Breast cancer has been recognized as a major threat to women's health and longevity particularly in North America. one of 9 women in the United States may be diagnosed to have breast cancer in her lifetime. Despite advances of ultrasound, magnetic resonance and optical imaging techniques, x-ray mammography remains the main tool for early detection of breast cancer and subsequent diagnostic workup. It is therefore of great importance to improve the x-ray mammography techniques to optimize the detection and diagnosis of breast cancer. With a desire to improve image quality and image management, there has been a strong motivation to shift from the conventional screen/film techniques to digital image acquisition techniques. Several digital mamrnography techniques have been developed and commercialized. Each of these techniques may have advantages in some aspects and drawbacks in others. The goals of this research are to optimize and investigate a digital mammography technique to improve the quality and utilization of the resulting digital mammograms. To achieve these goals, we will design, construct and investigate a Scanning Equalization Digital Mammography (SEDM) system using an amorphous selenium and amorphous silicon thin film transistor (aSe/aSi TFT) array based flat-panel imager as the x-ray detector. Slot scanning with regionally modulated beam width will be used to achieve both scatter rejection and exposure equalization. A novel image readout technique will be implemented and investigated to allow for electronic aft-collimation. A re-scaling technique will be implemented and tested to generate digital mammography images with appearance similar to that of a regular mammogram but with improved contrast-tonoise ratios (CNRs), equalized signal-to-noise ratios (SNRs) and enabling accurate transmission measurement. We will evaluate and investigate the proposed SEDM system with physical measurements and observers' performance studies based on phantom images designed to mimic clinical mammograms. The proposed system is expected to result in improved detection and visualization of microcalcifications and masses and better utilization of image data in both screening and diagnostic mammography. This is achieved through: (1) improved modulation transfer function (MTF) and detective quantum efficiency (DQE) with an aSe/aSi TFT based FP detector, (2) an approximately twofold increase of the detector exposure with similar or even better scatter rejection as compared to the anti-scatter grid technique, (3) a redistribution of x-ray fluence from highly transmitted areas to dense tissue regions (exposure equalization) to achieve more uniform image SNRs, and (4) provision of nearly scatterfree image data with equalized SNRs for better image processing, analysis and quantitative studies.