arterial spin labeling read-out...

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Arterial Spin LabelingRead-Out Options

Matthias Günther1,2,3

1 Fraunhofer MEVIS, Institute for Medical Image Computing 2 Faculty 01 (Physics/Electrical Engineering), University Bremen

3 mediri GmbH, Heidelberg, Germany

Learning objectives:

• to understand how ASL works on a sequence level

• to understand the pros and cons of various image acquisition

approaches

• to understand the general difference of 2D and 3D

approaches

• to be able to determine the appropriate sequence for certainapplications

Readout strategies for ASL


ASL preparation and readout are independent (in most cases)

ASL preparation• Continuous (labeling over long period of time in a small region)

Background suppression

Image acquisition part (readout)

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Inversion


• labeling-phase • control-phase

readout

post-labeling delay

Continuous ASL variants



ASL preparation• Continuous (labeling over long period of time in a small region)

• Pulsed (labeling for short period of time in a large region)

Background suppression

Image acquisition part (readout)

Inversion ss/ns


readout slice inversion slab


Inflow time TI

readout

saturation ss

Pulsed ASL variants

saturation slab BS inversion

QUIPSSII Q2TIPS

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ASL preparation:• Continuous (labeling over long period of time in a small region)

• Pulsed (labeling for short period of time in a large region)

Background suppression:

• Additional preparation • Not necessarily related to ASL

Image acquisition part (readout):


Background suppression (BS)

ASL signal (blood signal) very small compared to tissue signal (e.g. about 2-

3% in human brain)

→ small fluctuations in tissue signal corrupt ASL signal

Idea of BS: reduce tissue signal by (closely) nulling it at time of readout

→ tissue signal and ASL signal of same order → small fluctuations in tissue signal does not corrupt ASL signal

Sanjay Mani, John Pauly, Steven Conolly, Craig Meyer, Dwight Nishimura, MRM 37: 898-905 (1997)

tissue signal

blood signal

tissue signal

blood signal



DM Garcia et al., MRM 54:366–372 (2005)

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How can I null the signal at time of readout?

Sanjay Mani, John Pauly, Steven Conolly, Craig Meyer, Dwight Nishimura; MRM 37: 898-905 (1997)

Residual magnetization for different T1

One inversion pulse is needed for each T1-compartment to be nulled

Inversion ss/ns


readout slice inversion slab


Inflow time TI

readoutBS Inversion ns

saturation ss

Pulsed ASL variants

saturation slab BS inversion

Q2TIPS

Inversion



readout

saturation ss

BS Inversion ns

post-labeling delay

Continuous ASL variants

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EPI sequence scheme

Inflow time TI

readoutInversion ss/ns

saturation ss

BS Inversion ns

RF slice 2 RF slice 3 RF slice 4

DAQ

Slice

Phase

Read …

…

…

…

RF …

RF slice 1

multi-slice 2D-EPI

perfusion measurement

Wen-Ming Luh et al, MRM 41:1246–1254 (1999)

ASL in brain

EPI-readout, 60 averages, measurement time 5 min,

3T MR-Scanner

Abdominal perfusion measurement

B. Poncelet et al, MRM 41:510–519 (1999)

ASL in heart

EPI-readout, 108 averages, measurement time 10-12 min,

cardiac+breathing triggering

anatomic Tissue perfusion

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EPI sequence scheme

Inflow time TI


saturation ss

BS Inversion ns

RF(α) RF(α) RF(α)

DAQ

Slice

Phase

Read …

…

…

…

RF …

RF(α)

3D-EPI

E. L. Hall, P. A. Gowland, and S. T. Francis; Proc. Intl. Soc. Mag. Reson. Med. 18 (2010), p.517

3D-EPI ASL perfusion weighted images at 7T20 slices, 2x2x3mm3, SENSE P-2 and S – 1.5, 634 ms shot length, 50 averages.

bSSFP sequence scheme

Inflow time TI


balanced SSFP (trueFISP, FIESTA)

RF+ RF- RF- RF+ RF- RF+ RF- RF+ RF- RF+RF- RF+ RF+

DAQ

Slice

Phase

Read …

…

…

…

RF …

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ASL in the brain, healthy male volunteer

segmented true FISP ASL images acquired using eight averages,

TI=1200ms, measurement time for single slice 2.5 min

Grossman et al., JMRI. 2009 June ; 29(6): 1425–1431

bSSFP sequence scheme


ASL in kidneys, healthy male volunteer

bSSFP-readout, synchronized breathing, no cardiac triggering, hand-selected 26 (out

of 36) datasets were averaged, measurement time 4 min 03 s

sensitive to field inhomogeneities (banding artifacts)

Martirosian P, MRM 51:353–361 (2004)

Renal cyst

Inflow time TI


DAQ

Slice

Phase

Read …

…

…

…

RF …

RF

180°HASTE sequence scheme

HASTE

180° 180° 180° 180° 180°180°

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STAR-HASTE: perfusion imaging without magnetic

susceptibility artifact.

Chen et al: MRM 38:404-408 (1997)

„Multi-Organ-Shot“

ASL-technique

HASTE-readout

128x256-matrix

TE = 56 ms

TR = 4000 ms

Meas. time: 2 min


Günther M, PhD-Thesis, Heidelberg, Germany, 1999


V. Mai et al, JMRI 9:483–487 (1999)

ASL in lung, healthy male volunteer

HASTE-readout, TI 1300ms, 4 averages, measurement time ~25 s,

cardiac triggering

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ASL in kidneys, healthy 35y old volunteer

HASTE-readout, TI 1000ms, 4 averages, measurement time 30 s

S. Berr et al., JMRI 10:886–891 (1999)

Inflow time TI


saturation ss

DAQ

Slice

Phase

Read …

…

…

…

RF …

RF

180° 180° 180° 180° 180°BS Inversion ns

3D-GRASE sequence scheme

single-shot 3D-GRASE(also called 3D-FSE on GE-scanners)

segmented 3D GRASE pCASL

Turbofactor 12, EPI-factor 49

measurement time: 1:20 min, labeling time = 2000ms,

PLD = 1200 ms




PLD = 1200 ms




PLD = 1200 ms

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Skyra 3T

Imaging technique


Turbofactor 6, EPI-factor 27measurement time: 4 min, labeling time = 2000ms,

PLD = 1200 ms, 3x3x2 mm3

Inflow time TI


saturation ss

DAQ

Slice

Phase

Read …

…

…

…

RF …

RF

180° 180° 180° 180° 180°BS Inversion ns

Sequence scheme

3D-GRASE spiral(also called 3D-FSE on GE-scanners)


3D-FSE (3D-SPIRAL-GRASE)

D.Alsop et al.

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Readout technique

Comparison 2D- and 3D-readout strategy

2D-readout 3D-readout

TI varies from slice to slice

Limited number of slices

no “background suppression”

same TI for all slices

rel. high SNR

“background suppression”

whole brain coverage

low SNR

No saturation pulsesAfter application of saturation pulses

0

100

200

300

0 100 200

eff. 3D-Slab eff. 3D-Slab

Water phantomSlice profile

Use of modulated saturation pulses

Overlap! Overlap! Overlap!

3D Readout technique

image quality

acquisition

scheme

whole brain

SNR

other remarks

Comparison

EPI

poor

multi-slice

limited

low

broad availability,quasi standard,

sensitive to artifacts,

less suited for abdominal

imaging

3D-GRASE

inplane: good,along z: blur

3D

yes

high

excellent usability,

background suppression, can

also be used for abdominal

imaging

HASTE

blur along phase encode

single-slice

(inversions!)

limited

middle

Suitable for abdominal

imaging,often used for

lung imaging

bSSFP

excellent

single-slice

limited

middle

inflow-weighted (bright vessels!),

suitable for abdominal

imaging

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Take home messages:

• non-invasive, repeatable, flexible

• in general, ASL preparation and image acquisition are

independent

• optimal combination depends on application, knowledge of

available methods necessary

• for some applications (e.g. brain), 3D is preferred to 2D due to

SNR, coverage and suitability for background suppression

• follow recommendation of next slide

Arterial Spin Labeling: Read-Out Options

cor

cor

sagright

sagright

sagleft

sagleft

Vascular territory mapping

Dynamic angiography of AVM

Bolus arrival time at 4T,

meas. time 7 min

Enjoy the flexibility of Arterial Spin Labeling!

single average ASL at 3T

TI: 1500 ms, meas.time 5s!

Times series at 3T,

meas. time 3 min

arterial spin labeling read-out...

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