In x-ray imaging, the focal spot power density constrains further improvement of image resolution and imaging speed. The thermal conductivity of tungsten (W) limits the maximum power and minimum dimension of the focal spot allowed in x-ray sources. Annealed Pyrolytic Graphite (PG) has a thermal conductivity about 10 times higher than W in its a-b crystalline plane, but unsuitable to be used as x-ray source target alone due to its low atomic number. We will design and develop a novel W-PG laminate target that takes advantages of both materials and significantly improve x-ray source focal spot power density. Hereby, we propose two specific aims in this study: 1) Development of W-PG laminate target using chemical vapor deposition (CVD); 2) Evaluation and optimization of W-PG laminate target. Through the two-year study, a new anode fabrication process will be developed, which can be used to produce high performance x-ray sources.
The image resolution of x-ray systems is limited by the focal spot size of x-ray sources. Higher x-ray output is also desired especially in CT systems in order to accelerate imaging speed and reduce motion artifacts. Further improvements of focal spot size and tube output however are limited by the focal spot power density. The relatively low thermal conductivity of tungsten target constrains the maximum power that can be deposited on the focal spot. Improvement of focal spot power density is critically important to further improve the performance of x-ray systems. Annealed pyrolytic graphite (APG) has a thermal conductivity almost 10 times higher than that of tungsten. In this project, we will synthesize a novel W-PG laminate x-ray source target using chemical vapor deposition (CVD) method. The new target will allow a significant increase of focal spot power density thanks to the exceptional cooling performance of APG. We will evaluate the performance of the new anode using our multi-pixel thermionic emission x-ray (MPTEX) source. This technique is applicable to any other fixed or rotatory anode x-ray sources with tungsten targets.
