Imaging of acute stroke prior to treatment: current practice and evolving techniques

Abstract

Standard imaging in acute stroke is undertaken with the aim of diagnosing the underlying cause and excluding stroke mimics. In the presence of ischaemic stroke, imaging is also needed to assess patient suitability for treatment with intravenous thrombolysis. Non-contrast CT is predominantly used, but MRI can also exclude any contraindications to thrombolysis treatment. Advanced stroke imaging such as CT and MR angiography and perfusion imaging are increasingly used in an acute setting. In this review, we discuss the evidence for the application of these advanced techniques in the imaging of acute stroke.

Figure 1.

Acute stroke changes on non-contrast CT. Left image shows an area of hypodensity and loss of grey–white matter differentiation affecting the right basal ganglia and insular cortex (within box) consistent with an acute infarct. Compare with the normal left side. Right image shows a hyperdense mainstem of left middle cerebral artery in a different patient (arrow).

Figure 2.

Acute stroke changes on MRI. Acute lacunar infarct within the left thalamus as demonstrated on MRI. Infarct is high signal on T₂ weighted (left) and diffusion-weighted imaging (middle) but correspondingly low signal on apparent diffusion coefficient imaging (right).

Figure 3.

CT and MR angiography. Left image shows normal CT angiography through the circle of Willis. Time-of-flight MR angiography (middle image) and contrast-enhanced MR angiography (right image) of the neck arteries are compared in the coronal plane. Note significant artefacts on time-of-flight images (arrows).

Figure 4.

CT angiography (CTA) source images. CTA (left image) demonstrates an occlusion within the proximal left middle cerebral artery (arrow). When window settings are adjusted to view brain (right image), these “CTA source images” reveal that the left middle cerebral artery territory (within dotted line) is underperfused; affected area is hypodense relative to contralateral normal brain.

Figure 5.

CT perfusion maps showing commonly provided perfusion parameters of cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT) and time to peak (TTP). Anterior left middle cerebral artery territory perfusion defect showing decreased CBF and increased MTT and TTP. CBV is marginally increased. The difference between CBV and the other parameters suggests ischaemic but not yet infarcted tissue (i.e. penumbra, at risk). This patient proceeded to treatment with intravenous thrombolysis. P, posterior; R, right.