title: X-ray imaging with amorphous selenium: X-ray to charge conversion gain and avalanche multiplication gain.
abstract: Fluoroscopy is a low dose imaging technique. As such, a very sensitive detector is required to create images of good quality. Present day flat panel active matrix read out systems introduce an amount of noise that inhibits present direct and indirect methods from producing optimal quality images at fluoroscopic exposure rates (0.1-10 microR per frame). The gain of the direct conversion approach using amorphous selenium (a-Se) was investigated to determine whether by increasing the applied electric field, a gain sufficient to overcome the noise limitations of the active matrix could be achieved. Conversion gain and avalanche multiplication in a-Se were investigated as a function of electric field from 10 to 100 V/microm. Our results show a factor of 4 increase in conversion gain is available by increasing electric field from the current standard of 10 V/microm to 100 V/microm. Furthermore, we show that avalanche multiplication can provide an additional gain of up to 25. This increase in signal is sufficient to overcome the noise level encountered in flat panel detectors and permit fully quantum noise limited operation across the whole fluoroscopic range of exposure.
authors.affiliation: Sunnybrook & Women's College Health Science Centre, Imaging Research, Department of Medical Biophysics, University of Toronto, Toronto, Ontario M4N3M5, Canada.
authors.forename: Dylan C
authors.initials: DC
authors.lastname: Hunt
authors.forename: Sean S
authors.initials: SS
authors.lastname: Kirby
authors.forename: J A
authors.initials: JA
authors.lastname: Rowlands
mesh_terms: D004574:Electromagnetic Fields; D004867:Equipment Design; D019544:Equipment Failure Analysis / Q000295:instrumentation / Q000379:methods; D005240:Feasibility Studies; D005471:Fluoroscopy / Q000295:instrumentation*; D008422:Materials Testing / Q000295:instrumentation / Q000379:methods; D011786:Quality Control; D011856:Radiographic Image Enhancement / Q000295:instrumentation* / Q000379:methods; D015203:Reproducibility of Results; D012643:Selenium / Q000528:radiation effects*; D012680:Sensitivity and Specificity; D014963:X-Ray Intensifying Screens; D014965:X-Rays
chemical_list: D012643:Selenium