0:00

So one of the things we've touched on is wall motion

0:03

and a CT can look at, um, left ventricular volumes

0:07

and functions if acquired correctly.

0:09

So you're probably familiar with MRI

0:11

and Simpson's role where we take the ventricle

0:13

and we slice it up into different planes, look at the area

0:17

of each of the planes in the, the tubular ventricle,

0:20

and then, uh, account for the slice thickness and any gaps.

0:23

And then just do simple math.

0:24

So a sum of of areas turns to volumes,

0:27

and you can look at end diastolic volume.

0:29

You can do the same thing at systole

0:30

and then just do simple math to get an ejection fraction.

0:33

So here's how we do it with an MRI, you would, uh, draw each

0:36

of the circles and have the computer figure

0:39

out the areas for you.

0:40

And then take end diastolic volume,

0:43

minus the systolic volume over the end diastolic volume

0:46

and give an ejection fraction, which is the percent of blood

0:49

that's ejected by the ventricle in each beat, knowing

0:52

that normal is at least 55 and almost always less than 72.

0:56

However, um, a CT can skip a lot of those steps

0:59

and just measure volumes the way we would measure tumor

1:01

volumes or, uh, just taking a 3D volume.

1:03

Same concept though, same math.

1:05

It would get somehow the end diastolic volume

1:07

and the end systolic volume, uh, divided

1:09

by end diastolic volume.

1:11

Uh, another very important concept when you're looking at

1:14

the uh, uh, ejection fraction is you need

1:16

to acquire end systole and end diastole.

1:19

So certainly you don't wanna truncate your acquisition.

1:22

So if you're doing prospective trigger

1:23

techniques, you can't do function.

1:25

You wouldn't have your true end systole. End diastole.

1:28

Now, if you're lucky enough

1:29

to acquire the whole cardiac cycle,

1:30

and you may want to protocol things that way, um,

1:33

there's some other things you should think about when one

1:35

of them is getting motion free images.

1:38

So when you're looking at coronary motion, we know that the,

1:41

uh, sweet spot, if you have it in a slow

1:44

and steady heart rate, would be mid to late diastole.

1:47

So that's the imaging point

1:48

where there's least motion in all coronary segments.

1:50

By the way, the orange vessels here are one segments, one

1:54

through four, that's the right coronary artery segments.

1:56

Um, five and further are the LAD and circumflex.

2:00

So if you were lucky enough to have a slow

2:02

and steady heart rate, you would try

2:04

to choose a period in mid to late diastole

2:07

because there'd be less motion this's a second quiescent

2:10

period at mid to late systole,

2:12

and that extends into early diastole.

2:14

And so when you look at in systole, um,

2:16

there's a relatively slightly larger amount of motion,

2:19

but you may have only that choice,

2:20

especially if you have a high heart rate,

2:22

because the faster heart rates tends to, um, mean

2:26

that systole is a fixed phenomenon.

2:28

Diastole is relatively flexible and diastole shrinks.

2:31

Uh, at some point there's almost no

2:33

diastole and no time for filling.

2:35

Um, most of the heart rates

2:36

that we image in in cardiac imaging are gonna be in a

2:39

reasonable rate, but it's often preferable

2:41

to have some systolic imaging in case you need it.

2:44

And if you have the entire heart cardiac cycle,

2:45

then you can look at your ejection fractions,

2:48

look at wall thicknesses.

2:49

Here's an example just to show you, um, that,

2:52

that right coronary artery is the one that moves the most,

2:54

and it's just the way that anatomy is shaped.

2:56

So the center of the chest is in the, um, all over

2:58

The spine here. And what

2:59

you see here is

3:00

that the left anterior descending on this axial image, uh,

3:04

is moving the least.

3:05

The circumflex is in the left AV groove

3:08

and it moves the second most,

3:10

and then the right coronary artery moves the most.

3:12

And that's what this graph shows you as well,

3:13

that the right coronary outta velocity is get the highest.

3:16

So if you're gonna have a coronary motion artifact issue,

3:19

it's probably gonna be in your right.

3:21

And if you don't have it in diastole, you may have

3:23

to look in systole.

3:24

And I'll show you many examples of both diastole

3:27

and systole throughout the course.

3:29

By the way, it's good to talk

3:31

and think about radiation dose.

3:32

So if you throw away all data

3:34

and only acquire it one point, if you think you can nail it,

3:36

prospective triggering allows you to reduce radiation dose,

3:39

but it closes the door

3:41

to looking at the wall motion and the function.

3:44

Uh, and again, you need to look at every segment

3:46

of the coronary arteries

3:47

and see them well to preserve

3:49

that high negative predictive value.

3:50

So it's very important to get motion free images

3:53

of every coronary segment.