Development of a next generation X-ray CT with energy spectra of incident photons

2004年，我们用蒙特卡罗方法编写了X射线光子的光子传输代码，并评估了我们提出的光子计数方法的有效性。测试的目的是：（1）提高对比度分辨率，（2）降低X射线强度，（3）消除束硬化效应。模拟结果表明，与利用X射线能量注量的传统CT方法相比，我们可以将低水平对比度分辨率提高约三倍。对于光束硬化效应，我们可以通过权衡测量的能谱来消除伪影。我们将此方法应用于传统现代X射线系统可以获得的能谱，并取得了良好的效果。基于此，我们设计了一种新型CdTe材料的光子计数探测器，并用微焦点X射线管评估了探测器的性能。2005年我们用新开发的X射线探测器进行了多次实验，并将其性能与蒙特卡罗模拟数据的结果进行了比较。对于测试材料，我们选择了水、Fe、Ca、酒精，并使用光子计数方法测量了透射 X 射线。在本实验中，我们设置了几个阈值来区分 X 射线的能量，并将实验值与理想值进行比较。实验数据表明，我们可以使用能量加权计数数据来增加低密度对比度，并且还可以使用能量加权计数数据来减少束硬化伪影。不幸的是，重建的 CT 图像存在一些环形伪影，这些伪影是由探测器灵敏度的不均匀性引起的，但可以通过对测量的计数数据采用适当的插值方法来克服这个问题。

In 2004 we have made a photon transporting code with Monte Carlo method for x-ray photon and evaluated the validity of our proposed photon counting method. The test was performed in terms of (1)improvement of the contrast resolution, (2)reduction of x-ray intensity, and (3)elimination of the beam hardening effect. The results of simulations showed that we could improve the low level contrast resolution about three times compared with the conventional CT method which used the energy fluence of x-rays. For the beam hardening effect we could eliminated the artifacts by weighing the measured energy spectra. And we applied this method to the energy spectra which could be obtained with the conventional modern X-ray system and good results. With this consideration we designed a new photon counting detector which was made of CdTe material and evaluated the performance of the detector with a micro focus x-ray tube.In 2005 we performed several experiment with the newly developed x-ray detector and the performance was compared with the results of Monte Carlo simulation data. For the tested materials we chosen water, Fe, Ca, alcohol and we measured transmitted x-rays with the photon counting method. In this experiment we set several thresholds for discriminating x-rays with their energy and the experiment value was compared with the ideal value. The experiment data showed that we could increase the low density contrast with energy weighted count data and also decrease the beam-hardening artifacts with energy weighted count data. Unfortunately the reconstructed CT images had some ring artifacts which were caused by the non-uniformity of sensitivity of the detector, but this problem could overcome with an appropriate interpolation method for the measured count data.