Neurology advanced asl jy gauvrit

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

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

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

ASL principles • Data processing and quanNficaNon

4

-‐ =

Tag image Control image Perfusion image Cerebral blood flow (CBF) map

→

QuanNficaNon model

↓

IntroducNon

-‐ = →

↓

ASL principles •  ASL is a reliable technique for measuring CBF

•  ASL is a reproducible technique for measuring CBF

5 IntroducNon

ASL principles

6 IntroducNon

AcquisiNon

• ASL labeling • Slice acquisiNon

• MRI hardware

ASL principles

7 IntroducNon

AcquisiNon


• MRI hardware

Processing

• Preprocessing • CBF quanNficaNon

ASL principles

8 IntroducNon

AcquisiNon


• MRI hardware

Processing


ApplicaNons

• ArNfacts • Neuro • Others

ASL principles

9 IntroducNon

AcquisiNon


• MRI hardware

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

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

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

ASL principles

13 AcquisiNon

AcquisiNon


• MRI hardware

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

ASL principles

15 AcquisiNon

AcquisiNon


• MRI hardware

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

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

ASL principles

18 Image processing

AcquisiNon

• Marquage ASL • AcquisiNon des coupes

• Matériel IRM

Processing of images

• Preprocessing • QuanNficaNon

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

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

ASL principles

21 ApplicaNons

AcquisiNon


• MRI hardware

Processing


ApplicaNons

• ArNfacts • Neuro • Others

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

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

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

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

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

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

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

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

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

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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Neurology advanced asl jy gauvrit

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