<s>
Tomography	B-Algorithm
is	O
imaging	O
by	O
sections	O
or	O
sectioning	O
that	O
uses	O
any	O
kind	O
of	O
penetrating	O
wave	O
.	O
</s>
<s>
The	O
word	O
tomography	B-Algorithm
is	O
derived	O
from	O
Ancient	O
Greek	O
τόμος	O
tomos	O
,	O
"	O
slice	O
,	O
section	O
"	O
and	O
γράφω	O
graphō	O
,	O
"	O
to	O
write	O
"	O
or	O
,	O
in	O
this	O
context	O
as	O
well	O
,	O
"	O
to	O
describe.	O
"	O
</s>
<s>
A	O
device	O
used	O
in	O
tomography	B-Algorithm
is	O
called	O
a	O
tomograph	B-Algorithm
,	O
while	O
the	O
image	O
produced	O
is	O
a	O
tomogram	B-Algorithm
.	O
</s>
<s>
In	O
many	O
cases	O
,	O
the	O
production	O
of	O
these	O
images	O
is	O
based	O
on	O
the	O
mathematical	O
procedure	O
tomographic	B-Algorithm
reconstruction	I-Algorithm
,	O
such	O
as	O
X-ray	B-Library
computed	O
tomography	B-Algorithm
technically	O
being	O
produced	O
from	O
multiple	O
projectional	O
radiographs	O
.	O
</s>
<s>
Most	O
algorithms	O
fall	O
into	O
one	O
of	O
two	O
categories	O
:	O
filtered	O
back	O
projection	O
(	O
FBP	O
)	O
and	O
iterative	B-Algorithm
reconstruction	I-Algorithm
(	O
IR	O
)	O
.	O
</s>
<s>
Although	O
MRI(magnetic resonance imaging )	O
,	O
Optical	B-Application
coherence	I-Application
tomography	I-Application
and	O
ultrasound	B-Application
are	O
transmission	O
methods	O
,	O
they	O
typically	O
do	O
not	O
require	O
movement	O
of	O
the	O
transmitter	O
to	O
acquire	O
data	O
from	O
different	O
directions	O
.	O
</s>
<s>
In	O
MRI	B-Algorithm
,	O
both	O
projections	O
and	O
higher	O
spatial	O
harmonics	O
are	O
sampled	B-Algorithm
by	O
applying	O
spatially-varying	O
magnetic	O
fields	O
;	O
no	O
moving	O
parts	O
are	O
necessary	O
to	O
generate	O
an	O
image	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
since	O
ultrasound	B-Application
and	O
optical	B-Application
coherence	I-Application
tomography	I-Application
uses	O
time-of-flight	O
to	O
spatially	O
encode	O
the	O
received	O
signal	O
,	O
it	O
is	O
not	O
strictly	O
a	O
tomographic	B-Algorithm
method	O
and	O
does	O
not	O
require	O
multiple	O
image	O
acquisitions	O
.	O
</s>
<s>
Stationary	O
Computed	O
Tomography	B-Algorithm
for	O
Space	O
and	O
other	O
Resource-constrained	O
Environments	O
.	O
</s>
<s>
De	O
Man	O
,	O
"	O
Multisource	O
X-Ray	B-Library
and	O
CT	O
:	O
Lessons	O
Learned	O
and	O
Future	O
Outlook	O
,	O
"	O
in	O
IEEE	O
Access	O
,	O
vol	O
.	O
</s>
<s>
X-rays	B-Library
for	O
both	O
CT	O
and	O
angiography	O
,	O
combined	O
CT/MRI	O
and	O
combined	O
CT/PET	O
.	O
</s>
<s>
Discrete	B-Algorithm
tomography	I-Algorithm
and	O
Geometric	B-Algorithm
tomography	I-Algorithm
,	O
on	O
the	O
other	O
hand	O
,	O
are	O
research	O
areas	O
that	O
deal	O
with	O
the	O
reconstruction	O
of	O
objects	O
that	O
are	O
discrete	O
(	O
such	O
as	O
crystals	O
)	O
or	O
homogeneous	O
.	O
</s>
<s>
They	O
are	O
concerned	O
with	O
reconstruction	O
methods	O
,	O
and	O
as	O
such	O
they	O
are	O
not	O
restricted	O
to	O
any	O
of	O
the	O
particular	O
(	O
experimental	O
)	O
tomography	B-Algorithm
methods	O
listed	O
above	O
.	O
</s>
<s>
A	O
new	O
technique	O
called	O
synchrotron	O
X-ray	B-Library
tomographic	B-Algorithm
microscopy	O
(	O
SRXTM	O
)	O
allows	O
for	O
detailed	O
three-dimensional	O
scanning	O
of	O
fossils	O
.	O
</s>
<s>
capabilities	O
since	O
the	O
1990s	O
has	O
led	O
to	O
a	O
boost	O
of	O
high-end	O
synchrotron	O
tomography	B-Algorithm
in	O
materials	O
research	O
with	O
a	O
wide	O
range	O
of	O
different	O
applications	O
,	O
e.g.	O
</s>
<s>
Volume	O
rendering	O
is	O
a	O
set	O
of	O
techniques	O
used	O
to	O
display	O
a	O
2D	O
projection	O
of	O
a	O
3D	O
discretely	O
sampled	B-Algorithm
data	B-General_Concept
set	I-General_Concept
,	O
typically	O
a	O
3D	O
scalar	O
field	O
.	O
</s>
<s>
A	O
typical	O
3D	O
data	B-General_Concept
set	I-General_Concept
is	O
a	O
group	O
of	O
2D	O
slice	O
images	O
acquired	O
,	O
for	O
example	O
,	O
by	O
a	O
CT	O
,	O
MRI	B-Algorithm
,	O
or	O
MicroCT	O
scanner	B-Application
.	O
</s>
<s>
These	O
are	O
usually	O
acquired	O
in	O
a	O
regular	O
pattern	O
(	O
e.g.	O
,	O
one	O
slice	O
every	O
millimeter	O
)	O
and	O
usually	O
have	O
a	O
regular	O
number	O
of	O
image	O
pixels	B-Algorithm
in	O
a	O
regular	O
pattern	O
.	O
</s>
<s>
This	O
is	O
an	O
example	O
of	O
a	O
regular	O
volumetric	O
grid	O
,	O
with	O
each	O
volume	O
element	O
,	O
or	O
voxel	B-Algorithm
represented	O
by	O
a	O
single	O
value	O
that	O
is	O
obtained	O
by	O
sampling	O
the	O
immediate	O
area	O
surrounding	O
the	O
voxel	B-Algorithm
.	O
</s>
<s>
To	O
render	O
a	O
2D	O
projection	O
of	O
the	O
3D	O
data	B-General_Concept
set	I-General_Concept
,	O
one	O
first	O
needs	O
to	O
define	O
a	O
camera	O
in	O
space	O
relative	O
to	O
the	O
volume	O
.	O
</s>
<s>
Also	O
,	O
one	O
needs	O
to	O
define	O
the	O
opacity	O
and	O
color	O
of	O
every	O
voxel	B-Algorithm
.	O
</s>
<s>
This	O
is	O
usually	O
defined	O
using	O
an	O
RGBA	O
(	O
for	O
red	O
,	O
green	O
,	O
blue	O
,	O
alpha	O
)	O
transfer	O
function	O
that	O
defines	O
the	O
RGBA	O
value	O
for	O
every	O
possible	O
voxel	B-Algorithm
value	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
volume	O
may	O
be	O
viewed	O
by	O
extracting	O
isosurfaces	O
(	O
surfaces	O
of	O
equal	O
values	O
)	O
from	O
the	O
volume	O
and	O
rendering	O
them	O
as	O
polygonal	B-Algorithm
meshes	I-Algorithm
or	O
by	O
rendering	O
the	O
volume	O
directly	O
as	O
a	O
block	O
of	O
data	O
.	O
</s>
<s>
The	O
marching	B-Algorithm
cubes	I-Algorithm
algorithm	I-Algorithm
is	O
a	O
common	O
technique	O
for	O
extracting	O
an	O
isosurface	O
from	O
volume	O
data	O
.	O
</s>
<s>
Focal	B-Algorithm
plane	I-Algorithm
tomography	I-Algorithm
was	O
developed	O
in	O
the	O
1930s	O
by	O
the	O
radiologist	O
Alessandro	O
Vallebona	O
,	O
and	O
proved	O
useful	O
in	O
reducing	O
the	O
problem	O
of	O
superimposition	O
of	O
structures	O
in	O
projectional	O
radiography	O
.	O
</s>
<s>
In	O
a	O
1953	O
article	O
in	O
the	O
medical	O
journal	O
Chest	O
,	O
B	O
.	O
Pollak	O
of	O
the	O
Fort	O
William	O
Sanatorium	O
described	O
the	O
use	O
of	O
planography	O
,	O
another	O
term	O
for	O
tomography	B-Algorithm
.	O
</s>
<s>
Focal	B-Algorithm
plane	I-Algorithm
tomography	I-Algorithm
remained	O
the	O
conventional	O
form	O
of	O
tomography	B-Algorithm
until	O
being	O
largely	O
replaced	O
by	O
mainly	O
computed	O
tomography	B-Algorithm
in	O
the	O
late-1970s	O
.	O
</s>
<s>
Focal	B-Algorithm
plane	I-Algorithm
tomography	I-Algorithm
uses	O
the	O
fact	O
that	O
the	O
focal	O
plane	O
appears	O
sharper	O
,	O
while	O
structures	O
in	O
other	O
planes	O
appear	O
blurred	O
.	O
</s>
<s>
By	O
moving	O
an	O
X-ray	B-Library
source	O
and	O
the	O
film	O
in	O
opposite	O
directions	O
during	O
the	O
exposure	O
,	O
and	O
modifying	O
the	O
direction	O
and	O
extent	O
of	O
the	O
movement	O
,	O
operators	O
can	O
select	O
different	O
focal	O
planes	O
which	O
contain	O
the	O
structures	O
of	O
interest	O
.	O
</s>
