Sequences and Field of View
HIDEInteractive Transcript
0:02
I'd like to talk about wrist imaging technique,
0:04
and I have actually picked a series that
0:07
I normally would not use for the wrist.
0:09
A long TR 4317, a short TE, a proton
0:13
density image, which gives exquisite
0:16
anatomy but very poor contrast resolution.
0:19
So I'm really showing it for the anatomy, which by
0:22
the way, I'm not here to talk about right this moment.
0:25
I'm here to talk about the other ancillary
0:27
aspects of technique that are shown magnificently.
0:33
In this particular image that looks somewhat
0:35
T1 weighted, but it's not really T1 weighted.
0:39
And what are those aspects?
0:40
First, look to the left.
0:41
The patient's in a rigid coil.
0:44
The patient's hand is in pronation.
0:48
So, it's important, it's incumbent upon
0:51
you to realize how your technologist
0:55
has positioned the hand for your exam.
0:57
Is it over the head?
0:59
Is it at the side?
1:00
Is it in pronation?
1:02
Is it neutral?
1:03
Is it in supination?
1:05
Because this will alter the tissue relationships.
1:08
But even more important than that
1:10
is the overall field of view.
1:12
In other words, the circular area that you have
1:15
prescribed on your MR scanner to cover, and the
1:19
smaller that area is, the higher the resolution.
1:23
Now the field of view for a wrist
1:26
should be approximately 8 or less,
1:29
depending upon what you're chasing.
1:32
Ten is acceptable.
1:34
Twelve is borderline.
1:35
Anything above twelve, not acceptable.
1:38
The field of view in this case was eight.
1:42
The other area that I want to
1:43
concentrate on is the slice thickness.
1:47
For a high-quality wrist with a sequence that has
1:50
robust signal to noise, lots of signal, I like two
1:55
millimeters or less, down to about 0.5 millimeters.
2:00
I'll accept
2:01
two to three millimeters.
2:03
Much beyond three millimeters, probably not optimal.
2:08
And then one more caveat, the matrix.
2:12
The matrix also helps determine
2:15
the spatial detail and resolution.
2:18
We've got field of view, we've got
2:20
slice thickness, and now we have matrix.
2:24
I like, in the wrist, to have
2:25
a matrix that is asymmetric.
2:28
In other words, in the Y or phase-encoded direction,
2:31
you see we have this number here, 384, and in
2:35
the X direction, 512, because we don't have a
2:38
lot of time penalty when we use 384, and the
2:42
wrist really isn't a square structure anyway.
2:45
So we might put the 512 matrix this way, and the
2:50
384 matrix this way, and we might end up with some
2:54
pretty square voxels, saving ourselves a little time,
2:59
but still, the matrix, 384 by 512, is a high matrix.
3:04
Now how high will I go?
3:07
I'll go up to 1024.
3:10
I'll go up to 512 by 1024, or sometimes even
3:13
1024 by 1024, if I've got to have exquisite,
3:18
in-plane, pixel-by-pixel resolution.
3:22
So let's summarize.
3:23
Field of view, I like 8.
3:25
Slice thickness, I like 2 or less.
3:28
Matrix, I like somewhere around 256.
3:32
To 384 by 512 at the least, and I will go up to
3:37
1024 by 1024, but 512 by 1024 is still pretty good.
Stephen J Pomeranz, MD
Chief Medical Officer, ProScan Imaging. Founder, MRI Online
ProScan Imaging
© 2024 Medality. All Rights Reserved.