<s>
Intravoxel	B-Algorithm
incoherent	I-Algorithm
motion	I-Algorithm
(	O
IVIM	B-Algorithm
)	O
imaging	O
is	O
a	O
concept	O
and	O
a	O
method	O
initially	O
introduced	O
and	O
developed	O
by	O
Le	O
Bihan	O
et	O
al	O
.	O
</s>
<s>
to	O
quantitatively	O
assess	O
all	O
the	O
microscopic	O
translational	O
motions	O
that	O
could	O
contribute	O
to	O
the	O
signal	O
acquired	O
with	O
diffusion	B-Algorithm
MRI	I-Algorithm
.	O
</s>
<s>
It	O
is	O
responsible	O
for	O
a	O
signal	O
attenuation	O
in	O
diffusion	B-Algorithm
MRI	I-Algorithm
,	O
which	O
depends	O
on	O
the	O
velocity	O
of	O
the	O
flowing	O
blood	O
and	O
the	O
vascular	O
architecture	O
.	O
</s>
<s>
However	O
,	O
the	O
rate	O
of	O
signal	O
attenuation	O
resulting	O
from	O
pseudodiffusion	O
is	O
typically	O
an	O
order	O
of	O
magnitude	O
greater	O
than	O
molecular	O
diffusion	O
in	O
tissues	O
,	O
so	O
its	O
relative	O
contribution	O
to	O
the	O
diffusion-weighted	B-Algorithm
MRI	I-Algorithm
signal	O
becomes	O
significant	O
only	O
at	O
very	O
low	O
b	O
values	O
,	O
allowing	O
diffusion	O
and	O
perfusion	O
effects	O
to	O
be	O
separated	O
.	O
</s>
<s>
In	O
the	O
presence	O
of	O
the	O
magnetic	O
field	O
gradient	O
pulses	O
of	O
a	O
diffusion	B-Algorithm
MRI	I-Algorithm
sequence	O
,	O
the	O
MRI	O
signal	O
gets	O
attenuated	O
due	O
to	O
diffusion	O
and	O
perfusion	O
effects	O
.	O
</s>
<s>
where	O
is	O
the	O
volume	O
fraction	O
of	O
incoherently	O
flowing	O
blood	O
in	O
the	O
tissue	O
(	O
“	O
flowing	O
vascular	O
volume	O
”	O
)	O
,	O
the	O
signal	O
attenuation	O
from	O
the	O
IVIM	B-Algorithm
effect	O
and	O
is	O
the	O
signal	O
attenuation	O
from	O
molecular	O
diffusion	O
in	O
the	O
tissue	O
.	O
</s>
<s>
where	O
is	O
the	O
diffusion-sensitization	O
of	O
the	O
MRI	O
sequence	O
,	O
is	O
the	O
sum	O
of	O
the	O
pseudo-diffusion	O
coefficient	O
associated	O
to	O
the	O
IVIM	B-Algorithm
effect	O
and	O
,	O
the	O
diffusion	O
coefficient	O
of	O
water	O
in	O
blood	O
:	O
</s>
<s>
Several	O
models	O
have	O
been	O
proposed	O
to	O
describe	O
this	O
curvature	O
at	O
higher	O
b-values	O
,	O
mainly	O
the	O
“	O
biexponential	O
”	O
model	O
which	O
assumes	O
the	O
presence	O
of	O
2	O
water	O
compartments	O
with	O
fast	O
and	O
slow	O
diffusion	O
(	O
where	O
neither	O
compartment	O
is	O
the	O
from	O
IVIM	B-Algorithm
)	O
,	O
the	O
relative	O
'	O
fast	O
 '	O
and	O
'	O
slow	O
 '	O
labels	O
referring	O
to	O
restricted	O
and	O
hindered	O
diffusion	O
,	O
rather	O
than	O
pseudodiffusion/perfusion	O
and	O
true	O
(	O
hindered	O
)	O
diffusion	O
.	O
</s>
<s>
This	O
general	O
formulation	O
of	O
a	O
biexponential	O
decay	O
of	O
diffusion-weighted	O
imaging	O
signal	O
with	O
b-value	O
can	O
be	O
used	O
for	O
IVIM	B-Algorithm
,	O
which	O
requires	O
sampling	O
of	O
low	O
b-values	O
(	O
<	O
100	O
s/mm²	O
)	O
to	O
capture	O
pseudodiffusion	O
decay	O
,	O
or	O
for	O
restriction	O
imaging	O
,	O
which	O
requires	O
higher	O
b-value	O
acquisitions	O
(	O
>1000	O
s/mm²	O
)	O
to	O
capture	O
restricted	O
diffusion	O
.	O
</s>
<s>
Also	O
the	O
“	O
perfusion	O
”	O
parameters	O
accessible	O
with	O
the	O
IVIM	B-Algorithm
method	O
somewhat	O
differs	O
from	O
the	O
“	O
classical	O
”	O
perfusion	O
parameters	O
obtained	O
with	O
tracer	O
methods	O
:	O
“	O
Perfusion	O
”	O
can	O
be	O
seen	O
with	O
the	O
physiologist	O
eyes	O
(	O
blood	O
flow	O
)	O
or	O
the	O
radiologist	O
eyes	O
(	O
vascular	O
density	O
)	O
.	O
</s>
<s>
Indeed	O
,	O
there	O
is	O
room	O
to	O
improve	O
the	O
IVIM	B-Algorithm
model	O
and	O
understand	O
better	O
its	O
relationship	O
with	O
the	O
functional	O
vascular	O
architecture	O
and	O
its	O
biological	O
relevance	O
.	O
</s>
<s>
IVIM	B-Algorithm
MRI	O
was	O
initially	O
introduced	O
to	O
evaluate	O
perfusion	O
and	O
produce	O
maps	O
of	O
brain	O
perfusion	O
,	O
for	O
brain	O
activation	O
studies	O
(	O
before	O
the	O
introduction	O
of	O
BOLD	O
fMRI	B-Algorithm
)	O
and	O
clinical	O
applications	O
(	O
stroke	O
,	O
brain	O
tumors	O
)	O
.	O
</s>
<s>
Recent	O
work	O
has	O
proven	O
the	O
validity	O
of	O
the	O
IVIM	B-Algorithm
concept	O
from	O
fMRI	B-Algorithm
,	O
with	O
an	O
increase	O
in	O
the	O
IVIM	B-Algorithm
perfusion	O
parameters	O
in	O
brain	O
activated	O
regions	O
,	O
and	O
the	O
potential	O
of	O
the	O
approach	O
to	O
aid	O
in	O
our	O
understanding	O
of	O
the	O
different	O
vascular	O
contributions	O
to	O
the	O
fMRI	B-Algorithm
signal	O
.	O
</s>
<s>
IVIM	B-Algorithm
MRI	O
has	O
also	O
been	O
used	O
in	O
the	O
context	O
of	O
fMRI	B-Algorithm
in	O
a	O
negative	O
way	O
.	O
</s>
<s>
A	O
limitation	O
of	O
BOLD	O
fMRI	B-Algorithm
is	O
its	O
spatial	O
resolution	O
,	O
as	O
flow	O
increase	O
in	O
somewhat	O
large	O
arteries	O
or	O
veins	O
feed	O
or	O
drain	O
large	O
neuronal	O
territories	O
.	O
</s>
<s>
Several	O
groups	O
have	O
relied	O
on	O
this	O
trick	O
,	O
though	O
not	O
always	O
considering	O
referring	O
to	O
the	O
IVIM	B-Algorithm
concept	O
.	O
</s>
<s>
This	O
IVIM	B-Algorithm
concept	O
has	O
also	O
been	O
borrowed	O
to	O
improve	O
other	O
applications	O
,	O
for	O
instance	O
,	O
arterial	B-Algorithm
spin	I-Algorithm
labeling	I-Algorithm
(	O
ASL	O
)	O
or	O
to	O
suppress	O
signal	O
from	O
extracellular	O
flowing	O
fluid	O
in	O
perfused	O
cell	O
systems	O
.	O
</s>
<s>
However	O
,	O
IVIM	B-Algorithm
MRI	O
has	O
recently	O
undergone	O
a	O
striking	O
revival	O
for	O
applications	O
not	O
in	O
the	O
brain	O
,	O
but	O
throughout	O
the	O
body	O
as	O
well	O
.	O
</s>
<s>
Following	O
earlier	O
encouraging	O
results	O
in	O
the	O
kidneys	O
,	O
or	O
even	O
the	O
heart	O
,	O
IVIM	B-Algorithm
MRI	O
really	O
took	O
off	O
for	O
liver	O
applications	O
.	O
</s>
<s>
found	O
that	O
D*	O
was	O
significantly	O
reduced	O
in	O
cirrhotic	O
patients	O
,	O
which	O
,	O
according	O
to	O
the	O
IVIM	B-Algorithm
model	O
,	O
points	O
out	O
to	O
reduce	O
blood	O
velocity	O
(	O
and	O
flow	O
)	O
.	O
</s>
<s>
The	O
perfusion	O
fraction	O
,	O
f	O
,	O
which	O
is	O
linked	O
to	O
blood	O
volume	O
in	O
the	O
IVIM	B-Algorithm
model	O
,	O
remained	O
normal	O
,	O
confirming	O
earlier	O
results	O
by	O
Yamada	O
et	O
al	O
.	O
</s>
<s>
One	O
has	O
to	O
keep	O
in	O
mind	O
that	O
IVIM	B-Algorithm
imaging	O
has	O
a	O
differential	O
sensitivity	O
to	O
vessel	O
types	O
,	O
according	O
to	O
the	O
range	O
of	O
motion	O
sensitization	O
(	O
b	O
values	O
)	O
which	O
are	O
used	O
.	O
</s>
<s>
Signal	O
from	O
large	O
vessels	O
with	O
rapid	O
flow	O
disappears	O
quickly	O
with	O
very	O
low	O
b	O
values	O
,	O
while	O
smaller	O
vessels	O
with	O
slower	O
flow	O
might	O
still	O
contribute	O
to	O
the	O
IVIM	B-Algorithm
signal	O
acquired	O
with	O
b	O
values	O
larger	O
than	O
200	O
s/mm²	O
.	O
</s>
<s>
It	O
has	O
also	O
been	O
shown	O
that	O
the	O
parameter	O
f	O
,	O
often	O
related	O
to	O
perfusion	O
fraction	O
,	O
is	O
sensitive	O
to	O
differential	O
spin-spin	B-Algorithm
relaxation	I-Algorithm
rates	O
in	O
the	O
two	O
model	O
compartments	O
(	O
blood/tissue	O
)	O
and	O
can	O
thus	O
be	O
overestimated	O
in	O
highly-perfused	O
tissue	O
.	O
</s>
<s>
A	O
key	O
feature	O
of	O
IVIM	B-Algorithm
diffusion	B-Algorithm
MRI	I-Algorithm
is	O
that	O
it	O
does	O
not	O
involve	O
contrast	O
agents	O
,	O
and	O
it	O
may	O
appear	O
as	O
an	O
interesting	O
alternative	O
for	O
perfusion	O
MRI	O
in	O
some	O
patients	O
at	O
risk	O
for	O
Nephrogenic	O
Systemic	O
Fibrosis	O
(	O
NSF	O
)	O
.	O
</s>
