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Protocols: Triple rule out

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When thinking about how to modify protocols,

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it's important to have some understanding

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of what the default protocol is and how you

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would change that based on differing needs.

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So here's an example, triple rule out.

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So a triple rule out is done in some places, and what

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we're trying to do here is we're simultaneously trying

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to assess the pulmonary artery, aorta, and coronary

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artery, so that we are ruling out three things at once.

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Aortic dissection, pulmonary embolus, and

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we're assessing the patency of the coronary

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arteries, or confirming the patency.

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Uh, so three big chest pain diagnoses,

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dissection, PE, and acute coronary syndrome.

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So the first time you tell me that I'm not

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a fan of this, I think the problem with

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doing a triple rule out is that it becomes

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the default study for ruling out PE.

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That's the, that's the risk.

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But having said that, it's worth thinking

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about how one would change the protocol.

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The easiest out of these three to assess is the aorta.

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Because the aorta only needs a

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small amount of contrast to pacify.

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Both the pulmonary arteries and coronary

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arteries are the difficult ones.

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And coronary arteries are difficult because

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of the motion and because of their size.

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Pulmonary arteries are difficult because of the timing.

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If you get the timing wrong,

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then they become non-pacified.

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So, that means that we're dealing with two

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arteries of different characteristics, which

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are also in slightly different time zones.

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So the pulmonary artery optimally pacifies roughly

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eight to 10 seconds before the coronary artery.

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So the first thing you have to do is

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think about how do we pacify all three,

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not so that the best and nothing else is pacified,

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but so that all three are reasonably well pacified.

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And to do that, you have to trigger off the

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left atrium, that's sort of the middle ground.

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Generally, we trigger off the aorta for the

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coronary arteries, we trigger off the main

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pulmonary artery for the pulmonary artery,

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but the left atrium is good for all three.

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Now, also imaging the aorta and the pulmonary artery.

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We have to think about field of view.

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Field of view is going to increase.

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It's going to increase in the cranial-caudal direction.

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So instead of starting at the level of the

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main pulmonary artery, which is what we would

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for a coronary, we want to go above the arch.

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And we also have to go below the heart

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a little bit because we want to get the

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pulmonary arteries as they branch towards

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the, um, um, basilar segments of the lungs.

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So increased field of view, all things

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else being constant, means that your 60 00:03:02,285 --> 00:03:03,965 Contrast volume is going to increase.

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Thanks.

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Scan times can get longer, but you want the contrast

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to be hanging out there for a lot longer than normally.

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So you increase the contrast volume, and I'm just

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going to give you a ballpark figure by 20 mL.

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You reduce contrast rate.

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I'd say to about 4 or 4.5.

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69 00:03:21,369 --> 00:03:23,290 Normally, we have it at about 5.

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Trigger off the left atrium, and that

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should hopefully cover multiple time zones.

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A couple of other nuances.

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One is that you still want to get a very

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coned-down reconstruction of the heart.

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Because the spatial resolution is dependent on the

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field of view, and if you have a gigantic right

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to left field of view, you'll be degrading your in-

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plane spatial resolution for no reason whatsoever.

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So, two reconstructions: one of the chest,

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which is going to be full field of view, in order

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to be able to see the, um, following arteries and

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appreciate the aorta, and then another that is a

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very coned-down version, just looking at the heart.

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It's important, if you do these, to do regular quality

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checks, and your most important thing in your quality

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check is to look at the opacification of all three.

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You want to look at the opacification of

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the pulmonary artery, opacification of the

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coronary artery, left ventricle, and aorta.

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And they should ideally look like this

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image over here, where all three are,

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if not equally, but adequately opacified.

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94 00:04:32,380 --> 00:04:38,170 And if you are starting to find that you have some issues,

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tweak the timing depending on

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what structure is causing the problem.

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I imagine that in this sort of situation,

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as long as you get the coronary arteries mostly

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correct, you'll probably end up getting the

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pulmonary arteries right, at least to the um,

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segmental level, which should be mostly adequate.

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Thank you.

Report

Faculty

Saurabh Jha, MD

Co-Program Director, Cardiothoracic Imaging Fellowship, Associate Professor of Radiology

University of Pennsylvania

Tags

Vascular

Mediastinum

Coronary arteries

Chest

Cardiac

CTA

CT

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