Biomedical Imaging Division, School of Biomedical Engineering and Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA.
Med Phys. 2010 Oct;37(10):5238-42. doi: 10.1118/1.3488888.
Biological 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.
A 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.
The 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.
A 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.
临床和临床前成像中遇到的生物软组织主要由轻元素的原子组成，其元素组成几乎均匀，密度变化很小。因此，X 射线衰减对比相对较差，无法达到令人满意的灵敏度和特异性。相比之下，X 射线相位对比为软组织成像提供了一种新的机制。软组织的 X 射线相移比诊断 X 射线能量范围内的 X 射线吸收大约大一千倍，从而产生比衰减对比对应物更高的信噪比。因此，相位对比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，提供健康组织和恶性组织之间的高对比度分辨率。在这里，作者开发了一种新的相位恢复方法，从强度测量中重建物体平面上的相位图像。重建的相位图像是物体引起的相移的投影，并用作输入，使用层析重建算法重建物体内部的 3D 折射率分布。这种 X 射线折射率图像可以揭示软组织中的结构特征，具有极好的分辨率，可以区分健康组织和恶性组织。
提出了一种新的相位恢复方法，基于傍轴菲涅耳-基尔霍夫衍射理论，根据强度测量重建物体的 X 射线相位图像。作者的方法的主要优点是比传统的线性近似模型具有更高的精度，放宽了当前对缓慢相位变化的限制。通过使用菲涅耳衍射区域中不同距离处测量的强度图像消除自相关方程中的非线性项，将相位重建简化为线性逆问题。进行了数值实验以证明所提出方法的准确性和稳定性。
所提出的重建公式是传输强度方程（TIE）的推广。与传统相位恢复方法中使用的线性模型相比，它具有二阶精度。数值实验表明，所提出的相位重建方法的准确性和稳定性优于基于 TIE 的重建方法。
提出了一种从菲涅耳衍射区域中不同距离处测量的强度图像中重建物体引起的 X 射线相移图像的新方法。作者的方法具有二阶精度，能够稳定地重建物体的相移，克服了传统相位恢复技术所假设的缓慢相移的限制。
