DKFZ, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany.
Phys Med Biol. 2010 Mar 7;55(5):1327-41. doi: 10.1088/0031-9155/55/5/005. Epub 2010 Feb 4.
Coherent bremsstrahlung denotes the process of bremsstrahlung emission by electrons traversing a single crystal, causing prominent peaks in the resulting photon spectra at low energies. While this phenomenon has been known for decades, little attempt has been made to exploit its potential for megavoltage imaging, where the quality of images is affected by low contrast due to the lack of sufficient photons at the energy range suited for diagnostic purposes. We provide a theoretical foundation of coherent bremsstrahlung in the first-order Born approximation without confinement to high energies. Based on this theory, first evidence is given that diamond crystals are capable of boosting the amount of diagnostic photons by about 10-20%. It is shown that this behaviour is largely conserved for polychromatic electrons hitting thick targets, where multiple scattering dominates the energy distribution of the emitted photons.
相干韧致辐射是指电子穿过单晶体时的韧致辐射发射过程，在低能下会导致光子能谱中出现明显的峰值。尽管这一现象已经存在了几十年，但很少有人试图利用其在兆伏成像中的潜力，因为在适合诊断目的的能量范围内，由于光子数量不足，图像的质量会受到低对比度的影响。我们在无高能限制的一级玻恩近似下为相干韧致辐射提供了理论基础。基于这一理论，首次给出了钻石晶体能够将诊断用光子数量提高约 10-20%的证据。结果表明，这种行为在多色电子撞击厚靶时基本保持不变，其中多次散射主导着发射光子的能量分布。
