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Hello and welcome to Noon Conference hosted by MRI Online. In response to

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the changes happening around the world right now and the shutting down of

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in person events, we have decided to provide free Noon Conferences to all

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radiologists worldwide. Today, we are joined by Dr. Pamela Schaefer. Dr.

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Schaefer is the Vice Chair of Postgraduate Education and Fellowship Training,

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Director of MRI and Associate Director of Neuroradiology at Massachusetts

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General Hospital. She holds the Theresa McLeod Endowed Chair in Radiology

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Education and is a Professor of Radiology. A reminder that there will be

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a Q&A session at the end of the lecture, so please use the

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Q&A feature to ask your questions and we will get to as many

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as we can before our time is up. That being said,

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thank you all for joining us today. Dr. Schaefer, I'll let you take

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it from here. Okay, everybody can hear me now, I think?

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Yep, currently loud and clear. Awesome. All right. Sorry about that.

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You'd think a year after I started using Zoom, you'd think I'd be

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able to figure out how to unmute myself. Anyway, we're gonna be talking

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about acute ischemic stroke today and I have no disclosures.

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So this is kind of a graphic of what we're gonna be talking

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about. You have an acute clot. You have tissue that dies very quickly.

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It's kind of dead on arrival when you start imaging. It's called the

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core of the infarction. We're gonna talk about how you image that and

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measure that with CT and MR. And then there's the ischemic but viable

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tissue that may progress to infarction if you don't

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intervene. And we'll talk about how you measure that on perfusion imaging.

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And then of course we'll talk about how you measure the occlusion on

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CT and MRA. So recanalization strategies, do they improve outcome?

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Historically the NINDS trial was in 1995. It showed the benefit of IV

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tPA versus placebo. But the problem is there was only a 12%

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increase in good outcomes. This is data from the STOP STROKE study

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with IV tPA showing good outcomes in patients with an NIH stroke scale

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greater than 10, improving from 17% to 35%.

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The big year for stroke was 2015 and 2016 in which there were

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six trials that showed the benefit of treatment with IV plus IA therapy

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with stent retrievers versus IV therapy alone. It was the first time that

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imaging biomarkers were used in a standard way to look at brain parenchyma

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and vessel occlusion. And so the simplest trials just ruled out intracranial

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hemorrhage on noncontrast CT and looked for proximal occlusion on CTI or

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MRA. And some of them were more detailed where they actually evaluated the

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core with perfusion imaging and the penumbra with Tmax and we'll get into

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this a little bit more. But the bottom line is, why were all

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these trials successful when previous trials were not?

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The time to treat was a lot faster on average at approximately four

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hours and the percent recanalization rates with the stent retrievers were

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much higher in the 75% to 85% range versus

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much lower percentages with earlier devices, and you can see they all had

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very robust significance. And then this was the HERMES analysis of 1,278

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patients in five of the trials. And it just showed, again,

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how robust the results were that when they broke it out

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with age, all ages over 50 benefited. When they looked at noncontrast CT

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aspect scores, everything over five patients benefited whether or not they'd

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gotten IV therapy. ICA and M1 occlusions benefited. NIH stroke scales,

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all the categories over 10, etcetera. So very robust trials. And this really

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changed the way we practiced. So let's take a step back and talk

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about the essential useful imaging variables for treatment decisions. You

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have to know if there's clot or if there's hemorrhage 'cause it's a

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contraindication to TPA and IA therapy. You have to identify the clot location.

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It's necessary for IA treatment. You wanna identify the infarct core.

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It's tissue dead on arrival, greater than 70 to 100 ccs,

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is a contraindication for IA therapy in general

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because almost all patients with larger infarct cores have

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poor outcome. You wanna be able to identify collaterals

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because it predicts infarct growth. And you want to identify penumbral tissue

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to see if there is tissue at risk of infarction. And we'll talk

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about this in the setting of IA treatment and

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other strokes that don't have proximal occlusions. So starting with noncontrast

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CT, hypodensity on noncontrast CT is highly specific for infarction core.

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So when you see it, that area will infarct. The problem is that

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the detection requires a substantial increase in tissue water, which takes

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time to build up. So the sensitivity is only 45% in the first

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six hours. Obviously noncontrast CT is also helpful for excluding other

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causes of acute stroke. Contraindications to IV thrombolysis or the detection

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of hemorrhage. You can give IV thrombolysis safely even if you have an

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infarct core greater than one third of the MCA territory or greater than

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approximately 100 ccs. It always helps to use narrower windows. Here's a

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patient three hours status post right hemiparesis. Hard to see anything

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on this noncontrast CT when you window and level just right.

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You can see the left MCA infarction. This was the follow up showing

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that all of that progressed to infarction. Here's another case, noncontrast

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CT, very hard to see the hypodensity in the right basal ganglia. Can

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see a little bit better with narrower windows. So you want to use

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noncontrast CT, rule out the intracranial hemorrhage, use narrow windows

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for best detection. And then a semi quantitative way of measuring the infarct

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core that is used is the aspect score. So I hope that all

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of you have aspect scores of 10, which means your brain's normal.

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For each abnormal region you take off a point, so...