Objectives 자기공명영상을이용한확산 …

1 1 KSMRM Spring 2007 KSMRM Spring 2007 Objectives ..KSMRM Spring 2007 Content Perfusion( ) MRI Dynamic Contrast Enhanced (bolus passage) Dynamic Susceptibility Contrast (bolus tracking) Arterial spin labeling Diffusion( ) MRI Diffusion-weighted imaging Diffusion tensor imaging Fiber TrackingKSMRM Spring 2007pMRI: DCE or T1W PWI Common outputs: EES volume, CBF, CBV, Ktrans GD-DTPA : -> blood plasma : BBB (blood brain barrier) Tumor multiple sclerosis (MS) EES(Extravascular Extracellular Space ).

2 T1 T1 KSMRM Spring 2007 DCE: New Parameters constant rate: kep=PS/ve Transfer constant (Ktrans): BBB leakage PS flow permeability Limited permeability model (ex, MS): Ktrans=PS (flow>>PS) Limited flow model (ex, tumor): Ktrans=flow (flow<<PS) Permeability Map free software: LUPE programKSMRM Spring 2007 Problems of the DCE Method Protocol: 3D Fast GE T1W sequence TR<7 msec, TE< msec, FA=30 Problems: 1. AIF 2. (tissue homogeneity) 3. (spatial and temporal resolution) 4.

3 Perfusion permeability angiogenesis 5. Ktrans ve . 2 KSMRM Spring 2007pMRI: DSE or T2*W PWI Common outputs: CBF, CBV, MTT, Peak height, Percent signal recovery Susceptibility( ) , T2* . T2* relaxivity contrast ( R2*) . : EPI sequence . KSMRM Spring 2007 Dynamic PWI KSMRM Spring 2007A. Pre-injection baselineB. Contrast arrivalC. Peak signal changeD. RecirculationE. Post-injection baselineA. Arrival timeB. Maximum contrast concentrationC.

4 Full-width at half maximumChange in MRI signal due to passage of contrast agentFigure from Cerebral MR Perfusion. Sorensen and ReimerBook by Sorensen & P. Reimer, 2000 KSMRM Spring 2007 Flow Quantification AIF: flow brain-feeding artery : R2* (quadratic relation) . Phase flow quantification: Phase : flow quantification . KSMRM Spring 2007 CBF measurement in DSC)()()(tRtAIFCBFtCm =Cm(t) : measured concentration curve in tissueCBF : Cerebral Blood Flow [ml/100g/min]AIF (t) : Arterial Input functionR (t) : Residue function[Ostergaard et al.]

5 1996]knownunknown)()(sec)(min/601min)/10 0/()/()(tRtAIFgmlCBFkmlgtCHm = KSMRM Spring 2007 AIF And Partial Volume Effect (PVE) GE voxel PVE Artery main magnetic field parallel : PVE . Artery main magnetic field non-parallel PVE . local AIF 3 KSMRM Spring 2007 KSMRM Spring 2007 Deconvolution and Data Presentations Hematocrit : Dispersion flow Deconvolution singular value decomposition (SVD) Deconvolution : modified SVS Fourier method maximum-likelihood expectation maximization (MLEM) Data presentations : ROI voxel parameter ROI parameter.

6 KSMRM Spring 2007 Clinical Issues Percent signal recovery (PSR): Malignant glioma metastasis Metastasis PSR capillary GD-DTPA Glioma grading rCBV rCBV high grade tumor. : Oligodendroglioma grade vascularity rCBV . Grading Ktrans . KSMRM Spring 2007 KSMRM Spring 2007pMRI: ASL Common output: CBF ASL perfusion : RF arterial blood longitudinal magnetization PWI = Control - Labeled Development issues: blood labeling MT effect : Static tissue ASL : pulsed ASL (PASL) continuous ASL (CASL) velocity selective ASL(VS-ASL) Vascular Territory Imaging (VTI)KSMRM Spring 2007 PASL va CASL PASL : blood labeling : FAIR, PICORE, EPISTAR, UNFAIR, EST, TITL, DIPLOMA IDOL CASL.

7 Flow driven adiabatic inversion PASL SNR pseudo-CASL 4 KSMRM Spring 2007 Pseudo-continuous Flow Driven Adiabatic Inversion Repeated vs. continuous RF More compatible with current MRI RF amplifiers on Allows product body coil excite/array receive 2-3X SNR improvement Improved efficiency (~80% versus ~70% for AM control) 2X SNR improvement Total 5X SNR gain With background suppression >10X SNR gainRFGlabelcontrol800 secGarcia, de Garcia, de BazelaireBazelaire& Alsop, & Alsop, ISMRMISMRM20052005 KSMRM Spring 2007VS-ASL Wu WC, Wong EC, NeuroImage 2006 VSASL.

8 Blood (cutoff velocity Vc) cerebrovasculardiseases labeled blood blood T1 KSMRM Spring 2007 VTI Green=left ICA Red=right ICA Blue=basilar arteryGunther M 2006, MRM 56 VTI PASL feeding artery labeling . Cerebralvascular disease stenoticvessel carotid endarterectomy, stenting, bypass intervention .KSMRM Spring 2007 CBF and BOLD and CMRO2 ASL oxygen metabolism (CMRO2) CBF BOLD CMRO2 Dual-echo method: 1st echo=ASL 2nd echo=BOLD CMRO2 Single-echo method: addition=BOLD subtraction=CBF CMRO2 KSMRM Spring 2007 Improved Reliability with DIPLOMA ASL Jahng Radiology 2005 Test-retest on 13 subjects ICC=Intra-class correlation ICCKSMRM Spring 2007 Whole Brain ASL Perfusion MRI at 4 TImaging Parameters: x ; 3mm slices with gap; TR/TE=4200/11ms, 120 averages.

9 8 min5 KSMRM Spring 20073D ASL with 1min Acquisition 3D GraseSeq with 26 slices 1min acquisitionKSMRM Spring 2007 IntermissionKSMRM Spring 2007 Alexander Leemans, Tensor MRI (DTI)Brownian motion of molecules (microscopic)Diffusion (macroscopic)Diffusion?Einstein relation:26 rDt= r=displacement t=timesimilar physical principle water in water D = Diffusion CoefficientKSMRM Spring 2007 Alexander Leemans, Tensor MRI (DTI)Diffusion? free diffusionDis equal in all directionsisotropic diffusion restricted diffusionDis notequal in all directionsanisotropic diffusion 2D3 DKSMRM Spring 2007 Alexander Leemans, Tensor MRI (DTI)Diffusion tensor!

10 Mathematical framework to describe diffusion!xxxyxzyxyyyzzxzyzzDDDDDDDDD = D1 = DE E eigenvalue decomposition = E111xyzeee222xyzeee333xyzeee000000 = 1 2 3 ()11, e ()22, e ()33, e KSMRM Spring 2007dMRI: DWI Pulsed-gradient spin-echo (PGSE) echo-planar imaging (EPI) sequence b-value: trapezoidal gradient + =63032322 jiijGGb6 KSMRM Spring 2007 Improvements New PGSE-type sequence: Diffusion gradient eddy current Double-refocusedPGSE EPI sequence Minimization of susceptibility artifact.