Medical physicsX射线光栅干涉测量光束硬化和环形伪影校正的经验-X射线光栅
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X射线光栅干涉测量光束硬化和环形伪影校正的经验
目的: Talbot-Lau光栅干涉测量法能够使用多色X射线源，从而扩展了适用于相衬成像的潜在应用范围。然而，这些源不仅从样品而且从光栅引入了射束硬化效应。当于多色光源一起使用时，由于制造缺陷造成的光栅不均匀性会导致光谱不均匀性伪影。因此，吸收、相位和可见度对比度的不同能量依赖性带来了迄今为止限制可实现的图像质量的挑战。这项工作的目的是为基于光栅的 X 射线成像开发和验证一种校正策略，该策略解决了从成像对象和光栅产生的射束硬化。
方法: 所提出的双变量多项式扩展策略的灵感来自于为解决来主动调制器的光束硬化而执行的工作。考虑到光栅干涉测量的多重对比度特性，这种方法被扩展到每个对比度以获得三组校正系数，这些系数是从校准扫描凭经验确定的。使用桌面 Talbot-Lau 光栅干涉仪微计算机断层扫描 (CT) 系统采集带表低和高原子序数材料的水样和硅样品的CT结果，证明了该方法的可行性。使用来自无束硬化目标图像的均方误差 (MSE) 和样本重建图像内的标准偏差对诸如杯突和环形伪影之类的光谱伪影进行量化。最后，将使用水样开发的模型应用于固定的鼠肺样本，以证明对类似材料的稳健性。
结果: 水样的吸收 CT 图像受光谱伪影的影响最大，但经过校正以减少环形伪影后，观察到均方误差（MSE） 降低了 80%，标准偏差降低了57%。硅样品在所有对比度中都产生了严重的伪影，但经过校正，吸收的均方误差（MSE）的降低了 94%，相位降低了 96%，可见度图像降低了 90%。这些改进是由于消除了所有对比度的环形伪影，减少了吸收和相位图像中的杯突以及减少了可见性图像中的覆盖问题。当水校准系数应用于肺样本时，吸收对比度中最突出的环形伪影被消除。
结论: 所描述的方法是为了消除由于系统光栅和成像对象中的射束硬化而导致的吸收、相位和归一化可见性显微CT图像中的伪影，将均方误差（MSE） 降低了96%。该方法依赖于可以在任何系统上执行的校准，并且不需要详细了解X射线光谱、探测器能量响应、光栅衰减特性和缺陷，或成像对象的几何形状和成分。
Empirical beam hardening and ring artifact correction for x-ray grating interferometry (EBHC-GI)
Abstract
Purpose
Talbot-Lau grating interferometry enables the use of polychromatic x-ray sources, extending the range of potential applications amenable to phase contrast imaging. However, these sources introduce beam hardening effects not only from the samples but also from the gratings. As a result, grating inhomogeneities due to manufacturing imperfections can cause spectral nonuniformity artifacts when used with polychromatic sources. Consequently, the different energy dependencies of absorption, phase, and visibility contrasts impose challenges that so far have limited the achievable image quality. The purpose of this work was to develop and validate a correction strategy for grating-based x-ray imaging that accounts for beam hardening generated from both the imaged object and the gratings.
Methods
The proposed two-variable polynomial expansion strategy was inspired by work performed to address beam hardening from a primary modulator. To account for the multicontrast nature of grating interferometry, this approach was extended to each contrast to obtain three sets of correction coefficients, which were determined empirically from a calibration scan. The method’s feasibility was demonstrated using a tabletop Talbot-Lau grating interferometer micro-computed tomography (CT) system using CT acquisitions of a water sample and a silicon sample, representing low and high atomic number materials. Spectral artifacts such as cupping and ring artifacts were quantified using mean squared error (MSE) from the beam-hardening-free target image and standard deviation within a reconstructed image of the sample. Finally, the model developed using the water sample was applied to a fixated murine lung sample to demonstrate robustness for similar materials.
Results
The water sample’s absorption CT image was most impacted by spectral artifacts, but following correction to decrease ring artifacts, an 80% reduction in MSE and 57% reduction in standard deviation was observed. The silicon sample created severe artifacts in all contrasts, but following correction, MSE was reduced by 94% in absorption, 96% in phase, and 90% in visibility images. These improvements were due to the removal of ring artifacts for all contrasts and reduced cupping in absorption and phase images and reduced capping in visibility images. When the water calibration coefficients were applied to the lung sample, ring artifacts most prominent in the absorption contrast were eliminated.
Conclusions
The described method, which was developed to remove artifacts in absorption, phase, and normalized visibility micro-CT images due to beam hardening in the system gratings and imaged object, reduced the MSE by up to 96%. The method depends on calibrations that can be performed on any system and does not require detailed knowledge of the x-ray spectrum, detector energy response, grating attenuation properties and imperfections, or the geometry and composition of the imaged object.
文章中所使用的光栅是由德国Microworks生产定制、生产的（点击了解详情）。光栅具体参数如下：
