Low-exposure, high-quality multimodal speckle X-ray imaging via an intrinsic gradient-flow approach

Abstract: We present a new approach for retrieving dark-field, attenuation, and phase shift from speckle-based X-ray images. Speckle-based X-ray imaging (SBXI) images and quantifies how a sample modifies a reference near-field speckle pattern, which is generated by a randomly structured mask. Phase-shift images are useful because they reveal how materials in a sample refract the X-ray beam, providing contrast between similar low-density structures that are difficult to visualise in attenuation images. Dark-field images convey information about structures that are smaller than the spatial resolution and thus invisible in both attenuation and phase-shift images. In a previous work, we presented the Multimodal Intrinsic Speckle-Tracking (MIST) algorithm, which recovers the three complementary imaging modes from SBXI data by solving the associated Fokker-Planck equation. The algorithm presented in this work, the Gradient-Flow MIST, (1) reduces the amount of SBXI data required for image retrieval, (2) maintains the full generality of the X-ray Fokker-Planck equation, and (3) recovers dark-field images with higher quality than the previously proposed variants. We demonstrate the new gradient-flow MIST approach on experimental SBXI data acquired at the Australian synchrotron. This approach is anticipated to be useful in phase-contrast and dark-field applications that require simplicity in experimentation.