2 cm distal to the stenosis (D2). Diagnostic performance of CT-FFR was assessed by the area under the curve (AUC) of receiver operating characteristic curves by assuming invasive FFR <= 0.80 or 0.75 as hemodynamically significant stenosis. Results: Excellent intra- and inter-observer agreement (ICC range, 0.930-0.992) was observed for CT-FFR measurement in different positions. Under different FFR thresholds, the diagnostic performance of CT-FFRD1 showed perfect prediction with AUC values of 1.000 (95 % CI: 0.824, 1.000). The sensitivity, specificity and AUC of CT- FFRD1 <= 0.80 in detecting FFR <= 0.80 was 0.94 (95 % CI: 0.68, 1.00), 1.00 (95 % CI: 0.31, 1.00) and 0.969 (95 % CI: 0.772, 1.000), respectively. Similar performance of CT-FFRD1 <= 0.75 was obtained for identifying FFR <= 0.75 with the AUC of 0.964. The strongest correlation (r =0.915, p <0.001) and agreement (mean difference: 0.02, 95 % limits of agreement: 0.16 to 0.19) were observed between CT-FFRD1 and FFR. Conclusion: Cerebral CT -derived fractional flow reserve (CT-FFR) measured 1 cm distal to stenosis achieved the most comparable results with invasive FFR, which indicated its potentially promising clinical application for evaluating the functional relevance of intracranial artery stenosis.