Effect of detector blurring on spatial resolution in magnification mammography: A Monte Carlo study

Magnification is a special technique applied to symptomatic women, usually following a screening mammogram. In this case small focal spots are necessary in order to reduce the geometrical unsharpness caused by the extended distance between the breast and the detector. Especially when combined with Gaussian x-ray intensity distributions with small standard deviation (sigma), small foci can lead to high values of spatial resolution. However, this spatial resolution is degraded from the blurring of the detector utilized. The x-ray photons exiting the irradiated phantom do not necessarily interact at the point of intersection with the detector, and furthermore the generated image formation particles may spread inside the detector and be recorded at a distance from the interaction site. This causes a blurring of the initial image that can be studied by means of the Point Spread Function (PSF) and the subsequent Full Width at Half of the Maximum (FWHM) of the detector. Several authors have studied this effect theoretically. However, no studies have been performed towards the quantification of this blurring under magnification conditions. In this study Monte Carlo simulation techniques were utilized to study the effect of the detector blurring on spatial resolution in magnification mammography, for several focal spot sizes and intensity distributions.