<s>
Photoacoustic	B-Algorithm
imaging	I-Algorithm
or	O
optoacoustic	B-Algorithm
imaging	O
is	O
a	O
biomedical	O
imaging	O
modality	O
based	O
on	O
the	O
photoacoustic	O
effect	O
.	O
</s>
<s>
MHz	O
)	O
ultrasonic	B-Application
emission	O
.	O
</s>
<s>
The	O
generated	O
ultrasonic	B-Application
waves	O
are	O
detected	O
by	O
ultrasonic	B-Algorithm
transducers	I-Algorithm
and	O
then	O
analyzed	O
to	O
produce	O
images	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
the	O
magnitude	O
of	O
the	O
ultrasonic	B-Application
emission	O
(	O
i.e.	O
</s>
<s>
Since	O
blood	O
usually	O
has	O
orders	O
of	O
magnitude	O
higher	O
absorption	O
than	O
surrounding	O
tissues	O
,	O
there	O
is	O
sufficient	O
endogenous	O
contrast	O
for	O
photoacoustic	B-Algorithm
imaging	I-Algorithm
to	O
visualize	O
blood	O
vessels	O
.	O
</s>
<s>
Recent	O
studies	O
have	O
shown	O
that	O
photoacoustic	B-Algorithm
imaging	I-Algorithm
can	O
be	O
used	O
in	O
vivo	O
for	O
tumor	O
angiogenesis	O
monitoring	O
,	O
blood	O
oxygenation	O
mapping	O
,	O
functional	O
brain	O
imaging	O
,	O
skin	O
melanoma	O
detection	O
,	O
methemoglobin	O
measuring	O
,	O
etc	O
.	O
</s>
<s>
Δf	O
Primary	O
contrast	O
Δz	O
δz	O
δx	O
Speed	O
Hz	O
mm	O
μm	O
μm	O
Mvx/s	O
Photoacoustic	O
microscopy	O
50	O
M	O
Optical	O
absorption	O
3	O
15	O
45	O
0.5	O
Photoacoustic	B-Algorithm
tomography	I-Algorithm
5	O
M	O
Optical	O
absorption	O
50	O
700	O
700	O
0.5	O
Confocal	O
microscopy	O
Fluorescence	O
,	O
scattering	O
0.2	O
3-20	O
0.3-3	O
10-100	O
Two-photon	O
microscopy	O
Fluorescence	O
0.5-1.0	O
1-10	O
0.3-3	O
10-100	O
Optical	B-Application
coherence	I-Application
tomography	I-Application
300	O
T	O
Optical	O
scattering	O
1-2	O
0.5-10	O
1-10	O
20-4.000Scanning	O
laser	O
acoustic	O
microscopy	O
300	O
M	O
Ultrasonic	B-Application
scattering	O
1-2	O
20	O
20	O
10	O
Acoustic	O
microscopy	O
50	O
M	O
Ultrasonic	B-Application
scattering	O
20	O
20-100	O
80-160	O
0.1	O
Ultrasonography	O
5	O
M	O
Ultrasonic	B-Application
scattering	O
60	O
300	O
300	O
1	O
Table	O
1	O
.	O
</s>
<s>
Comparison	O
of	O
contrast	O
mechanisms	O
,	O
penetration	O
depth	O
( Δz	O
)	O
,	O
axial	O
resolution	O
( δz	O
)	O
,	O
lateral	O
resolution	O
( δx	O
=	O
δy	O
)	O
and	O
imaging	O
speed	O
of	O
confocal	O
microscopy	O
,	O
two-photon	O
microscopy	O
,	O
optical	B-Application
coherence	I-Application
tomography	I-Application
(	O
300	O
THz	O
)	O
,	O
ultrasound	B-Application
microscopy	O
(	O
50	O
MHz	O
)	O
,	O
ultrasound	B-Application
imaging	O
(	O
5	O
MHz	O
)	O
,	O
photoacoustic	O
microscopy	O
(	O
50	O
MHz	O
)	O
,	O
and	O
photoacoustic	B-Algorithm
tomography	I-Algorithm
(	O
3.5	O
MHz	O
)	O
.	O
</s>
<s>
Two	O
types	O
of	O
photoacoustic	B-Algorithm
imaging	I-Algorithm
systems	O
,	O
photoacoustic/thermoacoustic	O
computed	O
tomography	O
(	O
also	O
known	O
as	O
photoacoustic/thermoacoustic	O
tomography	O
,	O
i.e.	O
,	O
PAT/TAT	O
)	O
and	O
photoacoustic	O
microscopy	O
(	O
PAM	O
)	O
,	O
have	O
been	O
developed	O
.	O
</s>
<s>
A	O
typical	O
PAT	O
system	O
uses	O
an	O
unfocused	O
ultrasound	B-Application
detector	O
to	O
acquire	O
the	O
photoacoustic	O
signals	O
,	O
and	O
the	O
image	O
is	O
reconstructed	O
by	O
inversely	O
solving	O
the	O
photoacoustic	O
equations	O
.	O
</s>
<s>
A	O
PAM	O
system	O
,	O
on	O
the	O
other	O
hand	O
,	O
uses	O
a	O
spherically	O
focused	O
ultrasound	B-Application
detector	O
with	O
2D	O
point-by-point	O
scanning	O
,	O
and	O
requires	O
no	O
reconstruction	O
algorithm	O
.	O
</s>
<s>
In	O
a	O
PAT	O
system	O
,	O
the	O
acoustic	O
pressure	O
is	O
detected	O
by	O
scanning	O
an	O
ultrasonic	B-Algorithm
transducer	I-Algorithm
over	O
a	O
surface	O
that	O
encloses	O
the	O
photoacoustic	O
source	O
.	O
</s>
<s>
Photoacoustic	O
waves	O
are	O
generated	O
proportional	O
to	O
the	O
distribution	O
of	O
optical	O
absorption	O
in	O
the	O
target	O
,	O
and	O
are	O
detected	O
by	O
a	O
single	O
scanned	O
ultrasonic	B-Algorithm
transducer	I-Algorithm
.	O
</s>
<s>
Although	O
single-element	O
transducers	O
have	O
been	O
employed	O
in	O
these	O
two	O
systems	O
,	O
the	O
detection	O
scheme	O
can	O
be	O
extended	O
to	O
use	O
ultrasound	B-Application
arrays	O
as	O
well	O
.	O
</s>
<s>
Intrinsic	O
optical	O
or	O
microwave	O
absorption	O
contrast	O
and	O
diffraction-limited	O
high	O
spatial	O
resolution	O
of	O
ultrasound	B-Application
make	O
PAT	O
and	O
TAT	O
promising	O
imaging	O
modalities	O
for	O
wide	O
biomedical	O
applications	O
:	O
</s>
<s>
The	O
imaging	O
depth	O
of	O
photoacoustic	O
microscopy	O
is	O
mainly	O
limited	O
by	O
the	O
ultrasonic	B-Application
attenuation	O
.	O
</s>
<s>
axial	O
and	O
lateral	O
)	O
resolutions	O
depend	O
on	O
the	O
ultrasonic	B-Algorithm
transducer	I-Algorithm
used	O
.	O
</s>
<s>
An	O
ultrasonic	B-Algorithm
transducer	I-Algorithm
with	O
high	O
central	O
frequency	O
and	O
broader	O
bandwidth	O
are	O
chosen	O
to	O
obtain	O
high	O
axial	O
resolution	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
50MHz	O
ultrasonic	B-Algorithm
transducer	I-Algorithm
provides	O
15	O
micrometre	O
axial	O
and	O
45	O
micrometre	O
lateral	O
resolution	O
with	O
~	O
3mm	O
imaging	O
depth	O
.	O
</s>
<s>
Photoacoustic	B-Algorithm
imaging	I-Algorithm
was	O
introduced	O
recently	O
in	O
the	O
context	O
of	O
artwork	O
diagnostics	O
with	O
emphasis	O
on	O
the	O
uncovering	O
of	O
hidden	O
features	O
such	O
as	O
underdrawings	O
or	O
original	O
sketch	O
lines	O
in	O
paintings	O
.	O
</s>
<s>
Photoacoustic	O
images	O
,	O
collected	O
from	O
miniature	O
oil	O
paintings	O
on	O
canvas	B-Language
,	O
illuminated	O
with	O
a	O
pulsed	O
laser	O
on	O
their	O
reverse	O
side	O
,	O
revealed	O
clearly	O
the	O
presence	O
of	O
pencil	O
sketch	O
lines	O
coated	O
over	O
by	O
several	O
paint	O
layers	O
.	O
</s>
<s>
Photoacoustic	B-Algorithm
imaging	I-Algorithm
has	O
seen	O
recent	O
advances	O
through	O
the	O
integration	O
of	O
deep	O
learning	O
principles	O
and	O
compressed	O
sensing	O
.	O
</s>
<s>
For	O
more	O
information	O
on	O
the	O
deep	O
learning	O
applications	O
in	O
photoacoustic	B-Algorithm
imaging	I-Algorithm
,	O
see	O
Deep	B-Algorithm
learning	I-Algorithm
in	I-Algorithm
photoacoustic	I-Algorithm
imaging	I-Algorithm
.	O
</s>
