Large area CCD based imaging system for mammography

The authors have recently developed a digital X-ray imaging system based on a high resolution scintillator screen optically coupled to a specially designed large area CCD for use in mammographic procedures. The CCD consists of a 7 K×4 K array of 12 μm pixels, measuring 88.2 mm×51 mm and operated at room temperature, cooled only by ambient air circulation. With 12 μm pixels, the resulting limiting Nyquist frequency is 41.6 lp/mm. The readout electronics and software are designed to capture images with the full CCD resolution as well as with binning. Depending on the requirements of the application, the CCD may be binned in the 2×2 or the 4×4 configuration. Since the time required to read 28 million pixels is large, binning provides an option for rapid image acquisition at a reduced resolution. A fiberoptic faceplate is optically bonded to the CCD to simplify coupling of scintillator screens to the sensor. One important feature of the system is the lack of a fiberoptic taper, making the system smaller and easier to handle or move. Structured CsI(Tl) scintillator screens developed at RMD Inc., were used for the system evaluation. This paper discusses the system design, the characterization of the CCD sensor as well as the imaging performance of the system using mammography phantoms