Iranian Journal of Medical Physics
Volume:12 Issue: 3, Summer 2015

All biological samples emit ultra-low intensity light without any external stimulation. Recently, scientific communities have paid particular attention to this phenomenon, known as ultra-weak photon emission (UPE). UPE has been introduced in the literature as an alternative for biophoton, low-level chemiluminescence and ultra-weak bioluminescence, while it differs from ordinary bioluminescence, fluorescence and phosphorescence. Some UPE parameters including spectrum and intensity have been already recognized, while other features such as the main origin(s), statistical distribution and fractality of UPE are partially understood. Ultra-weak photon detection has a broad range of potential applications in different industries such as agriculture and medicine. The correlation between UPE and physiological state of a system facilitates the use of UPE as a completely non-invasive diagnostic method in cases such as cancer detection. In this review article, we aimed to provide useful information on specific characteristics, possible origin(s) and potential applications of UPE. Moreover, we introduced some physical models for UPE and presented several controversial hypotheses in this context.

As a tumor grows, the demand for oxygen and nutrients increases and it grows further if acquires the ability to induce angiogenesis. In this study, we aimed to present a two-dimensional continuous mathematical model for avascular tumor growth, coupled with a discrete model of angiogenesis. In the avascular growth model, tumor is considered as a single mass, which uptakes oxygen through diffusion and invades the extracellular matrix (ECM). After the tumor reaches its maximum size in the avascular growth phase, tumor cells may be in three different states (proliferative, quiescent and apoptotic), depending on oxygen availability. Quiescent cells are assumed to secrete tumor angiogenic factors, which diffuse into the surrounding tissue until reaching endothelial cells. The mathematical model for tumor angiogenesis is consisted of a five-point finite difference scheme to simulate the progression of endothelial cells in ECM and their penetration into the tumor. The morphology of produced networks was investigated, based on various ECM degradation patterns. The generated capillary networks involved the rules of microvascular branching and anastomosis. Model predictions were in qualitative agreement with experimental observations and might have implications as a supplementary model to facilitate mathematical analyses for anti-cancer therapies. Our numerical simulations could facilitate the qualitative comparison between three layers of tumor cells, their TAF-producing abilities and subsequent penetration of micro-vessels in order to determine the dynamics of microvascular branching and anastomosis in ECM and three different parts of the tumor.

Radiotherapy with small fields is used widely in newly developed techniques. Additionally, dose calculation accuracy of treatment planning systems in small fields plays a crucial role in treatment outcome. In the present study, dose calculation accuracy of two commercial treatment planning systems was evaluated against Monte Carlo method. Siemens Once or linear accelerator was simulated, using MCNPX Monte Carlo code, according to manufacturer’s instructions. Three analytical algorithms for dose calculation including full scatter convolution (FSC) in TiGRT, along with convolution and superposition in XiO system were evaluated for a small solid liver tumor. This solid tumor with a diameter of 1.8 cm was evaluated in a thorax phantom, and calculations were performed for different field sizes (1×1, 2×2, 3×3 and4×4 cm2). The results obtained in these treatment planning systems were compared with calculations by MC method (regarded as the most reliable method). For FSC and convolution algorithm, comparison with MC calculations indicated dose overestimations of up to 120%and 25% inside the lung and tumor, respectively in 1×1 cm2field size, using an 18 MV photon beam. Regarding superposition, a close agreement was seen with MC simulation in all studied field sizes. The obtained results showed that FSC and convolution algorithm significantly overestimated doses of the lung and solid tumor; therefore, significant errors could arise in treatment plans of lung region, thus affecting the treatment outcomes. Therefore, use of MC-based methods and super position is recommended for lung treatments, using small fields and beamlets.

One of the most important pre-processing steps in optical coherence tomography (OCT) is reducing speckle noise, resulting from multiple scattering of tissues, which degrades the quality of OCT images. The present study focused on speckle noise reduction and edge detection techniques. Statistical filters with different masks and noise variances were applied on OCT and test images. Objective evaluation of both types of images was performed, using various image metrics such as peak signal-to-noise ratio (PSNR), root mean square error, correlation coefficient and elapsed time. For the purpose of recovery, Kuan filter was used as an input for edge enhancement. Also, a spatial filter was applied to improve image quality. The obtained results were presented as statistical tables and images. Based on statistical measures and visual quality of OCT images, Enhanced Lee filter (3×3) with a PSNR value of 43.6735 in low noise variance and Kuan filter (3×3) with a PSNR value of 37.2850 in high noise variance showed superior performance over other filters. Based on the obtained results, by using speckle reduction filters such as Enhanced Lee and Kuan filters on OCT images, the number of compounded images, required to achieve a given image quality, could be reduced. Moreover, use of Kuan filters for promoting the edges allowed smoothing of speckle regions, while preserving image tissue texture.

Natural and artificial radionuclides are the main sources of human radiation exposure. These radionuclides, which are present in the environment, can enter the food chain. Rice is one of the most important food components in Iran. Radionuclides by transferring from soil to rice and entering the human body can affect human health. Fourteen samples of different varieties of rice, nine soil samples from rice fields and four samples of consumed water were collected from four villages around Gorgan, Iran. Specific activities of 226Ra, 232Th, 40K and 137Cs were determined in the samples, using gamma ray spectrometry and a high-purity germanium (HPGe) detector. Moreover, transfer factors of radionuclides from soil to rice were determined. Specific activities of 226Ra, 232Th, 40K and 137Cs were determined in the soil and rice samples. The annual effective dose due to rice grain consumption in Iranians varied from 20.50±0.74 to 68.40±11.71 µSv/y. Transfer factors from soil to rice for 40K and 226Ra varied from 0.09 to 0.13 and 0.02 to 0.07, respectively. The calculated annual effective dose due to rice grain consumption by Iranians was within the average annual global range. Therefore, this study indicated that radionuclide intake due to rice consumption had no consequence for public health. The calculated transfer factors were higher than that reported by the International Atomic Energy Agency (IAEA) in 2010; however, the values were much lower than measurements in Malaysia.

Radiation protection is an important safety issue for radiographers and patients. The aim of this study was to assess the observance of radiation protection regulations in radiology departments of Kermanshah University of Medical Sciences, Kermanshah, Iran. In total, 48 radiographers and 8 radiography rooms were evaluated in three hospitals of Kermanshah, Iran. Additionally, 120 patients were randomly selected in the present study. For data collection, a questionnaire on radiation protection devices, radiographers, and patients was completed. Data were analyzed, using Microsoft Excel. Based on the analysis, 56.8% of radiation protection devices were accessible to radiographers. Overall, 81.3% of radiographers stated that they utilized film badges for radiographic procedures, while only 71.7% had used these badges in practice. Additionally, 54.2% of radiographers claimed that they regularly performed medical check-ups; however, based on the documents available at personnel offices, only 43.8% had taken this measure into account. Also, 60.4% of radiographers claimed that they had participated in annual training courses, while based on the records, only 41.7% had participated in such courses. The majority of radiographers had no regard for radiation protection principles for either themselves or the patients. Apparently, not only hospital authorities, but also heads of departments ignore radiation protection principles for the patients and radiographers.

Two-dimensional gel electrophoresis (2DGE) is a powerful technique in proteomics for protein separation. In this technique, spot segmentation is an essential stage, which can be challenging due to problems such as overlapping spots, streaks, artifacts and noise. Watershed transform is one of the common methods for image segmentation. Nevertheless, in 2DGE image segmentation, the noise and artifacts of images cause over-segmentation in the watershed algorithm. In this study, we proposed a novel spot-enhancement anisotropic diffusion (SEAD) method, based on multi-scale second-order derivatives and eigensystemto enhance the spots and remove noise and artifacts. The proposed SEAD algorithm was plugged to a watershed transform in order to improve the performance of watershed segmentation algorithm. The performance of the proposed SEAD method was evaluated on synthetic and real 2DGE images. The proposed algorithm was compared with other segmentation methodsin terms of different criteria including efficiency, precision and true positive rate. The performance of the methods were evaluated in the presence of noise and the results were evaluated by t-test. According to the count of detected spots, precision and efficiency of the proposed method were 0.82 and 0.67 respectively. The precision and efficiency values of the comparative methods were as follows: 0.65 and 0.42 for MCW algorithm, 0.40 and 0.37 for BWT method, 0.74 and 0.53 for the method proposed by Kostopoulou and 0.76 and 0.55 for the method proposed by Mylona. The comparison of the proposed method with four other conventional methods revealed the superiority and effectiveness of the proposed SEAD method.

Lead-based shields are the most widely used attenuators in X-ray and gamma ray fields. The heavy weight, toxicity and corrosion of lead have led researchers towards the development of non-lead shields. The purpose of this study was to design multi-layered shields for protection against X-rays and gamma rays in diagnostic radiology and nuclear medicine. In this study, cubic slabs composed of several materials with high atomic numbers, i.e., lead, barium, bismuth, gadolinium, tin and tungsten, were simulated, using MCNP5 Monte Carlo code. Cubic slabs (30×30×0.05 cm3) were simulated at a 50 cm distance from the point photon source. The X-ray spectra of 80 kVp and 120 kVp were obtained, using IPEM Report 78. The photon flux following the use of each shield was obtained inside cubic tally cells (1×1×0.5 cm3) at a 5 cm distance from the shields. The photon attenuation properties of multi-layered shields (i.e., two, three, four and five layers), composed of non-lead radiation materials, were also obtained via Monte Carlo simulations. Among different shield designs proposed in this study, the three-layered shield, composed of tungsten, bismuth and gadolinium, showed the most significant attenuation properties in radiology, with acceptable shielding at 140 keV energy in nuclear medicine. According to the results, materials with k-edges equal to energies common to diagnostic radiology can be proper substitutes for lead shields.