<s>
Optical	B-Application
coherence	I-Application
tomography	I-Application
(	O
OCT	O
)	O
is	O
an	O
imaging	O
technique	O
that	O
uses	O
low-coherence	O
light	O
to	O
capture	O
micrometer-resolution	O
,	O
two	O
-	O
and	O
three-dimensional	O
images	O
from	O
within	O
optical	O
scattering	O
media	O
(	O
e.g.	O
,	O
biological	O
tissue	O
)	O
.	O
</s>
<s>
It	O
is	O
used	O
for	O
medical	B-Application
imaging	I-Application
and	O
industrial	O
nondestructive	O
testing	O
(	O
NDT	O
)	O
.	O
</s>
<s>
Optical	B-Application
coherence	I-Application
tomography	I-Application
is	O
based	O
on	O
low-coherence	O
interferometry	O
,	O
typically	O
employing	O
near-infrared	O
light	O
.	O
</s>
<s>
Depending	O
on	O
the	O
properties	O
of	O
the	O
light	O
source	O
(	O
superluminescent	O
diodes	O
,	O
ultrashort	O
pulsed	O
lasers	O
,	O
and	O
supercontinuum	O
lasers	O
have	O
been	O
employed	O
)	O
,	O
optical	B-Application
coherence	I-Application
tomography	I-Application
has	O
achieved	O
sub-micrometer	O
resolution	O
(	O
with	O
very	O
wide-spectrum	O
sources	O
emitting	O
over	O
a	O
~	O
100nm	O
wavelength	O
range	O
)	O
.	O
</s>
<s>
Optical	B-Application
coherence	I-Application
tomography	I-Application
is	O
one	O
of	O
a	O
class	O
of	O
optical	B-Algorithm
tomographic	I-Algorithm
techniques	O
.	O
</s>
<s>
Commercially	O
available	O
optical	B-Application
coherence	I-Application
tomography	I-Application
systems	O
are	O
employed	O
in	O
diverse	O
applications	O
,	O
including	O
art	O
conservation	O
and	O
diagnostic	O
medicine	O
,	O
notably	O
in	O
ophthalmology	O
and	O
optometry	O
where	O
it	O
can	O
be	O
used	O
to	O
obtain	O
detailed	O
images	O
from	O
within	O
the	O
retina	O
.	O
</s>
<s>
A	O
relatively	O
recent	O
implementation	O
of	O
optical	B-Application
coherence	I-Application
tomography	I-Application
,	O
frequency-domain	O
optical	B-Application
coherence	I-Application
tomography	I-Application
,	O
provides	O
advantages	O
in	O
the	O
signal-to-noise	O
ratio	O
provided	O
,	O
thus	O
permitting	O
faster	O
signal	O
acquisition	O
.	O
</s>
<s>
OCT	O
is	O
not	O
the	O
same	O
as	O
Optical	O
coherence	O
microscopy	O
(	O
OCM	O
)	O
,	O
which	O
"	O
is	O
a	O
microscopic	O
incarnation	O
of	O
optical	B-Application
coherence	I-Application
tomography	I-Application
(	O
OCT	O
)	O
"	O
that	O
can	O
be	O
used	O
for	O
3D	O
imaging	O
reconstruction	O
through	O
intrinsic	O
contrasting	O
of	O
back-scattered	O
(	O
coherent	O
)	O
light	O
.	O
</s>
<s>
Further	O
developed	O
in	O
1990	O
by	O
Naohiro	O
Tanno	O
,	O
then	O
a	O
professor	O
at	O
Yamagata	O
University	O
it	O
was	O
referred	O
to	O
as	O
heterodyne	O
reflectance	O
tomography	B-Algorithm
,	O
and	O
in	O
particular	O
since	O
1991	O
by	O
Huang	O
et	O
al.	O
,	O
in	O
Prof	O
.	O
James	O
Fujimoto	O
laboratory	O
at	O
Massachusetts	O
Institute	O
of	O
Technology	O
,	O
who	O
successfully	O
coined	O
the	O
term	O
“	O
optical	B-Application
coherence	I-Application
tomography	I-Application
”	O
.	O
</s>
<s>
OCT	O
has	O
interesting	O
advantages	O
over	O
other	O
medical	B-Application
imaging	I-Application
systems	O
.	O
</s>
<s>
Medical	B-Application
ultrasonography	I-Application
,	O
magnetic	O
resonance	O
imaging	O
(	O
MRI	O
)	O
,	O
confocal	O
microscopy	O
,	O
and	O
OCT	O
are	O
differently	O
suited	O
to	O
morphological	O
tissue	O
imaging	O
:	O
while	O
the	O
first	O
two	O
have	O
whole	O
body	O
but	O
low	O
resolution	O
imaging	O
capability	O
(	O
typically	O
a	O
fraction	O
of	O
a	O
millimeter	O
)	O
,	O
the	O
third	O
one	O
can	O
provide	O
images	O
with	O
resolutions	O
well	O
below	O
1	O
micrometer	O
(	O
i.e.	O
</s>
<s>
This	O
reflectivity	O
profile	O
,	O
called	O
an	O
A-scan	B-Algorithm
,	O
contains	O
information	O
about	O
the	O
spatial	O
dimensions	O
and	O
location	O
of	O
structures	O
within	O
the	O
item	O
of	O
interest	O
.	O
</s>
<s>
A	O
cross-sectional	O
tomogram	B-Algorithm
(	O
B-scan	O
)	O
may	O
be	O
achieved	O
by	O
laterally	O
combining	O
a	O
series	O
of	O
these	O
axial	O
depth	O
scans	O
(	O
A-scan	B-Algorithm
)	O
.	O
</s>
<s>
Optical	B-Application
coherence	I-Application
tomography	I-Application
(	O
OCT	O
)	O
is	O
a	O
technique	O
for	O
obtaining	O
sub-surface	O
images	O
of	O
translucent	O
or	O
opaque	O
materials	O
at	O
a	O
resolution	O
equivalent	O
to	O
a	O
low-power	O
microscope	O
.	O
</s>
<s>
Within	O
the	O
range	O
of	O
noninvasive	O
three-dimensional	O
imaging	O
techniques	O
that	O
have	O
been	O
introduced	O
to	O
the	O
medical	O
research	O
community	O
,	O
OCT	O
as	O
an	O
echo	O
technique	O
is	O
similar	O
to	O
ultrasound	B-Application
imaging	I-Application
.	O
</s>
<s>
Other	O
medical	B-Application
imaging	I-Application
techniques	I-Application
such	O
as	O
computerized	O
axial	O
tomography	B-Algorithm
,	O
magnetic	O
resonance	O
imaging	O
,	O
or	O
positron	O
emission	O
tomography	B-Algorithm
do	O
not	O
use	O
the	O
echo-location	O
principle	O
.	O
</s>
<s>
Components	O
include	O
:	O
super-luminescent	O
diode	O
(	O
SLD	O
)	O
,	O
convex	O
lens	O
(	O
L1	O
)	O
,	O
50/50	O
beamsplitter	O
(	O
BS	O
)	O
,	O
camera	O
objective	O
(	O
CO	O
)	O
,	O
CMOS-DSP	O
camera	O
(	O
CAM	O
)	O
,	O
reference	O
(	O
REF	O
)	O
,	O
and	O
sample	O
(	O
SMP	O
)	O
.	O
</s>
<s>
Spatially	O
encoded	O
frequency	O
domain	O
OCT	O
(	O
SEFD-OCT	O
,	O
spectral	O
domain	O
or	O
Fourier	O
domain	O
OCT	O
)	O
extracts	O
spectral	O
information	O
by	O
distributing	O
different	O
optical	O
frequencies	O
onto	O
a	O
detector	O
stripe	O
(	O
line-array	O
CCD	O
or	O
CMOS	B-Device
)	O
via	O
a	O
dispersive	O
element	O
(	O
see	O
Fig	O
.	O
</s>
<s>
The	O
drawbacks	O
of	O
this	O
technology	O
are	O
found	O
in	O
a	O
strong	O
fall-off	O
of	O
the	O
SNR	O
,	O
which	O
is	O
proportional	O
to	O
the	O
distance	O
from	O
the	O
zero	O
delay	O
and	O
a	O
sinc-type	O
reduction	O
of	O
the	O
depth-dependent	O
sensitivity	O
because	O
of	O
limited	O
detection	O
linewidth	O
.	O
</s>
<s>
(	O
One	O
pixel	O
detects	O
a	O
quasi-rectangular	O
portion	O
of	O
an	O
optical	O
frequency	O
range	O
instead	O
of	O
a	O
single	O
frequency	O
,	O
the	O
Fourier	O
transform	O
leads	O
to	O
the	O
sinc(z )	O
behavior	O
)	O
.	O
</s>
<s>
These	O
images	O
acquired	O
by	O
a	O
CCD	B-Algorithm
camera	I-Algorithm
are	O
combined	O
in	O
post-treatment	O
(	O
or	O
online	O
)	O
by	O
the	O
phase	O
shift	O
interferometry	O
method	O
,	O
where	O
usually	O
2	O
or	O
4	O
images	O
per	O
modulation	O
period	O
are	O
acquired	O
,	O
depending	O
on	O
the	O
algorithm	O
used	O
.	O
</s>
<s>
The	O
"	O
en-face	O
"	O
tomographic	B-Algorithm
images	O
are	O
thus	O
produced	O
by	O
a	O
wide-field	O
illumination	O
,	O
ensured	O
by	O
the	O
Linnik	O
configuration	O
of	O
the	O
Michelson	O
interferometer	O
where	O
a	O
microscope	O
objective	O
is	O
used	O
in	O
both	O
arms	O
.	O
</s>
<s>
Line-field	O
confocal	O
optical	B-Application
coherence	I-Application
tomography	I-Application
(	O
LC-OCT	O
)	O
is	O
an	O
imaging	O
technique	O
based	O
on	O
the	O
principle	O
of	O
time-domain	O
OCT	O
with	O
line	O
illumination	O
using	O
a	O
broadband	O
laser	O
and	O
line	O
detection	O
using	O
a	O
line-scan	O
camera	O
.	O
</s>
<s>
LC-OCT	O
produces	O
B-scans	O
in	O
real-time	O
from	O
multiple	O
A-scans	B-Algorithm
acquired	O
in	O
parallel	O
.	O
</s>
<s>
Focusing	O
the	O
light	O
beam	O
to	O
a	O
point	O
on	O
the	O
surface	O
of	O
the	O
sample	O
under	O
test	O
,	O
and	O
recombining	O
the	O
reflected	O
light	O
with	O
the	O
reference	O
will	O
yield	O
an	O
interferogram	O
with	O
sample	O
information	O
corresponding	O
to	O
a	O
single	O
A-scan	B-Algorithm
(	O
Z	O
axis	O
only	O
)	O
.	O
</s>
<s>
Parallel	O
or	O
full	O
field	O
OCT	O
using	O
a	O
charge-coupled	B-Algorithm
device	I-Algorithm
(	O
CCD	O
)	O
camera	O
has	O
been	O
used	O
in	O
which	O
the	O
sample	O
is	O
full-field	O
illuminated	O
and	O
en	O
face	O
imaged	O
with	O
the	O
CCD	O
,	O
hence	O
eliminating	O
the	O
electromechanical	O
lateral	O
scan	O
.	O
</s>
<s>
Three-dimensional	O
OCT	O
using	O
a	O
CCD	B-Algorithm
camera	I-Algorithm
was	O
demonstrated	O
in	O
a	O
phase-stepped	O
technique	O
,	O
using	O
geometric	O
phase	O
shifting	O
with	O
a	O
Linnik	O
interferometer	O
,	O
utilising	O
a	O
pair	O
of	O
CCDs	O
and	O
heterodyne	O
detection	O
,	O
and	O
in	O
a	O
Linnik	O
interferometer	O
with	O
an	O
oscillating	O
reference	O
mirror	O
and	O
axial	O
translation	O
stage	O
.	O
</s>
<s>
A	O
two-dimensional	O
smart	O
detector	O
array	O
,	O
fabricated	O
using	O
a	O
2µm	O
complementary	B-Device
metal	I-Device
–	I-Device
oxide	I-Device
–	I-Device
semiconductor	I-Device
(	O
CMOS	B-Device
)	O
process	O
,	O
was	O
used	O
to	O
demonstrate	O
full-field	O
TD-OCT	O
.	O
</s>
<s>
Optical	B-Application
coherence	I-Application
tomography	I-Application
is	O
an	O
established	O
medical	B-Application
imaging	I-Application
technique	I-Application
and	O
is	O
used	O
across	O
several	O
medical	O
specialties	O
including	O
ophthalmology	O
and	O
cardiology	O
,	O
and	O
is	O
widely	O
used	O
in	O
basic	O
science	O
research	O
applications	O
.	O
</s>
<s>
In	O
the	O
setting	O
of	O
cardiology	O
,	O
OCT	O
is	O
used	O
to	O
image	O
coronary	O
arteries	O
in	O
order	O
to	O
visualize	O
vessel	O
wall	O
lumen	O
morphology	O
and	O
microstructure	O
at	O
a	O
resolution	O
10	O
times	O
higher	O
than	O
other	O
existing	O
modalities	O
such	O
as	O
intravascular	O
ultrasounds	O
,	O
and	O
x-ray	O
angiography	O
(	O
intracoronary	B-Algorithm
optical	I-Algorithm
coherence	I-Algorithm
tomography	I-Algorithm
)	O
.	O
</s>
<s>
OCT	O
has	O
been	O
combined	O
with	O
fluorescence	B-Algorithm
molecular	I-Algorithm
imaging	I-Algorithm
to	O
enhance	O
its	O
capability	O
to	O
detect	O
molecular/functional	O
and	O
tissue	O
morphological	O
information	O
simultaneously	O
.	O
</s>
<s>
Optical	B-Application
coherence	I-Application
tomography	I-Application
is	O
also	O
applicable	O
and	O
increasingly	O
used	O
in	O
industrial	O
applications	O
,	O
such	O
as	O
nondestructive	O
testing	O
(	O
NDT	O
)	O
,	O
material	O
thickness	O
measurements	O
,	O
and	O
in	O
particular	O
thin	O
silicon	O
wafers	O
and	O
compound	O
semiconductor	O
wafers	O
thickness	O
measurements	O
surface	O
roughness	O
characterization	O
,	O
surface	O
and	O
cross-section	O
imaging	O
and	O
volume	O
loss	O
measurements	O
.	O
</s>
<s>
As	O
of	O
2014	O
,	O
attempts	O
have	O
been	O
made	O
to	O
use	O
optical	B-Application
coherence	I-Application
tomography	I-Application
to	O
identify	O
root	O
canals	O
in	O
teeth	O
,	O
specifically	O
canal	O
in	O
the	O
maxillary	O
molar	O
,	O
however	O
,	O
there	O
is	O
no	O
difference	O
with	O
the	O
current	O
methods	O
of	O
dental	O
operatory	O
microscope	O
.	O
</s>
