Download - Neurology advanced asl jy gauvrit
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ARTERIAL SPIN LABELING
Jean-‐Yves Gauvrit, Jean-‐Christophe Ferré University hospital of Rennes, Department of radiology and medical imaging Unit/Project VisAGeS U746 INRIA/INSERM, IRISA, UMR CNRS 6074 Plateforme Neurinfo
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IntroducNon • Arterial Spin Labeling (ASL) • MRI technique for assessing cerebral blood flow (Detre et al. MRM 1992)
• Non-‐invasive • Non-‐irradiaNng • No exogenous contrast agent injecNon
• Quan8ta8ve • Cerebral blood flow (CBS) • Reliable and reproducible
• Main disadvantage: low signal-‐to-‐noise ra8o (SNR) • Sequences available on MRI but confidenNal use
2 IntroducNon
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ASL principles • Image acquisiNon
1. Arterial spin labeling by a RF pulse 2. Inversion Nme TI: Nme needed for labeled spins to reach the volume of interest 3. AcquisiNon of the volume of interest A second acquisiNon of the volume of interest is then carried out without labeling
3 IntroducNon
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ASL principles • Data processing and quanNficaNon
4
-‐ =
Tag image Control image Perfusion image Cerebral blood flow (CBF) map
→
QuanNficaNon model
↓
IntroducNon
-‐ = →
↓
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ASL principles • ASL is a reliable technique for measuring CBF
• ASL is a reproducible technique for measuring CBF
5 IntroducNon
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ASL principles
6 IntroducNon
AcquisiNon
• ASL labeling • Slice acquisiNon
• MRI hardware
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ASL principles
7 IntroducNon
AcquisiNon
• ASL labeling • Slice acquisiNon
• MRI hardware
Processing
• Preprocessing • CBF quanNficaNon
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ASL principles
8 IntroducNon
AcquisiNon
• ASL labeling • Slice acquisiNon
• MRI hardware
Processing
• Preprocessing • CBF quanNficaNon
ApplicaNons
• ArNfacts • Neuro • Others
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ASL principles
9 IntroducNon
AcquisiNon
• ASL labeling • Slice acquisiNon
• MRI hardware
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ConNnuous ASL (CASL) • Historical method • ConNnuous (2-‐4s) and selecNve labeling of protons going through a tagging plane with an equilibrium state • Advantages • High SNR • Reliable CBF quanNficaNon
• But • High SAR and magne8za8on transfer effects (especially at 3T)
• Hardware limitaNon (no mulN-‐channel coil)
Detre et al. Magn Reson Med 1992
10 AcquisiNon
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Pulsed ASL (PASL) • Wide but short RF pulses • Upstream of the region of interest (box):
STAR, QUIPPS, Q2TIPS • Over the whole region of interest: FAIR
• Advantages • Easy implementaNon • MulN-‐channel coil • Parallel imaging possible
• MulN-‐TI possible (QUASAR: arterial transit Nme) • SelecNve vascular labeling possible
• But • Arterial transit effects • Lower SNR
Edelman et al. Radiology 1994 Wong et al. Magn Reson Med 1998 Petersen et al. Magn Reson Med 2006
11 AcquisiNon
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Pseudo-‐conNnuous ASL (pcASL) • “Hybrid” method • MulNple short RF over an extended period • Advantages • High SNR • Reproducibility +++ • Easy implementaNon
• But • No ArterialTransitTime determinaNon
Wu et al. Magn Reson Med 2007
12 AcquisiNon
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ASL principles
13 AcquisiNon
AcquisiNon
• ASL labeling • Slice acquisiNon
• MRI hardware
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Image acquisiNon • Context: low SNR Increase the number of acquisiNons (labeled-‐unlabeled image pairs) but increase in the acquisiNon Nme
-‐> “Clinical ” compromise 30 acquisiNons (~ 3min30)
• 2D SS EPI: most commonly used method • SaNsfactory SNR and fast acquisiNon • But distorNons
• 3D segmented SE-‐EG (i.e.: 3D GRASE) • Bemer SNR, less distorNons , and bemer coverage
• With suppression of the staNc Nssue signal (background suppression)
14 AcquisiNon
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ASL principles
15 AcquisiNon
AcquisiNon
• ASL labeling • Slice acquisiNon
• MRI hardware
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ASL: low SNR • Increase the magneNc field • Intrinsic increase in SNR • Bemer suppression of surrounding Nssue • Increase in the labeling duraNon (by lengthening of the longitudinal relaxaNon) • T1 blood: 1,5T -‐>1350 ms 3T-‐> 1650ms
Wang et al. Magn Reson Med 2002
16 AcquisiNon
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ASL: low SNR • Use of mulN-‐channel coils • Possible with PASL and pCASL • 12 channels-‐> 32 channels: SNR +39% • Parallel imaging possible
17 AcquisiNon
Ferré et al. JMRI 2012
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ASL principles
18 Image processing
AcquisiNon
• Marquage ASL • AcquisiNon des coupes
• Matériel IRM
Processing of images
• Preprocessing • QuanNficaNon
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Processing of ASL images
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ASL images Perfusion image
CBF pvc-‐CBF
Denoising
CorrecNon of parNal volume effects
QuanNficaNon CorrecNon of movements
RegistraNon on T1
SubtracNon
Image processing
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Processing of ASL images
20
ASL images Perfusion image
CBF pvc-‐CBF
Denoising
CorrecNon of parNal volume effects
QuanNficaNon CorrecNon of movements
RegistraNon on T1
SubtracNon
Image processing
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ASL principles
21 ApplicaNons
AcquisiNon
• ASL labeling • Slice acquisiNon
• MRI hardware
Processing
• Preprocessing • CBF quanNficaNon
ApplicaNons
• ArNfacts • Neuro • Others
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ASL arNfacts ASL-‐specific ar8facts • Vascular arMfacts • PASL>CASL • Arterial or venous • Labeled blood in the vessels • Arteries: related to arterial transit Nmes
• ReducNon by use of “crushers”
22 ApplicaNons
TI 1200 TI 1700
Without Crushers
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ASL arNfacts ASL-‐specific ar8facts • Vascular arMfacts • Loss of signal in the upper slices • Related to the relaxaNon of labeled protons • Caudo-‐cranial 2D, especially at 1.5T, reduced labeling Nme • Parallel imaging: decrease the acquisiNon Nme of slices and thus the Nme between slices (Wang et al. MRM 2005)
23 ApplicaNons
Deibler et al. AJNR 2008
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ASL arNfacts ASL-‐specific ar8facts • Vascular arMfacts • Loss of signal in the upper slices • Physiological hyperperfusion / hypoperfusion
Physiological changes in perfusion, parNcularly visible with PASL • Hyperperfusion areas (Mamo et al. Arch Neurol 1983)
• Hypoperfusion areas (Hendrikse et al. Radiology 2008): related to aTT
24 ApplicaNons
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ASL arNfacts Non-‐specific ar8facts • Movement arMfacts • MagneMc suscepMbility arMfacts • Related to SS-‐EG-‐EPI acquisiNon • Focal “hypoperfusion” • Decreased by non EPI imaging and parallel imaging (decrease of TE)
25 ApplicaNons
Without parallel imaging with GRAPPA 2 Ferré et al. JMRI 2012
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ApplicaNons of ASL • Cerebral perfusion assessment • Research – Neurosciences • Psychiatric disease • Depression (Duhameau et al. Psychiatry Research 2010)
• Neurovascular disease • In acute phase (Wang et al. Stroke 2012)
• In chronic phase
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MTT ASL
rCBV ASL
ApplicaNons
TTM ASL
rCBV (DSC) ASL
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ApplicaNons of ASL
• Tumor • Tumor characterizaNon (Wolf et al. JMRI 2005)
• Post-‐treatment follow-‐up (Weber et al. Invest Radiol 2004)
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rCBV ASL rCBV ASL
ApplicaNons
rCBV (DSC) ASL rCBV (DSC) ASL
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ApplicaNons of ASL • Cerebral perfusion assessment • Demen8a • Value +++ • Reveals hypoperfusion in AD, FTD…
(Du et al. Neurology 2006, Hu et al. Neurology 2010)
• European COST AcNon Arterial Spin Labeling in DemenMa • X Golay UCL -‐ 15 countries • ObjecNves • Standardizing and comparing ASL techniques • Developing image processing sovware • ValidaNng ASL as biomarker of the disease and its progression
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FDG PET ASL
ApplicaNons
Esquevin et al. JFR 2012
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ApplicaNons of ASL • ASL and funcNonal MRI acNvaNon • ASL allows neural acNvaNon mapping (ASLf) • Motor, somestheNc, speech funcNons…
• ASLf vs IRMf BOLD, seems (Raoult et al. Neuroimage 2011)
• + inter and intra individually reproducible • + spaNally specific • Bemer Nme resoluNon
• Clinical applicaNon not validated yet
29 ApplicaNons
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ApplicaNons of ASL • Extra-‐cerebral applicaNons
• Renal perfusion • Mainly FAIR techniques • Measurements correlated with PET (even with renal artery stenosis) • Good intra-‐ and inter-‐session reproducibility • Renal tumor characterizaNon (de Bazelaire et al. Acad Radiol 2005; Lanzmann et al. Radiology 2012)
• In experimental condiNons, perfusion of • Diseased bone • Pancreas • Uterus and placenta • Prostate
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Lanzmann et al. Radiology 2012
ApplicaNons
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Main advantages and disadvantages of ASL
Advantages Disadvantages
-‐ No irradiaNon
-‐ No exogenous contrast agent injecNon
-‐ Absolute quanNficaNon of Nssue blood flow
and Nssue transit Nme possible
-‐ Repeated measurements possible
-‐ Reproducibility
-‐ Low signal-‐to-‐noise raNo: Minimal acquisiNon Nme of 3 min
Limited spaNal resoluNon
-‐ QuanNficaNon of Nssue blood volume
impossible (i.e.: cerebral blood volume)
-‐ No standardizaNon of techniques (type of
labeling, image acquisiNon, post-‐processing)
among manufacturers
-‐ OpNmizaNon, automaNon and standardizaNon
of post-‐processing are sNll being developed
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Remember
• ASL: MRI method for perfusion assessment • Non-‐irradiaNng • No exogenous contrast agent • QuanNtaNve and reproducible
• Numerous techniques, characterized by • Labeling type (PASL or pcASL) • Image acquisiNon mode (2D or 3D / EPI…)
• Image processing: important step • There are ASL-‐specific ar8facts
• Close to clinical use
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