Multimodal CT in Stroke Imaging: New Concepts
Section snippets
Conventional CT: noncontrast CT
With its widespread availability, short scan time, noninvasiveness, and safety, CT has been the traditional first-line imaging modality for the evaluation of acute ischemic stroke. In the acute ischemic stroke setting, noncontrast CT is typically used to rule out intracranial hemorrhage (a contraindication to thrombolysis) or other stroke mimics (eg, tumor, infection, and so forth) that preclude the use of thrombolytic therapy and to detect early CT signs (ie, scans obtained within 6 hours of
CT angiography
Although conventional cerebral angiography is considered to be the gold standard for the evaluation of cerebrovascular disease, the advances in multidetector row CT (MDCT) technology have made CTA a valid alternative to conventional catheter-based cerebral angiography.31, 32 CTA is widely available, with fast, thin-section, volumetric spiral CT images acquired during the injection of a time-optimized bolus of contrast material for vessel opacification.33 With modern multisection CT scanners,
Perfusion CT
Within the last few years, PCT has become the third component in the multimodal CT assessment of acute ischemic stroke. There is considerable literature on the measurement and assessment of cerebral perfusion37 and a brief review is necessary to understand the parameters and quantitative data that PCT technique provides. In 1981, the landmark study by Jones and colleagues27 used a primate model to elucidate thresholds for MCA ischemia by restricting blood flow in an awake primate model with
Multimodal CT stroke protocol
Multimodal CT allows for the assessment of the four Ps: parenchyma, pipes, perfusion, and penumbra.51 Noncontrast CT allows one to rule out hemorrhage, CTA identifies intraarterial thrombus, and PCT can differentiate between at-risk (the so-called “penumbra”) and irreversibly damaged brain tissue.52 Multimodal CT offers rapid data acquisition and can be performed with modern CT equipment; a typical multimodal CT stroke protocol is depicted in Box 2. PCT is usually performed twice to increase
Summary
A multimodal CT protocol provides a comprehensive noninvasive survey of acute stroke patients with accurate demonstration of the site of arterial occlusion and its hemodynamic tissue status. It combines widespread availability with the ability to provide functional characterization of cerebral ischemia and could potentially allow more accurate selection of candidates for acute stroke reperfusion therapy.
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