Detective quantum efficiency of a direct‐detection active matrix flat panel imager at megavoltage energies

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Abstract
The use of an amorphous selenium (a‐Se) based direct‐detection active matrix flat‐panel imager (AMFPI) is studied for megavoltage imaging. The detector consists of a 1.2 mm copper front plate and 200 μma‐Se layer, and has a 85 μm pixel pitch. The Modulation Transfer Function (MTF), Noise Power Spectrum (NPS), and Detective Quantum Efficiency (DQE) are measured for 6 and 15 MV photon beams. A theoretical expression for the DQE is derived using a recently developed formalism for nonelementary cascade stages. A comparison of theory with experiment is good for the 6 and 15 MV beams. The model is used to explore the DQE for more typical pixel sizes. The results indicate that with proper modifications, such as a largera‐Se thickness, a direct flat‐panel AMFPI is a very promising detector for megavoltage imaging.