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Advanced Imaging TechniquesPerfusion Imaging

Prof. Dr. Frank G. ZöllnerComputer Assisted Clinical MedicineMedical Faculty Mannheim Heidelberg University

Theodor-Kutzer-Ufer 1-3D-68167 Mannheim, Germany

Frank.Zoellner@medma.uni-heidelberg.dewww.ma.uni-heidelberg.de/inst/cbtm/ckm

Prof. Dr. Zöllner I Slide 2I 10/30/2018

Learning Goals

� introduction to perfusion imaging

� basic MRI principles -> Physics of Imaging Techniques

� Goals:

1. How does the technique work ?

2. What kind of images do we receive?

3. Where is this applied to ?

� Slides of the lectures at https://www.umm.uni-heidelberg.de/inst/cbtm/ckm/lehre/index.html

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Prof. Dr. Zöllner I Slide 3I 10/30/2018

Reading� Alsop, D. et al. (2015). Recommended implementation of arterial spin-

labeled Perfusion mri for clinical applications: A consensus of theISMRM Perfusion Study group and the European consortium for ASL in dementia. Magnetic Resonance in Medicine, 73(1), 102–116.

� http://s434060124.online.de/aslindementiacms/basic-principles-of-asl-2

� Nery, F. et al. (2018). Non-Invasive Renal Perfusion Imaging UsingArterial Spin Labeling MRI: Challenges and Opportunities. Diagnostics, 8(1), 2.

� Sourbron, S. P., & Buckley, D. L. (2013). Classic models for dynamic contrast-enhanced MRI. NMR in Biomedicine, 26(8), 1004–1027.

� Cao et al. Gadolinium-based nanoscale MRI contrast agents for tumor imaging J. Mater. Chem. B, 2017, 5, 3431-3461

� Petrella et al., MR Perfusion Imaging of the Brain Techniques andApplications, American Journal of Roentgenology. 2000;175: 207-219

Prof. Dr. Zöllner I Slide 4I 10/30/2018

What is Perfusion?

� blood stream supports tissue with oxygenand nutrients

� tissue haemodynamics at capilarylevel� perfusion (Fp) measures for blood

flow (units: ml/100ml/min)

� permeability (PS) of the capilarrymembranes (units: ml/100ml/min)

� interplay gives information on tissuefunction

� can be measured non-invasive by MRI

Perfusion

Schmidt RF, Thews G, Lang F: Physiologie des Menschen. Springer, 2000

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Prof. Dr. Zöllner I Slide 5I 10/30/2018

Perfusion Imaging - Applications

brain

heart

kidney

lung

liver

Prof. Dr. Zöllner I Slide 6I 10/30/2018

How do we measure perfusion by MRI ?

� What do we need to see a flow in tissue?

� How is tissue and blood composed of ?

� What are the MRI properties of this ?

We need to differenciateblood and tissue!

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Prof. Dr. Zöllner I Slide 7I 10/30/2018

How do we measure perfusion by MRI ?

� two basic techniques� Arterial Spin Labeling (ASL)

endogenous tracer

� Dynamic Contrast Enhanced MRI (DCE-MRI)exogenous tracer

� Idea: change the contrast between flowing blood and stationary tissue

Prof. Dr. Zöllner I Slide 8I 10/30/2018

Arterial Spin Labeling (ASL)

� arterial blood used as endogenous, freely diffusible tracer� needs to be labeled (tagged) to be identified

� use of radio frequency inversion pulse

� basic scheme:read out volumelabeling slicelongitudinal magnetization

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Prof. Dr. Zöllner I Slide 9I 10/30/2018

Properties of ASL

� signal change due to the delivered, labeled magnetization is typically about 0.5% - 1.5% of the total signal

� need to average several pairs of tag/control to increase SNR

� ∆M is a perfusion-weighted (PW) image that directly reflects localperfusion

� however, perfusion signal does not only depend on vascular flow but

� Longitudinal relaxation times of blood and tissue,

� proton density,

� the transit time from labeling to imaging region

� the inflow time TI

� only quantification of PWI takes this into account

Prof. Dr. Zöllner I Slide 10I 10/30/2018

ASL - Imaging

� building blocks of ASl sequence

� inversion pulse

� readout

� bolus arrival time

� background suppression

t

Inversion ss/ns readoutQ2TIPSbackgroundinversion

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Prof. Dr. Zöllner I Slide 11I 10/30/2018

ASL – Imaging, Inversion scheme

� Pulsed ASL (PASL):

� use 1 RF pulse (180°) to invert spins� wait t=TI ms

� readout signal

� repeat without labeling slab

t

Inversion ss/ns readoutInversion time TI

Prof. Dr. Zöllner I Slide 12I 10/30/2018

ASL – Imaging, Inversion scheme

� (pseudo) continuous ASL ((P)CASL):

� continuously use RF pulse toinvert spins in thin slabfor labeling time t

� wait post label delay (PLD ~ TI)

� readout signal

� pseudo cont. → 1000 or more shapedRF pulses at a rate of ~ 1/ms

t

(P)CASL labeling readoutpost inversion delay(PLD)

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Prof. Dr. Zöllner I Slide 13I 10/30/2018

ASL – Labeling Schemes

� CASL

Alsaedi et al. Contrast Media Mol Imaging. 2018

Prof. Dr. Zöllner I Slide 14I 10/30/2018

ASL- Labeling Scheme

� EPISTAR (PASL)

Alsaedi et al. Contrast Media Mol Imaging. 2018

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Prof. Dr. Zöllner I Slide 15I 10/30/2018

ASL –Labeling Schemes

� FAIR (PASL)

Alsaedi et al. Contrast Media Mol Imaging. 2018

Prof. Dr. Zöllner I Slide 16I 10/30/2018

ASL - Readout

� readout block Independent of labeling scheme

� EPI, bFFSP, TSE, 3D – GRASE

� selection of readout scheme: SNR, CNR, time constraints

t

readout

courtesey of M.Günther

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Prof. Dr. Zöllner I Slide 17I 10/30/2018

ASL - Readout

� readout block Independent of labeling scheme

� EPI, SSFP, TSE, 3D - GRASE

t

readout

courtesey of M.Günther

Prof. Dr. Zöllner I Slide 18I 10/30/2018

ASL - Readout

� readout block Independent of labeling scheme

� EPI, SSFP, TSE, 3D - GRASE

t

readout

courtesey of F. Zimmer

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Prof. Dr. Zöllner I Slide 19I 10/30/2018

ASL - Readout

� readout block Independent of labeling scheme

� EPI, SSFP, TSE, 3D - GRASE

t

readout

courtesey of M.Günther

Prof. Dr. Zöllner I Slide 20I 10/30/2018

ASL - Readout

Alsop et al. , Magn Reson Med 2015

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Prof. Dr. Zöllner I Slide 21I 10/30/2018

ASL - Readout

� comparison of readout schemes

Nery et al. Diagnostics, 2018

Prof. Dr. Zöllner I Slide 22I 10/30/2018

ASL – Q2TIPS

� perfusion signal depends on inflow time TI

� but also: transit delay /bolus arrival time (BAT)

� time of the labeled blood to arrive at the tissue of interest

� use saturation pulses to shape the bolus, using e.g. „quantitative imaging of perfusion using a single subtraction with thin-slice TI1 periodic saturation” (Q2TIPS)

t

Q2TIPS

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Prof. Dr. Zöllner I Slide 23I 10/30/2018

ASL – Q2TIPS

� TI1 to TI1S consist of a train of 90° excitation pulses for saturation� TI2: inflow time

Luh et al, Magn Reson Med 1999

Prof. Dr. Zöllner I Slide 24I 10/30/2018

ASL – Background Suppression

� when calculating PWI by subtracting control from tag image → signal of static tissue is to be eliminated

� low SNR of the perfusion signal →small fluctuations in the tissue signal can corrupt the ASL signal

� background suppression to avoid signal from stationary tissue

� insert inversion pulses matching T1 of static tissues to besuppressed

t

Inversion ss/ns readoutQ2TIPSbackgroundinversion

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Prof. Dr. Zöllner I Slide 25I 10/30/2018

ASL – Background Suppression

two tissue species with a T1 of 1.5 s (blue) and 1.2 s (green)

Prof. Dr. Zöllner I Slide 26I 10/30/2018

ASL-Background Suppression

Alsop et al. , Magn Reson Med 2015

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Prof. Dr. Zöllner I Slide 27I 10/30/2018

ASL – Summary Imaging Technology