0:00

With MRI,

0:01

we have a more complicated set of

0:04

sequences that may be performed.

0:07

We usually will perform axial and coronal

0:09

T1-weighted scans without contrast,

0:12

followed by fat-suppressed T2-weighted scans and

0:16

then post-gadolinium-enhanced scans, again,

0:18

in axial and coronal planes.

0:20

It's very important for imaging of the orbit

0:22

that you have adequate fat suppression.

0:25

This is usually done with inversion recovery technique,

0:28

and this is done on the T2-weighted images,

0:31

as well as for the post-gadolinium T1-weighted scans.

0:35

You want to keep your TE's as short as possible because

0:40

of the potential for artifact at susceptibility

0:44

interfaces. For MRI,

0:46

the scanning protocol is a little bit more complicated.

0:49

We usually will perform axial and coronal T1-weighted

0:52

scans followed by T2-weighted scans and

0:55

post-gadolinium enhanced sequences.

0:58

Fat suppression is very important with respect to the

1:00

T2-weighted scans and the post-gadolinium-enhanced scans

1:03

because you want to make that fat

1:06

dark in signal intensity.

1:09

In order to reduce artifacts from bone-air interface,

1:13

we usually will use the shortest TE

1:16

possible on our T1 weighted scans,

1:18

as well as the post-gadolinium-enhanced T1-weighted

1:21

scans, and also for T2-weighted scanning as well.

1:24

In general,

1:25

inversion recovery fat suppression is preferred over

1:29

frequency-selective fat suppression. At some level,

1:33

you have to make the decision about whether the scanning

1:35

will include the brain or would be limited to the orbit.

1:38

As I said previously, for visual loss evaluation,

1:42

in most cases,

1:43

you're scanning both the orbit and the brain.

1:46

On rare occasions,

1:47

one may employ a high-resolution technique.

1:50

For this, we usually are using our 3D CISS sequence or Fiesta sequence,

1:56

which is the constructive interference in steady state.

1:59

This allows us, with MRI,

2:01

to have submillimeter scanning protocols.

2:05

For T1-weighted scanning, we use the VIBE technique,

2:08

which is Volumetric Interpolated Breath-hold Examination.

2:12

And once again,

2:13

this allows you to have sequences that are less than

2:16

1 mm in thickness and can be reconstructed

2:20

in any obliquity.

2:22

For vascular lesions,

2:24

we may also employ MRA or MRV techniques,

2:28

and these may be done either with

2:30

contrast or without contrast,

2:31

depending upon whether or not we are looking for high-flow

2:35

or slow-flow vascular malformations.

2:39

This is an example of a case that was done both

2:42

for the brain as well as for the orbits.

2:45

So we have some of the brain images,

2:47

which are the full field of view, as well as some

2:51

narrow field of view,

2:52

small field of view imaging of the orbits.

2:55

As I mentioned,

2:56

we will employ both T1-weighted scans as well

2:59

as T2-weighted scans through the orbits,

3:01

usually in the axial and/or coronal plane.

3:04

This is a thin-section coronal image, T1-weighted,

3:08

and you notice that the orbital fat is bright.

3:12

And we have a good definition of the extraocular

3:15

musculature, as well as the optic nerve sheath complex.

3:20

On the T2-weighted scan, as I mentioned,

3:23

we employ fat suppression.

3:25

So now one sees that the orbital fat is dark,

3:29

allowing us to see the optic nerve and the bright signal

3:33

intensity CSF around the optic nerve within the

3:36

optic nerve sheath. And the muscles are dark,

3:40

as you can see this temporalis muscle. Similarly,

3:43

the extraocular muscles are dark in signal intensity.

3:48

With respect to post-gadolinium enhanced scanning,

3:52

we employ fat suppression again,

3:55

so that fat which was previously

3:57

bright on the T1-weighted scan,

3:59

is now suppressed as dark signal intensity on the

4:03

post-gadolinium enhanced sequence. As you can see,

4:07

the extraocular muscles, as well as the optic nerve

4:10

sheath will show some elements of enhancement

4:13

in the normal instance. In this case,

4:16

we have a patient who has optic neuritis,

4:19

in which the right optic nerve is enhancing compared

4:23

to the normal left optic nerve,

4:25

which is non-enhancing.

4:28

You can see at the air-bone interface,

4:31

we do get some artifacts. And as I said,

4:34

this can be reduced by using the low

4:37

TE possible sequences that you can.

4:41

And in general,

4:43

we will perform these sequences both in the

4:45

coronal as well as the axial plane.

4:48

This is again post-gadolinium

4:50

T1 weighted with fat suppression,

4:53

allowing us to see the extraocular muscles very nicely,

4:56

the optic nerve and optic nerve sheath complex,

4:59

and the enhancing optic nerve on the right side

5:01

in this patient who has optic neuritis.

5:05

The brain is completed with the full field of view

5:09

imaging without fat suppression on post-gadolinium

5:12

enhanced scans, as you see here.