Using machine learning to predict carotid artery symptoms from CT angiography: A radiomics and deep learning approach

Purpose: To assess radiomics and deep learning (DL) methods in identifying symptomatic Carotid Artery Disease (CAD) from carotid CT angiography (CTA) images. We further compare the performance of these novel methods to the conventional calcium score. Methods: Carotid CT angiography (CTA) images from symptomatic patients (ischaemic stroke/transient ischaemic attack within the last 3 months) and asymptomatic patients were analysed. Carotid arteries were classified into culprit, non-culprit and asymptomatic. The calcium score was assessed using the Agatston method. 93 radiomic features were extracted from regions-of-interest drawn on 14 consecutive CTA slices. For DL, convolutional neural networks (CNNs) with and without transfer learning were trained directly on CTA slices. Predictive performance was assessed over 5-fold cross validated AUC scores. SHAP and GRAD-CAM algorithms were used for explainability. Results: 132 carotid arteries were analysed (41 culprit, 41 non-culprit, and 50 asymptomatic). For asymptomatic vs symptomatic arteries, radiomics attained a mean AUC of 0.96(+/- +/- 0.02), followed by DL 0.86(+/- +/- 0.06) and then calcium 0.79(+/- +/- 0.08). For culprit vs non-culprit arteries, radiomics achieved a mean AUC of 0.75(+/- +/- 0.09), followed by DL 0.67(+/- +/- 0.10) and then calcium 0.60(+/- +/- 0.02). For multi-class classification, the mean AUCs were 0.95(+/- +/- 0.07), 0.79(+/- +/- 0.05), and 0.71(+/- +/- 0.07) for radiomics, DL and calcium, respectively. Explainability revealed consistent patterns in the most important radiomic features. Conclusions: Our study highlights the potential of novel image analysis techniques in extracting quantitative information beyond calcification in the identification of CAD. Though further work is required, the transition of these novel techniques into clinical practice may eventually facilitate better stroke risk stratification.