Parametric digital subtraction angiography imaging for the objective grading of collateral flow in acute middle cerebral artery occlusion

Purpose To report the feasibility of parametric color coding digital subtraction angiography (DSA) in complementing traditional subjective way of leptomeningeal collateral assessment in acute middle cerebral artery (MCA) occlusions. Methods Thirty-three consecutive acute MCA occlusion patients who received endovascular treatment were recruited for investigation. Eighteen from 33 consecutive patients were included. The target downstream territory (TDT) of MCA and reference point at terminal ICA of each patient was contoured by 5 raters independently based on 2D-DSA at anterior-posterior view. Two parameters of relative maximum density of TDT ( rDensity max ) and peak time interval (ΔPT) between reference and TDT were extracted using parametric DSA analysis software. Inter-rater reliability was tested using intra-class correlation coefficients (ICC). Parameters with sufficient inter-rater reliability entered validity evaluation. Then the correlation test with the American Society of Interventional and Therapeutic Neuroradiology collateral grading (ACG) system and efficacy in predicting favorable clinical outcome was evaluated. Results The ICC of rDensity max and ΔPT were 0.983, 95% CI 0.968-0.993 and 0.831, 95% CI 0.705-0.923, respectively. The parameter rDensity max shows strong correlation with ACG score (r of Spearman correlation test is 0.869, P＜0.001) and mRS at 3 months (partial correlation coefficient is 0.616, P=0.009) while ΔPT_average didn’t. A cut-off point of 0.224 in rDensity max predicted favorable clinical outcome with high sensitivity and specificity. Conclusion The relative maximum contrast density of MCA territory on 2D DSA measured by parametric imaging technique appears to be a simple and reliable metric for the assessment of leptomeningeal collaterals in acute MCA occlusion cases.