William D. Fender

Radiographic Image Analysis Through Application Of The Radiographic Modulation Transfer Function And System Phase Response

Xeroradiographic and radiographic film image analysis through application of the radiographic modulation transfer function defined in this paper is a powerful analytical tool. This tool has been found to predict spatial and densitometric characteristics of an x-ray image for an arbitrary set of input object exposures and contrast variations with sufficient accuracy to allow meaningful comparisons of different types of radiographic imaging systems. This paper presents a simple computerized technique for the derivation of the radiographic modulation transfer function from the image of a knife edge test object. Techniques used for assessing the degree of system linearity over the output response range of interest and the role of the system phase response are also presented. Typical xeroradiographic, screened and unscreened film radiographic modulation transfer functions derived with the program are compared and discussed in the conclusion to the paper.

Quantification Of The Xeroradiographic Discharge Curve

A quantitative model has been developed to characterize the formation of an electro-static x-ray image on an amorphous selenium photoreceptor. The model is based on measurements of selenium x-ray photogeneration efficiency in the mammographic and radiographic energy ranges for internal fields E ranging from 1 to 12 volts per micron. The x-ray energy absorbed by the selenium for each neutralized surface charge is found to be 510 eV divided by E in volts per micron. X-ray source spectral distribution, kVp and mAs as well as photoreceptor thickness and initial surface potential are included in the comput-erized model. The effects of Compton back scatter and foreward scatter are included through judicious use of object absorption and attenuation coefficients. Discharge curves calculated from the model illustrating two extremes of object scattering are shown to be in close agreement with experimentally measured discharge curves.

Enhanced imaging process for xeroradiography

An enhanced mammographic imaging process has been developed which is based on the conventional powder-toner selenium technology used in the Xerox 125/126 x-ray imaging system. The process is derived from improvements in the amorphous selenium x-ray photoconductor, the blue powder toner and the aerosol powder dispersion process. Comparisons of image quality and x-ray dose using the Xerox aluminum-wedge breast phantom and the Radiation Measurements Model 152D breast phantom have been made between the new Enhanced Process, the standard Xerox 125/126 System and screen-film at mammographic x-ray exposure parameters typical for each modality. When comparing the Enhanced Xeromammographic Process with the standard 125/126 System, a distinct advantage is seen for the Enhanced equivalent mass detection and superior fiber and speck detection. The broader imaging latitude of enhanced and standard Xeroradiography, in comparison to film, is illustrated in images made using the aluminum-wedge breast phantom.