SU‐GG‐BRC‐06: An Enabling Technology for Very Low Exposure X‐Ray Imaging

Purpose: Medical procedures such as cardiac catheterization, angiography and the deployment of endovascular devices are routinely performed using x‐ray fluoroscopy, in which each image is obtained at very low x‐ray exposures. The imaging performance of current solid‐state flat panel detectors (FPD) is compromised by electronic noise at these low detector exposures (0.1–10 μR/frame). There is thus a clear need to develop an imaging detector with the quantum noise limited operation of an x‐ray image intensifier and the inherent advantages of a compact solid‐state device. Here we propose a technology that takes advantage of avalanche multiplication of charge in an amorphous selenium (a‐Se) photoconductor. Method and Materials: To determine whether this technology holds promise for next‐generation FPDs, we investigate the following: (1) device and material requirements for prevention of electrical breakdown, (2) leakage currents at high electric fields, (3) real‐time imaging capability and linearity, and (4) the compliance of an avalanche a‐Se photoconductor with low‐voltage image readout electronics. Results: Our results show that a distributed resistive layer coupled to the avalanche photoconductor enables breakdown‐free operation. We report, for the first time, avalanche gains exceeding 10⁴ in a solid‐state x‐ray detector, and leakage currents of only ∼10 pA/mm². The detector has a voltage‐programmable avalanche gain and can be operated in a linear regime at 30 frames per second over a five order of magnitude x‐ray exposure range, including the lowest clinical exposures encountered in fluoroscopy. Furthermore it is compatible with existing thin film transistor technology on which current FPDs are based. Conclusion: This detector technology should enable the development of next‐generation dose‐efficient FPDs for interventional radiology as well as advanced applications such as cone‐beam computed tomography or tomosynthesis. Combined with techniques such as region‐of‐interest fluoroscopy, our detector technology could significantly reduce radiation dose to the patient and physician.