Efficient Scatter Correction

描述（由申请人提供）：过去10年，CT图像的获取方式发生了重大变化。商用CT扫描仪已经从2片发展到64片，平板薄膜晶体管和其他更大面积的数字x射线探测器的发展已经产生了z轴范围为20厘米或更大的体积成像系统。随着同时被照射的组织体积的增加，到达探测器的散射辐射信号也随之增加。记录的投影图像中的散射信号导致图像对比度降低，拔罐和衰减系数的不准确性增加，重建的CT图像中出现条纹伪影。由于重建过程的非线性，即使只有几个百分点的散射比（SPRs）也会产生显著的条纹。图像采集过程中固有的增加的散射内容代表了这些新成像几何的基本限制，并且需要一种新的，有效的散射校正方法。有效的散射校正必须计算和校正每张图像中每个点的散射，不需要给患者额外的x射线剂量，不应该增加总扫描时间，不应该显著增加数据采集和3D图像可视化之间的时间，不应该引入新的伪影，并且应该广泛适用。我们开发了一种新的、基于编码器测量的散射校正方法，满足这些标准。该方法使用一次波束调制器对一次波束进行编码，同时使散射的频率特性相对不受影响。然后可以使用简单的图像处理来估计和去除投影数据中的散射信号。我们在一个性能良好、稳定的台式CT系统上进行了模拟和物理实验，得到了令人满意的结果。本研究计划的总体目标是扩展和优化我们的方法，并证明我们可以在30厘米均匀物体上实现5 HU的衰减系数精度，在可变衰减物体上实现10 HU的精度。（临床相关对象）用于三个临床系统。我们的方法有可能成为一种颠覆性的技术，可以显著改变当今临床系统的设计方式，并可以促进新的大容量CT成像系统的设计和转化到临床。

DESCRIPTION (provided by applicant): The last 10 years have seen significant changes in the way CT images are acquired. Commercial CT scanners have advanced from 2 to 64 slices, and the development of flat-panel thin-film transistor and other larger-area digital x-ray detectors have given rise to volumetric imaging systems with z-axis extents of 20 cm or greater. As the volume of tissue irradiated at the same time increases, so does the signal from scattered radiation that reaches the detector. The scatter signal in recorded projection images leads to a reduction in image contrast, to an increase in cupping and attenuation coefficient inaccuracy and to streak artifacts in the reconstructed CT images. Scatter-to-primary ratios (SPRs) of even a few percent produce significant streaks due to the non-linearity of the reconstruction process. The increased scatter content inherent in the image acquisition process represents a fundamental limitation of these new imaging geometries, and a new, efficient approach to scatter correction is needed. An efficient scatter correction must calculate and correct for scatter at each point in each image, should do so without requiring additional x-ray dose to the patient, should not increase the total scan time, should not add significantly to the time between data acquisition and 3D image visualization, should not introduce new artifacts, and should be widely applicable. We have developed a new, encoder-measurement-based approach for scatter correction that meets these criteria. The approach uses a primary beam modulator to encode the primary, while leaving the frequency characteristics of the scatter relatively unaffected. Simple image processing can then be used to estimate and remove the scatter signal from the projection data. We have promising results from simulations and from physical experiments on a well- characterized and stable bench-top CT system. The overall goal of this research program is to extend and optimize our approach, and to demonstrate that we can achieve an attenuation coefficient accuracy of 5 HU over a 30-cm uniform object and accuracy of 10 HU in an object with variable attenuation (ie. a clinically relevant object) for three clinical systems. Our approach has the potential to be a disruptive technology that could significantly change the way clinical systems are designed today, and could facilitate the design and translation into the clinic of new, large volume CT imaging systems.