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6 May 2004 Indirect flat-panel detector with avalanche gain
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A new concept - an indirect flat-panel detector with avalanche gain - for low dose x-ray imaging has been proposed. The detector consists of an amorphous selenium (a-Se) photoconductor optically coupled to a structured cesium iodide (CsI) scintillator. Under an electric field ESe, the a-Se is sensitive to light and converts the optical photons emitted from CsI into electronic signal. These signals can be stored and read out in the same fashion as in existing flat-panel detectors. When ESe is increased to > 90 V/μm, avalanche multiplication occurs. The avalanche gain ranges between 1-800 depending on ESe and the thickness of the a-Se layer dSe. The avalanche a-Se photoconductor is referred to as HARP (High-gain Avalanche Rushing amorphous Photoconductor). A cascaded linear system model for the proposed detector was developed in order to determine the optimal CsI properties and avalanche gain for different x-ray imaging applications. Our results showed that x-ray quantum noise limited performance can be achieved at the lowest exposure level necessary for fluoroscopy (0.1 μR) and mammography (0.1 mR) with a moderate avalanche gain of 20 (d = 1-2 μm). A laboratory test system using an existing HARP tube optically coupled (through a lens) to a CsI layer was built and the advantage of avalanche gain in overcoming electronic noise was demonstrated experimentally. One of the advantages of the avalanche gain is that it will permit the use of high resolution (HR) CsI (which due to its low light output has not previously been used in flat-panel detectors) to improve DQE at high spatial frequencies.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Wei Zhao, Dylan C. Hunt, Kenkichi Tanioka, and John A. Rowlands "Indirect flat-panel detector with avalanche gain", Proc. SPIE 5368, Medical Imaging 2004: Physics of Medical Imaging, (6 May 2004);

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