Purpose: Unlike fluorescence imaging utilizing an external excitation source, Cherenkov emissions and Cherenkov-excited luminescence occur within a medium when irradiated with high-energy x-rays. Methods to improve the understanding of the lateral spread and axial depth distribution of these emissions are needed as an initial step to improve the overall system resolution. Methods: Monte Carlo simulations were developed to investigate the lateral spread of thin sheets of high-energy sources and compared to experimental measurements of similar sources in water. Additional simulations of a multilayer skin model were used to investigate the limits of detection using both 6- and 18-MV x-ray sources with fluorescence excitation for inclusion depths up to 1 cm. Results: Simulations comparing the lateral spread of high-energy sources show approximately 100 × higher optical yield from electrons than photons, although electrons showed a larger penumbra in both the simulations and experimental measurements. Cherenkov excitation has a roughly inverse wavelength squared dependence in intensity but is largely redshifted in excitation through any distance of tissue. The calculated emission spectra in tissue were convolved with a database of luminescent compounds to produce a computational ranking of potential Cherenkov-excited luminescence molecular contrast agents. Conclusions: Models of thin x-ray and electron sources were compared with experimental measurements, showing similar trends in energy and source type. Surface detection of Cherenkov-excited luminescence appears to be limited by the mean free path of the luminescence emission, where for the given simulation only 2% of the inclusion emissions reached the surface from a depth of 7 mm in a multilayer tissue model.

中文翻译：

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X 射线束扫描期间组织中切伦科夫激发发光的理论横向和轴向灵敏度限制和分子报道分子的选择

目的：与利用外部激发源的荧光成像不同，当受到高能 X 射线照射时，切伦科夫发射和切伦科夫激发发光发生在介质内。作为提高整体系统分辨率的第一步，需要提高对这些发射的横向扩散和轴向深度分布的理解的方法。方法：开发蒙特卡罗模拟来研究高能源薄片的横向扩散，并与水中类似能源的实验测量进行比较。使用多层皮肤模型的附加模拟来研究使用 6 MV 和 18 MV X 射线源以及荧光激发的检测极限，内含物深度可达 1 cm。结果：比较高能量源横向扩散的模拟显示，电子的光产率比光子高约 100 倍，尽管电子在模拟和实验测量中都显示出更大的半影。切伦科夫激发在强度上具有大致反波长平方依赖性，但在通过任何距离的组织的激发中很大程度上红移。将计算出的组织中的发射光谱与发光化合物的数据库进行卷积，以产生潜在的切伦科夫激发的发光分子造影剂的计算排名。结论：将薄 X 射线和电子源模型与实验测量进行了比较，显示出能量和源类型的相似趋势。切伦科夫激发发光的表面检测似乎受到发光发射的平均自由程的限制，其中对于给定的模拟，在多层组织模型中，只有 2% 的夹杂物发射从 7 mm 的深度到达表面。