Simulation and Study of Temperature Distribution in Living Biological Tissues under Laser Irradiation

Introduction: With the rapid increase in use of lasers in medical treatments, it is important to understand the mechanisms of heat transfer in biological tissues in order to minimize damage to the tissues resulting from extra heat applied. The aim of this study is to investigate the temperature distribution in living biological tissues when laser irradiation is used in a treatment.Methods:  In this work a model was suggested to study the impact of several parameters such as (laser power, exposure time, laser spot size) on the temperature distribution within skin tissues when subjected to a laser source. A three-dimensional finite element thermal model of biological tissues was developed using bio-heat equation to describe heat transfer in living tissues.Results: Temperature distribution within skin tissues subjected to laser heating is calculated in details using the Finite element method and a suggested model; the results are presented in figures and tables showing the effects of Laser spot size, power and exposure time on temperature distribution within treated tissue.Conclusion: the results presented in this work  are expected to be useful in optimizing Laser spot size, power and exposure time for a variety of laser applications medicine and surgery.   

Polystyrene Microsphere Optical Properties by Kubelka–Munk and Diffusion Approximation with a Single Integrating Sphere System: A Comparative Study

The optical properties of 1 μm polystyrene in the wavelength range of 500–750 nm were estimated by using a white light spectrophotometric transmittance spectroscopy and a single integrating sphere system. To retrieve the optical characteristics, two analytical methods, namely, diffusion approximation and Kubelka–Munk were used, and then their results were compared with Mie theory calculations. The correspondence of the Kubelka–Munk scattering coefficient with Mie was obvious, and relative errors varied between 6.73% and 2.66% whereas errors varied between 6.87% and 3.62% for diffusion theory. Both analytical methods demonstrated the absorption property of polystyrene over the abovementioned wavelength range. Although absorption coefficient turned out to be much lower than scattering, constructing a realistic optical phantom requires taking into account absorption property of polystyrene. Complex refractive index of polystyrene based on these two methods was determined. Inverse Mie algorithm with scattering coefficient was also used to retrieve the real part of refractive index and absorption coefficient for calculating the imaginary part of refractive index. The relative errors of the real part did not exceed 2.6%, and the imaginary part was in consistence with the prior works. Finally, the presented results confirm the validity of diffusion theory with a single integrating sphere system

Optical properties in the visible range of two different India ink used as biological phantoms

The optical characteristics of two different brands of India ink, Parker Quink and Pelikan, as an absorber used in preparation a tissue-simulating phantom, have been investigated at visible wavelength range. For this purpose, a single integrating sphere system and a spectrophotometric transmission spectroscopy have been used to estimate the radiometric characteristics. Then, inverse adding-doubling algorithm was implemented to retrieve the optical coefficients of pure ink samples. Parker ink's absorption behavior turned out to incompatible with Pelikan over the present wavelength range. Furthermore, scattering property of both two brands has been exhibited and the albedo was calculated. Parker albedo showed a decremental behavior with wavelength and varied between 0.381 and 0.13. A structural profile of albedo was found for Pelikan, which varied between 0.366 and 0.03. This discrepancy might be explained by the variety of two brands composition besides experimental errors. Furthermore, Parker ink absorption variation turned out to be in correspondence to several tissues' absorption feature over broad wavelength ranges. Finally, Parker ink could be regarded as a better candidate to mimic absorption property for several tissues

Theoretical investigation of BODIPY based compounds as photosensitizers in photodynamic therapy

1040-1046In this work we carried out theoretical evaluation of the potential use of BODIPY and related compounds as photosensitizer in photodynamic therapy (PDT). Five compounds bearing the chromophore of 4,4-difluoro-4-bora-3a,4a-diazas- indacene (BODIPY) with substituent elements from the fourth column in the periodic table (Si-Ge-Sn-Pb) have been investigated. In the present study the density functional theory and its time dependent extension TD-DFT have been used to calculate the energy of ground, singlet-triplet excited states and energy for E s1 , E T2 o S o S The electronic absorption spectra, transition dipole moments (TDM) for spin-allowed S0→Sn and other properties have been calculated. The results of this work show that among the studied compounds, PM-Sn is potentially the best option for photosensitizer in PDT

Accurate derivation of THG conversion efficiency in periodically poled nonlinear medium and optimizing conversion parameters

We have derived a novel equation to accurately predict the third harmonic generation (THG) conversion efficiency in hybrid periodically poled nonlinear medium. Our equation considers the general case that takes both depleted pump regime and phase mismatching cases, resulting in more precise predictions of efficiency. This level of accuracy is crucial for certain applications like high-power THG lasers. Moreover, accurate calculation of THG power density is essential to prevent exceeding the crystal damage threshold. We applied our equation on hybrid MgO:PPLN crystal to determine the optimal SHG region length corresponding to two different power densities, namely, 0.25 and 0.5MW/cm2. The effect of crystal temperature on efficiency was also studies. Furthermore, a comparison between the derived equation and the commonly used nondepleted pump regime equation was performed. We found that the latter equation is significantly less accurate, particularly at high power densities, with the efficiency of the depleted pump regime being 50.6% less than nondepleted one. To demonstrate the effectiveness of the equation, our results were compared with experimental data, and we observed a good agreement between them

General solution of phase mismatched second harmonic conversion efficiency in periodically poled nonlinear medium

In this work we provide for the first time a novel and more accurate second harmonic generation (SHG) conversion efficiency equation for periodically poled nonlinear medium. We believe the equation derived in this work is more useful than equations reported in previous works which are limited because it is considering the case of either nondepleted pump regime or perfect phase matching. The equation derived in this work tackles the general case: depleted pump regime and phase mismatching which makes it important for theoretical – experimental study. We used MgO:PPLN crystal as an example to illustrate SHG conversion efficiency as function of crystal length, laser power density, crystal temperature and beam divergence. We included fundamental and second harmonic waves reflection at entrance and exit surfaces respectively and performed numerical solution using fifth-order Runge-Kutta method. The numerical results show excellent match with analytical results obtained from the derived formula. We compared our theoretical results with experimental results reported in the literature and the comparison shows a good match. Finally, we performed a comparison between depleted and nondepleted pump regime. The results show a difference of 20% between two efficiencies making nondepleted efficiency equation, which used in many theoretical – experimental comparisons, not accurate at high power densities

Palatini f(R) Gravity and Variants of k-/Constant Roll/Warm Inflation within Variation of Strong Coupling Scenario

We show that upon applying Palatini f(R), characterized by an αR2 term, within a scenario motivated by a temporal variation of strong coupling constant, then one obtains a quadratic kinetic energy. We do not drop this term, but rather study two extreme cases: α<<1 and α>>1. In both cases, one can generate a kinematically-induced inflationary paradigm. In order to fit the Planck 2018 data, the α>>1 case, called k-inflation, requires a fine tuning adjustment with nonvanishing nonminimal coupling to gravity parameter ξ, whereas the α<<1 case, studied in the constant-roll regime, can fit the data for vanishing ξ. The varying strong coupling inflation scenario remains viable when implemented through a warm inflation scenario with or without f(R) gravity