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ASL (Arterial Spin Labeling)

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on 23 July 2016

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Transcript of ASL (Arterial Spin Labeling)

Arterial Spin Labeling (ASL)
ASL steps
ASL Methods
Continuous ASL
(CASL)





Pulsed ASL
(PASL)




Velocity-Selective ASL
(VSASL)
Neck Coil
Background Tissue Signal Supression
3D Volume Acquisition
Conclusion
Objective

Evaluate the utility of ASL to measure perfusion* deficits in transient ischemic attack or minor stroke.
TIA is defined as a transient episode of neurological dysfunction, without acute infarction.
Labeling Efficiency
Labeling
Efficiency 2MoB
- Overcome SAR (specific absorption rate)



- Whole Brain Coverage



- Low Magnetization Transfer (MT) effects
How does MRI work?
MRI basics - BACKGROUND
Blood Flow Quantification
HYPOTHESIS
EXPERIMENT
SIGNIFICANCE
* delivery of oxygen and nutrients to tissues by means of blood , gives as well a rate of waste removal
Infarction
Blood Flow
Decreases
Arterial
Occlusion
Non-invasive ASL will demonstrate that perfusion abnormalities will be present in a number of TIA and minor stroke patients where DWI (even at high resolution) is normal.
- Developing of 3D whole-brain ASL sequence

- ASL scans will be examined for hypo- or
hyper-perfusion

- Assessing perfusion/diffusion mismatch

- # of patients with an ASL abnormality but no DWI
lesion will be recorded

- 30 day follow-up scan

- multivariate logistic regression

The detection of lesions in 20% more TIA patients would translate to 40,000-100,000 patients per year whose diagnosis would change from TIA to stroke and thus potentially alter their management.
Change clinical practice by encouraging the modification of MRI protocols to take advantage of their 'Teslas' (high magnetic field) and spend extra time (more minutes) to provide and improved initial diagnosis that will ultimately lead to better prognosis and guidance for early treatment.
BIBLIOGRAPHY
THANK YOU!
KEY PROPERTIES OF ASL
LABELING METHODS

CASL-PCASL


PASL


VSASL
Advantages Disadvantages

- High SNR
- Direct Control over
bolus duration


- High labeling efficiency
- Low SAR



- Insensitive to transit delays

- Sensitive to resonance offsets
- Higher SAR



- Low SNR



- Low SNR
- Relatively untested


METHOD EFFICIENCY
Conventional MRI Images vs ASL Perfusion Image
1. High Magnetic Field is applied

2. RF sinc pulse (90)

3. Precession Voltage

4. Acquire Signal
1. Tag endogenous arterial blood water by magnetic inversion (T1 relaxation)



2. Acquire the
Tag Image



3. Repeat the experiment without tag



4. Acquire
control image



5. Subtract:
Control image
-
Tag Image
THE DIFFERENCE IN MAGNETIZATION BETWEEN CONTROL AND TAG IMAGE
IS PROPORTIONAL TO REGIONAL CEREBRAL BLOOD FLOW.
ASL Concept
- MRI technique for measuring perfusion



- noninvasive (tracer blood flow)



- labeled blood flow change in tissue
magnetization




blood flow T1
STRATEGIES
CASL
[1] Talagala SL, Ye FQ, Ledden PJ, Chesnick S. Whole-brain 3d perfusion mri at 3.0 t using casl with a separate labeling coil. Magn Reson Med. 2004;52:131-140

[2] Hetzer S, Mildner T, Driesel W, Weder M, Moller HE. Shielded dual-loop resonator for arterial spin labeling at the neck. J Magn Reson Imaging. 2009;29:1414-1424

[3] Wong EC. An Introduction to ASL Labeling Techniques. J Magn Reson Imaging. 2014; 00:00-00

[4] Detre JA. Arterial Spin Labeled Perfusion MRI. MAGNETOM Flash. 1/2008.



[6] Campbell AM, Arterial Spin Labeling MRI of Cerebral Perfusion, University of Alberta, MSc Thesis.

[7] Hornak, JP. The Basics of MRI. 1996. eBook. <http://www.cis.rit.edu/htbooks/mri/inside.htm>.

[8] Schering, . MRI made easy. 1990. eBook.

[9] MRI principles 1. Film. 25 Feb 2014. <http://wwwyoutube.com/watch?v=lKp67IqQjH4&list=PL83FF1926FEC021DD&index=1>.
(change this for the correct video)

[10] "Functional MRI Laboratory." Arterial Spin Labeling. University of Michigan, n.d. Web. 25 Feb 2014. <http://fmri.research.umich.edu/research/main_topics/asl.php>.
=
Moc - Mot
Moc - Mot = actual magnetization difference

MoB = Equilibrium Magnetization of the blood that is inverted
CBF = Cerebral Blood Flow

L = 0.9 (Blood tissue partition function

a = 0.79 (inversion pulse efficiency)

T1 = longitudinal relaxation time

Scontrol = signal intensity from the control image

Slabel = signal intensity from the labelled image
ml/100g/min
TIA patient
Local Neck RF coils Advantages

* Remember to correct bibliography

* keep an eye on blank spaces

* speek loudly
Full transcript