Photon attenuation in computed tomography

Abstract

The analysis and understanding of results of computed tomography (CT) require an understanding of photon attenuation in matter. The high sensitivity and resolution of these devices coupled with the use of a polychromatic photon source require a level and breadth of understanding about photon attenuation not usually required in any particular subspecialty of radiological physics. With this goal in mind, a discussion of narrow-beam photon attenuation in matter is given and related to those problems currently underway in the field of computed tomography. Measurements and calculations of tissue properties are presented. Calculations of descriptive quantities relevant to polychromatic source attenuation and CT scanning are described and presented.

Computed tomography scan analysis of Site 941 cores, western mass-transport deposit, Amazon Fan

“…The response of CT scanners to biological materials with X-ray attenuation near that of water is fairly well known (McCullough, 1975) and shows that a density increase of 0.01 g/cm 3 corresponds to an increase of 10 units in the CT value. Device response to denser materials and those of different composition, such as soils and sediments, however, is less certain (e.g., Petrovic et al, 1982;Soh et al, 1993).…”

Case for an Improved Effective-Atomic Number for the Electronic Baggage Scanning Program

“…As shown in McCullough [10] an exponent of 3.8 is only representative of the Zdependence of the photoelectric absorption, and will consistently over-estimate the Z eff for other materials with high-Z constituents. Typical HME are dominated more by Compton than photoelectric absorption, and an optimal compromise would use a smaller exponent.…”

“…If higher-Z components are present in the materials, it becomes very difficult to fit Equation 2 to materials of interest. For example, McCullough [10] warns that:…”

“…Since that time, this formula has been used as a convenient "rule-of-thumb," though the exact choice of the exponent, p, has varied from observer to observer. Indeed, for best results, p should be chosen to fit the desired range of materials and spectra [8][9][10][11][12][13]. Given an optimal selection of p, this method has proven useful in the medical field for interpolating properties on specific systems and within the relatively narrow, and low-Z, range of materials of biological interest.…”

Calibrations for Analyzing Industrial Samples on Medical CT Scanners

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Computed tomography (CT) is a non-destructive technology that produces an image of an internal slice through a sample via the reconstruction of a matrix of X-ray attenuation coefficients [1,2]. An imaged slice can be divided into ann x n matrix of voxels (volume elements).

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