Background and Aims: 
The collateral circulation (CC) has prognostic value in stroke, but its utility in clinical practice remains unclear. We aimed to study the prognostic value of CC assessment in source images with different techniques: CT-angiography source images (CTASI), CT perfusion source images (CTPSI) and digital subtraction angiography (DSA), compared with a new scale applied in CTPSI named PATHS (Perfusion Acquisition for Thrombectomy Scale). Additionally we studied the relationship between the scores of the scales. 
Methods: 
Retrospective study of patients with MCA stroke and M1/terminal carotid occlusion treated with thrombectomy in our stroke center. Data were prospectively evaluated by a stroke neurologist and radiologist, blinded to clinical data. CC was evaluated using 7 scales: CTASI (Tan and Miteff scales), CTPSI (Calleja, Cao, ASITN and PATHS scales) and DSA (Christoforidis scale). Correlations were studied using Spearman method.
Results: 
N: 108. Median age:70 years(58-77), previous tPA 51.9%, mean NIHSS 17,4(SD:6,7). TICI>2a: 89,9%. All scales predicted functional outcome at 3 months(p≤0,02) and brain infarction at 24h(p≤0,02) except Christoforidis scale. In multivariate analysis PATHS was an independent predictor of 3 months mRS ≤3. In the convergence analysis the scales that used the same techniques(CTASI/CTPSI) showed a better correlation among them(p<0,01), but this strength was just moderate.
Conclusions: 
The CC assessment with different scales in source images has prognostic value and allows faster CC evaluation. PATHS showed a better prognostic value in our study so it might be considered for CC estimation in thrombectomy suitable patients. The moderate correlation between techniques suggest that their scores are not unchangeable.

COLLATERAL CIRCULATION ASSESSMENT USING PATHS IMPROVES OUTCOME PREDICTION COMPARED WITH OTHER SCALES IN MCA THROMBECTOMY TREATED PATIENTS