Adaptively variable frame-rate fluoroscopy with an ultra-fast digital x-ray tube based on carbon nanotube field electron emitters

Fluoroscopy is a radiological technique that provides real-time x-ray viewing in interventional and angiographic procedures. In fluoroscopic procedures, there are several issues have to be solved, such as a risk of radiation exposure to the patients and operators and low image qualities by motion blur. To lower the radiation dose and motion blur, most of fluoroscopic systems provide a pulse-mode operation. However, conventional systems adopt filament-based thermionic analog x-ray tubes that generate relatively longer x-ray pulses than a few milliseconds due to intrinsic difficulty in modulating electron emissions, thus still have many problems of motion blur for fast objects, unnecessary x-ray radiation, and mismatched frame rate to the moving objects. In this work, we tried to solve these problems by suggesting an adaptively variable frame-rate fluoroscopy with an ultra-fast digital x-ray tube (DXT) based on carbon nanotube (CNT) field electron emitters. We first fabricated a vacuum-sealed CNT DXT and its monoblock with a power generator for the fluoroscopic system. Ultra-short and high-frequency x-ray pulses of up to 500 ns at 1 MHz was achieved by the direct control of electron emission through an active current-control unit. X-ray pulse frames from the CNT DXT with a tube voltage of 120 kV and current of 20 mA were adaptively modulated in the range of 1-30 Hz according to the motion of objects, greatly improving temporal resolution with a reduced radiation dose. The adaptively variable frame-rate fluoroscopy could pave the way for both reducing x-ray doses and improving temporal and spatial resolution.