The contrast-detail behaviour of a photostimulable phosphor based computed radiography system

Abstract

Contrast-detail measurements were performed on a computed radiography imaging system as a function of detector entrance air kerma over the dose range from 0.743 microGy (0.085 mR) to 277 microGy (31.8 mR). A theoretical model of contrast-detail behaviour for a photostimulable phosphor computed radiography system has been derived, which is based on a modified version of the Rose theory of threshold detection. Included in the model are both system and x-ray quantum noise terms, as well as the response of the eye. The zero-frequency noise power of the computed film images was measured with a double-beam scanning microdensitometer. For a given detector dose, good agreement was found between the predicted and measured data when this measurement of system noise was included in the model. The contrast-detail results obtained for the computed radiography system were also compared with contrast-detail results for an image intensifier-TV based digital imaging system and a conventional film-screen system.

Dual-Energy Digital Mammography with a Full-Field aSi/CsI Flat-Panel Imager

“…The density of glandular tissue (1.04 g/cm 3 ) is greater than the density for adipose tissue (0.93 g/cm 3 ). Hence, for a fixed breast thickness, as the glandular tissue content of the breast increases, the breast density increases and additional low-energy x-ray photons are attenuated.…”

“…Defining a transformation of a pixel in the count domain y,-, such that y, = -log(C,.) Equation (4) If we assume a 2-tissue model of the breast (as in [3]), where the two tissues are fat and glandular, we have the following model for the noise-free log-count domain data:…”

“…<S>(keV) = a 0 + a x kVp + a 2 kVp 2 + a 3 kVp 3 where as =0 when kVp >=26 keV, <22=0 when kVp>=36 keV. For x-ray energy above 36 kVp, linear fits were used for all a, coefficients in the energy bins in Boone's model.…”

“…The CDRAD phantom is specially designed for evaluating the low-contrast performance of radiography systems. It consists of a 26.5 X26.5XI cm 3 Plexiglas plate containing a 15X15 array of 1.5X1.5 cm 2 regions, in which circular recesses of various depths and diameters were milled to create objects of various contrast levels and sizes. These depths and diameters range between 0.3-8.0 mm with 15 steps increasing logarithmically.…”

“…Ideally, it would be best to use images acquired at three separate energies to estimate the thickness of the three attenuating materials. 3 However, compared to the dual-energy subtraction imaging, three-energy subtraction imaging leads to excessive reduction of image SNR which would potentially require higher patient exposure, increased time to complete the exam (which could lead to motion artifacts), and more complicated subtraction image processing. Mammography differs from other radiographic procedures in that the breast is compressed to a largely uniform thickness (that can be easily measured) beyond which it tapers smoothly towards the edge.…”