<s>
Functional	B-Algorithm
ultrasound	I-Algorithm
imaging	I-Algorithm
(	O
fUS	O
)	O
is	O
a	O
medical	O
ultrasound	O
imaging	O
technique	O
of	O
detecting	O
or	O
measuring	O
changes	O
in	O
neural	O
activities	O
or	O
metabolism	O
,	O
for	O
example	O
,	O
the	O
loci	O
of	O
brain	O
activity	O
,	O
typically	O
through	O
measuring	O
blood	O
flow	O
or	O
hemodynamic	O
changes	O
.	O
</s>
<s>
Brain	O
activation	O
can	O
either	O
be	O
directly	O
measured	O
by	O
imaging	O
electrical	O
activity	O
of	O
neurons	O
using	O
voltage	O
sensitive	O
dyes	O
,	O
calcium	O
imaging	O
,	O
electroencephalography	O
,	O
or	O
magnetoencephalography	B-Algorithm
,	O
or	O
indirectly	O
by	O
detecting	O
hemodynamic	O
changes	O
in	O
blood	O
flow	O
in	O
the	O
neurovascular	O
systems	O
through	O
functional	B-Algorithm
magnetic	I-Algorithm
resonance	I-Algorithm
imaging	I-Algorithm
(	O
fMRI	B-Algorithm
)	O
,	O
positron	B-Application
emission	I-Application
tomography	I-Application
(	O
PET	O
)	O
,	O
Functional	B-Algorithm
near-infrared	I-Algorithm
spectroscopy	I-Algorithm
(	O
fNIRS	B-Algorithm
)	O
,	O
or	O
Doppler	B-Algorithm
ultrasonography	I-Algorithm
)	O
...	O
</s>
<s>
fMRI	B-Algorithm
and	O
PET	O
,	O
which	O
measure	O
the	O
blood-oxygen	O
level	O
dependent	O
(	O
BOLD	O
)	O
signal	O
,	O
were	O
the	O
only	O
techniques	O
capable	O
of	O
imaging	O
brain	O
activation	O
in	O
depth	O
.	O
</s>
<s>
In	O
fact	O
,	O
in-depth	O
imaging	O
of	O
cerebral	O
hemodynamic	O
responses	O
by	O
fMRI	B-Algorithm
,	O
being	O
noninvasive	O
,	O
paved	O
the	O
way	O
for	O
major	O
discoveries	O
in	O
neurosciences	O
in	O
the	O
early	O
stage	O
,	O
and	O
is	O
applicable	O
on	O
humans	O
.	O
</s>
<s>
However	O
,	O
fMRI	B-Algorithm
also	O
suffers	O
limitations	O
.	O
</s>
<s>
Also	O
,	O
spatially	O
resolved	O
fMRI	B-Algorithm
is	O
achieved	O
at	O
the	O
expense	O
of	O
a	O
substantial	O
drop	O
in	O
temporal	O
resolution	O
and/or	O
SNR	O
.	O
</s>
<s>
Finally	O
,	O
fMRI	B-Algorithm
is	O
not	O
appropriate	O
for	O
all	O
clinical	O
applications	O
.	O
</s>
<s>
For	O
example	O
,	O
fMRI	B-Algorithm
is	O
rarely	O
performed	O
on	O
infants	O
because	O
of	O
specific	O
issues	O
concerning	O
infant	O
sedation	O
.	O
</s>
<s>
Like	O
fMRI	B-Algorithm
,	O
Doppler	O
based	O
functional	O
ultrasound	O
approach	O
are	O
based	O
on	O
the	O
neurovascular	O
coupling	O
and	O
are	O
thus	O
limited	O
by	O
the	O
spatiotemporal	O
features	O
of	O
neurovascular	O
coupling	O
as	O
they	O
measure	O
cerebral	O
blood	O
volume	O
(	O
CBV	O
)	O
changes	O
.	O
</s>
<s>
CBV	O
is	O
a	O
pertinent	O
parameter	O
for	O
functional	O
imaging	O
that	O
is	O
already	O
used	O
by	O
other	O
modalities	O
such	O
as	O
intrinsic	O
optical	O
imaging	O
or	O
CBV-weighted	O
fMRI	B-Algorithm
.	O
</s>
<s>
Major	O
part	O
of	O
the	O
hemodynamic	O
response	O
occurs	O
in	O
small	O
vessels	O
;	O
however	O
,	O
conventional	O
Doppler	B-Algorithm
ultrasound	I-Algorithm
is	O
not	O
sensitive	O
enough	O
to	O
detect	O
the	O
blood	O
flow	O
in	O
such	O
small	O
vessels	O
.	O
</s>
<s>
In	O
functional	O
transcranial	O
Doppler	B-Algorithm
sonography	I-Algorithm
,	O
a	O
low	O
frequency	O
(	O
1-3MHz	O
)	O
transducer	O
is	O
used	O
through	O
the	O
temporal	O
bone	O
window	O
with	O
a	O
conventional	O
pulse	O
Doppler	O
mode	O
to	O
estimate	O
blood	O
flow	O
at	O
a	O
single	O
focal	O
location	O
.	O
</s>
<s>
Power	B-Algorithm
Doppler	I-Algorithm
is	O
a	O
Doppler	O
sequence	O
that	O
measures	O
the	O
ultrasonic	O
energy	O
backscattered	O
from	O
red	O
blood	O
cells	O
in	O
each	O
pixel	O
of	O
the	O
image	O
.	O
</s>
<s>
However	O
,	O
conventional	O
power	B-Algorithm
Doppler	I-Algorithm
imaging	O
lacks	O
sensitivity	O
to	O
detect	O
small	O
arterioles/venules	O
and	O
thus	O
is	O
unable	O
to	O
provide	O
local	O
neurofunctional	O
information	O
through	O
neurovascular	O
coupling	O
.	O
</s>
<s>
Functional	B-Algorithm
ultrasound	I-Algorithm
imaging	I-Algorithm
was	O
pioneered	O
at	O
ESPCI	O
by	O
Mickael	O
Tanter	O
's	O
team	O
following	O
work	O
on	O
ultrafast	O
imaging	O
and	O
ultrafast	O
Doppler	O
.	O
</s>
<s>
Ultrasensitive	O
Doppler	O
relies	O
on	O
ultrafast	O
imaging	O
scanners	O
able	O
to	O
acquire	O
images	O
at	O
thousands	O
of	O
frames	O
per	O
second	O
,	O
thus	O
boosting	O
the	O
power	B-Algorithm
Doppler	I-Algorithm
SNR	O
without	O
any	O
contrast	O
agents	O
.	O
</s>
<s>
fUS	O
measures	O
indirectly	O
cerebral	O
blood	O
volume	O
which	O
provides	O
an	O
effect	O
size	O
close	O
to	O
20%	O
and	O
as	O
such	O
is	O
quite	O
more	O
sensitive	O
than	O
fMRI	B-Algorithm
whose	O
BOLD	O
response	O
is	O
typically	O
only	O
a	O
couple	O
of	O
percents	O
.	O
</s>
<s>
Other	O
fMRI-like	O
modalities	O
such	O
as	O
functional	O
connectivity	O
can	O
also	O
be	O
implemented	O
.	O
</s>
<s>
Some	O
researchers	O
conducted	O
4D	O
functional	B-Algorithm
ultrasound	I-Algorithm
imaging	I-Algorithm
of	O
whole-brain	O
activity	O
in	O
rodents	O
.	O
</s>
<s>
Finally	O
,	O
they	O
perform	O
coherent	O
compounding	O
beamforming	O
of	O
decoded	O
echoes	O
to	O
produce	O
3D	O
ultrasonic	O
images	O
and	O
apply	O
a	O
spatiotemporal	O
clutter	O
filter	O
separating	O
blood	O
flow	O
from	O
tissue	O
motion	O
to	O
compute	O
a	O
power	B-Algorithm
Doppler	I-Algorithm
volume	O
,	O
which	O
is	O
proportional	O
to	O
the	O
cerebral	O
blood	O
volume	O
.	O
</s>
<s>
•	O
Inexpensive	O
and	O
more	O
practical	O
(	O
smaller	O
machine	O
,	O
transportable	O
)	O
,	O
compared	O
with	O
fMRI	B-Algorithm
.	O
</s>
<s>
Functional	B-Algorithm
ultrasound	I-Algorithm
imaging	I-Algorithm
has	O
a	O
wide	O
range	O
of	O
applications	O
in	O
research	O
and	O
in	O
clinical	O
practice	O
.	O
</s>
<s>
The	O
ability	O
to	O
image	O
cerebral	O
blood	O
volume	O
at	O
high	O
spatiotemporal	O
resolution	O
and	O
with	O
high	O
sensitivity	O
using	O
fUS	O
could	O
be	O
of	O
great	O
interest	O
for	O
applications	O
in	O
which	O
fMRI	B-Algorithm
reaches	O
its	O
limits	O
,	O
such	O
as	O
imaging	O
of	O
epileptic-induced	O
changes	O
in	O
blood	O
volume	O
.	O
</s>
<s>
Functional	B-Algorithm
ultrasound	I-Algorithm
imaging	I-Algorithm
can	O
be	O
applied	O
to	O
neonatal	O
brain	O
imaging	O
in	O
a	O
non-invasive	O
manner	O
through	O
the	O
fontanel	O
window	O
.	O
</s>
