Stroke Imaging during the acute phase

Current treatment guidelines recommend that AIS patients undergo non-invasive neuroimaging triage before endovascular treatment (EVT), which minimally includes a non-contrast head CT and CTA. CT perfusion (CTP) and MR perfusion-diffusion imaging may assist patient selection for endovascular thrombectomy.

MRI remains the gold standard in the assessment of cerebral ischemia and has been demonstrated to be both safe and efficacious in the triage of AIS patients. MRI may be particularly useful in the evaluation of AIS patients who present in late time windows and DWI has been utilized in concert with PWI in DEFUSE 3 trial in order to expand the time window for EVT.

AIS patient selection for EVT on the basis of a DWI-PWI mismatch is well established and correlated to improved functional and angiographic outcomes. Benefits of PWI include the identification of DWI-negative cerebral ischemia, matched perfusion deficits, and malignant perfusion profiles, all of which optimize patient selection for endovascular treatment. Additionally, PWI provides an indirect quantitative measurement of collateral vessel status, which is an established predictor of favorable outcomes following AIS.

Imaging with CT perfusion (CTP), when processed in a standardized manner and with appropriate thresholds, can estimate both the irreversibly injured ischaemic core and potentially salvageable ischaemic penumbra with reasonable accuracy.

The association of ischemic core and penumbral tissue volumes assessments with functional outcomes and treatment effect was examined in pooled data from 7 RCT (HERMES Collaboration).

Increased CTP ischaemic core volume was associated with reduced likelihood of functional independence. CTP mismatch volume was not associated with outcome. In patients with substantial endovascular reperfusion (>50%), age, ischaemic core volume and time from imaging to reperfusion were independent prognostic variables.

Similarly the associations of baseline imaging features and functional outcome, treatment effect were assessed in the HERMES Collaboration data base. Endovascular Thrombectomy has substantial benefit across all predefined neuroimaging subgroups including patients with large baseline infarcts, poor baseline collateral extent, presence of hyperdense MCA sign and large thrombus burden.