Truncation Correction for X-ray Phase-Contrast Region-of-Interest Tomography

Abstract

An X-ray Talbot-Lau grating interferometer enables imaging of X-ray phase contrast. It can measure material transitions that are difficult to observe with traditional attenuation X-ray, for example soft-tissue variations in medical diagnosis or weakly absorbing materials in optical inspection. Unfortunately, the field of view of a Talbot-Lau interferometer is limited to few centimeters due to manufacturing constraints of its gratings. For larger objects, this leads to truncation in the projection images. In a tomographic reconstruction, this truncation causes severe artifacts and prevents the reconstruction of quantitatively correct phase coefficients. In this article, we propose a setup and an algorithm that combine in one scan full-field attenuation with small-field phase measurements. This allows to extrapolate the phase measurements across the full field, and thereby to greatly alleviate truncation artifacts in the reconstructed volume. Evaluation on simulated and real data shows that the method can reliably reconstruct refraction index decrements, that it outperforms the state of the art, and that its performance is in many cases robust to deviations from the initial assumptions.