Lasers in Medicine
Year:2010 | Volume:7 | Issue:2 (36)|Papers Count:8

Background and Objectives: CR-39 plastic material with the chemical formula C10H18O7, addition to various scientific and research applications is the best option for medical lens. The color of CR-39 color changes by to laser irradiation and high-energy photons. CR-39 is also very sensitive to alpha radiation. Tracks make because stopping of alpha particle in CR-39. Along the every track, CR-39 is changed and its surface is damaged. The air contains radioactive radon gas that with progeny are famous as alpha particles emitter. Alpha that is decayed by radon and progeny, affect the performance of CR-39 plastics and remained tracks damage it. In this paper will try to use the Monte Carlo method, to simulate the density of damaged tracks and the depth of this damge in CR-39 that is produce by radon and progeny activity.Methods: In this simulation we need the data of stopping power of Alfa in air CR-39. This data are drawn from SRIM 2008 software. Radon in the air that is moving in a random place will randomly decay. Consequently, the alpha particles that arrived to CR-39 have a wide energy spectrum. By this simulation, the angle and energy spectrum of alpha particles that are descended on CR-39 is obtained introducing a new method trying to draw the CR-39 alpha particle range as a function of descended alpha particle energy. Activity of radon progeny is not equal with radon activity. The ratio of Radon progeny Activity’s to radon activity ratio (or equilibrium factor) is taken really.Result: Tracks are different angles, but maximum population is in 300 angles. Depth of damage caused by daily activities of radon is 35 mm. In depth of 15-25 mm that the track density is a little fluctuation, every track is corresponding with 100 Bq/m3 due to daily radon activity. Track density in this simulation is equal 0.142 (Track/cm2)/ (Bq.d/m3) that coincides with experimental results that reports by Lopez and et al.Conclusion: In medical application of CR-39, damages that produce by radon and progeny, gradually cause opaque lens, loss in resolution, change in refract index and finally produce light scattering in CR-39 plastic.

Pulse oximetry and oxygen saturation monitoring improve the medical care methods such as anesthesia and infants’ intensive care. Pulse oximetry method is basically more efficient than monitoring the fetal heartbeat since direct oxygen saturation measurement from fetal blood would be possible. The designing of device, including choice of an appropriate wavelength and space for monitoring, plays a significant role in improving its sensitivity to the depth and arterial pulse rate. This study simulates the interaction between light and tissue based on Monte Carlo’s method and uses the results to construct the pulse oximeter.Method: For this purpose, a 10-layered tissue model, with different sizes of thickness, including artery pulses of systole and diastole phases, has been considered. Also, this study focuses on the separation of information related to mother and fetus.Result: According to the best location of detectors and trial and error method, the optimal wavelengths of 675 and 800 nanometers have been achieved. Studying only the single effect of each one of (shot and electronic noises) on the model shows the significant difference between the percent of input oxygen saturation and outcome results. However, considering these noises simultaneously causes less difference. The simulation results are obtained in different wavelengths, using 106 photons and 49 detectors. The percentage of oxygen saturation, in comparison with the input database, has exhibited 2% error deviation from zero.

Background and Objectives: Osteoblast attachment on titanium surface is necessary to achieve new bone formation and osteogenesis. The purpose of the present study is to analyze the influence of Er- YAG laser irradiation (with two different powers) on titanium disk surface characteristics and human osteoblast like cells, saos-2, morphology.Material and methods: SLA titanium disks were radiated with two different power (n=10, 100mJ/pulse, n=10, 60 mJ/pulse). A control group of non- irradiated disks was also examined. After laser irradiation, saos-2 cells were cultivated on the titanium disks and examined with scaning electron microscopy.Results: the most finding of spread cells with pseudopodia that demonstrated maturation were observed on all the 3 groups (the irradiated and non- irradiated disks). statiscal analysis with kruskal-wallis test between groups revealed non- significant different (P<0.393).Conclusion: these results indicate that the Er:YAG laser irradiation in the 60mJ/pulse and the 100 mJ/pulse power dose not change the biocompatibility of SLA- titanium suface.

Background and Objectives: In this paper, the photothermal interaction of CO2 laser with human skin of 100 mm thickness was investigated and temperature distribution of the skin was comprehensively analyzed.Procedure: In this paper, the heat equation was applied to the human skin which was assumed to possess a planar shape and the effects of the laser radiation versus time, depth and laser power were investigated.Results: It is shown that there would be a maximum in temperature increase curve versus time occurring at depth of 1.23 mm inside the epidermis. This perhaps shows that laser radiations with powers more than 700 mW which is equivalent about 16 W/cm2 can take the skin and its epidermis section to the region of burning.

Introduction: Oral cancers are one of the most common worldwide cancers. Conventional therapies including surgery, radiotherapy and chemotherapy cause patients, disability. Photodynamic therapy (PDT) can destroy cancer cells selectively by preferential concentration of photosensitizer in neoplastic cells followed by local illumination of the tumor by light, an appropriate wavelength. The aim of this study is to review clinical studies focused on treatment of oral cancers by PDT.Search strategies: Data sources included electronic databases of Pubmed, Scopus, and Google Scholar. Key words of “Photodynamic therapy” and “Oral cancer” were used to access articles published between 1990 till 2010.Result: results included 25 articles that full texts of 17 articles were accessible. 5-aminolevulinic acid (ALA) is only suitable for treating extremely superficial oral tumors of 1-2 mm depth. Meta-tetrahydroxyphenylchlorin (mTHPC) is much more potent in destroying tumorous cells.Conclusion: According to the result of this review, photodynamic therapy is a non-invasive method of tumorous tissue destruction. More studies are needed to find ideal photosensitizer and light source to make PDT as a conventional therapy of head and neck cancers.