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Characterization of a spectroscopic detector for application in x-ray computed tomography

机译：用于X射线计算机断层扫描的光谱探测器的表征

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Recent advances in cadmium telluride (CdTe) energy-discriminating pixelated detectors have enabled the possibility of Multi-Spectral X-ray Computed Tomography (MSXCT) to incorporate spectroscopic information into CT. MultiX ME 100 V2 is a CdTe-based spectroscopic x-ray detector array capable of recording energies from 20 to 160 keV in 1.1 keV energy bin increments. Hardware and software have been designed to perform radiographic and computed tomography tasks with this spectroscopic detector. Energy calibration is examined using the end-point energy of a bremsstrahlung spectrum and radioisotope spectral lines. When measuring the spectrum from Am-241 across 500 detector elements, the standard deviation of the peak-location and FWHM measurements are ± 0.4 and ± 0.6 keV, respectively. As these values are within the energy bin size (1.1 keV), detector elements are consistent with each other. The count rate is characterized, using a nonparalyzable model with a dead time of 64 ± 5 ns. This is consistent with the manufacturer's quoted per detector-element linear-deviation at 2 Mpps (million photons per sec) of 8.9% (typical) and 12% (max). When comparing measured and simulated spectra, a low-energy tail is visible in the measured data due to the spectral response of the detector. If no valid photon detections are expected in the low-energy tail, then a background subtraction may be applied to allow for a possible first-order correction. If photons are expected in the low-energy tail, a detailed model must be implemented. A radiograph of an aluminum step wedge with a maximum height of 20 mm shows an underestimation of attenuation by about 10% at 60 keV. This error is due to partial energy deposition from higher energy (＞60 keV) photons into a lower-energy (～60 keV) bin, reducing the apparent attenuation. A radiograph of a polytetrafluoroethylene (PTFE) cylinder taken using a bremsstrahlung spectrum from an x-ray voltage of 100 kV filtered by 1.3 mm Cu is reconstructed using Abel inversion. As no counts are expected in the low energy tail, a first order background correction is applied to the spectrum. The measured linear attenuation coefficient (LAC) is within 10% of the expected value in the 60 to 100 keV range. Below 60 keV, low counts in the corrected spectrum and partial energy deposition from incident photons of energy greater than 60 keV into energy bins below 60 keV impact the LAC measurements. This report ends with a demonstration of the tomographic capability of the system. The quantitative understanding of the detector developed in this report will enable further study in evaluating the system for characterization of an object's chemical make-up for industrial and security purposes.
机译：碲化镉（CdTe）能量分辨像素化探测器的最新进展使多光谱X射线计算机断层扫描（MSXCT）能够将光谱信息纳入CT。 MultiX ME 100 V2是基于CdTe的X射线光谱探测器阵列，能够以1.1 keV能量仓增量记录20至160 keV的能量。设计了硬件和软件以使用此光谱探测器执行射线照相和计算机断层扫描任务。使用a致辐射光谱的终点能量和放射性同位素光谱线检查能量校准。在500个检测器元件上测量来自Am-241的光谱时，峰位和FWHM测量的标准偏差分别为±0.4和±0.6 keV。由于这些值在能量仓大小（1.1 keV）之内，因此检测器元件彼此一致。使用死区时间为64±5 ns的不可瘫痪模型来表征计数率。这与制造商给出的每个探测器元素线性偏差在2 Mpps（百万光子/秒）下所引用的8.9％（典型值）和12％（最大值）一致。比较测量光谱和模拟光谱时，由于检测器的光谱响应，在测量数据中可见低能尾巴。如果在低能尾部没有预期的有效光子检测，则可以应用背景减法以进行可能的一阶校正。如果在低能尾部中期望有光子，则必须实施详细的模型。铝制台阶楔的最大高度为20 mm的射线照片显示，在60 keV时，衰减低估了约10％。此错误是由于从较高能量（＞ 60 keV）的光子到较低能量（〜60 keV）的光柱中的部分能量沉积，从而降低了视在衰减。使用Abel倒置，使用致辐射光谱从100 kV X射线电压经1.3 mm Cu过滤获得的聚四氟乙烯（PTFE）圆柱体的射线照片。由于在低能尾部中没有期望的计数，因此将一阶背景校正应用于频谱。在60至100 keV的范围内，测得的线性衰减系数（LAC）在预期值的10％以内。低于60 keV，校正光谱中的低计数以及从大于60 keV的能量入射光子进入60 keV以下的能量仓的部分能量沉积会影响LAC测量。该报告以系统层析成像能力的演示结尾。对本报告中开发的检测器的定量理解将有助于对工业和安全性目的评估对象化学成分表征系统进行进一步研究。

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