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ASL (Arterial Spin Labeling)
Transcript of ASL (Arterial Spin Labeling)
Background Tissue Signal Supression
3D Volume Acquisition
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.
- Overcome SAR (specific absorption rate)
- Whole Brain Coverage
- Low Magnetization Transfer (MT) effects
How does MRI work?
MRI basics - BACKGROUND
Blood Flow Quantification
* delivery of oxygen and nutrients to tissues by means of blood , gives as well a rate of waste removal
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
- 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.
KEY PROPERTIES OF ASL
- High SNR
- Direct Control over
- High labeling efficiency
- Low SAR
- Insensitive to transit delays
- Sensitive to resonance offsets
- Higher SAR
- Low SNR
- Low SNR
- Relatively untested
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
3. Repeat the experiment without tag
THE DIFFERENCE IN MAGNETIZATION BETWEEN CONTROL AND TAG IMAGE
IS PROPORTIONAL TO REGIONAL CEREBRAL BLOOD FLOW.
- MRI technique for measuring perfusion
- noninvasive (tracer blood flow)
- labeled blood flow change in tissue
blood flow T1
 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
 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
 Wong EC. An Introduction to ASL Labeling Techniques. J Magn Reson Imaging. 2014; 00:00-00
 Detre JA. Arterial Spin Labeled Perfusion MRI. MAGNETOM Flash. 1/2008.
 Campbell AM, Arterial Spin Labeling MRI of Cerebral Perfusion, University of Alberta, MSc Thesis.
 Hornak, JP. The Basics of MRI. 1996. eBook. <http://www.cis.rit.edu/htbooks/mri/inside.htm>.
 Schering, . MRI made easy. 1990. eBook.
 MRI principles 1. Film. 25 Feb 2014. <http://wwwyoutube.com/watch?v=lKp67IqQjH4&list=PL83FF1926FEC021DD&index=1>.
(change this for the correct video)
 "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
Local Neck RF coils Advantages
* Remember to correct bibliography
* keep an eye on blank spaces
* speek loudly