New signal extraction method in x-ray differential phase contrast imaging with a tilted collinear analyzer grating

Abstract

In a grating interferometer-based x-ray differential phase contrast (DPC) imaging system, an analyzer grating (i.e. a G2 grating) is typically used to help record the important refraction information obtained with the phase stepping technique. Such a method requires the sequential movement of the G2 grating as well as multiple x-ray exposures to perform phase stepping, and thus conventional DPC imaging is very time-consuming. Additionally, it also has some mechanical instability issues due to the movement of the G2 grating. To accelerate the data acquisition speed and achieve single shot x-ray DPC imaging with a collinear type G2 grating, in this study, a new signal extraction method had been investigated. With this alternative approach, a non-zero angle of rotation between the diffraction pattern (generated by the G1 grating) and the collinear G2 grating is used during the entire data acquisition. Due to this deliberate grating misalignment, a visible moire pattern with a certain period shall be detected. Initial experiments have demonstrated that this new signal extraction method is able to provide us with three different types of signal: absorption, differential phase, and the dark field image signals. Although the spatial resolution for both the differential phase and the dark field images is blurred by several pixel length due to the used interpolation operation, the absorption image maintains the same spatial resolution as in the conventional x-ray imaging. This developed novel signal analysis method enables single shot DPC imaging and can greatly reduce the data acquisition time, thus facilitating the implementation of DPC imaging in the medical field.