X-ray imaging

A method of aligning at least one mask in an X-ray imaging apparatus in at least one translational and/or rotational direction of the at least one mask, the mask having a plurality of apertures, the method including:

• (a) directing X-rays from a source (2) in a z-direction through the mask to the X-ray detector orientated perpendicularly to the X-rays, the X-ray detector having pixels arranged in an x-direction and in a perpendicular y-direction;
• (b) for each of a plurality of potential alignment positions in at least one of the translational and/or rotational directions, translating the mask in the x- or y-direction with respect to the X-ray detector to a plurality of translational position increments, identifying for pixels in the detector the translational position increment corresponding to an extremum of the detected intensity profile for that pixel, and hence identifying steps in a predetermined function which separates the regions of the detector that have the same position of the extremum for all pixels in that area;
• (c) selecting the alignment position in which the steps in the identified translational position increment over the two-dimensional area of the pixel detector are minimised and/or aligned with the x- and y-directions, and
• (d) moving the mask to the selected alignment position.