Reply:

We thank Drs Singh, Zerna, and Menon for their interest in our study,¹ and we are grateful for the opportunity to address their comments. First, we would like to acknowledge the utility and value of multiphase CT angiography as a development in the assessment of acute stroke, first described by the Calgary Stroke Program. It is a dynamic, versatile, and multipurpose tool,² with benefit in the detection of distal intracranial arterial occlusions as previously described by Yu et al.³ The purpose of our study was to demonstrate the effectiveness of an easily communicated imaging sign on multiphase CTA, “the delayed vessel sign,” which we have found to be intuitively understood even by junior trainees. It is a reliable indicator of an intracranial arterial occlusion, providing a rapid method to identify the precise site of occlusion. The sign is distinct from “asymmetric pial enhancement,” which we separately evaluated in our article; in clinical practice, we have found it to be a subtler imaging feature, especially when associated with distal vessel occlusions. We have recently developed a new postprocessing technique “subtraction multiphase CT angiography,” which increases the conspicuity of the delayed vessel sign by suppressing normally enhancing vessels (including pial vessels), enabling faster detection of intracranial arterial occlusions.⁴