Direct selenium x-ray detector for fluoroscopy RF and radiography

摘要

The use of selenium alloys for direct conversion fluoroscopy flat-panel detectors has been underestimated. The purpose of this paper is to demonstrate the salient features of a selenium-based detector designed for R&F applications. The detector has an active area of 30 cm $MUL 27 cm and comprises 2048 $MUL 1792 pixels at 150 micrometer pitch. The geometric fill factor is 66%, but experimental evidence supports the fact that internal electric field bending leads to an effective fill factor approaching unity. The detector is designed to support full resolution images at 15 frames/second, and 896 $MUL 1024 resolution at 30 frames/second. The detector is coated with a simple coplanar 'p-i-n' selenium diode structure which has a dark current less than 100 pA/cm$+2$/. The thickness of this structure is 1000 micrometer to absorb 77% of a NEMA standard fluoroscopy beam. Measurements show we have obtained an x-ray sensitivity of 4400pC/mR/cm$+2$/, which translates to 1212 collected charges per absorbed x-ray. Resolution was measured to be near the theoretically predicted values, with a modulation of 63% at the Nyquist limit of 3.33 lp/mm. Phantom images were obtained at a frame rate of 15 frames per second, and negligible lag was observed in this image sequence.