Time-resolved and continuous wave diffuse transmittances of near IR light through cylindrical phantoms were measured for the purpose of inhomogeneity detection and image reconstruction. Performed model experiment for homogeneous and inhomogeneous cylindrical phantoms provides a complete experimental data set for optical tomography. Some of the acquired data are presented. Possibility to use them for validation of analytical and numerical models of photon propagation is demonstrated. Good agreement with an analytical solution and 2D FEM simulated data was reached. A new index for inhomogeneity detection is introduced and its effectiveness is demonstrated.

We will present tow methods leading to the solution for the problem of anisotropical light scattering by arbitrarily shaped bodies. Each method converts the equation of radiative transfer and the boundary conditions valid at the boundary of the scattering medium into a set of Fredholm integral equations of the second kind, i.e. an inhomogeneous set of linear equations for the unknown boundary values of the intensity. The two different equations will be derived for the sphere and cylinder resp., and shown to be valid for arbitrarily shaped bodies. Numerical results will be presented. The integral equation approach leads to the construction of a class of non-radiating source distributions and invisible bodies.

The propagation of photons in media for which the diffusion approximation does not hold is investigated. To that end simulations are performed with a finite-difference discrete- ordinate transport code and compared to analytical diffusion calculations. Differences between these transport simulations and diffusion calculations point to features specific for non-diffusive photon migration in homogeneous and heterogeneous tissues.

We present a reconstruction scheme which solves the inverse linear problem in optical absorption tomography for radially symmetric objects. This is a relevant geometry for optical diagnosis in soft tissues, e.g. breast, testis and even head. The algorithm utilizes an invariance property of the linear imaging operator in homogeneously scattering media. The inverse problem is solved in the Fourier space of the angular component leading to a considerable dimension reduction which allows to compute the inverse in a direct way using singular value decomposition. There are two major advantages of this approach. First the inverse operator can be stored in computer memory and the computation of the inverse problem comprises only a few matrix multiplications. This makes the algorithm very fast and suitable for parallel execution. On the other hand we obtain the spectrum of the imaging operator that allows conclusions about reconstruction limits in the presence of noise and gives a termination criterion for image synthesis. To demonstrate the capabilities of this scheme reconstruction results from synthetic and phantom data are presented.

The ill-posed inverse problem is not an issue that is only restricted to optical tomography, but indeed a very common issue in image reconstruction problems in astronomy, geological surveying, and medical imaging in general. In this paper we investigate the consequences of ill-posed problems, and show that correct reconstruction is generally not possible using conventional linear inversion techniques because latter methods disregard contributions of the nullspace. We describe the rationale of a novel image reconstruction method that estimates the nullspace contribution using prior knowledge in a maximum-aposteriori- probability framework. We illustrate our concept by an example of optical tomographic reconstruction from simulated and experimental data.

Time and space resolved measurements of diffuse backscattered light form turbid media were performed to determinate the optical coefficients of biological tissues. The reflectance maps registered on a streak camera were analyzed with two different methods based on the diffusion approximation. These fast and practical methods were initially tested on suspensions of latex spheres in water to compare the experimental results with the theoretical coefficients derived from Mie theory. Measurements were then achieved on biological tissues.

For many different optical applications in medical diagnosis, like optical biopsy or optical tomography, it is important to know about the local varying optical tissue parameters. Only the knowledge of these parameters (mu) _a, (mu) _s' allows a proper interpretation of particular fluorescence or scattering intensities. THe research presented here deals with basic investigations about the extraction of optical parameters in the first cell layers from the tissue surface down to the depth of some millimeters. The paper includes results from fiberbased measurements with Intralipid20 phantoms in infinite and semi-infinite geometry and a discussion about the possibilities to develop a flying-spot scanner. This frequency domain scanning device is under construction. It can be applied within the validity range of the diffusion approximation and provides a full (mu) _a and (mu) _s detection possibility in a 2D, non-contract mapping mode.

A reconstruction method based on the diffusion approximation for the light propagation in turbid media and on a minimization strategy is presented. A higher accuracy for the forward simulation and a considerable reduction of the computational effort are reached by solving a partial differential equation for the difference between the time- dependent photon density in an inhomogeneous object and the density in the homogeneous case given by an analytic expression. The calculations are performed by a 2D-FEM algorithm, but considering a time-dependent corrective factor the 3D situation is well approximated. The number of free variables of the inverse problem can be strongly reduced by exploiting a priori information such as the search for single inhomogeneities within a relatively homogeneous object, a typical situation for breast cancer detection.

In this paper we discuss diffraction effects on laser computed tomography and time-resolved imaging in a random medium. Our basic point is that light diffracted by an object embedded in a random medium contains useful and important information about its structure and therefore should be included in the imaging process. To support this point of view, we compute diffracted fields from opaque and semi-transparent cylindrical objects of various sizes. Based on these results we conclude that to improve imaging in random media, diffraction effects should be taken into account, even for cases in which the size of the observed object is much larger than the optical wavelength.

Effective scattering coefficients in the range of (sigma) _eff equals 20 - 5000 cm^-1 and absorption coefficients of (kappa) equals 0 - 200 cm^-1 of densely packed turbid materials are determined from the radial distribution of reflectivity R((rho) ) upon laser spot irradiation. A scanning reflectometer with micrometer resolution is presented for the experimental determination of R((rho) ). The experimental reflectance curves are fitted with analytical solutions of the equation of transfer, which to this end is expanded into a series of spherical harmonics, P₁, P₃, P₄... Comparison with Monte-Carlo simulations shows that the first series member, P₁, describes only the range far from the center of irradiation, while the whole P₅-set fits the entire reflectance curve. Results are given for a series of powders and for porcine aorta. The anisotropy parameter of scattering of alumina powder is determined to g approximately equals 0.24 from the laterally resolved degree of polarization of light reflected from the vicinity of the incident laser spot.

Theoretical and computer modeling approaches, such as Mie theory, radiative transfer theory, diffusion wave correlation spectroscopy, Monte Carlo simulation method were applied for tissue optics analysis in a process of its clearance. CW collimated transmittance and forward scattering measurements as well as intensity correlation experiments were used for tissue structure and optical properties monitoring. Conrolled tissue samples of the human sclera were taken. A chemical applicator-conrollers Trazograph, glucose and polyethileneglycol solutions were used. On the base of sclera samples clearance investigation the general principles of tissue optical and structural parameters controlling were established.

With laser-Doppler flowmetry (LDF) there can be examined qualitatively parameters of microcirculation such as flux, concentration, and speed of the erythrocytes in tissues. The LDF procedure is based on the signal processing of Doppler- shifted laser light. LDF measuring gear doesn't provide information on the origin of the backscattered photons, i.e. about the extension of the inspected tissue range. These and other information, which are important for the diagnostic judgement of the microcirculation of the tissue, can be estimated with the help of a computer simulation. Therefore the authors have developed a computer program which is able to simulate LDF measurements.

Time-resolved laser tomography is a promising technique for noninvasive laser examination of structure and condition of biotissues. The results of Monte-Carlo simulations discussed in this paper are related with time-resolved laser Doppler tomography of blood transport in the tissues. In this technique the temporal variations of the optical signal carry information about blood transport. By simulating laser light propagation in a human skin model an opportunity for in-depth by selecting the photons with short, medium, and long transit times. As an example a possibility for detection of a small blood vessel embedded in dermis is considered.

To explain the ablation of cortical bone with Ho:YAG-laser radiation a model for tissue ablation at scattering dominated conditions was developed. It states a logarithmic increase of the ablation rate as a function of laser intensity, which is proportional to the penetration depth of diffusion theory. The model considers the increase of the radiant energy fluence rate inside of the scattering medium, which is described by the accumulation factor. Solving an inhomogeneous diffusion equation for the case of isotropic scattering the radiant energy fluence rate was calculated, which delivers an analytical expression for the accumulation factor.

Int his article, we analytically present the influence of the systematic error due to the theoretical assumptions on the blood oxygenation determination using a 'phase-only' dual-wavelength phase-modulation spectroscopy (PMS). To approach an accurate quantification of hemoglobin saturation, an empirical method to experimentally acquire the initial phase-shift value in oxygenation quantification form PMS data is investigated on blood-perfused phantom. Our results show that the quantification error of blood oxygenation determination can be substantially compensated by using the acquired (theta) ₀^(lambda ) method and is confirmed to be less than 10 percent by comparison with the measured results of the Pt electrode.

There are many dynamic tests in the last years where an exercise using a specific muscle is assessed by near-IR spectroscopy. It is not possible to find studies of static positions of the human body where one part of it is changing alternately to the normal position. The result gives the deoxygenation and blood volume signals in the same way as when a muscle is exercised. The important differences are in the turn on-off time when the arm changes the position, the effect of training after six days doing the same test, and the difference in the calibration signals before and after each test.

A procedure is presented to release soft x-rays onto yeast cell membrane allegedly damaging the resident enzymatic processes connected with fermentation. The damage is expected to be restricted to regulating fermentation processes without interference with respiration. By this technique fermentation is followed leading to CO₂ production, and respiration resulting in global pressure measurements. A solid state pressure sensor system has been developed linked to a data acquisition system. Yeast cells cultures have been investigated at different concentrations and with different nutrients. A non-monotone response in CO₂ production as a function of the delivered x-ray dose is observed.

The theoretical and experimental studies were carried out for statistical characteristics of photon paths in strongly scattering media dependently on type of inhomogeneities, boundary conditions and method of measurements. The possibility to represent the signal perturbations due to the macroinhomogeneities as an integral along the mean photon path is used to solve the tomography reconstruction problem in terms of volume quantization. The optimum quantization scale is chosen on the basis of area across which the macroinhomogeneity characteristics are averaged.

In a turbid medium illuminated by a collimated light beam the effect of the attenuation of the coherent field is usually described by assuming a single scattering model. This approximation is justified if we limit to consider weak diffusive media in which the individual scatterers does not differ substantially from the surrounding medium. However in order to replicate the scattering properties of turbid biological media it is important to explore the range corresponding to high volume concentrations of random particles where multiple scattering effects must be taken into account. In this paper we extend the Keller theory for the calculation of the attenuation constant by including third order terms in the perturbation expansion of the stochastic equation governing wave propagation in dense random media. We have derived a new analytical expression for the quadratic and cubic coefficient in concentration as a function of the scatterers diameter and of the light wavelength in the medium. The paper presents numerical calculations of these coefficients for various particles diameters and concentrations.

We present a sensor for acquisition of cross-sectional images of volume scatterers, we call it 'spectral radar'. Medical and technical applications are possible. The sensor is a modified Michelson interferometer, with a broad bandwidth light source. The scattering amplitude a(z) along one vertical axis from the surface into the bulk can be measured within one exposure. No reference arm scanning is necessary. Measurement results of stationary and non stationary scattering phantoms, human skin and of a fish eye in vitro are shown.

Imaging of highly scattering objects in scattering media can play an important part in assessing melanoma in human skin. The technique to be presented is based on frequency modulated continuous waves using a coherent tunable semiconductor laser irradiating a Michelson interferometer. The electrically tunable laser is characterized and the procedure to linearize the instantaneous frequency with time is described. The temporal point spread function of dilute milk is measured. Finally the performance of our imaging system is demonstrated on 2D-images of solid scattering phantoms and of an eye of a pig.

The technique of execution of any movement in Judo is extremely important. The coaches want tests and tools easy to use and cheaper, to evaluate the progress of a judoist in the tatame. In this paper we present a test developed by Mirallas, which has his name 'Test of Mirallas' to evaluate the maximal power capacity of the judoist. The near infrared spectroscopy (NIRS) signals were obtained to have a measurement of the metabolic work of the flexor carpi ulnaris and radialis muscles, during the execution of the ippon-seoi-nage movement, allowing this measurement to assess by NIRS the maximal oxygen uptake. Also obtained were tympanic, skin forehead, and biceps brachii temperatures during the test time and recovery phase to study the effects of ambient conditions and the post-exercise oxygen consumption. The deoxygenation and blood volume signals obtained gave different results, demonstrating the hypothesis of the coaches that some judoist do the execution of the ippon-seoi-nage movement correctly and the rest didn't. The heart rate frequency obtained in the group of judoist was between 190-207 bpm, and in the minute five of post-exercise was 114-137 bpm; the time employed in the MIrallas's test were from 7 feet 14 inches to 13 feet 49 inches, and the total of movements were from 199 to 409. The data obtained in the skin forehead, and skin biceps brachii confirms previous works that the oxygen consumption remains after exercise in the muscle studied. According to the results, the test developed by Mirallas is a good tool to evaluate the performance of judoist any time, giving better results compared with standard tests.

The electrotherapy field has been generated as a technique to improve the muscles of people affected by various pathologies. For this reason the electrotherapy is increasing its use as part of a treatment in muscle therapy. However there are not studies related to electrostimulation and near-IR spectroscopy. This work was designed to assess by near-IR spectroscopy the effects of electrostimulation in the vastus medialis, applying a tetanic contraction in this muscle with a compensated rectangular impulse at 100Hz, tolerating the subject 10mA of current. In the results obtained, we have not observed significant variations in the deoxygenation and blood volume signals, whereas as light change was observed comparing the calibration signals before and after to apply electrostimulation. It is postulated that electrostimulation only increases the diameter of the vessels, because the muscle doesn't do a metabolic work, and the heart rate frequency of the subject has not increased.

This study has been focused to find the importance of the consumption of oxygen for a muscle that works supporting the weight of the human body. The oxygen uptake at rest level is a data know, but by near-IR spectroscopy can be assessed the oxygen uptake used for a muscle. The energy required by the human body is partially used to produce the energy that help to move the human structure. The oxygen required by the muscles to produce the energy to support the human body has been defined as weight oxygen consumption. The purpose of this study was to assess by near-IR spectroscopy the amount of relative oxygenation/deoxygenation that a muscle requires at rest level and a middle-term rest level.

The spectra K((lambda) ) and parameter p equals (epsilon) (1 - (mu) ) for the cases of high pathology of blood in a wide spectral region cannot be reconstructed with a high accuracy, using only for model of weak absorption. The analysis of a large experimental data shows that the possibility of absorption spectra K((lambda) ) reconstruction is taken into account by means losses on boundary of two medium slabs. The new algorithm of inverse problem solving is supposed for increasing of spectra K((lambda) ) accuracy. The absorption coefficients reconstruction of blood healthy persons and patients in a wide spectral region by using supposed algorithm and theoretical ones are analyzed. The possibility of derivative hemoglobins and their decomposition products concentration in blood is shown in future with more accuracy than earlier.

Possibility of interaction between the two optically coupled samples of whole human blood as studied. A quartz cuvette was placed inside a vial for a liquid scintillation counter. Saline diluted whole blood was poured into the vial and either undiluted blood or saline was poured into the cuvette. Respiratory burst (RB) was initiated in blood placed into the vial, and luminol-dependent chemiluminescence (LCL) was registered. Blood placed in the cuvette affected photon emission from blood placed in the vial. Blood of another group of donors enhanced photon emission from the 'partner' sample. Some properties of blood taken from the cuvette after being in the contact with the sample in which RB was induced changed in comparison with the same blood that was contacting with the non-stimulated sample. Exposed blood has lost the ability to attenuate light emission from the fresh portion of blood in which RB was induced. Besides its own LCL in response to addition of zymosan was different from that of the control These results suggest that two chemically separated but optically coupled samples of blood can interact.

We have performed time-resolved imaging of diffusely scattering solid phantoms containing an optical inhomogeneity with increased absorption or scattering to simulate a human breast with a tumor inside. Images based on time-domain quantities derived from measured distributions of times of flight of photons are compared to those based on Fourier components. Investigations of contrast and signal- to-noise ratio of transillumination images recorded at different exposure times, i.e. at different numbers of photons detected, show that full images of the phantoms can be obtained within a few minutes only. In addition, we demonstrate that low power picosecond semiconductor lasers are suited for fast time-resolved imaging.

The purpose of this research is to investigate and improve the possibilities of optical coherence tomography for evaluation and imaging of the skin structure and dermatological diseases as melanoma. Single point detection, as done with a photodiode on the human eye was not successful in reaching high resolutions in strong scattering media as the skin. Therefore, an experimental setup with a very sensitive slow-scan CCD-camera and a suitably adapted interferometric arrangement was built. Measurements were performed on models and ex vivo biological material up to a depth of 2 mm. Developments concerning a specially shaped fast detector head with on-line analogue data processing are presented.

We adapted a method, the 'coherence radar', that was originally developed for the precise measurement of surface topology, to measure bulk properties within strongly scattering media. The sensor is based on short-coherence- interferometry. It enables the 2D observation of light propagation in scattering media with a high temporal resolution. The measurements are carried out by observing photons that traveled form an entrance focus through the bulk of the sample, and back to the surface. The source of information is the speckle contrast. One important result is that during the propagation a sharp photon horizon evolves. This photon horizon can be used for the detection on inhomogeneities in the scattering properties. In solid samples we measured absorbing obstacles with a depth of 320 micrometers and a depth uncertainty of < 5 percent. The measuring time is about 30 seconds. The observation of the photon horizon can also be realized in 'life' volume scatterers with moving scattering particles. First in vivo measurements of human skin have been successful.