1 Computer Science and Software Engineering, Concordia University, 1455 boul. De Maisonneuve O., Montreal, QC, H3G 1M8, Canada. m_ktar@encs.concordia.ca.
2 Computer Science and Software Engineering, Concordia University, 1455 boul. De Maisonneuve O., Montreal, QC, H3G 1M8, Canada.
3 Department of Diagnostic Radiology, Kingston Health Sciences Centre, Kingston General Hospital, Kingston, ON, K7L 2V7, Canada.
4 Electrical and Computer Engineering, Concordia University, 1455 boul. De Maisonneuve O., Montreal, QC, H3G 1M8, Canada.

Purpose: Collateral evaluation is typically done using visual inspection of cerebral images and thus suffers from intra- and inter-rater variability. Large open databases of ischemic stroke patients are rare, limiting the use of deep learning methods in treatment decision-making.

Methods: We adapted a pre-trained EfficientNet B0 network through transfer learning to improve collateral evaluation using slice-based and subject-level classification. Our method uses stacking and overlapping of 2D slices from a patient's 4D computed tomography angiography (CTA) and a majority voting scheme to determine a patient's final collateral grade based on all classified 2D MIPs. Class imbalance is handled in the evaluation process by using the focal loss with class weight to penalize the majority class.

Results: We evaluated our method using a nine-fold cross-validation performed with 83 subjects. Mean sensitivity of 0.71, specificity of 0.84, and a weighted F1 score of 0.71 in multi-class (good, intermediate, and poor) classification were obtained. Considering treatment effect, a dichotomized decision is also made for collateral scoring of a subject based on two classes (good/intermediate and poor) which achieves a sensitivity of 0.89 and specificity of 0.96 with a weighted F1 score of 0.95.

Conclusion: An automatic and robust collateral assessment method that mitigates the issues with the small imbalanced dataset was developed. Computer-aided evaluation of collaterals can help decision-making of ischemic stroke treatment strategy in clinical settings.