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Empirical investigation of the signal performance of a high‐resolution, indirect detection, active matrix flat‐panel imager (AMFPI) for fluoroscopic and radiographic operation
Author(s) -
Antonuk L. E.,
ElMohri Y.,
Siewerdsen J. H.,
Yorkston J.,
Huang W.,
Scarpine V. E.,
Street R. A.
Publication year - 1997
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.597918
Subject(s) - photodiode , pixel , dot pitch , optics , active matrix , x ray detector , image sensor , physics , image resolution , signal (programming language) , digital radiography , flat panel detector , optical transfer function , detector , optoelectronics , materials science , radiography , computer science , thin film transistor , electrode , nuclear physics , programming language , quantum mechanics
Signal properties of the first large‐area, high resolution, active matrix, flat‐panel imager are reported. The imager is based on an array of 1536×1920 pixels with a pixel‐to‐pixel pitch of 127 μm. Each pixel consists of a discrete amorphous silicon n‐i‐p photodiode coupled to an amorphous silicon thin‐film transistor. The imager detects incident x rays indirectly by means of an intensifying screen placed over the array. External acquisition electronics send control signals to the array and process analog imaging signals from the pixels. Considerations for operation of the imager in both fluoroscopic and radiographic modes are detailed and empirical signal performance data are presented with an emphasis on exploring similarities and differences between the two modes. Measurements which characterize the performance of the imager were performed as a function of operational parameters in the absence or presence of illumination from a light‐emitting diode or x rays. These measurements include characterization of the drift and magnitude of the pixel dark signal, the size of the pixel switching transient, the temporal behavior of pixel sampling and the implied maximum frame rate, the dependence of relative pixel efficiency and pixel response on photodiode reverse bias voltage and operational mode, the degree of linearity of pixel response, and the trapping and release of charge from metastable states in the photodiodes. In addition, x‐ray sensitivity as a function of energy for a variety of phosphor screens for both fluoroscopic and radiographic operation is reported. Example images of a line‐pair pattern and an anthropomorphic phantom in each mode are presented along with a radiographic image of a human hand. General and specific improvements in imager design are described and anticipated developments are discussed. This represents the first systematic investigation of the operation and properties in both radiographic and fluoroscopic modes of an imager incorporating such an array.