ISC 2024 | Debating the use of CT perfusion for detection of medium vessel occlusions
Johanna Ospel, MD, University of Calgary, Calgary, Alberta, Canada, discusses current uncertainties in the management of acute ischemic stroke due to medium vessel occlusion (MeVOs), namely optimal detection and treatment strategies. MeVOs (M2/3, A2/3, and P2/3 segment occlusions) are smaller and more distal than large vessel occlusions, making detection more difficult. Therefore, the need for advanced imaging for MeVO detection is a key talking point in the field currently. While CT perfusion (CTP) offers clear visibility of MeVOs, its availability is limited. Other techniques, including multiphase CT angiography (CTA) can also be used in this setting. Dr Ospel argues that a faster, more accessible imaging technique is more important than one that gives the highest quality images given the urgency of stroke treatment. Ongoing randomized, clinical trials assessing the use of endovascular therapy in MeVOs should help to answer the question of which imaging paradigm should be used, with some trials employing CTP and others using multiphase or single-phase CTA. This interview took place during the International Stroke Conference 2024 in Phoenix, AZ.
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Transcript (edited for clarity)
Medium vessel occlusions are occlusions that are a little bit smaller than the very large vessel occlusions that we’re used to see frequently and treat frequently. And currently there are a few uncertainties. So one of them is how to detect them. And that’s the topic of my debate because they’re relatively hard to see. It’s kind of a small little vessel that suddenly stops...
Medium vessel occlusions are occlusions that are a little bit smaller than the very large vessel occlusions that we’re used to see frequently and treat frequently. And currently there are a few uncertainties. So one of them is how to detect them. And that’s the topic of my debate because they’re relatively hard to see. It’s kind of a small little vessel that suddenly stops. And the other also very interesting question is how to treat them, because currently we don’t have very high level evidence to suggest that endovascular treatment, meaning catheter-based removal of clots, is beneficial for these vessel occlusions and that’s currently investigated in several randomized trials. And it’s kind of a chicken and egg problem. If you can’t detect them, then you can’t treat them because you’re not aware of them. So that’s kind of why these two things are tightly tied together.
There are different imaging techniques, we call them advanced imaging techniques, to visualize the brain parenchyma a little bit better. And CT perfusion is one of them. It’s probably the most widely used one where intravenous contrast is injected and then the brain is scanned many, many times, 45 or even 50 or 60 times. And then those beautiful colored brain maps are generated, and medium vessel occlusions are really easy to detect on CT perfusion just because there’s a wedge shaped red or orange defect and that is the area that’s affected by the medium vessel occlusion. So they’re really easy to find because they point directly towards the site of occlusion. But that being said, not every hospital has the possibility to perform CT perfusion. It requires kind of a special software, special post-processing. And there are other imaging techniques that are also very well suited to detect medium vessel occlusions. One of them is multiphase CTA, for example, where it’s kind of an abbreviated version of CT perfusion. So instead of 45 or 50 times the brain is just scanned three times. And then those three maps are put next to each other and the area where the vessels fill later and wash out later, that’s the area that’s affected by the occlusion. It’s black and white, but you can see occlusions just as well on multiphase CTA. And then there’s even the option to kind of overlay all three phases and generate maps that are similar to CT perfusion. They’re a little bit more noisy because there are less data points than with CT perfusion but it’s good enough to detect vessel occlusions.
And my argument would be you don’t need to have beautiful maps that look awesome. You just need them to be good enough to detect vessel occlusions. And I think we should do imaging that’s just good enough to answer our questions, but we shouldn’t attempt to make it beautiful and perfect because time is brain. And we get to treat the patient faster if we kind of acquire only the images that are necessary and not more than that.
We haven’t paid much attention until recently to those occlusions because they were just treated with intravenous thrombolysis, with drugs that dissolve the clot. But now that we have those ongoing thrombectomy trials for medium vessel occlusions people are starting to pay more attention. And I think that those trials will basically answer the question, which imaging paradigm should be used? Some of them use CT perfusion, some of them use multiphase CTA. Some sites in our trial ESCAPE-MeVO for instance, they only use single phase CTA. So that’s another option. Just a very, very basic imaging protocol. And I hope that by kind of pooling all those trials together, in 1 or 2 years from now, we’ll be able to find out which imaging paradigm is the best one. There is evidence to suggest now that either multiphase or CT perfusion, kind of helped over and beyond single phase CTA to detect medium vessel occlusion. So some form of advanced imaging is beneficial. But which form is just enough and which one is better than the other is not sure at this point I think.
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