Abstract 247: Visual versus Computer Software Assessment of Perfusion in Anterior Circulation Stroke Treated with Mechanical Thrombectomy
Authors: Rigler Igor , Gspan Tina , Frol Senta , Oblak Janja Pretnar 
Published: March 2024

Introduction
In the absence of an automated software analysis, the role of computed tomography perfusion (CTP) in a real time clinical practice is not well established. In a pilot study on 318 acute ischemic stroke (AIS) patients treated with mechanical thrombectomy (MT), we established that visual, semi quantitative evaluation of CTP strongly correlates with clinical outcome, independently of collateral circulation status and ASPECT score. The visual CTP assessment was based only on TTP (time to peak) perfusion maps that are widely accessible, simple to perform on any CT scanner and easy to analyze even by a non‐specialized radiologist. To expand on these results, we are currently performing a direct comparison of the visual and computer‐based CTP assessment and their independent prediction of clinical outcome in AIS patients treated with MT in anterior circulation.

Methods
The single center consecutive CT investigations of AIS patients treated with MT in the anterior circulation were evaluated retrospectively. ASPECT score and collateral circulation evaluation based on the Maas score were determined. CTP assessments, performed either by the visual or computer based method, were graded into four categories, from least to most favorable. Visual grading was based on the percentage of »black regions« on TTP parametric maps, which represent a complete fallout of signal and presumably correlate with infarction core, in comparison to the whole area of the hypo‐perfused territory. Computer based CTP assessment was performed by syngo® Neuro Perfusion CT software. Ischemic core was defined as an area with reduced relative cerebral blood flow (rCBF) below 30% and the hypo‐perfused territory as an area with time to maximum (Tmax) residue function exceeding 6 seconds. The relative volumes of the core were transformed into percentages and graded accordingly. The primary endpoint was excellent functional outcome defined as modified Rankin Scale (mRS) ≤2 at 90 days after MT.

Results
In the pilot study, we included 318 patients, with 142 (45%) having mRS≤ 2 after 90 days, and the mortality rate was 24%. The visually determined CTP grade demonstrated statistically significant independent correlation with the clinical outcome, irrespective of the collateral circulation, ASPECT score and age (OR 2.5; p= 0.011). As an extension of the pilot study, we are undergoing analysis of 1029 patients that underwent MT from 2013 until the end of 2022. The preliminary findings point towards a good correlation between the visual and computer based CTP assessment.

Conclusion
The preliminary results of the ongoing direct comparison of the visual and computer based CTP assessment point towards a good correlation with concordant predictability of clinical outcome of both methods. The results of this study provide an additional scientific background for using the visual semi‐quantitative CTP evaluation in clinical practice for patients who are candidates for MT. As this method is simple and easy to use, it can be performed in almost any CT unit, even without a software program for CTP analysis or advanced subspecialized knowledge in neuroradiology.