IRANIAN JOURNAL OF MEDICAL PHYSICS
Year:2003 | Volume:1 | Issue:3|Papers Count:9

Positron emission tomography (PET) is an intrinsically quantitative tool that provides a unique and unparalleled approach for clinicians and researchers to interrogate the heart noninvasively. The ability to label substances of physiological interest with positron-emitting radioisotopes has permitted insight into normal blood flow and metabolism and the alterations that occur with disease states. Positron emission tomography (PET) of the heart has evolved as a unique, noninvasive approach for the assessment of myocardial perfusion, metabolism, and function. Because of the intrinsic quantitative nature of PET measurements as well as the diverse compounds that can be labeled with positron-emitting radioisotopes, studies with PET have provided rich insight into the physiology of the heart under diverse conditions.      

Introduction: One of the main parameters in a successful brachytherapy treatment of cancers is dose calculation. 1921 is a radioactive choice for interstitial of the cancers. To deliver an accurate predefined dose to the tumor it is necessary to use a suitable dosimetric method. One of these methods is Monte Carlo simulation and dose calculation. Materials & Methods: In this investigation MCNP4B Monte Carlo Codes are used to calculate depth dose at different distances from two types of 1921sources, one with one centimeter length and 0.1 mm diameter as a line source and the other with 0.5cm with 0.3 mm diameter as a point source. F4 and F6 tallies of the MCNP4B codes are used to calculate air kerma, exposure rate, and radial' doses at different points in a Plexiglas and water phantoms. Result & Discussion: Obtained air kerma strength and exposure for wire source are 3.87 ?Gy.m2.h-1 and 4.42 ?R.m2.h-1 and for point source are 3.6287 ?Gym2.h-1 and 4.13 ?R.m2.h-1 respectively. Obtained dose rate constant for wire source using F4 and F6 tallies were the same and equal to 1.13 cGy.U-1.h-l with a 4.4% differences with experimental results measured by TLD method. Experimental results measured by TLD method are more in confirmation when F6 tally is used in Comparison with F4.    

Introduction: Although there have been an extensive study about voltage dependent Na+ and K+, yet there is not any interpretation based on digital simulation to show the properties of these gates against the different voltage commends effect. In most electrophysiological studies by taking advantage of rectangular voltage in the method of voltage-clamp to the cell in the vicinity of ionic channels inhibitory solutions with different concentrations, that cause activate or deactivate one or both gates, and registration the current flow from membrane, properties of the gates have been considered. Methods and Materials: In this research while simulating excitable cell model, the effect of Quasi trapezoidal voltage commands in related to closing and disclosing voltage dependent Na+ and K+ channels, in Hodgkin-Huxley excitable cell model is studied. Results: In applying of Quasi trapezoidal voltage commands with short pulse width and long fall time constant, the gates of K+ almost became deactivated and the time of voltage dependent Na+ channel conduction separately can be controlled. Also with the use of Quasi trapezoidal voltage commands that has long pulse width and determined time constant, closing time of K+ gates can be controlled. Appling of Quasi trapezoidal voltage commands along with long raise time constant, voltage dependent Na+ channels almost deactivated while voltage dependent K+ channels were activated. Discussion: The cell electrical activity is prompted by alterations ionic channel conduction and the alterations of ionic conductions of voltage dependent Na+ and K+ channels arise from activate or deactivate of these channel gates. So by controlling the gates of a cell we are able to control its electrical activity, and by performing a special process, learning and memory could be possible. Meanwhile pure current ionic can be separated, and without pharmacological tools utilizing, that can have an inhibitory effect on the ionic channel situation and make it difficult considering the physiological conditions study.      

Introduction: Registration of scattered photons along with the primary photons is a major cause of degrading image quality and quantitative accuracy in single photon emission tomography. To deal with the problem some techniques have been developed. Deconvolution is the technique that considers the effect of scatter as convolution of the primary photons with a scatter function. Therefore the image of the non-scattered photons could be extracted from a mixed image of scattered and non-scattered photons using a deconvolution technique. Methods and materials: In this study the complex wavelet wiener deconvolution was used as a method of deconvolution. We used Monte Carlo generated phantoms to simulate the scattered and scatter free Images. Results: This simulated study showed that the method improves the image quality and quantitative accuracy up to 1.5 dB in comparison to scatter reduction in the energy window of 20%. Conclusion: Complex wavelet wiener deconvolution has the potential to be used as an efficient scatter compensation method. Other deconvolution methods such as iterative may also be used on the high pass sub-bands components of complex wavelet decomposition as a complementary method.      

Introduction: This article describes an effort for diagnosing breast cancer from mammography findings by using a non linear mathematical model in the form of Logistic Regression Analysis. Materials & Methods: The data were extracted from 122 adult women's mammography films by an expert radiologist equipped with 12 diagnosis criteria, then the model was fed by these data. Because all of the patients after mammography were undergone breast biopsy, their pathology reports were collected and coded (benign cases by 0 and malignant cases by 1). The data were entered to the model and after being ensured by model's train ability, the data were clustered into two groups, train group (82 sets) and test group (40 sets), and were entered to the model again. The software calculated probability of being benign or malignant for the test group cases, the probability was represented in the range 0 to 1. The output of model was then compared to pathology codes and the results were reported as model's prediction on the test group cases. Result & Discussion: As a result model ability to predict sensitivity, specificity and accuracy was, in order, 83%, 77%,80% and radiologist ability to predict these definitions was in order, 92%, 69%, 86%.      

Introduction: Fluoroscopy is an important diagnostic technique in medicine. Among fluoroscopic procedures barium swallow (BS) and upper gastrointestinal (UGI) account for a large number of examinations. During these procedures, the thyroid of patients is normally irradiated by the primary and scatter ionizing radiation causing both the deterministic and hazardous effects on this tissue. Therefore the assessment of absorbed doses to the thyroid from these examinations becomes necessary. In addition, to perform these examinations, it is normally required that the radiologists and other radiation workers and paramedics stay in the fluoroscopic room. This puts the clinicians body and their various organs/tissues, especially their thyroid, under the secondary/scatter ionizing radiation. This research was carried out to estimate the thyroid absorbed doses of patients and radiation workers involved in fluoroscopic examinations at four different large scale general hospitals in Tehran. Material & Methods: To assess the patient and radiation worker thyroid doses, Li-F thermoluminescent dosimeters (TLDs) were used which are known as TLD-100 and made by Harshaw Company. The TLD cubic chips were first annealed and read out using an appropriate consistent oven to make their background stored counts free. Then, they were exposed to know various amounts of radiation at Karaj Secondary Standard Dosimetry Laboratory of Iran, enabling us to determine a calibration curve for them over the range of exposure common in fluoroscopic procedures. The results of this dose assessment were also compared with those obtained in other countries and with the reference dose levels recommended by some radiation protection organizations. Results: The results indicated an average absorbed dose to the thyroid of patients of 7.89 mGy (SE: 1.33) and 2.97 mGy (SE: 0.43) for the BS and UGI fluoroscopic examinations respectively. Corresponding values estimated for the radiation workers were 0.70 mGy (SE: 0.01) and 0.14 mGy (SE:0.01)for the BS and UGI examinations respectively. Furthermore, estimating the annual frequencies of the above examinations from the hospitals records revealed an annual collective dose to the thyroid of the radiation workers of 9.5 and 11.6 mSv for the BS and UGI examinations respectively. Conclusion: While our mean value of the patient thyroid absorbed dose from UGI examinations was within the range of the values reported by some researchers, it was either far less or more than some other reports. On the other hand our mean value of the patient thyroid absorbed dose from BS examinations was six folds that reported in Spain. Finally, our estimated staff dose for the thyroid was 4.1% of the dose equivalent value for this organ recommended by the US NCRP and DOE.      

Introduction: We proposed an automated segmentation of suspicious clustered microcalcifications on digital mammograms. The algorithm consists three main processing steps for this purpose. Materials & Methods: In the first step, the improvement of the microcalcifcations appearance by using the "a trous wavelet" transform which could enhance the high frequency content of breast images was performed. In the second step, individual microcalcifications were segmented using wavelet histogram analysis on overlapping subplanes. Then, the extracted histogram features for each subplane used as an input to a fuzzy rule-based classifier to identify subimages containing microcalcifications. In the third step, subtractive clustering was applied to assign individual microcalcifications to the closest cluster. Finally, features of each cluster were used as input to another fuzzy rule-based classifier to identify suspicious clusters. Result & Discussion: The results of the applied algorithm for 47 images containing 16 benign and 31 malignant biopsy cases showed a sensitivity of 87% and the average of 0.125 false positive clusters per image.      

Introduction: Different physiological states and external stimulus affect the elastic properties of carotid artery. Non-invasive early detection of atherosclerotic damage would be great significance with regard to risk stratification and presymptomatic treatment of patients with atherosclerotic disease. We studied normal and atherosclerotic common carotid artery in women. Materials & Methods: The diameter and cross-sectional area changes of carotid artery were measured by B-mode sonography. Indirect blood pressure measurement was performed immediately after measurement of the pulsatile vessel diameter. From relative diameter changes (strain) and pulse pressure (stress) were calculated elastic parameters. Peak systolic and end diastolic velocities were determined in RCCA by color Doppler sonography. We estimated the static pressure change and then, elastic parameters in RCCA. Result: The results showed that the variation of diameter and elastic parameters estimated by brachial artery pressure and static pressure change in atherosclerotic group are significantly differ than normal women. Discussion: The results show that usage of static pressure changes for estimation of elastic parameters in normal and atherosclerotic arteries have higher significant level. We purpose that by applying these methods, we could detect atherosclerosis early in disease process.    

Introduction: Working with unsealed radioactive sources in nuclear medicine centers carries the potential risk of contamination. Radioisotopes spreading in environment are entered into the body by inhalation, ingestion and through skin and cause internal contamination. So the many aspects of radiation measurement and consequent protection should become a primary consideration any time radioactive materials are used. To study the possible contamination from radioactive sources used in diagnostic purposes, five nuclear medicine centers in Tehran with different working conditions were chosen and information about design of department, the type and daily usage of radiopharmaceuticals, the number of staff and patients were collected. The research have been performed in three stages in each center Materials and methods: At first stage the levels of airborne activity, in different parts of each center were measured using a portable air sampler. Although the results show some levels of air contamination in every part (99mTc=0-0. 79Bq/m3 & 131I=0.3-8.8Bq/m3), whit the maximum value in hot laboratories, but they are much less than permissible contamination limits (99mTc=8 × 105Bq/m3 & 131I=4×102Bq/m3) (P<0.01). In the second stage, wipe tests were performed to assess the levels of contamination in working surfaces and equipments. The results indicate that some surfaces, in centers no.(l) (99mTc=343 Bq/cm2 & 131I=345 Bq/cm2) and (2) (131I=97Bq/cm2) at hot laboratories, were contaminated more than permissible limits (99m?Tc=300Bq/cm2 & 131I=30Bq/cm2) (P<0.01).That was possibly due to heavy workloads in these centers. Although the measurement show contamination in all of the surfaces (99m?Tc=0.02-373Bq/cm2 & 131I=0.02-380Bq/cm2), but they are less than permissible limits (P<0.01). In the third stage, surface contamination to staff was monitored directly by a NaI (T1) scintillator. The contamination survey was carried out 95 times (5 times for each of 19 radiation workers). The measurements revealed contamination of hands in 5 cases (99m? Tc=11Bq/cm2 & 131I=13Bq/cm2). This study suggests that contamination of the body surface most probably occurs in hot laboratories, during the generator elution, compounding (Kit preparation), and unit - dose dispensing. Conclusion: The findings show that none of these centers were not good (more or less) at: department designing, standards about necessary areas of work rooms, the kind of materials were used to build the department and ventilation systems. The staff was not qualified correctly to avoid/control the contamination (if it occurs).The centers were not equipped with uncontaminating chemicals and equipments.