We designed a photoacoustic probe to determine the depths of epidermal melanin layer and port wine stain (PWS) in human skin. We present experimental data showing limitations in its use. We developed acrylamide tissue phantoms with optical properties matched to shoe of human PWS skin. We determined the limit in resolving epidermal and PWS layers. Additionally, we determined the maximum epidermal melanin concentration that allowed threshold detection of the PWS layer. Finally, we compared the photoacoustic signals from the tissue phantoms and human PWS skin.

This paper reports the burn diagnosis that is based on the measurement of photoacoustic waves from skin, where the acoustic waves originate from the absorption of light by blood. For this purpose, a transducer composed of a ring-shaped piezoelectric film and a quartz fiber was made. An optical parametric oscillator (500 - 650 nm) was used as a light source and its output pulses were coupled to the quartz fiber. To investigate the optimum light wavelength, we conducted experiments using rat burn models. We demonstrated that the superficial dermal burn (SDB), deep dermal burn (DDB), deep burn (DB), and control (healthy skin) could be clearly differentiated based on the photoacoustic signals induced by the light of 532 - 580nm.

The optical properties of human skin in the UV-range are not exactly known. Furthermore, the precise wavelength dependency of important photobiological processes (such as induction of skin cancer) could not be settled yet, either. A better knowledge of the optical properties is necessary in order to achieve a better understanding of UV-induced effects on human skin. Optoacoustics is a new approach to investigate the wavelength dependent optical properties of human skin in the UV-range. This technique allows non-invasive measurements on human skin in vivo, that are indispensable to gain meaningful results concerning the processes induced by UV-radiation in the living tissue. First attempts at measuring UV-induced optoacoustic transients of human skin in vivo and tissue phantoms with a new detector are shown. For analysis, fitting of simulated data onto the experimental data is applied in order to improve the determination of optical properties. First measurements of wavelength dependent optical properties in the UVB-(280-315 nm) and UVA-II-range (290-330 nm) comparing stained artificial layers to human skin in vivo are presented.

The goal of this work is to analyze the capabilities of a new photothermal (PT) radiometry system to control temperature during laser thermal therapy. The main feature of this system is the combination of two spectral channels: infrared (IR) and microwave (MW) ranges. The first channel provides information about the temperature distribution around the surface and subsurface of absorbing structures. The second channel provides information about the localized laser-induced thermal effects occurring much more deeply, up to 3-5 cm. Experimental in vitro data obtained with a near- IR diode laser are presented, focusing on the estimated capabilities of the new MW radiometry as a system for providing feedback control for interstitial laser therapy. Further modifications of this system are suggested for PT radiometric confocal microscopy. The modifications are based on the combination of PT radiometry in time-resolved and frequency-domain modes, with confocal microscopy using reflected scanning modes. The potential advantages of these new approaches are discussed, including the imaging of tissue chromophores with high spatial resolution based on radiometric measurements of laser-induced thermal gradients.

Mapping of internal temperature field in biological tissues is one of the urgent problems of modern medical diagnostics. One of the possible ways of obtaining internal temperature distribution is in application of focused antennae with large aperture and small focal waist in acoustical brightness thermometers (ABT). This work presents the developed ABT with focused antennas well as the results of experimental investigation of localization of heated sources by spatial scanning of focused antenna for two different regimes of signal receiving - compensation and correlation ones. Besides that the receiving antenna field for these regimes was investigated experimentally. The phantom in the form of polystyrene tube filled with heated oil and placed in water was used as a source in the experiments on object localization. 2D scanning was carried out by displacement of receiving antenna long principal axis. Maximum value of ABT output signal was observed when phantom was positioned in antenna focus. No solving of inverse problem is required to obtain tomographic image, thus improving efficiency and reliability of object localization. This work was supported by Russian Foundation for Basic Research and 6th competition-expertise of young scientists of Russian Academy of Sciences.

This work present the results of experimental study of applicability of acoustical brightness thermometry (ABT) in monitoring of internal temperature during laser hyperthermia and interstitial therapy. In these experiments the radiation of pulse repetition Nd:YAG laser (1064 nm) and continuous diode laser (800 nm) were used as heating sources. Experiments were performed in vitro by insertion of optical fiber inside the objects - optically transparent gelatin with incorporated light absorbing heterogeneities and samples of biological tissues (e.g. liver). During laser heating, internal temperature in absorbing heterogeneity and at fiber end were monitored by means of multi-channel ABT. The independent temperature control was performed with tiny electronic thermometer incorporated in heated zones. The results of experiments demonstrated reasonable sensitivity and accuracy of ABT for real-time temperature control during different kind of laser thermal therapies. According to preliminary data, ABT allow to measure temperature in depth up to 3-5 cm (depends on tissue properties) with spatial resolution some mm. Obtained data show that ABT is a very promising tool to give quantitative measure for different types of energy deposition (laser, microwave, focused ultrasound etc) at the depth commonly encountered in tumors of vital organs. Besides, ABT could give information about diffusion effects in heated zones or optical absorption. This work was supported by Russian Foundation for Basic Research and 6th competition-expertise of young scientists of Russian Academy of Sciences.

Investigation of features of diagnostic methods is usually carried out with specially prepared biological samples in vitro or with artificially designed model tissue-like media - phantoms. This paper describes OA investigation of large- scale phantoms on the base of water-like media (such as gelatin) for simulation of large organs of human body. The necessity of accounting influence of limited band width on the magnitude of recorded OA signal has been investigated both theoretically and experimentally. Experimental calibration curves for used ultrasonic transducers have been obtained. Method of OA signal compression has been described. This method allows to achieve acceptable longitudinal resolution at high transducer sensitivity by means of using resonant probes instead of quasi-resonant ones. The 2D tomograms of large-scale phantoms containing optical inhomogeneities have been obtained by mechanical scanning system. Application of such method gives an opportunity to perform OA investigation of human organs with one-side access. This work was supported by Russian Foundation for Basic Research and 6th competition-expertise of young scientists of Russian Academy of Sciences.

Various phantoms have been used to assess the ability of transmission mode photoacoustic imaging to visualize blood vessels. A Q switched Nd:YAG laser operating at 1.06micrometers was used as the pulsed excitation source. Detection of the photoacoustic signals was achieved by mechanically scanning a photodiode across the reflected output beam of a Fabry Perot polymer film ultrasound sensor to simulate 1D and 2D detector arrays. The depth profile of a 1.3mm thick polymer sheet ((mu) _a=0.8mm^-1) immersed to a depth of 2cm in an Intralipid scattering solution ((mu) _s=1mm^-1, (mu) _a=0.03mm^-1 was imaged using a 1D detector scan and a simple line-of-sight approach to image reconstruction. An arrangement comprising three 3 lines of PMMA tubing of internal diameter 62.5micrometers , arranged at different heights and filled with human blood, was immersed at depths of up to 7mm in the Intralipid solution. Using a radial backprojection algorithm, 2D and 3D images were reconstructed from 1D and 2D detector scans respectively. The vessels could be observed as high contrast features on the images. Lateral resolution, limited by the detector aperture was 0.33mm and the axial resolution was 0.15mm.

Time resolved detection of laser-induced pressure profiles permits sensitive and high-resolution measurements of distribution of absorbed optical energy in optically scattering and opaque media, such as blood. We report experimental measurements of optical properties in the whole blood of animals at various levels of oxygen saturation and analytical calculations of relative concentrations of oxy- and deoxy- hemoglobin. The results show that optoacoustic profiles are sensitive to small variations in optical properties of blood. When measured with absolutely calibrated acoustic transducers at two different laser wavelengths, 757-nm and 1064-nm, the total hemoglobin concentration and its oxygenation level can be determined from the optoacoustic profiles. The value of thermoacoustic efficiency of pressure wave generation by laser irradiation was also determined from experiments. Erythrocyte sedimentation and aggregation rate was studied, since these phenomena affect spatial distribution of optical energy in blood upon laser irradiation. Erythrocyte sedimentation rate was calculated from kinetic changes in optoacoustic profiles. The results encourage development of various applications of optoacoustic spectroscopy in monitoring of blood properties in vitro and in human tissues.

Using very sensitive photoacoustical detectors we localized and monitored the blood content in tissue. In these detectors a PVdF-layer has been used as piezo-electric material and also fibers for the illumination of the sample are integrated. The resolution is about 20micrometers in depth and about 50-100micrometers laterally. The wavelengths of the laser light were 532 and 1064 nm. With these colors we can measure at different depths in tissue. The measurements concerned blood perfusion in real tissue: vessels in chicken breast, in test animals at various positions and in the human arm.

Aggressive malignant tumors may be diagnosed based on relative concentration of oxyhemoglobin and deoxyhemoglobin in the tumor microvasculature. Optoacoustic images of breast cancer and prostate cancer may be acquired at two laser wavelengths matching maximum of oxyhemoglobin (1064-nm, Nd:YAG laser) and deoxyhemoglobin (760-nm, Alexandrite laser). Two optoacoustic systems operating in forward and backward mode respectively for breast cancer and prostate cancer detection, employing arrays of ultravide-band piezoelectric transducers and multichannel electronics was described. After systems testing and calibration in phantoms, initial experiments were performed on patients with suspicious tumors. Quantitative analysis of two-color optoacoustic images was correlated with biopsy and histology. Possibility for tumor differentiation was demonstrated.

A study of pulsed-microwave-induced thermoacoustic tomography in biological tissues is presented. A backprojection algorithm based on rigorous theory is used to reconstruct the cross-sectional image from the thermoacoustic measurement in a circular configuration that encloses the sample under study. The results demonstrate the possibility of application in detecting small tumors buried in biological tissues using microwave absorption contrast and ultrasound spatial resolution. Finally, the method is compared with laser-induced thermoacoustic tomography.

For enhanced optoacoustic imaging in biomedical applications more than one-dimensional detection is required. Tomographic images comparable to ultrasound B-scans can be generated with linear arrays. This work presents a detection scheme for such an array based on piezoelectric films. Each single detector consists of a ring shaped active area with a diameter of less than one millimeter, which leads to a high lateral resolution. Because of the small dimensions of the systems it is suitable for applications with limited accessibility like ophthalmic or endoscopic use. The sensitivity of a single detector is close to 0.5 mV/bar. First measurements on layered tissue phantoms made of gelatine and absorbing films show the potential of such an array for depth profiling as well as for two-dimensional imaging of simple structures.

Photoacoustic and photothermal (PT) methods in live cells studies allow to realize direct monitoring as they do not require cell pretreatment with chemicals and because the sources of output signal are cell chromophores. The origin of PT signals from single cells that are irradiated with short pump laser pulse was studied experimentally under different rates of cell metabolism. The cells in different metabolic status were found to produce PT response of specific shape that occurs in specific pump energy region for each pump wavelength. This type of PT response is associated with secondary phenomena that are induced in cells by thermal impact. An ability of live cell to produce such PT response was found to depend upon the redox state of cell respiratory chain (RC) components that absorb pump laser radiation. The results of PT studies of in vitro modulation of hepatocyte metabolic state are presented as function of RC state (reduced/oxidized) and laser parameters (wavelength and energy). Obtained results show that several parameters of laser-cell interaction depend upon RC redox state: shape and amplitude of PT response from single cell, energy threshold for laser damage to cell.

We present a fully automated mobile laser spectrometer with photoacoustic (PA) detection for trace gas analysis. A novel PA cell design permits extracavity measurements with detection limits in the sub-ppb concentration range. The setup also allows measurements with low-power sources such as quantum cascade lasers (QCL). The multicomponent capability as an important feature of the spectrometer is realized by the implementation of two sealed-off CO₂ lasers with ¹²CO₂ and ¹³CO₂ fillings covering the spectral range between 868 cm^-1 and 1088 cm^-1 with 132 laser lines. The performance is demonstrated with measurements on air samples with a priori unknown composition. In particular we report on the analysis of samples taken during surgery on human breast tissue with a high-frequency (HF) electro-knife in a hospital. Besides advantages of less bleeding and lower risk of infection, the drawback of this technique is the generated fume, which in general contains dozens of species at low concentrations, some of them presumably harmful to the patient and the medical team. Our analysis of an unfiltered fume sample revealed a total of 15 species. Most of their concentrations were below the allowed workplace concentrations (if at all available). 2-Furan-carboxaldehyde (C₅H₄O₂), however, exceeded this value of 2 ppm considerably.

We present a pulsed photoacoustic (PA) spectrometer based on a frequency doubled, continuously tunable high pressure CO₂ laser. A quasi-phasematched diffusion-bonded GaAs crystal is implemented for second harmonic generation (SHG) and has advantages over well-known non-linear infrared (IR) materials such as AgGaSe₂ and ZnGeP₂, like high-average power capabilities, and high damage threshold. GaAs has a large non-linear coefficient (d₁₄ = d₃₆ = 150 pm/V), is transparent in the range 1 - 16 m, features low absorption and high thermal conductivity, but it is not birefringent. The periodically poled crystal is anti-reflection-coated (AR) for the 10 m and 5 m range, and consists of 53 GaAs plates of ~106 m thickness for first-order quasi-phase-matching. With 80 mJ pump energy we achieved up to 1 mJ SHG pulse energy. A non-resonant PA gas cell equipped with an 80-microphone-array is employed sealed-off and in flow mode. We use the fundamental as well as the SHG radiation for our spectroscopic measurements. To our best knowledge, we present the first PA spectra measured with such a system in the 5 m range, e. g., on NO buffered in N₂ at atmospheric pressure and room temperature. The performance of this novel PA spectrometer is illustrated by various examples of biological interest.

Adaptive laser-based ultrasound detection uses laser homodyne detection in an adaptive interferometer to detect ultrasound displacements. This technique has been applied to non-destructive evaluation for detection of surface displacements. However, in biomedical ultrasound applications, ultrasound displacements of interest may be inside tissue and the detection light beam may need to propagate through turbid media. Here we report laser-based adaptive ultrasonic detection that can detect ultrasound displacements inside or through turbid media using a fsec-laser as the light source in an adaptive optical coherence detection scheme. The use of an interferometer and a femtosecond laser gates out the unwanted scatter while still allowing homodyne detection. In our laser-based ultrasound system, an adaptive Mach-Zehnder interferometer is based upon two-wave mixing in semiconductor quantum-well films. It provides depth information inside the sample by adjusting the optical delay in the reference beam arm. Homodyne detection was experimentally studied for low intensity and highly wavefront distortion caused by turbid media. Using this system, ultrasonic homodyne signals through 11 MFP turbid media have been successfully detected.

Image reconstruction algorithm for three-dimensional laser optoacoustic imaging system (LOIS) is proposed and tested in computer-simulating experiments. It was assumed that acoustic transducers were evenly distributed with 3-degree interval along polar and azimuthal angles on the surface of a 100-mm diameter hemisphere, all optoacoustic sources were located inside the hemisphere of a slightly smaller diameter. At the first stage of calculations, the initial data in a form of spherical surface integrals were converted into the plane surface integrals. We deduced an approximate analytical formula for this conversion. At the second stage, the three-dimensional Radon transform algorithm was applied for reconstruction of optoacoustic sources. Three- dimensional images of computer-simulated spherical objects were generated. Quality of reconstructed images was evaluated with the following four criteria: The noise level on the entire tomogram, the step-transfer function, the loss-of-contrast function and the contrast-dimension relation. These quality criteria may be employed to characterize any tomography systems regardless of the type of technology employed. Image analysis demonstrated that the artifact level associated with data conversion from spherical into planar coordinates did not exceed 10%. A 1-mm spatial resolution could be obtained with the proposed algorithm, provided the signal-to-noise ratio equals approximately 3 on the tomogram. Very small (0.5-mm diameter) and small (3-mm diameter) spherical tumors could be revealed on optoacoustic tomograms if their contrast equals at least 6 and 0.3, respectively.

An optoacoustic imaging algorithm uses backprojection of the time-resolved velocity potential to map the sources of pressure waves detected by an array of acoustic detectors. The relationship between pressure (P) and velocity potential (vp) is P = -rho*d(vp)/dt, or vp = -Integral(P dt)/rho where rho is density, t is time, and d(vp)/dt is the time derivative of the velocity potential. In a forward calculation, a computer simulation can predict the complex pressure waves arriving at each of an array of detectors due to any arbitrary spatial distribution of initial pressure generation. In an inverse calculation, such computer-simulated experimental measurements are used to spatially map the initial pressure source which in optoacoustic imaging corresponds to the initial distribution of pulsed laser energy deposition. Hence, the performance of the inverse calculation as an image reconstruction algorithm could be tested using ideal computer-simulated data. In this report, the image reconstruction algorithm was systematically tested to specify the expected performance under optimal conditions, to illustrate the source/detector geometries that frustrate image reconstruction, and to assess the impact of measurement noise. Typical reconstruction errors were +/- 20%.

Laser optoacoustic tomography system (LOIS) for breast cancer detection and diagnostics utilizes optical generation of acoustic pressure profiles in tumors and piezoelectric detection of these pressure transients within an ultra- wideband of ultrasonic frequencies. Temporal profile of optoacoustic pulses provides information on tumor dimensions and its location inside the breast. A finite spatial dimension of receiving transducers results in distortions of the optoacoustic profile and corresponding reduction of the resolution in LOIS. The impulse response approach for calculation of the pulse profiles originated from a uniformly absorbing sphere and detecting with a rectangular transducer was employed. The pressure profiles were expressed as convolution integrals of velocity-potential distribution over the transducer surface with the corresponding impulse response function. The impulse response distribution over the transducer surface with the corresponding impulse response function. The impulse response function was evaluated for different locations of optoacoustic sources with respect to the receiving transducer. Numerical simulations were performed for acoustic transducers with dimensions of 1x10 mm and located on the cylindrical surface with radius of 60-mm. Results demonstrated that detected N-shaped pressure profiles become smoother and their duration increases with increased linear dimensions of the transducer. This effect depends on relative position of the spherical acoustic source and the detector.