Jerrold L. Boxerman

This paper explored whether CT perfusion (CTP) imaging significantly affected our decision to administer intra-arterial therapy (IAT) in patients with acute stroke beyond the information from noncontrast CT (NCCT), CT angiography (CTA), and the NIH Stroke Scale (NIHSS). This was a contentious issue in the neuroradiology community at the time of publication, and our experience at Rhode Island Hospital suggested that CTP was not significantly altering decisions made with NCCT, CTA, and NIHSS. By computing high inter-group Kappa scores between two groups of neuroradiologists—one using NCCT, CTA, and CTP for IAT triage, and the other using NIHSS in lieu of CTP—we concluded that CTP did not significantly influence IAT triage in patients with acute MCA stroke beyond NCCT, CTA, and NIHSS. When unblinded to CTP, the neuroradiologists using NIHSS in lieu of CTP revised an insignificant number of their decisions. Based on these results, we modified our clinical practice management of patients with MCA stroke by limiting CTP only to those cases with uncertain time of onset (eg, wake-up strokes), thereby realizing potential for cost savings, faster treatment, and radiation dose reduction. Since publication of this paper, our stroke imaging algorithm has become thrombectomy-driven, relying primarily on NCCT, NIHSS, and CTA for assessment of large vessel occlusion and a “collateral score,” and MR perfusion with quantitation of DWI infarct core and “time to peak”-based penumbra have replaced CTP entirely.

We acknowledge that the optimal postprocessing algorithms for defining infarct core (irreversibly dead brain) and ischemic penumbra (at-risk, potentially salvageable brain tissue) have yet to be determined, and that our CTP methodology may not yield “correct” core and penumbra estimates

compared with histopathology or even diffusion-weighted MRI. However, our objective was to simply determine whether one would arrive at the same IAT triage decision using NCCT, CTA, and NIHSS instead of a CTP-driven approach based on common methodology that has appeared in the literature, and we feel that we met our objective in this paper.

Since the publication of this study, we have seen less of an interest at our institution and at others in using perfusion imaging to determine the volume of penumbra. In conversation with neuroradiologists at other centers as well, we have seen less and less of an interest in using CT perfusion parameters to define the penumbra in those patients with large clinical deficit (high NIHSS) and a corresponding large vessel occlusion.

While the use of perfusion imaging in clear-cut interventional candidates can be debated (early in time window, large vessel occlusion, large clinical deficit), we believe there is still a role for perfusion imaging in other situations. For example, patients may present with a large vessel occlusion without a large clinical deficit. Perhaps perfusion imaging can help select patients at higher risk for clinical decline. Similarly, patients who present with an acute extracranial carotid occlusion (either from dissection or atherosclerotic disease) and patent intracranial vessels may also be candidates for perfusion imaging to assist in further triage.

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