<s>
Imaging	B-Algorithm
phantom	I-Algorithm
,	O
or	O
simply	O
phantom	O
,	O
is	O
a	O
specially	O
designed	O
object	O
that	O
is	O
scanned	O
or	O
imaged	O
in	O
the	O
field	O
of	O
medical	B-Application
imaging	I-Application
to	O
evaluate	O
,	O
analyze	O
,	O
and	O
tune	O
the	O
performance	O
of	O
various	O
imaging	O
devices	O
.	O
</s>
<s>
Phantoms	O
were	O
originally	O
employed	O
for	O
use	O
in	O
2D	O
x-ray	B-Library
based	O
imaging	O
techniques	O
such	O
as	O
radiography	O
or	O
fluoroscopy	O
,	O
though	O
more	O
recently	O
phantoms	O
with	O
desired	O
imaging	O
characteristics	O
have	O
been	O
developed	O
for	O
3D	O
techniques	O
such	O
as	O
SPECT	O
,	O
MRI	O
,	O
CT	O
,	O
Ultrasound	B-Application
,	O
PET	B-Application
,	O
and	O
other	O
imaging	O
methods	O
or	O
modalities	O
.	O
</s>
<s>
For	O
instance	O
,	O
phantoms	O
made	O
for	O
2D	O
radiography	O
may	O
hold	O
various	O
quantities	O
of	O
x-ray	B-Application
contrast	I-Application
agents	I-Application
with	O
similar	O
x-ray	B-Library
absorbing	O
properties	O
to	O
normal	O
tissue	O
to	O
tune	O
the	O
contrast	O
of	O
the	O
imaging	O
device	O
or	O
modulate	O
the	O
patients	O
exposure	O
to	O
radiation	O
.	O
</s>
<s>
In	O
such	O
a	O
case	O
,	O
the	O
radiography	O
phantom	O
would	O
not	O
necessarily	O
need	O
to	O
have	O
similar	O
textures	O
and	O
mechanical	O
properties	O
since	O
these	O
are	O
not	O
relevant	O
in	O
x-ray	B-Library
imaging	O
modalities	O
.	O
</s>
<s>
However	O
,	O
in	O
the	O
case	O
of	O
ultrasonography	O
,	O
a	O
phantom	O
with	O
similar	O
rheological	O
and	O
ultrasound	B-Application
scattering	O
properties	O
to	O
real	O
tissue	O
would	O
be	O
essential	O
,	O
but	O
x-ray	B-Library
absorbing	O
properties	O
would	O
not	O
be	O
needed	O
.	O
</s>
