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

Introduction: Over 1340 Iranian pregnant female, exposed to diagnostic x-rays during 1984 to 1994, referred to our center investigation and estimation of the absorbed dose to their embryo or fetus. They were almost all the patients exposed to x-rays in the whole country in 10 years. Materials and Methods: Two sets of questioner filed for each patient and all the exposing condition and setting information obtained from the radiology centers concerned. The absorbed dose to embryo or fetus accurately calculated and in some cases measured in a phantom for each patient The youngest patient at the time of irradiation was 15 and the oldest was 51 with an average of 28.624±5.961 years old. Results and Discussion: The AP and lateral thickness of patient's abdomen on average were 18.078±0.162 cm and 24.630± 8.365 cm respectively. The average weight of patients was 59.285±12.945 kg. Ranging from 30 kg to 122 kg. The marriage age of the patients on average was 19.398±4.107 years ranging from 9 to 42 years old. The average age of fetus when exposed to x-rays was 31.22±18.76 days. About %20 of the patients had exposures in 2 to 4 more sessions. The average fetal dose was 0.68±0.381 cGy with over 0/037 from 1 to 9 cGy.      

Introduction: RF receives and transmits inhomogeneity is one of the most effective causes of image nonuniformity in MRI images and is considered as an important source of error in quantitative studies. one Part of this inhomogeneity is the characteristic of RF coils and another part of it, is due to the interaction of RF field with the body being imaged. Materials and methods: In this study, RF field inhomogeneity of a volume head coil is measured in human brain (in vivo) as well as in water and oil phantoms, using a simple method that has been proposed by this group. Results and discussion: The results showed that RF inhomogeneity n water phantom is more than its value in oil phantom, even more than its value in human brain In vivo conditions. Non-uniformity of the pattern shows that in both Invivo and water phantom cases, standing wave effect is dominant under our experimental conditions, which may cause overestimations in real values of RF inhomogenity parameters and so image quality factors, therefore, it should be considered in designing MR phantoms.  

Introduction: Digital radiology places very high demands on the networking and digital storage infrastructure of hospitals. In addition to having quite stringent requirements on the quality of the images displayed to the radiologist. much of the technical challenge resides in the necessity of displaying desired images as rapidly as possible. Materials and Methods: We present an infrastructure for progressive transmission and compression of medical images, which can refine an initial image by increasing the detail information not only in scale-space, but also in coefficient precision. The approach is based on the Embedded Zerotree Wavelet (EZW) algorithm. This algorithm. Offers a tremendous amount of flexibility in meeting the bandwidth and image quality constraints in a radiological imaging environment. Results and discussion: We propose an application of the EZW algorithm in progressive medical image transmission in which it can specify and control both the resolution constraint and rate constraint. The presented method can provide a framework for lossy image compression, with performance far superior to those provided by the standard JPEG algorithm. Also Due      

In Radiation therapy, geometric errors are the major factors which influence the geometric reproducibility during the treatment course. The whole effect these geometric errors referred as field placement error (FPE) and can be detected and measured using radiotherapy portal film. Head and neck fields are susceptible for occurrence of these errors due to the mobility of head. Complete fixation is needed for, reducing of geometric errors. In the present research we designed ahead holder in, our department and the; geometric errors without; and with .our homemade. Head holder was measured and estimated. A head holder was designed and made, from Perspex. For portal filming a conventional radiography film and cassette with a 1 mm copper front screen were used. Two groups of patient were selected. Eight patients for first phase and 6 patients were considered. For each patient 1 simulation 5 portal films were taken. The field placement errors were measured by comparing simulation and portal films. In patients who treated without head holder the average geometric errors along the X and Y-axis were 11.2 and 9.5 mm respectively. The standard deviation of geometric errors distribution was 9.9 and 7.8 mm along the X and Y respectively. Using head holder average geometric errors were reduced to 4.7 and 5.4 mm along the X, Y-axis respectively. The standard deviation of geometric errors distribution was 4.2 and 4.3 mm along the X and Y respectively. Considering the 5 mm as a maximum acceptable error, 63.6% and 26% error were estimated for the without and with holder patients respectively. According to the results of this study use of head holder and portal filming is recommended for reducing of geometric errors treatment of head and neck fields. For decreasing the geometric errors to standard values, controlling and optimizing of all factors are essential.      

Background: In radiotherapy in-vivo dosimetry is an effective method of quality assurance (QA) in order to check the patient irradiation, position and overall treatment procedure. Measuring of accuracy and reproducibility of entrance doses and transmission ratios are an important part in QA program. Accuracy should lie between ±5% of prescribed dose as recommended by ICRU. Object of this study was QA of two newly installed and operating Cobalt -60 units. Methods and Material: In this research QA has been performed on two Cobalt-60 teleradiotherapy, THERATRON machines manufactured by AECL of CANADA, using ionization chamber (IC) and thermoluminescent dosimeters.(TLD). Results of each treatment field measurement by both dosimeters were compared with those of prescribed doses. Results Deviations measured by IG and TLD were ±0.56 % and ±3.79% of prescribed doses respectively. The mean deviations of reproducibility for seven treatment fields measured by IC and TLD were 0.83% and 15%. Mean deviations of measured transmission ratios from calculated ratios in both cobalt machines were 2.55% and 12.2% for IC and TLD respectively. The reproducibilities of treatment fields were measured 2.46% by IC and 23% by TLD. Discussion: Relatively fair accuracy (±4%) obtained in this study shows a good stability and functionality of therapy irradiators. Very low differences between measured and prescribed doses, indicating accurate routine calculations in physics section. Evaluating accuracy and reproducibility of transmission ratios can be used for tissue inhomogeneity correction. Using TLD needs special considerations regarding thermal heating and calibration.      

Recently computerized analysis of toco cardiogram has been used for diagnosis of fetal disorder both during pregnancy and labour. Both fetal heart rate (FHR) and uterine contraction (TOCO) signal have specified parameters which by anglicizing these data and their relationship, the fetal well being can be studied. The objective was to compute the specified parameters and to investigate the signal relationships for fast and more reliable diagnosis. The software displays both real time FHR and TOCO signals, graphically. The curve can also be scrolled and at any time interval a report containing the measured and calculated parameters, can be generated. The required data are collected from a fetal monitoring system using an AID interface card and  transferred to a pc. To examine the validity of the processed data;. they are collected from 32 patients referred to Valiasr hospital. All the parameters including Baseline, Signal loss, Acceleration, Deceleration, Contraction peak, Tachycardia, Bradycardia, Sinusoidal pattern, STV, were determined and were compared to specialist diagnosis. The results show that the software is able to determine not only the parameters of signal but also diagnosis fetal abnormalities.      

The purpose of our research was to deliver the maximum heat needed to destroy the tumoral tissue while minimizing the heat damage to the normal tissue. Modeling of laser absorption is the most important parameter in laser therapy treatment planning. Some models of laser absorption have been proposed and are currently in use. In this paper we propose a simulation method based on Monte Carlo code and evaluate the results of this simulation with experimental data. For modeling the laser absorption and finding the matrix of energy absorption in tissue Monte Carlo method (MCML cod) was used. The heat transfer in tissue was modeled by finite difference method by which the temperatures of each point in different time were calculated. For this modeling we used Delphi programming language. The difference between simulation and experimental results in the power range of 0.25-1W/mm2 and 1-3 W/mm2 was 5% and 10% respectively. In the simulation 90% of energy was absorbed in the first cm of liver depth. For I watt laser beam with waist of 1, 2 and 4 mm the maximum energy absorbed by tissue were 15,6 and 1.5 j/cm3 respectively. For optimizing the treatment by lasers, verification of beam and tissue parameters are essential and use of Monte Carlo method as a powerful tool is suggested.      

The major goal of radiation therapy is the delivery of a prescribed radiation to target volume and preserving normal tissue. There are several geometric factors, which tend to compromise this goal. Geometric errors (field placement errors) cause the treatment fields not to be reproducible during the treatment course. In this study geometric errors of radiotherapy fields determined by portal films. Proper film and thickness of cassette front screen to produce the highest contrast were selected in radiotherapy by CO60 gamma rays and 12MV X-rays. 20 patients with head and neck and pelvis region tumors were chosen for our study. On average 4 portal films were taken for each patient during their treatment course. A total of 82 portal films were obtained. For each patient portal films compared with the simulator film and fields placement error were measured for each case. Average systematic and random errors as well as angle of rotation were calculated. The Calculated values were 10.3±6.8 mm along X-axis, 11.3± 13 along Y-axis and angle of rotation was 3.8±3.9. Field placement errors, considering 5 mm as a tolerance limit was 60% along X-axis and 64% along Y-axis. Results of this study shows that systematic and random errors were higher than values previously suggested by other investigations. The problem seems to exist due to lack of immobilization devices, positioning lasers and portal imaging.      

3D dose distributions measurement is required for verifying both dose calculation and treatment delivery in complex treatment approaches, such as brachytherapy and conformal radiotherapy. We have proposed an effective method for this verification using MR image signal intensity changes in response to absorbed dose in Fricke gel. Applying a stepped cooling method, we reached a linear response up to 15Gy with a sensitivity of 2.78Gy-1 for optimum imaging parameters TR/TE/500/20, utilizing a 0.5 TMR scanner. Minimium detectable dose was about 1Gy with an uncertainty about 2% for higher doses. Short imaging time of about 2.5 minutes compared to imaging time needed in R1 and R2 based  approaches, prevented the diffusion of ferric ions and therefore data distortion was greatly avoided. Our results of 2-D dose-mapping in compliance with Nucletron radiotherapy treatment plans for a cylindrical phantom, showed MRI gel dosimetry based on image intensity changes has a great potential for 3D dose distributions evaluations in medical dosimetry applications with a less complicated implementation and also a reasonable time requirement.