<s>
Optical	B-Algorithm
coherence	I-Algorithm
tomography	I-Algorithm
angiography	I-Algorithm
(	O
OCTA	O
)	O
is	O
a	O
non-invasive	O
imaging	B-Application
technique	I-Application
based	O
on	O
optical	B-Application
coherence	I-Application
tomography	I-Application
(	O
OCT	B-Application
)	O
developed	O
to	O
visualize	O
vascular	O
networks	O
in	O
the	O
human	O
retina	O
,	O
choroid	O
,	O
skin	O
and	O
various	O
animal	O
models	O
.	O
</s>
<s>
OCTA	O
may	O
make	O
use	O
of	O
speckle	B-Algorithm
variance	I-Algorithm
optical	I-Algorithm
coherence	I-Algorithm
tomography	I-Algorithm
.	O
</s>
<s>
OCTA	O
uses	O
low-coherence	O
interferometry	O
to	O
measure	O
changes	O
in	O
backscattered	B-Algorithm
signal	I-Algorithm
to	O
differentiate	O
areas	O
of	O
blood	O
flow	O
from	O
areas	O
of	O
static	O
tissue	O
.	O
</s>
<s>
This	O
form	O
of	O
OCT	B-Application
requires	O
a	O
very	O
high	O
sampling	O
density	O
in	O
order	O
to	O
achieve	O
the	O
resolution	O
needed	O
to	O
detect	O
the	O
tiny	O
capillaries	O
found	O
in	O
the	O
retina	O
.	O
</s>
<s>
Recent	O
advancements	O
in	O
OCT	B-Application
acquisition	O
speed	O
have	O
made	O
it	O
possible	O
the	O
required	O
sampling	O
density	O
to	O
obtain	O
a	O
high	O
enough	O
resolution	O
for	O
OCTA	O
.	O
</s>
<s>
OCT-A	O
was	O
first	O
introduced	O
in	O
clinical	O
eyecare	O
2014	O
.	O
</s>
<s>
To	O
simply	O
put	O
it	O
,	O
the	O
backscattered	B-Algorithm
light	O
reflected	O
back	O
from	O
static	O
samples	O
would	O
remain	O
the	O
same	O
over	O
multiple	O
B-scans	O
while	O
the	O
backscattered	B-Algorithm
light	O
reflected	O
back	O
from	O
moving	O
samples	O
would	O
fluctuate	O
.	O
</s>
<s>
The	O
split-spectrum	O
amplitude	O
decorrelation	O
angiography	O
(	O
SSADA	O
)	O
algorithm	O
calculates	O
the	O
decorrelation	O
in	O
the	O
reflected	O
light	O
that	O
is	O
detected	O
by	O
the	O
OCT	B-Application
device	O
.	O
</s>
<s>
With	O
the	O
development	O
of	O
Fourier-domain	O
OCT	B-Application
,	O
spectral-domain	O
OCT	B-Application
,	O
and	O
swept	O
source	O
signal	O
acquisition	O
time	O
was	O
greatly	O
improved	O
making	O
OCTA	O
possible	O
.	O
</s>
<s>
Initial	O
efforts	O
to	O
measure	O
blood	O
flow	O
using	O
OCT	B-Application
utilized	O
the	O
Doppler	O
effect	O
.	O
</s>
<s>
This	O
was	O
deemed	O
Optical	O
Doppler	O
Tomography	O
;	O
the	O
development	O
of	O
spectral	O
domain	O
OCT	B-Application
(	O
SD-OCT	O
)	O
and	O
swept-source	O
OCT	B-Application
(	O
SS-OCT	O
)	O
greatly	O
improved	O
scan	O
times	O
since	O
this	O
phase	O
information	O
was	O
readily	O
accessible	O
.	O
</s>
<s>
Commercial	O
OCT-A	O
devices	O
also	O
emerged	O
around	O
this	O
time	O
,	O
beginning	O
with	O
the	O
OptoVue	O
AngioVue	O
in	O
2014	O
(	O
SD-OCT	O
)	O
and	O
the	O
Topcon	O
Atlantis/Triton	O
soon	O
after	O
(	O
SS-OCT	O
)	O
.	O
</s>
<s>
The	O
current	O
gold	O
standards	O
of	O
angiography	O
,	O
fluorescein	B-Algorithm
angiography	I-Algorithm
(	O
FA	O
)	O
and	O
indocyanine	O
green	O
angiography	O
(	O
ICGA	O
)	O
,	O
both	O
require	O
dye	O
to	O
be	O
injected	O
.	O
</s>
