Jean Yves Gauvrit, ASL - Arterial Spin Labeling, jfim ifupi milan 2018
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Jean Yves Gauvrit, ASL - Arterial Spin Labeling, jfim ifupi milan 2018
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Jean Yves Gauvrit, ASL - Arterial Spin Labeling, jfim ifupi milan 2018
- 1. ARTERIAL SPIN LABELING Pr Jean-Yves Gauvrit, Pr 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 1st Italian-French Update Imaging – IFUPI Advanced Multiparametric Imaging - How to use in daily practice MILAN March 23-24 2018
- 2. Introduction • Arterial Spin Labeling (ASL) • MRI technique for assessing cerebral blood flow (Detre et al. MRM 1992, Dixon et al. MRIM 1986) • Non-invasive • Non-irradiating • No exogenous contrast agent injection • Quantitative • Cerebral blood flow (CBS) • Reliable and reproducible • Functional MRI and MR Angiography • Main disadvantage: low signal-to-noise ratio (SNR) • Sequences available on MRI but confidential use 2 Introduction
- 4. ASL principles • Data processing and quantification 4 - = Tag image Control image Perfusion image Cerebral blood flow (CBF) map → Quantification model ↓ Introduction - = → ↓
- 10. Continuous ASL (CASL) • Historical method • Continuous (2-4s) and selective labeling of protons going through a tagging plane with an equilibrium state • Advantages • High SNR • Reliable CBF quantification • But • High SAR and magnetization transfer effects (especially at 3T) • Hardware limitation (no multi-channel coil) Detre et al. Magn Reson Med 1992 10 Acquisition
- 11. 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 implementation • Multi-channel coil • Parallel imaging possible • Multi-TI possible (QUASAR: arterial transit time) • Selective 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
- 12. Pseudo-continuous ASL (pcASL) • “Hybrid” method • Multiple short RF over an extended period (1second) • Advantages • High SNR • Reproducibility +++ • Easy implementation • But • No ArterialTransitTime determination Wu et al. Magn Reson Med 2007 12 Acquisition
- 14. Image acquisition • Context: low SNR Increase the number of acquisitions (labeled-unlabeled image pairs) but increase in the acquisition time -> “Clinical ” compromise 30 acquisitions (~ 3min30) • 2D SS EPI: most commonly used method • Satisfactory SNR and fast acquisition • But distortions • 3D segmented SE-EG (i.e.: 3D GRASE) • Better SNR, less distortions , and better coverage • With suppression of the static tissue signal (background suppression) 14 Acquisition
- 16. ASL: low SNR • Increase the magnetic field • Intrinsic increase in SNR • Better suppression of surrounding tissue • Increase in the labeling duration (by lengthening of the longitudinal relaxation) • T1 blood: 1,5T ->1350 ms 3T-> 1650ms Wang et al. Magn Reson Med 2002 16 Acquisition
- 17. ASL: low SNR • Use of multi-channel coils • Possible with PASL and pCASL • 12 channels-> 32 channels: SNR +39% • Parallel imaging possible 17 Acquisition Ferré et al. JMRI 2012
- 21. ASL artifacts ASL-specific artifacts • Vascular artifacts • PASL>CASL • Arterial or venous • Labeled blood in the vessels • Arteries: related to arterial transit times • Reduction by use of “crushers” 21 Applications TI 1200 TI 1700 Without Crushers
- 22. ASL artifacts ASL-specific artifacts • Vascular artifacts • Loss of signal in the upper slices • Related to the relaxation of labeled protons • Caudo-cranial 2D, especially at 1.5T, reduced labeling time • Parallel imaging: decrease the acquisition time of slices and thus the time between slices (Wang et al. MRM 2005) 22 Applications Deibler et al. AJNR 2008
- 23. ASL artifacts ASL-specific artifacts • Vascular artifacts • Loss of signal in the upper slices • Physiological hyperperfusion / hypoperfusion Physiological changes in perfusion, particularly visible with PASL • Hyperperfusion areas (Mamo et al. Arch Neurol 1983) • Hypoperfusion areas (Hendrikse et al. Radiology 2008): related to aTT 23 Applications
- 24. ASL artifacts Non-specific artifacts • Movement artifacts • Magnetic susceptibility artifacts • Related to SS-EG-EPI acquisition • Focal “hypoperfusion” • Decreased by non EPI imaging and parallel imaging (decrease of TE) 24 Applications Without parallel imaging with GRAPPA 2 Ferré et al. JMRI 2012
- 25. Applications 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 25 MTT ASL Applications TTM ASL
- 26. Applications of ASL • Tumor • Tumor characterization (Wolf et al. JMRI 2005) • Pituitary Gland Tumor-Skull BaseTumor • Post-treatment follow-up (Weber et al. Invest Radiol 2004) 26 rCBV ASL rCBV ASL Applications rCBV (DSC) ASL rCBV (DSC) ASL
- 27. Applications of ASL • Cerebral perfusion assessment • Dementia • Value +++ • Reveals hypoperfusion in AD, FTD… (Du et al. Neurology 2006, Hu et al. Neurology 2010) • European COST Action Arterial Spin Labeling in Dementia • X Golay UCL - 15 countries • Objectives • Standardizing and comparing ASL techniques • Developing image processing software • Validating ASL as biomarker of the disease and its progression 27 FDG PET ASL Applications Esquevin et al. JFR 2012
- 29. Applications of ASL: fASL 29 Applications • Absolute quantification of DSC-induced modifications • Usefulness for longitudinal follow-up • Good intra-individual reproducibility • Localization and quantification • Improved spatial precision of neuronal activity • Smaller area but anatomically more precise • Less sensitivity to venous contamination Raoult et al. Neuroimage 2011, Aguirre et al. Neuroimage 2002
- 33. Applications of ASL : (ASL)MRA • Dynamic ASL-MRA (time-resolved spin labeled MRA) • ASL labeling + cardiac gating • No constraints related to exogenous contrast agent bolus => very high temporal resolution 50-100ms vs. >500ms for dynamic MRA (gadolinium) • Potential clinical usefulness: characterization of arterio-venous malformations (MAVs) 33 Dynamic MRA Yan et al. Radiology 2010; Xu et al. JMRI 2010; Langman et al. Eur Radiol 2011 Applications
- 36. Applications of ASL • Extra-cerebral applications • Renal perfusion • Mainly FAIR techniques (pulsed over the whole region of interest) • Measurements correlated with PET (even with renal artery stenosis) • Good intra- and inter-session reproducibility • Renal tumor characterization (de Bazelaire et al. Acad Radiol 2005; Lanzmann et al. Radiology 2012) • In experimental conditions, perfusion of • Diseased bone • Pancreas • Uterus and placenta • Prostate 36 Lanzmann et al. Radiology 2012 Applications
- 38. Remenber • ASL: Access to the different compartments pertaining to “neurovascular coupling” • fASLf is an alternative to fMRI BOLD for detecting cerebral activation • Dynamic ASL-MRA: possibility of high temporal resolution (<100ms) • Clinical validation of fASL and ASL-MRA is currently ongoing 38
- 39. Remember • ASL: MRI method for perfusion assessment • Non-irradiating • No exogenous contrast agent • Quantitative and reproducible • Numerous techniques, characterized by • Labeling type (PASL or pcASL) • Image acquisition mode (2D or 3D / EPI…) • Image processing: important step • There are ASL-specific artifacts • Close to clinical use 39