Tables of X-Ray Mass Attenuation Coefficients and Mass Energy–Absorption Coefficients NISTIR 5632
This page provided by the National Institute of Standards and Technology (NIST) presents tables and graphs of the photon mass attenuation coefficient and the mass energy-absorption coefficient for all of the elements Z = 1 to 92, and for 48 compounds and mixtures of radiological interest. The tables cover energies of the photon (x-ray, gamma ray, bremsstrahlung) from 1 keV to 20 MeV. The compilation is intended to be used as reference data in radiation shielding and dosimetry computations.
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- "Leaf is made of W700ICRU, with density í µí¼ of 19.3 g/cm 3 . X-ray mass attenuation coefficient í µí¼ í µí± /í µí¼ of tungsten leaf is 0.05 cm 2 /g for photon energy of 1.5 MeV. Beam angle í µí»¼ í µí°µ about collimator rotation axis is 15.8 ∘ , which is determined by field size (FS) and source to axis distance (SAD). "
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ABSTRACT: Lateral penumbra of multileaf collimator plays an important role in radiotherapy treatment planning. Growing evidence has revealed that, for a single-focused multileaf collimator, lateral penumbra width is leaf position dependent and largely attributed to the leaf end shape. In our study, an analytical method for leaf end induced lateral penumbra modelling is formulated using Tangent Secant Theory. Compared with Monte Carlo simulation and ray tracing algorithm, our model serves well the purpose of cost-efficient penumbra evaluation. Leaf ends represented in parametric forms of circular arc, elliptical arc, Bézier curve, and B-spline are implemented. With biobjective function of penumbra mean and variance introduced, genetic algorithm is carried out for approximating the Pareto frontier. Results show that for circular arc leaf end objective function is convex and convergence to optimal solution is guaranteed using gradient based iterative method. It is found that optimal leaf end in the shape of Bézier curve achieves minimal standard deviation, while using B-spline minimum of penumbra mean is obtained. For treatment modalities in clinical application, optimized leaf ends are in close agreement with actual shapes. Taken together, the method that we propose can provide insight into leaf end shape design of multileaf collimator.
Available from: ijates.org
- "The simulation parameters were chosen to imitate the settings of the real CT scans. Namely, photon beam energy is set to 57 KeV, with the corresponding value µ H2O ≈ 0.2 cm −1 (see). The output resolution is 512 × 512 pixels, pixel distance is chosen to 0.06 cm. "
Available from: Muhammad U. Ghani
- "The amount of the phase change is determined by the refractive index of the tissue which is equal to n = 1 − δ + iβ (1) where δ, the refractive index decrement, is responsible for x-ray phase shift, and β, the imaginary part of n, is responsible for the x-ray absorption. The requirement in conventional mammography that sufficient differences in β should exist between the tissues is fulfilled by operating at low tube energies and one gets a good soft tissue contrast  . The compromise is made on the dose delivered to the tissue at the expense of superior image quality for the accurate diagnosis. "
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ABSTRACT: The objective of this study was to investigate the optimization of a high energy in-line phase sensitive x-ray imaging prototype under different geometric and operating conditions for mammography application. A phase retrieval algorithm based on phase attenuation duality (PAD) was applied to the phase contrast images acquired by the prototype. Imaging performance was investigated at four magnification values of 1.67, 2, 2.5 and 3 using an acrylic edge, an American College of Radiology (ACR) mammography phantom and contrast detail (CD) phantom with tube potentials of 100, 120 and 140 kVp. The ACR and CD images were acquired at the same mean glandular dose (MGD) of 1.29 mGy with a computed radiography (CR) detector of 43.75 μm pixel pitch at a fixed source to image distance (SID) of 170 cm. The x-ray tube focal spot size was kept constant as 7 μm while a 2.5 mm thick aluminum (Al) filter was used for beam hardening. The performance of phase contrast and phase retrieved images were compared with computer simulations based on the relative phase contrast factor (RPF) at high x-ray energies. The imaging results showed that the x-ray tube operated at 100 kVp under the magnification of 2.5 exhibits superior imaging performance which is in accordance to the computer simulations. As compared to the phase contrast images, the phase retrieved images of the ACR and CD phantoms demonstrated improved imaging contrast and target discrimination. We compared the CD phantom images acquired in conventional contact mode with and without the anti-scatter grid using the same prototype at 1.295 mGy and 2.59 mGy using 40 kVp, a 25 μm rhodium (Rh) filter. At the same radiation dose, the phase sensitive images provided improved detection capabilities for both the large and small discs, while compared to the double dose image acquired in conventional mode, the observer study also indicated that the phase sensitive images provided improved detection capabilities for the large discs. This study therefore validates the potential of using high energy phase contrast x-ray imaging to improve lesion detection and reduce radiation dose for clinical applications such as mammography.
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