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Neurology advanced asl jy gauvrit
1. ARTERIAL
SPIN
LABELING
Jean-‐Yves
Gauvrit,
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
2. IntroducNon
2
IntroducNon
• Arterial
Spin
Labeling
(ASL)
• MRI
technique
for
assessing
cerebral
blood
flow
(Detre
et
al.
MRM
1992)
• Non-‐invasive
• Non-‐irradiaNng
• No
exogenous
contrast
agent
injecNon
• Quan8ta8ve
• Cerebral
blood
flow
(CBS)
• Reliable
and
reproducible
• Main
disadvantage:
low
signal-‐to-‐noise
ra8o
(SNR)
• Sequences
available
on
MRI
but
confidenNal
use
3. IntroducNon
ASL
principles
• Image
acquisiNon
1.
Arterial
spin
labeling
by
a
RF
pulse
2.
Inversion
Nme
TI:
Nme
needed
for
labeled
spins
to
reach
the
volume
of
interest
3.
AcquisiNon
of
the
volume
of
interest
A
second
acquisiNon
of
the
volume
of
interest
is
then
carried
out
without
labeling
3
4. 4
IntroducNon
ASL
principles
• Data
processing
and
quanNficaNon
QuanNficaNon
model
↓
-‐
Control
image
→
=
Tag
image
Perfusion
image
Cerebral
blood
flow
(CBF)
map
5. IntroducNon
ASL
principles
• ASL
is
a
reliable
technique
for
measuring
CBF
• ASL
is
a
reproducible
technique
for
measuring
CBF
5
10. AcquisiNon
10
ConNnuous
ASL
(CASL)
• Historical
method
• ConNnuous
(2-‐4s)
and
selecNve
labeling
of
protons
going
through
a
tagging
plane
with
an
equilibrium
state
• Advantages
• High
SNR
• Reliable
CBF
quanNficaNon
• But
• High
SAR
and
magne8za8on
transfer
effects
(especially
at
3T)
• Hardware
limitaNon
(no
mulN-‐channel
coil)
Detre
et
al.
Magn
Reson
Med
1992
11. AcquisiNon
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
implementaNon
• MulN-‐channel
coil
• Parallel
imaging
possible
• MulN-‐TI
possible
(QUASAR:
arterial
transit
Nme)
• SelecNve
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
11
12. AcquisiNon
Pseudo-‐conNnuous
ASL
(pcASL)
• “Hybrid”
method
• MulNple
short
RF
over
an
extended
period
• Advantages
• High
SNR
• Reproducibility
+++
• Easy
implementaNon
• But
• No
ArterialTransitTime
determinaNon
Wu
et
al.
Magn
Reson
Med
2007
12
14. AcquisiNon
14
Image
acquisiNon
• Context:
low
SNR
Increase
the
number
of
acquisiNons
(labeled-‐unlabeled
image
pairs)
but
increase
in
the
acquisiNon
Nme
-‐>
“Clinical
”
compromise
30
acquisiNons
(~
3min30)
• 2D
SS
EPI:
most
commonly
used
method
• SaNsfactory
SNR
and
fast
acquisiNon
• But
distorNons
• 3D
segmented
SE-‐EG
(i.e.:
3D
GRASE)
• Bemer
SNR,
less
distorNons
,
and
bemer
coverage
• With
suppression
of
the
staNc
Nssue
signal
(background
suppression)
16. AcquisiNon
16
ASL:
low
SNR
• Increase
the
magneNc
field
• Intrinsic
increase
in
SNR
• Bemer
suppression
of
surrounding
Nssue
• Increase
in
the
labeling
duraNon
(by
lengthening
of
the
longitudinal
relaxaNon)
• T1
blood:
1,5T
-‐>1350
ms
3T-‐>
1650ms
Wang
et
al.
Magn
Reson
Med
2002
17. AcquisiNon
17
ASL:
low
SNR
• Use
of
mulN-‐channel
coils
• Possible
with
PASL
and
pCASL
• 12
channels-‐>
32
channels:
SNR
+39%
• Parallel
imaging
possible
Ferré
et
al.
JMRI
2012
18. Image
processing
ASL
principles
AcquisiNon
Processing
of
images
• Marquage
ASL
• AcquisiNon
des
coupes
• Matériel
IRM
• Preprocessing
• QuanNficaNon
18
19. 19
Image
processing
Processing
of
ASL
images
CorrecNon
of
movements
SubtracNon
QuanNficaNon
Perfusion
image
ASL
images
Denoising
CBF
pvc-‐CBF
RegistraNon
on
T1
CorrecNon
of
parNal
volume
effects
20. 20
Image
processing
Processing
of
ASL
images
CorrecNon
of
movements
SubtracNon
QuanNficaNon
Perfusion
image
ASL
images
Denoising
CBF
pvc-‐CBF
RegistraNon
on
T1
CorrecNon
of
parNal
volume
effects
22. ApplicaNons
22
ASL
arNfacts
ASL-‐specific
ar8facts
• Vascular
arMfacts
• PASL>CASL
• Arterial
or
venous
• Labeled
blood
in
the
vessels
• Arteries:
related
to
arterial
transit
Nmes
TI
1200
TI
1700
• ReducNon
by
use
of
“crushers”
Without
Crushers
23. ApplicaNons
23
ASL
arNfacts
ASL-‐specific
ar8facts
• Vascular
arMfacts
• Loss
of
signal
in
the
upper
slices
• Related
to
the
relaxaNon
of
labeled
protons
• Caudo-‐cranial
2D,
especially
at
1.5T,
reduced
labeling
Nme
• Parallel
imaging:
decrease
the
acquisiNon
Nme
of
slices
and
thus
the
Nme
between
slices
(Wang
et
al.
MRM
2005)
Deibler
et
al.
AJNR
2008
24. ApplicaNons
ASL
arNfacts
ASL-‐specific
ar8facts
• Vascular
arMfacts
• Loss
of
signal
in
the
upper
slices
• Physiological
hyperperfusion
/
hypoperfusion
Physiological
changes
in
perfusion,
parNcularly
visible
with
PASL
• Hyperperfusion
areas
(Mamo
et
al.
Arch
Neurol
1983)
• Hypoperfusion
areas
(Hendrikse
et
al.
Radiology
2008):
related
to
aTT
24
25. 25
ApplicaNons
ASL
arNfacts
Non-‐specific
ar8facts
• Movement
arMfacts
• MagneMc
suscepMbility
arMfacts
• Related
to
SS-‐EG-‐EPI
acquisiNon
• Focal
“hypoperfusion”
• Decreased
by
non
EPI
imaging
and
parallel
imaging
(decrease
of
TE)
Without
parallel
imaging
with
GRAPPA
2
Ferré
et
al.
JMRI
2012
26. 26
ApplicaNons
ApplicaNons
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
MTT
TTM
ASL
ASL
rCBV
rCBV (DSC)
ASL
ASL
27. 27
ApplicaNons
ApplicaNons
of
ASL
• Tumor
• Tumor
characterizaNon
(Wolf
et
al.
JMRI
2005)
• Post-‐treatment
follow-‐up
(Weber
et
al.
Invest
Radiol
2004)
rCBV
A
rCBV
(DSC)
A
SL SL
rCBV
rCBV (DSC)
ASL
ASL
28. 28
ApplicaNons
ApplicaNons
of
ASL
• Cerebral
perfusion
assessment
• Demen8a
FDG
PET
ASL
• Value
+++
• Reveals
hypoperfusion
in
AD,
FTD…
(Du
et
al.
Neurology
2006,
Hu
et
al.
Neurology
2010)
Esquevin
et
al.
JFR
2012
• European
COST
AcNon
Arterial
Spin
Labeling
in
DemenMa
• X
Golay
UCL
-‐
15
countries
• ObjecNves
• Standardizing
and
comparing
ASL
techniques
• Developing
image
processing
sovware
• ValidaNng
ASL
as
biomarker
of
the
disease
and
its
progression
29. ApplicaNons
ApplicaNons
of
ASL
• ASL
and
funcNonal
MRI
acNvaNon
• ASL
allows
neural
acNvaNon
mapping
(ASLf)
• Motor,
somestheNc,
speech
funcNons…
• ASLf
vs
IRMf
BOLD,
seems
(Raoult
et
al.
Neuroimage
2011)
• +
inter
and
intra
individually
reproducible
• +
spaNally
specific
• Bemer
Nme
resoluNon
• Clinical
applicaNon
not
validated
yet
29
30. 30
ApplicaNons
ApplicaNons
of
ASL
• Extra-‐cerebral
applicaNons
• Renal
perfusion
• Mainly
FAIR
techniques
Lanzmann
et
al.
Radiology
2012
• Measurements
correlated
with
PET
(even
with
renal
artery
stenosis)
• Good
intra-‐
and
inter-‐session
reproducibility
• Renal
tumor
characterizaNon
(de
Bazelaire
et
al.
Acad
Radiol
2005;
Lanzmann
et
al.
Radiology
2012)
• In
experimental
condiNons,
perfusion
of
• Diseased
bone
• Pancreas
• Uterus
and
placenta
• Prostate
31. 31
Main
advantages
and
disadvantages
of
ASL
Advantages
-‐
No
irradiaNon
Disadvantages
-‐
Low
signal-‐to-‐noise
raNo:
-‐
No
exogenous
contrast
agent
injecNon
Minimal
acquisiNon
Nme
of
3
min
-‐
Absolute
quanNficaNon
of
Nssue
blood
flow
Limited
spaNal
resoluNon
and
Nssue
transit
Nme
possible
-‐
QuanNficaNon
of
Nssue
blood
volume
-‐
Repeated
measurements
possible
impossible
(i.e.:
cerebral
blood
volume)
-‐
Reproducibility
-‐
No
standardizaNon
of
techniques
(type
of
labeling,
image
acquisiNon,
post-‐processing)
among
manufacturers
-‐
OpNmizaNon,
automaNon
and
standardizaNon
of
post-‐processing
are
sNll
being
developed
32. 32
Remember
• ASL:
MRI
method
for
perfusion
assessment
• Non-‐irradiaNng
• No
exogenous
contrast
agent
• QuanNtaNve
and
reproducible
• Numerous
techniques,
characterized
by
• Labeling
type
(PASL
or
pcASL)
• Image
acquisiNon
mode
(2D
or
3D
/
EPI…)
• Image
processing:
important
step
• There
are
ASL-‐specific
ar8facts
• Close
to
clinical
use
