Source Q Gate Drain TFT X-ray Light Structured X -ray phosphor (CsI) n Charge Adjacent I line Photodiode Storage capacitor High voltage f4f Incident x -rays Stored charge Gate line Drain node Top electrode Dielectric layer Selenium photoconductor Charge collection electrode (pixel size) Thin-Film-Transistor Storage capacitor Glass substrate Performance of a prototype 32x32 pixel indirect X-ray imager based on a lateral Selenium passive pixel sensor Rasoul Keshavarzi 1 , Kai Wang 2 , Mohammad Y. Yazdandoost 3 , Kyung-Wook Shin 1 , Feng Chen 1 , Shaikh Hasibul Majid 1 , Shiva Abbaszadeh 1 , Karim S. Karim 1 1 Electrical & Computer Engineering, University of Waterloo, Waterloo, Ontario, Canada 2 Apple Inc., Cupertino, California, USA 3 Teledyne Dalsa Corp., Waterloo, Ontario, Canada ABSTRACT An interface has been developed to capture frames taken by X-ray array imagers up to 64x64 pixels. An application specific integrated circuit (ASIC) designed solely for X-ray flat panel imaging readout circuitry, manufactured by FLIR® called Indigo (also known as ISC9717), was used as part of charge-amplifier block. An Altera Cyclone II FPGA is used to serve three purposes: Create pulses required for gate-driver block, Receive fast-stream data coming from the Indigo chip, and Send data through RS-232 protocol over a serial cable to a personal computer. Initial results for a 32x32 passive pixel sensor (PPS) with lateral amorphous Selenium metal-semiconductor-metal (MSM) photodetector were presented in [1]. This work focuses more on methods used to improve the images obtained from the array. Sharper images produced in sync with the light source are presented. In addition, insight into array readout circuitry and capturing a frame from an array is discussed. Keywords: Array Readout Circuitry, Amorphous Selenium, X-ray imaging, Lateral Selenium, Passive Pixel Sensor 1. INTRODUCTION X-ray detectors transform high-energy photons in X-ray beams into an electrical signal such as voltage or current. The detection itself can be achieved by two different mechanisms as of Direct and Indirect methods. In the direct method, the photon energy in X-ray beam creates some charges that are detected by electronic components. In the indirect method, there is a medium in this process, for example the X-ray beam hits a material that creates visible light proportional to X- ray beam intensity, and then the visible light is detected by means of an electronic circuit. Indirect detection [2] Direct detection [2] Figure 1. Indirect versus direct detection In terms of pixel architectures, X-ray detectors are divided into two major groups of Passive and Active types. Passive Pixel Sensors (PPS) have traditionally been detecting X-ray signals without any amplification. Active Pixel Sensors (APS) were developed in the last decade with in-pixel amplification. Medical Imaging 2012: Physics of Medical Imaging, edited by Norbert J. Pelc, Robert M. Nishikawa, Bruce R. Whiting, Proc. of SPIE Vol. 8313, 83135O · © 2012 SPIE · CCC code: 1605-7422/12/$18 · doi: 10.1117/12.912286 Proc. of SPIE Vol. 8313 83135O-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/25/2015 Terms of Use: http://spiedl.org/terms