Average Linear Attenuation Coefficient Research Articles

An Experimental Study on the Measurement of Gamma-Ray Linear Attenuation Coefficients with Transmission Factors for Ispir and Kızılcahamam Dry Bean

In the present work, the gamma-ray linear attenuation coefficients (µ) and transmission factors (TF) were measured for Erzurum Ispir dry bean (IDB) and Ankara Kızılcahamam dry bean (KDB). Photons of the Am-241 point source with an energy of 59.54 keV, an Energy Dispersive X-Ray Fluorescence Spectrometer (EDXRFS), and a Si (Li) detector were used in the experiment. As a result, it was observed that the average transmission factor of Erzurum İspir dried beans was higher than that of Ankara Kızılcahamam dry beans, and the average linear attenuation coefficient was smaller. This means that Ankara Kızılcahamam dry beans absorb more gamma rays than Erzurum İspir dry beans, that is, they interact more with gamma rays.

Determination of natural radioactivity levels and gamma radiation attenuation coefficients in propolis samples and the study of its antioxidant properties

Abstract Thanks to its rich content, propolis has been used to protect the hive from all kinds of external influences and for disinfection by bees. Furthermore, it is an important marker for monitoring environmental pollution because the main sources of propolis are plant and secretions. So, the present study aimed to research radiation attenuation capability and the natural radioactivity level of propolis samples. For this reason, both natural radioactivity concentrations (226Ra, 232Th and 40K) and attenuation coefficients (Linear and Mass) in the propolis samples collected from 10 different points in Turkey were measured using high purity germanium detector (HPGe). The average natural radioactivity concentrations in samples were found to be 0.56 ± 0.19, 2.65 ± 0.31 and 70.08 ± 2.42 Bq/kg for 226Ra, 232Th and 40K, respectively. These values were much lower than the average world values (35 Bq/kg for 226Ra, 30 Bq/kg for 232Th and 400 Bq/kg for 40K) reported by United Nations Scientific Committee on Effects of Atomic Radiation (UNSCEAR) in foodstuff. The average linear attenuation coefficient, mass attenuation coefficients and half value layer values for gamma rays with 59.54 keV energy were determined as 0.1970 cm−1, 0.1831 cm2 g−1 and 3.56 cm, respectively. In addition, antioxidant properties of the samples were measured using total phenolic content and ferric reducing antioxidant power. Their correlations with radioactivity were investigated.

Histogram analysis- a useful tool for tissue characterization in brain CT

Introduction: Pixel value in computed tomography (CT) gives the average linear attenuation coefficient of the scanned material in the path of the x-ray beam, being normalized to that of water. It is known that attenuation coefficient or HU value is a function of the chemical characteristic of the material and of the x-ray energy. The CT image shows the HU value by a shade of gray in each pixel. Human eye is often not able to discriminate gray shadows; whose grayness are close to each other. Therefore, when two different tissues have very similar chemical characteristics they may not be distinguishable in the CT image by human eyes. For this reason, in CT image, it is difficult to distinguish between brain tumor and ischemia, in the hypodense area. The aim of this study is to use histogram analysis, based on the frequency distribution of the HU values in brain CT images to evaluate the possibility of distinguishing tumor from ischemia. Materials and Methods: We collected 150 axial slices of brain CT, from known hypodense areas belonging to ischemia and tumor with similar appearance. They contained 75 samples of each type. Minimum, maximum, and mean HU values of ROI inside the lesions were used to make the histogram, cumulative and probability percentage distribution. We used 10 unknown cases, 5 tumors and 5 ischemia, to evaluate our finding. Results: Bar chart and linear diagram histogram show that the minimum, maximum and mean of HU values are higher in ischemia cases. Also, the median of the cumulative distributions of minimum, maximum and mean appear at higher HU values for ischemia. The probability of occurrence of ischemia cases increases with increasing HU values of minimum, maximum and mean while the behavior of the tumor cases is completely reverse. We have done the same data analysis for 10 unknown cases. Our predictions match in 80% of the cases, with the radiologist’s conclusion, who were unaware of our findings. Conclusion: Histogram analysis may be used as an effective tissue characterization tool in non-enhanced brain CT images. This method could distinguish hypodense areas of ischemic lesion from tumor, as is seen, for the first time, in the present study.

CT tube current for attenuation map in a combined PET/CT system: obese patient simulated phantom study

The CT portion of PET/CT provides attenuation correction of the PET emission scan. This study was performed to evaluate how much the CT tube current can be lowered while still providing attenuation maps on PET images. Two body phantoms (outside diameters of 300 and 500mm) were used to investigate, and PET/CT acquisitions were performed with an Aquiduo PCA-7000B (Toshiba Medical Systems, Otawara, Japan). The CT scan was performed with the following parameters (120kVp; 0.5-s rotation; 10, 20, 40, 80, 160, 200, 320, 460mA). After the CT scan, PET images for (18)F-FDG (5.3kBq/mL) were obtained for 4min/bed position. The linear attenuation coefficients for (18)F-FDG in 300- and 500-mm phantoms, pixel values and SD of CT images, radioactivity concentration values and hot- and cold-sphere contrast on PET images in the 500-mm phantom were evaluated. In the 300-mm phantom, all eight tube currents gave average linear attenuation coefficients of approximately 0.095cm(-1). In contrast, the average linear attenuation coefficients of the 500-mm phantom at 10, 20, and 40mA were significantly decreased (0.081, 0.087, and 0.092cm(-1), respectively; p<0.05) as compared to 0.096cm(-1) of the other tube currents. Further, CT pixel values decreased 10 and 20mA. Thus, the background radioactivity concentration values at 10 and 20mA were substantially underestimated to be 57 and 80%, respectively (p<0.05); the hot-sphere contrast values at 10 and 20mA were 0.26 and 0.29; the cold-sphere contrast values at 10, 20, and 40mA were -0.33, -0.16, and 0.08. Although the linear attenuation coefficients in the 300-mm phantom remained the same with varying CT tube currents, the 500-mm phantom yielded significant differences in the range 10-40mA. Therefore, the CT tube currents for attenuation correction should be adjusted over 40mA in obese patients.

Gamma-ray absorption using rubber—lead mixtures as radiation protection shields

In the present study five samples of special rubber–lead were fabricated each of them consists of lead and rubber with different weight ratios. The fabrication was carried out through the process of mixing under compression pressure. Gamma-ray transmission method was employed to determine the linear attenuation coefficient for narrow collimated mono-energetic beams of gamma-rays emitted from 241Am 0.059, 152Eu 0.13 and 137Cs 0.662 MeV. The linear attenuation coefficient of standard rubber–lead shield was also experimentally determined. The percentage of lead in standard rubber–lead shield was determined through the calibration curve or by a simple computer program written in MATLAB. All prepared samples are characterized as flexible and gives a good homogeneity. samples no. 4 & 5 offers the best performance as a radiation protection shields. The results showed an inverse proportionality between the linear attenuation coefficient μl and E, and μl has a direct proportionality with mixing ratios (sample density). The results showed an inverse proportional between the half value layers and the average linear attenuation coefficients of the various samples.

Gamma Ray Shielding from Saudi White Sand

This study is a comparison of gamma ray linear attenuation coefficient of two typs of shielding materials made of Saudi white and red sand. Each shield was consisted of one part of cement two parts of sand in addi-tion to water. Different thicknesses were tested. The concentrations of all elements in each shield material were determined by Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The results obtained from the ICP-MS were used in MCNP4B (Monte Carlo N-Particle Transport Computer Code System) [1] to calculate the attenuation coefficient. The theoretical (MCNP4B) and the experimental calculations were found to be in a good agreement. In the casw of the largest thickness used, 28cm, the gamma ray intensity passing through the white sand shield was approximately half of the intensity obtained through the red sand shield. The average linear attenuation coefficients were found to be 0.17cm-1 and 0.15cm-1 for white and red sand shields respectively. The study shows that white sand is better for attenuating gamma ray compared to the red sand.

Determination of crushed stone volume in concrete cores from hydroelectric power plant dams by three-dimensional tomography

In this paper we present the results of a methodology for obtaining the volume of crushed stones using industrial tomography in concrete cores from hydroelectric power plant dams. In order to apply the appropriate voltage in the X-ray tube during radiograph acquisition, the average linear attenuation coefficients (μ) of the cement paste and the mortar were determined. The two-dimensional tomographic images were reconstructed using 180 digital X-ray projections obtained by an industrial tomograph. The 3D tomography images were rendered using slices in the bitmap format and the VTK (Visualization Toolkit) open source library, and finally, the Marching Cubes algorithm was used for the volumetric visualisation of the data. The low contrast resolution was also evaluated. The methodology for volume determination was evaluated using two phantoms (one with cement paste and another with mortar).

Investigation into the impact of couch sag on delivered dose

The effect of couch sag on treatment delivery accuracy has been investigated by modelling the variation of delivered dose from planned dose due to the difference between the treatment and simulation couches. The couch sag of the Siemens (Concord, USA) Primus linac was determined relative to the couch sag of the Siemens (Germany) Sensation 4 CT Scanner. A phantom planning study was then undertaken to evaluate the likely clinical impact of the couch sag through an evaluation of changes in dose distribution, dose volume histograms and monitor units. The couch sag was simulated by altering the angle of the CT gantry when obtaining image studysets. A second investigation into the effects of couch sag was undertaken using an existing patient CT studyset. For this investigation, the couch sag was simulated by appropriate rotation of the gantry and collimator angles. The effect of couch sag on calculated monitor units (MU) was found to be statistically insignificant. The small monitor unit changes observed were likely to result from differences in the average linear attenuation coefficient along the beam path to the isocentre. The major differences seen however were in the regions away from the central axis. The dose volume histograms showed that both the bladder and rectum were further spared with increasing tilt angle whilst the PTV dose was unchanged. The only issue at South West Sydney Cancer Services (SWSCS) in terms of patient position variation arises from the angle induced by the couch sag (or more precisely, the difference in couch sag angle between the CT and Linac couches). Due to the relatively uniform structures (of PTV, bladder and rectum), and the proximity of these critical structures to the isocentre, this angular rotation about the isocentre did not cause any major variations to the DVH, MU and isodoses for realistic levels of couch sag (i.e. less than 20mm).

High-Resolution X-ray Computed Tomography as a Tool for Visualization and Quantitative Analysis of Igneous Textures in Three Dimensions

High-resolution X-ray computed tomography of igneous rocks provides a rapid, non-destructive means to acquire textural data and imagery in three dimensions. Tomographic images are maps of the spatial variations within a specimen of the average linear attenuation coefficient for the input X-ray spectrum, a quantity that depends strongly on mass density and also on atomic number. Visualization of these data benefits from the ability to view sections through the specimen in any location and orientation, and from the ability to extract features of particular interest and display perspective views of them in arbitrary orientation. These images can then be animated to facilitate comprehension of three-dimensional textural relationships. The numerical character of the method also makes these data sets inherently rich in the metrical information required for quantitative characterization and statistical analysis of the sizes, shapes, locations, and interrelations of textural components in igneous rocks.

Comparing two methods for calculating phantom scatter

Two methods are compared for calculating the field-size dependence of the phantom scatter component of dose for x-ray beams. One model sums three Gaussian distributions; the other model is a two-parameter function. With a measurement of the beam quality as input to determine parameters, both models accurately reproduce the relative phantom scatter. However, there are important differences between the models. For all beam energies, the two-parameter model characterizes the absolute phantom scatter as a function of depth and field size, while, also for all beam energies, the six-parameter Gaussian model characterizes the relative phantom scatter at a single depth of 10 cm. For small field sizes, the phantom scatter calculated from the two-parameter model agrees with Monte Carlo calculations better than the Gaussian model. In the Gaussian model, the parameters can be obtained for beam energies between and 25 MV by linear interpolation based on the measured beam quality. In the two-parameter model, and for energies above 4 MV, the parameters can be obtained using linear functions of the dose-weighted average linear attenuation coefficient, which is related to beam quality.

Relations between scatter factor, quality index and attenuation for x-ray beams

The relations between the attenuation factor, the normalized phantom scatter factor and the quality index are examined using a semiempirical formula for the dose on the central axis of an x-ray beam in water. The study is restricted to depths and field sizes sufficient for electron equilibrium. The results are compared with data in the recent literature. It is concluded that for x-ray beams in the energy range 4-25 MV the normalized scatter factors can be calculated from the dose-weighted average linear attenuation coefficient in water, determined from transmission measurements in a narrow-beam geometry or from the quality index.

Changes in the linear attenuation coefficient of canine appendicular bone following intravenous infusion of strontium lactate, measured using gamma-ray computed tomography.

Changes in the average linear attenuation coefficient (LAC) within a fixed measurement volume in the proximal end of the dog tibia, which contains trabecular bone and associated soft tissues (the trabecular bone "space"), were monitored continuously using gamma-ray computed tomography (gamma-CT) prior to, during, and following intravenous infusion of strontium (Sr) lactate. An infusion of 1.3-4.7 g of Sr over a period of 110-160 minutes into 20-kg dogs resulted, within 6-8 hours, in an increase of 0.019-0.045 cm-1 (P less than 0.002) in the LAC. Calibration of the gamma-CT system showed that 0.44 mg/cm3 of Sr produced a change of 0.01 cm-1 in the LAC. Using this conversion factor, the Sr concentration in the trabecular bone space resulting from infusion, as measured by flame atomic absorption spectroscopy, agreed with that predicted by the change observed in the LAC. Sr present in the serum and urine was consistent with the changes observed in the LAC over the study period. Control dogs infused with mineral-free solutions showed no change in LAC. Calcium equivalents required to give the changes observed in the LAC using Sr indicate that variations in skeletal turnover in man can be monitored in the peripheral skeleton using gamma-CT.

Automated image analysis for bone density measurements using computed tomography

Quantitative trabecular bone density (TBD) measurements in the appendicular skeleton, using computer tomography, are described. Pixel-value frequency histograms are generated, to determine the spatial coordinates of the centers of mass distribution for both bones in the image field. A line joining these centers is used as an axis for subsequent enhancement of horizontal image features, and for radial fan searches, to separate bone images in the analysis field. One bone image is then deleted and the outer contour of the remaining bone is determined using cross-correlation and mathematical morphology operators. This contour is then used as a template to calculate average linear attenuation coefficients (LACs) over 1-pixel-wide annuli for TBD calculation. Data from 33 individual subjects (1251 images) have been processed using both automatic and manual analysis methods. Both methods give the same numerical values for TBD, but the automatic method has slightly better precision. The analysis method is general and is adaptable to other imaging situations.