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A parabolic mirror-based proximally
actuated photoacoustic endoscope
Chiye Li, Joon-Mo Yang, Ruimin Chen, Konstantin
Maslov, Qifa Zhou, et al.
Chiye Li, Joon-Mo Yang, Ruimin Chen, Konstantin Maslov, Qifa Zhou, K.
Kirk Shung, Lihong V. Wang, "A parabolic mirror-based proximally actuated
photoacoustic endoscope," Proc. SPIE 8581, Photons Plus Ultrasound:
Imaging and Sensing 2013, 858148 (4 March 2013); doi: 10.1117/12.2005494
Event: SPIE BiOS, 2013, San Francisco, California, United States
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A parabolic mirror-based
proximally actuated
photoacoustic endoscope
Chiye Li
1, 3
, Joon-Mo Yang
1, 3
, Ruimin Chen
2
, Konstantin Maslov
1
, Qifa Zhou
2
, K. Kirk Shung
2
,
and Lihong V. Wang
1,
*
1
Optical Imaging Laboratory, Depart
ment of Biomedical Engineeri
ng, Washington University in St.
Louis, One Brookings Drive, Campus
Box 1097, St. Louis, Missouri, 63130, USA
2
Ultrasonic Transducer Resource Ce
nter, Department of Biomedical
Engineering, University of
Southern California, 1042 Downey Way, Univer
sity Park, DRB 130, Los Angeles, CA 90089, USA
ABSTRACT
We have developed a new photoacoustic endoscopic probe specifically designed for human urogenital imaging. The
endoscopic probe uses a parabolic mirror-based mechanical scanning mechanism, providing an angular field of view of
270°. And it has a rigid, dome shaped end section for smooth cavity introduction. Here we introduce the new
endoscope’s design and imaging
principle, and present experimental results validating its
in vivo
imaging ability.
Keywords
: Photoacoustic endoscopy, human urogenital imaging, cancer diagnosis, functional imaging.
1. INTRODUCTION
Cancer is an emerging public health problem as people live
longer and the population increases. As strategies to this
problem, early detection and monitoring during therapy are important parts of cancer control. Considering the high false
negative rate of current cervical cancer screening, new cost-effective and more reliable diagnostic methods are
necessary to complement current screening methods. For imaging tumors in deep-seated organs, developments of
tomographic endoscopic techniques are
important because such techniques can
provide direct visions of tumors and
facilitate accurate diagnosis. A
lthough traditional endoscopic u
ltrasound technique is widely
used for human urogenital
imaging, they do not sufficiently provide important pathophysiological information.
Now, photoacoustic endoscopy (PAE)
1-4
embodying photoacoustic tomography (PAT)
5, 6
in a small probe is emerging
as a new, minimally invasive imaging tool for diagnosing diseases in internal organs, such as gastrointestinal tracts
1, 3, 4,
7
and urogenital systems
8-11
. Many neoplasms are associated with angiog
enesis and show abnormal metabolic rates
12
.
Based on the strong spectroscopic, functional,
and angiographic imaging capability of PAT
5, 6, 12-15
, PAE can be used for
diagnosing many urogenital system dis
eases such as endometrial cancer and pr
ostate cancer. In this study, we have
developed a new photoacoustic endoscopic probe for targeting such applications and demonstrated its
in vivo
imaging
ability through an animal experiment.
2.
MATERIALS AND METHODS
2.1.
Photoacoustic endoscopic system
The endoscopic probe is constructed with a rigid form for operator’s more convenient handling during diagnostic
procedures, and the probe body has a streamlined structure with a dome shaped distal end for smooth cavity
introduction.
Figure 1(a)
shows a schematic of the endoscope. In the
distal section, all optical and mechanical
components are encapsulated in a medical-grade stainless steel tubular housing with an outer diameter of ~12.7 mm and
3
These authors contributed equally to this work.
*
Corresponding author:
lhwang@biomed.wustl.edu
Photons Plus Ultrasound: Imaging and Sensing 2013, edited by Alexander A. Oraevsky, Lihong V. Wang,
Proc. of SPIE Vol. 8581, 858148 · © 2013 SPIE · CCC code: 1605-7422/13/$18 · doi: 10.1117/12.2005494
Proc. of SPIE Vol. 8581 858148-1
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(a
)
Ultrasonic transducer -
Parabolic mirror
Prism
Optical fiber
Stepper motor
Belt and pulley
Optical fiber
(b)
PA endoscopic probe
PA signal
Function
generator
Torque
Trigger
Laser pulse
Stepper
motor
I Amplifier
1
Laser
1
Amplified PA
DAQ
1
A
~50 cm in length. The endoscope employs a parabolic shape s
canning mirror actuated by a
stepper motor located at the
proximal end and performs a side scan, providing an angular field of view of ~270°. This parabolic mirror was custom-
made, and it enables the acoustic focusing with a lower geom
etric aberration than our previous acoustic lens-based
focusing methods
2
. The endoscope is comprised of the dome shape tubular stainless steel housing that encapsulates all
elements, and a central tube that is sta
tically located along axis of the endoscope and includes an optical fiber for light
delivery, and a tubular rigid shaft that rotates between
the two receiving the torque from the stepper motor.
Figure 1.
(a) Schematic of the endoscopic probe. (b) A di
agram showing the entire endoscopic system. The
stepper motor, laser system
, and DAQ card are synchronized to the tr
ansistor-transistor
logic (TTL) signals
provided by the function generator.
Laser pulses exiting the optical fiber are reflected by an optical
prism and then sent to the target tissue to generate PA
signals. Some of the generated photoacoustic (PA) waves are then collected by the parabolic mirror, reflected, and
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o
L
27
I
00
1
Tungsten wir
finally dete
c
systems. Fo
r
system and
d
2.2.
S
y
stem
To quantify
water tank t
o
B-scan ima
g
yields an A
-
measureme
n
The endosc
o
(~450 g; Ha
r
with ~4% i
s
supplied thr
o
on the skin
mJ/pulse).
All procedu
r
Committee
a
3.1.
Resolu
t
The resolut
i
tungsten wi
r
treated as a
l
spread func
t
transverse r
e
Fig
u
ang
u
3.2.
Anima
l
In
Figure 3
figures, PA
skin tissue,
e
c
ted by a flat
r
this endosco
p
d
ata acquisitio
n
validation
the endoscop
e
o
gether with t
h
g
ing in a
p
lan
e
-
line number
o
n
t of resolution
o
pe’s
in vivo
i
m
r
lan National
C
s
oflurane, we
o
ugh a nose c
o
to provide ac
o
r
es in the ani
m
a
t Washington
t
ion
i
on of the en
d
r
e has a suffic
i
l
ine target in t
h
t
ion of the sy
s
e
solution of 10
u
re 2.
A repre
s
u
lar field of vie
w
l
ima
g
in
g
res
u
, we present
t
signals mostl
y
e
ven from mor
ultrasonic tra
n
p
ic syste
m
, a
n
(DAQ) card.
e
’s spatial res
o
h
e probe and p
l
e
perpendicula
r
o
f 800 per B-s
s.
m
aging abilit
y
C
ustomer Ser
v
mounted the
o
ne. We remo
v
o
ustic couplin
g
m
al experime
n
University in
S
d
oscopic syst
e
i
ently length
w
h
is resolution
e
s
te
m
. We app
5
μm and a ra
d
s
entative PA im
a
w
of covering 2
7
u
lts
t
hree represen
t
y
representing
h
e
than 5m
m
d
e
n
sduce
r
(~40
M
function gene
r
o
lution, we im
a
l
aced the wire
r
to the wire
w
can. We reco
r
y
was also val
i
v
ice Center) as
animal on a
v
ed hair on the
g
. Then, PA i
m
n
ts followed t
h
S
t. Louis.
3.
em
is determi
n
w
ith a diamete
r
e
xperimen
t
.
Fi
g
l
ied an envel
o
d
ial resolution
a
ge of a 20 μ
m
7
0°.
t
ative PA B-s
c
h
emoglobin d
i
e
pth.
M
Hz, LiNbO
3
r
ator is used t
o
a
ged a ~20 μ
m
target at the f
o
w
ith an angula
r
r
ded 100 B-sc
a
i
dated
b
y ima
g
a form of a h
a
stage and ma
i
rat abdomen
u
m
aging was i
n
h
e protocol ap
p
RESULTS
n
ed by acous
t
r
smaller than
t
g
ure 2
shows
t
o
pe detection
(
of 59 μ
m
.
m
thick tungsten
c
an images ac
i
stribution we
r
3
).
Fi
g
ure 1(b
o
drive the st
e
m
thick tungst
e
o
cal position
o
r
step size of
0
a
n images an
d
g
ing the abdo
m
a
ndheld probe
i
ntained the
a
u
sing hair rem
o
n
itiated using
a
p
roved by th
e
t
ics
p
arameter
s
t
he endoscope
t
he acquired P
A
(
Hilbert trans
f
wire. This im
a
quired from t
h
r
e detected fro
m
)
shows the
e
e
pper motor,
a
e
n wire. We i
m
o
f the endosco
p
0
.45° for the s
c
d
averaged the
m
m
en of an adu
. After induci
n
a
nesthesia wit
h
o
val lotion an
d
a
laser wavel
e
e
Institutional
A
s
. Since the
i
’s spatial reso
l
A
B-scan ima
g
f
ormation) an
d
a
ge shows the e
n
h
e rat abdom
e
m
a very larg
e
e
ndoscope’s
pe
a
nd to trigger
t
m
mersed the
w
p
e. We then p
e
c
anning mirro
r
m
for a more
a
lt Sprague Da
w
n
g an initial a
n
h
1.5–2.0% is
d
spread ultras
o
e
ngth of 523
n
A
nimal Care
a
i
maged ~20
μ
l
ution, the wir
e
g
e that represe
n
d
finally deter
m
n
doscope’s
e
n. As shown
e
depth
b
eneat
h
e
ripheral
t
he laser
w
ire in a
e
rformed
r
, which
accurate
w
ley rat
n
esthesia
oflurane
o
und gel
n
m (~0.6
a
nd Use
μ
m thick
e
can be
n
ts a line
m
ined a
in these
h
the rat
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(a)
(b)
(c)
Figure 3.
PA B-scan images acqui
red from a rat abdomen.
4.
DISCUSSION
We have implemented a new PA endoscope with a design specifically targeted for human urogenital imaging
application and validated the endoscope’s imaging ability through a phantom and animal experiment. The endoscope is
fully-encapsulated and it has a streamlined structure with a dome shaped distal end for smooth cavity introduction. Also,
in forming the endoscope’s housing, we utilized medical-gra
de stainless steels to comply with the material safety
requirement. By coaxially aligning the optical illumination an
d the acoustic detection, we could achieve a more efficient
overlapping of the two over a large radial range.
In contrast to our previous endoscopes that use micromotors, this endoscope adopts a proximal actuation mechanism;
thereby the distal section’s length could be shortened and
the mechanical B-scan frame
rate would potentially reach up
to 30 Hz, although the current imaging speed (~1 Hz) is
limited by the capacities of the employed DAQ card and laser
system. Our next direction is to improve the DAQ part and
to combine the endoscope with a compact laser system for
use in clinical rooms. Also, we will enable volumetric imag
ing by adding a pullback scanning to the B-scan mechanism
and also enable PA and
US dual-mode imaging.
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We thank Seema Dahlheimer for her attentive reading of the manuscript. This work was sponsored in part by
National Institutes of Health grants R01 CA157277
, R01 EB000712, R01 EB008085, R01 CA134539, U54
CA136398, R01 CA159959, and P41 EB002182. L.W. has a financial interest in Microphotoacoustics, Inc.
and Endra, Inc., which, however, did not support this work.
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ACKNOWLEDGEMENT
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