Introduction: Computed tomography (CT) has numerous applications in clinical procedures but its main problem is its high radiation dose to the patients compared to other imaging modalities using x-ray. CT delivers approximately high doses to the nearby tissues due to the scattering effect, fan beam (beam divergence) and limited collimator efficiency. The radiation dose from multi-slice scanners is greater than the single-slice scanners and since multi-slice scanners increasingly employ a wide beam, 100 mm ion chambers currently used in measuring the CTDI100, are not capable of accurately measuring the total dose profile of the slice width. Therefore, the CT dose is underestimated by using them. The purpose of this study is to measure the Computed Tomography Dose Index (CTDI) of a GE multi-slice CT scanner (64-slice) using polymer gel dosimetry based on MRI imaging (MRPD). CTDI is the sum of point doses along the central axis and estimates the average patient dose during CT scanning.Materials and Methods: For measuring CTDI, after designing and fabricating the phantom and preparing the MAGIC gel, MRI imaging using a 1.5 T Siemens MRI scanner was performed with the imaging parameters of ST=2 mm, NEX=1, TE=20-640 ms and TR=2000 ms. CTDI was measured with a 100 mm ion chamber (CTDI100) and also the MAGIC gel with MRPD method for 10 mm and 40 mm CT scan nominal widths.Results: Following the MEASUREMENT of the CTDI100 for 10 mm and 40 mm nominal slice widths of the multi-slice scanner using both ion chamber and MAGIC gel, the results showed that the ion chamber underestimates CTDI100 by 28.71% and 14.03% compared to gel for 10 mm and 40 mm respectively.Discussion and Conclusion: It was concluded from this study that gel dosimeters have the capability to measure CTDI in wide beams of multi-slice CT scanners whereas 100 mm standard ion chamber due to its limited length is not reliable even for a 10 mm beam width. In addition, due to the 3 dimensional nature of gel dosimetry, by using a MAGIC polymer gel, it is possible to obtain a lot of important information from the mentioned profiles such as the actual slice thickness and z-axis geometric efficiency. In addition to the stated parameters, the percentages of the total and partial homogeneities in the slice plane can be obtained only from gel dosimetry. The results of this study show that MAGIC polymer gel dosimetry based on MRI can be used as a supplementary method to using conventional ion chamber dosimetry especially in MEASUREMENTs for slice widths greater than 2 mm.

Introduction: Computed tomography dose index (CTDI) phantoms are used to optimize CT examinations in terms of image quality and the received dose. In this study, we aimed to develop cost-effective head CTDI phantoms from polyester-resin (PESR) materials as alternative phantoms. Material and Methods: The PESR was mixed with methyl ethyl ketone peroxide (MEKP) as a catalyst. The ratios of MEKP to PESR were 1: 150, 1: 200, 1: 250, and 1: 300, respectively. The phantom dimensions were designed similar to the standard CTDI phantom, i. e., length of 15 cm and diameter of 16 cm with five holes (diameter, 1. 31 cm). The CTDI MEASUREMENTs using the PESR-MEKP phantoms were compared with the CTDI MEASUREMENTs using the standard polymethyl methacrylate (PMMA) phantom. Results: The results showed that the CTDI values of the PESR-MEKP phantoms were slightly higher (up to 6%) than the standard PMMA phantom. It was found that the CTDI measured by the PESR-MEKP phantom with a ratio of 1: 300 had the least significant difference from the standard PMMA phantom,also, at this ratio, the phantom was the most homogeneous. Conclusion: The head CTDI phantoms based on PESR-MEKP materials were developed and evaluated in this study. It was found that the PR-MEKP phantom with a MEKP-to-PESR ratio of 1: 300 was insignificantly different from the standard PMMA phantom. Also, the phantom was constructed easily at a more reasonable cost, compared to the standard phantom.

Objective(s): Size specific dose estimate (SSDE) is a new parameter that includes patient size factor in its calculation. Recent studies have produced mixed results on the utility of SSDE, especially when automatic exposure control (AEC) was used. The objective of the study was to find out if there is a relationship between patient size and each of the parameters, SSDE and CTDIvol, when AEC is used. Methods: CT data of consecutively selected 111 patients were included for analysis. CTDIvol values of the CT scans were extracted for each patient. Effective diameter of each patient was calculated as geometric mean of anteroposterior and lateral diameters measured on axial CT images. Corresponding conversion factors for effective diameters were obtained from American Association of Physicists in Medicine (AAPM) report 204. SSDE was obtained as the product of CTDIvol and conversion factor values. Linear regression model was used to evaluate the relationship between patient size and the parameters SSDE and CTDIvol. Results: Mean weight was 62 (11. 5) and range was 34-103 kg. Median CTDIvol (mGy) on AEC mode was 7. 27(IQ range 7. 27, 7. 65) and mean effective diameter was 26. 2 cm (2. 4). Mean SSDE (mGy) was 10. 6 (0. 84). Good positive correlation was obtained between CTDIvol and effective diameter (r=0. 536; p<0. 0005). Strong inverse correlation was noted between SSDE and effective diameter (r=-0. 777; p<0. 0005). Linear regression model for establishing relationship between CTDIvol and effective diameter showed slope of 0. 314mGy/cm (R=0. 561; R2=0. 314; P<0. 0005) whereas between effective diameter and SSDE slope was-0. 23mGy/cm (R=0. 676; R2=0. 457; P< 0. 0005). Conclusion: The study shows that CTDIvol and SSDE vary but divergently, with patient size. SSDE is a better estimate of patient radiation dose from CT of MPI SPECT/CT than CTDIvol in systems that use automated exposure control.

Background: Computed tomography (CT) is one of the most used imaging modalities and is one of the main sources of population exposure. Recently, patient doses are estimated through CT dose index (CTDI) phantoms as a reference to calculate CTDI volume (CTDIvol) values followed by calculating equilibrium dose (Deq). This study aimed to improve MEASUREMENT methods for equilibrium dose and the effective dose using the American Association of Physicists in Medicine-Task Group Report No.111 (AAPM-TG111).Methods: Using standard phantom of polymethylmethacrylate (PMMA) and pencil ionization chamber, the values of CTDI100 and  e (CTDI100), and DL(0) were calculated followed by calculating equilibrium dose, hence obtaining the total effective dose.Findings: The average equilibrium dose in according to the CTDI100 and CTDIvol was found to be 26.11 and 58.99, respectively; which was based on the value of 19.4 and 42.4 mGy recorded by CT console. Differences between CTDIvol and Deq were 34.58% and 39.12% based on the experiments setting up by the CT-weighted and volume dose index, respectively.Conclusion: Differences between values of CTDIvol and Deq were consistent with the literature results. Overall, weighted dose index of CT systems is not sufficient to determine patient’s dose and using new recommended indices are required.

Purpose: Relatively much research has been done into theorizing and its importance. However, the number of studies related to the understanding of contexts is very negligible and so far no framework has been provided including indicators and evaluation methods. This research has been done with the aim of achieving the indicators related to theorizing and subsequently presenting a formula to measure the potential and theorizing capacity of scientific institutes. Method: Library and field methods have been used to collect information. Data were first collected through a checklist and then through the AHP questionnaire. Questionnaire was distributed among experts and AHP method was used to analyze the data. Expert Choice software was used to analyze the data obtained from the AHP questionnaire. Findings: The results indicate that individual index is 9 times more important than non-individual index in the theorizing process. A pairwise comparison of individual sub-indices showed that "awareness of theorizing" and "research ability”,have an equal portion in theorizing. The "coherence of personality traits" is sextuple as important as the "awareness of theorizing”, . "Coherence of personality traits" up to sextuple "research ability" can be considered important in the theorizing process. A pairwise comparison of non-individual index sub-indices showed that "communication level" is twice as important as "institutional index level". However, the “, effect level" is twice as important as the "communication level". The "communication level" is 7 times more important than the "management index level". The "effect level" can be considered 7 times more important than the "institutional index level". "Institutional index level" is quadruple more important than "management index level". The "effect level" is extremely important compared to the "management index level". Conclusion: Although theorizing is done by a researcher or a group of researchers, but ultimately, it is a collective matter or at least, several components are involved in its formation. Theorizing is a coherent, dynamic, purposeful and thoughtful practice whose results can lead researchers to recognize the credible generalizable relationship between causes and effects. Finally, the formula Tp= (0. 9I + 0. 1NI) was presented, which can be used to assess the capacity of theorizing in institutes.

Thyroid exposure to radiation in brain computed tomography (CT) scan is of great value since it is considered as a vital organ. This study aimed to investigate the absorbed dose of thyroid by various protocols of head CT in patients referring to 64‑ slice CT scan center and to compare the values with the calculated dose by imaging performance and assessment of CT (ImPACT) method. Also, the values of CT scan dose index (CTDI) were calculated with semiconductor detector. In this cross‑ sectional study, 120 outpatients including three groups of forty individuals over 40 years old referring to the hospital radiology centers in Tehran for head CT were chosen and 3 thermo‑ luminescence dosimeter (TLD‑ GR200) were applied on thyroid gland of each patient. For brain CT, Absorbed and effective doses of thyroid gland were calculated by ImPACT software. In addition, semiconductor detector in head CTDI phantom calculated CTDI for the applied protocols. Mean effective dose of thyroid gland in brain scan group was calculated by TLD and ImPACT software which showed no significant difference (P < 0. 001). Mean effective dose of thyroid gland in unidirectional and bi‑ directional sinus scan by TLD and ImPACT software were different significantly (P < 0. 001). Also, the differences between CTDI values shown by brain and sinus scan protocol with semiconductor detector and those CTDI were significant (P < 0. 001). The calculated values of absorbed dose and effective doses of thyroid by TLD and ImPACT software were not significantly different. Mean effective dose calculated for thyroid gland in head scans by TLD and ImPACT was less than the annual permissive level for thyroid gland suggested by International Committee on Radiological Protection. In this study, calculated values of thyroid effective dose in brain scan with 64‑ slice scanner were less than the calculated values in a similar study.