Arterial Spin Labelling Perfusion - Usage Examples
HIDEInteractive Transcript
0:00
So, now we're going to talk a little bit
0:02
about arterial spin labeling perfusion,
0:05
which is a noncontrast technique.
0:08
Basically, you get a control image, and
0:12
then magnetization of blood in the NAC
0:16
is inverted using radiofrequency pulses,
0:19
and then you subtract the two images
0:22
and you're able to create ASL maps.
0:27
This is from Dr.
0:28
Saharachuk's article in Neuroimaging Clinics
0:30
of North America, and it's labeled CBF map.
0:33
It is a measurement of CBF
0:35
and transit time together.
0:37
So that's arterial spin labeling in a nutshell.
0:41
So how do we use it?
0:44
So it's, it has a high
0:46
negative predictive value.
0:47
So these patients come into the ED
0:49
and they have right-sided weakness.
0:50
For example, this patient did, but
0:52
you had normal DWI and normal ASL.
0:54
So then you think it has high
0:57
negative predictive value for stroke.
0:58
So it means if she's got a stroke, she's got
0:59
a tiny stroke, or she's got some stroke mimic,
1:02
and this turned out to be hemiplegic migraine.
1:05
So normal ASL has a high
1:06
negative predictive value.
1:09
Here's another example.
1:11
Patients come in with right-sided paresis.
1:12
They come in with hemiplegia.
1:14
You have a normal MRI of the neck and MRI
1:16
of the head and DWI is read as normal.
1:19
Maybe there's slight hyperintensity.
1:20
They're hard to tell.
1:21
If you have this elevated signal in the ASL
1:23
and in the thalamus, and that's kind of classic
1:26
of seizures because the thalamus is a relay
1:28
station between cortex and the brainstem.
1:31
So that's another classic example.
1:35
And then, just like other perfusion
1:38
techniques, you can have a matched defect.
1:40
So this patient had a left homonymous
1:43
hemianopsia, has an acute stroke in the
1:44
posterior temporal occipital region, and has a
1:47
defect on the ASL images that's the same size.
1:50
No proximal vessel embolus on the MRA and the
1:54
follow-up CTA just shows that the impact didn't
1:57
extend because you have a matched defect.
2:00
So you see, does not require
2:02
aggressive treatment.
2:04
And then the other scenario, here's a
2:05
patient who has a carotid occlusion,
2:08
normal cross-filling across on the CTA,
2:11
normal bilateral MCAs and ACAs, normal
2:14
DWI, but there's a big ASL defect.
2:21
Uh, this patient also had CBF and MTT maps
2:23
and you can see there's low CBF and marked
2:25
increase in the transit time in that region.
2:28
A couple of days later, she got a follow-up DWI
2:31
and you can see some of that area infarcted.
2:32
So, just like other perfusion,
2:34
it can show you tissue at risk.
Pamela W Schaefer, MD, FACR
Professor of Radiology, Vice Chair of Education
Massachusetts General Hospital
© 2025 Medality. All Rights Reserved.