Iranian Journal of Medical Physics
Volume:17 Issue: 5, Sep Oct 2020

This study aimed to establish the conversion factors to normalize the output dose of volumetric computed tomography dose index (CTDIvol) to the patient dose (i.e. size-specific dose estimate (SSDE)) for various phantom diameters and tube voltages.

In-house cylindrical acrylic phantoms with physical diameters ranging from 8 to 40 cm were developed in this study. Each phantom had a hole in the center and four holes in the peripheral areas. The phantoms were scanned by a Siemens Somatom Definition AS CT Scanner using different tube voltages (i.e. 80, 100, 120, and 140 kVps) and with 200 mAs and 10 mm slice thickness. In addition, the doses in every hole and phantom were measured using a Raysafe X2 CT Sensor. The weighted SSDE (SSDEw) values were calculated using the five holes in every measurement. The size-conversion factors for the body and the head CTDI phantoms were established by dividing the SSDEw for various sizes with the SSDEw at the water-equivalent diameter of 33.90 cm and 16.95 cm, respectively.

The results revealed that the size-conversion factor exponentially decreased with an increase in the phantom size. It was also found that the size-conversion factor was affected by the tube voltages. Furthermore, the different size-conversion factor between 80 and 140 kVp was more than 15% in very thin and obese patients.

Higher accuracy of the size-specific dose estimation can be achieved considering the impact of the tube voltages beside the size of the patient.

Human activities, such as mining, result in the elevation of natural ionizing radiation in the environment. Jos-Plateau, Nigeria, including Kuru-Jos has experienced commercial tin mining in the past, and local mining is still being practiced in this area. Therefore, it is important to assess the radiation exposure due to grown crops and the farm soils in Kuru-Jos, Nigeria. In total, four crops and soil samples were randomly collected from farmlands in Kuru-Jos. The radioactivity levels in the soil and food samples were measured using a thallium-activated sodium-iodide detector coupled to a Canberra series 10 plus Multi-Channel Analyzer. The effective dose rates in soils and food crops along with the cancer risks in the crops were determined. According to the results, the highest mean activity concentrations of 40K, 226Ra, and 232Th in the food crops were 456±126.0Bq/Kg (yam), 46.9±9.6Bq/kg (yam), and 31.6±23.9Bq/Kg (maize), respectively. Moreover, the mean activity concentrations of 40K, 226Ra, and 232Th in farm soil were determined at 1105.6±357.7Bq/Kg (cassava), 167.5±37.6Bq/Kg (yam), and 205.4±124.4Bq/Kg (Guinea corn), respectively. Additionally, yam crop had the highest mean ingestion effective dose of 1231.9µSv/y, and maize crop indicated the minimum mean value of 304.1±179.1µSv/y. The cancer risks of and for yam and cassava, respectively, were higher than the world average value (i.e., 1.0x10-3). The results indicated a high radioactivity level which is in line with the results obtained from other areas in Jos-Plateau, Nigeria; however, there have been no radiological health plague reports from the areas so far.

The image quality of computed tomography (CT) can be seriously lowered by metal implants of patients. These implants are known to exert a significant impact on diagnostic accuracy due to artifacts. The current study aimed to assess the usefulness of Metal Artifact Reduction (MAR) software in the reduction of metal artifacts, in comparison to iterative reconstruction algorithm (IDREAM). Water phantom with raw chicken leg underwent CT scan (Sinovision, Insitum 16) before (reference group (GPref) and after metal implantation: ((GPA (IDREAM without MAR) and GPB(IDREAM with MAR)).  A total number of 30 patients [GP1 (instrumented spine (n=15)), GP2 (Brain clips (n=15))] underwent CT scan (Sinovision ,Insitum 16). GP1 and GP2 were reconstructed using two procedures including IDREAM without MAR vs.  2: IDREAM with MAR. All images were evaluated using subjective and quantitative assessment. In subjective image quality assessment, the scores of MAR images were higher than IDREAM images (P<0.05) as indicated by four radiologists. The absolute CT difference (ΔCT) and Artifact index (AI) demonstrated that MAR appeared to be superior for the reduction of metal artifacts (P<0.05). As evidenced by the obtained results, MAR software can be efficiently used for metal artifact reduction in computed tomography (instrumental spine and brain clips).

Nowadays, many people use medicinal plants to manage diseases; therefore, detailed knowledge of the type and level of elements present in these plants is of prominent importance.The present study aimed to determine the weight fraction of 12 elements in the five most common medicinal plants in Iran. The names of these plants are caraway (Carum carvi), savory (Satureja hortensis), purslane (Portulaca oleracea), fenugreek (Trigonella foenum-graecum), and milk thistle (Silybum marianum) which were purchased from herbal pharmacies.

The neutron activation method was used to determine the elements. In the current study, neutrons from the research reactor core in Tehran, Iran were used and gamma spectra from radionuclides were recorded using a high purity germanium detector. The mass fractions of 12 elements were determined in the five abovementioned plants.

Caraway had the maximum amounts of elements of Fe (8,789 ppm), Cr (8 ppm), and Na (517 ppm) among the selected plants. The savory contained maximum levels of Mn (95 ppm), Cl (3,702 ppm), Ca (18,328 ppm), K (21,562 ppm), and V (2.7 ppm) and the lowest amount of Fe (195 ppm), Zn (13 ppm), Ca (2,243 ppm), Al (99ppm), Mn (26 ppm), and Mg (177ppm) were observed in fenugreek.

The highest levels of Cr and Mg were obtained for caraway (8 ppm) and pursalne (3,915 ppm), respectively. These elements can help to decrease blood cholesterol and triglyceride levels. Furthermore, the results showed that these herbs were rich in essential nutrients for metabolic functions.

The aim of this study was to determine the accuracy of two different immobilization methods in patient positioning in cranial radiotherapy. The six-dimensional (6D) target localization accuracy of using a dedicated stereotactic mask was compared with that of a conventional head mask by the ExacTrac system.

A total of 56 patients with cranial lesions were included in this study (26 patients with a dedicated stereotactic mask and 30 subjects with a conventional head mask). The ExacTrac image-guided positioning system was utilized to obtain daily translational and rotational patient positioning displacement from the intended position. The 6D setup data was analyzed to obtain population mean, systematic and random errors, and three-dimensional (3D) vector shifts in all the patients.

The population mean values of setup errors were comparable with both immobilization systems; however, the spread as indicated by population systematic and population random errors was more in the use of a conventional head mask. The mean values of the 3D vector shifts were 2.09±1.00 and 4.51±3.38 mm with the use of a dedicated stereotactic mask and conventional head mask, respectively. The frequency distribution of maximum rotational deviation and statistical analysis demonstrated a significant difference in immobilization accuracy between stereotactic immobilization and 3-clamp immobilization (P<0.05).

The results revealed that there was a significant reduction in target positioning errors with a dedicated stereotactic mask, compared to that with a conventional cranial mask. Furthermore, a dedicated stereotactic mask is required to keep rotational deviations within system correctable limits.

Adaptive response is one of the important concepts in radiobiology. The present report aimed to transfer the radio-adaptation via serum.
In total, 50 male adult Wistar rats were randomly divided into 6 groups, including control, serum control, low-dose (100cGy), low-dose/lethal, serum/lethal, and lethal (8Gy). Exposure was carried out by a linear accelerator (Elekta Synergy® Platform) with a 40×40cm field size. The animals were monitored in terms of the endpoints of the survival rate, and at the first stage, the rats were exposed to the low doses of radiation. Subsequently, the serum was injected intraperitoneally under sterile conditions 6 h after low-dose exposure. The Kaplan Meier Survival Curve was used to evaluate the survival rate (P<0.05).
There was a significant difference among different groups regarding the survival rates. Moreover, a statistically significant difference was observed between low-dose/lethal and low-dose/serum, low-dose/lethal and lethal, and low-dose/serum and lethal (P=0.001). Similarly, there was a statistically significant difference between the control and experimental groups regarding the survival rates (P=0.001).
To the best of our knowledge, this method can lead to immunological responses or unknown mechanisms that result in the increased survival adaptive response to subsequent high-dose radiation.

The rapid use of computed tomography (CT) scan is of great concern, due to increase in patients’ dose. Optimization of CT protocol is a vital issue in dose reduction. This study aimed to optimize radiation dose in cranial CT and assess modifications in image quality under radiation dose reduction.
A poly(methyl methacrylate) phantom was used for quality control test on CT scanners. Data of 214 scan parameters, dose indicators; volume CT dose index (CTDIvol) and dose-length product (DLP) of patients who underwent cranial CT scans were collected. The data were grouped into three, with respect to the slice numbers of 24, 28, and 32. Tube voltage (kVp) and slice thickness were constant; (110 kVp and 4.8 mm, respectively), at variable tube currents (mAs). A one-sample t-test was used to compare the dose indicator values of the hospital protocol with a recommended protocol. Scan parameters were optimized for radiation dose against image quality.
Increased mAs resulted in increased CTDIvol and DLP at constant kVp and slice thickness. Moreover, dose indicators recorded the lowest and highest values at the slice numbers of 24 and 32, respectively. An increase in slice numbers affected dose indicators. Dose indicators recorded significant reduction (P<0.001) in comparison to the recommended protocol.
Optimization of CT protocol considers radiation dose and image quality. Radiologists adopted protocols acquired with lower scan parameters and dose indicators lower than the recommended achievable dose limit of 58 mGy.

Recent studies have acknowledged the potential of convolutional neural networks (CNNs) in distinguishing healthy and morbid samples by using heart sound analyses. Unfortunately the performance of CNNs is highly dependent on the filtering procedure which is applied to signal in their convolutional layer. The present study aimed to address this problem by applying filter bank learning concept in CNNs. In proposed method, the filter bank of CNN is updated based on a cross-entropy minimization rule to extract higher-level features from spectral characteristics of the heart sound signal. The deeper level of the extracted features in parallel with their spectral-based nature leads to better discrimination between healthy and morbid heart sounds. The proposed method was applied to three different heart sound datasets of PASCAL-A, PASCAL-B, and Kaggle, including normal and abnormal categories. The proposed method obtained a true positive rate (TPR) between minimally 86% and maximally 96% (if FPR=0%) among all the examined datasets. In addition, the false-positive rate (FPR) was obtained as 7-8% (if TPR=100%) among the mentioned datasets. Finally, the accuracy was achieved in the range of 93-98% when the FPR was 0% and within the range of 96-96.5% when the TRP was 100%. Increased TPR in the proposed method (96% for the proposed method vs. 87% for CNN) in parallel with a decrease in its FPR (7% for the proposed method vs. 10% for CNN) showed the proposed method's superiority against its well-known alternative in automated self-assessment of the heart.

In dual-energy computed tomography (DECT), the Hounsfield values of a substance measured at two different energies are the basic data for finding the chemical properties of a substance. The trends of Hounsfield unit (HU) alterations following the changes in energy are different between the materials with high and low Zeff. The present study aimed to analyze the basic principles related to the attenuation coefficient of x-ray photons and a quantitative explanation is given for the mentioned behavior or trend.
A mathematical expression was derived for the HU difference between two different scanner voltages. Attenuation coefficients of diverse substances, such as methanol, glycerol, acetic acid, the aqueous solution of potassium hydroxide, and water were calculated for x-ray scanners operating differently at distinct applied voltages and with diverse inherent or added filters.
Findings of the current study demonstrated that the negative or positive outcome of HU(V1) - HU(V2) equation is not determined by the electron density of a substance. However, it is affected by the effective atomic number (Zeff) of the material and machine parameters specified by the source spectrum.
According to our results, the sign of HU difference [HU(V1) – HU(V2)] for the variable cases of V2 and V1 gives an indication of the effective atomic number of the material under study. The obtained results might be of diagnostic value in the DECT technique.