To CTA and Perfusion CT or Not – What’s Best for Stroke Triage?

When it comes to treating patients suspected of stroke, CT angiography (CTA) and perfusion CT have become integral parts of assessment and triage. But, should they be done with every patient?

Despite the benefits of these scans, the answer isn’t clear cut. In a point-counterpoint series published in the American Journal of Roentgenology, experts from the University of Wisconsin School of Medicine and Public Health and University of Pennsylvania Perelman School of Medicine debated the merits of routine use of both scans.

“CTA and perfusion CT have become crucial imaging techniques for making an appropriate diagnosis and triaging these patients to the best therapy,” said Howard A. Rowley, M.D., professor of radiology, neurology, and neurosurgery, as well as chief of neurological MRI, at Wisconsin. “Although the value of the information from these studies has been established, the clinical implementation and application of these studies remain varied.”

The Case for Routine Use

To support more consistent CTA use, Rowley and his colleague Anthony D. Kuner, M.D., a radiologist at Wisconsin, pointed to its reliability in identifying large-vessel occlusion for faster triage to mechanical thrombectomy or aspiration and its ability to pinpoint a potential cause of hemorrhage and assess active bleeding.

In fact, they said, Wisconsin providers perform CTA for all emergent stroke evaluations.

“This uninterrupted approach that does not rely on interpretation of head CT yields rapid image acquisition that facilitates faster treatment decisions,” they said.

They also advocated for using perfusion CT at any time during the stroke window because it offers several benefits. Alongside identifying and characterizing stroke mimics, including migraine, tumor, infection, and seizures, it may also be the only imaging technique to capture abnormal findings in as many as 25 percent of cases.

“Recognizing early parenchymal changes on CT and localizing thrombi may be difficult in the charged setting of acute stroke triage,” they said. “Even normal perfusion imaging findings remain helpful because they provide greater confidence in interpretation of negative examination findings, as well as confident disposition.”

Routine use can also streamline workflow and create a predictable, coordinated stroke team approach, reducing delays, indecisions, wrong decisions, and incomplete examinations. Doing these exams more frequently can also make providers more proficient with interpretation.

The Flip-Side of Routine Use

But, there are other considerations with CTA and perfusion CT, said Linda J. Bagley, M.D., associate program director of the Perelman neuroradiology fellowship, and her colleague Laurie A. Loevner, M.D., division chief of neuroradiology. Using these techniques incorrectly is associated with risk.

It is possible, when perfusion CT is conducted with CTA of the cervical and intracranial vasculature, that patients can experience radiation doses between two and 10 times greater than with a heat CT alone, they said.

In addition, employing these strategies prompts a stroke alert that can divert needed resources from other patients – those with sepsis, pulmonary embolism, or trauma – potentially leading to worse outcomes. It is better, they said, if CTA and perfusion CT are reserved for patients who are actual candidates for mechanical thrombectomy. In fact, they said, implementing an automated post-processing platform has resulted in a 1,500-percent increase in their use of CTA and perfusion CT, corresponding to a 150-to-200-percent increase in thrombectomies – half of which were for patients with stroke mimicking conditions.

Providers should also keep in mind that perfusion CT is inherently limited by a poor signal-to-noise ratio and can be subject to multiple artifacts, such as patient motion and sub-optimal bolus timing. Existing data also shows, they said, that the benefit of perfusion CT patient selection is questionable for patients who present within six hours of symptom onset or those whose symptoms are localized to posterior circulation.

“[Perfusion] CT studies are of questionable reliability, and CTA/perfusion CT may subject patients to an increased radiation dose and possibly divert resources from other critically ill patients, thereby delaying their care,” they said. “More importantly, [perfusion] CT studies often serve as a means to exclude patients from thrombectomy, a relatively low-risk procedure that is cost effective and of benefit to most patients who present within 24 hours of symptom onset with a confirmed large-vessel occlusion.”

Still, said Kuner and Rowley, routine incorporation of CTA and perfusion CT is a best practice for both early and late windows of triage because it give providers the most opportunity for assessment that can guide treatment decisions.

“Stroke triage is ‘like a box of chocolates,” they said, quoting the movie Forrest Gump. “’You never know what you’re gonna get.’ CTA and [perfusion] CT help reveal the hidden.”

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