Dark-field imaging is an x-ray technique used to highlight subpixel, typically micrometer-scale, density fluctuations. It is often used alongside standard attenuation-based and also phase-contrast x-ray imaging, which both see regular use in tomography. We present x-ray dark-field computed tomography (CT) with a laboratory edge-illumination setup. The dark-field contrast is shown to increase linearly with the x-ray path length through the imaged object, a prerequisite for the use of standard tomographic reconstruction approaches. A multimaterial, custom-built phantom is used to show how dark-field contrast CT can complement attenuation contrast CT for the separation of materials based on their microstructure. As an example of a more complex, biological sample, we present a model rat heart. We show, by comparison with attenuation contrast tomography, that dark-field enables the identification of additional structures undetected through the attenuation contrast channel, as well as offering a consistently sharper reconstructed image
