Enabling High-Dose X-Ray Imaging Modalities via Nanophotonic Thermal Management in X-Ray Tubes

X-ray imaging is one of the most important clinical tools for detection and diagnosis of disease. In the United States, over 80 million CT scans are performed each year, but they consume vast amounts of energy: for a single-source CT scanner, approximately 25,000 kWh per year with an additional 40% for cooling (in total, the equivalent of three U.S. homes). Furthermore, imaging modalities such as phase-contrast imaging can reveal detailed information about objects, but precisely due to insufficient cooling, many commercially available X-ray tubes are not bright enough to translate them to the clinic. Thus, the inability to meet demanding brightness and power requirements, primarily driven by cooling limitations, hinders the deployment of these transformative technologies. However, improved thermal management can address these challenges. In X-ray tubes, there is a thermal bottleneck that prevents high-power (i.e., high-brightness) operation, originating from radiative heat transfer between the anode, made of tungsten, and the evacuated housing. In systems that exchange heat via radiation, thermal management has been revolutionized by photonic crystals designed to achieve a desired emissivity [1]. For example, it has been theoretically and experimentally demonstrated that tungsten photonic crystals can be used as spectrally selective emitters for thermophotovoltaics [2]. We propose that using nanophotonics to tailor emissivity in X-ray tubes, where radiation is the dominant mode of heat transfer, could lead to improvements in thermal management, alleviating both the demanding power requirements of existing CT scanners and the thermal bottleneck preventing transformative imaging modalities reliant on high doses. To illustrate the concept of nanophotonic thermal management in X-ray tubes, we use rigorous coupled wave analysis (RCWA) to calculate the spectral directional emissivity of a tungsten photonic crystal via Kirchhoff’s law of thermal radiation. Incorporating our nanophotonic design into a heat transfer model of an X-ray tube, we estimate the hottest (i.e., limiting) temperature in the X-ray tube as a function of the operating power. We predict that nanophotonic thermal management can lead to a &gt;2× enhancement in the operating power of an X-ray tube at typical operating temperatures. Alternatively, we predict that at typical operating powers, our proposal can lead to a &gt;15% reduction in the operating temperature, decreasing the cooling load. S. P. gratefully acknowledges support from the NSF GRFP under Grant No. 2141064. S. C. acknowledges support from the Korea Foundation for Advanced Studies Overseas PhD Scholarship. This work is supported in part by the U. S. Army Research Office through the Institute for Soldier Nanotechnologies at MIT, under Collaborative Agreement Number W911NF-23-2-0121.<br/><br/>References<br/>[1] W. Li, S. Fan, Opt. Express. 26, 15995 (2018).<br/>[2] Y. X. Yeng, M. Ghebrebrhan, P. Bermel, W. R. Chan, J. D. Joannopoulos, M. Soljačić, I. Celanovic, Proc. Natl. Acad. Sci. 109, 2280 (2012).