X-ray Linear Attenuation Coefficient Research Articles

Layered BiOI single crystals capable of detecting low dose rates of X-rays

Detecting low dose rates of X-rays is critical for making safer radiology instruments, but is limited by the absorber materials available. Here, we develop bismuth oxyiodide (BiOI) single crystals into effective X-ray detectors. BiOI features complex lattice dynamics, owing to the ionic character of the lattice and weak van der Waals interactions between layers. Through use of ultrafast spectroscopy, first-principles computations and detailed optical and structural characterisation, we show that photoexcited charge-carriers in BiOI couple to intralayer breathing phonon modes, forming large polarons, thus enabling longer drift lengths for the photoexcited carriers than would be expected if self-trapping occurred. This, combined with the low and stable dark currents and high linear X-ray attenuation coefficients, leads to strong detector performance. High sensitivities reaching 1.1 × 103 μC Gyair−1 cm−2 are achieved, and the lowest dose rate directly measured by the detectors was 22 nGyair s−1. The photophysical principles discussed herein offer new design avenues for novel materials with heavy elements and low-dimensional electronic structures for (opto)electronic applications.

Development of an US, MRI, and CT imaging compatible realistic mouse phantom for thermal ablation and focused ultrasound evaluation

Tissue mimicking phantoms (TMPs) play an essential role in modern biomedical research as cost-effective quality assurance and training tools, simultaneously contributing to the reduction of animal use. Herein, we present the development and evaluation of an anatomically accurate mouse phantom intended for image-guided thermal ablation and Focused Ultrasound (FUS) applications. The proposed mouse model consists of skeletal and soft tissue mimics, whose design was based on the Computed tomography (CT) scans data of a live mouse. Advantageously, it is compatible with US, CT, and Magnetic Resonance Imaging (MRI). The compatibility assessment was focused on the radiological behavior of the phantom due to the lack of relevant literature. The X-ray linear attenuation coefficient of candidate materials was estimated to assess the one that matches best the radiological behavior of living tissues. The bone part was manufactured by Fused Deposition Modeling (FDM) printing using Acrylonitrile styrene acrylate (ASA) material. For the soft-tissue mimic, a special mold was 3D printed having a cavity with the unique shape of the mouse body and filled with an agar-based silica-doped gel. The mouse phantom accurately matched the size and reproduced the body surface of the imaged mouse. Tissue-equivalency in terms of X-ray attenuation was demonstrated for the agar-based soft-tissue mimic. The phantom demonstrated excellent MRI visibility of the skeletal and soft-tissue mimics. Good radiological contrast between the skeletal and soft-tissue models was also observed in the CT scans. The model was also able to reproduce realistic behavior during trans-skull sonication as proved by thermocouple measurements. Overall, the proposed phantom is inexpensive, ergonomic, and realistic. It could constitute a powerful tool for image-guided thermal ablation and FUS studies in terms of testing and optimizing the performance of relevant equipment and protocols. It also possess great potential for use in transcranial FUS applications, including the emerging topic of FUS-mediated blood brain barrier (BBB) disruption.

Attenuation coefficient in the energy range 14–36 keV of 3D printing materials for physical breast phantoms

Objective. To measure the monoenergetic x-ray linear attenuation coefficient, μ, of fused deposition modeling (FDM) colored 3D printing materials (ABS, PLAwhite, PLAorange, PET and NYLON), used as adipose, glandular or skin tissue substitutes for manufacturing physical breast phantoms. Approach. Attenuation data (at 14, 18, 20, 24, 28, 30 and 36 keV) were acquired at Elettra synchrotron radiation facility, with step-wedge objects, using the Lambert–Beer law and a CCD imaging detector. Test objects were 3D printed using the Ultimaker 3 FDM printer. PMMA, Nylon-6 and high-density polyethylene step objects were also investigated for the validation of the proposed methodology. Printing uniformity was assessed via monoenergetic and polyenergetic imaging (32 kV, W/Rh). Main results. Maximum absolute deviation of μ for PMMA, Nylon-6 and HD-PE was 5.0%, with reference to literature data. For ABS and NYLON, μ differed by less than 6.1% and 7.1% from that of adipose tissue, respectively; for PET and PLAorange the difference was less than 11.3% and 6.3% from glandular tissue, respectively. PLAorange is a good substitute of skin (differences from −9.4% to +1.2%). Hence, ABS and NYLON filaments are suitable adipose tissue substitutes, while PET and PLAorange mimick the glandular tissue. PLAwhite could be printed at less than 100% infill density for matching the attenuation of glandular tissue, using the measured density calibration curve. The printing mesh was observed for sample thicknesses less than 60 mm, imaged in the direction normal to the printing layers. Printing dimensional repeatability and reproducibility was less 1%. Significance. For the first time an experimental determination was provided of the linear attenuation coefficient of common 3D printing filament materials with estimates of μ at all energies in the range 14–36 keV, for their use in mammography, breast tomosynthesis and breast computed tomography investigations.

Determination of the X-ray Linear Attenuation Coefficient of Clay-Originated Bricks in Central Java Province, Indonesia

The widespread use of radioactivity has culminated in adverse health consequences and has generated an entire health science study. It is established practice that certain precautions must be taken to avoid potential exposure to ionizing radiation like an x-ray. One way to control radiation hazards external is to use a radiation shield. In this study, clay-originated bricks were used as a shield and determine its linear attenuation coefficient of x-ray radiation. The bricks were collected from 5 regencies in Central Java province. Digital fluoroscopy was used as an x-ray radiation source and operated in 81 kV 32 mAs; also, it associated with the multi-purpose detector. It shows that linear attenuation coefficient of Boyolali, Klaten, Magelang, Temanggung, and Semarang bricks respectively are 0.8896 cm<sup>-1</sup>; 0.7455 cm<sup>-1</sup>; 0.7115 cm<sup>-1</sup>; 0.7254 cm<sup>-1</sup>; and 0.7972 cm<sup>-1</sup>. Furthermore, we calculate the half-value layer of each brick and indicates that brick from Boyolali is the most effective as a shielding among others that can reduce half value of x-ray radiation dose. This research is expected to enhance the systems integration of radiation shielding safeties and allow for the effective treatment of radiation sources for both humans and the environment.

Mineralogy of fine-grained matrix, fine-grained rim, chondrule rim, and altered mesostasis of a chondrule in Asuka 12169, one of the least altered CM chondrites

Mineralogy of fine-grained matrix (FGM), fine-grained rim (FGR), chondrule rim, and altered mesostasis of a chondrule from the Asuka (A) 12169 CM3.0 chondrite was investigated by field emission scanning electron microscopy (FE-SEM), synchrotron radiation-based X-ray nano-tomography (SR-XCT), and transmission electron microscopy (TEM). SR-XCT and TEM observations revealed that both FGM and FGR contain abundant amorphous silicate embedding nano-inclusions (most are Fe–Ni sulfide). Although the amorphous silicate is more or less hydrated based on the analysis of the X-ray linear attenuation coefficients in SR-XCT, there are no areas filled by abundant phyllosilicate even in three dimensions. However, FGM and FGR contain ~2-10 μm-sized aggregates composed of tochilinite, nano-inclusions of possible magnetite, and poorly crystalline serpentine without sharp boundaries with the surroundings. It is unlikely that the heterogeneity resulted from brecciation and mixing of materials that experienced different degrees of aqueous alteration, but more likely from a very early stage of aqueous alteration that proceeded heterogeneously depending on locally different chemistry. Chondrule mesostasis near the surface of a chondrule was altered to saponite with tochilinite-rich aggregates. These observations indicate that the degree aqueous alteration of A 12169 is very low and that it is comparable with that of Acfer 094, ALH 77307, and the least altered areas of Paris.

Characterization of 3-Dimensional Printing and Casting Materials for use in Computed Tomography and X-ray Imaging Phantoms

Imaging phantoms are used to calibrate and validate the performance of medical computed tomography (CT) systems. Many new materials developed for three-dimensional (3D) printing processes may be useful in the direct printing or casting of biomimetic and geometrically accurate CT and X-ray phantoms. The X-ray linear attenuation coefficients of polymer samples were measured to discover materials for use as tissue mimics in phantoms. This study included a cohort of polymer compounds that were tested in cured form. The cohort consisted of 101 standardized polymer samples fabricated from: two-part silicones and polyurethanes used in commercial casting processes; one-part optically cured polyurethanes used in 3D printing; and fused deposition thermoplastics used in 3D printing. The testing was performed with a commercial micro-CT imaging system from 40 kVp to 140 kVp. The X-ray linear coefficients of the samples and human tissues were plotted with error bars to allow the reader to identify suitable mimics. The X-ray linear attenuation coefficients of the tested material samples spanned a wide range of values, with a small number of them overlapping established human tissue mimic values. Twenty 3D printer materials and one castable polyurethane tracked nylon and polymethyl methacrylate (PMMA) as established X-ray mimics for fat. Five 3D printer materials tracked water as an established X-ray mimic for muscle.

A Mineral X-ray Linear Attenuation Coefficient Tool (MXLAC) to Assess Mineralogical Differentiation for X-ray Computed Tomography Scanning

X-ray computed tomography (XCT) is becoming one of the most important techniques in the geosciences. The technique relies on linear attenuation coefficient differences in order to reveal the internal structure of the rocks. In this work, we present a new excel macro tool, called MXLAC, which is a data bank with an excel interface that uses density, X-ray energy and the mineral chemical formula to allow users to calculate mineral linear attenuation coefficients that can then be used to determine discrimination between mineral pairs. Elements within a mineral and specified by the chemical formula, determine how the X-ray beam is attenuated. Analysis of a variety of scanned mineral pairs with similar densities and attenuation coefficients indicates that an attenuation coefficient difference of greater than or equal to 6% at 45.5 keV effective X-ray energy is required for effective discrimination between two minerals using XCT with single energy scanning. This means that mineral pairs, such as quartz and pyrophyllite cannot be discriminated using the current XCT instruments due to the fact that the attenuation coefficient difference is less than 1.9% at 45.5 keV effective X-ray energy. Garnets and a variety of other minerals were used as examples to illustrate the importance of knowing the actual chemical formula of the mineral to demonstrate whether they can be partially or fully discriminated from each other.

Analysis of Impregnation Mechanism of Weft-Knitted Commingled Yarn Composites by Staged Consolidation and Laboratory X-Ray Computed Tomography

Absorption-based microcomputed tomography (µCT) scans using polychromatic X-ray sources are frequently used to analyse the microstructure of polymer-matrix composites. Assuming the proportionality between linear X-ray attenuation coefficients and grey levels in the reconstructed µCT images, segmentation techniques can be used to conduct qualitative and quantitative analyses. Nevertheless, the reliability of such analyses is limited in partially consolidated composites formed of commingled yarns due to low contrast induced by beam hardening and partial volume effect. This paper aims at investigating the possibility of using low-contrast µCT images to analyse fibre bed deformation and impregnation mechanism by staged consolidation of a weft-knitted fabric of commingled thermoplastic/glass yarns. The experimental work is focused on the effect of the compaction ratio of the consolidation cycle. Absorption-based µCT analyses are conducted for representative samples using a voxel size of 10 µm and a constant energy-level of the X-rays source. Preliminary qualitative analyses of the raw reconstructed images indicate that beam hardening is the most significant in the case of the non-consolidated sample and that partial volume effect makes it difficult to visually distinguish between dry and impregnated zones inside the yarns at a compaction ratio of 63%. Thus, two image-quality descriptors, viz. contrast and signal-to-noise ratio are evaluated based on the K-means clustering method to follow their variation for four consolidation levels. The corresponding volume fractions of glass fibres, thermoplastic matrix and voids are compared with the results of a second weight-controlled thresholding method. Considering that the weight-controlled thresholding method is less sensitive to beam hardening, it is confirmed that obtaining reliable segmentation results based on the K-means method requires a contrast around 0.5 and signal-to-noise ratio lower than 3. The results from the comparison with the classical consolidation scenario of commingled yarns confirm the potential of using µCT images of different qualities to characterize partially consolidated weft-knitted fabrics.

Contrast-enhanced repacked soil cores as a proxy for soil organic matter spatial arrangement

Soil organic matter (SOM) plays a key role in soil structure formation, although the bidirectional relationship between SOM and the soil pore network is complex and needs further investigation. Despite great advances provided by X-ray computed microtomography (µCT), it has only been used in a few studies to investigate the organic matter 3D-arrangement within the soil matrix. Results are based on the X-ray linear attenuation coefficient (α), and mixtures of organic and mineral soil fractions could imply overlapping of information that makes any segmentation procedure difficult. The aim of this study was to visualise, segment, and quantify the particulate organic matter fraction (POM) within the soil matrix through X-ray µCT in combination with contrast agents (phosphomolybdic acid and silver nitrate). Two series of repacked soil cores, ‘dry’ and ‘wet’, were scanned through X-ray µCT at a 7-µm resolution. Different segmentation approaches were tested to separate POM from other soil phases: manual, global, and local thresholding methods. Reported algorithms were also compared with a supervised grey value-based (GV) approach followed by morphological operations. Results showed contrast agents increased α of POM, simplifying its identification and the following segmentation on dry cores. The POM was discriminated from the mineral fraction and its content correctly estimated. This was particularly accurate when applying manual thresholding or GV approach with respect to indicator kriging, suggesting that operator-based ability to set threshold level is still the best solution for accurate POM segmentation. Beyond single-phase accounting, different thresholding algorithms and morphological operations also affected POM morphological characteristics. In particular, the simpler was an object shape, the easier was its segmentation. Improvements are thus required to increase the efficiency of automated thresholding algorithms. Moreover, wet cores were exposed to washing-out phenomena that compromised any digital image processing and further POM quantification, implying that more effort should be made to find other suitable staining agents.

Clinical Use of Opportunistic Computed Tomography Screening for Osteoporosis.

* Opportunistic use of computed tomography (CT) allows assessment of bone status from studies obtained for other purposes.* The linear x-ray attenuation coefficient is known as the Hounsfield unit (HU).* HU values can be determined for any region of interest using standard imaging software.* HU values strongly correlate with bone mineral density.* A threshold of <135 HU for the L1 vertebral body indicates a risk for osteoporosis.* HU values have been used to assess other bone regions, including the wrist, proximal and distal end of the femur, and sacrum, to predict future fracture and the presence of osteoporosis.* Opportunistic use of CT aids in the identification of patients who are not otherwise suspected to be at risk for osteoporosis.

An iterative method to estimate x-ray attenuation coefficients in computed tomography

Introduction: The basis of image formation in Computed Tomography (CT) lies in the x-ray linear attenuation coefficient of the scanned material. Compton scattering and photoelectric effect are the dominant interactions of the x-ray photons with the subject, in the range of diagnostic radiology. These two coefficients are important in tissue characterization by Dual-Energy CT (DECT), determination of electron density and dose calculation in treatment planning system. The aim of this paper is to calibrate the CT system, to calculate Compton scattering and photoelectric effect by an iterative method. Materials and Methods: Chemical compounds with known effective atomic number and electron density were scanned at 80, 110, and 130kVp. HU values of these compounds were used to calculate Compton scattering and photoelectric effect by an iterative method. The calculated coefficients were used to estimate the HU values of liquid samples and solid rods made of polymers, to evaluate our findings Results: The coefficients were found up to the fifth order of iteration and the coefficients were found to match the data with 95% confidence at 80, 110, and 130 kVp. The maximum deviation between the calculated and actual HU values were less than 3% for liquid and solid samples at these kVp values. Conclusion: Calibration of CT system by known chemical samples, by using iterative method of data analysis may give very accurate idea about the x-ray attenuation coefficients of samples. Results of this study may be used in tissue characterization by DECT inversion, and to estimate electron density and dose distribution in treatment planning systems

Observation of glassy state relaxation during annealing of frozen sugar solutions by X-ray computed tomography

Glassy phase formation in a frozen product determines various properties of the freeze-dried products. When an aqueous solution is subjected to freezing, a glassy phase forms as a consequence of freeze-concentration. During post-freezing annealing, the relaxation of the glassy phase and the ripening of ice crystals (i.e. Ostwald ripening) spontaneously occur, where the kinetics are controlled by the annealing and glass transition temperatures. This study was motivated to observe the progress of glassy state relaxation separate from ice coarsening during annealing. X-ray computed tomography (CT) was used to observe a frozen and post-freezing annealed solutions by using monochromatized X-ray from the synchrotron radiation. CT images were successfully obtained, and the frozen matrix were analyzed based on the gray level values that were equivalent to the linear X-ray attenuation coefficients of the observed matters. The CT images obtained from rapidly frozen sucrose and dextrin solutions with different concentrations gave clear linear relationships between the linear X-ray attenuation coefficients values and the solute concentrations. It was confirmed that the glassy state relaxation progressed as increasing annealing time, and this trend was larger in the order of the glass transition temperature of the maximally freeze-concentrated phase. The sucrose-water system required nearly 20 h of annealing time at −5 °C for the completion of the glassy phase relaxation, whereas dextrin-water systems required much longer periods because of their higher glass transition temperatures. The trends of ice coarsening, however, did not perfectly correspond to the trends of the relaxation, suggesting that the glassy phase relaxation and Ostwald ripening would jointly control the ice crystal growth/ripening kinetics, and the dominant mechanism differed by the annealing stage.

Three-dimensional study by synchrotron radiation computed tomography of melt distribution in samples doped to enhance contrast

AbstractThe three-dimensional distribution of melt in partially molten synthetic samples compositionally corresponding to diopside (90 wt.%)–anorthite (10 wt.%) and doped with PbO, WO3, MoO3, or Cs2O to enhance contrast was studied by X-ray computed tomography (CT) with synchrotron radiation. The heavy elements were strongly concentrated in the melt and contributed to an increase of the X-ray linear attenuation coefficient (LAC) of it. PbO was found to be compatible with silicate melt (>20 wt.% in solution) and incompatible with diopside crystals. Other oxides WO3 (∼10 wt.%), MoO3 (∼5 wt.%) and Cs2O (< 5 wt.%) are also soluble only in the melt. Such doping is useful not only for LAC control in X-ray CT measurements, but also for systematic control of the structure (wetting properties, distribution and connectivity) of partial melt. This technique gives basic information for discussion of the 3D distribution of partial melt having different wetting properties. As PbO was most effective in visualization of the diopside–anorthite partially molten system, CT images of the PbO-bearing sample were used for further 3D investigation of distribution. A distribution of dihedral angles at solid-melt-solid triple junctions ranging from 22 to 55° was observed with the 3D data. This range in angle distribution was probably caused by anisotropy of crystals and the result supports the argument that there is some limitation in a theoretical framework of stereology which estimates the 3D structure based on 2D observations. Investigators have begun to apply X-ray CT to the study of the 3D distribution of partial melts in rocks using synchrotron radiation. Our study on the effect of doping is one approach for developing a technique to investigate 3D melt distribution.

Evaluating Clinical Stopping Power Estimation from a Radiotherapy Dual Energy CT Scanner

The use of dual energy computed tomography (DECT) is increasingly considered in particle therapy (PT) to reduce the range of uncertainties attributed to the conversion of X-ray linear attenuation coefficients into relative stopping power (RSP). DECT scanners equipped with clinically available image conversion software can now be found in PT centers. In this work, RSP calculated on the basis of clinical DECT scanner software (syngo. via) was compared to a validated published procedure (Hudobivnik) for calibration and pediatric head phantoms. Based on material inserts, the average difference between RSP values calculated using syngo. via (Hudobivnik) against reference values were 1.0% (0.7%). This difference excludes the lung inserts as the syngo. via method does not provide Z(eff) values for CT numbers < -500 HU. An analysis of the head phantom showed overall a good agreement with all RSP differences within 1% between the syngo. via and Hudobivnik methods. The use of clinically available syngo. via provides equivalent accuracy as a validated RSP calculation method.

Three-dimensional Observation of Nonmetallic Inclusion Clusters in Solid Metal by X-ray Micro-CT

In this study, we developed a method of observing three-dimensional (3D) inclusion clusters in metal. The theory of X-ray micro-computed tomography (CT) is generally introduced. The criteria on determining the sample size and energy of X-ray beam is set according to the characteristics of the beamline BL20XU available at Spring-8, which is the largest synchrotron radiation facility. The Al–TiB2 and Al–SiC system were measured by the X-ray micro-CT available in beamline BL20XU at Spring-8. The determination of the sample size the energy of X-ray beam are discussed on basis of the X-ray linear attenuation coefficient (LAC) and the transmission rate of Al–TiB2 and Al–SiC system. The limitation of the charge coupled device (CCD) camera, such as spatial resolution and observing field, are taken into consideration as well. Phase retrieval method is applied to reduce the noises of tomographic images for Al–SiC system due to its poor contrast. The 3D particle clusters of TiB2 and SiC are reconstructed by self-developed program. The fractal dimension of TiB2 and SiC clusters are calculated around 2.7. The feasibility of observing alumina cluster in steel is discussed on basis of the latest capability of beamline BL20XU at Spring-8.

Dual-energy X-ray analysis using synchrotron computed tomography at 35 and 60 keV for the estimation of photon interaction coefficients describing attenuation and energy absorption.

A novel method for dual-energy X-ray analysis (DEXA) is tested using measurements of the X-ray linear attenuation coefficient μ. The key is a mathematical model that describes elemental cross sections using a polynomial in atomic number. The model is combined with the mixture rule to describe μ for materials, using the same polynomial coefficients. Materials are characterized by their electron density Ne and statistical moments Rk describing their distribution of elements, analogous to the concept of effective atomic number. In an experiment with materials of known density and composition, measurements of μ are written as a system of linear simultaneous equations, which is solved for the polynomial coefficients. DEXA itself involves computed tomography (CT) scans at two energies to provide a system of non-linear simultaneous equations that are solved for Ne and the fourth statistical moment R4. Results are presented for phantoms containing dilute salt solutions and for a biological specimen. The experiment identifies 1% systematic errors in the CT measurements, arising from third-harmonic radiation, and 20-30% noise, which is reduced to 3-5% by pre-processing with the median filter and careful choice of reconstruction parameters. DEXA accuracy is quantified for the phantom as the mean absolute differences for Ne and R4: 0.8% and 1.0% for soft tissue and 1.2% and 0.8% for bone-like samples, respectively. The DEXA results for the biological specimen are combined with model coefficients obtained from the tabulations to predict μ and the mass energy absorption coefficient at energies of 10 keV to 20 MeV.

Description and characterization of a novel method for partial volume simulation in software breast phantoms.

A modification to our previous simulation of breast anatomy is proposed to improve the quality of simulated x-ray projections images. The image quality is affected by the voxel size of the simulation. Large voxels can cause notable spatial quantization artifacts; small voxels extend the generation time and increase the memory requirements. An improvement in image quality is achievable without reducing voxel size by the simulation of partial volume averaging in which voxels containing more than one simulated tissue type are allowed. The linear x-ray attenuation coefficient of voxels is, thus, the sum of the linear attenuation coefficients weighted by the voxel subvolume occupied by each tissue type. A local planar approximation of the boundary surface is employed. In the two-material case, the partial volume in each voxel is computed by decomposition into up to four simple geometric shapes. In the three-material case, by application of the Gauss-Ostrogradsky theorem, the 3D partial volume problem is converted into one of a few simpler 2D surface area problems. We illustrate the benefits of the proposed methodology on simulated x-ray projections. An efficient encoding scheme is proposed for the type and proportion of simulated tissues in each voxel. Monte Carlo simulation was used to evaluate the quantitative error of our approximation algorithms.

A method to determine the density of foods using X-ray imaging

Density of foods is an important physical property, which depends on structural properties of food. For porous foods such as baked foods, accurate measurement of density is challenging since traditional density measurement techniques are tedious, operator-dependent and incapable of precise volume measurement of foods. To overcome such limitations, a methodology was developed using both digital radiography (DR) and computed tomography (CT) X-ray imaging to directly determine density of foods. Apparent density was determined directly from X-ray linear attenuation coefficients by scanning at 40, 60, 80kVp on DR and 45, 55, 70kVp on CT. The apparent density can be directly determined using CT however sample thickness is needed to determine density using DR. No significant difference (p<0.05) was observed between density obtained from traditional methods, with density determined from X-ray linear attenuation coefficients. Density determined on CT for all foods with mean 0.579g/cm3 had a standard deviation, SD=0.0367g/cm3. Density determination using X-ray linear attenuation was found to be a more efficient technique giving results comparable with conventional techniques.

Calculating the quantitative characteristics of x-ray and gamma-ray attenuation by optical glasses

Based on data concerning the density of glasses, the mass fractions of the chemical elements that enter into the composition of the glasses, and their mass attenuation coefficients of photonic radiation with a quantum energy from 20 keV to 3 MeV, the linear x-ray and gamma-ray attenuation coefficients of typical optical and radiation-resistant glasses are calculated. The chemical elements in the composition of the glasses are indicated that have the maximum effect on the linear attenuation coefficient of photonic radiation by glasses of the crown and flint groups. The thicknesses of the layers of these glasses are determined that attenuate the γ radiation of the radionuclides Co60 (1.25 MeV) and Cs137 (0.661 MeV) to one-half and one-tenth.

A method for estimating radiation interaction coefficients for tissues from single energy CT

A parametric model for the x-ray linear attenuation coefficient is used to describe the compositional dependence of Hounsfield numbers measured by medical CT scanners. Measurements with materials of known density and composition, that span and evenly sample the compositional range of tissues, are written as linear simultaneous equations and solved for model coefficients. An algorithm is identified for this purpose. Results are expressed as atomic cross-sections in units of barn per electron divided by the attenuation coefficient for water. With the CT scanner characterised, a virtual CT scan can be simulated to predict HN for tissues based upon their known density and composition. Similar calculations using the tabulations and mixture rule deliver attenuation coefficients and mass energy absorption coefficients for mono-energetic radiation 10 keV to 20 MeV. Results are presented for measurements with a radiotherapy CT simulator, the RMI-467 phantom with tissue substitute materials, plus common polymer materials and silicon. Published measurements with earlier generations of the phantom and tissue substitutes using different CT scanners are also considered. Measured atomic cross-sections differ from expectations for mono-energetic radiation due to the use of a filtered spectrum and energy integrating detection system. The cross-sections for different CT scanners are similar, without large variations with kVp. Results are presented showing the relationship between predicted HN for tissues, electron density and photon interaction coefficients for healthy tissues and mono-energetic radiation. A strategy is suggested for accommodating strongly attenuating materials such as calculi and metallic implants.