Iranian Journal of Medical Physics
Volume:3 Issue: 11, 2006

For more than eight decades researchers have tried to predict diagnostic X-ray spectra. Image quality, patient's dose and ionization chamber read out are some of the quantities affected by energy spectra. In this study MCNP-4C has been employed to simulate the diagnostic X-ray spectra of a common X-ray tube. The effects of various targets, filters, tube voltages ripples, anode angles on the energy spectrum have been investigated. The input file of MCNP-4C consists of geometry and data cards. In order to simulate x-ray energy spectra an input file was created. In this file individual cards for geometry of the x-ray tube, electron source, energy ranges,. .. were defined. To simulate electron transport in the surrounding media, electron production, photon production and full bremsstrahlung angular distribution have been studied. Photon interactions with matter and the corresponding phenomenon such as electron production and coherent scattering have been considered. Simulated diagnostic x-ray spectrum acquired for tube voltages of 60, 70, 80 and 90 kVp (when 1.2 mm Al and 0.5 mm Be filters were applied), x-ray spectrum were also obtained for tube voltage of 100, 110, 120, 130 and 140 (when 2.5 mm Al and 1.2 mm Be filters were applied). The aforementioned simulations were performed for anode angles of 9, 12, 15, 18 and 21 degrees. To assess the effect of voltage ripple, x-ray spectrum were calculated for no ripple and 3, 5, 10, 15, 20, 25, 30, 50 and 100% ripples.Discussion and Individual spectra acquired by MCNP-4C simulation was compared with the corresponding one reported by IPEM report number 78. Every two sets of data were statistically examined by pair T-test. Very good agreements were achieved. Therefore this study confirms that simulation of x-ray spectra of common x-ray tubes can be preformed by MCNP-4C with good accuracy. The effects of target material, tube voltage, and voltage ripple and anode angle on an individual spectra are discussed.

Since nuclear medicine imaging has been widely used as a diagnostic tool, improving the image quality is of significant importance. But this improvement is not provided by the conventional collimators. Slit-slat (SS) collimators have been proposed for this purpose, although the optimization of such collimators has not been performed yet. The purpose of this study was to evaluate the performance of a gamma camera with slit-slat collimator and its comparison against one with a hexagonal collimator. The two systems were simulated by Monte Carlo method and the simulated result was compared against the experimental one. The thickness of NaI (Tl) crystal for the simulated gamma camera system for both the slit-slat and Hexagonal collimator was set to be 3/8 inch. The collimator parameters were chosen the same as it is for low energy general purpose (LEGP) collimator. The simulated SS collimators consisted of 50 lead plates and the imaging was performed by rotating the SS collimator from 0º to 180º in 73 steps of 2.5º each. The spatial resolution, detection efficiency, geometric efficiency and modulation transfer function (MTF) of this system for both the hexagonal and SS systems were evaluated and compared. Moreover the MTF of the SS system was confirmed by the Fourier Transform of Point Spread Function. Based on the MTF value, the obtained results showed that the spatial resolution of the above mentioned systems are the same, whereas the relative detection efficiency of the SS system is about 51.1 times greater than that of the hexagonal one. Also the geometric efficiency of SS system is 1.34 times greater than that of the hexagonal one.Discussion and The results of this study show that the SS collimators have great advantages over the hexagonal ones by providing much higher detection efficiency as well as higher geometric efficiency while maintaining a comparable spatial resolution. Therefore, using SS collimator makes it possible to have a better image quality and less imaging time. Also a lower dose of radioactive material is required to be injected into the patients as a result of higher detection efficiency.

The exposure to the electromagnetic fields coming from the mobile handset and base station antenna has been on the rise due to the increase in the usage of mobile telephone. This study was planned to evaluate the effects of exposure to 950 MHz GSM electromagnetic field on the electrical impedance of hippocampus. 56 naive male Wistar Rats (3 month old, 220±15 g) randomly divided into seven groups. One sham group, three groups exposed to an electromagnetic field of 950 MHz with 0.835 mW/cm2 and the other three groups were exposed to a field of 950 MHz with power density of 1.166 mW/cm2. During a three day period, the exposed groups were subjected to ten sessions of forty five minutes of electromagnetic field each. After the last exposure, the electrical impedance of the hippocampus between the perforant path and dentate gyrus was measured, The analysis of the data showed no significant difference between the sham and the exposed groups with 0.835 mW/cm2 power density. While for 1.166 mW/cm2 power density, the modulated 950 MHz and GSM electromagnetic fields had significantly less electrical impedance.Discussionand The results of this study indicated that the exposure of rat whole body to electromagnetic waves of 950 MHz with power density of 1.166mW/cm2 could reduce hippocampus electrical impedance.

In recent years, the applications of interventional techniques (angiography) have rapidly been increased. To perform these procedures, the cardiologists have to stay close to the radiation field for a long screening time. Therefore, they are prone to receive relatively high doses of radiation. The magnitude of the dose received per procedure depends on several factors such as the type of X-ray equipment and of course the approach adopted by the cardiologist to perform the examination. In this study, the doses received by the organs of interest were measured at two educational hospitals in Mashhad. The measurements were carried out for 98 coronary angiography (CA) and 31 precutaneaus transluminal coronary angioplasty (PTCA) procedures (55 CA and 18 PTCA were performed at hospital A and 43 CA and 13 PTCA at hospital B). Five and seven cardiologists were assessed at hospital A and B, respectively. The dose received by their thyroid, gonads, right and left hand was measured by thermoluminescent dosimeters (TLD). For this purpose, TLDs were placed in PMMA holders and were mounted on their wrists of both hands, underneath of the lead shield adjacent to gonads and thyroid. The mean dose received by the organs (thyroid, gonads, right and left hands) of individual cardiologist was determined. In coronary angiography the highest mean dose received by thyroid and gonads were 100.3 µSv and 83.6 µSv, respectively. The mean left hand dose was in the range of 31.8-358.7 µSv and the corresponding range for the right hand was 12-124 µSv. In PTCA, the lowest mean dose of thyroid, gonads, the right and left hands were 18.7, 20, 69 and 152.1 µSv, respectively and the highest corresponding values were 58.7, 46.7, 119.4 and 245.8 µSv.Discussion and In this study, no significant difference was detected between hospital A and B (P<0.05). Based on the calculated dose values, it can be concluded that each cardiologist should on the average, perform no more than 25 angiography cases per week, to avoid exceeding the dose equivalent limits recommended by ICRP-60.

Photodynamic therapy with 5-Aminolevunilic acid (5ALA) is believed to be useful in treating the superficial or accessible malignant tumors. Nevertheless, several problems exist in using this photosensitizer due to its side effects and the uncertainty in its location inside the target cells. The Treatment efficacy can be provided a improved lower dose of the dye can be used while coming up with a better way of determining its ldation. To achieve these aims, electrical pulses were utilized to facilitate 5ALA entry into the cells. This research was carried out on Wehi-164 fibrosarcoma cell line and its subcutaneous tumors of Balb/c mouse (in vitro and in vivo). Photodynamic treatments using 5ALA were designed on different groups, in the presence and absence of electrical pulses. Electrical doses were applied using a pulse square electroporator prior to the cell incubation with 5ALA and just 10 minutes after its intratumoral injection. Afterwards, illumination was applied by a non-coherent light source in the wavelength peak of 630 nm. The cell survival rate was determined for in vitro assessments by MTT test. For the in vivo studies, the tumor volume was calculated and the histopathologic examination was performed. Based on the vitro data presented, the least cell survival has been obtained for 1 mM concentration of 5ALA with 900 V/cm pulses in higher illumination doses. At 0.2 mM ALA and higher illumination dose with electrical pulses, the cell survival has presented a significant difference in comparison to the similar group without pulse. On the basis of the histopathological experiments, necrosis is induced around the injection site of the dye in the tumor models in the completely treated tumors. The regressive percent of tumors in the control group, the group receiving only electrical pulses, the one receiving photodynamic without any pulse and the group reciving photodynamic with pulses was 1.7, 2.6, 42.0 and 82.2, respectively.Discussion and It seems that the efficacy of photodynamic treatments can be improved by applying electrical pulses at the beginning of cell incubation in the presence of a low concentration dye. Utilizing electrical doses with photodynamic therapy also damages the tumor. It is predicted that the obtained result is caused by the increased 5ALA concentration in the permeated cells following the application of pulses. Therefore, an improved tumor response can be achieved with a lower dose of photosensitizer in these synergistic cures, while reducing the side effects of the dyes.

Electrocardiography signal is a primary criterion for medical practitioners to diagnose heart diseases. In this study, a non-invasive specific HOS-HM [Higher-Order Statistics and their Hermitian Model] algorithm for the early detection of morphological arrhythmias was developed. One of the most significant advantages of this algorithm is its accuracy and reliability in comparison to other existing model-based methods. In this algorithm, second, third and fourth order cumulants of an ECG signal are computed. These cumulants are modeled by Hermitian basis functions. The model parameters are used as a feature vector to classify heart arrhythmias using 1-NN classifier. The final classification is formed by the combination and classification of the result of each cumulant model as it is illustrated in the result section. This algorithm has been computed for its efficiency based on its specificity and sensitivity. In this experiment, 9367 different beats were used (5621 training data and 3746 testing data). The MIT/BIH arrhythmia database was used as the reference At first, the results of arrhythmia detection using the parameters of the 20th order of the Hermite model of each 2nd, 3rd and 4th order cumulants were considered separately. The sensitivity of 97.01% and specificity of 99.30% was obtained for the 2nd cumulant. For the 3rd order cumulant the obtained sensitivity and specificity was 98.35% and 99.61%, respectively. The obtained sensitivity and specificity for the 4th order cumulant was 98.48% and 99.64%, respectively. For 4th order cumulant were obtained. By combining the results obtained according to each cumulant and using the suggested algorithm, the sensitivity of 98.59% and the specificity of 99.67% were achieved indicating the power of its detection. Discussion and This method is unique and it is used for the first time to detect normal beat and four different heart arrhythmias including Premature Ventricular Beat, Atrial Premature Beat, Right Bundle Branch Block and Left Bundle Branch Block – with high level of specificity and sensitivity.

Photodynamic therapy (PDT) is currently one of the fundamental basis for the treatment of cancer. In photodynamic therapy, a photosensitizer that is matched to the wavelength of the laser beam is injected into the patient. Single wavelength laser radiation causes selective photochemical reactions which result in specific biological changes. This treatment does not have any side effects although the patients will become transiently photosensitive. The treatment depends on several parameters including the concentration of photosensitizer and oxygen in the target tissue, laser wavelength, and time of irradiation and laser power density. The time of irradiation is considered the key element in the process. In this paper, a mathematical model is proposed to estimate the optimal time of laser radiation and to investigate how the treatment’s success varies over time.Methods and Materials: In order to simulate the laser-photosensitizer interaction, the porfimer sodium (photofrin) is used. This is a hematoporphyrin derivative and the most applicable photosensitizer in PDT. To activate photofrin, FDA has suggested to use the wavelength of 630 nm. Although photofrin can be activated using some shorter wavelength but 630 nm is the optimum wavelength in photofrin’s activation range, with the maximum penetration in tissues (3-8 mm). Each section of the biologic tissue has been assumed to be comprised of arterial and non-arterial tissue, both of which have been considered to be homogeneous. The simulation program has been based on solving a linear optimization equation. The results suggest that the simulated model accurately yields the optimal time for laser irradiation of the target tissue. Determining the optimal time is based on balancing between maximum tumor destruction and minimum damage to healthy tissues. The developed model in this paper can also be applied to other photosensitizers.Discussion and Photodynamic therapy has great potential for cancer therapy particularly using photosensitizers with high affinity for cancerous cells. The goals of this study are 1) to model the concentration of the photosensitizer in the blood and tissue, and 2) to optimize the photodynamic therapy treatment using simulation without the need to undergo expensive and tedious clinical trials and errors.

Virtual bronchoscopy has recently been descried as a technique for performing simulated bronchoscopy using data obtained from multidetector computed tomography (MDCT), which provides large high-resolution 3D images of the chest. To use the virtual flythrough method and some of the quantitative analysis, a camera path should be planned. A rapid, robust and most automated path planning method which enables virtual-bronchoscopic 3D-MDCT image analysis and follow on image-guided bronchoscopy. The final path is suitable for quantitative airway analysis and smooth virtual navigation. The proposed method is a new combination of distance transformation for start and end point detection and to initialize the primary path and snake-based models for centering the primary path with some of novelty to improve the overall performance of the algorithm. This method has been applied on several synthetic and rubber phantoms as well as real datasets of human airways. Comparison of the proposed method with the previous path planning approaches shows the efficiency of the new method. There are no missing or false branches in the final path of airways by various amounts of branches and quality. All end points and branches were also detected accurately. By using different scanners with different quality for real dataset, it was found that the algorithm has less sensitivity to hardware and performance of previous stages in whole virtual bronchoscopy system. The computation time of the algorithm is shorter than the previous works by a factor of 2 in best quality mode.Discussion and The Proposed algorithm is fully-automated which does not require any interaction by the user. The combination of distance transformation and snake-based model guarantees the detection of all the end points and close approximation of the central axis, respectively, raise the thin and continuous path in output which is proper for virtual navigation into the airways. Because of the higher speed of the algorithm, the proposed method could be used for real-time and intra-operative procedures.