0:01

Okay, this next topic is T2 mapping cardiac MRI.

0:05

T2 mapping cardiac MRI is another mapping

0:08

technique, similar to T1 mapping as just described.

0:11

It's used for direct quantitative

0:13

measurement of the T2 time of tissue.

0:16

It's useful for detection of edema.

0:19

And in most situations, you're

0:21

probably going to find it,

0:23

it's more reliable than dark

0:24

blood images, with less artifact.

0:26

So, um, if you take a look at this image on the right

0:29

hand side of the slide, uh, if you do a lot of dark

0:32

blood T2 imaging, you often see something like this

0:36

here in the upper left-hand corner, which is that you

0:39

have signal dropout for the myocardium of interest,

0:42

uh, which is not particularly useful.

0:45

With a lot of expertise and trial and error,

0:49

a lot of times you can get pretty good,

0:51

reproducible dark blood T2-weighted images.

0:53

However, I have to say, of all the various sequences

0:57

that we do, that this one is the hardest to really

1:00

get good quality imaging all the time. The T2 mapping

1:03

sequences are a little more forgiving in general.

1:06

It seems to, in my experience, work more consistently.

1:10

And then the nice thing about that is,

1:11

just like T1 mapping, you get a number.

1:14

And so you're not left scratching your head with,

1:16

as you are with the T2 dark blood, you know,

1:18

is this a little bit of edema, or is it normal?

1:21

You can use a number and use a cut

1:23

point to decide whether or not

1:24

you see edema in this particular patient.

1:27

So, how do they work?

1:29

They're bright blood or, um,

1:31

Turbo Spin Echo-based sequences

1:33

that, similar to T1 curve, use varied T2

1:36

preparation times to sample the T2 weighted

1:38

tissues after various T2 preparation times.

1:43

They're helpful in myocarditis or

1:45

acute infarction to identify edema.

1:48

I also have to note that I think

1:49

they're helpful in sarcoidosis as well.

1:52

If you're looking for acute involvement of sarcoidosis.

1:56

Not infrequently, I find that we'll have patients

1:58

referred for sarcoid, and you'll see some scar.

2:01

But then the question will be, well, is this

2:03

active sarcoid or is this old sarcoid, and the

2:06

presence of edema that matches the scar would

2:08

suggest this is more of an active process.

2:11

Here's an example of one of

2:13

the T2 preparation techniques.

2:14

This is an SSFP, or steady-state free precession,

2:17

based technique pulled out of the literature.

2:20

And in this technique, they basically use three

2:23

different acquisitions with different T2 preparations.

2:27

Um, the bottom line is each

2:28

one is essentially a longer TE.

2:31

So you have a T2 prep of zero and then elongating TEs

2:34

of 24 and 55, uh, which allows more time for T2 decay.

2:40

And that T2 decay curve is created.

2:43

And from that curve can be created a

2:45

pixel-by-pixel plot of the T2 time.

2:48

Just like with T1, we have normal reference T2

2:52

values available from this normal reference range

2:55

paper, uh, which is extremely useful for any type of

2:59

reference you're trying to find for a whole variety

3:02

of different measurements that we do in cardiac MRI.

3:04

In T2, um, there's a decent body of literature

3:07

out there looking at the normal T2 times.

3:10

Um, you can see here in the right side of this

3:13

table, um, normal T2 times range around the kind of

3:18

low to mid-fifties, um, depending on technique.

3:22

Generally, if you're doing three Tesla, you're

3:25

going to find that T2 times are a little longer.

3:28

Although if you look here at this graph,

3:29

the lowest T2 time is the one from

3:31

this Philips 3T at 45 milliseconds.

3:34

So it's not perfect.

3:37

And for that reason, it's really important

3:39

to establish site-specific reference ranges.

3:42

That's accomplished by basically

3:45

acquiring a whole bunch of cases.

3:47

And if you have patients who you know are normal

3:50

in terms of they get evaluated for rule-out

3:52

HCM, rule-out sarcoidosis, and the case ends up

3:55

being normal, then you can use those to establish

3:57

local reference ranges to figure out what

4:00

your local norms are, because there's always a

4:02

little bit of difference between every scanner.

4:05

And that's useful to identify the correct T2.

4:09

So how do we use T2 clinically?

4:11

I would say, like I said, sarcoid

4:13

is a really important use.

4:14

And then the biggest use, particularly now

4:16

with all of the COVID-related issues that we're

4:19

facing and COVID myocarditis, I think myocarditis

4:22

is really a key application of T2 mapping.

4:26

If you're having any familiarity with myocarditis,

4:28

the Lake Louise criteria were the original way to

4:32

diagnose myocarditis, and they included basically

4:36

early gadolinium enhancement, late gadolinium

4:39

enhancement, and then also the T2 ratio from

4:43

dark blood T2 images compared to normal muscle.

4:48

The problem with that whole thing was that nobody

4:50

wants to acquire early gad enhancement images.

4:53

It's kind of a pain and, you know, waste time.

4:56

It's just more time in the scanner.

4:58

And then the T2 dark blood images,

5:00

as we've talked about, are often unreliable.

5:02

So the new Lake Louise criteria includes both

5:06

T2 and T1 mapping, which is really helpful.

5:10

And the bottom line for this is if you have to

5:13

support the diagnosis of myocarditis, you'd like

5:16

to see a T1 abnormality, and that can be either

5:19

abnormal native T1, increased ECV, or regional LGE.

5:26

So that's all shown in this bottom row right here.

5:30

So you want to have some sort of sequence that shows

5:34

abnormal T1 and a sequence that shows abnormal T2.

5:39

And so that can be either your dark blood images

5:41

if they worked out well for you, or a T2 map.

5:44

And so it's nice to be able to get

5:45

all of these things in one protocol

5:49

and then have a much more reliable

5:50

way to evaluate for myocarditis.

5:53

And then down below you can, you know,

5:55

you can have these cases where, um,

5:57

you know, it's kind of a borderline case.

5:58

Maybe you have a T2 and not a T1, or T1 and not a T2.

6:02

Um, and if you have some supportive criteria,

6:04

um, like perhaps a systolic dysfunction

6:07

or pericarditis, that might push you

6:09

to say, this is probably myocarditis,

6:13

although it doesn't meet all the criteria.

6:15

What's an abnormal T2?

6:16

Well, in a paper that was used to establish

6:19

this Lake Louise criteria, they had a

6:21

number of 57 milliseconds that they used.

6:24

You know, I think for me clinically,

6:26

probably about, you know, 60 milliseconds

6:28

or so is a good number to keep in your head.

6:30

You know, if you see something above 60, that's

6:32

probably abnormal, but again, you really want

6:35

to establish your local reference ranges to make

6:37

sure that that's the correct number for you.