Gold nanoparticles have received much attention due to their potential diagnostic and therapeutic applications. Gold
nanoparticles are attractive in many biomedical applications because of their biocompatibility, easily modifiable
surfaces for targeting, lack of heavy metal toxicity, wide range of sizes (35-100 nm), tunable plasmonic resonance
peak, encapsulated site-specific drug delivery, and strong optical absorption in the near-infrared regime. Specifically,
due to their strong optical absorption, gold nanoparticles have been used as a contrast agent for molecular photoacoustic
(PA) imaging of tumor. The plasmonic resonance peak of the gold nanocages (AuNCs) was tuned to the near-infrared
region, and the ratio of the absorption cross-section to the extinction cross-section was approximately ~70%, as
measured by PA sensing. We used PEGylated gold nanocages (PEG-AuNCs) as a passive targeting contrast agent on
melanomas. After 6-h intravenous injection of PEG-AuNCs, PA amplitude was increased by ~14 %. These results
strongly suggest PA imaging paired with AuNCs is a promising diagnostic tool for early cancer detection.
This study demonstrates a method for measuring the optical absorption cross-sections (σa) of Au-Ag nanocages and Au
nanorods using photoacoustic (PA) sensing. PA signals are directly proportional to the absorption coefficient (μa) of the
nanostructure. For each type of nanostructure, we first obtained μa from the PA signal by benchmarking against a linear
calibration curve (PA signal vs. μa) derived from a set of methylene blue solutions with different concentrations. We
then calculated σa by dividing the μa by the corresponding concentration of the Au nanostructure. Additionally, we
obtained the extinction cross-section (σe, sum of absorption and scattering cross-sections) from the extinction spectrum
recorded using a conventional UV-vis-NIR spectrometer. From the measurements of σa and σe, we were able to easily
derive both the absorption and scattering cross-sections for each type of gold nanostructure. This method can potentially
provide the optical absorption and scattering properties of gold nanostructures and other types of nanomaterials.
The purpose of this study is to map non-invasively sentinel lymph nodes (SLNs) and lymphatic vessels of rats in vivo
using FDA-approved indocyanine green (ICG) and two non-ionizing imaging modalities: volumetric spectroscopic
photoacoustic (PA) imaging, which measures optical absorption, and planar fluorescence imaging, which measures
fluorescent emission. SLNs and lymphatic vessels were clearly visible after a 0.2 ml-intradermal-injection of 1 mM ICG
in both imaging systems. We also imaged deeply positioned lymph nodes in vivo by layering biological tissues on top of
rats. These two modalities, when used together with ICG, have the potential to map SLNs in axillary staging and to
study tumor metastasis in breast cancer patients.
We have succeeded in implementing ring-shaped light illumination ultrasound-modulated optical tomography (UOT) in reflection mode. The system used intense acoustic bursts and a charge-coupled device (CCD) camera-based speckle contrast detection method. In addition, the implementation allows placing the tissue sample below (not within) an acoustic coupling water tank and scanning the tissue without moving the sample. Thus, the UOT system is more clinically applicable than previous transmission-mode systems. Furthermore, we have successfully imaged an ex vivo methylene-blue-dyed sentinel lymph node (SLN) embedded at a depth of 13 mm in chicken breast tissue. This UOT system offers several advantages: noninvasiveness, nonionizing radiation, portability, cost effectiveness, and the possibility of combination with ultrasound pulse-echo imaging and photoacoustic imaging. One potential application of the UOT system is mapping SLNs in axillary staging for breast cancer patients.
Sentinel lymph node biopsy (SLNB) has been widely performed and become the standard procedure for axillary staging
in breast cancer patients. In current SLNB, identification of SLNs is prerequisite, and blue dye and/or radioactive
colloids are clinically used for mapping. However, these methods are still intraoperative, and especially radioactive
colloids based method is ionizing. As a result, SLNB is generally associated with ill side effects. In this study, we have
proposed near-infrared Au nanocages as a new tracer for noninvasive and nonionizing photoacoustic (PA) SLN mapping
in a rat model as a step toward clinical applications. Au nanocages have great features: biocompatibility, easy surface
modification for biomarker, a tunable surface plasmon resonance (SPR) which allows for peak absorption to be
optimized for the laser being used, and capsule-type drug delivery. Au nanocage-enhanced photoacoustic imaging has
the potential to be adjunctive to current invasive SLNB for preoperative axillary staging in breast cancer patients.
We have succeeded in implementing ring-shaped light illumination ultrasound-modulated optical tomography (UOT) in
both transmission and reflection modes. These systems used intense acoustic bursts and a charge-coupled device
camera-based speckle contrast detection method. By mounting an ultrasound transducer into an optical condenser, we
can combine the illuminating light component with the ultrasound transducer. Thus, the UOT system is more clinically
applicable than previous orthogonal mode systems. Furthermore, we have successfully imaged an ex vivo
methyleneblue-dyed sentinel lymph node (SLN) embedded deeper than 12 mm, the mean depth of human sentinel lymph nodes, in
chicken breast tissue. These UOT systems offer several advantages: noninvasiveness, nonionizing radiation, portability,
cost-effectiveness, and possibility of combination with ultrasound pulse-echo imaging and photoacoustic imaging. One
potential application of the UOT systems is mapping SLNs in axillary staging for breast cancer patients.
Sentinel lymph node biopsy (SLNB), a less invasive alternative to axillary lymph node dissection (ALND), is routinely
used in clinic for staging breast cancer. In SLNB, lymphatic mapping with radio-labeled sulfur colloid and/or blue dye
helps identify the sentinel lymph node (SLN), which is most likely to contain metastatic breast cancer. Even though
SLNB, using both methylene blue and radioactive tracers, has a high identification rate, it still relies on an invasive
surgical procedure, with associated morbidity. In this study, we have demonstrated a non-invasive single-walled carbon
nanotube (SWNT)-enhanced photoacoustic (PA) identification of SLN in a rat model. We have used single-walled
carbon nanotubes (SWNTs) as a photoacoustic contrast agent to map non-invasively the sentinel lymph nodes (SLNs) in
a rat model in vivo. We were able to identify the SLN non-invasively with high contrast to noise ratio (~90) and high
resolution (~500 μm). Due to the broad photoacoustic spectrum of these nanotubes in the near infrared wavelength
window we could easily choose a suitable light wavelength to maximize the imaging depth. Our results suggest that this
technology could be a useful clinical tool, allowing clinicians to identify SLNs non-invasively in vivo. In the future,
these contrast agents could be functionalized to do molecular photoacoustic imaging.
Sentinel lymph node biopsy (SLNB) has become the standard method of axillary staging for patients with breast cancer and clinically negative axillae. Even though SLNB using both methylene blue and radioactive tracers has a high identification rate, it still relies on an invasive surgical procedure with associated morbidity. Axillary ultrasound has emerged as a diagnostic tool to evaluate the axilla, but it can only assess morphology and cannot specifically identify sentinel lymph nodes (SLNs). In this pilot study, we propose a noninvasive photoacoustic SLN identification system using methylene blue injection in a rat model. We successfully image a SLN with high optical contrast (146±41, standard deviation) and good ultrasonic resolution (~500 µm) in vivo. We also show potential feasibility for clinical applications by imaging 20- and 31-mm-deep SLNs in 3-D and 2-D, respectively. Our results suggest that this technology would be a useful clinical tool, allowing clinicians to identify SLNs noninvasively in vivo.
We apply ultrasound-modulated optical tomography (UOT) to image ex-vivo methylene-blue-dyed sentinel lymph nodes embedded in 3.2-cm-thick chicken breast tissues. The UOT system is implemented for the first time using ring-shaped light illumination, intense acoustic bursts, and charge-coupled device (CCD) camera-based speckle contrast detection. Since the system is noninvasive, nonionizing, portable, relatively cost effective, and easy to combine with photoacoustic imaging and single element ultrasonic pulse-echo imaging, UOT can potentially be a good imaging modality for the detection of sentinel lymph nodes in breast cancer staging in vivo.
A deep reflection-mode photoacoustic imaging system was developed and demonstrated to possess a maximum imaging
depth up to 38 mm in chicken breast tissue. Using this system, structures in the thoracic cavity and vasculature in
cervical area of rats were clearly imaged. Particularly, part of the heart was imaged. In the thoracic cavity, the right
atrium imaged, which is one of deepest, was situated ~7 mm deep. In the cervical area, common carotid artery and
jugular vein were imaged, which are appropriate for the study of oxygenation between artery and vein. In the abdominal
cavity, the embedded structures of a kidney, spinal cord, and vena cava inferior were also clearly imaged in situ and in
vivo. The depth of the vena cava inferior was as deep as ~15 mm in vivo. This study shows the depth capability of the
system in animals. This imaging modality can be a useful tool to diagnose the disease of organs by assessing the
morphological and functional changes in the blood vessels and the organs.
A reflection-mode photoacoustic (PA) imaging system was designed and built to image deep structures in biological tissues. We chose near-infrared laser pulses of 804-nm wavelength for PA excitation to achieve deep penetration. To minimize unwanted surface signals, we adopted dark-field ring-shaped illumination. This imaging system employing a 5-MHz spherically focused ultrasonic transducer provides penetration up to 38 mm in chicken breast tissue. At the 19-mm depth, the axial resolution is 144 µm and the transverse resolution is 560 µm. Internal organs of small animals were imaged clearly.
A deep reflection-mode photoacoustic (PA) imaging system was designed and implemented to visualize deep structures
in biological tissues. To achieve good penetration depth, we chose near IR laser pulses at 804 nm wavelength for the
generation of photoacoustic waves. To avoid overshadowing the deep PA signals by the surface PA signals, we
employed dark-field illumination. To achieve good lateral resolution, we chose spherically focused high-numericalaperture
ultrasonic transducers with 5 MHz or 10 MHz center frequencies. By using these transducers, we achieved 153
&mgr;m and 130 &mgr;m axial resolutions, respectively, at 19.5 mm depth in 10% porcine gelatin containing 1% intralipid. The
system was applied to imaging internal organs of small animals. Compared with our previous high-frequency (50-MHz)
photoacoustic microscope, we scaled up the imaging depth while maintaining the ratio of the imaging depth to axial
resolution more than 100. In addition, we studied the scalability of the imaging depth and the resolution with ultrasound
frequency.
KEYWORDS: Head, Transducers, In vivo imaging, Brain, Optical fibers, Blood vessels, Photoacoustic tomography, 3D image processing, Image resolution, Imaging systems
A three-dimensional in vivo near-infrared photoacoustic tomography imaging system was newly designed and built to
visualize the structure of a whole small animal head. For high sensitivity, a single flat 2.25MHz low frequency
transducer, whose active element size is 6mm, was employed. To increase the penetration depth of light, a wavelength
of 804nm in the NIR range, which matches the oxy- and deoxy-hemoglobin isosbestic point, was chosen. To avoid
strong photoacoustic signal generation from the skin surface, we applied dark field illumination. To illuminate
efficiently, we split the laser light into two beams, which were delivered to an animal by two mirrors and were finally
homogenized by two ground glasses. To complete the dark field illumination, the transducer was located in the middle
of two light sources. Two key devices for the in vivo imaging were rotating devices and animal holders. The rotating
devices were composed of two parts, located at the top and bottom, which rotated at the same angular speed. The
holders were composed of a head holder and a body holder. Both holders fixed the animal firmly to reduce motion
artifacts. This system achieved radial resolution of up to 260μm. We accomplished successful in vivo imaging of arterial
and venous vessels deeply, as well as superficially, with the animal head of up to 1.7cm diameter. The technique forms
a basis for functional imaging, such as measurement of the oxygen consumption ratio in the brain, which is a vital
parameter in a brain disease research.
In this study, we demonstrate the potential of photoacoustic tomography for the study of traumatic brain injury (TBI) in rats in vivo. Based on spectroscopic photoacoustic tomography that can detect the absorption rates of oxy- and deoxy-hemoglobins, the blood oxygen saturation and total blood volume in TBI rat brains were visualized. Reproducible cerebral trauma was induced using a fluid percussion TBI device. The time courses of the hemodynamic response following the trauma initiation were imaged with multi-wavelength photoacoustic tomography with bandwidth-limited spatial resolution through the intact skin and skull. In the pilot set of experiments, trauma induced hematomas and blood oxygen saturation level changes were detected, a finding consistent with the known physiological responses to TBI. This new imaging method will be useful for future studies on TBI-related metabolic activities and the effects of therapeutic agents.
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