Iranian Journal of Medical Physics
Year:2010 | Volume:6 | Issue:3-4 (24-25)|Papers Count:9

Introduction: SPECT is a diagnostic imaging technique the main disadvantage of which is the existence of Poisson noise. So far, different methods have been used by scientists to improve SPECT images. The Wavelet Transform is a new method for de-noising which is widely used for noise reduction and quality enhancement of images. The purpose of this paper is evaluation of noise reduction in SPECT images by wavelet.Material and Methods: To calculate and simulate noise in images, it is common in nuclear medicine to use Monte Carlo techniques. The SIMIND software was used to simulate SPECT images in this research. The simulated and real images formed using the current typical (hexagonal) collimators were de-noised by different types of wavelets.Results: The best type of wavelet was selected for SPECT images. The results demonstrated that the best type of wavelet in the simulated and real images increased Signal to Noise Ratio (SNR) by 33% and 45% respectively. Also, Coefficient of Variation (CV) decreased by 77% and 71% respectively, while Contrast of Recovery (CR) was reduced by only 4% and 9% respectively.Conclusion: Comparing the results for real SPECT images in this paper with previously acquired results in real PET images, it can be concluded that the images of both nuclear medicine systems using Wavelet Transform differ in SNR and CR by only 5% and 7% respectively, and in CV by about 20%. Therefore, wavelet transform is applicable for nuclear medicine image de-noising.

Introduction: Nasopharyngeal carcinoma is one of the most common malignancies in the head and neck region and radiotherapy is its treatment of choice. In spite of the fact that it is widely used, due to the presence of many sensitive organs or tissues in this region, patients may suffer from a wide range of side effects. One such sensitive tissue is the spinal cord. If the absorbed dose to spinal cord is greater than its tolerance dose, then myelopathy and Lhermitte’s sign are not avoidable.Material and Methods: Thehead and neck of a Rando phantom (reference man) was employed as a hypothetical patient suffering from nasopharyngeal carcinoma. The full course of treatment consisted of three phases. At the beginning of every phase, an oncologist used a simulator to delineate the surface of the Rando Phantom for treatment. TLD chips (TLD-100) were employed for dose measurement. TLD chips were inserted in the previously made holes on the surface of selected slices adjacent to second cervical to fourth thoracic vertebra. Absorbed dose by TLDs were read by a Harshaw 3500 TLD reader.Results: Total measured dose (in Gy) of various parts of spinal cord adjacent to second cervical to fourth thoracic vertebra varied widely and were as follows respectively: 15.24±1.31, 50.31±1.06, 49.15±2.77, 47.48±1.42, 54.56±2.6, 48.92±0.6, 45.1±0.45. In other words, the range of doses received by different segments of the spinal cord could be as wide as 15.24 to 54.56 Gy.Conclusion: Although the spinal cord was excluded at the end of the first phase, a significant change in the absorbed dose at the end of the first and second phases was not observed. In phase three, the anterior neck field was replaced by a lateral field and the spinal cord absorbed dose was reduced considerably. According to our results, absorbed doses of the spinal cord segments corresponding to the region confined between the third cervical to third thoracic vertebra were more than the 47 Gy recommended tolerance dose value. Therefore, special attention must be paid to protect this sensitive tissue while the treatment is performed. Application of modern techniques such as IMRT, if available, will reduce the unnecessary dose the spinal cord and its consequent biological risks considerably.

Introduction: Various computer assisted medical procedures such as dental implant, orthodontic planning, face, jaw and cosmetic surgeries require automatic quantification and volumetric visualization of teeth. In this regard, segmentation is a major step.Material and Methods: In this paper, inspired by our previous experiences and considering the anatomical knowledge of teeth and jaws, we propose a hybrid technique for teeth segmentation and visualization in CT volumetric data. The major steps of the proposed techniques are as follows: (1) Separation of teeth in CT dataset; (2) Initial segmentation of teeth in panoramic projection; (3) Final segmentation of teeth in CT dataset; (4) 3D visualization of teeth.Results: The proposed algorithm was evaluated in 30 multi-slice CT datasets. Segmented images were compared with manually outlined contours. In order to evaluate the proposed method, we utilized several common performance measures such as sensitivity, specificity, precision, accuracy and mean error rate. The experimental results reveal the effectiveness of the proposed method.Discussion and Conclusion: In the proposed algorithm, the variational level set technique was utilized to trace the contour of the teeth. In view of the fact that this technique is based on the characteristics of the overall region of the tooth image, it is possible to extract a very smooth and accurate tooth contour using this technique. For the available datasets, the proposed technique was more successful in teeth segmentation compared to previous techniques.

Introduction: Photodynamic therapy is a noninvasive therapeutic method for tumors with a maximum depth of 5 mm. On the other hand, most photosensitizers are also susceptible to ultrasound waves (the basis of sonodynamic therapy). Therefore, it is expected that a combination of the two therapeutic methods will increase effectiveness of photodynamic therapies for lower doses of sensitizer and curing deeper tumors. This study evaluates the synergistic effects of photodynamic and sonodynamic therapies.Materials and methods: The study was conducted on a colon carcinoma tumor model in Balb/c mice. The colon carcinoma tumors were induced in the mice by subcutaneous injection. Twenty four hours after intraperitoneal injection of Zinc Phthalocyanine liposome as a sensitizer, at first ultrasound irradiation with a known frequency and intensity was performed followed by illumination of the tumor area. Evaluation of the treatment efficacy was done using daily measurement of the tumors and calculation of their relative volumes. Also, all control groups were considered to confirm the effect of each therapeutic option in the study.Results: In the first ten days post treatment, the relative volumes of all groups decreased significantly in comparison with the main control group, but the best response was observed in the photodynamic or sonodynamic therapy groups. The longest doubling time of tumor size was related to groups under photodynamic, sonodynamic and main therapies, and the shortest belonged to the control group.Discussion and conclusion: Zinc phthalocyanine liposome is both a photosensitizer and son sensitizer. Photodynamic and sonodynamic therapies can be efficient in retarding tumor growth rate. In this study, combination of the two methods did not cause improved therapeutic outcomes. It is predicted that this result is related to the choice of therapeutic agents and could be optimized in future.

Introduction: Delivering maximum dose to tumor and minimum dose to normal tissues is the most important goal in radiotherapy. According to ICRU, the maximum acceptable uncertainty in the delivered dose compared to the prescribed dose should be lower than 5%, and this is because of the relationship between absorbed dose, tumor control and normal tissue damage. Absorbed dose accuracy is investigated by an in vivo dosimetry method. In this paper, we compared absorbed dose in the tumors of the breast and pelvic region against the calculated dose. The amount of deviations and the factors that cause this deviation in dose delivery to patients and some methods for decreasing them were evaluated.Materials and methods: The entrance and exit doses of 36 pelvic-region cancer patients and 38 breast cancer patients who were treated by cobalt-60 teletherapy were measured using p-type diodes. It should be noted that the transmission method was used to assess the dose at isocenter. Two ionization chambers (0.6 cc and 0.3 cc) were used for calibration and determination of the correction coefficients in water and slab phantoms. Deviations between calculated and measured doses of entrance, exit and midline points were calculated and the results were shown using histograms.Results: The average and standard deviation for entrance, exit and midline points for pelvis cancer were assessed to be about 0.10%, -1.86% and -1.35% for mean deviation and 5.03%, 7.32% and 5.86% for standard deviation, respectively. The corresponding data for breast cancer were 0.78%, 5.29% and 3.59% for mean deviation and 5.97%, 10.23% and 9.86%, respectively. There was no significant difference between the calculated and measured doses (p>0.1), except exit dose in breast cancer (p<0.05). The temperature and angle of incidence correction factors were neglected due to their less than 1% deviations.Discussion and Conclusions: Some error sources are patient setup error, patient motion and dose calculation algorithm error (due to ignoring inhomogeneity and patient curvature). As no significant deviations were found in midline dose, the method used has an acceptable accuracy. In vivo dosimetry can perform a basic role in the quality control of radiotherapy departments.

Introduction: It is important that biological and health effects from the induction of currents and fields in the body by extremely low frequency (ELF) fields are fully explored to determine the effects produced at the molecular, cellular and organ levels. The objective of this study was to evaluate the intensity of ELF electromagnetic fields and its probable relationship with hematological changes among operators in a heavy metal industry site. This is a case study. In the present study, 205 workers exposed to electromagnetic fields (EMF) were working in four categories: (1) induction furnace workers, (2) induction hardening workers, (3) welders, (4) computer operators.Material and Methods: A variety of methods for exposure assessment have been devised and applied to epidemiological studies of the effects of EMF in occupational settings. The methods range from rather crude job-classification methods, to sophisticated job-exposure matrix (JEM) modeling based on personal exposure measurements and reconstruction of past exposure. Monitoring procedures were carried out to measure the levels of exposure to ELF electric and magnetic fields. The strength of the electric and magnetic fields were measured by a dosimetric method (NIOSH 203).Workers’ blood samples were collected and analyzed for identifying different blood parameters. The results of hematological changes of workers in their medical files were also used for evaluation.Results: Measurements showed a high strength of ELF field at the induction furnace workplace. Total electric field ranged from 2.3 to 2452.3 V/M and magnetic field from 1 to 325.1 mT. In other workshops including induction hardening, total electric field ranged from 2.45 to 68.5 V/M, magnetic field from 1.3 to 20.4 mT, total electric field from 1.02 to 11.23 V/M, magnetic field from 0.12 to 3.25 mT in the welding department and finally for computer operators this range was 20.1 to 186.2 V/M for electric field and 0.07 to 0.25 mT for magnetic field.Conclusion: Mean value of WBC and MCV increased significantly among exposed induction furnace workers group (P<0.05), but RBC decreased. Mean value of WBC, MCHC and MCV increased significantly among the exposed induction hardening workers group (P<0.05), but RBC and Hgb decreased. Mean value of WBC, MCV and Hgb increased significantly among the exposed welders group (P<0.05), but Hgb in relation with age decreased. Mean value of RBC and MCH decreased significantly among exposed computer operators group (P<0.05).

Introduction: It is a common protocol to use 201Tl for the rest and 99mTc for the stress cardiac SPECT imaging. Theoretically, both types of imaging may be performed simultaneously using different energy windows for each radionuclide. However, a potential limitation is the cross-contamination of scattered photons from 99mTc and collimator X-rays into the 201Tl energy window. We used a middle energy window method to correct this cross-contamination.Material and Methods: Using NCAT, a typical software torso phantom was generated. An extremely thin line source of 99mTc activity was placed inside the cardiac region of the phantom and no activity in the other parts. The SimSET Monte Carlo simulator was used to image the phantom in different energy windows. To find the relationship between projections in different energy windows, deconvolution theory was used. We investigated the ability of the suggested functions in three steps: Monte Carlo simulation, phantom experiment and clinical study. In the last step, SPECT images of eleven patients who had angiographic data were acquired in different energy windows. All of these images were compared by determining the contrast between a defect or left ventricle cavity and the myocardium.Results: We found a new 2D kernel which had an exponential pattern with a much higher center. This function was used for modeling 99mTc down scatter distribution from the middle window image. X-ray distribution in the 201Tl window was also modeled as the 99mTc photo peak image convolved by a Gaussian function. Significant improvements in the contrasts of the simultaneous dual 201Tl images were found in each step before and after reconstruction. In comparison with other similar methods, better results were acquired using our suggested functions.Conclusion: Our results showed contrast improvement in thallium images after correction, however, many other parameters should be evaluated for clinical approaches. There are many advantages in simultaneous dual isotope imaging. It halves imaging time and reduces patient waiting time and discomfort. Identical rest/stress registration of images also facilitates physicists’ motion or attenuation corrections and physicians’ image interpretation.

Introduction: Skin dose and depth dose distribution of some beta sources that can contaminate skin or protective clothing covering the skin have been calculated using VARSKIN2.Materials and Methods: In this research, absorbed dose to skin and depth dose from the skin surface have been calculated for 90Sr/90Y, 147Pm, 32P beta emitter radioisotopes by using input parameters: activity of source, cover thickness, cover density, air gap thickness, radiation time and different source geometries.Results: Absorbed dose variation was calculated for beta sources in different source forms, namely, point, 2-D disk, cylindrical, spherical and slab sources. The results show that a cylindrical source causes the minimum damage to skin cells. Therefore, this shape of source is the best with respect to radiation protection.Discussion and conclusion: The VARSKIN2 code is a very useful tool for skin dosimetry, as well being fast, accurate and user friendly. It can be used for dose optimization calculations especially for beta sources over human skin.