0:00

So let's take a moment to talk about perfusion.

0:03

You know, what I showed you so far was just a single phase

0:06

of perfusion, and that's often all you get

0:08

with a coronary CT

0:09

because you're just looking at one, uh, point in time,

0:12

which is the, the time which happens

0:13

to enhance the arteries best.

0:15

Um, but if we looked broadly at a set of myocardium, um,

0:19

and injected contrast

0:21

and had a magical, uh, device

0:23

that could keep taking CT scans repeatedly,

0:26

or if you're doing a nuclear scan, you can run that

0:29

and image the radio tracer repeatedly,

0:31

or an MRI you can image, uh, repeatedly.

0:34

You would see that as we inject contrast at first pass, um,

0:38

you would have relatively normal

0:40

and, uh, rapid enhancement of healthy myocardium.

0:44

What we saw in the example

0:46

of the LAD profusion abnormality on that MRI, we saw

0:50

that there was an area of regional hypoperfusion

0:53

and we weren't really sure whether

0:54

that was ischemic myocardium.

0:56

Were infarcted myocardium.

0:57

The fact is there'll be a hypo enhancement

1:00

and the one will look worse than the other,

1:01

but you won't know until you get another time point.

1:04

So, um, one time point tells you

1:06

that there's some abnormality, a second time point,

1:08

and with MRI, you look between seven and 40 minutes later

1:12

and a ct it's maybe five

1:13

to eight minutes as your sweet spot.

1:15

But what you're seeing is

1:17

that there is extracellular accumulation of contrast

1:21

and I'll give you an example of that, um, in a moment.

1:24

But what you would see is

1:25

that there's a late enhancement phenomenon.

1:28

The fibrous tissue

1:29

and the intracellular spaces start to enhance.

1:31

So if you give two time points,

1:33

you'll know there's a relative abnormality

1:35

and you look late, you'll see

1:36

that there's a hyper enhancement relatively in an infarcted

1:39

myocardial segment, whereas there'll be deen enhancement

1:43

just like normal myocardium in the live

1:45

but ischemic myocardium.

1:46

So, um, first pass

1:48

and delayed images can help differentiate.

1:50

So let's illustrate that.

1:52

So scar enhances late

1:53

and that would be if you just have a late enhancement image,

1:56

then you wouldn't know whether there's a,

1:58

a relative hypoperfusion,

1:59

but just late accumulation of contrast.

2:02

Here's an MRI of that.

2:03

So this is on the left, a normal patient

2:05

with normal healthy inferior wall

2:07

and on the right an infarct.

2:08

So this is somebody with a pretty much

2:10

transmural inferior wall infarct.

2:12

And it's also a nice chance to review our segmental anatomy.

2:15

So there's an anterior lateral inferior septal

2:18

and this does look like the mid myocardial segment.

2:20

I don't see two papillary muscles

2:22

'cause I think they were just a little high

2:23

and also one of them may be infarcted in this case.

2:26

So, um, whether you're looking at an MRI

2:28

or a CT scan, we're injecting small molecules,

2:32

whether it's gadolinium or iodine.

2:34

So I've just illustrated iodine here. Tightly packed.

2:37

Normal healthy myocytes don't have a lot

2:39

of intracellular space.

2:41

Infarcted, fibrous, uh, infiltrated myocytes

2:44

that have now died and been replaced by fiber.

2:46

Um, they have lots of extracellular space,

2:48

so a late phenomenon would, would allow for accumulation

2:51

of those small molecules and that can happen with CT or mri.

2:55

The reference here is just a CT paper we did comparing

2:57

to mr, but the idea

2:58

Is those small molecules arrive late and stay late

3:02

because they're not well perfused.

3:03

And that's a good way on those late images

3:05

to differentiate infarct from ischemia.

3:08

The same thing happens in the nuclear lab,

3:10

but you might do a 24 hour delayed image

3:12

to let thallium accumulate, which is rarely done these days.

3:16

And just so that you can see

3:17

what this would look like in the pathology lab, um, this is,

3:21

uh, one of the first papers of delayed enhancement.

3:23

MRI kind of a fundamental in the field.

3:25

And you can see this is a, uh, a specimen

3:28

where there is fibro fatty infiltration.

3:30

In an LED infarct, there's the interseptal wall.

3:32

This is a pathology, uh, specimen.

3:35

And right before that was taken, uh, and

3:37

before the, uh, I think it's a dog was sacrificed,

3:40

this is an MRI of that same segment

3:43

and you can see that there was a late

3:44

enhancement phenomenon.

3:46

So, um, very exquisite detail

3:48

and really perfect matching of the gadolinium, uh,

3:51

infiltrating to that extracellular space outlining the

3:53

fibrous tissue.