European Synchrotron Radiation Facility, Grenoble, France.
IEEE Trans Image Process. 2010 Sep;19(9):2428-36. doi: 10.1109/TIP.2010.2048608.
We consider the phase retrieval problem in 3-D holotomography for strongly absorbing objects. Holotomography combines phase retrieval from Fresnel diffraction patterns with tomographic reconstruction to reconstruct the 3-D refractive index distribution. The main interest is the increase in sensitivity of up to three orders of magnitude compared to standard, absorption based tomography. Most existing algorithms are based upon linearization of the forward problem. This is motivated by the large problem size, since it yields computationally efficient solutions. Here, the mixed approach is used, which allows for both strong absorption and long propagation distances. Previous implementations have shown promising results, but in practice often suffer from strong low frequency artifacts. To address this problem, we introduce a homogeneous object assumption through a regularizing term based upon the absorption image. This allows the homogeneous object assumption to be introduced only in the low frequency range. The proportionality constant between absorption and refractive index is assumed to be known. The regularizing parameter is found using the standard L-curve technique. The benefits of our approach are illustrated using data measured at the European Synchrotron Radiation Facility. Low frequency noise in the reconstruction is alleviated, but the result is only quantitative in the areas of the sample where the homogeneous object assumption is fulfilled.
我们考虑了强吸收物体的 3D 全息层析成像中的相位恢复问题。全息层析成像将菲涅耳衍射模式的相位恢复与层析重建相结合，以重建 3D 折射率分布。主要的兴趣在于与基于吸收的标准层析相比，灵敏度提高了三个数量级。大多数现有的算法都基于正向问题的线性化。这是由于问题规模较大，因为它产生了计算效率高的解决方案。在这里，使用了混合方法，允许强吸收和长传播距离。以前的实现已经显示出有希望的结果，但在实践中，往往受到强烈的低频伪影的影响。为了解决这个问题，我们通过基于吸收图像的正则化项引入了均匀物体假设。这允许在低频范围内引入均匀物体假设。吸收和折射率之间的比例常数被认为是已知的。正则化参数是使用标准的 L 曲线技术找到的。我们的方法的好处通过在欧洲同步辐射设施测量的数据得到了说明。重建中的低频噪声得到了缓解，但结果仅在满足均匀物体假设的样品区域具有定量意义。
