0:00

Okay, let's talk about shoulder pulsing sequences,

0:05

and we're going to focus on instability for our pulsing sequence

0:09

assessment, although the general pulsing sequences that we

0:13

use are going to be similar even for rotator cuff pathology.

0:17

But this is a section that is focused on the two

0:21

basic types of instability, multidirectional micro

0:25

instability, and single-event macro instability.

0:28

Okay.

0:29

And we are going to also focus on the direction of

0:32

instability, severity of instability, and so on.

0:36

But right now let's tackle the axial projection.

0:40

Now you've got two choices for the axial projection.

0:43

You can either go what I call fat-weighted or

0:45

T1-weighted, or you could go gradient-weighted.

0:50

And my preference when you're dealing with instability,

0:53

especially macro instability where you have dislocation

0:56

or locking, my preference is to go with gradient echo.

1:00

And then I, I know that I'm going to have somewhere in my

1:02

arsenal a T1-weighted image and another projection so I can

1:06

look at the bony anatomy and the status of the glenoid, etc.

1:10

So, in terms of gradient echo imaging and the axial

1:13

projection, you've got, uh, two major jumping-off points.

1:17

You can either go two-dimensional gradient echo,

1:20

which gives you a slightly thicker section and

1:25

perhaps better contrast resolution, or you

1:27

could go 3D, where the sections can be 1 or 1.

1:30

2 millimeters, but the contrast resolution

1:34

and detail are not quite as good.

1:35

And this is true throughout the entire body, not just MSK.

1:41

Then you've also got different

1:42

types of gradient echo sequences.

1:44

Some of the newer ones have better signal-to-noise,

1:48

and they work really well, especially with 3D imaging.

1:51

And these are known as adage or additive gradient echo.

1:54

MERGE, MEDIC, and MFFE.

1:57

This happens to be an adage image, and these are a

1:59

series of very thin section axial gradient echo images.

2:04

Now the gradient echo image, uh, its strength is in

2:07

looking at fibrocartilaginous tissue, which is this

2:11

macerated tissue right here, which is abnormal, and hyaline

2:14

cartilage tissue, which is this gray tissue right here.

2:17

And there's going to be hyaline cartilage on both

2:20

the humeral side and the glenoid side of the joint,

2:22

although admittedly that's hard to appreciate.

2:25

On this specific axial series.

2:29

What does gradient echo not do well?

2:32

It doesn't do bone well, especially if

2:35

it's in phase gradient echo imaging.

2:38

Now you can add fat suppression to

2:39

your gradient echo imaging or not.

2:41

That's going to be a dealer's choice,

2:43

uh, type of opportunity there.

2:45

Um, in my opinion, uh, either way is fine.

2:49

Whatever you used to are comfortable with because

2:51

most gradient echoes that you're going to perform

2:53

in the axial projection are going to be in phase.

2:55

Water emphasized GREs.

2:58

So you're gonna get a free arthrographic effect.

3:00

In other words, if somebody's dislocated, or had some

3:03

form of trauma or instability, there's gonna be an

3:05

effusion in the joint, there's gonna be blood in the

3:07

joint, so you've got basically a free arthrogram.

3:09

You don't need to put anything in the joint.

3:13

The other thing that gradient echo

3:14

is good for is looking at tendons.

3:18

Especially inside the tendon.

3:20

In fact, we use it for tendons throughout the body.

3:23

But on the other side, the yin and the yang, the yang

3:25

is, it's not very good for muscle, or muscle injuries.

3:28

So good for tendon, not for muscle.

3:31

Bad for bone, or not so good for bone, but

3:34

good for hyaline cartilage and fibrocartilage.

3:37

Now in the axial projection, this patient's unfortunate

3:41

anterior inferior labrum is just macerated, it's

3:45

pulverized, and it's rolled over medially, it's

3:49

medialized towards the midline, lifting up the periosteum.

3:53

It's squished under the periosteum in the axial projection.

3:58

Not only is it squished under it anteroposterior,

4:02

it's also squished under it in the coronal projection.

4:06

So there's axillary involvement.

4:08

Here is blood, that's bloody tissue.

4:10

This is labral tissue, under

4:12

the more superficial periosteum.

4:15

So it's medialized in the axillary

4:17

region, and it's medialized anterior.

4:19

But I'm not showing it so much for the

4:21

pathology, which is an anterior labral

4:24

periosteal sleeve avulsion, or ALPSA lesion.

4:27

I'm showing it for the axial pulsing sequence.

4:32

Now, if you're using a T1 weighted image, it's gonna

4:34

be a lot easier to spot your Hill Sachs abnormalities.

4:37

Here's a T1 down below.

4:39

We're talking axial right now.

4:41

When you get down a little bit lower,

4:43

there's usually an area of flattening in the

4:46

posterior aspect of the humerus right there.

4:48

That's much lower down.

4:50

Do not confuse that for a Hill Sachs type lesion.

4:54

It's a little easier to assess,

4:56

as I said, on a T1 weighted image.

4:58

T1, stronger for bone interface with other tissues.

5:02

Gradient echo, stronger for hyaline and

5:04

fibrocartilage interface with other tissues.

5:08

So that's the axial projection.

5:11

Just a quick caveat, by the way, if you're looking at labra

5:14

on an axial GRE, when you're up high, you find the labrum,

5:18

and as you go down, whatever fissures, whatever recesses you

5:22

have up high, they should close down when you get down low.

5:26

Now they're not closing down

5:27

because this is a pulverized labrum.

5:29

Another little pearl, is as you go from high to low,

5:32

the labrum should always get bigger and blacker when

5:34

you go from high to low in the axial projection.

5:36

And it doesn't matter whether it's

5:38

a GRE or another pulsing sequence.

5:41

So with that pearl, let's move on to another

5:45

projection, the most favored nation status

5:47

in the shoulder, the coronal projection.