In this work, we introduce an improved prototype of the imaging system that combines three-dimensional optoacoustic tomography (3D-OAT) and laser ultrasound tomography slicer (2D-LUT) to obtain coregistered maps of tissue optical absorption and speed of sound (SOS). The imaging scan is performed by a 360 degree rotation of a phantom/mouse with respect to a static arc-shaped array of ultrasonic transducers. A Q-switched laser system is used to establish optoacoustic illumination pattern appropriate for deep tissue imaging with a tunable (730-840 nm) output wavelengths operated at 10 Hz pulse repetition rate. For the LUT slicer scans, the array is pivoted by 90 degrees with respect to the central transducers providing accurate registration of optoacoustic and SOS maps, the latter being reconstructed using waveform inversion with source encoding (WISE) technique. The coregistered OAT-LUT modality is validated by imaging a phantom and a live mouse. SOS maps acquired in the imaging system can be employed by an iterative optoacoustic reconstruction algorithm capable of compensating for acoustic wavefield aberrations. The most promising applications of the imaging system include 3D angiography, cancer research, and longitudinal studies of biological distributions of optoacoustic contrast agents (carbon nanotubes, metal plasmonic nanoparticles, fluorophores, etc.).
Ultrasound endoscopy has been proven effective in identifying and staging relatively advanced tumors in esophageal or colon wall lining. When combined with optoacoustic imaging modality, the endoscopy examination may prove beneficial in detecting also early stage tumors as well as more accurate staging of advanced tumors based on functional - anatomical maps. Here we present a prototype of a dual-modality optoacoustic – laser ultrasound (OA-LUS) endoscopy system with enhanced imaging capabilities. The system consists of a rotating 90° off-axis parabolic reflector which is acoustically coupled to a flat 8-element transducer array. A parabolic mirror serves dual purpose of directing light towards a sample and reflecting incoming optically generated ultrasound signals towards a detector. LUS modality is enabled by placing an optically absorbing and acoustically transparent polymeric membrane in the path of laser light to generate broadband and non-reverberating transient ultrasound waves propagating towards the sample. Focused system detects ultrasound signals and reconstructs the image similar to optoacoustic mode. Presence of a delay between optically generated and reflected acoustic signals allows concurrent image acquisition in OA and LUS modalities.
A new experimental approach for measurements of temperature dependence of the Grüneisen parameter in optically absorbing solutions is proposed. Two-dimensional optoacoustic (OA) imaging is used to improve accuracy of signal amplitude measurements and spatial localization of the studied samples. We estimated OA response of optically absorbing solutions measuring median intensity of OA images within the region of interest (ROI) as a function of temperature. We showed that when normalized to its value at a particular temperature, OA image intensity becomes an accurate metric reflecting temperature changes of Grüneisen parameter regardless of local optical fluence and absorbance, assuming those remain constant with temperature. Using the proposed method we studied temperature dependence of aqueous solutions of nickel and cupric sulfate in the range from 4 to 40°C. Obtained results were compared with temperature dependence for the Grüneisen parameter of DI-water, which we measured by using carbon ink colloid. We also found that Grüneisen-temperature relationship for nickel sulfate exhibits linear trend with respect to the concentration, and is independent of coupling medium and laser excitation wavelength.In the future, the developed methodology could be adopted for important applications of in vivo optoacoustic temperature monitoring.
In this work, we investigate a novel reconstruction method for laser-induced ultrasound computed tomography (USCT) breast imaging that circumvents limitations of existing methods that rely on ray-tracing. There is currently great interest in developing hybrid imaging systems that combine optoacoustic tomography (OAT) and USCT. There are two primary motivations for this: (1) the speed-of-sound (SOS) distribution reconstructed by USCT can provide complementary diagnostic information; and (2) the reconstructed SOS distribution can be incorporated in the OAT reconstruction algorithm to improve OAT image quality. However, image reconstruction in USCT remains challenging. The majority of existing approaches for USCT breast imaging involve ray-tracing to establish the imaging operator. This process is cumbersome and can lead to inaccuracies in the reconstructed SOS images in the presence of multiple ray-paths and/or shadow zones. To circumvent these problems, we implemented a partial differential equation-based Eulerian approach to USCT that was proposed in the mathematics literature but never investigated for medical imaging applications. This method operates by directly inverting the Eikonal equation without ray-tracing. A numerical implementation of this method was developed and compared to existing reconstruction methods for USCT breast imaging. We demonstrated the ability of the new method to reconstruct SOS maps from TOF data obtained by a hybrid OAT/USCT imager built by our team.
In this work we introduce an improved prototype of three-dimensional imaging system that combines optoacoustic tomography (OAT) and laser ultrasound tomography (LUT) to obtain coregistered maps of tissue optical absorption and speed of sound (SoS). The OAT scan is performed by a 360 degree rotation of a mouse with respect to an arc-shaped array of ultrasonic transducers. A Q-switched laser system is used to establish optoacoustic illumination pattern appropriate for deep tissue imaging with a tunable (730-840 nm) output wavelengths operated at 10 Hz pulse repetition rate. A 532 nm wavelength output, being mostly absorbed within a narrow superficial layer of skin, is used to outline the visualized biological object. Broadband laser ultrasound emitters are arranged in another arc pattern and are positioned opposite and orthogonal to the array of transducers. This imaging geometry allows reconstruction of volumes that depict SoS distributions from the measured time of flight data. The reconstructed LUT images can subsequently be employed by an optoacoustic reconstruction algorithm to compensate for acoustic wavefield aberration and thereby improve accuracy of the reconstructed images of the absorbed optical energy. The coregistered OAT-LUT imaging is validated in a phantom and live mouse using a single-slice system prototype.
Gold-based contrast agents, gold nanorod (GNR), were designed for the enhancement of optoacoustic signal. After synthesis, the GNR-CTAB complexes were modified by pegylation (PEG), or replacement of CTAB (cetyl trimethylammonium bromide) with MTAB (16-mercaptohexadecyl trimethylammonium bromide) for coverage of gold nanorods with heparin (GNR-HP). Modified GNR are purified through centrifugation and filtration. GNRCTAB can be used as a model of positively charged gold surface for quantitative optoacoustic sensing in GNRbacteria interactions, whereas GNR-PEG and GNR-HP can be used as negatively charged gold surface models. We studied controlled agglomeration of contrast agents with the bacteria E.Coli and Vibrio Cholerae. For bacterial sensing, the localized plasmon resonance peak shifts as a function of electrostatic binding, which was detected with two different wavelengths through 3D optoacoustic imaging.
We report on findings from the clinical feasibility study of the ImagioTM. Breast Imaging System, which acquires two-dimensional opto-acoustic (OA) images co-registered with conventional ultrasound using a specialized duplex hand-held probe. Dual-wavelength opto-acoustic technology is used to generate parametric maps based upon total hemoglobin and its oxygen saturation in breast tissues. This may provide functional diagnostic information pertaining to tumor metabolism and microvasculature, which is complementary to morphological information obtained with conventional gray-scale ultrasound. We present co-registered opto-acoustic and ultrasonic images of malignant and benign tumors from a recent clinical feasibility study. The clinical results illustrate that the technology may have the capability to improve the efficacy of breast tumor diagnosis. In doing so, it may have the potential to reduce biopsies and to characterize cancers that were not seen well with conventional gray-scale ultrasound alone.
We developed the first prototype of dual-modality imager combining optoacoustic tomography (OAT) and laser
ultrasound tomography (UST) using computer models followed by experimental validation. The system designed
for preclinical biomedical research can concurrently yield images depicting both the absorbed optical energy
density and acoustic properties (speed of sound) of an object. In our design of the UST imager, we seek to
replace conventional electrical generation of ultrasound waves by laser-induced ultrasound (LU). While earlier
studies yielded encouraging results [Manohar, et al., Appl. Phys. Lett, 131911, 2007], they were limited to
two-dimensional (2D) geometries. In this work, we conduct computer-simulation studies to investigate different
designs for the 3D LU UST imager. The number and location of the laser ultrasound emitters, which are
constrained to reside on the cylindrical surface opposite to the arc of detectors, are optimized. In addition to
the system parameters, an iterative image reconstruction algorithm was optimized. We demonstrate that high
quality volumetric maps of the speed of sound can be reconstructed when only 32 emitters and 128 receiving
transducers are employed to record time-of-flight data at 360 tomographic view angles. The implications of the
proposed system for small animal and breast-cancer imaging are discussed.
KEYWORDS: Ultrasonography, Imaging systems, Acoustics, 3D image processing, Tomography, Visualization, Signal attenuation, 3D modeling, Ultrasound tomography, Pre-clinical research
In this work, we introduce a novel three-dimensional imaging system for in vivo high-resolution anatomical and functional whole-body visualization of small animal models developed for preclinical or other type of biomedical research. The system (LOUIS-3DM) combines a multi-wavelength optoacoustic and ultrawide-band laser ultrasound tomographies to obtain coregistered maps of tissue optical absorption and acoustic properties, displayed within the skin outline of the studied animal. The most promising applications of the LOUIS-3DM include 3D angiography, cancer research, and longitudinal studies of biological distribution of optoacoustic contrast agents (carbon nanotubes, metal plasmonic nanoparticles, etc.).
A three-dimensional mouse imaging system combining optoacoustic tomography and laser ultrasound (LOUIS-
3DM) has been developed. It features broadband laser ultrasound emitters positioned opposite an array of
transducers. This imaging geometry allows reconstruction of images that either depicts the speed of sound
distribution from measured time of flight data, or acoustic attenuation from the measured signal amplitude. We have
investigated the performance of two laser ultrasound source designs, both easily adaptable to a commercial imaging
system: small diameter source (600 μm) generated off a flat surface, and larger diameter (3 mm) spherical source.
Laser energy requirements are modest, well below 1 mJ per pulse for either design. Their performance at normal
incidence is comparable both in amplitude and frequency response. However, off-axis generation differs
dramatically and the shortcomings of the simple flat emitter design are evident. We show that, in order to achieve
optimal performance through proper illumination of the detector array, spherical wave front characteristics are
desired.
Gold nanorods (GNR) with a peak absorption wavelength of 760 nm were prepared using a seed-mediated method. A
novel protocol has been developed to replace hexadecyltrimethylammonium bromide (CTAB) on the surface of GNR
with 16-mercaptohexadecanoic acid (MHDA) and metoxy-poly(ethylene glycol)-thiol (PEG), and the monoclonal
antibodies: HER2 or CD33. The physical chemistry property of the conjugates was monitored through optical and zetapotential
measurements to confirm surface chemistry. The plasmon resonance is kept in the near infrared area, and
changes from strong positive charge for GNR-CTAB to slightly negative for GNR-PEG-mAb conjugates are observed.
The conjugates were investigated for different cells lines: breast cancer cells and human leukemia lines in vivo
applications. These results demonstrate successful tumor accumulation of our modified PEG-MHDA conjugates of GNR
for HER2/neu in both overexpressed breast tumors in nude mice, and for thermolysis of human leukemia cells in vitro.
The conjugates are non-toxic and can be used in pre-clinical applications, as well as molecular and optoacoustic imaging,
and quantitative sensing of biological substrates.
In this report we introduce a novel experimental design for non-invasive scanning optoacoustic microscopy that utilizes
an off-axis parabolic mirror. Such reflector provides ideal and lossless conversion of a spherical wavefront into a plane
wave and enables diffraction-limited ultrasound focusing. We have designed and build a custom broadband transducer
with 0-19 MHz bandwidth and nominal sensitivity of 15 μV/Pa. With 17 dB amplification and noise level of ~ 1.6 mV
the estimated sensitivity limit of our experimental setup is 15 Pa. Using the reflector with numerical aperture of 0.5, we
have demonstrated lateral resolution limit of ~ 100 micrometers in test phantoms.
We introduce a novel experimental design for non-invasive scanning optoacoustic microscopy that utilizes a parabolic
surface for ultrasound focusing. We demonstrate that off-axis parabolic mirrors made of sufficiently high acoustic
impedance materials work as ideal reflectors in a wide range of apertures and provide lossless conversion of a spherical
acoustic wavefront into a plane wave. We further test the performance of a custom optoacoustic imaging setup which
was developed and built based on these principles. The achieved resolution limit of 0.3 mm, with NA of 0.5 and the
transducer bandwidth of 5 MHz, matches the resolution limit defined by diffraction. Although further improvements of
current experimental setup are required to achieve resolution similar to leading microscopy systems, this proof-of-concept
work demonstrates the viability of the proposed design for optoacoustic microscopy applications.
We developed an optoacoustic biosensor intended for the detection of bloodborne microorganisms using
immunoaffinity reactions of antibody-coupled gold nanorods as contrast agents specifically targeted to the antigen
of interest. Optoacoustic responses generated by the samples are detected using a wide band ultrasonic transducer.
The sensitivity of the technique has been assessed by determining minimally detectable optical density which
corresponds to the minimum detectable concentration of the target viral surface antigens. Both ionic solutions and
gold nanorods served as the contrast agent generating the optoacoustic response. The sensitivity of Nano-LISA is at
least OD=10-6 which allows reliable detection of 1 pg/ml (depending on the commercial antibodies that are used).
Adequate detection sensitivity, as well as lack of non-specific cross-reaction between antigens favors NanoLISA as
a viable technology for biosensor development.
In the present work, we demonstrate a potential use of gold nanorods as a contrast agent for selective photothermal
therapy of human acute leukemia cells (HL-60) using a near-infrared laser. Gold Nanorods (GNR) are synthesized
and conjugated to CD33, a 67 kDa glycoprotein found on the surface of myeloid cells that belongs to the
sialoadhesin family of proteins. After pegylation, or conjugation with CD33 antibody, GNR were non-toxic for
acute and chronic leukemia cells. We used a Quanta System q-switched titanium sapphire laser emitting at a center
wavelength of 755 nm. Each sample was illuminated with 1 laser shot at either high or low fluence. Both laser
modes were used in 3 independent cell probes. HL-60 cells were treated for 45 min with GNR conjugated with mAb
CD33, or with GNR-Pegylated particles. After laser application, the cells were resuspended and analyzed to cell
viability with Trypan blue exclusion assay. GNR-CD33 conjugates significantly increase the percentage of cell
death as compared with a control group after laser illumination: a 3 fold increase is observed.
Optoacoustic (OA) tomography has demonstrated utility in identifying blood-rich malignancies in breast tissue. We describe the development and characterization of a laser OA imaging system for the prostate (LOIS-P). The system consists of a fiber-coupled Q-switched laser operating at 757 nm, a commercial 128-channel ultrasonic probe, a digital signal processor, and software that uses the filtered radial back-projection algorithm for image reconstruction. The system is used to reconstruct OA images of a blood-rich lesion induced in vivo in a canine prostate. OA images obtained in vivo are compared to images acquired using ultrasound, the current gold standard for guiding biopsy of the prostate. Although key structural features such as the urethra could be identified with both imaging techniques, a bloody lesion representing a highly vascularized tumor could only be clearly identified in OA images. The advantages and limitations of both forward and backward illumination modes are also evaluated by collecting OA images of phantoms simulating blood vessels within tissue. System resolution is estimated to be 0.2 mm in the radial direction of the acoustic array. The minimum detectable pressure signal is 1.83 Pa. Our results encourage further development toward a dual-modality OA/ultrasonic system for prostate imaging and image-guided biopsy.
We present our findings from a real-time laser optoacoustic imaging system (LOIS). The system utilizes a Q-switched Nd:YAG laser; a standard 128-channel ultrasonic linear array probe; custom electronics and custom software to collect, process, and display optoacoustic (OA) images at 10 Hz. We propose that this system be used during preoperative mapping of forearm vessels for hemodialysis treatment. To demonstrate the real-time imaging capabilities of the system, we show OA images of forearm vessels in a volunteer and compare our results to ultrasound images of the same region. Our OA images show blood vessels in high contrast. Manipulations with the probe enable us to locate and track arteries and veins of a forearm in real time. We also demonstrate the ability to combine a series of OA image slices into a volume for spatial representation of the vascular network. Finally, we use frame-by-frame analysis of the recorded OA video to measure dynamic changes of the crossection of the ulnar artery.
In this work we modified light illumination of the laser optoacoustic (OA) imaging system to improve the 3D
visualization of human forearm vasculature. The computer modeling demonstrated that the new illumination design that
features laser beams converging on the surface of the skin in the imaging plane of the probe provides superior OA
images in comparison to the images generated by the illumination with parallel laser beams. We also developed the
procedure for vein/artery differentiation based on OA imaging with 690 nm and 1080 nm laser wavelengths. The
procedure includes statistical analysis of the intensities of OA images of the neighboring blood vessels. Analysis of the
OA images generated by computer simulation of a human forearm illuminated at 690 nm and 1080 nm resulted in
successful differentiation of veins and arteries. In vivo scanning of a human forearm provided high contrast 3D OA
image of a forearm skin and a superficial blood vessel. The blood vessel image contrast was further enhanced after it was
automatically traced using the developed software. The software also allowed evaluation of the effective blood vessel
diameter at each step of the scan. We propose that the developed 3D OA imaging system can be used during
preoperative mapping of forearm vessels that is essential for hemodialysis treatment.
We present results from a clinical case study on imaging breast cancer using a real-time interleaved two laser
optoacoustic imaging system co-registered with ultrasound. The present version of Laser Optoacoustic Ultrasonic
Imaging System (LOUIS) utilizes a commercial linear ultrasonic transducer array, which has been modified to include
two parallel rectangular optical bundles, to operate in both ultrasonic (US) and optoacoustic (OA) modes. In OA mode,
the images from two optical wavelengths (755 nm and 1064 nm) that provide opposite contrasts for optical absorption of
oxygenated vs deoxygenated blood can be displayed simultaneously at a maximum rate of 20 Hz. The real-time aspect of
the system permits probe manipulations that can assist in the detection of the lesion. The results show the ability of
LOUIS to co-register regions of high absorption seen in OA images with US images collected at the same location with
the dual modality probe. The dual wavelength results demonstrate that LOUIS can potentially provide breast cancer
diagnostics based on different intensities of OA images of the lesion obtained at 755 nm and 1064 nm. We also present
new data processing based on deconvolution of the LOUIS impulse response that helps recover original optoacoustic
pressure profiles. Finally, we demonstrate the image analysis tool that provides automatic detection of the tumor
boundary and quantitative metrics of the optoacoustic image quality. Using a blood vessel phantom submerged in a
tissue-like milky background solution we show that the image contrast is minimally affected by the phantom distance
from the LOUIS probe until about 60-65 mm. We suggest using the image contrast for quantitative assessment of an OA
image of a breast lesion, as a part of the breast cancer diagnostics procedure.
In this report we demonstrate improved three-dimensional optoacoustic tomography in test samples. High quality
tomographic data and images were obtained from phantom of mice being 2.5 cm in diameter. Capillaries filled with
cupric sulfate, ferrous sulfate and nickel sulfate solutions, and immersed in a scattering medium were used for these
tests. The brightness of reconstructed phantom images was found to match accurately the absorption profiles of test
solutions. Hence, optoacoustic imaging can be applied in preclinical research to perform in vivo absorptivity
measurements to deduce functional information on blood oxygen levels or concentration of contrast agents.
We have investigated the limitations of our laser ultrasonic plane wave δ-source. In theory, the device is capable of
producing an acoustic impulse with a bandwidth exceeding 30 MHz. However, a bandwidth of 12 MHz is measured with
a calibrated wideband hydrophone. A test setup was designed and built. It permits the investigation of experimental
parameters that alter the generated acoustic impulse: laser pulse duration, laser spatial profile, and absorber opacity.
Laser energy spatial profile is the main contributor to the narrowing of the frequency band. Our findings are presented,
along with further justifications for a device with very large effective area.
We develop a system for three-dimensional whole-body optoacoustic tomography of small animals for applications in preclinical research. The tomographic images are obtained while the objects of study (phantoms or mice) are rotated within a sphere outlined by a concave arc-shaped array of 64 piezocomposite transducers. Two pulsed lasers operating in the near-IR spectral range (755 and 1064 nm) with an average pulsed energy of about 100 mJ, a repetition rate of 10 Hz, and a pulse duration of 15 to 75 ns are used as optical illumination sources. During the scan, the mouse is illuminated orthogonally to the array with two wide beams of light from a bifurcated fiber bundle. The system is capable of generating images of individual organs and blood vessels through the entire body of a mouse with spatial resolution of ~0.5 mm.
We designed, fabricated and tested the laser optoacoustic imaging system for breast cancer detection (LOIS-64), which fuses optical and acoustic imaging techniques in one modality by utilizing pulsed optical illumination and ultrawide-band ultrasonic detection of resulting optoacoustic (OA) signals. The system was designed to image a single breast slice in craniocaudal or mediolateral projection with an arc-shaped array of 64 ultrawide-band acoustic transducers. The system resolution on breast phantoms was at least 0.5 mm. The single-channel sensitivity of 1.66 mV/Pa was estimated to be sufficient for single-pulse imaging of 6 to 11 mm tumors through the whole imaging slice of the breast. The implemented signal processing using the wavelet transform allowed significant reduction of the low-frequency (LF) acoustic noise, allowed localization of the optoacoustic signals from tumors, and enhanced the contrast and sharpened the boundaries of the optoacoustic images of the tumors. During the preliminary clinical studies on 27 patients, the LOIS-64 was able to visualize 18 out of 20 malignant lesions suspected from mammography and ultrasound images and confirmed by the biopsy performed after the optoacoustic tomography (OAT) procedure.
We demonstrated the ability to detect surface antigens, associated with pathogens, utilizing laser optoacoustic
spectroscopy with antibody-coupled gold nanorods (GNR) as a contrast agent specifically targeted to the antigen of
interest. The sensitivity of the technique has been assessed by determining the minimum detectable concentration of a
surface antigen from biological samples. We compared the sensitivity and applicability of two different methods for
detecting optoacoustic responses, using either optical or piezoelectric sensors. Biological samples were adsorbed to the
inside walls of detachable, flat-bottomed plastic micro-wells, and then probed with appropriate antibodies conjugated
with gold nanorods. If the target antigens were present, the antibody-nanoparticle conjugates were bound, while any
nonadsorbed nanoparticles were washed out of the wells. Optoacoustic signals were generated from the bound nanorods
using a pulsed pump laser at wavelengths corresponding to one of the peak absorptions of the nanorods. Optoacoustic
responses were obtained from the samples using both detection modalities. The sensitivity, suitability, ease of use of
each method were assessed and compared. Initial results indicate that optical detection gives comparable sensitivity as
the piezoelectric method, and further enhancement of the detection sensitivity is possible for both methods. An
advantage of the piezoelectric detection method is that it may be implemented in a more compact assembly, compared to
the optical method, however, the optical method may be less sensitive to external electromagnetic and acoustic noise.
Further evaluation will be required to refine these measurements. The results with both methods indicate that the use of
antibody-targeted nanorod contrast agents, with laser-optoacoustic detection, is a promising technology for the
development of rapid in vitro diagnostic tests.
KEYWORDS: Transducers, Acoustics, Sensors, Calibration, Wavefronts, Ultrasonography, Signal attenuation, Pulsed laser operation, Image restoration, Signal to noise ratio
Comprehensive characterization of optoacoustic transducers is achieved through the analysis of their frequency
response using a procedure of measuring angular dependence of the transducer sensitivity to the ultrawide-band
delta pulse. The testing was performed under standard repeatable operating conditions. Back-illumination of a
blackened, acoustically matched, planar surface with a short laser pulse creates an acoustic impulse which was used
as an ultrawide-band ultrasonic source. The bandwidth of such a source extends well over 10 MHz (6dB point at 16
MHz for illumination with a 16 ns pulse) and the low frequency
roll-off is around 300 kHz. Analysis of the angular
dependence of the frequency response yields invaluable directivity information about the detector under study,
which in turn permits accurate forward and inverse problem models.
We developed a 3D whole-body optoacoustic tomography system for applications in preclinical research on mice. The
system is capable of generating images with resolution better than 0.6 mm. Two pulsed lasers, an Alexandrite laser
operating at 755 nm and a Nd:YAG laser operating at 532 nm and 1064nm were used for light delivery. The
tomographic images were obtained while the objects of study (phantoms or mice) were rotated within a sphere outlined
by a concave arc-shaped array of 64 piezo-composite transducers. During the scan, the mouse was illuminated
orthogonally to the array with two wide beams of light from a bifurcated fiber bundle. Illumination at 532 nm showed
superficial vasculature, but limited penetration depth at this wavelength prevented the detection of deeper structures.
Illumination at 755 and 1064 nm showed organs and blood vessels, respectively. Filtering of the optoacoustic signals
using high frequency enhancing wavelets further emphasized the smaller blood vessels.
We describe two laser optoacoustic imaging systems for breast cancer detection based on arrays of acoustic detectors
operated manually in a way similar to standard ultrasonic breast imaging. The systems have the advantages of standard
light illumination (regardless of the interrogated part of the breast), the ability to visualize any part of the breast, and
convenience in operation. The first system could work in both ultrasonic and optoacoustic mode, and was developed
based on a linear ultrasonic breast imaging probe with two parallel rectangular optical bundles. We used it in a pilot
clinical study to provide for the first time demonstration that the boundaries of the tumors visualized on the optoacoustic
and ultrasonic images matched. Such correlation of coregistered images proves that the objects on both images
represented indeed the same tumor. In the optoacoustic mode we were also able to visualize blood vessels located in the
neighborhood of the tumor. The second system was proposed as a circular array of acoustic transducers with an axisymmetric
laser beam in the center. It was capable of 3D optoacoustic imaging with minimized optoacoustic artifacts
caused by the distribution of the absorbed optical energy within the breast tissue. The distribution of optical energy
absorbed in the bulk tissue of the breast was removed from the image by implementing the principal component analysis
on the measured signals. The computer models for optoacoustic imaging using these two handheld probes were
developed. The models included three steps: (1) Monte Carlo simulations of the light distribution within the breast
tissue, (2) generation of optoacoustic signals by convolving
N-shaped pressure signals from spherical voxels with the
shape of individual transducers, and (3) back-projecting processed optoacoustic signals onto spherical surfaces for image
reconstruction. Using the developed models we demonstrated the importance of the included spatial impulse response of
the optoacoustic imaging system.
We developed an improved signal and image processing of optoacoustic data collected by our laser optoacoustic
imaging system designed for breast cancer detection (LOIS-B). The implemented wavelet-based signal processing
allowed significant reduction of the low-frequency acoustic noise, improved contrast and localization of the optoacoustic
sources of interest. The system was able to differentiate phantoms mimicking breast tumors based on the contrast and
morphology of their images. The implemented wavelet-based signal processing also facilitated high (0.5 mm) resolution
of the phantoms mimicking parallel blood vessels in the presence of large-amplitude low-frequency acoustic artifacts.
The application of the 3D radial back projection image reconstruction algorithm allowed visulaization of the tumor
phantoms located beyond the imaging slice of the arc-shaped array of transducers. The visualization of slices parallel to
the array of transducers with individual adjustment of the image palette for each particular slice eliminated the image
artifacts caused by the large gradient of the laser fluence orthogonal to the array of transducers.
Ultrasound imaging is the current gold standard for guiding biopsy of prostate. Optoacoustic imaging yields higher
contrast in detection of malignant tissues. The two techniques provide complementary information. We are currently
developing a hybrid laser optoacoustic and ultrasound imaging system for prostate tumor detection (LOUIS-P). The
optoacoustic part consists of a fiber-coupled Q-switched laser operating at either 757 nm or 1064 nm attached to a
commercially-available 128-channel ultrasonic probe modified for optimal detection of optoacoustic signals, a digital
signal processor with 128 independent channels, and software that uses the radial (filtered) backprojection algorithm to
reconstruct tomographic images. We evaluated system-imaging performance using test objects submerged in milky
water, and poly(vinyl-chloride) plastisol tissue phantoms simulating malignant lesions. LOUIS-P demonstrates potential
as a clinical technique for minimally invasive imaging and diagnosis of prostate cancer.
A three-dimensional laser optoacoustic imaging system was developed, which combines the advantages of optical
spectroscopy and high resolution ultrasonic detection, to produce high contrast maps of optical absorbance in tissues.
This system was tested in a nude mouse model of breast cancer and produced tissue images of tumors and vasculature.
The imaging can utilize either optical properties of hemoglobin and oxyhemoglobin, which are the main endogenous
tissue chromophores in the red and near-infrared spectral ranges, or exogenous contrast agent based on gold nanorods.
Visualization of tissue molecules targeted by the contrast agent provides molecular information. Visulization of blood at
multiple colors of light provides functional information on blood concentration and oxygen saturation. Optoacoustic
imaging, using two or more laser illumination wavelengths, permits an assessment of the angiogenesis-related
microvasculature, and thereby, an evaluation of the tumor stage and its metastatic potential.
The optoacoustic imaging system was also used to generate molecular images of the malignancy-related receptors
induced by the xenografts of BT474 mammary adenocarcinoma cells in nude mice. The development of the latter images
was facilitated by the use of an optoacoustic contrast agent that utilizes gold nanorods conjugated to monoclonal
antibody raised against HER2/neu antigens. These nanorods possess a very strong optical absorption peak that can be
tuned in the near-infrared by changing their aspect ratio. The effective conversion of the optical energy into heat by the
gold nanorods, followed by the thermal expansion of the surrounding water, makes these nanoparticles an effective
optoacoustic contrast agent. Optical scattering methods and x-ray tomography may also benefit from the application of
this contrast agent. Administration of the gold nanorod bioconjugates to mice resulted in an enhanced contrast of breast
tumors relative the background of normal tissues in the nude mouse model. The combination of this novel contrast agent
and optoacoustic imaging has the potential to become a useful imaging modality, for preclinical research in murine
models of cancer and other human diseases.
In an effort of developing clinical LANTCET (laser-activated nano-thermolysis as cell elimination technology) we
achieved selective destruction of individual tumor cells through laser generation of vapor microbubbles around clusters
of light absorbing gold nanorods (GNR) selectively formed in target tumor cells. Among all gold nanoparticles,
nanorods offer the highest optical absorption in the near-infrared. We applied covalent conjugates of gold nanorods with
targeting vectors such as monoclonal antibodies CD33 (specific for Acute Myeloid Leukemia), while GNR conjugates
with polyethylene-glycol (PEG) were used as nonspecific targeting control. GNR clusters were formed inside the tumor
cells at 37 °C due to endocytosis of large concentration of nanorods accumulated on the surface of tumor cells targeted at
4 °C. Formation of GNR clusters significantly reduces the threshold of tumor cell damage making LANTCET safe for
normal cells. Appearance of GNR clusters was verified directly with optical resonance scattering microscopy.
LANTCET was performed in vitro with living cells of (1) model myeloid K562 cells (CD33 positive), (2) primary
human bone marrow CD33-positive blast cells from patients diagnosed with acute myeloid leukemia. Laser-induced
microbubbles were generated and detected with a photothermal microscope equipped with a tunable Ti-Sa pulsed laser.
GNT cluster formation caused a 100-fold decrease in the threshold optical fluence for laser microbubble generation in
tumor cells compared with that in normal cells under the same targeting and irradiation conditions. Combining imaging
based on resonance optical scattering with photothermal imaging of microbubbles, we developed a method for detection,
image-guided treatment and monitoring of LANTCET. Pilot experiments were performed in flow mode bringing
LANTCET closer to reality of clinical procedure of purging tumor cells from bone marrow grafts.
The development of gold nanoparticles for molecular optoacoustic imaging is a very promising area of research and development. Enhancement of optoacoustic imaging for molecular detection of tumors requires the engineering of nanoparticles with geometrical and molecular features that can enhance selective targeting of malignant cells while optimizing the sensitivity of optoacoustic detection.
In this article, cylindrical gold nanoparticles (i.e. gold nanorods) were fabricated with a plasmon resonance frequency in the near infra-red region of the spectrum, where deep irradiation of tissue is possible using an Alexandrite laser. Gold nanorods (Au-NRs) were functionalized by covalent attachment of Poly(ethylene glycol) to enhance their biocompatibility. These particles were further functionalized with the aim of targeting breast cancer cells using monoclonal antibodies that binds to Her2/neu receptors, which are over expressed on the surface of breast cancer cells. A custom Laser Optoacoustic Imaging System (LOIS) was designed and employed to image nanoparticle-targeted cancer cells in a phantom and PEGylated Au-NRs that were injected subcutaneously into a nude mouse. The results of our experiments show that functionalized Au-NRs with a plasmon resonance frequency at near infra-red region of the spectrum can be detected and imaged in vivo using laser optoacoustic imaging system.
We have designed, fabricated and tested a new laser optoacoustic imaging system (LOIS-64/16) for quantitative
optoacoustic tomography of breast cancer. The system was designed to create a single slice of an optoacoustic image of
the breast with 64 ultrawide band acoustic transducers. Other 16 transducers on the back of the acoustic probe were used
to reconstruct the light distribution inside the breast. The system resolution was at least 0.5 mm for high-aspect-ratio
objects. Maximum system sensitivity was 4.8 mV/Pa and the RMS noise of 3.1 mV, which allowed imaging of small
(less than 1 cm) tumors at depths over 3 cm. The directivity of the optoacoustic transducers used in LOIS-64/16 assured
that the signal detection was better than 70% of the maximum for about 75% of the imaging slice and reduced quickly
for signals coming from out of the imaging slice. Implemented signal processing allowed significant reduction of the
low-frequency acoustic noise and localizing the small OA signals. The system was able to differentiate phantoms
mimicking tumors and malformations visualized in clinics based on the contrast and morphology of their images
obtained at 1064 nm and 757 nm.
A contrast agent for optoacoustic imaging and laser therapy of early tumors is being developed based on gold
nanocolloids strongly absorbing visible and near-infrared light. The optoacoustic signals obtained from gold nanospheres
and gold nanorods solutions are studied. In the case of 100 nm nanospheres as an example, a sharp increase in the total
area under the curve of the optoacoustic signal is observed when the laser fluence is increased beyond a threshold value
of about 0.1 J/cm2. The change in the optoacoustic signal profile is attributed to the formation of water vapor bubbles
around heated nanoparticles, as evidenced via thermoacoustic microscopy experiments. It has been determined that,
surprisingly, gold nanoparticles fail to generate detectable nanobubbles upon irradiation at the laser fluence of ~2
mJ/cm2, which heats the nanoparticles up to 374°C, the critical temperature of water. Only when the estimated
temperature of the particle reaches about 10,000°C, a marked increase of the optoacoustic pressure amplitude and a
changed profile of the optoacoustic signals indicate nanobubble formation. A nanoparticle based contrast agent is the
most effective if it can be activate by laser pulses with low fluence attainable in the depth of tissue. With this goal in
mind, we develop targeting protocols that form clusters of gold nanocolloid in the target cells in order to lower the
bubble formation threshold below the level of optical fluence allowed for safe laser illumination of skin. Experiments
and modeling suggest that formation of clusters of nanocolloids may improve the sensitivity of optoacoustic imaging in
the detection of early stage tumors.
We have designed, fabricated and tested a new 128-channel laser optoacoustic imaging system (LOIS-128) for cancer
diagnostics consisting of an acoustic probe with 128 PVDF transducers, a digital signal processor with 128 independent
channels, and software for reconstruction of optoacoustic images. The system was capable of continuous planar imaging
(at rates up to 1 Hz) of small (less than 1 cm) tumors at depths over 6 cm. The directivity of the optoacoustic transducers
used in LOIS-128 assured that signal detection at all angles within a narrow imaging slice was at least 40% of the
maximal signal. The signal detection was better than 70% of the maximum for about 75% of the image in the image
slice and close to zero for signals coming from out of the image slice. LOIS-128 could image high-aspect-ratio objects
with about 0.5 mm resolution. Finally, with the designed image reconstruction algorithm we were able to estimate
absorption coefficients for test objects with accuracy of at least 5%.
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