<s>
Optical	B-Application
coherence	I-Application
tomography	I-Application
(	O
OCT	B-Application
)	O
is	O
a	O
technique	O
that	O
displays	O
images	O
of	O
the	O
tissue	O
by	O
using	O
the	O
backscattered	B-Algorithm
light	O
.	O
</s>
<s>
Not	O
only	O
conserving	O
the	O
excellence	O
of	O
OCT	B-Application
,	O
doppler	B-Algorithm
optical	I-Algorithm
coherence	I-Algorithm
tomography	I-Algorithm
also	O
combines	O
the	O
doppler	O
effect	O
principle	O
as	O
a	O
whole	O
,	O
which	O
result	O
in	O
tomographic	B-Algorithm
images	I-Algorithm
with	O
high	B-Algorithm
resolution	I-Algorithm
.	O
</s>
<s>
Due	O
to	O
the	O
recognized	O
significance	O
of	O
noninvasive	O
techniques	O
of	O
imaging	O
in	O
the	O
medical	O
field	O
,	O
especially	O
for	O
imaging	O
in	O
vivo	O
blood	O
flow	O
,	O
OCT	B-Application
has	O
become	O
a	O
popular	O
research	O
topic	O
recently	O
.	O
</s>
<s>
Not	O
only	O
conserving	O
the	O
excellence	O
of	O
OCT	B-Application
,	O
Doppler	B-Algorithm
Optical	I-Algorithm
Coherence	I-Algorithm
Tomography	I-Algorithm
also	O
combines	O
the	O
Doppler	O
effect	O
principle	O
as	O
a	O
whole	O
,	O
which	O
results	O
in	O
tomographic	B-Algorithm
images	I-Algorithm
with	O
high	B-Algorithm
resolution	I-Algorithm
with	O
static	O
and	O
moving	O
constituents	O
.	O
</s>
<s>
The	O
same	O
disadvantages	O
occur	O
when	O
using	O
the	O
spectrogram	O
method	O
to	O
do	O
in	O
vivo	O
tissue	O
structure	O
and	O
flow	O
velocity	O
imaging	O
,	O
as	O
spectral-domain	O
OCT	B-Application
is	O
limited	O
to	O
fast	O
imaging	O
.	O
</s>
<s>
Phase-resolved	O
Doppler	O
OCT	B-Application
,	O
based	O
around	O
the	O
invention	O
of	O
Fourier-Domain	O
OCT	B-Application
,	O
was	O
invented	O
to	O
overcome	O
these	O
limitations	O
.	O
</s>
<s>
There	O
are	O
two	O
types	O
of	O
Doppler	O
OCT	B-Application
:	O
Time	O
domain	O
Doppler	O
OCT	B-Application
and	O
Fourier	O
Domain	O
Doppler	O
OCT	B-Application
.	O
</s>
<s>
The	O
basic	O
principle	O
of	O
Phase-resolved	O
Doppler	O
OCT	B-Application
uses	O
the	O
phase	O
change	O
between	O
sequential	O
A-line	O
scans	O
for	O
velocity	O
image	O
reconstruction	O
.	O
</s>
<s>
While	O
decoupling	O
the	O
spatial	O
resolution	B-Algorithm
and	O
velocity	O
sensitivity	O
in	O
flow	O
images	O
,	O
again	O
it	O
increases	O
imaging	O
speed	O
.	O
</s>
<s>
Because	O
of	O
its	O
exceptionally	O
high	O
spatial	O
resolution	B-Algorithm
and	O
velocity	O
sensitivity	O
,	O
Doppler	O
OCT	B-Application
has	O
its	O
own	O
position	O
in	O
the	O
field	O
of	O
biomedical	O
research	O
and	O
clinical	O
medicine	O
.	O
</s>
<s>
Doppler	B-Algorithm
Optical	I-Algorithm
Coherence	I-Algorithm
Tomography	I-Algorithm
is	O
an	O
extension	O
of	O
OCT	B-Application
,	O
where	O
it	O
combines	O
the	O
Doppler	O
effect	O
principle	O
to	O
achieve	O
high	B-Algorithm
resolution	I-Algorithm
tomographic	B-Algorithm
images	I-Algorithm
in	O
biological	O
tissues	O
.	O
</s>
<s>
And	O
because	O
of	O
its	O
high	B-Algorithm
resolution	I-Algorithm
and	O
velocity	O
sensitivity	O
,	O
there	O
are	O
many	O
applications	O
in	O
the	O
medical	O
field	O
.	O
</s>
<s>
The	O
basic	O
phenomenon	O
of	O
Doppler	O
OCT	B-Application
can	O
be	O
explained	O
below	O
.	O
</s>
<s>
Light	O
hits	O
the	O
moving	O
particles	O
and	O
is	O
backscattered	B-Algorithm
from	O
the	O
sample	O
.	O
</s>
<s>
Doppler	O
OCT	B-Application
measures	O
the	O
light	O
backscattered	B-Algorithm
from	O
the	O
sample	O
medium	O
.	O
</s>
<s>
The	O
instrumentation	O
system	O
of	O
Doppler	O
OCT	B-Application
is	O
an	O
extension	O
of	O
the	O
system	O
of	O
OCT	B-Application
.	O
</s>
<s>
It	O
also	O
uses	O
a	O
fiber	O
optic	O
Michelson	O
interferometer	O
with	O
a	O
broadband	B-General_Concept
light	O
as	O
a	O
source	O
.	O
</s>
<s>
After	O
the	O
light	O
emitting	O
from	O
the	O
broadband	B-General_Concept
light	O
source	O
,	O
the	O
light	O
goes	O
through	O
a	O
2	O
,	O
2	O
fiber	B-Device
coupler	I-Device
,	O
which	O
split	O
the	O
light	O
equally	O
and	O
separately	O
into	O
the	O
reference	O
and	O
samples	O
arms	O
.	O
</s>
<s>
The	O
light	O
that	O
goes	O
through	O
the	O
sample	O
arms	O
enters	O
the	O
sample	O
medium	O
and	O
backscattered	B-Algorithm
.	O
</s>
<s>
Fourier	B-Algorithm
Transform	I-Algorithm
relations	O
between	O
the	O
time	O
domain	O
signals	O
and	O
spectral	O
domain	O
signals	O
are	O
shown	O
in	O
the	O
equations	O
above	O
,	O
which	O
correspond	O
to	O
the	O
two	O
types	O
of	O
OCT	B-Application
.	O
As	O
a	O
result	O
,	O
the	O
time	O
domain	O
method	O
and	O
the	O
Fourier	O
domain	O
method	O
can	O
both	O
achieve	O
high-resolutions	B-Algorithm
.	O
</s>
<s>
Time	O
domain	O
Doppler	O
OCT	B-Application
uses	O
the	O
spectrogram	O
method	O
to	O
create	O
the	O
image	O
.	O
</s>
<s>
The	O
short-time	O
fast	O
Fourier	B-Algorithm
transformation	I-Algorithm
(	O
STFFT	O
)	O
is	O
used	O
to	O
calculate	O
the	O
power	O
spectrum	O
.	O
</s>
<s>
When	O
the	O
velocity	O
resolution	B-Algorithm
is	O
increased	O
,	O
imaging	O
speed	O
and	O
spatial	O
resolution	B-Algorithm
are	O
decreased	O
.	O
</s>
<s>
Phase-resolved	O
Doppler	O
OCT	B-Application
uses	O
this	O
phase	O
change	O
to	O
develop	O
flow	O
velocity	O
images	O
,	O
which	O
can	O
obtain	O
both	O
high	O
imaging	O
speed	O
,	O
high	O
velocity	O
sensitivity	O
,	O
and	O
high	O
spatial	O
resolution	B-Algorithm
.	O
</s>
<s>
The	O
standard	B-General_Concept
deviation	I-General_Concept
of	O
the	O
Doppler	O
spectrum	O
is	O
as	O
follow	O
:	O
</s>
<s>
Changing	O
flow	O
velocity	O
impacts	O
the	O
value	O
of	O
the	O
standard	B-General_Concept
deviation	I-General_Concept
.	O
</s>
<s>
As	O
a	O
result	O
,	O
the	O
standard	B-General_Concept
deviation	I-General_Concept
becomes	O
larger	O
.	O
</s>
<s>
Fourier	O
domain	O
OCT	B-Application
measures	O
interference	O
fringes	O
in	O
the	O
spectral	O
domain	O
.	O
</s>
