Neuroimaging of cerebrovascular status and hemodynamics has vastly improved our understanding of stroke mechanisms and provided information for therapeutic decision-making. CT techniques are the most commonly used techniques due to wide availability, rapid acquisition and acceptable tolerance. Numerous multimodal CT techniques have been developed in the last few years. We summarize and explain the various multimodal CT acquisition techniques within three categories based on the scanning mode, namely static mode (single-phase CTA), multiple static mode (multi-phase CTA) and continuous mode (CT perfusion and dynamic CTA). Post-processing methods based on different acquisition modes are also introduced in an easy manner by focusing on the information extracted and products generated. We also describe the applications for these techniques along with their advantages and disadvantages.

Background: Clot characteristics and porosity at the proximal portion of an arterial occlusion may influence potential recanalization. Thrombus permeability may be a factor in intravenous thrombolysis, whereas such features of clots prior to endovascular thrombectomy remains largely unexplored. We developed a technique to image clot porosity and yield quantitative measures that may predict mechanical recanalization. Methods: Consecutive cases of large artery occlusion (ICA or proximal M1 MCA) with single-phase CT angiography (CTA) acquired immediately prior to endovascular thrombectomy were analyzed. 3D-reconstruction, vessel segmentation, centerline extraction, signal intensity gradient calculations and surface mapping of CTA yielded porosity images and quantitative measures. Porosity measures were correlated with angiography parameters and procedural details. Results: 53 consecutive cases of acute stroke with contemporaneous sCTA and DSA were used to generate porosity images. Technical limitations precluded image processing in 9 cases, due to diminished contrast conspicuity in close proximity to bone interfaces. Porosity features on resulting images and the quantitative measures of clot penetration varied markedly, even within the subset of M1 or ICA occlusions, respectively. The occlusions often exhibited long segments (mean 18 ± 11 mm) of luminal narrowing before complete occlusion. Current analyses examine whether higher porosity or greater proximal contrast penetration of the clot is associated with faster recanalization and fewer device passes during endovascular thrombectomy. Conclusions: Clot porosity images and quantitative measures of proximal contrast penetration may be generated from routine CTA. Imaging of clot porosity may be a useful adjunct in planning of endovascular procedures and future strategies may focus on distinguishing atherosclerotic versus thromboembolic large artery occlusions.

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Background: CT angiography (CTA) is routinely acquired in acute ischemic stroke, providing data on extent of collaterals yet current techniques compromise either spatial or temporal resolution. We developed and validated a novel imaging technique from standard or single-phase CTA to discriminate both the spatial and temporal blood flow features in leptomeningeal collaterals. Methods: Consecutive acute ischemic stroke patient data, including single-phase CTA (sCTA) followed immediately by digital subtraction angiography (DSA), in the setting of ICA or proximal MCA occlusions were analyzed. Three-dimensional (3D) reconstruction and surface mapping of collateral flow gradients on sCTA was performed. Quantitative output of flow gradients in individual collateral vessels was correlated with DSA ASITN collateral grade. Results: 75 consecutive cases of acute stroke due to ICA or proximal MCA occlusion were analyzed with contemporaneous sCTA and DSA. Automatic post-processing of collateral gradient maps and generation of quantitative data output followed 3D reconstruction and segmentation of sCTA. sCTA collateral gradient mapping was feasible in all cases, compared to limitations in availability of DSA collateral grades. Poor collateral status on DSA (ASITN 0-1) was evident as limited extent and color-mapped gradients on sCTA. In contrast, sCTA gradient mapping provided more detailed distinction between subjects of intermediate or partial DSA collaterals (ASITN 2) and also amongst complete, but delayed DSA collaterals (ASITN 3). sCTA gradient mapping provided quantitative data on the delay of collateral flow in individual cortical vessels. Conclusions: CTA collateral gradient mapping can routinely provide detailed data on both the extent and delay of collaterals, using standard sCTA acquisition. This novel imaging technique may provide key information to distinguish the wide variability of ASITN grades 2-3, most commonly encountered in acute stroke.