فهرست مطالب

Iranian Journal of Medical Physics
Volume:6 Issue: 24, 2010

106 صفحه،
تاریخ انتشار: 1389/01/25
تعداد عناوین: 10

فارسی
English

انتخاب همه

De-Noising SPECT Images from a Typical Collimator Using Wavelet Transform

Farshid Babapour Mofrad, Ali Abbaspour Tehrani-Fard, Babak Ebrahimi, Dariush Sardari Pages 1-12

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) collimator 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.

Abstract View Paper Original: Persian
An Assessment of Spinal Cord Dose Following Radiotherapy of Nasopharyngeal Cancer by TLD and Rando Phantom

Mohammad Taghi Bahreyni Toossi, Eftekhar Rajab Bolokat, Raham Salek, Shahram Baiani, Hamid Gholamhoseinian, Mohsen Layegh, Hamid Saeidi Saedi Pages 13-18

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.

Abstract View Paper Original: Persian
A Hybrid Method for Segmentation and Visualization of Teeth in Multi-Slice CT scan Images

Mohammad Hosntalab, Reza Aghaeizadeh Zoroofi, Ali Abbaspour Tehrani-Fard, Gholamreza Shirani Pages 19-28

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 variationallevel 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.

Abstract View Paper Original: Persian
Verification of the Accuracy of the Delivered Dose in Pelvic and Breast Cancer Radiotherapy by in-vivo Semi-Conductor Dosimetry

Hamidreza Shabani, Mahmood Allahverdi, Mahbod Esfahani, Mehdi Aghili, Abbas Takavar, Mohammd Reza Taghizade, Zahratizmaghz, Ali Vaezzade Pages 38-45

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.

Abstract View Paper Original: Persian
Evaluation of Extremely Low Frequency (ELF) Electromagnetic Fields and Their Probable Relationship with Hematological Changes among Operators in Heavy Metal Industry

Mehdi Roknian, Parvin Nassiri, Hojat Zeraati, Mohammad Gholami Pages 47-57

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 b ased 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 μT. 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 μT, total electric field from 1.02 to 11.23 V/M, magnetic field from 0.12 to 3.25 μT 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 μT 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).

Abstract View Paper Original: Persian
Compensation of Cross-Contamination in Simultaneous 201Tl/99mTc Myocardial Perfusion SPECT Imaging

Faraz Kalantari, Hossein Rajabi, Nahid Yaghoobi, Ahmad Bitarafan Pages 58-71

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 photopeak 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

Abstract View Paper Original: Persian
Skin Dosimetry of Some Beta Sources using the VARSKIN2 Code

Ali Asghar Mowlavi, Azam Sadat Afzali Pages 73-81

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.

Abstract View Paper Original: Persian

علمی مصوب

Iranian Journal of Medical Physics

دوماهنامه پزشکی به زبان انگلیسی

آخرین شماره | آرشیو

ISSN: 2252-0309 eISSN: 2345-3672

از شماره 33 بصورت انگلیسی منتشر می شود.

صاحب امتیاز:

دانشگاه علوم پزشکی مشهد

مدیر مسئول:

دکتر محمدعلی عقابیان

سردبیر:

دکتر محمدتقی بحرینی طوسی

تلفن نشریه: ۰۵۱-۳۸۰۰۲۳۱۹

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فهرست مطالب

Iranian Journal of Medical Physics Volume:6 Issue: 24, 2010

Iranian Journal of Medical Physics

Iranian Journal of Medical Physics

Iranian Journal of Medical Physics
Volume:6 Issue: 24, 2010