Solid state x-ray image intensifier array: Design, construction & evaluation
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Stroke is one of the leading causes of death and permanent disability worldwide. According to the world health organization on an average 15 million people suffer from the vascular diseases worldwide every year. The diagnosis and treatment of the vascular diseases is done under x-ray imaging using minimally invasive image guided interventional procedures. The success of these procedures requires the imaging detectors to have high resolution to be able to detect plaque; blood clots and various other small anatomical structures along with the small devices that are used for the treatment. Additionally these detectors should also have high sensitivity to keep the radiation exposures to the minimum level. Current x-ray imaging detectors such as the XIIs and the FPDs have inherent limitations and do not meet these demands. To meet these demands our group at Toshiba Stroke and Vascular Research center at University at Buffalo has designed and developed a new high resolution, high sensitivity, large field of view dynamic x-ray detector based on the Electron Multiplying Charge Coupled Devices (EMCCDs) called as the Solid State X-ray Image Intensifier (SSXII). This work entails the design, construction and evaluation of the SSXII. The front end of the SSXII consists of a x-ray scintillator converting x-rays into light, a fiber optic taper that is used to provide large field of view and an EMCCD with a preinstalled fiber optic plate. The backend consists of all the driving and readout electronics for EMCCD. Two versions of the SSXII were developed. The first version was a single module SSXII for high resolution region-of-interest imaging and the second version was a 2x2 array of SSXII for low resolution large field of view imaging. The complete electronics for both the detectors was designed from the discrete component level. The SSXII provides high resolution x-ray images of up to 9-10 line pairs per mm. Through the use of unique solid state image intensification by EMCCDs the detector provides large dynamic range and high sensitivity. Noise performance of the detector is also evaluated demonstrating superior performance compared to FPD. Other important properties such as detector linearity and quantum region limited operation are also demonstrated. The effect of cooling on the gain of the detector is also demonstrated. The SSXII has the capability of operating at15 frames per sec un-binned and 30 frames per sec with binning. The large and extensible field of view of the detector through the use of 2x2 array is also demonstrated. To interface more number of arrays and provide even larger field of view a custom multiple module multiplexer integrated circuit (MMMIC) was designed and manufactured. Each MMMIC can multiplex data from the three imaging modules. Multiple MMMICs can be connected in multistage cascade configuration to interface any arbitrary M x N array of imaging modules. It also supports the use of different binning modes providing an adjustable spatial resolution while maintaining a pre-determined display bandwidth. The operation of three MMMICs in a two stage configuration, multiplexing data from the 2x2 array of SSXII is demonstrated. SSXII through the use of MMMIC has a potential to replace the current state-of the art x-ray detectors by inheriting all their advantages and overcoming all their limitations providing a high resolution, high sensitivity and large field of view real-time x-ray imaging detector.