A detector for scanned projection radiography

A solid-state electronic x-ray detector, the multilinear array (MLA), was developed for general-purpose digital overhead radiography (DOR). The image sensor of the MLA consists of an x-ray phosphor affixed to approximately 29,000 photodiodes. The image sensor is rectangular (35.2 cm X 1.05 cm) and is designed for scanned projection imaging with a 1.05-cm-thick fan beam. The MLA incorporates charge-coupled device circuitry that performs time-delay integration of the photocharge. The MLA is installed in a prototype DOR system that generates a 35.2-cm X 35.8-cm image with a 2,014 X 2,048 12-bit image matrix and 0.175-mm pixels. The scan time per image is 7 seconds, and the exposure time of any given point of a patient is 0.21 seconds. Operational principles of the MLA are described, performance measurements presented, and images acquired with the prototype DOR system shown. The MLA has an exposure latitude of 333:1 10% modulation transfer function response at 1.8 cycles per millimeter, 15% detector detective quantum efficiency (DQE) at 60 keV, and 78% scatter DQE under high-scatter imaging conditions. DOR images of a contrast-detail phantom are superior to those produced by conventional medium-speed screen-film radiography.