IRANIAN JOURNAL OF MEDICAL PHYSICS
Year:2009 | Volume:5 | Issue:2 (20-21)|Papers Count:12

Introduction: Electroporation is a technique for increasing the permeability of the cell membrane to otherwise non-permeate molecules due to an external electric field. This permeability enhancement is detectable if the induced transmembrane voltage becomes greater than a critical value which depends on the pulse strength threshold. In this study, the variability of the electric field threshold and the minimal transmembrane voltage resulting in detectable electroporation of the plasma membrane of spherical and irregularly shaped cells have been investigated.Materials and Methods: Spherical cells of different dimensions and attached cells of various shapes were selected. The chosen cells were exposed to 100 µs electric pulses with incrementing amplitudes. Electroporation was detected by an increase in the fluorescence caused by an influx of Ca2+ and the threshold electric field for each cell was recorded. A 3D geometrical model of each cell was constructed from its cross sectional images. Simulation using the finite element method was performed to obtain the critical induced transmembrane voltage for each individual cell.Results: The magnitudes of the electric field strength threshold and critical transmembrane voltage versus cell radius were obtained for spherical cells. To investigate the effects of cell shapes and orientations on the field strength threshold and critical voltage, the considered attached cells were categorized into three different groups. Field strength threshold and critical voltage was obtained for each cells and the results for the different groups were compared.Discussion and Conclusion: Size, shape and orientation of cells affect the critical transmembrane voltage and all these elements in turn influence the electric field threshold and, therefore, the efficiency of electroporation.

Introduction: All of the people worldwide are exposed to low levels of radiation. Cancer induction and genetic disorders are among the hazards of low level exposure. In some cases, radiation close to hot springs is higher than normal areas due to a high concentration and the decay products of Ra-226. Given the use of hot springs by the general public because of their therapeutic properties, preparation of a guideline based on radiation levels of hot springs is believed to be necessary. In this study, gamma dose rate in the vicinity of hot springs in Kerman province was measured and the dose rates for sensitive organs were calculated.Materials and Methods: The equipments used in this study were an RDS-110 survey meter, a tripod with an aluminum frame, a chronometer and a thermometer. After defining 19 stations (one near each hot spring), the survey meter was fixed horizontally one meter above the hot spring and the gamma dose rate was recorded during one hour. Then, using the corresponding coefficients, equivalent, effective, bone marrow and reproductive organs dose rates were calculated. Independent T test and variance analysis were used for comparison of the means.Results: Gamma absorbed dose rates near nineteen hot springs in Kerman province was measured. The results showed that Amirekeykhosravi Spring had the highest annual dose rate (1.65±0.54 mSvy-1) and Gharayoob Spring had the lowest annual dose rate (0.53±0.23 mSvy-1). Also, the annual bone marrow and reproductive organs dose rates were within the ranges 0.42±0.18 mSvy-1 to 1.32±0.43 mSvy-1 and 0.43±0.19 mSvy-1 to 1.34±0.44 mSvy-1, respectively.Discussion and Conclusion: This study shows that the maximum annual dose rate in the vicinity of the hot springs in Kerman province was 120% higher than the outdoors annual dose rate for normal areas. This is due to the existence of radioactive elements in spring water and the high altitude of the springs from the sea level. Due to the high dose rate to sensitive organs, it is suggested that Chegeri, Ghaneghah, Gharayoob, Joshan and Chaharfarsakh springs are used as spas. Also, according to the results, there is no correlation between the gamma dose rate and the temperature of the springs.

Introduction: Evoked potentials arisen by stimulating the brain can be utilized as a communication tool between humans and machines. Most brain-computer interface (BCI) systems use the P300 component, which is an evoked potential. In this paper, we evaluate the use of the hidden Markov model (HMM) for detection of P300. Materials and Methods: The wavelet transforms, wavelet-enhanced independent component analysis  (W-ICA), and HMM combined with a multi-layer perceptron (MLP) neural network were used for P300 detection in electroencephalogram (EEG) signals. The BCI2005 competition dataset was used for their evaluation. First, electrooculogram (EOG) artifacts in the EEG signals were removed using W-ICA. Then, background EEG noise was suppressed using a B-Spline wavelet transform. Finally, these signals were classified using the HMM. Results: We used accuracy, sensitivity, specificity, positive predictive value, and negative predictive value to evaluate the performance of the proposed algorithm. The primary results in this research show that the HMM can perform much better using an auxiliary classifier. To this end, an MLP neural network was used to select the classes based on the outputs of the HMM models. The classification rates obtained for 15 and 5 times averaged test signals were 81.6% and 50.7% respectively. Discussion and Conclusion: Based on the obtained results, we may conclude that the HMM can be used for online P300 detection.

Introduction: As a physical treatment, electrochemical therapy (ECHT) has provided an effective and useful approach for treating localized tumors. The chemical changes due to a direct electric current destroy the tumor. This study evaluates the effect of electrical dose and polarity on the efficacy of the treatment of a colon tumor model.Materials and Methods: In order to induce tumors, 5´ 105 CT26 cells were injected into the right dorsal side of 100 Balb/c mice subcutaneously. When the mean volume of the tumors reached 350±50 mm3, they were randomly divided into 2 control and 8 test groups, each consisting of 10 mice. Six platinum electrodes (3 cathodes and 3 anodes) were inserted into the base and the apex of each tumor. Electrical doses of 0, 10, 20, 30 or 40 C/cm3 were then applied. Tumors volumes were subsequently measured daily and the mortalities were recorded. A histopatholological study was also performed.Results: After ECHT, a decrease in tumor volume and also an increase in necrosis and cumulative survival were statistically significant. In the control groups, the tumors were not destroyed and the mice did not survive more than 50 days. With 40 C/cm3 electrical dosage and anode electrode polarity applied to bases of the tumors, 80% of the tumors showed complete response until 120 days post-treatment. Increasing the electrical dose caused a statistically significant effect on the complete response percentage and the cumulative survival fraction. Applying anode polarity to the bases of the tumors produced better results although without statistical significance.Discussions and Conclusions: Complete response in the treatment groups (10 to 80 percent) demonstrates the antitumor effects and the high potential of electrolysis for tumors eradication. Also, occurrence of only one death event in the highest electrical dose group and the good health of the animals until 120 days after treatment demonstrate that electrolysis is a safe technique.

Introduction: Breast cancer is a leading cause of death among females throughout the world. Currently, radiologists are able to detect only 75% of breast cancer cases. Making use of computer-aided design (CAD) can play an important role in helping radiologists perform more accurate diagnoses.Material and Methods: Using our hybrid method, the background and the pectoral muscle were removed from mammography images and image contrast was enhanced using an adaptive density weighted method. First, suspected regions were extracted based on mathematical morphology and adaptive thresholding approaches. Then, in order to reduce the false positives in the suspected regions obtained in the first stage, the corresponding features were extracted using a wavelet transform, followed by the application of a support vector machine to detect masses.Results: A Mammographic Image Analysis Society (MIAS) database was used to evaluate the performance of the algorithm. The sensitivity of 81% and specificity of 84% were achieved in detecting masses. Improvement of sensitivity and specificity with our proposed hybrid algorithm was demonstrated by subjective expert-based and objective ROC-based techniques in comparison with the currently acceptable method by Masotti.Disscusion and Conclusion: In this paper, a hybrid method of pixel-based and region-based mass detection approaches is proposed to increase the specificity of the results. The accessory stage (using wavelet features) increased the sensitivity by 30%. It can be concluded that the proposed algorithm is an efficient and robust method for different types of mass detection in low-quality mammography images.

Introduction: In this study, we utilized the MCNP4C Monte Carlo code to quantitatively evaluate the influence of crystal size and material on intercrystal scatter and parallax effects.Materials and Methods: For each of the 5 selected crystals (BGO, LSO, LYSO, LuAP, GSO), transport of 511 keV photons originating from a point source and incident on the central crystal of a block detector consisting of a 13×13 array of 4 mm × 4 mm × 20 mm crystals was simulated. Functions such as position detection accuracy (PDA) and point spread function (PSF) in different crystals were considered by changing the parameters such as crystal thickness, crystal pixel size and gamma ray angle of incidence. The code was validated against the simulated data published by Shao et al.Results: The results of the simulations and their analysis showed that increasing the crystal pixel size increased the PDA and decreased the ICS but increasing the crystal thickness decreased the PDA and increased the ICS.Discussion and Conclusion: By considering the attenuation properties of 511 keV photons, we conclude that BGO is the most appropriate crystal for reducing the intercrystal scattering phenomenon. However, the higher light yield and lower decay time of LSO and LYSO makes them the most appropriate crystals for use in PET systems. The obtained functions for intercrystal scattering can be used for recovering spatial resolution and improving image quality in the image reconstruction process.

Introduction: Age-related Macular Degeneration (AMD) is one of the most important causes of irreversible blindness in the developed world and prevents the affected person from performing simple tasks such as reading, driving and facial recognition. In the AMD, new blood vessels grow underneath the retina in a process called choroidal neovascularisation (CNV). There is much interest in the quantification of the angiographic features of CNV, as these parameters are used as markers for monitoring the response to CNV treatment. To date, the techniques used in angiographic analysis are based on subjective interpretation by experienced clinicians. The goal of the present study was to propose an automatic algorithm for determining the extent of CNV.Materials and Methods: The proposed algorithm was used to analyze indocyanine angiograms of 12 patients with CNV. The angiograms were acquired by a confocal scanning laser ophthalmoscope. The algorithm included an adaptive Wiener filtering technique, a top-hat morphology method and a new thresholding technique based on a modification of Otsu’s method. The area of each lesion was obtained and compared with a subjective evaluation of CNV. Finally, each area was expressed in square millimeters by making a cylindrical tube filled with indocyanine green.Results: The CNV area was determined by the proposed algorithm and an observer. No significant differences were observed between the two data sets (p>0.05).Discussion and conclusion: This study demonstrates that the proposed algorithm based on a modification of Otsu’s method can be used to measure the area of CNV.

Introduction: Pressure sores refer to lesions that are produced while a constant pressure causes necrotic tissue to grow. The need for a better comprehension of the process has led researchers to artificial generation of pressure sores. Modeling the mechanical behavior of tissue will provide a better understanding of this process as well as a more suitable selection of system parameters.Materials and Methods: In this research, the mechanical behavior of tissue was modeled using the finite element method. A system with pressure sensors and a suitable feedback mechanism was used to generate pressure sores. The elastic parameters of tissue were obtained using uniaxial tensile strength tests. The thicknesses of skin layers were calculated by taking microscopic images of skin samples and using Motic Images 2000 version 1.2 software.Results: The results of the finite element modeling illustrate the strain and stress profiles in tissue layers. The maximum values of deviatory strain occurred under the border of the disc in the muscle layer. Deviatory and shear stresses reached their maximum values under the center of the disc in the skin layers.Discussion and Conclusion: The simulation and experimental results are in good agreement. Therefore, the introduced model may be used for better comprehension of tissue behavior. Better results may be obtained by finding a more accurate method for calculating tissue parameters.

Introduction: Radiation effects observed in cells that are not irradiated are known as non-targeted effects. Radiation induced bystander effect (RIBE) as a kind of non-targeted effect has been introduced in recent years. RIBE occurs in unexposed cells which are related to adjacent or distant irradiated cells. RIBE contradict with "target theory" which necessitates radiation traversal through the nucleus for affecting cells. Methods: To understand this phenomenon, some investigations and review articles which deal with this subject were studied. Most investigators have applied in vitro experimental methods to investigate RIBE in animal or human cells, but in vivo experiments are also increased in recent years. Results: Both low and high LET radiation cause RIBE. Cell responses to RIBE are including: cell death, chromosomal damage, mutagenesis, neoplastic transformation, genomic instability, cell cycle delay, modification of gene expression and radiosensitivity alteration. At low doses that only some cells are irradiated this phenomenon is significant. However RIBE exists at high doses, due to predomination of direct radiation effects it is less considered. There is link between RIBE and other non-targeted effects such as adaption and genomic instability. Conclusion: At low doses, there is no linear relationship between outcome and the number of cells hit by radiation. Thus this will affect the basic principle of defining dose limits which have been initiated by linear no threshold curve. There is a scope to exploit RIBE in radiotherapy, and also it is important to avoid undesirable bystander effects in normal tissues.