Professional paper

https://doi.org/10.46419/vs.54.4.10

Which tissue properties are visible in X-ray images?

Selim Pašić ; Faculty of Veterinary Medicine University of Zagreb, Croatia
Antea Klobučar ; Ministry of Defence, Armed Forces of the Republic of Croatia, Croatian Navy, Croatia

Abstract

This paper aims to connect the fundamental properties of tissues with the results obtained in the image, by analysing the physical principles of interaction that lead to the absorption of X-ray photons in tissue. Using an example, we illustrate that it is possible to have a super diagnostic device that could replace modern and future diagnostic devices. Each tissue imaging technique is based on unique physical principles, and therefore sees specific tissue properties that other diagnostic devices (techniques) cannot see. X-ray imaging is based on the attenuation (weakening) of the X-ray beam after it passes through the tissue. The main mechanisms of X-ray photon-tissue interaction are the photoelectric effect (total absorption of photon energy) and Compton scattering (partial absorption of photon energy). The photoelectric effect dominates at low and partially medium energies and becomes very weak with increasing energy, while Compton scattering dominates at medium and higher energies. By analysing both absorption processes, after reducing the linear attenuation coefficient to common physical quantities, we find that that in the Compton scattering regime, the contrast in the image is determined by differences in tissue density, while in the photoelectric effect regime, contrast depends on tissue density and strongly on the ordinal number of elements making up the tissue. We provide approximate contrast values for basic formations and tissues, as well as descriptions of their properties, density and ordinal number of the elements of which they are composed. Computed tomography (CT) sees exactly the same tissue properties as the classical X-ray technique. In this paper, the principle of computed tomography is explained using an explicit two-dimensional example. It is based on the imagined division of the tissue into small volumes (voxels), and imaging the tissue from multiple positions, where equations for radiation absorption are set for each position. In the resulting system of equations, the linear attenuation coefficients for each voxel are unknown quantities, whose values are determined by numerically solving the system of equations, and are displayed on a suitable colour scale in a three-dimensional image.

Keywords

X-ray imaging; computed tomography; attenuation; X-ray radiation

Hrčak ID:

286877

URI

https://hrcak.srce.hr/286877

Publication date:

15.12.2022.

Article data in other languages: croatian

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