Recent developments in fly scan methods for phase and multi-contrast x-ray micro-CT based on amplitude modulated beams

Beam tracking and edge illumination are phase contrast imaging techniques that rely on amplitude modulated x-ray beams to generate sensitivity to refraction and scattering. While each technique has its advantage (“single shot” three-contrast imaging in beam tracking; the ability to work with relatively large pixels in edge illumination), they also share a common drawback, namely that the modulator shields parts of the sample and, thus, prevents those areas from contributing to the image (under-sampling). Sample stepping, by which frames are acquired with the sample in a different position relative to the modulator (sometimes referred to as “dithering”) can produce well-sampled images. However, in computed tomography (CT), stepping must be performed at each rotation angle, enforcing step-and-shoot acquisitions and leading to long scan times. To enable faster acquisitions, fly scan compatible scanning schemes based on “roto-translating” the sample in the modulated x-ray beam were recently developed. This article reviews these schemes and provides practical guidance for their implementation.