Using optoacoustic imaging for measuring the temperature dependence of Grüneisen parameter in optically absorbing solutions.

Grüneisen parameter is a key temperature-dependent physical characteristic responsible for thermoelastic efficiency of materials. We propose a new methodology for accurate measurements of temperature dependence of Grüneisen parameter in optically absorbing solutions. We use two-dimensional optoacoustic (OA) imaging to improve accuracy of measurements. Our approach eliminates contribution of local optical fluence and absorbance. To validate the proposed methodology, we studied temperature dependence of aqueous cupric sulfate solutions in the range from 22 to 4 °C. Our results for the most diluted salt perfectly matched known temperature dependence for the Grüneisen parameter of water. We also found that Grüneisen-temperature relationship for cupric sulfate exhibits linear trend with respect to the concentration. In addition to accurate measurements of Grüneisen changes with temperature, the developed technique provides a basis for future high precision OA temperature monitoring in live tissues.

Laser optoacoustic imaging system for detection of breast cancer.

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 mVPa 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.

Finesse and sensitivity gain in cavity-enhanced absorption spectroscopy of biomolecules in solution.

We describe a 'wet mirror' apparatus for cw cavity-enhanced absorption measurements with Bacteriochlorophyll a (BChla) in solution and show that it achieves the full sensitivity gain ( approximately 2.3 x 10(4)) afforded by the finesse (3.4 x 10(4)) and loss distribution of our optical resonator. This result provides an important proof-of-principle demonstration for solution-phase cavity-enhanced spectroscopy; straightforward extrapolation to a system with state-of-the-art low-loss mirrors and shot-noise-limited performance indicates that single molecule sensitivity in liquids is within reach of current technology. With the probe laser locked to the cavity resonance, our instrument achieves a sensitivity approximately 3.4 x 10(-8)/ radicalHz (for a sample of length 1.75 mm) with 100 kHz bandwidth and can reliably detect sub-nM concentrations of BChla with 1 ms integration time.

Laser nanothermolysis of human leukemia cells using functionalized plasmonic nanoparticles.

In the present work, we present the use of gold nanorods as plasmonic nanoparticles for selective photothermal therapy of human acute (HL-60) and chronicle (K-562) leukemia cells using a near-infrared laser. We improved a published methodology of gold nanorods conjugation to generate high yields of narrow band gold nanorods with an optical absorption centered at 760 nm. The manufactured nanorods were pegylated and conjugated with monoclonal antibody to become non-toxic as biocompatible nanothermolysis agent. Gold nanorods are synthesized and conjugated to CD33 monoclonal antibody. After pegylation, or conjugation with CD33 antibody, gold nanorods were non-toxic to acute and chronic leukemia cells. Our modified gold nanorods CD33 conjugates shown high level of accumulation for both leukemia cell lines, and successful used for nanothermolysis of human leukemia cells in vitro. Each sample was illuminated with 1 or 3 laser shots as for low and for high laser fluence. The radiation was provided by a Quanta Systems q-switched titanium sapphire laser, and the system was designed for maximum sample coverage using non-focused illumination. HL-60 and K-562 cells were treated for 45 min with gold nanorods CD33 conjugated, or with pegylated gold nanorods. The effect of pulsed-laser nanothermolysis for acute and chronic leukemia cells were investigated with cell counting for number of living cells, percentage of cell death and functional parameters such as damage of cell membrane and metabolic activity. Gold nanorods CD33 conjugates significantly increase cell damage for low fluence laser and completely destroyed cancer cells after 3 pulses for low fluence (acute leukemia) and for high fluence laser as for HL-60 (acute) and for K-562 (chronicle) leukemia cells.

Biocompatible Gold Nanorod Conjugates for Preclinical Biomedical Research.

Gold nanorods 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 on the surface of the nanorods with 16-mercaptohexadecanoic acid and metoxy-poly(ethylene glycol)-thiol, and the monoclonal antibody HER2. The physical chemistry properties of the conjugates were monitored through optical and zeta-potential measurements to confirm surface chemistry changes. The efficiency of the modifications was quantified through measurement of the average number of antibodies per gold nanorod. The conjugates were investigated for different cells lines: BT-474, MCF7, MCF10, MDCK, and fibroblast. The results show successful cell accumulation of the gold nanorod HER2 conjugates in cells with HER2 overexpression. Incubation of the complexes in heparinized mouse blood demonstrated the low aggregation of the metallic particles through stability of the spectral properties, as verified by UV/VIS spectrometry. Cytotoxicity analysis with LDH release and MTT assay confirms strong targeting and retention of functional activity of the antibody after their conjugation with gold nanorods. Silver staining confirms efficient specific binding to BT-474 cells even in cases where the nanorod complexes were incubated in heparinized mouse blood. This is confirmed through in vivo studies where, following intravenous injection of gold nanorod complexes, silver staining reveals noticeably higher rates of specific binding in mouse tumors than in healthy liver.The conjugates are reproducible, have strong molecular targeting capabilities, have long term stability in vivo and can be used in pre-clinical applications. The conjugates can also be used for molecular and optoacoustic imaging, quantitative sensing of biological substrates, and photothermal therapy.

Highly purified biocompatible gold nanorods for contrasted optoacoustic imaging of small animal models.

We developed a methodology for high yield synthesis of gold nanorods (GNR) with narrow band optical absorption centered at 760 nm. GNR were purified from hexadecyltrimethylammonium bromide (CTAB) and coated with polyethylene glycol (PEG). The molar ratio between GNR and PEG (1÷50000) was optimized to make the conjugate a biocompatible PEG-GNR contrast agent for optoacoustic (OA) imaging. In vitro toxicity studies showed no significant change in survival rates of cultured normal (IEC-6, MDCK) and cancer (SKBR3 and HEPG2) cells after they were incubated with 0.125 to 1.25 nM PEG-GNR solutions. In vivo toxicity studies in nude mice showed no pathological changes in liver after the IV injection of GNR. Significant enhancements of OA contrast in comparison to images of untreated mice were observed 1 hour after the GNR injection in a dose of 20 mg gold per kg of body mass.

Real-time optoacoustic monitoring and three-dimensional mapping of a human arm vasculature.

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.

Optoacoustic imaging of the prostate: development toward image-guided biopsy.

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.

Whole-body three-dimensional optoacoustic tomography system for small animals.

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 approximately 0.5 mm.

Measurement of the spectral directivity of optoacoustic and ultrasonic transducers with a laser ultrasonic source.

Comprehensive characterization of wideband ultrasonic transducers and specifically optoacoustic detectors is achieved through the analysis of their frequency response as a function of the incident angle. The tests are performed under well-defined, repeatable operating conditions. Backillumination of a blackened, acoustically matched planar surface with a short laser pulse creates an acoustic impulse which is used as a wideband ultrasonic source. Upon illumination with a short laser pulse, the bandwidth of our source shows a -6 dB point of 12 MHz and a low-frequency roll-off around 300 kHz. Using proprietary software, we examine thoroughly the planarity of the emitted wave front within a specified amplitude cutoff and phase incoherence. Analysis of the angular dependence of the frequency response yields invaluable directivity information about the detector under study: a necessary component toward accurate optoacoustic image reconstruction and quantitative tomography. The laser ultrasonic source we developed is the main feature of our directivity measurement setup. Due to its simplicity, it can easily be adapted to various calibration devices. This paper focuses on the development and characterization of the flatness and the bandwidth of our wideband ultrasonic source.

High sensitivity of in vivo detection of gold nanorods using a laser optoacoustic imaging system.

The development of a contrast agent for a laser optoacoustic imaging system (LOIS) can significantly widen preclinical and clinical applications of this imaging modality for early detection of cancerous tumors. Gold nanorods were engineered to enhance the contrast for optoacoustic imaging. Under in vivo conditions, 25 microL of gold nanorods solution at a concentration of 1.25 pM were injected into nude mice and detected using a single-channel acoustic transducer. LOIS was used to visualize the distribution of gold nanoparticles at a concentration of 125 pM in vivo when 100 microL of solution of gold nanoparticles was delivered subcutaneously. Our results suggest that LOIS can be used for in vivo detection of gold nanorods at low concentrations and the nanoparticles can be engineered to enhance the diagnostic power of optoacoustic imaging.

Near-infrared spectroscopy of ethylene and ethylene dimer in superfluid helium droplets.

The nu(5)+nu(9) spectra of ethylene, C(2)H(4), and its dimer, solvated in helium nanodroplets, have been recorded in the wavelength region near 1.6 microm. The monomer transitions show homogeneous broadening of approximately 0.5 cm(-1), which is interpreted as due to an upper state vibrational relaxation lifetime of approximately 10 ps. Nearly resonant vibrational energy transfer (nu(5)+nu(9)-->2nu(5)) is proposed as the relaxation pathway. The dimer gives a single unresolved absorption feature located 4 cm(-1) to the red of the monomer band origin. The scaling of moments of inertia upon solvation in helium is 1.18 for the monomer and >2.5 for the dimer. In terms of the adiabatic following approximation, this classifies the monomer as a fast rotor and the dimer as a slow rotor.