Use of MRA in Acute Stroke Imaging
HIDEInteractive Transcript
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Today, we're going to discuss MRA
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in acute stroke imaging.
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So compared to CTA in the neck,
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it's pretty equivalent to CTA for
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identifying severe stenosis,
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and it's better than CTA for identifying
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subacute hemorrhage in the wall of the
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dissection or in the false lumen.
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CTA is better than MRA for hairline
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residual lumen versus occlusion,
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for delineating intravascular thrombus
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for identifying residual patency and stents,
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and for webs,
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FMD and several other pathologies.
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And then, as far as the head,
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detection of large vessel occlusion,
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contrast-enhanced MRA and gradient echo
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combined are equivalent to CTA for
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identifying large vessel occlusions.
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In collateral circulation,
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you can see on MRA,
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but is probably better on CTA.
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So as far as MR angiography in the head,
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we typically get time-of-flight MRA.
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It's about 80% to 90% sensitive
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for large vessel occlusion.
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There's some flow effects that can cause problems,
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but pretty sensitive.
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And then, contrast-enhanced MRA is greater
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than 90% sensitive for detecting
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large vessel occlusion.
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CTA, the CTA shows good collaterals,
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you can see them on MRA as well,
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but CTA is probably better.
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However, having said all this,
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you can acquire this fast head and neck MRA,
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and it's pretty good for delineating degree
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of stenosis in the carotid and large vessel occlusion.
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And this, combined with the gradient echo that
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I showed you before, remember,
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the SWI was greater than 90%.
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The gradient echo is 70% to 90%.
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The two in combination are equivalent to CTA
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for detecting large vessel occlusion.
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And then, this is just a paper showing the
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differences between contrast-enhanced and
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non-contrast-enhanced MRA in the head.
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So, here's a time-of-flight MRA.
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This patient has a distal ICA occlusion,
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and what's happening is there's such slow
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flow that the vessel gets saturated
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out and you can't see it at all.
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But on this time-resolved MRA,
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so on this contrast-enhanced MRA,
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you can see exactly where the occlusion is,
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and the gradient echo also showed
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where the occlusion is.
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And this also matches what
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you see on angiography.
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So, the combination of a contrast-enhanced
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and gradient echo is going to be equivalent
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to CTA and angiography
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for identifying the site of occlusion.
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So, let's look at some cases.
Pamela W Schaefer, MD, FACR
Professor of Radiology, Vice Chair of Education
Massachusetts General Hospital
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