arterial spin labeling read-out...
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1
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
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)
2
Inversion
Readout strategies for ASL
• labeling-phase • control-phase
readout
post-labeling delay
Continuous ASL variants
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)
• Pulsed (labeling for short period of time in a large region)
Background suppression
Image acquisition part (readout)
Inversion ss/ns
Readout strategies for ASL
readout slice inversion slab
• labeling-phase • control-phase
Inflow time TI
readout
saturation ss
Pulsed ASL variants
saturation slab BS inversion
QUIPSSII Q2TIPS
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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)
• Pulsed (labeling for short period of time in a large region)
Background suppression:
• Additional preparation • Not necessarily related to ASL
Image acquisition part (readout):
Readout strategies for ASL
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
Readout strategies for ASL
Background suppression (BS)
DM Garcia et al., MRM 54:366–372 (2005)
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Readout strategies for ASL
Background suppression (BS)
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 strategies for ASL
readout slice inversion slab
• labeling-phase • control-phase
Inflow time TI
readoutBS Inversion ns
saturation ss
Pulsed ASL variants
saturation slab BS inversion
Q2TIPS
Inversion
Readout strategies for ASL
• labeling-phase • control-phase
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
readoutInversion ss/ns
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
readoutInversion ss/ns
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
Abdominal perfusion measurement
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
readoutInversion ss/ns
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
Abdominal perfusion measurement
Günther M, PhD-Thesis, Heidelberg, Germany, 1999
Abdominal perfusion measurement
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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Abdominal perfusion measurement
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
readoutInversion ss/ns
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
segmented 3D GRASE pCASL
Turbofactor 6, EPI-factor 49
measurement time: 1:20 min, labeling time = 2000ms,
PLD = 1200 ms
segmented 3D GRASE pCASL
Turbofactor 6, EPI-factor 25
measurement time: 1:20 min, labeling time = 2000ms,
PLD = 1200 ms
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Skyra 3T
Imaging technique
segmented 3D GRASE pCASL
Turbofactor 6, EPI-factor 27measurement time: 4 min, labeling time = 2000ms,
PLD = 1200 ms, 3x3x2 mm3
Inflow time TI
readoutInversion ss/ns
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)
Readout strategies for ASL
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
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