Iranian Journal of Medical Physics
Year:2006 | Volume:3 | Issue:12|Papers Count:9

Introduction: Nowadays, medical imaging plays an important role in the health care systems around the world. Diagnostic radiology is still a fundamental technique by providing valuable services to the society. Undoubtedly diagnostic radiology is by far the largest contributor of radiation dose to the society as a whole from the man made sources. The national radiation protection board (NRPB) introduced the use of diagnostic reference levels (DRLs) as an efficient standard for optimizing the radiation protection of patients. The physical parameter recommended for monitoring the (DRLs) in conventional radiography was the entrance kin dose (ESD) and methods for measuring it were clearly described in NRPB standard protocol. Materials and Methods: In this study, the dose measurements were carried out in 15 radiological centers. The data were collected for 1183 radiographs of adult patients. The sample of patients was chosen so that the eight of the patients was in the range of 40-107 kg. A total of eight typical x-ray examinations were chosen or the study. The entrance surface dose (ESD) was directly measured by thermoluminescence dosimeters (TLDs).Results: The average skin dose (mGy) of patients arising from x-ray examinations included in this study are as following: Chest PA- 0.34, chest Lat- 0.82, lumbar spine AP- 2.76, lumbar spine PA- 5.2, pelvis AP- 1.9, abdomen AP- 2.1, skull PA- 1.78, skull Lat- 0.96. Discussion and Conclusion: So far the national DRLs for Iran have not been reported. Therefore, our results were compared against those reported by NRPB for UK. It is evident that the average ESDs obtained in this work for abdomen AP, pelvis AP, lumbar AP and lumbar Lat examination do not exceed DRLs values worked out by NRPB. On the contrary for chest PA, chest Lat, skull PA and skull the ESD acquired in this study was higher in comparison with the DRLs suggested by NRPB. The differences are related to different film screen speeds and techniques used in the radiological departments included in these two studies. With respect to the role of radiographic parameters on the patient dose, it is possible to optimize these parameters to maintain the image quality while reducing patient dose.

Introduction: In the present research, by the use of Monte Carlo method the TG-43 dosimetry parameters of 125I model 6711 have been determined and its relative dose has also been calculated. Materials and Methods: 125I model 6711 brachytherapy source which is manufactured by Amersham Company and has been approved by the American Association of physicists in Medicine (AAPM) was used in this simulation. The Source was considered in the center of 30 cmx30 cm x 30 cm water and soft tissue phantom and the relative dose variation along the parallel and perpendicular direction to the source axis were calculated using MCNP 4C code. Water having a density of 1 gram per cubic centimeter composed of two hydrogen atoms and one oxygen atom and soft tissue with density of 1.04 gram per cubic centimeter with accurate composition was used in this simulation. Results: In this research, the percentage depth dose (PDD) variation along the different axis parallel and perpendicular to the source has been calculated using F6: p tally with less than 5% relative error. These data were then used to derive the isodose curves for PDD= 125%, 100%, 75%, 50% and 25%. Also, anisotropy function F(r,q) and radial dose function g(r) have been calculated for the source. Discussion and Conclusion: The percentage dose variation and dosimetry parameters have been calculated in this research are in good agreement with the results of others. This finding can be used to improve brachytherapy result with this source. Since the absorbed dose near a source is high and its gradient is significant, only Monte Carlo simulation can be used for an accurate calculation. The results demonstrate a useful approach using MCNP code in dose calculation that can be applied in other fields of medical physics.

Introduction: Nowadays, cardiac arrhythmias are one of the most important life-threatening factors in the world. Electrocardiogram (ECG) is an exclusive non-invasive tool for cardiac arrhythmias detection (CAD). Intelligent methods of detecting cardiac arrhythmias are the best and assured ways for accurate and real-time detection methods to satisfy this purpose. Materials and Methods: Artificial neural networks (ANNs) are efficient and intelligent tools for solving diverse problems in pattern recognition tasks such as detection and classification. These networks are the simple models of human nervous system having powerful capability in modeling and parallel processing in addition to having simple structures. In this research, a novel method of detecting cardiac arrhythmias is proposed by the use of a wavelet network (WN). This network is an innovative tool, which incorporates the advantages of ANNs in learning, predicting in addition to the high accuracy and multi-resolution analysis of wavelet transform (WT). Wavelet network also has the capability of activation function selection in respect to the given signal and distinctive algorithms for network architecture optimization. Results: In this study, the data from MIT-BIH database were used to implement this novel method. The obtained result has an accuracy of 98.8% which is an improvement in comparison with the similar works. Discussion and Conclusion: The result of this work shows a higher accuracy in compared to the one obtained from other methods such as neural networks and wavelet transform.

Introduction: X-ray is the most important and applicable tool in medicine, which is utilized in radiography and radiotherapy. Considering the difficulties exist in measuring x-ray profile there have been tremendous efforts to determine the profile by employing computational methods. FLUKA code is one of the multi purpose Monte Carlo codes, which can be used to simulate x-ray tubes. In the previous papers, MCNP results have been benchmarked with experimental data. In this work, the result obtained from Fluka code is compared to the data from MCNP code. Materials and Methods: MCNP 4C and Fluka 2006 codes have been employed to simulate x-ray profile. For the simulation of x-ray profile MCNP 4C and FLUKA2006codes were employed. The Geometry of the tubes has been implesmented accurately in the simulation. The angle of electrons' departure for electrons from the cathode is exactly considered in order to get 1.2mm focal spot. The anode is made from Tungsten with an angle of 12 degree. The thickness of the aluminum filter is 1.2 mm. Results: The result of x-ray profile from FLUKA and MCNP codes are determined prior to and after the filter. In order to survey the filter effects, the ratio of the profile before the filter to the one after the filter for both codes in 120 ke V is calculated. Discussion and Conclusion: The result obtained from MCNP and FLUKA codes are comparable in the range of bremsstrahlung spectra, but there are some differences between the results of FLUKA and MCNP codes especially in specific x-ray peaks, The most important feature to be used to evaluate the quality of x-ray tubes profiles and the filter effects are the bremsstrahlung x-ray profile. Therefore, both FLUKA and MCNP codes are fairly good in simulatingx-ray tubes profiles.

Introduction: Scattered photons are one of the main causes of degrading the contrast of lesions and resolution in SPECT imaging of the heart that result in error in quantification. The usual technique for the rejection of scattered photons is through energy windowing. However, because of limited energy resolution of current scintillation cameras it is impossible to avoid scatter photons from detection. Modeling of Compton scattering through finding suitable functions was proposed in this study. These functions were used for scatter correction through deconvolution in next step. Materials and Methods: Monte Carlo simulation was used for creating projections of three different activity sources: a line source passed through left ventricle, a point source placed in left ventricle and finally real activity distribution of Tc-99m in torso organs. All of these sources were placed in a digital attenuation phantom which modeled a real patient body. Images of primary and scattered photons were acquired separately. Convolution and 2D deconvolution in Fourier domain was applied for estimating the primary projections through total ones. Results: In the first step, scatter and total images were modeled as convolution of a modified exponential function with primary image. The best exponent value was determined for each of 64 views (0.115 to 0.150 according to heart to detector distance). In the next step, these functions were used for scatter correction through deconvolution. Sum of the square differences between the primary and scatter corrected images were decreased considerably, myocardium to cavity contrast increased for all of 64 views (34% ±10%). Good agreement between the real primary and scatter corrected images were also found. Discussion and Conclusion: These results indicate that deconvolution technique for the scatter compensation can significantly reduce the degrading roles of scattering in quantitative SPECT imaging.

Introduction: Decision making and diagnosis of certain diseases can be a challenge for physicians. Neural networks have been used as clinical decision support systems. These networks are powerful algorithms which are capable of learning complex patterns and maintaining their accuracy even in cases when some data is missing. Congestive heart failure (CHF) and chronic obstructive pulmonary disease (COPD) have many similar symptoms which can make their distinction difficult especially at the time of admission or where the access to echocardiography is limited. Materials and Methods: The multilayer perceptron (MLP) and radial basis function(RBF) neural networks were used to differentiate between congestive heart failure and chronic obstructive pulmonary disorder patients (n=266) using 43 clinical variables which were normalized following consultations with cardiologists. Bayesian regularization was used to improve the generalization of the MLP network. To design the RBF network, K-Means clustering was used to select the centers of radial basis functions, k-nearest neighborhood to define the spread and forward selection to select the optimum number of radial basis functions. A ten-fold cross validation was used to assess the generalization procedure. Results: The MLP led to a sensitivity of 88.3 %, specificity of 83.7% and an area under receiver operating characteristic curve (AUC) of 91.9±1.7 while RBF network resulted in 79.6 % sensitivity, 93 % specificity and AUC of 92.7±1.7. Discussion and Conclusions: Neural networks have been developed as a diagnostic algorithm in many clinical decision support systems and this study like many others confirms their ability to perform well in diagnosing certain diseases such as differentiating between COPD and CHF.

Introduction: Low extinction coefficient of photosensitizers is considered to be one of the limitations in the efficacy of photodynamic therapy. It is also a well known fact that each photosensitizer is activated at a specific wavelength of the light spectrum, which is the main limitation encountered in deep therapies. In this research, electrical activation of two photosensitizers have been studied in in-vitro conditions to find out the probable synergistic effect of electric pulses and light in order to improve the efficacy of treatments for the deeply seated tissues. Materials and Methods: The study was carried out on Wehi-164 fibrosarcoma cell line of Balb/c mouse using two different doses of electric pulses, light as well as two concentrations of the dye. Two hours after the incubation of the cells with 5-Aminolevalenic Acid (5-ALA) and Zinc phthalocyanine sulfate, square electric pulses generated by an electroporator BTX, and illuminating by a non coherent light source at peak wavelengths of 630 and 670 nm was performed. Twenty four hours post treatment the cell survival percentages were determined using MTT method and then it was compared against the control.Results: Significant difference was obtained when 0.2 mM of 5-ALA, low and high doses of light and pulses of 900 and 1000 V/cm as well as when the concentration of 5-ALA was increased to 1 mM and three light doses (0, 16, 54 J/cm2) were applied. Significant difference was observed between the samples receiving and not receiving pulses upon using a concentration of one  mM of Zinc phthalocyanine and lower light dose. Similar results were obtained under the following conditions: 10 mM concentration of the dye and higher light dose1 mM concentration of the dye, 0 and 1000 V/cm pulses in the dark and lower light dose10 mM concentration of the dye, 0 and 800 V/cm pulses in the dark and higher light dose Discussion and Conclusion: It seems that electric pulses activate high concentration of protoporphyrin IX. Also, 1000 V/cm pulses are more effective in the activation of 5-ALA than 900 V/cm pulses. It is predicted that the 1000 V/cm pulses applied on post incubated cells with 1mM concentration of Zinc phthalocyanine have been able to activate the dye in the absence of light exposure. Overall it seems that increasing the height of electric pulses is more effective in the process of the activation of dyes.

Introduction: Glioma comprises about 50% of all primary central nervous system malignancies. Despite using surgery, radiotherapy and chemotherapy as means of treatment the prognosis for these patients remains poor. Efforts to improve the treatment of malignant Glioma include radiosensitization of cancer cells using Iododexyuridine (lUdR) as a thymidine analogue, which is preferentially incorporated into the DNA of tumor cells to sensitize them to radiation.Materials and Methods: In this study, we achieved Do for Glroma A 172 cell line in monolayer culture which was 1.7 Gy for exponentially growing cells and 2.2 Gy for plateau cells respectively. 1 mM IUdR alone induces significant cytogenetic aberrations in A 172 glioblastoma cell line.  Results: The number of cytogenetic aberrations induced by IUdR demonstrated a considerable discrepancy between exponentially growing and plateau phase cells. The value of sensitizing Enhancement Ratio (SER) derived through colony assay was equal to 1.36 for exponentially growing cells and 1.04 for plateau cells, whereas metaphase analysis showed 2.49 for exponentially growing cells and 1.05 for plateau phase cells. Discussion and Conclusion: Different findings of SER values between colony assay and metaphase analysis methods might be due to the repair time given to the cells during colony assay method. The difference in SER values between exponentially growing cells and plateau cells is probably due to different uptake of IUdR by cells in these two phases One of the main barriers for the effectiveness of IUdR when accompanied with external beam therapy is the presence of Go cells. As the drug alone induces aberrations, continuous long intra-arterial infusion of IUdR in place of intra-venouse infusion, may lead to better results.