Analytic image reconstruction in local phase-contrast tomography.
ABSTRACT Phase-contrast tomography is a non-interferometric imaging technique for reconstructing the refractive index distribution of a weakly absorbing object from a set of tomographic projection measurements. In many practical situations, the spatial resolution of the reconstructed image can be increased by minimizing the field of view (FOV) of the imaging system. When the object of interest is larger than the FOV, the measured projections are truncated and one is faced with a local tomography reconstruction problem. In this work, we analytically and numerically investigate the problem of reconstructing tomographic images from truncated phase-contrast projection data. A simple backprojection algorithm for reconstructing object discontinuities from truncated phase-contrast projection data is proposed and investigated that involves no explicit filtering of the projection data. We also investigate the use of the filtered backprojection algorithm and a local tomography reconstruction algorithm developed for absorption CT. These reconstruction algorithms are implemented and numerically investigated to corroborate our theoretical assertions.
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- "A significant amount of work has been done on the question of tomographic reconstruction using x-ray PBI. Key works include, but are not limited to, (i) Cloetens et al (1997), who reconstructed raw x-ray propagation-based phase-contrast data using filtered backprojection to give an edge-enhanced three-dimensional representation of the object; (ii) Cloetens et al (1999) on 'holotomography', which utilized through-focal-series phase retrieval methods originally developed in the field of electron microscopy, in the context of quantitative x-ray phase-contrast tomography; (iii) x-ray phase-contrast tomography which incorporated the transport-of-intensity equation (Teague 1983) for the phase retrieval analysis of each projection prior to three-dimensional reconstruction (Mayo et al 2003, McMahon et al 2003); (iv) Bronnikov's merging of the phase retrieval and tomography steps into a single algorithm for the case of a transparent object (Bronnikov 2002), together with the generalization of this work by Gureyev et al (2006); (v) extension of Wolf's work on diffraction tomography (Wolf 1969), in the context of x-ray phase contrast, by Anastasio and Pan (2000); (vi) Myers et al (2010) on phase retrieval tomography of few-material objects using a limited number of views, together with work on gradient-sparse objects by Sidky et al (2010); and (vii) local phase-contrast tomography (Anastasio et al 2004, Shi et al 2005, Gureyev et al 2007). For a balanced overview of the contemporary state of the art in x-ray phase-contrast tomography, we refer to the proceedings of the Conference on Developments in X-Ray Tomography VII, edited by Stock (2010). "
ABSTRACT: We demonstrate interface-specific propagation-based x-ray phase retrieval tomography of the thorax and brain of small animals. Our method utilizes a single propagation-based x-ray phase-contrast image per projection, under the assumptions of (i) partially coherent paraxial radiation, (ii) a static object whose refractive indices take on one of a series of distinct values at each point in space and (iii) the projection approximation. For the biological samples used here, there was a 9-200 fold improvement in the signal-to-noise ratio of the phase-retrieved tomograms over the conventional attenuation-contrast signal. The ability to 'digitally dissect' a biological specimen, using only a single phase-contrast image per projection, will be useful for low-dose high-spatial-resolution biomedical imaging of form and biological function in both healthy and diseased tissue.Physics in Medicine and Biology 11/2011; 56(23):7353-69. DOI:10.1088/0031-9155/56/23/002 · 2.92 Impact Factor
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- "In agreement with other publications (Anastasio et al., 2004; Jorgensen et al., 1998), we obtained useful data even when reconstructing our local data with a global method. The effect of concentric gradients was not as pronounced as described by Jorgensen et al. (1998), which might be due to the fact that Fig. 9. Portion of microvasculature from the left frontal cortex. "
ABSTRACT: There is a wide range of diseases and normal physiological processes that are associated with alterations of the vascular system in organs. Ex vivo imaging of large vascular networks became feasible with recent developments in microcomputed tomography (microCT). Current methods permit to visualize only limited numbers of physically excised regions of interests (ROIs) from larger samples. We developed a method based on modified vascular corrosion casting (VCC), scanning electron microscopy (SEM), and desktop and synchrotron radiation microCT (SRmicroCT) technologies to image vasculature at increasing levels of resolution, also referred to as hierarchical imaging. This novel approach allows nondestructive 3D visualization and quantification of large microvascular networks, while retaining a precise anatomical context for ROIs scanned at very high resolution. Scans of entire mouse brain VCCs were performed at 16-microm resolution with a desktop microCT system. Custom-made navigation software with a ROI selection tool enabled the identification of anatomical brain structures and precise placement of multiple ROIs. These were then scanned at 1.4-microm voxel size using SRmicroCT and a local tomography setup. A framework was developed for fast sample positioning, precise selection of ROIs, and sequential high-throughput scanning of a large numbers of brain VCCs. Despite the use of local tomography, exceptional image quality was achieved with SRmicroCT. This method enables qualitative and quantitative assessment of vasculature at unprecedented resolution and volume with relatively high throughput, opening new possibilities to study vessel architecture and vascular alterations in models of disease.NeuroImage 09/2006; 32(2):626-36. DOI:10.1016/j.neuroimage.2006.03.043 · 6.36 Impact Factor
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ABSTRACT: Propagation-based phase-contrast tomography is a non-interferometric imaging technique that can reconstruct the complex refractive index distribution of an object. To accomplish such a reconstruction, however, the measured phase-contrast projections must be untruncated. We have demonstrated recently that the mathematical theory of local computed tomography (CT), which was originally developed for absorption CT, can be applied naturally for understanding the problem of reconstructing the location of image boundaries from truncated phase-contrast projections. In this work, we reveal that, for two-dimensional objects, the magnitude of refractive index discontinuities can be reconstructed from truncated phase-contrast projections acquired in the near-Fresnel zone. We show that these magnitudes can be reliably reconstructed using algorithms that were developed originally for local absorption CT.Proceedings of SPIE - The International Society for Optical Engineering 10/2004; DOI:10.1117/12.560183 · 0.20 Impact Factor