Evaluation of cerebral collateral status using computed tomography angiography in ischemic stroke: review of manual and automated methods

In ischemic stroke, the condition of cerebral collateral circulation is one of the key factors determining the outcome. Digital subtraction angiography is considered the gold standard of evaluation of cerebral collateral circulation. However, computed tomography angiography is the most widely used method characterized by high level of conformity with subtraction angiography. Currently, several scales of visual evaluation of collateral circulation development in images obtained by computed tomography angiography are used. The scales describe the territory of stroke-associated cerebral artery, as well as details of various areas of the territory. The association between the score and severity of neurological deficit and volume of cerebral ischemia was demonstrated in numerous studies. However, consensus on the most reliable method of description of cerebral collateral status has not been reached. Use of modern methods of processing of medical images and artificial intelligence allowed to make a significant step towards automatization of collateral status evaluation with such benefits as high processing speed and resistance to subjective opinion. Despite low number of studies on this subject, implementation of automated solutions has already showed its effectiveness. In this review, scales for manual evaluation of cerebral collateral status are considered, their reliability is described, and current approaches to automated evaluation of collateral circulation in ischemic stroke are presented.