0:01

Okay, the next sequence that we will

0:03

discuss is, uh, black blood imaging.

0:05

Um, here's an example of two

0:07

cases with black blood imaging.

0:09

On the left, this is actually a 14-year

0:11

old boy who presented with chest pain.

0:14

And on the right, a 33-year-old

0:16

man who presented with chest pain.

0:18

In both cases, these patients have had

0:20

the eventual diagnosis of myocarditis.

0:23

And the black blood images are helpful to look for

0:25

edema in the myocardium that is part of that diagnosis.

0:28

So, on the left-hand image, this is a four-chamber

0:31

image, and you can see this bright signal here

0:34

along the lateral wall of the left ventricle.

0:37

And on the right-hand image, you can

0:38

see this bright signal, which is in the

0:40

anteroseptum, extending inferiorly into the

0:43

inferoseptum and even the inferior wall.

0:46

So, on the black blood images, we often use

0:50

T2 weighting, and the T2 weighting allows

0:53

us to see this edema and identify areas

0:56

of acute abnormality in the myocardium.

0:59

And in the right clinical setting, and particularly

1:01

in somebody with suspected myocarditis,

1:03

this is really diagnostic for an acute problem,

1:07

uh, acute myonecrosis in this region.

1:10

Black blood images are called black blood because

1:12

you can see that obviously the blood is there.

1:15

And that's because of a nulling sequence

1:16

that we will talk about in a second.

1:18

And they're different from other sequences in

1:20

cardiac MRI in that they're just static images.

1:23

You do not have any cine imaging with black blood CMR.

1:27

So what are some important facts about black blood CMR?

1:30

You may hear other terms, double IR or

1:34

triple IR, triple inversion recovery.

1:36

Those are often heard when describing black blood CMR.

1:40

I'ts an ECG-gated spin echo image, so it's not

1:44

gradient echo, different from bright blood imaging,

1:48

different from perfusion imaging, for instance.

1:51

This is the only spin echo sequence

1:52

that we're going to use in cardiac MRI.

1:55

As we know, spin echo sequences are

1:57

slow, and that's why we can really

1:59

only get static images for black blood.

2:01

We cannot use it for cine because

2:02

it's just too slow of an acquisition.

2:05

Black blood CMR is high resolution generally,

2:09

and it's really used for tissue characterization.

2:11

So, unlike the other, um, types of acquisitions,

2:14

the gradient echo acquisitions used for

2:17

identifying motion and things like that,

2:20

this is really specific to tissue characterization.

2:23

And in particular, we often use

2:26

T2 weighted images for edema, and we may

2:28

use T1 weighted images for morphology.

2:31

The way it works, and the reason it's called double

2:33

IR or triple IR, is because it actually involves

2:36

multiple inversion recovery pulses to null blood.

2:39

So in the setting of double IR, that's two

2:41

180-degree inversion recovery pulses that

2:43

null the blood to give you dark signal.

2:46

And in those situations, in those patients,

2:49

you may want to do a T1 weighted image.

2:51

That's the most common.

2:53

The reason T1 here is in parentheses is because,

2:56

you know, as we know T1, you have to have a short

2:59

TE and a short TR, well, it turns out that we can

3:03

certainly get a short TE with black blood imaging,

3:06

but the TR is often dependent on the patient's heart rate.

3:09

And really it corresponds to the R to R interval.

3:12

So because you're acquiring chunks of data in the

3:14

same part of the cardiac cycle from one beat to

3:17

another, just like the cine imaging, you're using

3:19

multiple chunks of data to combine to make one image.

3:22

The TR actually turns out is the distance between

3:25

one chunk of data and one heartbeat to the next.

3:28

And so if the patient has a nice high heart

3:30

rate with a really short interval between each

3:32

heartbeat, then you can get a really nice short TR.

3:35

But if a patient has a low heart rate, then your

3:38

TR is going to be longer, and your T1 weighting

3:41

will sort of start to become more proton density.

3:44

So that's why the T1 here is in parentheses.

3:47

T2 weighted images, absolutely we can get

3:50

high quality T2 weighted images with black blood

3:52

CMR because we can do a long TR and a long TE.

3:56

Typically, to achieve that long TR, we acquire

3:59

actually images after skipping a heartbeat.

4:02

So we'll go some chunk of data at heartbeat 1,

4:05

skip heartbeat 2, and then acquire

4:07

the next chunk of data on heartbeat 3.

4:10

So that allows us to get a really

4:11

long TR between each acquisition.

4:14

Oftentimes, we'll see the black blood STIR

4:17

imaging, which is also known as III-R,

4:20

and that's what we saw in those first set of slides.

4:23

And that actually is basically one additional

4:26

inversion pulse that's used to null fat

4:29

as you saw on that previous exam.

4:31

Other notes about black blood CMR, the T2 is,

4:35

in particular, has a really slow acquisition.

4:38

So, I mentioned that you're acquiring data, you're

4:41

skipping a heartbeat, and you're acquiring more data.

4:43

So, if you think about it, that can be

4:45

a long breath hold, multiple heartbeats,

4:47

particularly if a patient has a slow heart rate.

4:49

So, it's not uncommon for us to have

4:51

a lot of artifacts on T2 weighted images

4:54

because patients just can't

4:55

hold their breath that long.

4:57

So we'll see that a lot, and you may have to reduce

4:59

resolution in order to get good quality images.

5:03

One potential solution in patients who are having

5:05

trouble holding their breath is to acquire the exams

5:07

as a HASTE, half acquisition spin echo sequence,

5:11

but those end up being noisier and lower resolution.

5:15

So there's a bit of a trade-off there.

5:17

And then one other problem that we run into with black

5:19

blood imaging is artifactual bright signal in the lumen

5:23

from slow blood flow in patients with poor function.

5:27

So that means that the areas of black

5:29

blood actually don't turn out black.

5:31

They're not nulled.

5:32

So, in particular, the blood right near

5:35

the subendocardium of the left ventricle.

5:38

Often there's a lot of slow flow,

5:40

particularly in the various trabeculations.

5:42

And so those will result in residual bright

5:46

signal in the lumen that can be sometimes

5:48

mistaken for bright signal in the myocardium.

5:50

So you don't want to make that mistake

5:52

in patients with poor ejection fraction.

5:54

I'm just going to show two more examples.

5:56

This is an example of T1 weighted black blood imaging.

6:01

These are both patients

6:03

who had a suspicion for ARVC.

6:06

And so we acquired these images in particular

6:08

to look at the interface of the fat in the

6:11

epicardial region with the right ventricle.

6:13

And so in this case, you can nicely see the fat sitting

6:17

on top of the right ventricle, and you can get a

6:19

nice look at the right ventricular free wall muscle.

6:22

And same thing here on the short axis images.

6:25

Um, and this is what we use the T1 weighted

6:28

dark blood images for the most often.

6:30

Um, the only other situation where we often

6:32

use T1 weighted dark blood images would be

6:34

in cardiac mass characterization, uh,

6:37

which will be discussed in a different course.