ABSTRACT
To improve methods of laser hyperthermia for the treatment of bulk malignant neoplasms, an urgent task is the development of techniques and devices that automatically control heating at a given tissue depth and ensure its uniformity. The article proposes the concept of a system for performing hyperthermia with real-time spectroscopic temperature control and surface cooling, which allows to record spectra of diffusely scattered radiation and fluorescent signal from various depths of biological tissues by the means of the variation of the angle and distance between the fiber source of laser radiation and the receiving fiber. Theoretical and experimental modeling of the spatial distribution of diffusely scattered radiation and temperature inside the tissue with a fiber optic device providing surface cooling of the irradiated tissue, and recording spectral information from a given depth in real time, is presented. Simulation of radiation propagation in biological tissues, depending on the distance between the source and the receiver and the angle of their tilt, was carried out using the Monte Carlo method. Modeling of the temperature distribution inside the tissues was carried out by means of a numerical solution of the heat conduction equation. Experimental modeling was carried out on phantoms of biological tissues simulating their scattering properties as well as accumulation of the investigated nanoparticles doped with Nd3+ ions. It was shown that inorganic nanoparticles doped with rare-earth Nd3+ ions can be used as temperature labels for feedback to the therapeutic laser. According to the results of the theoretical simulation, optimal configurations of the relative arrangement of the fibers were chosen, as well as the optimum surface cooling temperatures for the given power densities. The heating of the phantom of the neoplasm containing the investigated nanoparticles doped with Nd3+ ions by laser radiation with an 805-nm wavelength and power density of 1 W/cm2 up to 42 °C at a depth of 1 cm while maintaining the surface temperature within the limits of the norm was demonstrated.
Subject(s)
Cold Temperature , Hyperthermia, Induced , Laser Therapy , Models, Theoretical , Nanoparticles/chemistry , Neodymium/chemistry , Luminescence , Monte Carlo Method , Neoplasms/therapy , Optical Devices , Phantoms, ImagingABSTRACT
This research is focused on the 4f-5d transitions in Ce(3+) centers doped into tetragonal ß-SrAlF(5) single crystals belonging to the I4(1)/a space group. The presence of four non-equivalent Sr(2+) sites in this compound leads to the appearance of three spectroscopically non-equivalent Ce(3+) luminescence centers, which can be well distinguished using a time-resolved laser spectroscopy technique. All 4f-5d transitions have slightly varying excitation and emission energies with characteristic probabilities resulting in several decay times that can be determined experimentally. One of these centers experiences strong perturbation due to a defect nearby, probably the O(2-) impurity ion substituting for the F(-) ion and acting as a charge compensator as well. Identification of these photoluminescence centers is performed using crystal field calculations. The crystal field parameters are calculated for two identified centers using the structural data for SrAlF(5); diagonalization of the crystal field Hamiltonian results in obtaining the splitting of the Ce(3+) 5d states. This method allows 'regular' unperturbed Ce(3+) centers with selected Sr(2+) sites to be assigned.
Subject(s)
Aluminum/chemistry , Cerium/chemistry , Fluorides/chemistry , Ions/chemistry , Luminescent Measurements/methods , Models, Chemical , Spectrum Analysis/instrumentation , Strontium/chemistry , Crystallization , Luminescence , PhotonsABSTRACT
Detailed analysis of the spectroscopic properties of the YAlO(3) crystals doped with manganese ions has been performed. The exchange charge model of the crystal field was used to calculate the crystal field parameters and energy levels of the Mn(4+) and Mn(5+) ions in YAlO(3). It was shown that both ions contribute to the formation of the absorption spectra. The calculated energy levels are in good agreement with the main observed absorption peaks. Comparison of the Racah parameters B for both ions in YAlO(3) with those for free ions shows a significant role played by the covalent effects, especially for Mn(5+).
