Detectors for Digital Mammography 2

The X-ray detector is the heart of a digital mammography system. Its improved characteristics of dynamic range and signal-to-noise ratio provide inherent advantages over screen-fi lm technology. Detector technologies used for digital mammography can be distinguished by the acquisition geometry into scanning or full-fi eld detectors, by energy conversion mechanism into phosphor-based and nonphosphor-based detectors and by how the detector signal is converted into an image value into signal-integrating and quantum-counting systems. Reading of the detector signal can be integrated into the detector assembly or the detector can be in the form of a sensitive plate in a portable cassette, which is moved to a separate device for readout. Detector performance characteristics vary among these different technological approaches. An understanding of the physics on which detector operation is based can help explain these differences. Various image processing operations can be carried out to correct for spatial nonuniformities in detector response and to improve the effective spatial resolution of the detector. In addition, use of a digital detector provides opportunities for more sophisticated automatic control of exposure factors for image acquisition.