Iranian Journal of Medical Physics
Year:2003 | Volume:1 | Issue:2|Papers Count:8

Introduction: Deconvolution technique is very sensitive to error, which makes it extremely unstable. It is therefore difficult to implement an accurate and stable deconvolution procedure in routine clinical practice. We feel that the technique may be made stable at the cost of accuracy and resolution. Though stability is quite important factor for the reliability of a technique but accuracy can be ignored too. We have observed that optimum filtration is extremely important in deconvolution analysis. Due to versatile change in. the pattern of data, adjustment of the filter for performing the optimal, Filtration is a very difficult task especially in routine work. We have done some basic work on curve filtration, which may be used for optimum filtration of time activity curves.Material & Methods: Being most suitable for renal studies matrix method has been used for deconvolution analysis. The main problem with matrix method is its sensitivity to the error in early points of input and output curves, which are quite erroneous. To overcome this problem we have designed an algorithm. We calculated the first and second point of IRF by both deconvolution technique and another technique (modified Rutland formula). We have modified Rutland's formula for intravascular background subtraction and used it for calculation of first and second point of IRF curve. If these points match with those estimated by matrix method then the calculation is continued otherwise the values are rejected and calculation started again by ignoring first point of both input and output curve. The method was found to be stable and accurate.Results & Discussion: Seventy two normal kidneys (36 pairs) were used to estimate normal values of transit time parameters. For all the parameters, approximately the mean 2 s.d. was accepted as normal range and values beyond mean 3 s.d. were treated as abnormal. The values between these two ranges were assumed to be the borderline values. These values were taken to interpret abnormal or prolonged transit times in patients with renal disorders. There was no statistical difference between the average value for left and right kidney transit time parameters. 

Introduction: Fast processing and accurate fetal heart rate estimation in FHR monitoring systems are important factors. In addition, the ability to determine the heart rate from weak or noise corrupted Doppler signals is the other goals.Methods: To achieve these conditions, Using improved data reduction and pitch detection techniques an optimized algorithm compared to the proposed methods such as conventional ACF(1), and pitch detection algorithms (2), is presented.Results & Conclusion: The Fast Fetal Heart Rate (FFHR) algorithm is capable of reliable and fast estimation.

Introduction: The accurate delivery of dose to the clinical target volume in radiotherapy can be affected with many different factors. With increased interest in 3-D conformal therapy and also in the context of multicenter clinical trials, it is necessary to provide standard techniques to assure quality in delivering treatment. An anthropomorphic phantom can be employed to verify the quality and consistency of treatments by mimicking the many steps involved in a radiotherapy process.Material and Methods: An anthropomorphic pelvic and cervix phantom was designed and fabricated to be used for imaging, treatment planning, and dosimetry application in the treatment of cervical cancer. The phantom was made of mm acrylic plates and each plate was machined and modeled based upon CT slices from a patient study. Most of the phantom was made of acrylic while contours of femur and the vertebral column were filled with appropriate materials. The CT numbers from patient images were used to adjust the composition of bone equivalent material. During the simulations, a Foley catheter and a rectal tube filled with a proper contrast agent were used to distinguish bladder and rectum from the remainder of the phantom. A23323 PTW intra- cavitary chamber which was cross calibrated against a NE 2581 ionization chamber was placed in special holes machined in phantom for dosimetry applications. The dose delivered to the isocenter (cervix), bladder and rectum were calculated using a 2D Plato treatment planning system and were compared with measured values.Results: The phantom is to be used to evaluate the consistency of a range of processes in radiation therapy, simulation, planning and delivery of treatment for cervical cancer.Conclusions: The objective of this study is to use the phantom to verify the accuracy and consistency of treatments in one institution and in national collaborative clinical trials, during acceptance testing of treatment planning systems and as an educational tool, for dosimetric research problems and for QA in radiation treatment of cervical carcinoma.

Introduction: Transmyocardial Laser Revascularization (TMLR) has a good potential in treatment of some disease however the mechanism of action is not well known. Most probably channel's geometrical shape and thermal damage have an important role in its function. Unfortunately there have been significant discrepancies in the follow up results of TMLR.Materials & Methods: The Nd: YAG laser beam, with powers of 85w and 105w was delivered to left ventricle of sheep heart through a 500mm fiber optic. The fiber penetration speed into the tissue were 1.2mm/s and 2.4mm/s. Results and Discussion: All the channels had elliptical cross sections. The reduction of dimensions and surfaces of channels cross sections were statistically significant when the laser power increased and the fiber speed was kept constant. Channels cross sections were decreased by increasing of the fiber speed while the laser power was kept constant. Under the above conditions the differences in channel's cross-sections were not statistically significant.

Introduction: One of imaging modalities in medicine is ultrasound system. The conventional ultrasound images are two-dimensional; however three-dimensional images offer better observation and interpretation. To create ultrasound three-dimensional images, special transducers with two-dimensional arrays are used. These transducers consist of piezoelectric elements arranged two dimensionally, since the construction of such two dimensional transducers are complex; simulation of the transducers is an appropriate approach to optimize their beam pattern for a particular application.Material & Methods: For this purpose in this research all the relevant beam pattern equations are derived and then manipulated for the simulation. All the variable parameters, such as element size, element spacing, number of elements, and excitation amplitude, frequency and phase can be altered by user to optimize beam pattern for the particular application.Results: By analyzing the results the effects of changes in the transducer parameters on the beam pattern pressures are displayed in different modes graphically. Then the optimization process can be performed.The optimization is shown graphically and can be analyzed efficiently. This software can be utilized as an appropriate tool for the design of one or two dimensional array transducers.

Introduction: The three major components of the dose under a shielding block namely: - Iran Research Centre For Science & Technology In Medicine (1) the transmitted primary dose, which depends on the energy of the primary radiation and the thickness of the block; (2) the external scatter component which depends on the head geometry, field size and proximity of the patient to the blocking tray; and (3) the phantom scatter which depends on the energy of the primary beam, the shape and size of the unshielded area, the depth of point of interest and its proximity to the edge of the unshielded area.This paper describes measurements done to comparison between measured dose and calculated dose by treatment planning system and algorithm suggested. Because the prescribed dose is sometimes limited by critical organ doses within the irradiated volume, so it is important to know the dose under a block accurately.Material and Methods: Depth doses and crossbeam profiles of cerrobend blocks ranging in widths 1, 3, 5cm were taken using an automated water phantom. The measured values in center and border of phantom obtained by a chamber 0.125cc. Algorithm BTF used for calculation dose under cerrobend blocks with a 20×20cm field.Results: The measured dose values were compared with a new suggested algorithm and Plato TPS in cancer institute of Imam hospital. The measured dose under shielding blocks obtained from 9.6% to 25.9%. The more significant differences obtained between measured values and TPS in center and edge of field, but there were no significant differences between measured values and BTF algorithm.Discussion: The most differences were observed between measured and TPS values for 1cm block width in the center of field. This difference can be due to ignoring of absorb and scatter values from narrow shielding blocks.This can be concluded that the radiation dose under shielding blocks can be considerably higher than expected values. Therefore with consideration of the results and importance of critical structures shielding, BTF algorithm suggested can be useful for reduction of dose errors under blocks.

Introduction: -81 is routinely produced almost everywhere in the world. This is a gamma and positron emitter radioisotope, which may potentially be used for PET and SPECT imaging. However it is mainly used in Rubidium-Krypton generator. In this study a soluble compound of Rubidium that is suitable for intravenous injection was produced. The product was biologically evaluated.Methods and Materials: Rubidium was produced in cyclotron using proton bombardments. The purity of the final product was measured using chromatographic and spectroscopic methods. The product was formulate9 and injected to the rates to determine the biological distribution.Results: The chemical and radioisotopic purity of the product was acceptable. The optimum time for imaging was found to be three hours after injection.Conclusion: Our results proved that the product is suitable for clinical investigation. Our center is capable of weekly production of isotope.

Introduction: Surface electromyogram Decomposition can be useful for the diagnosis of neuromuscular disease. Due to the surface detection problems and motor unit action potential (MUAP) overlaps, which increase with the muscle voluntary contraction (MVC), finding a solution to the decomposition problem is a very important key. The number and the position of detection electrodes affect the decomposition results. Therefore, a suitable solution will be the utilization of signal modeling and finding the best array of detection electrodes for decomposition purposes. In this paper, the latest sEMG Biceps modeling has been used to determine the best array of detection electrodes.Material & Methods: Latest Biceps sEMG signal modeling was used in the following experiments for reaching the best array of detection electrodes.1- X-axis electrode displacement effect analysis for one motor unit.2- X-axis electrode displacement effect analysis for motor units with different size and depth.3- Z-axis electrode displacement effect analysis for motor units with same size and different position.4- Different coordination electrodes affect analysis for motor units with the same or different center.Results & Discussion: The results of this work can be used to find the best array and give some ideas for optimizing the decomposition algorithms. The best position of motor unit signal detection is the above of motor unit and same direction with it. This position must be between innervations zone and tendon. Differential detection is preferred. For increasing decomposition ability, X-axis electrode distribution must be the same as X-axis motor unit distribution.Because of uniform X-axis motor unit distribution in biceps, differential detection electrode with uniform X-axis distribution can be used. So, at minimum, three differential electrodes (six electrodes) must be used in the beginning, middle and the end of muscle width.