0:00

Dr. Finazzo, let's introduce one of the tools

0:01

3 00:00:03,420 --> 00:00:06,300 in MRI, which is the analysis of fat on MR.

0:06

And I've got an in-phase gradient echo, an out

0:10

of-phase gradient echo, so-called OOPGRE, an IP,

0:14

in-phase gradient echo on the left, and then on

0:17

the right is a T2 spin echo with fat suppression.

0:21

Now, for those of you youngins out there, the

0:23

reason you know this is an out-of-phase MRI is

0:27

because of this India ink appearance of structures.

0:31

That contain water, like the kidney.

0:33

The kidney has water in it, surrounded by fat.

0:35

So, if I outline this India ink phenomenon,

0:38

it's this black line right here.

0:40

That.

0:42

Because you have water inside the kidney

0:45

against fat in the retroperitoneum.

0:47

And this is called chemical shift

0:49

effect, if you want the science of it.

0:51

Which occurs in the X-encoded direction.

0:54

Which is right to left or left to right.

0:57

Now, if we now analyze our mass, which is a cyst,

1:02

basically, it's got water signal intensity on these

1:05

gradient echo images and water signal intensity on

1:07

the T2, and we look at the mass, we see that there

1:10

is that black line between our water-containing

1:13

mass, I'll draw over it again right there,

1:18

and the surrounding fat.

1:21

On the other hand, if we look at our out-of-phase

1:23

image, and by the way, if you want to know how to do

1:26

this, all you've got to do is look at your manual.

1:27

Your vendor is going to tell you.

1:29

Here's the T.E.

1:30

35 00:01:30,555 --> 00:01:33,725 you choose for out-of-phase imaging, happens to be

1:33

2.2, and here's the T.E.

1:35

38 00:01:35,295 --> 00:01:36,805 you use for in-phase imaging.

1:36

So you don't have to memorize that,

1:38

it's going to come in a little booklet for you.

1:40

Now look at your lesion, which has water in it,

1:43

your so-called cyst against the water inside the

1:47

kidney, a water-containing structure, water against

1:50

water, no India ink black interface between the two.

1:54

So if you could go ahead now and help us define

1:57

how you use that and what it means in terms

1:59

of bulk fat and voxel fat or intravoxel fat.

2:04

So, a couple of things.

2:06

So whenever we look, we're looking for fat

2:08

really in cases to try to distinguish, uh,

2:12

angiomyolipomas from renal cell carcinoma.

2:17

Because as we know, both, uh, AMLs and renal

2:22

cysts, uh, excuse me, both angiomyolipomas

2:28

and clear cell carcinomas will enhance.

2:31

And how we can differentiate those two

2:33

entities is by identifying bulk fat.

2:37

And if we can see bulk fat, we can say clearly

2:40

it's an AML and go on to the next case.

2:42

Bulk fat is macroscopic fat.

2:43

61 00:02:44,334 --> 00:02:46,594 Bulk fat is macroscopic fat,

2:46

and that's when we see this chemical shift.

2:49

And as you had pointed out,

2:53

when you see, uh, India ink interposed between a

2:58

lesion and bulk fat, then you're not dealing

3:01

with bulk fat within the lesion itself.

3:06

And in this example, we know we're dealing

3:09

with a non-bulk fat lesion because we don't see

3:13

this line either internally between fluid and

3:17

fluid interface or within the lesion itself.

3:21

In a companion case to that, where we were asked

3:25

to evaluate an indeterminate small renal mass.

3:29

And here in the in-phase, out-of-phase.

3:32

We clearly see an India ink, uh, interface

3:36

between the lesion and the kidney, which

3:40

is, you know, vascular, fluid, and vascular.

3:44

So this line lets us know that

3:47

we're dealing with bulk fat.

3:48

And this is an angiomyolipoma in a

3:50

classic woman who's 43 years old.

3:53

Um, and even though this is a very

3:55

easy example to illustrate, finding

3:59

bulk fat is sometimes very difficult.

4:02

And another tool you can use is

4:04

your fat-suppressed sequences.

4:06

And in this case, for example, the T2 fat

4:09

suppressed, it follows fat on all sequences.

4:13

But the reality is, is CT, even though

4:15

this is an MR core, CT is, uh, more, uh,

4:19

favorable in trying to identify bulk.

4:21

So just to summarize, in the other case

4:24

we showed, we had a mass that was water.

4:29

And it was surrounded by fat.

4:32

So we had water against the background.

4:34

I'll make the fat a different color.

4:35

I'll make the fat blue.

4:37

And then between those two interfaces, we had an

4:40

India ink sign because we had water against fat.

4:42

So we had the interface out here.

4:45

In this case, we've got a fatty lesion in the

4:48

center surrounded by water inside the kidney.

4:52

And so we have the India ink sign,

4:54

fat with a background of water.

4:56

And then you top that off by saying, on the

4:59

T2 fat suppression image, which is on the

5:01

far right, the signal intensity of our fat

5:04

containing lesion suppressed just like the

5:06

subcutaneous fat in the back of the patient.

5:09

Pomeranz and Finazzo out.