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This special issue of Journal of Physics D: Applied Physics is dedicated to Professor Valery V Tuchin, one of the pioneers in biomedical optics. Professor Tuchin's contributions to the field of biomedical optics are diverse and cover areas such as fundamental aspects of tissue optics, laser spectroscopy and clinical applications of light waves.

Born on 4 February 1944 by the Volga River in Saratov, Russia, Valery received his education from Saratov State University (SSU), Department of Physics, graduating in 1966 with a master of science in radiophysics and electronics. He defended his first dissertation for Candidate of Sciences in Optics in 1973 on the 'Study of Spectral Characteristics of Gas Discharge Lasers by a Small Disturbing Signal', and carried on to defend his second dissertation for Doctor of Sciences in quantum electronics in 1982 on 'Laser Modulation and Technical Fluctuations'.

His professional experience and positions are mostly connected with SSU: from 1966 to 1970 he was an engineer in the Research Institute of Mechanics and Physics; from 1971 he was invited to teach firstly as an Assistant Professor at the Chair of Optics, then as a Senior Lecturer and Associate Professor of the same Chair (1973–1982). Since 1982 he has been a Full Professor as Head of Chair of Optics. From 1982 to 1989 he was Dean of the Faculty of Physics. Since 1989 he has also been working for the Russian Academy of Sciences as Head of the Laboratory of Laser Diagnostics of Technical and Living Systems at the Precision Mechanics and Control Institute of the Saratov Branch of the Russian Academy of Sciences. In 2004 he initiated and became a director of the International Research–Education Institute of Optics and Biophotonics at SSU.

Professor Tuchin's contributions to the fields of optical and laser measurements, biomedical optics and the fundamentals of laser and photo medicine are reflected in his more than 200 peer-reviewed papers and books. His latest books include Tissue Optics: Light Scattering Methods and Instrumentation for Medical Diagnosis (SPIE Tutorial Texts in Optical Engineering, volume TT38, 2000), Handbook of Optical Biomedical Diagnostics (SPIE Press, volume PM107, 2002), Coherent-Domain Optical Methods for Biomedical Diagnostics, Environmental and Material Science (Kluwer Academic Publishers, volumes 1 and 2, 2004), and Optical Polarization in Biomedical Applications, (Springer Verlag, 2005, co-authored with Lihong Wang and Dmitry Zimnyakov). He is the holder of more than 20 patents.

Professor Tuchin and his group have designed and developed light scattering and coherence-domain techniques, as well as polarization-sensitive diagnostic methods and instrumentation for early diagnostics and monitoring of disease in ophthalmology, dermatology and other branches of medicine. His latest achievements are in the field of tissue optical clearing using biocompatible immersion agents. The research group headed by Professor Tuchin at Saratov State University actively collaborates with numerous university laboratories, research centres and companies in Russia and worldwide. There is no doubt that it is a leading group in the world in this field.

Professor Tuchin has made numerous and important contributions to designing and teaching biomedical optics courses, and organizing schools for junior scientists and students. During the last decade, he has been an instructor for more than 20 SPIE and OSA short courses on biomedical optics for international audiences of PhD students, engineers, private company workers, and medical doctors in USA, Germany, Hungary, Finland, China and Singapore. He is a guest Professor of Huazhong University of Science and Technology and of Tianjin University in China.

He actively serves as an editorial board member and reviewer for a number of high ranking scientific journals, including Journal of Biomedical Optics (USA), Quantum Electronics (Russia), Journal of Applied Nonlinear Dynamics (Russia), Lasers in the Life Sciences (USA) and Journal of X-Ray Science and Technology (USA).

Professor Tuchin has organized numerous international conferences, including the following well-known symposia: SPIE's Annual Conference on Coherence-Domain Optical Methods and Optical Coherence Tomography in Biomedicine (San Jose, 1997–2005, co-chaird by J Izatt and J Fujimoto) and SPIE's Annual Fall School for Young Scientists and Students on Optics, Laser Physics, and Biophysics (Saratov, 1997–2005). Recently, together with Professor Brian Wilson from the Ontario Cancer Institute and Dr Stoyan Tanev from Vitesse Re-Skilling Canada, he has been a co-director of the NATO Advanced Study Institute in Biophotonics (Biophotonics—from Fundamental Principles to Health, Environment, Security and Defence Applications, Ottawa, Canada, 29 September–9 October 2004).

He is one of the leading scientists in Russia, being an Honoured Science Worker of the Russian Federation (since 1999), winner of the Russian Federation individual grant for leading scientists (1994–2003), an active member of the International Academy of Informatization and the Russian Academy of Natural Sciences, and a recipient of the George Soros Professor Award in 1997, 1998 and 1999. In 2005, he became a Fellow of SPIE.

Because of all of Professor Tuchin's achievements, contributions, and dissemination activities in the field of biomedical optics, we felt that there was a debt to be repaid by encouraging his students, co-workers and colleagues to contribute to this special issue in his honour. This issue of Journal of Physics D: Applied Physics therefore highlights recent research in biomedical optics that has been influenced, both directly and indirectly, by Professor Tuchin's work.

Twenty-seven papers are included in this special issue. The first paper, By Professor Tuchin, gives an overview of the current status of the optical clearing approach in biomedical optics, a new and novel approach pioneered by him, while the second paper describes current developments in optical coherence tomography, its theory and applications with close attention paid to biomedical imaging and its metrological issues. The third overview paper is dedicated to the current development and evaluation of automated systems for detection and classification of banded chromosomes. The next four papers are concerned with the optical properties of biotissues and how those properties can be manipulated by exogenous agents and particles. There are seven papers presenting and discussing the latest developments in optical coherence tomography and microscopy, including theoretical modelling, experimental investigations and light source developments. The photoacoustic effect from biological tissue and cells can be used to efficiently monitor a number of parameters in biotissues. In this regard, we have included five papers in this special issue that cover monitoring of temperature, tissue coagulation and glucose, imaging and photoacoustic tweezers. A further three papers describe current developments in using near-infrared spectroscopy to perform noninvasive glucose measurement and to monitor rat breast tumour oxygen consumption. The remaining papers cover miscellaneous topics in biomedical optics, including resonance Raman spectroscopic investigations in dermatology, a near-infrared fluorescence catheter for atherosclerotic plaque detection, fibre-optic systems applicable to measuring the thickness of transparent tissues and tumor diagnosis, and a lattice of optical islets in photomedicine.

We thank all the authors for their valuable contributions and their prompt responses to the reviewers' comments. We are also very grateful to the reviewers for their hard work and their considerable efforts to meet tight deadlines.

This paper aims to review recent results on the optical clearing of the naturally turbid biological tissues and blood using the optical immersion technique, which is well known in physical science and is applied for the reduction of light scattering and undesirable reflections in the optical system. Basic principles of the technique, its advantages, limitations and future are discussed. The refractive index matching concept for enhancement of in-depth light penetration into tissues and blood is presented on the basis of in vitro and in vivo studies using optical spectroscopy, polarization and coherence-domain techniques. The index matching of scatterers and ground matter by means of administration of clearing agents is under discussion. The optical properties of tissues with basic multiple scattering, which are transformed to a low scattering mode, are analysed. It is shown that light reflection, transmission, scattering and polarization can be effectively controlled. The possibilities of using the optical immersion method for diagnostic purposes based on contrasting of abnormalities, on in-depth profiling of tissue and blood and on monitoring of endogenous and exogenous matter diffusion within tissue are demonstrated.

In this paper, we review the developments in optical coherence tomography (OCT) for three-dimensional non-invasive imaging. A number of different OCT techniques are discussed in some detail including time-domain, frequency-domain, full-field, quantum and Doppler OCT. A theoretical treatment is given and some relevant comparisons made between various implementations. The current and potential applications of OCT are discussed, with close attention paid to biomedical imaging and its metrological issues.

Automated detection and classification of banded chromosomes may help clinicians diagnose cancers and other genetic disorders at an early stage more efficiently and accurately. However, developing such an automated system (including both a high-speed microscopic image scanning device and related computer-assisted schemes) is quite a challenging and difficult task. Since the 1980s, great research efforts have been made to develop fast and more reliable methods to assist clinical technicians in performing this important and time-consuming task. A number of computer-assisted methods including classical statistical methods, artificial neural networks and knowledge-based fuzzy logic systems, have been applied and tested. Based on the initial test using limited datasets, encouraging results in algorithm and system development have been demonstrated. Despite the significant research effort and progress made over the last two decades, computer-assisted chromosome detection and classification systems have not been routinely accepted and used in clinical laboratories. Further research and development is needed.

The optical properties of human skin, subcutaneous adipose tissue and human mucosa were measured in the wavelength range 400–2000 nm. The measurements were carried out using a commercially available spectrophotometer with an integrating sphere. The inverse adding–doubling method was used to determine the absorption and reduced scattering coefficients from the measurements.

Characteristics of organic–mineral complexes have been theoretically and experimentally studied in the paper, based on the method of integral light scattering indicatrix. Modelling of optical properties was realized using models of the coated spherical particles with a shell which is constant and changeable in the refractive index profile. General regularities have been revealed and generalized parameters for the method of integral light scattering indicatrix have been suggested.

Protecting human skin against harmful UV-B radiation coming from the sun is currently a problem. Due to the decreased thickness of the ozone layer, a more dangerous amount of UV-B light reaches the surface of our planet. This causes increased frequency of skin diseases. Titanium dioxide (TiO₂) fine particles are embedded with sunscreens into the skin to effectively attenuate UV-B radiation. This study evaluates the most appropriate size of such particles assuming they are spheres. The distribution of TiO₂ particles within the skin, achieved with topically applied sunscreens, is determined experimentally by the tape-stripping technique. Computer code implementing the Monte Carlo method is used to simulate photon migration within the plain 20 µm thick horny layer matrix partially filled with nano-sized TiO₂ particles. Dependences of harmful UV-B radiation of 307–311 nm absorbed by, backscattered from and transmitted through the horny layer on the concentration of TiO₂ particles are obtained and analysed. As a result, particles of 62 nm are found to be the most effective in protecting skin against UV-B light.

Laser-induced bubble formation around nanoparticles may play a crucial role in selective laser nanophotothermolysis of cancer cells targeted with nanoparticles. In this paper, we propose theoretically, and confirm experimentally, a new dynamic mode for selective cancer treatment that involves the overlapping of bubbles inside the cell volume. This bubbles-overlapping mode (BOM) can dramatically increase the efficiency of cancer treatment by laser-heated nanoparticles as a result of the large damage range. On the basis of nanoparticle optics below the diffraction limit and the kinetic model of bubble dynamics, we found the criteria and conditions (interparticle distance and particle size and concentration) for BOM initiation in cancer cells by laser radiation. Using MDA-MB-231 breast cancer cells, we showed that the optimal size range of the gold nanoparticles for effective laser initiation of BOM is 30–40 nm and the lower concentration limit is n ≈ 2.44 × 10¹¹ cm^–3 (i.e. the absolute number of particles homogeneously distributed inside a tumour cell is n ≈ 430). It was demonstrated that the formation of nanoclusters on the cell surface with sizes larger than the sizes of individual nanoparticles, may further increase the efficiency of the laser treatment of cancer.

In this work, Monte Carlo simulation is used to obtain model optical coherence tomography (OCT) signals from a horizontally orientated blood layer at different stages of red blood cell (RBC) aggregation and sedimentation processes. The parameters for aggregating and sedimenting blood cells were chosen based on the data available from the literature and our earlier experimental studies. We consider two different cases: a suspension of washed RBCs in physiological solution (where aggregation does not take place) and RBCs in blood plasma (which provides necessary conditions for aggregation). Good agreement of the simulation results with the available experimental data shows that the chosen optical parameters are reasonable. The dependence of the numbers of photons contributing to the OCT signal on the number of experienced scattering events was analysed for each simulated signal. It was shown that the maxima of these dependences correspond to the peaks in the OCT signals related to the interfaces between the layers of blood plasma and blood cells. Their positions can be calculated from the optical thicknesses of the layers, and the absorption and scattering coefficients of the media.

Optical coherence tomography (OCT) offers great potential for clinical applications in terms of its cost, safety and real-time imaging capability. Improvement of its resolution for revealing sub-layers or sub-cellular components within a tissue will further widen its application. In this study we report that carbon pigment, which is frequently present in the lungs of smokers, could be used as a contrast agent to improve the OCT imaging of lung tissue. Carbon produced an intense bright OCT image at a relatively deep location. The parallel histopathological section analysis confirmed the presence of carbon pigment in such tissues. The underlying mechanism of the OCT image formation has been discussed based on a model system in which carbon particles were dispersed in agar gel. Calculations and in-depth intensity profiles of OCT revealed that higher refractive index particles with a size close to or smaller than the wavelength would greatly increase backscattering and generate a sharp contrast, while a particle size several times larger than the wavelength would absorb or obstruct the light path. The naturally occurring contrast agent could provide a diagnostic biomarker of lung tissue in smokers. Furthermore, carbon under such circumstances, can be used as an effective exogenous contrast agent, with which specific components or tissues exhibiting early tumour formation can be optically labelled to delineate the location and boundary, providing potential for early cancer detection and its treatment.

In this paper we investigate the effect of multiple scattering on Doppler optical coherence tomography (DOCT) images of model blood vessels embedded in a medium with optical properties similar to those of the human dermis. Furthermore, we quantify the deviation of the acquired velocity profiles from that known to exist within a glass capillary at various depths within the scattering media.

A flow phantom consisting of a glass tube containing whole blood flowing under laminar conditions submerged in a variable depth of Intralipid was used to simulate a blood vessel within the cutaneous microcirculation. DOCT images and velocity profiles of the tube acquired at various depths within the Intralipid are compared with those obtained from the same tube in a non-scattering medium with the same refractive index.

In this contribution we examine a methodology to avoid parasitic cross-correlation terms in spectral optical coherence tomography (SOCT) images. The optimal conditions of optical power and exposure time are found theoretically and confirmed experimentally to ensure that parasitic images are hidden under the shot noise. An upper limit on useful exposures may then be estimated. In a case of SOCT imaging of the retina this limit is below the ANSI safety limit.

Optical coherence tomography and polarization-sensitive optical coherence tomography images of equine articular cartilage are presented. Measurements were made on intact joint surfaces. Significant (e.g. × 2) variations in the intrinsic birefringence were found over spatial scales of a few millimetres, even on samples taken from young (18 month) animals that appeared visually homogeneous. A comparison of data obtained on a control tissue (equine flexor tendon) further suggests that significant variations in the orientation of the collagen fibres relative to the plane of the joint surface exist. Images of visually damaged cartilage tissue show characteristic features both in terms of the distribution of optical scatterers and of the birefringent components.

Intensity correlations of a Ti : sapphire, Kr/Ar and a white-light supercontinuum were performed to quantify the typical signal amplitude fluctuations and hence ascertain the comparative output stability of the white-light supercontinuum source for confocal laser scanning microscopy (CLSM). Intensity correlations across a two-pixel sample (n = 1000) of up to 98%, 95% and 94% were measured for the Ti : sapphire, Kr/Ar and white-light supercontinuum source, respectively. The white-light supercontinuum noise level is therefore acceptable for CLSM, with the added advantage of wider wavelength flexibility over traditional CLSM excitation sources. The relatively low-noise white-light supercontinuum was then used to perform multiple wavelength sequential CLSM of guinea pig detrusor to confirm the reliability of the system and to demonstrate system flexibility.

Two-photon excitation fluorescence (TPEF) and second-harmonic generation (SHG) are relatively new promising tools for the imaging and mapping of biological structures and processes at the microscopic level. The combination of the two image-contrast modes in a single instrument can provide unique and complementary information concerning the structure and the function of tissues and individual cells. The extended application of this novel, innovative technique by the biological community is limited due to the high price of commercial multiphoton microscopes. In this study, a compact, inexpensive and reliable setup utilizing femtosecond pulses for excitation was developed for the TPEF and SHG imaging of biological samples. Specific cell types of the nematode Caenorhabditis elegans were imaged. Detection of the endogenous structural proteins of the worm, which are responsible for observation of SHG signals, was achieved. Additionally, the binding of different photosensitizers in the HL-60 cell line was investigated, using non-linear microscopy. The sub-cellular localization of photosensitizers of a new generation, very promising for photodynamic therapy (PDT), (Hypericum perforatum L. extracts) was achieved. The sub-cellular localization of these novel photosensitizers was linked with their photodynamic action during PDT, and the possible mechanisms for cell killing have been elucidated.

To improve the safety and efficacy of thermal therapy, it is necessary to map tissue temperature in real time with submillimetre spatial resolution. Accurate temperature maps may provide the necessary control of the boundaries of the heated regions and minimize thermal damage to surrounding normal tissues. Current imaging modalities fail to monitor tissue temperature in real time with high resolution and accuracy. We investigated a non-invasive optoacoustic method for accurate, real-time monitoring of tissue temperature during thermotherapy. In this study, we induced temperature gradients in tissue and tissue-like samples and monitored the temperature distribution using the optoacoustic technique. The fundamental harmonic of a Q-switched Nd : YAG laser (λ = 1064 nm) was used for optoacoustic wave generation and probing of tissue temperature. The tissue temperature was also monitored with a multi-sensor temperature probe inserted in the samples. Good agreement between optoacoustically measured and actual tissue temperatures was obtained. The accuracy of temperature monitoring was better than 1°C, while the spatial resolution was about 1 mm. These data suggest that the optoacoustic technique has the potential to be used for non-invasive, real-time temperature monitoring during thermotherapy.

Non-invasive laser-induced photoacoustic tomography (PAT) is a promising imaging modality in the biomedical optical imaging field. This technology, based on the intrinsic optical properties of tissue and ultrasonic detection, overcomes the resolution disadvantage of pure-optical imaging caused by strong light scattering and the contrast and speckle disadvantages of pure ultrasonic imaging. Here, we report a PAT experimental system constructed in our laboratory. In our system, a Q-switched Nd : YAG pulse laser operated at 532 nm with a 8 ns pulse width is used to generate a photoacoustic signal. By using this system, the two-dimensional distribution of optical absorption in the tissue-mimicking phantom is reconstructed and has an excellent agreement with the original ones. The spatial resolution of the imaging system approaches 100 µm through about 4 cm of highly scattering medium.

In this paper we have applied the laser optoacoustic technique for real time noninvasive monitoring of thermal damage in tissues. Changes in tissue optical properties during coagulation were detected by measuring and analysing amplitude and temporal characteristics of optoacoustic signals. Coagulation of liver, myocardium and prostate was induced by interstitial continuous wave Nd : YAG laser irradiation of the samples or by conductive heating. Real time detection of thermally-induced changes in optical properties was performed with sensitive wide-band acoustic transducers. Combination of optoacoustic and diffuse reflectance technique was applied for determination of tissue optical properties: effective attenuation, total diffuse reflectance, reduced scattering coefficient and absorption coefficient. The optical properties did not change up to temperature of coagulation (about 53°C) and sharply increased during heating up to 70°C. Monitoring of the expansion of interstitial coagulation front within freshly excised canine tissues was performed in real time with spatial resolution of about 0.6 mm. The results of our study suggest that this technique can potentially be used for real time precise thermotherapy of malignant and benign lesions at depths of the order of the centimetre.

Non-invasive glucose monitoring is one of the most active areas in biomedical research. Various techniques have been developed over the years to meet the clinical requirements of non-invasive monitoring in the physiologically relevant glucose concentration range, but without a breakthrough. This paper used the pulsed photoacoustic (PA) technique to study glucose-induced changes in pig whole blood and 1% Intralipid™ using an Nd : YAG laser with wavelengths of 1064 and 532 nm as the optical energy source. Scattering properties of the sample significantly affect the laser-induced pressure waves. Glucose was found to affect both the scattering and the absorption properties of the samples. The results showed an increase of 11.4%/500 mg dl⁻¹ added glucose in the peak-to-peak value of the PA signal in blood at 1064 nm, whereas the corresponding increase was only 1.35%/500 mg dl⁻¹ in 1% Intralipid™. At a wavelength of 532 nm, the glucose increased the peak-to-peak value of the PA signal by 6.0%/500 mg dl⁻¹ added glucose in blood. On the whole, the pulsed PA technique proved to be an efficient tool for the study of glucose-induced changes in blood and tissue phantoms in vitro.

A novel noninvasive optical technique for manipulating particles and cells is presented that utilizes laser-generated forces in an absorbing medium surrounding the particles or cells. In this technique, a laser pulse creates near-object acoustic waves, which during interaction with the objects lead to then being moved or trapped. The main optical schemes are considered, and a theory is presented for this new optical tool, namely photoacoustic (PA) tweezer with pulsed laser. The magnitudes of forces acting on polystyrene particles suspended in water were estimated as a function of the particles' properties for circular and ring geometries of the laser beam. Results of our preliminary experiments demonstrated proof that the manipulation, trapping and even rotation of cells is possible with PA tweezers.

Although the non-invasive glucose measurement technique based on near-infrared (NIR) spectroscopy has been an active research area for over twenty years, a reliable monitoring method has not been established yet. The key problem is that the spectral variations due to glucose concentration are extremely small compared to that from other biological components. In addition, there are also some ambiguous time-dependent physiological processes, which make the explanation of the model more difficult, especially in the universal calibration. Therefore, in order to produce a model that is related to the actual spectral variation of glucose, reproducible measurements and clinical validation experiments that improve the selectivity and signal to noise ratio of glucose measurement are needed. In this paper, chance correlation in spectroscopy analysis is investigated, which is one of the obstacles to achieving successful NIR spectroscopy analysis, especially in in vivo measurement. The reasons for chance correlation in the in vitro and in vivo experiments are analysed. Methods to avoid it are suggested accordingly and verified with the in vitro experiments. We also investigate the chance correlation for the in vivo NIR diffuse reflectance spectroscopy monitoring blood. Results show that there is significant signal variation after glucose is taken, and the potential chance correlation factors including the instrument-related and physiology-related variations during the in vivo experiments do not contribute to the multivariate model for glucose concentration.

This study develops a mathematical model for calculating the tumour oxygen consumption rate and investigates the correlation with tumour volume. Near-infrared spectroscopy (NIRS) was used to measure changes of oxygenated haemoglobin concentration (Δ[HbO₂]) before and after potassium chloride (KCl) induced cardiac arrest. Measurements were made in five 13762NF mammary adenocarcinomas implanted in female adult Fisher 344 rats, while the anaesthetized rats breathed air. After 5–10 min of baseline NIRS measurement, KCl overdose was administered intravenously in the tail. NIRS showed a significant drop in tumour vascular oxygenation immediately following KCl induced cardiac arrest. The tumour oxygen consumption rate was calculated by fitting the model to the measured Δ[HbO₂] data, and a relationship between the tumour oxygen consumption rate and tumour volume was analysed using linear regression. A strong negative linear relationship was found between the mean tumour oxygen consumption rate and tumour volume. This study demonstrates that the NIRS can provide an efficient and real-time approach to quantify tumour oxygen consumption rate, while further development is required to make it non-invasive.

In the practice of non-invasive blood glucose measurement by near-infrared (NIR) diffuse reflectance spectroscopy, an optical probe usually directly contacts skin in order to eliminate specular reflection. In this paper, the influence of contact state on the diffuse reflectance in vivo and the variation trend of diffuse reflectance with contact time under the same contact pressure, are investigated at wavelengths ranging from 1100 to 1700 nm. The result shows that the diffuse reflectance decreases with increasing contact pressure under the contact state. At a certain applied pressure, the diffuse reflectance fluctuates significantly at the beginning of contact, and the fluctuation becomes stable with elapsing contacting time. It is our aim in this paper to find out the optimal contact state and optimal measuring time, in order to reduce the influence of contact pressure on diffuse reflectance measurements. It is found from our experiments that, for in vivo measurement, the optimal contact state appears when the skin is pressed to about 0.5 mm by the probe, where the probe contacts the palm entirely, and that the optimal measuring time is at the 30th second since the probe contacting with the measuring site. Putting the above conclusions into practice, the repeatability of spectra is improved greatly.

Resonance Raman spectroscopy was used as a fast and non-invasive optical method of measuring the absolute concentrations of beta-carotene and lycopene in living human skin.

Beta-carotene and lycopene have different absorption values at 488 and 514.5 nm and, consequently, the Raman lines for beta-carotene and lycopene have different scattering efficiencies at 488 and 514.5 nm excitations. These differences were used for the determination of the concentrations of beta-carotene and lycopene. Using multiline Ar⁺ laser excitation, clearly distinguishable carotenoid Raman spectra can be obtained which are superimposed on a large fluorescence background. The Raman signals are characterized by two prominent Stokes lines at 1160 and 1525 cm⁻¹, which have nearly identical relative intensities. Both substances were detected simultaneously.

The Raman spectra are obtained rapidly, i.e. within about 10 s, and the required laser light exposure level is well within safety standards. The disturbance of the measurements by non-homogeneous skin pigmentation was avoided by using a relatively large measuring area of 35 mm².

It was shown that beta-carotene and lycopene distribution in human skin strongly depends upon the skin region studied and drastically changed inter-individually. Skin beta-carotene and lycopene concentrations are lower in smokers than in non-smokers and higher in the vegetarian group.

We present a one-dimensional optical fibre-based imaging catheter specifically developed for the atherosclerotic plaque detection of emerging novel near infrared fluorescence imaging agents. We show that femtomole amounts of fluorochromes can be detected, especially in the presence of a blood-free medium. We further studied the catheter responses for a wide range of laser powers and biologically relevant concentrations of fluorochrome. In vitro tissue-like phantoms and human carotid plaque specimen measurements further demonstrate the feasibility of atherosclerotic plaque detection.

A low-cost, high-resolution, fibre optic system for non-contact thickness measurement of ocular tissues in cadaver eyes was developed. The optical system uses direct modulation at 100 kHz of a 670 nm laser diode delivered to a single-mode fibre coupler. The output of the fibre coupler is focused onto the tissue using a high numerical aperture aspheric lens mounted on a motorized translation stage. Light reflected from the sample is collected by the fibre coupler and sent to a photoreceiver. Peaks in the power signal are detected when the focal point of the aspheric lens coincides with the tissue boundaries. The thickness is proportional to the distance between successive peaks. The optical system has a sensitivity of 52 dB, which corresponds to a detectable change in the refractive index of 0.005 at a boundary-assuming specular reflection. With a focusing numerical aperture of 0.68, the resolution is 4.0 µm and the precision is ± 0.2 µm. The optical system was used to measure the corneal layers and lens capsule thickness of cadaver monkeys eyes. The system was able to measure the thickness of the epithelium, stroma and Descemet's membrane of the cornea, as well as the lens capsule and lens epithelial cell layer.

Laser based fibre-optic surgery procedures are commonly used in minimal invasive surgery. Despite the development of precise and efficient laser systems there are also innovative attempts in the field of bio-medical diagnostics. As a direct result of the tissue's optical properties most applications are focused on the visible wavelength range of the spectrum. The extension of the spectrum up to the mid-infrared (IR) region will offer a broad range of possibilities for novel strategies with a view to non-invasive diagnostics in medicine. We describe a method to detect differences between diseased and normal tissues, which involve Fourier transform IR microspectroscopy and fibre-optics methods. Regions of interest on 10 µm thin tissue sections were mapped using an IR microscope in transmission mode. After IR-mapping, the samples were analysed using standard pathological techniques. Quadratic discriminant and correlation analyses were applied to the IR maps obtained allowing differentiation between cancerous and normal tissue. The use of optical fibres, transparent in the mid-IR, allowed measurements to be made in the attenuated total reflectance (ATR)-mode at a remote location. The IR sensor is in contact with the sample that shows characteristic absorption lines. The total transmission of the fibre and the sample will decrease at these lines. This method can be used to determine the absorption of a sample in a non-destructive manner. In this paper we report on our efforts to develop an IR fibre-optic sensor for tissue identification as well as to differentiate between malignant and healthy tissue in vivo. We also describe the technical design of the laboratory set-up and the results of developments made. Silver halide fibres and a special sensor tip were used for the ATR measurements on tissue specimens. The results indicate that fibre-optic IR spectrometry will be a useful tool for bio-diagnostics.

A majority of photothermal applications of laser and non-laser light sources in medicine (in particular, in dermatology) are based on the paradigm of (extended) selective photothermolysis. However, realization of this principle in its strict form may not always be possible and/or practical. Spatial (or geometric) selectivity (as opposed to wavelength and temporal selectivity) can provide an alternative approach delivering effective and safe treatment techniques. A method of creating a lattice of localized areas of light–tissue interaction (optical islets) is an example of this 'spatially confined' approach. The lattice of optical islets can be formed using a variety of energy sources and delivery optics, including application of lenslet arrays, phase masks and matrices of exogenous chromophores. Using a state-of-the-art theory of optical and thermal light–tissue interactions and a comprehensive computer model of skin, we have conducted a theoretical and numerical analysis of the process of formation of such a lattice in human tissue. Effects of the wavelength, beam geometry, pulsewidth and physical properties of tissues have been considered. Conditions for obtaining optical, thermal and damage islet lattices in the human skin without inducing adverse side effects (e.g. bulk damage) have been established.