In this work, for the first time, we have demonstrated the biological effects upon in vitro growth of bacteria and human peripheral blood erythrocytes of the irradiation with speckle-like highly-gradient laser light. Measurements of the growth of Staphylococcus aureus with and without antibiotic irradiated with uniform or interference pattern of intensity spatial distribution have shown strong dependence on the spatial frequency of the irradiation. Maximum inhibition of the bacteria growth was achieved at the frequency 1000 fringes/mm. It was also found that human blood erythrocytes exposure to such radiation at the power density typical for laser phototherapy could damage the erythrocytes. A possible explanation of the photo-biological effects of laser speckle irradiation relying on the electron-ion processes similar to those that occur under inhomogeneous illumination in inorganic media and called photo-stimulated diffusion of ions (Dember effect) is proposed and discussed.
Monochromatic light therapy (MLT) is still not a clinical modality due to conflicting and low predictable outcomes. This likely is due to the mismatch between the accuracy of optical dosimetry employing the theoretically predicted or empirically found dosages and the dynamic requirements of photobiostimulation to dosage. The same doses delivered to a target area can be stimulatory or not depending on the dynamic changes of tissue optical parameters in vivo. Since the optical parameters of tissue and, hence, the radiant energy absorbed in the target area change during the treatment, it is important monitoring and coordinating the dosage with these changes.
In this paper we analyze potentials of advancing to dosimetry that meets the dynamic requirements of the MLT to dosage. Both the tissue optical clearing and the feedback control of irradiation are considered. It is pointed out that the key physiological parameter influencing the variability of actual dose is the blood microcirculation. Even the optimal doses of continuous light irradiation may produce negative therapeutic effect at the time when the target tissue is depleted of blood and cannot maintain the energetic requirements of treatment. It is shown that synchronization of irradiation with the patient's pulse and breathing waves excludes cycles of negative responses and individualize the dosage.
Spectral study of light dosimetry for clinical LLT based on a simplified one-dimensional model of a two-layered medium analyzed within the limits of Kubelka-Munk approximation is presented. The relationship between the surface irradiance and the fluence rate seeing by a target at a given depth in tissues is studied for various irradiating wavelengths. The behavior of the fluence rate is also examined as a function of a blood volume fraction in tissues. Strong dependence of the fluence rate in skin on irradiating wavelengths has found in visible spectrum from about 600nm to about 800nm. In contrast, the fluence rate does not change much over the near infrared region from 800nm t0 1,300nm. Spectral dosimetry in blood content muscles exhibits progressive increase of the fluence rate over visible and near infrared ranges. It has shown that blood perfusion of tissues differently affects the fluence rate at various wavelengths. The discussed model allows estimation of the surface irradiance required to provide the therapeutic value of the fluence
rate at a target.
We present theoretical calculations and experimental imaging results that demonstrate the possibility of extending viewing distances through blood simply by selection of an ‘optimal’ illuminating wavelength and use of a camera with appropriate parameters. Based on a simple one-dimensional model of image signal formation and employing Kubelka- Munk theory of light transport in a turbid medium, we derive an analytical expression that describes the effect of optical properties of the medium and camera parameters on image signal. Experimental images of an artificial target placed behind a sample of human blood of different thickness taken in transmission and reflection modes confirm the predicted imaging possibilities. An optical-difference offset technique developed to enhance image contrast is demonstrated as well.
Claims of different effects of cold laser (CL) irradiation may be attributable to the competition of different reaction channels activated by CL and/or the unreproducibility of irradiation conditions. This study is concerned about reproducibility of the conditions of irradiation. We present a comparative analysis of the correlation between irradiation characteristics and biostimulation parameters, and show that the leading cause of treatment unreproducibility is the discrepancy of therapeutical and true irradiation doses. We analyze different approaches of true dose determination, influence of blood content and microcirculation on dosage and describe principles of true doses generating. It is shown that only on-line regulation of both parameters of dosage, CL power and temporal mode of irradiation, allows the determination of individual true dose. Problems of designing CL with feedback for on-line regulation of dosage parameters are also described.
The changes of diffuse reflected light by tissues with blood pulse circulation as function of external pressure was studied. The experimental measurements were performed with steady state and pulsatile components of the photoplethysmographic signal taken from human finger under compression. Specially designed reflection-mode sensor registered the true waveform of pulse waves. The unexpected change of the pulsatile amplitude from increasing to decreasing with compression was found. To explain this effect a Kubelka-Munk approximation model of a deformable medium with embedded particles of different types and concentrations was developed. On the basis of this model it is shown that the observed optomechanical effect is brought about by a shift of the balance between blood pressure and the external pressure of stressed vessel walls and surrounding media. The results show capability of photoplethysmographic technique to detect very small local tissue stress changes and to measure local vessel wall elasticity.
The use of Gaussian probing beams for measuring parameters of distributed lenses is well known. But common methods become invalid in widespread cases when investigated media contain additive scattering inhomogeneities. This report is devoted to the usual scheme generalization able to overcome mentioned restrictions. It is shown that utilizing arbitrary paraxial probing beams, characterized by space-angle intensity moments, enables us to solve this task effectively. The equations for evolution of moments in lens-like media with small- scale stochastic inhomogeneity are derived and analyzed, on which basis some recommendations are made for fast and suitable measurement of medium parameters.
The application of probing beam space-angle intensity moments for investigation of optically inhomogeneous biological objects is considered. Special attention is paid to measurements of lens-like inhomogeneities in the presence of scattering caused by small-scale fluctuations of refraction. The results can be used in ophthalmology for non-invasive early detection of cataractous changes in human eye lens and in laboratory experiments with blood fluxes.
The use of space-angle intensity moments in description and characterization of a paraxial laser beam with small-scale inhomogeneities of its transverse shape is presented. The connection between the moments and customary beam characteristics is discussed. The equations of moments evolution in lens-like optical media with small-scale scattering inhomogeneity are derived and analyzed, on the basis of which some recommendations for fast and suitable medium parameters determination are made.
The new model of biotissue as a medium with two kinds of inhomogeneities -- small-scale, representing randomly placed scatterers and absorbers, and large-scale, corresponding to the macroscopic structures -- is proposed. The first and second moments of space-angle intensity distribution of the optical beam propagating in such medium are considered. It is shown that the possibility exists to define parameters of each scale inhomogeneity separately through the moments measurements for conditions often realized in medicine. The results are suitable for development of optical non-invasive diagnostic methods.
The discharge current influence on the homogeneous broadening of the spectral lines in the gas-discharge media by direct collisions of the excited atoms with free electrons and also through collision broadening changing because of the gas heating by discharge current is considered. It was established that homogeneous broadening and hence the frequency shift of the spectral line depend essentially on the thermal condition of the laser work. The theoretical calculations are confirmed by the experimental measurements of the dependence of the homogeneous broadening of spectral line 3s2 - 2p4 neona in the He-Ne laser on the discharge current magnitude. For the homogeneous broadening determination by the experimentally measured Lamb dip characteristics a new computation method was developed, which can be used both in single-mode and two axial modes conditions of laser generation. It has been shown that on its basis and using known dependencies of the collision broadening of the spectral lines on the pressure, there can be realized an express-control of the main sources of the generation frequency unreproducibility in the sealed off discharge tubes, such as gas pressure and relative excitation of the laser system.
Direct measurements of radial optical inhomogeneity in long narrow elements (gas-discharge tubes, optical fibers, filamental crystals, etc.) entail some difficulties conditioned both by geometry and by littleness of optical properties absolute variations, especially critical in absorptive photothermospectroscopy. At the same time, in many such cases transverse optical inhomogeneity is close to lens-like type. It allows us to realize convenient and accurate procedure for measuring such inhomogeneity, disposing the inhomogeneous sample into the laser resonator and observing the inhomogeneity effect on the characteristics of generated radiation. This report presents general theoretic foundations for the proposed approach. Some variants of this procedure are analyzed and their advantages over common ones are shown. Experimental examination of the proposed method with an example of the He-Ne discharge element has shown its validity and usefulness.
A model of the calculation of the diffuse reflection of the living tissue based on Kubelka-Munk theory is presented. The equation describing the relationship between backscattering of the living tissue and radiation parameters, inanimate tissue optical characteristics, and chromophores concentration is outlined. The use of the method in clinical dosimetry is given.