Attenuation Correction in SPECT during Image Reconstruction using an Inverse Monte Carlo Method: A Simulation Study
Shahla
Ahmadi
M.Sc. in Nuclear Engineering, Faculty of Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
author
Hossein
Rajabi
Associate Professor, Medical Physics Dept., Faculty of Medicine, Tarbiat Modares University, Tehran, Iran
author
Farshid
Babapoor
Assistant Professor, Nuclear Engineering Dept., Faculty of Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
author
Faraz
Kalantari
Ph.D. Student, Medical Physics Dept., Faculty of Medicine, Tarbiat Modares University, Research Institute for Nuclear Medicine, Tehran University of Medical Sciences,Tehran, Iran
author
text
article
2011
eng
Introduction: The main goal of SPECT imaging is to determine activity distribution inside the organs of the body. However, due to photon attenuation, it is almost impossible to do a quantitative study. In this paper, we suggest a mathematical relationship between activity distribution and its corresponding projections using a transfer matrix. Monte Carlo simulation was used to find a precise transfer matrix including the effects of photon attenuation. Material and Methods: List mode output of the SIMIND Monte Carlo simulator was used to find the relationship between activity distribution and pixel values in projections. The MLEM iterative reconstruction method was then used to reconstruct the activity distribution from the projections. Attenuation-free projections were also simulated. Reconstructed images from these projections were used as reference images. Our suggested attenuation correction method was evaluated using three different phantom configurations: uniform activity and uniform attenuation phantom, non-uniform activity and non-uniform attenuation phantom, and NCAT torso phantom. The mean pixel values and fits between profiles were used as quantitative parameters. Results: Images free from attenuation-related artifacts were reconstructed by our suggested method. A significant increase in pixel values was found after attenuation correction. Better fits between profiles of the corrected and reference images were also found for all phantom configurations. Discussion and Conclusion: Using a Monte Carlo method, it is possible to find the most precise relationship between activity distribution and its projections. Therefore, it is possible to create mathematical projections that include the effects of attenuation. This helps to have a more realistic comparison between mathematical and real projections, which is a necessary step for image reconstruction using MLEM. This results in images with much better quantitative accuracy at a cost of computation time and memory.
Iranian Journal of Medical Physics
Mashhad University of Medical Sciences
2345-3672
8
v.
3
no.
2011
1
12
https://ijmp.mums.ac.ir/article_7224_6954640a735300c0fd4c003a60335b1e.pdf
dx.doi.org/10.22038/ijmp.2011.7224
Excess Cancer Risk Assessment from Some Common X-Ray Examinations in Sabzevar County
Mohammad Taghi
Bahreyni Toossi
Prof., Medical Physics Dept., Medical Physics Research Center, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran
author
Hassan
Zarghani
Ph.D. Student of Medical Physics, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran
author
text
article
2011
eng
Introduction: Nowadays ionizing radiation has a considerable contribution in medical diagnostic and treatment. Using ionizing radiation is increasing rapidly, so biological effects of ionizing radiation should be considered more. X-rays in the range of diagnostic radiology have hazardous effects and risks that are defined as random effects. These effects obey the LNT hypothesis that occur at low doses and include many types of cancer and genetic mutations. So it is very important to assess the risk of exposure in medical examinations. Cancer is one of these hazardous risks caused by low dose ionizing radiation that may occur during life after exposure. According to BEAR 7, low dose radiation is defined as radiation that produces doses near zero up to 100 mSv. Materials and Methods: This work was carried out in eight radiology centers in the Sabzevar county of Iran for 485 patients in eight typical x-ray examinations chosen for the study: chest PA, chest AP, lumbar spine AP, lumbar spine LAT, pelvis AP, abdomen AP, skull AP and Lat. In order to estimate the excess cancer risk, we need to obtain collective effective dose caused by radiation in the study population. Usually effective dose offers precise assessment of radiography examination injuries in adult patients. In this study, we used the PCXMC Monte Carlo based software to obtain effective dose and organ dose. This software calculates organ and effective dose following input of patient and radiographic conditions. Results: Average patient weight and height, entrance surface dose, parameters used for each type of examination, and DAP values were entered. Effective dose, collective effective dose, number of radiographs per year and the excess cancer risk arising from these radiographic examinations were then calculated. Discussion and Conclusion: Excess risk of fatal cancer due to x-ray examinations in the study population was calculated by collective effective dose. This risk in the population is about 0.42 cases suffering fatal cancer per year in this county. If the doses from other diagnostic radiology procedures, in which absorbed dose to patients are considerably higher than conventional radiography, are added to this amount, then the excess risk will be significantly greater than that obtained in this assessment.
Iranian Journal of Medical Physics
Mashhad University of Medical Sciences
2345-3672
8
v.
3
no.
2011
13
19
https://ijmp.mums.ac.ir/article_7225_6dd7ffb1c918245677f2cc4a2766ecf1.pdf
dx.doi.org/10.22038/ijmp.2011.7225
Pathological Assessment of Brain White Matter in Relapsing-Remitting MS Patients using Quantitative Magnetization Transfer Imaging
Khodarahm
Pahlevan
M.Sc. of Medical Physics, Medical Physics Dept., Faculty of Medicine, Tehran University of Medical Sciences, Teheran, Iran
author
Nader
Riyahi-Alam
Prof., Medical Physics Dept., Faculty of Medicine, Tehran University of Medical Sciences, Teheran, Iran
author
Mohammad Hossein
Harirchian
Associate Professor, Neurology Dept., Faculty of Medicine, Tehran University of Medical Sciences, Teheran, Iran
author
Kavoos
Firouznia
Associate Professor, Radiology Dept., Faculty of Medicine, Tehran University of Medical Sciences, Teheran, Iran
author
Majid
Shakiba
Research Assistant, Medical Image Center, Imam Khomeini Hospital, Tehran University of Medical Sciences, Teheran, Iran
author
Alireza
Bozorgy
Neurology Resident, Neurology Dept., Faculty of Medicine, Tehran University of Medical Sciences, Teheran, Iran
author
Morteza
Bakhtiary
M.Sc. of Medical Physics, Medical Physics Dept., Faculty of Medicine, Tehran University of Medical Sciences, Teheran, Iran
author
Behrooz
Rafiei
M.Sc. of Medical Physics, Imaging Center, Imam Khomeini Hospital, Tehran, Iran
author
Masumeh
Fouladi
M.Sc. of Medical Physics, Medical Physics Dept., Faculty of Medicine, Tehran University of Medical Sciences, Teheran, Iran
author
text
article
2011
eng
Introduction: Multiple sclerosis (MS) is characterized by lesions in the white matter (WM) of the central nervous system. Magnetic resonance imaging is the most specific and sensitive method for diagnosis of multiple sclerosis. However, the ability of conventional MRI to show histopathologic heterogeneity of MS lesions is insufficient. Quantitative magnetization transfer imaging (qMTI) is a relatively new method to investigate pathologic processes of the brain tissue occurring in MS patients. Material and Methods: Voxel-based analyses allow regional comparisons between groups to be made for the whole brain in a single analysis. This is done by coregistering data from all individual subjects to a reference brain, generally referred to as the "standard space", and then comparing them on a voxel-by-voxel basis. This study aimed to analyze whole-brain quantitative T1 maps, not to find global changes or changes in selected regions, but specifically to investigate the spatial distribution throughout the brain of T1 increases in MS WM with respect to control WM. In this study, 11 healthy controls, 10 relapsing-remitting (RR) MS patients and 13 CIS patients were studied using MT-MRI imaging. MT parameters, including magnetization transfer ratio (MTR), magnetization transfer rate between free protons and restricted macromolecular protons, Ksat and longitudinal relaxation times (with and without MT saturation pulse), T1sat and T1free values were evaluated. Results: The results showed that, at a group level, there is widespread involvement of WM throughout the brain in CIS MS and especially in RRMS, where a significant T1 increase was found in 15.58% of WM voxels (normals < RR). Discussion and Conclusion: This study demonstrates that WM in large parts of the brain is susceptible to disease processes in RR and CIS MS
Iranian Journal of Medical Physics
Mashhad University of Medical Sciences
2345-3672
8
v.
3
no.
2011
21
29
https://ijmp.mums.ac.ir/article_7226_0c1b007c23186d520090c05517d93bff.pdf
dx.doi.org/10.22038/ijmp.2011.7226
Dosimetric Evaluation of Linac Photon Small Fields using MAGIC Polymer Gels
Hossein
Hasani
M.Sc. Student in Medical Radiation Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
author
Hasan
Nedaie
Assistant Professor, Radiotherapy and Oncology Dept., Tehran University of Medical Sciences, Cancer Research Center, Center Institute, Tehran, Iran
author
Mohammad Hasan
Zahmatkesh
Associate Professor, Medical Physics Dept., Novin Medical Radiation Institute, Tehran, Iran
author
Mahmood
Allahverdi
Associate Professor, Medical Physics Dept., Tehran University of Medical Sciences, Tehran, Iran
author
Saeid
Bagheri
M.Sc. of Medical Physics, Novin Medical Radiation Institute, Shahid Beheshti University, Tehran, Iran
author
Sajad
Mirzaie
M.Sc. Student in Medical Radiation Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
author
text
article
2011
eng
Introduction: In radiotherapy, methods of treatment planning are becoming increasingly more complicated. This requires verification of the doses delivered to increasingly smaller and more precise regions. Radiotherapy techniques are continuously employing smaller and smaller field sizes to deliver tighter radiation doses with higher therapeutic ratios, generating interest among researchers to provide reliable dosimetry for beams and treatment plans collimated to small field sizes. In this study, the dosimetry of these fields was evaluated in clinical applications by using polymer gel dosimetry. Material and Methods: The MAGIC polymer gel was used in this study. The gel samples were manufactured and poured into phantoms and calibration vials and were irradiated with a 6 MV x-ray beam. The R2 maps of the dose distributions were obtained from the gel MR images. The depth dose distributions and dose profile measurements were measured in different fields at a depth of 5 cm in gel, and were compared against another technique using a pinpoint chamber. Results: Comparison of the results of gel and pinpoint chamber measurements showed largest differences between the dose profile measurements in the low dose regions (near the edges). In these regions, the pinpoint-chamber measured penumbra width was at most 3.2 mm wider than those given by gel dosimeters. For a 30 × 30 mm2 field, maximum difference between gel and pinpoint chamber was 2 mm within the depth of maximum dose region, and were 2 mm, 3 mm and 2 mm for 20 × 20 mm2, 10 × 10 mm2 and 5 × 5 mm2 fields, respectively. The maximum differences within the buildup region for 30 × 30 mm2, 20 × 20 mm2, 10 × 10 mm2 and 5 × 5 mm2 fields were 9%, 4.5%, 2% and 9%, respectively. Discussion and Conclusion: The differences in the depth dose distributions and dose profile measurements between MAGIC polymer gel and pinpoint chamber are attributable to different factors. The dosimetry of these fields using ionization chambers has limitations regarding uncertainty, due to the relatively large sizes of ionization chambers with respect to small field sizes and the lack of charged-particle equilibrium in such small fields. Pinpoint chambers are too large for very small photon fields and smaller dosimeters should be used. Fewer limitations in the dosimetry of small fields exist when using polymer gel dosimeters. Hence polymer gel dosimeters are suitable for dosimetry of photon small fields.
Iranian Journal of Medical Physics
Mashhad University of Medical Sciences
2345-3672
8
v.
3
no.
2011
31
39
https://ijmp.mums.ac.ir/article_7227_d23783b29f722ec0141842c9dcb411ae.pdf
dx.doi.org/10.22038/ijmp.2011.7227
The Role of MRSI in Target Volume Definition for Radiation Therapy of Prostate Cancer
Mostafa
Robatjazi
Ph.D Student of Medical Physics, Medical Physics Dept., Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran
author
Seyed Rabie
Mahdavi
Assistant Professor, Medical Physics Dept., Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran
author
Bahram
Bolouri
Assistant Professor, Radiation Oncology Dept., Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran
author
Alireza
Nikoofar
Assistant Professor, Radiation Oncology Dept., Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran
author
text
article
2011
eng
Introduction: Recently, magnetic resonance spectroscopic imaging (MRSI), as a functional imaging method, has been used for clinical target volume definition. In this study, we used this method to define the target volume in prostate radiotherapy. Material and Method: In this study, we used images of 20 prostate cancer cases. MRSI and MRI images were fused with CT images. Then, treatment planning was preformed for each patient using three methods: CT, CT+MRI and CT+MRSI planning. Results: The volumes of MRICTV and MRIPTV were on average 12.83% and 8.97% lower than the corresponding CTCTV and CTPTV volumes, respectively. For MRSI, the CTV and PTV volumes were 21% and 27.41% greater than the corresponding CT-based volumes. Maximum dose to rectum showed a 0.58% increase in MRSI relative to CT, and 1.09% reduction in MRI relative to CT. Maximum dose variation in femoral heads showed a 5.4% increase in MRSI relative to CT and 0.67% reduction in MRI relative to CT. Discussion and Conclusion: Application of MRSI for target volume definition of prostate cancer leads to an increase in this volume in comparison to CT planning alone. In this imaging technique, protocol and resolution should be considered to determine the target volume exactly.
Iranian Journal of Medical Physics
Mashhad University of Medical Sciences
2345-3672
8
v.
3
no.
2011
41
48
https://ijmp.mums.ac.ir/article_7228_8ad26bbaa45cf22f9a4b2ad8cdde7032.pdf
dx.doi.org/10.22038/ijmp.2011.7228
Extraction of the Longitudinal Movement of the Carotid Artery Wall using Consecutive Ultrasonic Images: a Block Matching Algorithm
Mehravar
Rafati
Ph.D. in Medical Physics, Medical Physics Dept., Tarbiat Modares University, Tehran, Iran
author
Manijhe
Mokhtari Dizaji
Prof., Medical Physics Dept., Tarbiat Modares University, Tehran, Iran
author
Hojabr
Saberi
Associate Professor, Radiology Dept., Tehran University of Medical Sciences, Imaging Center of Imam Khomaini Hospital, Tehran, Iran
author
Effat
Soleimani
Ph.D. Student in Medical Physics, Medical Physics Dept., Tarbiat Modares University, Tehran, Iran
author
text
article
2011
eng
Introduction: In this study, a computer analysis method based on a block matching algorithm is presented to extract the longitudinal movement of the carotid artery wall using consecutive ultrasonic images. A window (block) is selected as the reference block in the first frame and the most similar block to the reference one is found in the subsequent frames. Material and Methods: The program was applied to the common carotid artery of ten healthy subjects and the longitudinal movement of the arterial wall was extracted in three cardiac cycles. Manual measurements were carried out to validate the automatic method. The maximum, minimum and average longitudinal displacements of the arterial wall were extracted from the automatic method and compared with the manual measurements, with 10 mm displacement of two blocks in first frame. Results: Paired t-test analysis showed no significant differences between the automatic and manual methods (p>0.05). There was significant correlation between the changes in the instantaneous longitudinal movement of the common carotid artery measured with the manual and automatic methods (correlation coefficient 0.97, p<0.05). Bland-Altman analysis with the agreement region of 0.03 to 0.17 mm and difference average of 0.10±0.03 mm indicated good agreement of the two methods. Discussion and Conclusion: This study shows that the block matching algorithm can automatically extract the longitudinal movement of the arterial wall from consecutive ultrasonic images.
Iranian Journal of Medical Physics
Mashhad University of Medical Sciences
2345-3672
8
v.
3
no.
2011
49
59
https://ijmp.mums.ac.ir/article_7229_763221b281baa5ea575aabe96b40b147.pdf
dx.doi.org/10.22038/ijmp.2011.7229
Assessment of Extremely Low Frequency (ELF) Electric and Magnetic Fields in Hamedan High Electrical Power Stations and their Effects on Workers
Farshid
Ghorbani Shahna
Assistant Professor, Occupational Health Dept., Faculty of Public Health and Research Center for Health Science, Hamedan University of Medical Sciences, Hamedan, Iran.
author
Mahboobeh
Eshaghi
Ph.D. Student of Occupational Health, Faculty of Public Health, Hamedan University of Medical Sciences, Shiraz, Iran.
author
Tahereh
Dehghanpour
B.Sc. of Occupational Health, Faculty of Public Health, Hamedan University of Medical Sciences, Shiraz, Iran.
author
Zohre
Karami
B.Sc. of Occupational Health, Faculty of Public Health, Hamedan University of Medical Sciences, Shiraz, Iran.
author
text
article
2011
eng
Introduction: Public and occupational exposure to extremely low frequency (ELF) electric and magnetic fields induced by electrical equipment is a significant issue in the environment and at the workplace due to their potential health effects on public health. The purpose of this study was assessment of the electric and magnetic fields intensities and determination of mental and psychological effects of occupational exposure in the high voltage electric power stations in the city of Hamadan, Iran. Material and Methods: The intensities of the magnetic and electric fields were measured at eight high voltage electric power stations at three different intervals of sources using an HI-3604 instrument. A two-part questionnaire was used to assess mental and psychological effects of the exposure to these fields. Two groups of control and case workers including 30 samples were selected to determine the exposure effects. Results: The results of field measurements showed the highest average electric field intensity was related to the CVT unit with 3110 V/m at a 2 m distance from the source and the lowest average was related to the control room with 1.35 V/m next to the source. Also, the highest and lowest magnetic field intensities were close to the transformator 2 and the battery room (50.42 and 1.31 mG), respectively. Discussion and Conclusion: The intensities of electric and magnetic fields in the selected stations are lower than the ACGIH and ICNIRP standard levels for occupational exposures. The results obtained indicate that the distribution of these fields was nonlinear around the sources and the effects observed on exposed workers were non-thermal.
Iranian Journal of Medical Physics
Mashhad University of Medical Sciences
2345-3672
8
v.
3
no.
2011
61
71
https://ijmp.mums.ac.ir/article_7230_a7f665c374cc059316e4f59360c660ab.pdf
dx.doi.org/10.22038/ijmp.2011.7230
Optimization of 3D Planning Dosimetry in a Breast Phantom for the Match Region of Supraclavicular and Tangential Fields
Somayeh
Nourollahi
M.Sc.in Medical Physics, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran
author
Mahmoud
Allahverdi
Associate Professor, Medical Physics Dept., Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran
author
Mahbod
Esfahani
M.Sc.in Medical Physics, Radiotherapy Dept., Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran
author
Mehdi
Aghili
Assistant Professor, Radiotherapy Dept., Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran
author
Vahid
Changizi
Assistant Professor, Radiology Technology Dept., Faculty of Allied Medical Sciences, Tehran University of Medical Sciences, Tehran, Iran
author
text
article
2011
eng
Introduction: The complex geometry of breast and also lung and heart inhomogeneities near the planning target volume (PTV) result in perturbations in dose distribution. This problem can result in overdosage or underdosage in the match region of the three treatment fields. The purpose of this study is to create a homogeneous dose distribution in the match region between the supraclavicular and tangential fields, utilizing Gafchromic EBT film for dosimetry. Material and Methods: In this study, a slab phantom was designed with lung- and heart-equivalent inhomogetenities. Our measurements were carried out using Gafchromic EBT film. Irradiations were performed using the 6 MV photon beam of a Varian 2100 Clinac linear accelerator. Three-dimensional treatment planning and dose calculations were carried out using the RT Dose Plan software. The conventional method with source-to-skin distance match and a 3D method with source-to-axis distance match under different combinations of parameters such as gantry, collimator and couch rotations as well as asymmetric fields were utilized. Results: The results demonstrated differences between the 3D and conventional techniques. The best results in the match region were observed using the 3D method with asymmetric technique (maximum area of overlap = 0.43 cm2, depth of overlap = 3.55 cm, and average width of overlap = 0.75 cm). Discussion and Conclusion: This study shows that the EBT film is a suitable tool for two-dimensional distribution dosimetry and relative dose measurements. The study shows difficulties in achieving a homogenous dose distribution in the match region of supraclavicular and tangential fields and also demonstrates the effects of setup parameters on matching of treatment fields.
Iranian Journal of Medical Physics
Mashhad University of Medical Sciences
2345-3672
8
v.
3
no.
2011
73
81
https://ijmp.mums.ac.ir/article_7231_689819d8da742906c1d72a2dae111bcc.pdf
dx.doi.org/10.22038/ijmp.2011.7231