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-coded digital subtraction angiography (DSA) in complementing the traditional, subjective way of leptomeningeal collateral assessment in acute middle cerebral artery (MCA) occlusions. METHODS: Thirty-three consecutive patients with acute MCA occlusion who received endovascular treatment were recruited for investigation. Eighteen of 33 consecutive patients were included. The target downstream territory (TDT) of MCA and reference point at terminal internal carotid artery of each patient was contoured by 5 raters independently on the basis of anteroposterior 2-dimensional DSA. Two parameters of relative maximum density of TDT (rDensitymax) and peak time interval (Delta PT) between reference and TDT were extracted by the use of parametric DSA analysis software. Interrater reliability was tested with intraclass correlation coefficients. Parameters with sufficient interrater reliability entered validity evaluation. Then, the correlation test with the American Society of Interventional and Therapeutic Neuroradiology collateral grading system and efficacy in predicting favorable clinical outcome was evaluated. RESULTS: The intraclass correlation coefficient of rDensitymax and Delta PT were 0.983, 95% confidence interval 0.968- 0.993 and 0.831, 95% confidence interval 0.705-0.923, respectively. The parameter rDensitymax showed a strong correlation with the American Society of Interventional and Therapeutic Neuroradiology collateral grading system score (r of Spearman correlation test = 0.869, P < 0.001) and mRS at 3 months (partial correlation coefficient = 0.616, P = 0.009), whereas Delta PT_average did not. A cut-off point of 0.224 in rDensitymax predicted a favorable clinical outcome with high sensitivity and specificity. CONCLUSIONS: The relative maximum contrast density of MCA territory on 2-dimensional DSA measured by parametric imaging technique appears to be a simple and reliable metric for the assessment of leptomeningeal collaterals in cases of acute MCA occlusion.