Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA.
Department of Radiation Physics, Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA.
Med Phys. 2018 Dec;45(12):5543-5554. doi: 10.1002/mp.13234. Epub 2018 Nov 8.
This work proposes a semiempirical correction method for attenuation of x-ray fluorescence (XRF) photons and/or an excitation beam during direct XRF imaging (i.e., mapping) of gold nanoparticle (GNP) distribution utilizing gold L-shell XRF photons.
The current method was first devised by finding the two following relationships: (a) ratio of gold XRF peak intensity (L at ~9.7 keV and L at ~11.4 keV) vs pathlength of XRF photons; (b) XRF photon counts produced (N ) vs scattered photon counts produced (N ). Monte Carlo simulations were performed using the Geant4 tool kit to characterize the aforementioned relationships for different tissue-like media. The applicability of the method was tested experimentally by acquiring 2D L-shell XRF images of custom-made phantoms using an experimental benchtop x-ray fluorescence computed tomography setup.
The results show that the ratio of gold L-shell XRF peak intensities allowed an estimation of the pathlength of XRF photons, thus can be utilized to correct for attenuation of XRF photons after emission. The results also demonstrate that N , through a proportionality where the exponent T depends on the energy of scattered photons, could be used to correct for attenuation of an excitation beam prior to producing XRF photons. The corrected XRF signal was found independent of the densities of tissue-like media present along the passage of an excitation beam or emitted XRF photons.
The current results suggest that the developed attenuation correction method plays an essential role for the detection of GNPs on the order of parts-per-million, and also for the determination of GNP concentration/location within the imaging object made of tissue-like media, without any prior knowledge of the imaging object shape, under the conditions deemed relevant to biomedical applications of gold L-shell XRF-based imaging.
本工作提出了一种半经验修正方法，用于修正直接利用金 L 壳层 X 射线荧光（XRF）光子对金纳米颗粒（GNP）分布进行 XRF 成像（即映射）时 XRF 光子和/或激发束的衰减。
该方法首先通过找到以下两个关系来设计：（a）金 XRF 峰强度（L 在约 9.7 keV 和 L 在约 11.4 keV）与 XRF 光子路径长度的比值；（b）产生的 XRF 光子计数（N）与产生的散射光子计数（N）的比值。使用 Geant4 工具包进行蒙特卡罗模拟，以描述不同类组织介质中的上述关系。通过使用实验台式 X 射线荧光计算机层析成像设置获取定制的体模的二维 L 壳层 XRF 图像，对该方法的适用性进行了实验测试。
结果表明，金 L 壳层 XRF 峰强度比允许估计 XRF 光子的路径长度，因此可以用于校正发射后 XRF 光子的衰减。结果还表明，N 可以通过一个比例关系来校正激发束衰减，其中指数 T 取决于散射光子的能量。在产生 XRF 光子之前，N 可以通过一个比例关系来校正激发束衰减，其中指数 T 取决于散射光子的能量。校正后的 XRF 信号与激发束或发射 XRF 光子穿过的类组织介质的密度无关。
目前的结果表明，所开发的衰减校正方法对于检测ppm 级别的 GNP 以及确定成像物体中 GNP 的浓度/位置起着至关重要的作用，该成像物体由类组织介质制成，无需事先了解成像物体的形状，在被认为与基于金 L 壳层 XRF 的成像的生物医学应用相关的条件下。
