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Basic dosimetry and beam-quality characterization
Published in Gavin Poludniowski, Artur Omar, Pedro Andreo, Calculating X-ray Tube Spectra, 2022
Gavin Poludniowski, Artur Omar, Pedro Andreo
For a photon fluence Φ incident on a given target material of density ρ, the mean fraction of photons d interacting along a distance in the target defines the linear attenuation coefficient μ. Its unit is cm−1. The reciprocal of μ defines the mean free path or mean path length traversed by a photon between two consecutive interactions.1 As inferred from its definition, the linear attenuation coefficient depends strongly on the mass density of the material, a constraint removed by the mass attenuation coefficient, , which is defined as
X-ray Interactions in Matter
Published in Ken Holmes, Marcus Elkington, Phil Harris, Clark's Essential Physics in Imaging for Radiographers, 2021
Total mass attenuation coefficient can be defined as:The fractional reduction of X-rays per unit mass of the medium.
Photon Beams, Dose, and Kerma
Published in Eric Ford, Primer on Radiation Oncology Physics, 2020
In Chapter 5 we used a quantity called the “mass attenuation coefficient” (e.g. Figure 5.1.4). This quantity was related to the probability of interaction of the photon. Now we consider in greater detail the meaning of the mass attenuation coefficient and how it relates to the properties of a photon beam.
The interaction of gamma radiation with drugs used in cholinergic medications
Published in International Journal of Radiation Biology, 2020
Berna Oto, Gökhan Oto, Zekiye Madak, Esra Kavaz
The attenuation of electromagnetic radiation passing through a material can be determined theoretically using WinXCom code. This code is based on the mixture rule (Gerward et al. 2004), μρ)i is the mass attenuation coefficient and wi is the fractional weight of the ith constituent element. The mass attenuation coefficient (μρ) is a measure of penetration of gamma radiation for any material. The computed μρ values were then used to calculate the effective atomic numbers and electron density of the investigated drugs. Effective atomic number (Zeff) is an useful parameter in determining interaction of gamma rays with a material. Because the values of Zeff change with the gamma energy, it is not right to define this parameter with a single number. The effective atomic number (Zeff) for photon interaction is defined by (Manohara et al 2008): fi is the mole fraction, Zi is the atomic number, Aiatomic mass and (μ/ρ)i is the mass attenuation coefficient of the ith element in the material. Finally, electron density, Nel (the number of electrons per unit mass, electron/g) can be determined from (Manohara et al 2008): A〉 is the mean atomic mass of the material.
Estimation of energy absorption buildup factors of some human tissues at energies relevant to brachytherapy and external beam radiotherapy
Published in International Journal of Radiation Biology, 2019
The elemental composition of the tissues such as soft tissue, brain, breast, lung, adipose tissue and bone (cortical) was taken from ICRU report 44 (1989) (Table 1). In order to calculate buildup factors for the selected tissues, an equivalent atomic number must be assigned to each material at each energy. Since the buildup factor mainly originates from incoherent scattering, the equivalent atomic number is calculated using the ratio of incoherent scattering to total attenuation with incoherent scattering. For this purpose, the ratios of incoherent scattering coefficient to total attenuation coefficients for elements as well as tissues were obtained first using WinXCOM computer software (Gerward et al. 2001, 2004), which was early developed as the XCOM software (Berger and Hubbell 1999). Then, the below linear logarithmic formula was used to calculate equivalent atomic numbers of the tissues: R is the ratio of incoherent scattering coefficient to total mass attenuation coefficient for the tissues at each energy.
An update on nanoparticle-based contrast agents in medical imaging
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2018
Neda Naseri, Elham Ajorlou, Fatemeh Asghari, Younes Pilehvar-Soltanahmadi
CT is one of the most important diagnostic tools in medical imaging today in terms of cost, efficiency and availability and has become an important part of modern medicine. This technique can construct detailed cross-sectional images of many various tissues in human body. Since atomic number, electron density and consequently X-ray attenuation coefficient of different tissue in body is different, based on this fact, the CT is able to distinguish between different tissues to produce images for body structures and tissues. Mass attenuation coefficient determines the loss of X-ray photon intensity via interactions with matter. Generally, tissues that are denser and consist of large quantities of electron rich elements absorb higher amounts of X-rays beam, while less dense materials absorb lesser amounts [27].