Higher-order phase shift reconstruction approach.
Higher-order phase shift reconstruction approach.
复制标题
高阶相移重构方法。
DOI：
10.1118/1.3488888
复制
发表时间：
2010
期刊：
影响因子：
3.8
通讯作者：
Wang,Ge
中科院分区：
文献类型：
--
作者：
Cong,Wenxiang;Wang,Ge
目的临床和临床前影像中遇到的生物软组织主要由原子序数较低的轻元素原子组成，元素组成基本均匀，密度变化不大。因此，X射线衰减对比度相对较差，不能达到令人满意的敏感性和特异性。相比之下，X射线位相衬度为软组织成像提供了一种新的机制。软组织的X射线相移在诊断X射线能量范围内比X射线吸收大约一千倍，产生比衰减对比度更高的信噪比。因此，相位对比度成像是一种很有前途的技术，可以揭示软组织的详细结构变化，在健康和恶性组织之间提供高对比度分辨率。本文提出了一种新的相位恢复方法，利用光强测量重建物面上的位相图像。重建的相位图像是由对象引起的相移的投影，并且用作使用层析重建算法重建对象内部的3D折射率分布的输入。这种X射线折射率图像能够显示软组织的结构特征，具有很好的分辨率来区分健康和恶性组织。方法基于近轴菲涅耳-基尔霍夫衍射理论，提出了一种新的相位恢复方法来重建物体的X射线相位图像。这种方法的主要优点是比传统的线性近似模型具有更高的阶数精度，从而放宽了电流缓慢相位变化的限制。利用在菲涅耳衍射区不同距离测量的光强图像，消除了菲涅耳衍射图自相关方程中的非线性项，将位相重构简化为线性逆问题。结果所提出的重建公式是强度输运方程(TIE)的推广。与传统的相位恢复方法中使用的线性模型相比，该方法具有二阶精度。数值实验表明，该相位重建方法的精度和稳定性优于基于Tie的相位重建方法。结论提出了一种从菲涅耳衍射区不同距离处测量的强度图像中提取物体引起的X射线相移图像的新方法。该方法具有二阶精度，能够稳定地恢复物体的相移，克服了传统相位恢复技术假设的缓慢相位变化的限制。
PurposeBiological soft tissues encountered in clinical and preclinical imaging mainly consists of atoms of light elements with low atomic numbers and their elemental composition is nearly uniform with little density variation. Hence, x‐ray attenuation contrast is relatively poor and cannot achieve satisfactory sensitivity and specificity. In contrast, x‐ray phase‐contrast provides a new mechanism for soft tissue imaging. The x‐ray phase shift of soft tissues is about a thousand times greater than the x‐ray absorption over the diagnostic x‐ray energy range, yielding a higher signal‐to‐noise ratio than the attenuation contrast counterpart. Thus, phase‐contrast imaging is a promising technique to reveal detailed structural variation in soft tissues, offering a high contrast resolution between healthy and malignant tissues. Here the authors develop a novel phase retrieval method to reconstruct the phase image on the object plane from the intensity measurements. The reconstructed phase image is a projection of the phase shift induced by an object and serves as input to reconstruct the 3D refractive index distribution inside the object using a tomographic reconstruction algorithm. Such x‐ray refractive index images can reveal structural features in soft tissues, with excellent resolution differentiating healthy and malignant tissues.MethodsA novel phase retrieval approach is proposed to reconstruct an x‐ray phase image of an object based on the paraxial Fresnel–Kirchhoff diffraction theory. A primary advantage of the authors’ approach is higher‐order accuracy over that with the conventional linear approximation models, relaxing the current restriction of slow phase variation. The nonlinear terms in the autocorrelation equation of the Fresnel diffraction pattern are eliminated using intensity images measured at different distances in the Fresnel diffraction region, simplifying the phase reconstruction to a linear inverse problem. Numerical experiments are performed to demonstrate the accuracy and stability of the proposed approach.ResultsThe proposed reconstruction formula is a generalization of the transport of intensity equation (TIE). It has the second‐order accuracy compared to the linear model used in the conventional phase retrieval approach. The numerical experiments demonstrate that the accuracy and stability of the proposed phase reconstruction method outperforms the TIE‐based reconstruction method.ConclusionsA novel approach has been proposed to retrieve an x‐ray phase shift image induced by an object from intensity images measured at different distances in the Fresnel diffraction region. The authors’ approach has the second‐order accuracy and is able to retrieve the phase shift of an object stably, overcoming the restriction of slow phase variation assumed by the conventional phase retrieval techniques.