Virtual cut flow, an innovative noninvasive 4D ASL MRI biomarker of EIC bypass patency

Extracranial-intracranial (EIC) bypasses are used to treat Moya-Moya syndrome and complex aneurysms. Evaluating bypass patency is vital. Current methods include intraoperative techniques like indocyanine angiography, micro-doppler probes, and postoperative non-invasive imaging. However, adjudicating the frequent discordant imaging results is done via conventional digital subtraction angiography (DSA) despite its associated risks. Our study aims to quantitatively evaluate bypass patency by introducing a novel biomarker, the virtual cut-flow index (VCFI) derived from 4D-PACK MRI imaging. We prospectively reviewed consecutive adult patients who underwent bypass surgery at our institution between January and October 2023. MR angiography was performed, employing 4D-PACK (four-dimensional pseudo-continuous arterial spin labeling (4D-pCASL)-based angiography using CENTRA-keyhole and view sharing) imaging. We measured arterial signal intensity using regions of interest (ROIs) placed on the superficial temporal artery (STA) and a branch of the middle cerebral artery (MCA) post-bypass. We modeled signal evolution using linear regression and extracted slope α coefficients and then calculated the virtual cut-flow index (VCFI) using the equation VCFI = αMCA/αSTA. We included 18 patients corresponding to 19 bypasses. The median VCI was significantly higher in patients with a patent bypass compared to those with an occluded bypass (87.33 vs. 19.87%; p < 0.05). The median αMCA coefficient was significantly higher in patients with a patent bypass compared to those with an occluded bypass (69.21 vs. 11.34; p < 0.05). The median αSTA coefficient was significantly higher in patients with a patent bypass compared to those with an occluded bypass (102.74 vs. 44.74; p < 0.05). We introduced a novel noninvasive biomarker, the virtual cut-flow index, as a new means to assess bypass patency. While DSA remains the gold standard, VCFI offers a promising avenue for quantitative evaluation, potentially enhancing postoperative monitoring and influencing surgical planning.