Amorphous selenium flat panel detectors for medical applications

Different technologies for making X-ray sensitive active matrix flat-panel imagers (AMFPI) are reviewed for applications in digital radiography and fluoroscopy. Aspects of imaging performance requiring improvement are identified and potential new detector concepts addressing these issues are briefly described. The rationale is given for the investigation of a new detector concept—an indirect conversion FPI with avalanche gain—for low-dose X-ray imaging. This detector consists of an amorphous selenium (a-Se) photoconductor optically coupled to a structured cesium iodide (CsI) scintillator. Under an electric field E_Se, the a-Se is sensitive to light and converts the optical photons emitted from CsI into electronic signal that can be stored and read out in the same fashion as in existing AMFPI. When E_Se is increased to >90 V/μm, avalanche multiplication occurs. The avalanche gain ranges between 1-800 depending on E_Se and the thickness of the a-Se layer. The avalanche a-Se photoconductor is referred to as High-gain Avalanche Rushing amorphous Photoconductor. The feasibility of two detector configurations based on avalanche gain, each using a different image readout method, are under investigation. Their advantages are compared to other AMPFI technologies for digital radiography and fluoroscopy.