0:00

Sequences, foot and ankle,

0:03

1.5 Tesla, standard, basic, basic imaging.

0:09

Now, this is going to illustrate something

0:12

different from other vignettes that you

0:14

have heard, or may hear, regarding 3 Tesla,

0:17

where we narrowed the field of view, and low

0:20

field, where we emphasized the strengths of

0:23

low field imaging and the foot and ankle.

0:25

Here we've done something a little bit different,

0:29

but something that's a little irreverent,

0:31

but vey practical. What have we done that's irreverent?

0:35

We've opened the field of view so that the

0:38

reader and the clinician can see almost

0:41

everything down to the metatarsal head.

0:44

When might you do that?

0:46

Well, when you have a good magnet, 1.

0:49

1.5T, where you can open the field of view

0:50

And you have good signal to noise, and

0:52

and you're not really sure exactly where

0:55

proximal to distal the pathology is.

0:58

So you're on more of a search and destroy mission.

1:01

You don't have one single

1:02

focus or nidus to attack.

1:05

And that's not a bad thing at all.

1:07

And if you're reading, you might

1:09

start with your water-weighted

1:10

image just kind of scrolling around.

1:12

We've also done something else that's a

1:15

little atypical, not necessarily irreverent,

1:17

but we've talked about it before.

1:19

And that is, we have not plantar-flexed the foot.

1:23

We plantarflex the foot commonly to rid ourselves

1:28

of magic angle effect, also known as the 55.6-degree artifact,

1:31

35 00:01:32,475 --> 00:01:34,495 or the anisotropic artifact.

1:35

So now, if the foot is at a right angle,

1:39

these tendons are going to be coursing

1:41

in a direction that's much like this.

1:45

And so, if you image straight on down, you're

1:49

you're going to run into a curved tendon, and it's

1:51

going to exhibit a lot of magic angle effect,

1:54

because as the tendon curves 55 degrees to the

1:58

magnetic board, this exacerbates the artifact.

2:01

So what happens is, on a short TE

2:04

TE sequence, a gradient echo, a T1,

2:07

the tendons are going to turn gray.

2:09

And that is a problem.

2:11

But we didn't do that this time.

2:13

We simply put the foot in the neutral position.

2:18

And we didn't oblique the axials or

2:21

the coronals for specific structures.

2:24

In other words, if we have a tendon, we've

2:27

already said in some of the other vignettes,

2:28

if the tendon's like this, then we want

2:32

our axials to look something like this.

2:34

Always perpendicular to our tendon.

2:37

We didn't do that this time.

2:39

We did everything orthogonal.

2:41

The coronal, right here, straight orthogonal.

2:44

The axial, straight orthogonal.

2:46

So, simple, simple.

2:48

Easy for your technologist.

2:50

If you're a high quality, experienced reader,

2:53

with this type of image quality of a

2:55

1.5T, no problem.

2:57

You're gonna do fine by going back and forth.

3:01

But be aware that those of you that are

3:03

less experienced may get hamstrung by

3:06

magic angle effect and long tendons.

3:09

Now there is another very

3:11

interesting concept illustrated here.

3:15

For those of you that have seen other vignettes,

3:17

we said that tendons and plantarflexion, great.

3:23

For ligaments, especially the collaterals

3:25

when you plantarflex, maybe not so much.

3:30

Now, I don't like to be on screen that much

3:32

because, you know, I'm not a very attractive guy.

3:34

But here is the... here's the

3:38

anterior talofibular ligament.

3:39

So when you plantarflex,

3:42

look at what happens to the ligament.

3:43

It starts to flatten out.

3:46

And so, now, your axials may be tangent to the

3:49

ligament, and the ligament becomes harder to see.

3:54

So if you're in the neutral dorsiflex position,

3:57

now you're going to be cutting perpendicular

3:59

to the ligament, and look how easy it is to see

4:02

the all-important anterior talofibular ligament.

4:05

Let me line things up here for you.

4:07

And get them scrolling together nice and big.

4:12

And let's look at that ligament.

4:14

Just as an illustration.

4:16

There it is right there.

4:17

Oh, that is gorgeous.

4:19

Let's make it even bigger.

4:21

I'm into big.

4:23

Look how gorgeous and easy that is to

4:25

see on all three pulsing sequences.

4:29

That's why many individuals

4:31

like the neutral position.

4:33

Because, as you know, the most commonly injured

4:35

ligament in the ankle is this one right here.

4:38

And we're interested in the

4:39

calcaneal fibular ligament.

4:41

That one's a lot harder to see.

4:42

There it is right there.

4:44

But it does better in the plantarflex position.

4:46

But that will be a story for another day.

4:48

But for the most commonly injured ligament of

4:51

the foot and ankle, neutral positioning wins.

4:56

So, this is a garden variety study.

4:58

You can see we've done a total of three

5:01

axials, which we would do for tendons.

5:03

Two sagittals.

5:05

So we have a T1 and a proton density,

5:08

fat suppression sequence-sensitive

5:12

qualifying sequence, an atomic sequence,

5:15

and we also did two direct coronal sequences,

5:20

a T1 and a T2. Was all that necessary?

5:23

No, it wasn't.

5:24

Probably five sequences is the max you should be

5:27

doing in the foot, but you should mix and match.

5:30

You should have at least one PD spur, one T2,

5:33

one T1, and if you want, a gradient echo with

5:37

2D or 3D, and maybe add, if you wish,

5:42

one of those repeated in another projection that

5:45

shows the pathology of interest optimally.

5:48

For instance, if it's an Achilles,

5:50

you might want two sets of sagittals.

5:53

If it's a posterior tibial tendon,

5:55

then you want at least two or

5:57

three short axis axial oblique images.

6:01

So, that's a basic, basic, very comprehensive,

6:05

high-quality set of images on

6:09

1.5T, showing you an expanded field of view

6:12

to cover both the foot and the ankle at

6:14

the same time with total respectability.