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.

Physical and psychophysical characterization of a novel clinical system for digital mammography

“…[2][3][4] Many approaches have been explored for reading out signals in a-Se plates. [5][6][7] Currently, to our knowledge, all the commercial FFDM systems consisting of a-Se detectors employ a readout based on an active matrix array of thin film transistors ͑TFTs͒. 8 In order to improve on the noise limits associated with the standard readout of a-Se detectors, a novel clinical FFDM system ͑named AMULET͒ has been manufactured by FUJIFILM and recently introduced in the market.…”

Development of a novel direct X-ray detector using photoinduced discharge (PID) readout for digital radiography

“…The MTF shows that the directional dependence is due to the bottom electrode line defining the resolution in the X-direction and the width of the line beam and pixelated floating metal. This result shows the possibility of hole-mode PID readout X-ray detector using the pixelated metal as the charge accumulation layer unlike the previous studies of the electron-mode using electron trap layer like As 2 Se 3 [1][2][3]. The hole-mode PID method is meaningful since hole has a higher mobility-lifetime product value in a-Se.…”

“…Recently, there have been several proposals for X-ray detectors using PID readout for low noise and high resolution because these do not use an active matrix array (AMA) [1][2][3]. These include the photoconductively activated switching (PAS) readout method and the non-pixelated dual photoconductor (NPIXDP) readout method, which have already been proposed by D.M.…”

Recent Developments of Amorphous Selenium-Based X-Ray Detectors: A Review

“…Several studies have investigated the use of the avalanche process of a-Se in medical imaging applications [47], [54], [56]- [60] as well as crystallography [55], [61]. Yet these studies did not fully extend to large area FPXI.…”