0:00

Okay, so let's take a look at the first case.

0:03

First start off with just a touch of history.

0:05

This is a patient referred for a

0:08

possible aortic valve replacement,

0:11

and as is a great indication for a coronary ct,

0:14

this is preoperative, uh, evaluation

0:16

of the coronary arteries.

0:18

This is very possible that we spare this patient an invasive

0:21

angiogram, um, as easier for other, uh, heart surgery.

0:24

But of course, you wanna do one sternotomy.

0:26

So if there was any coronary disease, you'd like to know

0:28

that ahead of time to plan out, uh,

0:30

whether you'd wanna revascularize

0:32

or have any need for a cardiac cath.

0:34

So the surgeons, uh, saw the patient

0:36

and ask for a coronary ct.

0:38

Uh, couple things I look at.

0:39

When I look at a coronary ct, the first thing I do is say,

0:43

is there good coverage of the heart?

0:44

So, um, axial images are a kind of a key part of the review,

0:48

uh, but it could also, um, be easily seen on a sal.

0:52

So this is just the, the cone down coronary series.

0:55

As you know, we like to use a smaller field of view

0:58

because we're maximizing spatial resolution.

1:00

So this is an image that's 512 by 512 pixels.

1:04

So with a field of view that's 20 something odd.

1:08

It's a a little better spatial resolution than if we used a

1:11

full field of view, or we would throw away a lot

1:13

of our resolution on the peripheral structures.

1:15

There's a finite limit.

1:16

You can't keep conning down until you, uh,

1:19

you can, but you won't.

1:21

Additionally, uh, add resolution.

1:22

There's an intrinsic line pair resolution of the CT scanner.

1:26

So we like around, you know, between 1525, uh, somewhere in

1:30

that range, uh, field of view that includes the heart in the

1:34

x and y axis and the Z axis.

1:36

Of course, you want to cover the entire heart.

1:38

You really just need from the, uh, the proximal coronaries

1:41

to the distal, but you wanna have a little wiggle room

1:44

because the heart can move

1:45

during the different phases of the cardiac cycle.

1:48

Okay, so we've ascertained that we like the image quality.

1:50

Uh, the next thing I look at is, uh,

1:52

look for slab artifacts.

1:54

Depending on the type of ECG gating, um,

1:57

you might have prospective triggering.

1:59

So it's a step and shoot mode.

2:00

This one was done in a retrospective gated mode.

2:03

So retrospective is gating

2:04

and prospective is ECG triggering, strictly speaking.

2:07

But the step and shoot mode would be, uh, axial, sequential,

2:11

so every other heartbeat.

2:12

Whereas this, uh, acquisition is done in a helical mode,

2:15

so continuous acquisition, um,

2:17

and then retrospectively bend out into different phases.

2:20

So whatever phase we ask for here, um, the important thing

2:23

to look for is there's not motion, um, in the heart.

2:26

And the most important thing is to look

2:28

for motion in the sternum.

2:29

The reason being, if it's a breathing artifact,

2:31

there's no amount of reconstruction

2:33

or fancy tricks you can do to salvage the exam.

2:35

This would just be a, a non invaluable exam.

2:38

In fact, at our service, we check every exam on the table.

2:40

We're running scans a hundred mile radius all the way up

2:43

into other states actually.

2:45

So when a patient's on the coronary CT table, um,

2:48

tech runs our protocol, uh, calls us for an image check,

2:51

and we just quickly verify exactly what I just talked about.

2:54

So, enhancement coverage,

2:56

and are there any irreconcilable artifacts?

2:59

Um, and if not, then we say clear to go.

3:01

Um, the other thing that, uh, we kind of look at last, uh,

3:05

when we're doing our image check is

3:06

check that atrial appendage.

3:08

So you can see here, uh,

3:09

this is a normally enhancing little oddly shaped atrial

3:12

appendage, got kind of an angulation,

3:14

which has turned out to be protective.

3:16

Um, there's a, a middle cardiac vein, uh,

3:19

as it turns the border and becomes the,

3:21

the great cardiac vein here.

3:22

Don't confuse that venous structure

3:24

with the atrial appendage,

3:25

but the important thing being,

3:27

if there's any doubt at all, you can sort it out later.

3:29

Sometimes pericardial fluid, like this case right here, um,

3:32

is insinuating around the appendage.

3:34

Just get the delay. You can

3:35

sort it out in the reading room later.

3:37

You only have about a minute or two.

3:38

Um, some scanners actually reconstruct so slowly

3:41

that you don't know whether you need the delay.

3:43

So if it's really older technology, you may even,

3:45

in some cases, apriori specify

3:48

to get a delay just to roll out thrombus.

3:50

As you know, there's mixing artifact,

3:51

and that can be hard to differentiate from thrombus,

3:54

especially in people with atrial fibrillation.

3:56

This, this, uh, patient has a larger atrial size,

3:59

so they may have some AFib,

4:00

but early, uh, ification

4:03

that has mixing artifact is impossible to distinguish.

4:05

So, uh, one situation we do that in, even

4:08

with fast scanners, uh, AFib, pre-op, uh,

4:10

atrial fibrillation, uh, isolation patients.

4:13

So anyone, you know, pre PVI mapping automatic delay,

4:17

the risk is just so high,

4:18

and the, the annoyance of having

4:20

to bring a patient back over just some artifact is, uh,

4:23

important to get around.

4:24

So we've got a great scan, no artifacts.

4:27

Talk for a moment about gating here.

4:29

So this is a systolic image. How do I know that?

4:31

Well, you can see the, the, uh, aortic valve is open.

4:34

Um, and so you can see the, uh, the leaflets,

4:37

the mitral valve is closed.

4:38

And what we do in, in most of our cases these days, uh,

4:41

these are all, the case I'll show you,

4:43

I think are gonna be almost a hundred percent dual source

4:45

of some make and model.

4:48

Uh, but, uh, that means there's high temporal resolution.

4:51

So we image everyone in iso volumetric relaxation.

4:54

Sometimes we add the entire cardiac cycle,

4:56

like in this case, but just wanted to show you,

4:58

we have tightly spaced, uh,

5:00

reconstructions every couple of milliseconds.

5:02

I think it's every 20 milliseconds, uh, from late systole to

5:06

early diastole.

5:08

So somewhere in that range,

5:09

there's always a motion free image at every coronary artery.

5:12

Uh, if you remember when we looked at that ECG tracing,

5:15

that was the, uh, second, uh, best quiescent period

5:18

during the cardiac cycle.

5:19

Why don't we always image in diastole? Well, it varies.

5:22

I'll give you our complete cardiac cycle here.

5:25

Um, and you can see that, uh, yes,

5:27

the images are relatively motion free, intentionally noisy

5:30

because we're using radiation dose protection.

5:32

But the proper diastolic phase varies

5:35

widely based on heart rate.

5:37

Um, this patient had a heart rate of 55, so any

5:42

selection during the cardiac cycle, uh,

5:44

will potentially be good, provided you freeze the motion.

5:48

But, um, no need to, you know, adjust this protocol, uh,

5:52

if the patient had a higher heart rate.

5:54

Um, so this is a nice luxury that we have a patient

5:56

That's, uh, uh, already got a slow heart rate.

5:58

Doesn't always happen in, in real practice.

6:00

And so no adjustments needed. Sly works for everybody. Okay?

6:04

Um, sly works, but you need a little bit of a range

6:07

because it's not, uh, there's no one perfect phase

6:09

and even the different, um, coronaries.

6:11

So as I page through here, I'm looking, all right,

6:13

this is a good phase.

6:14

I might look at for the right coronary artery maybe,

6:16

but here, um, but the left,

6:18

it might be a slightly more preferable phase,

6:20

just a few milliseconds away.

6:22

So with a little bit of temporal span,

6:24

we can solve any issue

6:26

and keep the doctors out of the reading room.

6:28

The doctors aren't giving medicines.

6:29

The nurses are, and, uh,

6:31

the techs are using a standardized protocol, um,

6:34

helps you scale another scan every 20 minutes.

6:37

You don't have to make a big production out of each one.

6:39

Um, also I'm paid to interpret.

6:41

I'm not paid to do nursing work.

6:42

Nurses are pretty good at that.