Kandlakunta Praneeth, Thomas Allan, Tan Yuewen, Khan Rao, Zhang Tiezhi
Department of Radiation Oncology, Washington University in St. Louis School of Medicine, St. Louis, MO, United States of America.
Biomed Phys Eng Express. 2019 Feb;5(2). doi: 10.1088/2057-1976/aae55f. Epub 2019 Jan 24.
Distributed x-ray sources enable novel designs of x-ray imaging systems. However, the x-ray power of such sources is limited by the focal spot power density of the fixed anode. To further improve x-ray output, we have designed and evaluated a diamond-W transmission target for multi-pixel x-ray sources. The target features a thin layer of tungsten deposited on a diamond substrate. The thickness of tungsten layer was optimized for maximum fluence through Monte Carlo simulations. Finite element thermal simulations were performed to evaluate focal spot temperature in the target under different power loadings and dwell duration. The results showed that the optimal thickness of the tungsten layer in the W-diamond transmission target is linearly proportional to the electron energy. A 5-6 m tungsten thickness is suitable for the kVps ranges from 60 kVp to 140 kVp. A W-diamond transmission target produces up to 20% more x-ray fluence than a traditional W reflection target in the beam center depending on the kVp settings. The x-ray spectrum of the transmission target shows less characteristic x-rays than that of reflection target. The thermal performance of W-diamond targets for peak power is significantly better than that of reflection targets. The maximum focal spot power densities of W-diamond transmission and W reflection targets are both strongly dependent on the dwell duration. For longer pulse durations, the W-diamond target allows as much as a four-fold increase in power and an eight-fold increase in power density in comparison to a traditional W reflection target for the same temperature spikes. The stability of the W-diamond bond needs to be tested experimentally. Nevertheless, the W-diamond transmission target is an appealing target that can significantly simplify the design and improve the performance of distributed x-ray sources.
分布式X射线源使X射线成像系统的新颖设计成为可能。然而，此类源的X射线功率受到固定阳极焦点功率密度的限制。为了进一步提高X射线输出，我们设计并评估了一种用于多像素X射线源的金刚石-钨透射靶。该靶的特点是在金刚石衬底上沉积了一层薄钨。通过蒙特卡罗模拟优化了钨层的厚度以实现最大注量。进行了有限元热模拟以评估在不同功率负载和驻留持续时间下靶中的焦点温度。结果表明，W-金刚石透射靶中钨层的最佳厚度与电子能量成线性比例。5-6μm的钨厚度适用于60 kVp至140 kVp的千伏峰值范围。根据千伏峰值设置，W-金刚石透射靶在光束中心产生的X射线注量比传统W反射靶多20%。透射靶的X射线光谱显示出比反射靶更少的特征X射线。W-金刚石靶在峰值功率下的热性能明显优于反射靶。W-金刚石透射靶和W反射靶的最大焦点功率密度都强烈依赖于驻留持续时间。对于更长的脉冲持续时间，与传统W反射靶相比，在相同温度峰值下，W-金刚石靶的功率可增加四倍，功率密度可增加八倍。W-金刚石键的稳定性需要通过实验进行测试。尽管如此，W-金刚石透射靶是一个有吸引力的靶，它可以显著简化分布式X射线源的设计并提高其性能。
