In vivo three-dimensional photoacoustic tomography of a whole mouse head.
ABSTRACT An in vivo photoacoustic imaging system was designed and implemented to image the entire small animal head. A special scanning gantry was designed to enable in vivo imaging in coronal cross sections with high contrast and good spatial resolution for the first time to our knowledge. By use of a 2.25 MHz ultrasonic transducer with a 6 mm diameter active element, an in-plane radial resolution of approximately 312 microm was achieved. Deeply seated arterial and venous vessels in the head measuring up to 1.7 cm in diameter were simultaneously imaged in vivo with 804 nm wavelength laser excitation of photoacoustic waves.
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ABSTRACT: Optical imaging techniques use visual and near infrared rays. Despite their considerably poor penetration depth, they are widely used due to their safe and intuitive properties and potential for intraoperative usage. Optical imaging techniques have been actively investigated for clinical imaging of lymph nodes and lymphatic system. This article summarizes a variety of optical tracers and techniques used for lymph node and lymphatic imaging, and reviews their clinical applications. Emerging new optical imaging techniques and their potential are also described.Korean journal of radiology: official journal of the Korean Radiological Society 01/2015; 16(1):21-31. · 1.32 Impact Factor
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ABSTRACT: We have developed a fast 3D photoacoustic imaging system based on a sparse array of ultrasound detectors and iterative image reconstruction. To investigate the high frame rate capabilities of our system in the context of rotational motion, flow, and spectroscopy, we performed high frame-rate imaging on a series of targets, including a rotating graphite rod, a bolus of methylene blue flowing through a tube, and hyper-spectral imaging of a tube filled with methylene blue under a no flow condition. Our frame-rate for image acquisition was 10 Hz, which was limited by the laser repetition rate. We were able to track the rotation of the rod and accurately estimate its rotational velocity, at a rate of 0.33 rotations-per-second. The flow of contrast in the tube, at a flow rate of 180 muL/min, was also well depicted, and quantitative analysis suggested a potential method for estimating flow velocity from such measurements. The spectrum obtained did not provide accurate results, but depicted the spectral absorption signature of methylene blue , which may be sufficient for identification purposes. These preliminary results suggest that our high frame-rate photoacoustic imaging system could be used for identifying contrast agents and monitoring kinetics as an agent propagates through specific, simple structures such as blood vessels.Proceedings of SPIE - The International Society for Optical Engineering 01/2009; · 0.20 Impact Factor
Article: 3D photoacoustic imaging[Show abstract] [Hide abstract]
ABSTRACT: Our group has concentrated on development of a 3D photoacoustic imaging system for biomedical imaging research. The technology employs a sparse parallel detection scheme and specialized reconstruction software to obtain 3D optical images using a single laser pulse. With the technology we have been able to capture 3D movies of translating point targets and rotating line targets. The current limitation of our 3D photoacoustic imaging approach is its inability ability to reconstruct complex objects in the field of view. This is primarily due to the relatively small number of projections used to reconstruct objects. However, in many photoacoustic imaging situations, only a few objects may be present in the field of view and these objects may have very high contrast compared to background. That is, the objects have sparse properties. Therefore, our work had two objectives: (i) to utilize mathematical tools to evaluate 3D photoacoustic imaging performance, and (ii) to test image reconstruction algorithms that prefer sparseness in the reconstructed images. Our approach was to utilize singular value decomposition techniques to study the imaging operator of the system and evaluate the complexity of objects that could potentially be reconstructed. We also compared the performance of two image reconstruction algorithms (algebraic reconstruction and l1-norm techniques) at reconstructing objects of increasing sparseness. We observed that for a 15-element detection scheme, the number of measureable singular vectors representative of the imaging operator was consistent with the demonstrated ability to reconstruct point and line targets in the field of view. We also observed that the l1-norm reconstruction technique, which is known to prefer sparseness in reconstructed images, was superior to the algebraic reconstruction technique. Based on these findings, we concluded (i) that singular value decomposition of the imaging operator provides valuable insight into the capabilities of a 3D photoacoustic imaging system, and (ii) that reconstruction algorithms which favor sparseness can significantly improve imaging performance. These methodologies should provide a means to optimize detector count and geometry for a multitude of 3D photoacoustic imaging applications.Proceedings of SPIE - The International Society for Optical Engineering 06/2010; · 0.20 Impact Factor
In vivo three-dimensional photoacoustic
tomography of a whole mouse head
Kwang Hyun Song
Optical Imaging Laboratory, Department of Biomedical Engineering, Texas A&M University,
College Station, Texas 77843
Department of Pathobiology, Texas A&M University, College Station, Texas 77843
Lihong V. Wang
Optical Imaging Laboratory, Department of Biomedical Engineering, Texas A&M University,
College Station, Texas 77843
Received April 4, 2006; revised May 15, 2006; accepted May 17, 2006;
posted May 26, 2006 (Doc. ID 69679); published July 25, 2006
An in vivo photoacoustic imaging system was designed and implemented to image the entire small animal
head. A special scanning gantry was designed to enable in vivo imaging in coronal cross sections with high
contrast and good spatial resolution for the first time to our knowledge. By use of a 2.25 MHz ultrasonic
transducer with a 6 mm diameter active element, an in-plane radial resolution of ?312 ?m was achieved.
Deeply seated arterial and venous vessels in the head measuring up to 1.7 cm in diameter were simulta-
neously imaged in vivo with 804 nm wavelength laser excitation of photoacoustic waves. © 2006 Optical
Society of America
OCIS codes: 170.5120, 170.3880, 170.0110.
Photoacoustic tomography (PAT) is a novel imaging
modality that is nonionizing and highly sensitive to
optical absorption of biological tissue, especially
blood in vessels.1In addition, PAT has a deeper
penetration depth than other high-resolution pure
optical imaging modalities,2,3because the latter lose
approximately one transport mean free path as a re-
sult of strong light scattering, whereas the former re-
mains unaffected. PAT combines the merits of both
optical and ultrasonic imaging and hence provides
both high optical contrast and good ultrasonic
PAT has been successfully applied to visualize the
structures of a number of different biological tissues.
Using PAT, Wang et al. obtained in vivo images of ce-
rebral blood vessels on the cortex of a rat brain where
the vessels were within 2–3 mm of the tissue
surface.6,7They presented in situ three-dimensional
mouse brain imaging by using the same system, but
the resolution for deep structures was far inferior to
that for shallow vessels.8Kruger et al. demonstrated
in situ whole-head three-dimensional imaging of a
nude mouse by use of an ultrasonic transducer
array.9In their study the deeply located blood ves-
sels, such as the circle of Willis, anterior cerebral ar-
tery, and other arterial vessels, were not imaged with
good spatial resolution or high contrast, even though
the superficial venous vessels, such as the jugular
vein around the head, were clearly imaged. In the
present study we designed an in vivo whole-mouse-
head PAT system. We successfully imaged in vivo
deep arterial vessels as well as superficial venous
vessels with high contrast and good spatial resolu-
tion in coronal views.
Figure 1 shows a schematic of the newly designed
system. To maximize the optical penetration depth
and to select an isosbestic point of molar extinction
coefficient of oxy- and deoxy-hemoglobin, we chose an
804 nm wavelength output as the excitation source
from a Q-switched Nd:YAG laser (LS-2137/2, LOTIS
TII)-pumped tunable Ti:sapphire laser (LT-2211A,
LOTIS TII). To illuminate efficiently, the excitation
light was divided by a beam splitter (BS1-784-50,
CVI Laser) into two beams, which were then deliv-
Fig. 1. Schematic of the experimental setup of photoacous-
tic tomography for in vivo whole-head small animal imag-
ing. Sa, sapphire.
August 15, 2006 / Vol. 31, No. 16 / OPTICS LETTERS
0146-9592/06/162453-3/$15.00© 2006 Optical Society of America
ered to the sample by two mirrors and homogenized
by ground glasses. The pulsed laser energy was
exposure for skin at the 804 nm wavelength10
(?15.5 mJ/cm2for each beam). To avoid generation
of strong photoacoustic (PA) signals from the surface
of the object near the ultrasonic transducer, we ap-
plied side illumination in a spirit similar to dark-field
A high signal-to-noise ratio is indispensable for de-
tecting weak PA signals from locations deep within
an object. Therefore we used a 2.25 MHz ultrasonic
transducer (V323, Panametrics, Waltham, Mass.)
with a 6 mm diameter active element and a 65.6%
bandwidth at 6 dB, where the relatively low fre-
quency and large active area are conducive to a high
signal-to-noise ratio. A flat transducer was employed
in place of a focused one to allow the application of
the modified back projection algorithm for image
reconstruction.12To minimize the interference of sur-
face signals and maximize the detection of deep sig-
nals from the head, we placed the ultrasonic trans-
ducer between two beams. Finally, the computer
acquired all of the amplified and digitized signals and
reconstructed the distribution of the optical absorp-
tion in the imaging plane.
Two particular devices in the scanning gantry, the
rotation stages and mouse holders, as shown in Fig.
1, were designed in house for in vivo imaging. The ro-
tation stages have two parts, one located at the top
and the other at the bottom, which rotate at the same
angular speed. The mouse holders are composed of a
head holder, which fixes the teeth and provides oxy-
gen, and a body holder, which fixes the body and
maintains the body temperature. The body holder is
waterproof because the animal and the ultrasonic
transducer are immersed in water to couple the PA
waves from the animal to the ultrasonic transducer.
The scanning radius of the ultrasonic transducer is
To evaluate the image resolution of the designed
system, we imaged nine carbon fibers (6 ?m in diam-
eter) and two human hairs (30 ?m in diameter) fixed
in a 15% porcine gelatin with 0.5% Intralipid-20%,
the reduced scattering coefficient of which was esti-
mated to be 2.1 cm−1.13Figure 2(a) shows the PAT
image of the phantom; bright spots indicate the high
optical absorption of the carbon fibers and hairs. Fig-
ure 2(b) shows the radial and tangential resolutions
measured from the carbon fibers in the image. The
radial resolution, defined by the FWHM of the main
lobe, is approximately 312±5 ?m (standard error),
which is close to the theoretically predicted value.12
The tangential resolution of the system deteriorates
as the imaging point moves away from the imaging
center owing to the aperture effect.5,12
A nude mouse (Harlan Company) weighing ap-
proximately 20 g was employed for in vivo head im-
aging. General anesthesia was subcutaneously ad-
ministered to the nude mouse every hour. During
data acquisition, pure oxygen was provided through
dimensional whole-head in vivo images of the nude
mouse in the coronal view. Because of the side illumi-
nation, light energy exponentially decays from the
surface inward, which results in generation of much
weaker signals in deep regions. To compensate for
light attenuation in the images, we estimated the flu-
ence distribution of light in the head by using a
Monte Carlo simulation and then normalized the re-
constructed PA image by using a two-dimensional flu-
ence map.14Because hemoglobin is the strongest op-
tical absorber in the near-IR spectral region and
generates strong PA signals, the most prominent
structures in PAT images are blood vessels. Most of
the blood vessels in a head are branches of the ca-
rotid artery and the jugular vein. Here the major
blood vessels were segmented with heuristically cho-
sen thresholds such that the segmented major ves-
sels appear in all of the pseudocolor images, which
are then superimposed on the original grayscale im-
ages. Some key vessels are identified as shown in
For whole-head PAT to be used in practical appli-
cations, the time resolution and the slice thickness
need to be improved. The current data acquisition
in gelatin. Objects are perpendicular to the imaging plane.
(Note that fibers are not exactly perpendicular to the imag-
ing plane, so distortion exists due to the slice thickness.)
The grayscale bar indicates the magnitude of optical ab-
sorption. (B) Radial and tangential resolutions with stan-
dard errors. Dashed curve with circles, radial resolution;
solid curve with squares, tangential resolution, showing
the aperture effect of the transducer.
(A) PAT image of nine carbon fibers and two hairs
OPTICS LETTERS / Vol. 31, No. 16 / August 15, 2006
time for one slice was 13 min, which can be shortened
with an ultrasonic transducer array system. The im-
aging system employed here had a large slice thick-
ness for two reasons: the wide reception angle of the
transducer in the elevation direction and the strong
light scattering inside the biological tissue. The slice
thickness (elevation resolution) is approximately
equal to the diameter of the ultrasonic transducer. A
cylindrically focused transducer
dimensional reconstruction algorithm can be used to
minimize the slice thickness. The reconstruction al-
gorithm adopted here assumed that the distribution
of light fluence and acoustic speed were homogeneous
in the imaging plane. However, because of the side il-
lumination, the distribution of light fluence was, in
fact, inhomogeneous. In addition, when PA signals
travel through heterogeneous biological tissues, such
as brain, muscle, blood vessels, skin, and trachea,
they suffer from acoustic speed aberrations. To
achieve higher accuracy, the reconstruction algo-
rithm needs to be modified to consider these two
types of heterogeneity.
In this study we accomplished in vivo three-
dimensional whole-head imaging by using PAT. We
were able to image deep arterial vessels, such as the
circle of Willis, as well as superficial venous vessels
with good spatial resolution and high contrast in
coronal views in vivo for the first time to our knowl-
edge. Previous studies have been confined to superfi-
cial or in situ imaging. We believe that our work can
be extended to the study of cerebral hemodynamic
changes by simultaneously measuring oxygen satu-
ration and cerebral blood volume, the two key param-
eters for monitoring brain activities related to brain
tumors, ischemia, stroke, etc.15
We thank Jung-Taek Oh, Meng-Lin Li, Konstantin
Maslov, Geng Ku, and Xueyi Xie for technical assis-
tance and Sergiu V. Similache for assistance with
animal handling. The project was sponsored by Na-
tional Institutes of Health grants R01 EB000712 and
R01 NS46214. L. Wang’s email address is lwang
@tamu.edu; K. H. Song’s is email@example.com.
1. S. L. Jacques and S. A. Prahl, “Absorption spectra for
biological tissues,” http://omlc.ogi.edu/.
2. V. Ntziachristos, J.Ripoll,
Weissleder, Nat. Biotechnol. 23, 313 (2005).
3. G. Ku and L.-H. Wang, Opt. Lett. 30, 507 (2005).
4. R. O. Esenaliev, A. A. Karabutov, and A. A. Oraevsky,
IEEE J. Sel. Top. Quantum Electron. 5, 981 (1999).
5. G. Ku, X. Wang, G. Stoica, and L.-H. Wang, Phys. Med.
Biol. 49, 1329 (2004).
6. X. Wang, Y. Pang, G. Ku, X. Xie, G. Stoica, and L.-H.
Wang, Nat. Biotechnol. 21, 803 (2003).
7. X. Wang, G. Ku, M. A. Wegiel, D. J. Bornhop, G. Stoica,
and L.-H. Wang, Opt. Lett. 29, 730 (2004).
8. X. Wang and L.-H. Wang, Opt. Lett. 28, 1739 (2003).
9. R. A. Kruger, W. L. Kiser Jr., D. R. Reinecke, G. A.
Kruger, and K. D. Miller, Mol. Imaging 2, 113 (2003).
10. American National Standards Institute, “American
national standard for the safe use of lasers,” ANSI
Z136.1 (American National Standards Institute, 2000).
11. K. Maslov, G. Stoica, and L.-H. Wang, Opt. Lett. 30,
12. M. Xu and L.-H. Wang, Phys. Rev. E 67, 056605 (2003).
13. S. T. Flock, S. L. Jacques, B. C. Wilson, W. M. Star, and
M. J. C. van Gemert, Lasers Surg. Med. 12, 510 (1992).
14. L.-H. Wang, S. L. Jacques, and L. Zheng, Comput.
Methods Programs Biomed. 47, 131 (1995).
15. J. F. Adam, H. Elleaume, G. L. Duc, S. Corde, A. M.
Charvet, I. Troprès, J. F. L. Bas, and F. Estève, J.
Cereb. Blood Flow Metab. 23, 499 (2003).
head photoacoustic tomography of a nude mouse in coronal
views. Images were obtained from the anterior to the pos-
terior parts of the brain with a depth separation of 1 mm
between adjacent scans. Arrows indicate higher optical ab-
sorption in blood vessels. The photographs (G) and (H) of
the cross sections were taken after PAT data acquisition for
comparison with corresponding PAT images (B) and (E), re-
spectively. 1, Anterior cerebral artery; 2, mandibular alveo-
lar artery; 3, 4, arterial vessels; 5, posterior communication
artery; 6, internal cerebral artery; 7, median fissure; 8,
venous vessel; 9, facial vein; 10, facial artery; 11, sublin-
gual artery; 12, jugular vein; 13, venous vessel.
(Color online) In vivo three-dimensional whole-
August 15, 2006 / Vol. 31, No. 16 / OPTICS LETTERS