Correction method for differential phase contrast imaging

摘要

The present invention generally refers to a correction method for grating-based X-ray differential phase contrast imaging (DPCI) as well as to an apparatus which can advantageously be applied in X-ray radiography and tomography for hard X-ray DPCI of a sample object or an anatomical region of interest to be scanned. More precisely, the proposed invention provides a suitable approach that helps to enhance the image quality of an acquired X-ray image which is affected by phase wrapping, e.g. in the resulting Moiré interference pattern of an emitted X-ray beam in the detector plane of a Talbot-Lau type interferometer after diffracting said X-ray beam at a phase-shifting beam splitter grating. This problem, which is further aggravated by noise in the obtained DPCI images, occurs if the phase between two adjacent pixels in the detected X-ray image varies by more than π radians and is effected by a line integration over the object's local phase gradient, which induces a phase offset error of π radians that leads to prominent line artifacts parallel to the direction of said line integration.

主权项

1. An apparatus, serving as an interferometer setup and having an optical axis, said apparatus for imaging an object by means of electromagnetic waves or matter waves, wherein the object causes an altered phase information of the electromagnetic waves or matter waves according to a local refraction index, the apparatus comprising;
a radiation source for emitting the electromagnetic waves or matter waves for transmission through said object; a radiation detector for detecting these electromagnetic waves or matter waves; and a pixel-correcting processor configured for gaining information representative of the object's local phase gradient (∂Φ(x, y)/∂x) in at least one transverse direction perpendicular to the interferometer setup's optical axis, wherein said processor is configured for determining the pixel positions of noisy pixels and/or determining at which pixel positions of a detected phase gradient image the local phase gradient exceeds a predefined threshold value and marking these pixels as “bad”, performing a line integration over the local phase gradient, thus yielding an integrated phase gradient image, analyzing the integrated phase gradient image for characteristic line artifacts occurring behind pixels of strong phase gradient which have been marked as “bad” and introducing a correction phase offset of 2π radians or an integer multiple thereof at the position of each “bad” pixel if analysis shows that a measured 2π phase offset error or an integer multiple thereof between immediately adjacent line artifacts which is induced by said line integration persists after passing a pixel that has been marked as “bad” so as to compensate said 2π phase offset error or an integer multiple thereof.