0:00

When thinking about how to modify protocols,

0:05

it's important to have some understanding

0:09

of what the default protocol is and how you

0:13

would change that based on differing needs.

0:16

So here's an example, triple rule out.

0:19

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

0:22

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

0:25

to assess the pulmonary artery, aorta, and coronary

0:28

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

0:33

Aortic dissection, pulmonary embolus, and

0:36

we're assessing the patency of the coronary

0:38

arteries, or confirming the patency.

0:41

Uh, so three big chest pain diagnoses,

0:47

dissection, PE, and acute coronary syndrome.

0:52

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

0:54

a fan of this, I think the problem with

0:56

doing a triple rule out is that it becomes

0:58

the default study for ruling out PE.

1:03

That's the, that's the risk.

1:05

But having said that, it's worth thinking

1:09

about how one would change the protocol.

1:12

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

1:17

Because the aorta only needs a

1:18

small amount of contrast to pacify.

1:21

Both the pulmonary arteries and coronary

1:23

arteries are the difficult ones.

1:25

And coronary arteries are difficult because

1:28

of the motion and because of their size.

1:31

Pulmonary arteries are difficult because of the timing.

1:33

If you get the timing wrong,

1:34

then they become non-pacified.

1:37

So, that means that we're dealing with two

1:41

arteries of different characteristics, which

1:46

are also in slightly different time zones.

1:48

So the pulmonary artery optimally pacifies roughly

1:51

eight to 10 seconds before the coronary artery.

1:54

So the first thing you have to do is

1:56

think about how do we pacify all three,

2:02

not so that the best and nothing else is pacified,

2:07

but so that all three are reasonably well pacified.

2:11

And to do that, you have to trigger off the

2:12

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

2:17

Generally, we trigger off the aorta for the

2:19

coronary arteries, we trigger off the main

2:20

pulmonary artery for the pulmonary artery,

2:22

but the left atrium is good for all three.

2:27

Now, also imaging the aorta and the pulmonary artery.

2:32

We have to think about field of view.

2:33

Field of view is going to increase.

2:35

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

2:40

So instead of starting at the level of the

2:42

main pulmonary artery, which is what we would

2:44

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

2:47

And we also have to go below the heart

2:49

a little bit because we want to get the

2:51

pulmonary arteries as they branch towards

2:53

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

2:58

So increased field of view, all things

3:00

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

3:03

Thanks.

3:04

Scan times can get longer, but you want the contrast

3:06

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

3:10

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

3:12

going to give you a ballpark figure by 20 mL.

3:15

You reduce contrast rate.

3:18

I'd say to about 4 or 4.5.

3:20

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

3:24

Trigger off the left atrium, and that

3:26

should hopefully cover multiple time zones.

3:31

A couple of other nuances.

3:33

One is that you still want to get a very

3:37

coned-down reconstruction of the heart.

3:40

Because the spatial resolution is dependent on the

3:42

field of view, and if you have a gigantic right

3:46

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

3:49

plane spatial resolution for no reason whatsoever.

3:52

So, two reconstructions: one of the chest,

3:56

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

3:59

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

4:02

appreciate the aorta, and then another that is a

4:04

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

4:09

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

4:11

checks, and your most important thing in your quality

4:14

check is to look at the opacification of all three.

4:18

You want to look at the opacification of

4:20

the pulmonary artery, opacification of the

4:22

coronary artery, left ventricle, and aorta.

4:24

And they should ideally look like this

4:26

image over here, where all three are,

4:28

if not equally, but adequately opacified.

4:32

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

4:38

tweak the timing depending on

4:40

what structure is causing the problem.

4:45

I imagine that in this sort of situation,

4:49

as long as you get the coronary arteries mostly

4:51

correct, you'll probably end up getting the

4:54

pulmonary arteries right, at least to the um,

4:57

segmental level, which should be mostly adequate.

5:00

Thank you.