0:01

Cardiac CT, there are generic artifacts

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and some special to the procedure.

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There are multiple ways of

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categorizing these artifacts.

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The way I think about them is motion,

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ECG synchronization, and acquisition.

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They have different solutions.

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Some have no solutions, and

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some have immediate solutions.

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So here's an example of an artifact

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that's kind of there, not much you can do

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about, and that's poor contrast bolus.

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There's nothing you can do about it at

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that time except for maybe scan the patient

0:42

again if you're not happy with the quality.

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But it's obviously worthwhile

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thinking why there was poor contrast.

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And it could be patient factors or it could be

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technical factors such as timing of the bolus,

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where the tracker was placed, what the patient's

1:01

injection fraction is, so on and so forth.

1:05

Here's another artifact that is a consequence of the

1:09

scan duration, which is known as the banding artifact.

1:11

Thank you. And it happens because from the start

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of the study to the bottom of the study, that

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is, the start of the field of view to the bottom

1:18

of the field of view, contrast density changes.

1:21

It generally happens when you

1:22

take a long time to, um, acquire.

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And these slabs are like these kind of,

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you know, boundaries between the two time

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zones of contrast and classification.

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So really not much you can do about

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these, just be aware of why they occur.

1:40

And, um, just.

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Be careful not to call stenosis at

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a point where the band goes through.

1:49

There are others that may have some solutions.

1:53

One is the imaging noise.

1:56

You can deal with that by increasing the MAS,

1:58

although that would be in a subsequent study.

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So something to kind of put in the report

2:03

so that future CT operators would be aware.

2:07

At the time, you can increase the slice thickness.

2:11

That will come with some

2:13

degradation of spatial resolution.

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And the third is iterative reconstruction.

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Which is offered on certain scanners, not all

2:20

scanners, and that simply is post-processing.

2:25

So it's a post-processing solution, which is very neat.

2:28

The example I'm giving you is quite dramatic,

2:32

no doubt, but there are grainy images that have

2:34

been improved with the iterative reconstruction.

2:40

An easy one to resolve is motion artifact,

2:45

if you have more than one phase.

2:47

This typically occurs in the RCA, which, by virtue of

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where it lives in the anterior AV groove, moves a lot.

2:54

It moves one of the most out of all of the arteries.

2:58

So you could reconstruct a diastolic phase,

3:01

like 75%, and find that it works for everything.

3:04

The LAD, the distal RCA, the circumflex, and find that

3:08

the mid RCA is stubborn and doesn't respond to it.

3:12

And to deal with that, you just have to go

3:14

back, if you've done retrospective gating, and

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find a different phase, maybe a systolic phase.

3:20

If you have prospective gating, then clearly,

3:24

you only have one shot at it and therefore

3:28

you can't correct for such artifacts.

3:32

It's important first and foremost when

3:35

you see motion artifacts to decide

3:37

whether it's respiratory or cardiac.

3:40

Because if it's cardiac, it could

3:41

be from ECG synchronization.

3:44

If it's respiratory, then there's not a whole

3:47

lot you can do except for making sure that

3:49

your future breath hold instructions are good.

3:53

So the way to distinguish the two

3:55

is that if you have a respiratory

3:59

motion, then look at the sternum and you'll

4:01

get a stair-step artifact in the sternum.

4:04

Cardiac pulsation is just

4:08

restricted to the heart and the things

4:09

that connect with the heart, like

4:10

the pulmonary arteries and the aorta.

4:13

The sternum is not affected by cardiac motion.