The presence of a lesion with delay time (DT) longer than 4 seconds at 24-hour post-EVT perfusion imaging appeared to be the most informative candidate no-reflow definition for outcome assessment.
Key Findings
Results
Among candidate no-reflow definitions tested across eight perfusion maps and stepwise thresholds, any residual lesion with delay time (DT) longer than 4 seconds on 24-hour post-EVT perfusion imaging showed the strongest discrimination for poor 90-day functional outcome.
Primary cohort of 67 patients with mTICI 2c or 3 recanalization after EVT who had pre-EVT and 24-hour post-EVT CT or MR perfusion imaging.
AUC was 0.72 (95% CI: 0.57, 0.86; P < .001).
Primary screening defined no reflow as any residual hypoperfusion lesion for each map-threshold combination; poor outcome was mRS >2 at 90 days.
Results
About one in five patients in the primary cohort met the DT >4 s no-reflow definition despite successful recanalization, and these patients had much higher odds of poor functional outcome.
14 of 67 patients (21%) had no reflow by this definition.
Poor functional outcome occurred in 11 of 14 (79%) with no reflow versus 11 of 53 (21%) with reflow.
Odds ratio, 12.14 (95% CI: 3.38, 54.63; P < .001), from multivariable Firth penalized logistic regression.
Results
No-reflow status was associated with greater infarct growth than reflow status.
Median infarct growth was 24.1 mL (IQR, 3.7-40.7 mL) with no reflow versus 0 mL (IQR, -10.1 to 6.1 mL) with reflow (P < .001).
Infarct growth was a secondary outcome.
Results
The findings were consistent in an independent cohort.
The independent cohort comprised 54 patients (median age, 69 years [IQR, 62-78 years]; 28 female).
Data came from two prospective multicenter imaging registries recruiting between June 2016 and July 2022.
Methods
The best-performing definition was further evaluated using residual lesion volume and reperfusion index cutoffs.
Delay time quantifies the delay in contrast material arrival between arterial input and brain tissue.
Associations were assessed with multivariable Firth penalized logistic regression, suited to small samples.
What This Means
Even when doctors successfully reopen a blocked brain artery with a clot-removal procedure (thrombectomy), some patients still do poorly. One suspected reason is the 'no-reflow' phenomenon, in which tiny blood vessels in the brain fail to get blood flow back even though the main artery is open. There has been no agreed way to define no reflow on imaging. This study tested many possible definitions using brain perfusion scans taken 24 hours after the procedure.
The best-performing definition was the presence of any area where blood arrival was delayed by more than 4 seconds (delay time). In 67 patients, about 21% met this definition. Of these, 79% had a poor outcome at 90 days (meaning significant disability), compared with 21% of patients without such an area. Those with no reflow also had more growth of the stroke-damaged area (median 24.1 mL versus 0 mL). Results were consistent in a separate group of 54 patients.
This research suggests that a follow-up perfusion scan could help identify patients whose microvascular blood flow has not recovered, which may help explain poor outcomes after successful procedures. The groups studied were small, and this is a definition-finding analysis, so the threshold would need confirmation in larger studies before use in routine care or in testing treatments aimed at no reflow.
Xu T, Chen C, Manning N, Cheung A, Cordato D, Blair C, et al.. (2026). No Reflow at Perfusion Imaging: Thresholds That Distinguish Functional and Tissue Outcome Groups in Acute Stroke.. Radiology. https://doi.org/10.1148/radiol.253025