Xi'an University of Posts and Telecommunications, Xi'an, Shaanxi 710121, People's Republic of China.
Phys Med Biol. 2018 Jul 2;63(13):135015. doi: 10.1088/1361-6560/aaca14.
In computed tomography (CT), the polychromatic characteristics of x-ray photons, which are emitted from a source, interact with materials and are absorbed by a detector, may lead to beam-hardening effect in signal detection and image formation, especially in situations where materials of high attenuation (e.g. the bone or metal implants) are in the x-ray beam. Usually, a beam-hardening correction (BHC) method is used to suppress the artifacts induced by bone or other objects of high attenuation, in which a calibration-oriented iterative operation is carried out to determine a set of parameters for all situations. Based on the Helgasson-Ludwig consistency condition (HLCC), an optimization based method has been proposed by turning the calibration-oriented iterative operation of BHC into solving an optimization problem sustained by projection data. However, the optimization based HLCC-BHC method demands the engagement of a large number of neighboring projection views acquired at relatively high and uniform angular sampling rate, hindering its application in situations where the angular sampling in projection view is sparse or non-uniform. By defining an objective function based on the data integral invariant constraint (DIIC), we again turn BHC into solving an optimization problem sustained by projection data. As it only needs a pair of projection views at any view angle, the proposed BHC method can be applicable in the challenging scenarios mentioned above. Using the projection data simulated by computer, we evaluate and verify the proposed optimization based DIIC-BHC method's performance. Moreover, with the projection data of a head scan by a multi-detector row MDCT, we show the proposed DIIC-BHC method's utility in clinical applications.
在计算机断层扫描（CT）中，从源发射的 X 射线光子的多色特性与材料相互作用并被探测器吸收，这可能导致信号检测和图像形成中的束硬化效应，尤其是在高衰减材料（例如骨骼或金属植入物）在 X 射线束中的情况下。通常，使用束硬化校正（BHC）方法来抑制由骨骼或其他高衰减物体引起的伪影，其中进行校准导向的迭代操作以确定适用于所有情况的一组参数。基于 Helgasson-Ludwig 一致性条件（HLCC），已经提出了一种基于优化的方法，通过将 BHC 的校准导向迭代操作转换为求解由投影数据支持的优化问题来实现。然而，基于优化的 HLCC-BHC 方法需要使用大量在相对较高且均匀的角度采样率下获取的相邻投影视图，这阻碍了其在投影视图的角度采样稀疏或不均匀的情况下的应用。通过定义基于数据积分不变约束（DIIC）的目标函数，我们再次将 BHC 转换为求解由投影数据支持的优化问题。由于它只需要在任何角度下一对投影视图，因此所提出的 BHC 方法可以适用于上述具有挑战性的场景。我们使用计算机模拟的投影数据评估和验证了所提出的基于优化的 DIIC-BHC 方法的性能。此外，我们还使用多探测器列 MDCT 进行头部扫描的投影数据，展示了所提出的 DIIC-BHC 方法在临床应用中的实用性。
