Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, USA.
Phys Med Biol. 2011 May 7;56(9):2791-816. doi: 10.1088/0031-9155/56/9/011. Epub 2011 Apr 5.
The goal of this paper was to investigate the benefits that could be realistically achieved on a microCT imaging system with an energy-resolved photon-counting x-ray detector. To this end, we built and evaluated a prototype microCT system based on such a detector. The detector is based on cadmium telluride (CdTe) radiation sensors and application-specific integrated circuit (ASIC) readouts. Each detector pixel can simultaneously count x-ray photons above six energy thresholds, providing the capability for energy-selective x-ray imaging. We tested the spectroscopic performance of the system using polychromatic x-ray radiation and various filtering materials with K-absorption edges. Tomographic images were then acquired of a cylindrical PMMA phantom containing holes filled with various materials. Results were also compared with those acquired using an intensity-integrating x-ray detector and single-energy (i.e. non-energy-selective) CT. This paper describes the functionality and performance of the system, and presents preliminary spectroscopic and tomographic results. The spectroscopic experiments showed that the energy-resolved photon-counting detector was capable of measuring energy spectra from polychromatic sources like a standard x-ray tube, and resolving absorption edges present in the energy range used for imaging. However, the spectral quality was degraded by spectral distortions resulting from degrading factors, including finite energy resolution and charge sharing. We developed a simple charge-sharing model to reproduce these distortions. The tomographic experiments showed that the availability of multiple energy thresholds in the photon-counting detector allowed us to simultaneously measure target-to-background contrasts in different energy ranges. Compared with single-energy CT with an integrating detector, this feature was especially useful to improve differentiation of materials with different attenuation coefficient energy dependences.
本文旨在研究在配备能量分辨光子计数 X 射线探测器的微计算机断层扫描（microCT）成像系统上能够实现的实际效益。为此，我们构建并评估了一个基于此类探测器的 microCT 系统原型。该探测器基于碲化镉（CdTe）辐射传感器和专用集成电路（ASIC）读出电路。每个探测器像素都能够同时对超过六个能量阈值的 X 射线光子进行计数，从而实现了能量选择 X 射线成像的功能。我们使用多色 X 射线辐射和具有 K 吸收边的各种滤波材料来测试系统的光谱性能。然后，对一个包含用各种材料填充的孔的圆柱形 PMMA 体模进行了层析成像。结果还与使用强度积分 X 射线探测器和单能（即非能量选择）CT 获得的结果进行了比较。本文描述了系统的功能和性能，并展示了初步的光谱和层析成像结果。光谱实验表明，能量分辨光子计数探测器能够测量标准 X 射线管等多色源的能谱，并分辨成像所用能量范围内存在的吸收边。然而，光谱质量因包括有限的能量分辨率和电荷共享在内的退化因素而受到影响。我们开发了一个简单的电荷共享模型来再现这些失真。层析实验表明，光子计数探测器中多个能量阈值的可用性使我们能够同时在不同的能量范围内测量目标与背景的对比度。与使用积分探测器的单能 CT 相比，该功能对于改善具有不同衰减系数能量依赖性的材料的区分特别有用。
