<s>
A	O
contrast	B-Algorithm
agent	I-Algorithm
(	O
or	O
contrast	B-Algorithm
medium	I-Algorithm
)	O
is	O
a	O
substance	O
used	O
to	O
increase	O
the	O
contrast	B-Device
of	O
structures	O
or	O
fluids	O
within	O
the	O
body	O
in	O
medical	B-Application
imaging	I-Application
.	O
</s>
<s>
Contrast	B-Algorithm
agents	I-Algorithm
absorb	O
or	O
alter	O
external	O
electromagnetism	O
or	O
ultrasound	B-Application
,	O
which	O
is	O
different	O
from	O
radiopharmaceuticals	B-Algorithm
,	O
which	O
emit	O
radiation	O
themselves	O
.	O
</s>
<s>
In	O
x-ray	B-Library
imaging	O
,	O
contrast	B-Algorithm
agents	I-Algorithm
enhance	O
the	O
radiodensity	O
in	O
a	O
target	O
tissue	O
or	O
structure	O
.	O
</s>
<s>
In	O
magnetic	O
resonance	O
imaging	O
,	O
contrast	B-Algorithm
agents	I-Algorithm
shorten	O
(	O
or	O
in	O
some	O
instances	O
increase	O
)	O
the	O
relaxation	O
times	O
of	O
nuclei	O
within	O
body	O
tissues	O
in	O
order	O
to	O
alter	O
the	O
contrast	B-Device
in	O
the	O
image	O
.	O
</s>
<s>
Contrast	B-Algorithm
agents	I-Algorithm
are	O
commonly	O
used	O
to	O
improve	O
the	O
visibility	O
of	O
blood	O
vessels	O
and	O
the	O
gastrointestinal	O
tract	O
.	O
</s>
<s>
The	O
types	O
of	O
contrast	B-Algorithm
agent	I-Algorithm
are	O
classified	O
according	O
their	O
intended	O
imaging	O
modalities	O
.	O
</s>
<s>
For	O
radiography	O
,	O
which	O
is	O
based	O
on	O
X-rays	B-Library
,	O
iodine	O
and	O
barium	O
are	O
the	O
most	O
common	O
types	O
of	O
contrast	B-Algorithm
agent	I-Algorithm
.	O
</s>
<s>
Various	O
sorts	O
of	O
iodinated	B-Algorithm
contrast	I-Algorithm
agents	O
exist	O
,	O
with	O
variations	O
occurring	O
between	O
the	O
osmolarity	O
,	O
viscosity	O
and	O
absolute	O
iodine	O
content	O
.	O
</s>
<s>
Gadolinium	O
is	O
used	O
in	O
magnetic	O
resonance	O
imaging	O
as	O
an	O
MRI	B-Algorithm
contrast	I-Algorithm
agent	I-Algorithm
or	O
gadolinium-based	O
contrast	B-Algorithm
agent	I-Algorithm
(	O
GBCA	O
)	O
.	O
</s>
<s>
This	O
causes	O
water	O
around	O
the	O
contrast	B-Algorithm
agent	I-Algorithm
to	O
relax	O
quickly	O
,	O
enhancing	O
the	O
quality	O
of	O
the	O
MRI	O
scan	O
.	O
</s>
<s>
Microbubbles	O
are	O
used	O
as	O
contrast	B-Algorithm
agents	I-Algorithm
for	O
sonographic	B-Application
examination	O
,	O
specifically	O
echocardiograms	B-Application
,	O
for	O
the	O
detection	O
of	O
a	O
cardiac	O
shunt	O
.	O
</s>
<s>
These	O
are	O
small	O
enough	O
to	O
pass	O
through	O
the	O
capillaries	O
and	O
are	O
used	O
to	O
increase	O
the	O
contrast	B-Device
in	O
the	O
left	O
ventricle	O
,	O
improving	O
the	O
visualization	O
of	O
its	O
walls	O
.	O
</s>
<s>
The	O
drop	O
in	O
density	O
on	O
the	O
interface	O
between	O
the	O
gas	O
in	O
the	O
bubble	O
and	O
the	O
surrounding	O
liquid	O
strongly	O
scatters	O
and	O
reflects	O
the	O
ultrasound	B-Application
back	O
to	O
the	O
probe	O
.	O
</s>
<s>
This	O
process	O
of	O
backscattering	B-Algorithm
gives	O
the	O
liquid	O
with	O
these	O
bubbles	O
a	O
high	O
signal	O
,	O
which	O
can	O
be	O
seen	O
in	O
the	O
resulting	O
image	O
.	O
</s>
