Nuclear and Radiological Engineering and Medical Physics Programs, Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
Phys Med Biol. 2010 Feb 7;55(3):647-62. doi: 10.1088/0031-9155/55/3/007. Epub 2010 Jan 13.
A conventional x-ray fluorescence computed tomography (XFCT) technique requires monochromatic synchrotron x-rays to simultaneously determine the spatial distribution and concentration of various elements such as metals in a sample. However, the synchrotron-based XFCT technique appears to be unsuitable for in vivo imaging under a typical laboratory setting. In this study we demonstrated, for the first time to our knowledge, the possibility of performing XFCT imaging of a small animal-sized object containing gold nanoparticles (GNPs) at relatively low concentrations using polychromatic diagnostic energy range x-rays. Specifically, we created a phantom made of polymethyl methacrylate plastic containing two cylindrical columns filled with saline solution at 1 and 2 wt% GNPs, respectively, mimicking tumors/organs within a small animal. XFCT scanning of the phantom was then performed using microfocus 110 kVp x-ray beam and cadmium telluride (CdTe) x-ray detector under a pencil beam geometry after proper filtering of the x-ray beam and collimation of the detector. The reconstructed images clearly identified the locations of the two GNP-filled columns with different contrast levels directly proportional to gold concentration levels. On the other hand, the current pencil-beam implementation of XFCT is not yet practical for routine in vivo imaging tasks with GNPs, especially in terms of scanning time. Nevertheless, with the use of multiple detectors and a limited number of projections, it may still be used to image some objects smaller than the current phantom size. The current investigation suggests several modification strategies of the current XFCT setup, such as the adoption of the quasi-monochromatic cone/fan x-ray beam and XFCT-specific spatial filters or pinhole detector collimators, in order to establish the ultimate feasibility of a bench-top XFCT system for GNP-based preclinical molecular imaging applications.
传统的 X 射线荧光计算机层析成像（XFCT）技术需要使用单色同步加速器 X 射线来同时确定样品中各种元素（如金属）的空间分布和浓度。然而，基于同步加速器的 XFCT 技术似乎不适合在典型的实验室环境下进行体内成像。在本研究中，我们首次展示了使用多色诊断能量范围内的 X 射线对含有金纳米颗粒（GNPs）的小动物大小的物体进行 XFCT 成像的可能性，这些 GNPs 的浓度相对较低。具体来说，我们制作了一个由聚甲基丙烯酸甲酯塑料制成的体模，其中包含两个圆柱形柱体，分别填充有浓度为 1wt%和 2wt%的 GNPs 的生理盐水溶液，模拟小动物体内的肿瘤/器官。然后，使用微焦点 110 kVp X 射线束和碲化镉（CdTe）X 射线探测器在铅笔束几何形状下对体模进行 XFCT 扫描，对 X 射线束进行适当滤波并对探测器进行准直。重建图像清楚地识别出两个填充 GNPs 的柱体的位置，其对比度水平与金浓度水平直接成正比。另一方面，当前的铅笔束 XFCT 实施方式对于使用 GNPs 进行常规体内成像任务还不实用，尤其是在扫描时间方面。然而，通过使用多个探测器和有限数量的投影，它仍然可以用于对小于当前体模尺寸的某些物体进行成像。当前的研究提出了几种当前 XFCT 设置的修改策略，例如采用准单色锥形/扇形 X 射线束和 XFCT 专用空间滤波器或针孔探测器准直器，以确定基于 GNPs 的临床前分子成像应用的台式 XFCT 系统的最终可行性。
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