Abstract
Grating-based X-ray interferometry offers vast potential for imaging materials and tissues that are not easily visualised using conventional X-ray imaging. Tomographic reconstruction based on X-ray interferometric data provides not only access to the attenuation coefficient of an object, but also the refractive index and information about ultra-small-angle scattering. This improved functionality comes at the cost of longer measurement times because existing projection-based signal extraction algorithms require not only a single measurement per projection angle but several with precise grating movements in between. This obstacle hinders the adaptation of grating-based interferometry into a continuously rotating gantry. Several solutions to this problem have been proposed but all suffer from major drawbacks. We present results using an iterative reconstruction algorithm working directly on the interferograms. The suggested direct approach enables improved image quality, since interpolations and unnecessary assumptions about the object are circumvented. Our results demonstrate that it is possible to successfully reconstruct the linear attenuation coefficient, the refractive index and the linear diffusion coefficient, which is a measure related to ultra-small-angle scattering, using a single measurement per projection angle and without any grating movements. This is a milestone for future clinical implementation of grating-based phase-contrast and dark-field contrast X-ray computed tomography.
Highlights
Computed Tomography (CT), a method which combines a series of X-ray images taken from different angles and uses computer processing to create cross-sectional images, is the backbone of current diagnostic medical imaging
For energy integrating X-ray detectors and for photon counting detectors at sufficient flux we can assume that the measured intensities Ii are Gaussian distributed around their expected values Ii with variance σi[2]
In this study we presented a strategy for data acquisition and reconstruction, designed for grating-based computed tomography (GBCT), that is compliant with the demands of clinical applications, in particular a continuously rotating gantry
Summary
Computed Tomography (CT), a method which combines a series of X-ray images taken from different angles and uses computer processing to create cross-sectional images, is the backbone of current diagnostic medical imaging. In addition to techniques that require only a single interferogram per projection angle, a solution that overcomes the need for precise mechanical grating movements (but still requires multiple measurements per angular position) has been presented: Electromagnetic phase-stepping (EPS)[14] employs electrical beam steering to move the object’s projection slightly across the detector while a deliberately created Moiré fringe pattern is fixed on the detector. Several of these shifted images can be combined to form a pseudo phase-stepping. These three sets are separately reconstructed to generate three independent volumes of the underlying object properties: the attenuation projections contain information about the spatial distribution of the linear attenuation coefficient, the differential phase-contrast projections are connected to the refractive index decrement, and the dark-field projections allow reconstruction of the linear diffusion coefficient[3]
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