Interactive Transcript
0:00
Isotropic imaging.
0:03
It's key for coronary.
0:06
So what exactly is it?
0:07
The term basically means that the spatial
0:12
resolution is the same in all three
0:17
planes, three planes being X, Y, and Z.
0:23
So spatial resolution is very important for coronary
0:29
because coronary arteries tend to be very small.
0:31
So we want to see the small diameter structures
0:35
and be able to quantify the degree of stenosis.
0:37
There are two types of spatial resolution.
0:39
There's the in-plane.
1:41
Which is the XY plane, which is the lower-lying
1:45
fruit because all you have to do is increase
1:48
the matrix size, narrow the field of view, and
1:51
you can get very high spatial resolution.
1:54
The more difficult part is getting a
1:56
spatial resolution through the Z axis.
1:59
So XY will create the pixel, Z will create
2:01
the voxel, and that depends on detector width.
2:06
Many of us now are used to CT scans with multiple
2:09
detectors, with very thin, small detector sizes
2:13
in detectors, but that wasn't always the case.
2:16
And so as we approach isotropic
2:18
imaging, because we're never quite there
2:21
perfectly, it's really a
2:24
testament to the progress of CT.
2:28
To tell you how far we've gone,
2:29
this is the first CT scan done.
2:32
The first-generation scanner.
1:35
CT of the head, which alongside the fact that it
1:38
appears very grainy, took a long time to acquire.
1:42
Parameters are 3x3x13mm.
1:45
That's the in-plane spatial resolution is 3mm.
1:48
Again, it wasn't very difficult to get
1:49
3 millimeters in-plane, but through
1:52
plane, slice thickness is 13 millimeters.
1:54
Where are we today?
1:56
Here's a curved MPR of the coronary artery, which,
2:00
by the way, is something you can only do well.
2:04
That is 3D manipulation and reformation
2:06
because we have isotropic imaging.
2:09
It's 0.4 by 0.4 by 0.5.
2:09
2:10
46 00:02:10,835 --> 00:02:11,425
2:11
So the degree of improvement
2:13
is by 100, but not just that.
2:16
It's the fact that we're able to deliver this with
2:19
a reasonable radiation dose.
2:23
One of the reasons why coronary CTA took off and
2:25
coronary MR didn't is because of spatial resolution.
2:29
Coronary MRA, actually the first papers for
2:32
coronary MRA came before coronary CTA, but
2:35
even now with the 3 Tesla, which is very much
2:38
a powerful signal-to-noise magnet, you still
2:42
struggle to get less than three millimeters.
2:44
I mean, you can, but that might
2:46
increase the scan time too much.
2:52
MR, spatial resolution and scan time are related
2:55
because to increase spatial resolution, you
2:57
would need to increase the number of slices
3:01
or partitions, as I said, and increase the
3:05
phase matrix, increase the phase matrix.
3:08
You increase the scan time.
3:10
So you get a penalty.
3:12
CT, spatial resolution and acquisition and
3:15
temporalization are mostly unrelated, mostly.
3:19
So this is what happens when
3:21
you don't have isotropic voxels.
3:23
You get what's known as a stair-step artifact,
3:25
which is fine if you're looking at the femur.
3:28
It's not so good if you're looking at the
3:30
coronary artery where those stair steps
3:32
themselves can be a source of confusion and
3:35
artificially create stenosis when there isn't any.
3:40
So to recap.
3:42
Coronary arteries are tortuous.
3:44
They don't travel along a single plane.
3:46
They go in and out of plane.
3:48
So in order to be able to see an
3:51
artery, for example, at this point here and
3:55
know exactly what the degree of stenosis
3:57
is, you can't cut it axially, coronally, or sagittally.
4:02
You have to go along the long axis
4:04
of the artery and cut through it
4:06
orthogonally.
4:08
So it's a two-step thing, but you're only able to
4:09
do that if it doesn't matter which plane you're in.
4:13
So it doesn't matter if you're in
4:14
axial, coronal, or off-axial plane.
4:16
The fact that you have isotropic voxels
4:20
means that there's no informational loss.
4:23
And it's not just good having isotropic because you
4:27
can have isotropic imaging with five millimeters
4:29
by five millimeters by five millimeters.
4:32
The point is you want to have isotropic
4:33
and thin, not just isotropic, and both of
4:37
which are necessary for coronary imaging.
4:40
So how has the spatial resolution improved?
4:42
And I think that this is a lecture in its own right.
4:47
You can even write a book on it.
4:50
Two things to appreciate.
4:50
The first is that the detectors
4:52
have become much more efficient.
4:55
The power of the CT scan has increased.
4:59
So we're delivering more iodine flux, but
5:02
we're getting more out of that iodine flux.
5:04
So we're not wasting radiation.
5:06
So in a sense, things are more powerful,
5:09
but also things are more efficient.
5:10
So power and efficiency.
5:12
Has resulted, along with multiple other things,
5:16
in us being able to do isotropic imaging without
5:20
hugely penalizing in terms of radiation dose.
5:24
Thank you.
© 2024 MRI Online. All Rights Reserved.