title: Digital radiography using amorphous selenium: photoconductively activated switch (PAS) readout system.
abstract: A new amorphous selenium (a-Se) digital radiography detector is introduced. The proposed detector generates a charge image in the a-Se layer in a conventional manner, which is stored on electrode pixels at the surface of the a-Se layer. A novel method, called photoconductively activated switch (PAS), is used to read out the latent x-ray charge image. The PAS readout method uses lateral photoconduction at the a-Se surface which is a revolutionary modification of the bulk photoinduced discharge (PID) methods. The PAS method addresses and eliminates the fundamental weaknesses of the PID methods--long readout times and high readout noise--while maintaining the structural simplicity and high resolution for which PID optical readout systems are noted. The photoconduction properties of the a-Se surface were investigated and the geometrical design for the electrode pixels for a PAS radiography system was determined. This design was implemented in a single pixel PAS evaluation system. The results show that the PAS x-ray induced output charge signal was reproducible and depended linearly on the x-ray exposure in the diagnostic exposure range. Furthermore, the readout was reasonably rapid (10 ms for pixel discharge). The proposed detector allows readout of half a pixel row at a time (odd pixels followed by even pixels), thus permitting the readout of a complete image in 30 s for a 40 cm x 40 cm detector with the potential of reducing that time by using greater readout light intensity. This demonstrates that a-Se based x-ray detectors using photoconductively activated switches could form a basis for a practical integrated digital radiography system.
authors.affiliation: Imaging Research, Sunnybrook Health Sciences Centre, Department of Medical Biophysics, University of Toronto, 2075 Bayview Avenue, Toronto, Ontario, M4N 3M5, Canada. nik@sri.utoronto.ca
authors.forename: Nikita
authors.initials: N
authors.lastname: Reznik
authors.forename: Philip T
authors.initials: PT
authors.lastname: Komljenovic
authors.forename: Stephen
authors.initials: S
authors.lastname: Germann
authors.forename: John A
authors.initials: JA
authors.lastname: Rowlands
mesh_terms: D004566:Electrodes; D011856:Radiographic Image Enhancement / Q000379:methods*; D015203:Reproducibility of Results; D012643:Selenium
chemical_list: D012643:Selenium