Development and evaluation of a new high-sensitivity, region-of-interest, x-ray imaging system for neuro-interventional applications
Yadava, Girijesh Kumar
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Neurovascular image-guided interventional (IGI) procedures require very high resolution (3 to 10 lp/mm), large dynamic range, and real-time imaging capability for visualization and navigation of endovascular devices during the diagnosis and treatment of cerebral strokes. Current state-of-the-art x-ray detectors (flat-panel and x-ray image intensifier) are unable to satisfy such requirements. A new high-sensitivity micro-angiographic fluoroscopic (HSMAF) detector is being developed to satisfy the need of high resolution in both neurovascular angiography and fluoroscopy using one detector. The HSMAF detector consists of a 300 μm thick CsI(Tl) scintillator coupled to a variable-gain dual-stage Gen2 microchannel plate (MCP) image intensifier, followed by direct fiber-optic coupling with a CCD camera. It is a region-of-interest (ROI) detector with high-resolution, high-sensitivity, large dynamic range, low instrumentation-noise, and virtually no lag in high-frame-rate real-time acquisitions, as required in neurovascular IGI procedures. In this work, the generalized objective performance comparison of a state-of-the-art x-ray image intensifier and previously developed high-resolution micro-angiographic detector was used to study the current challenges and possible improvements in future developments. Quantum accounting diagram and linear-systems-cascade-model analysis were used for the theoretical assessment of the imaging chains of two detector designs involving mirror-lens and direct fiber-optic couplings. The experimental performance assessment of the custom-built detector was carried out in terms of phantom studies and standard objective performance measures such as MTF and DQE. Preliminary practical uses of the HSMAF in in-vivo animal-model IGI procedures were also demonstrated. The generalized total-system evaluation approach was implemented for objective assessment of the HSMAF detector in simulated neurovascular angiographic conditions. A new practical metric, called Instrumentation Noise Equivalent Exposure (INEE), was developed to gauge the range of quantum limited performance of x-ray imagers in low dose fluoroscopic applications. Results of simulation and experimental measurements were used to validate the practicality of this metric. Preliminary applications and results of the current work suggest that there may be unique advantages for the clinical implementation of the new HSMAF detector, and it has the potential to greatly advance the accuracy and effectiveness of minimally invasive catheter-based IGI procedures.