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Digital Slot Scan Mammography Using CCDs

A desirable mammography imaging system should offer high spatial resolution, high sensitivity, a wide dynamic range and a means of limiting detected x-ray scatter. Significant scatter reduction can be obtained with a slot scan acquisition format with minimal attenuation of the primary beam. A potential receptor for digital mammography is comprised of a x-ray screen optically coupled directly to a CCD detector. The dynamic range of our current front-illuminated CCD is about 400 using factory supplied readout circuitry. The high spatial resolution of the CCD (22.4 1p/mm at Nyquist frequency) and the x-ray screen are reduced by poor optical contact at this time. X-rays which interact with the2CCD generate a moderate signal (25-30% of the optical signal) when a thin (22mg/cm2) Gd2O2S:Tb screen is used. Image segments of a Kodak breast phantom were acquired with both the screen-CCD detector and the CCD detector alone. Substantial improvements in detector performance could be achieved by utilizing a back-illuminated CCD with a slow scan, correlated double sampled readout and a structured x-ray screen. The concept of direct optical coupling with structured screens can be implemented in high energy digital scanning systems.