Multidirectional x-ray phase-contrast imaging with 1D modulators

Beam-tracking (BT) is an x-ray phase-contrast imaging technique that requires a single absorption mask, making it simpler to implement than approaches relying on two or more masks or gratings, such as edge-illumination or grating interferometry. Conventional 1D-BT, based on linear masks splitting the beam into individual beamlets, is sensitive to refraction and dark-field signals only along the direction transverse to the beamlets, while multidirectional sensitivity requires 2D masks. However, 2D masks suffer from reduced photon transmission and a quadratic increase in the number of stepping positions needed for full sample illumination, resulting in longer acquisition times. Here, we present multi1D-BT, an acquisition scheme that achieves multidirectional sensitivity in the transmission and differential phase (refraction) channels using a 1D mask, by combining two consecutive acquisitions rotated 90° with respect to each other. The method is validated on a polymethyl methacrylate test phantom and an ex vivo insect specimen, comparing multi1D-BT against 2D-BT acquisitions obtained with 2D structured modulators with (nearly) matching periods and apertures. In our experiments, multi1D-BT achieved a three times faster acquisition with similar or better image quality compared to conventional 2D-BT: the signal-to-noise ratio in the refraction signal was 35%–70% higher, and up to two times higher when compared at matched exposure time, while the contrast-to-noise ratio in the transmission signal was more than doubled. These findings indicate that multi1D-BT can provide fast, multidirectional differential phase and transmission imaging using simpler and more widely available 1D modulators, at the cost of requiring image registration between the two orthogonal acquisitions.