A new method of treating open-angle glaucoma is proposed. The concept of non-stationary thermo-mechanical stress under laser radiation in the wavelength range 1000-1600 nm in the structural elements of the anterior segment of the eye is developed. The solution of the problem of forced vibrations of a viscoelastic medium showed that a significant part of the cavitation pores formed in the negative phase of the laser-wave is stable and does not collapse with increasing pressure. The results of clinical studies have shown the stability of the laser-induced hypotensive effect over four years of follow-up.
A technique is presented for solving the problem of the thermomechanical effect of a pulsed laser beam on an absorbing medium, based on the numerical simulation of three-dimensional equations of the motion of continuous media in the Lagrange form. The structure of the excited acoustic pulses is analyzed depending on the space-time characteristics of the laser pulses.
The conditions for deep, controlled, low-temperature (cavitational) laser dissection of biological tissues through the formation of a directional wave of enlightenment are considered.
The theory of photo-thermal and photo-mechanical effects in absorbing media under action of short laser pulses has been developed based on numerical solution of motion equations for continuous media in the Lagrange form and heat transfer equation.
A computer model of the dynamics of temperature field in multilayer biological structure, containing a blood vessel, as a
result of the action of pulse laser radiation was worked out. The calculations were done with regard to the diffraction of
radiation and the heat exchange at the vessel boundary with the surroundings. The possibility of use of pulse modulated
laser radiation for the increase of the homogeneity of vessel walls coagulation and the decrease of the risk of tissue
injury, determined by phase transition, was considered.
A computer model of the dynamics of temperature field in multilayer biological structure, containing a blood vessel, as a
result of the action of pulse laser radiation was worked out. The calculations were done with regard to the diffraction of
radiation and the heat exchange at the vessel boundary with the surroundings. The possibility of use of pulse modulated
laser radiation for the increase of the homogeneity of vessel walls coagulation and the decrease of the risk of tissue
injury, determined by phase transition, was considered.
A computer model of blood vessel heating by pulse laser irradiation incident on the upper skin layer (epidermis) is suggested. The model is a multilayered half-infinite structure. The depths, optical (absorption and scattering), mechanical and thermal-optical properties of layers are in agreement with the real properties of epidermis and dermis of skin. The exterior of model object (epidermis) is illuminated by light beam of cylindrical form with homogeneous intensity distribution along the cross section. The blood vessel, situated in dermis, is simulated by infinite circular cylinder. Calculations of the dynamics of temperature field inside blood vessel taking into account an inhomogeneous distribution of volumetric heat release within it under the action of pulse laser irradiation of skin were made.
We are developing new diagnostic and therapeutic technologies for leukemia based on selective targeting of leukemia cells with gold nanoparticles and thermomechanical destruction of the tumor cells with laser-induced microbubbles. Clusters of spherical gold nanoparticles that have strong optical absorption of laser pulses at 532 nm served as nucleation sites of vapor microbubbles. The nanoparticles were targeted selectively to leukemia cells using leukemia-specific surface receptors and a set of two monoclonal antibodies. Application of a primary myeloid-specific antibody to tumor cells followed by targeting the cells with 30-nm nanoparticles conjugated with a secondary antibody (IgG) resulted in formation of nanoparticulate clusters due to aggregation of IgGs. Formation of clusters resulted in substantial decrease of the damage threshold for target cells. The results encourage development of Laser Activated Nanothermolysis as a Cell Elimination Therapy (LANCET) for leukemia. The proposed technology can be applied separately or in combination with chemotherapy for killing leukemia cells without damage to other blood cells. Potential applications include initial reduction of concentration of leukemia cells in blood prior to chemotherapy and treatment of residual tumor cells after the chemotherapy. Laser-induced bubbles in individual cells and cell damage were monitored by analyzing profile of photothermal response signals over the entire cell after irradiation with a single 10-ns long laser pulse. Photothermal microscopy was utilized for imaging formation of microbubbles around nanoparticulate clusters.
An advanced model of blood vessel heating by laser radiation is proposed for tasks of laser skin surgery and therapy. Blood vessel is modeled by infinite circular cylinder situated in skin dermis. Heat conduction equation taking into account the inhomogeneous internal source function is calculated. The source function inside the blood vessel is calculated according to the theory of diffraction of electromagnetic radiation on infinite circular cylinder. Dynamics of the temperature fields inside the vessels as a function of vessel diameters and duration of irradiance is calculated for the wavelength of 0.532 μm. It is determined the irradiance conditions whereby the near-homogeneous heating along the perimeter of walls of blood vessels on minimum laser exposure to surrounding tissues is achieved.
The radial distribution of Gaussian beams radiation intensity on the focal plain of the ocular optical system has been calculated using the human eye Modulation Transfer Function. The dependencies of the distribution on the distance to the beam's constriction have been analyzed for the visible spectral range at a given eye accommodation. More consideration has been given to the conditions of the most `sharp' focusing of laser beams onto the retina (the most dangerous cases) and to the typical errors arising in the process retinal irradiance distribution measurement through the pupil. The analogous model has been created for the eyes of some animals. The results of calculations are in a good agreement with direct measurements data at the back pole of enucleated rabbit eyes.
Action on biotissues of power laser pulses about 20 nsec was investigated by using high level mathematical model. The system of equations contains five unknown functions: temperature, pressure, axial and radial convection velocity, density. The 2D solution gives these functions depending upon the laser pulse shape and duration, power and spectral band of radiation. Calculations have been carried out for eye's fundus tissues. It has been found a kind of feedback between radiation power and rate of local tissue cooling. An increase in the irradiation power is accompanied by the growth of convective heat transfer and rate of medium cooling. Peculiarity of this phenomenon have been studied.
High level mathematical models have been used for optimizing regimes of photocoagulation of choroid new growths with minimal damage of the sensitive retina. Supposed spectral range and temporal irradiation regimes have given good results in experiments and in clinics.
A mathematical model of interaction between laser radiation and multilayer biological tissue has been developed. At a pulse duration shorter than 1 ms acoustic or shock waves are generated in the tissues simultaneously with a rapid temperature rise. At radiation power densities lower than approximately 109 W/cm2 in the absence of phase transition acoustic vibrations arise from thermal expansion of the heated volume.
The article is devoted to photocoagulation of the chorioretinal complex by two laser wavelengths (lambda) 1 and (lambda) 2 simultaneously with a controlled ratio of these components intensities. The thermal and biological effects such as mixing under definite conditions is equivalent to the effect of dye laser mono-chromatic radiation with the variable wavelength within the range from (lambda) 1 to (lambda) 2.
The report includes information about the new solid laser ophthalmocoagulator working at two wavelengths (lambda) 1 and (lambda) 2 simultaneously with a controlled ratio of these components intensities. The thermal and biological effects such as mixing in our conditions is equivalent to the effect of dye laser mono-chromatic radiation with the variable wavelength within the range from (lambda) 1 to (lambda) 2.
In this paper we consider the results of investigations and mathematical modeling of the main physical processes leading to fundus tissue destruction under the action of 10 ns - 1. 0 s radiation pulses of the visible and near IR spectral ranges as applied to the tasks of laser ophthalmosurgery. The model generates relative dimensions of coagulation and boundaries of destruction the model for different lasers and laser exposures. Applications for treatment and diagnosis of different eye diseases are also considered. 1.
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