AMBER: a scanning multiple-beam equalization system for chest radiography

Conventional chest radiography is limited by the small useful exposure range of radiographic film. The wide variation in absorption thickness of different parts of the chest results in areas of under- and over-exposure. An advanced multiple-beam equalization system, AMBER, controls local exposure delivered to the film. The system has a row of 20 modulators in front of the x-ray tube, each able to change the height of the local slit beam during scanning. Changes are made in response to measurements from a linear detector array in front of the film cassette. This array consists of 20 individually functioning detectors coupled through electronic feedback loops to the 20 modulators. A scan is obtained in 0.8 second with a local exposure time of approximately 50 msec. AMBER results in radiographs with significantly improved exposure of the mediastinum without overexposure of the lungs.