Super-resolution X-ray imaging with hybrid pixel detectors using electromagnetic source stepping

Abstract

With increasing demand for high-resolution X-ray images, the super-resolution method allows to estimate a single high-resolution image from several low-resolution images. Hybrid pixel detectors provide high-quality and low-resolution images, which makes them particularly well suited for super-resolution. However, such detectors consist of a limited number of pixels at high cost. Applying super-resolution with hybrid pixel detectors shows that it is a viable method to obtain high-resolution images. The point-spread function of such detectors can be idealised to be 1 pixel, adding no blur into the image making such detectors the ideal choice for the application of super-resolution X-ray imaging. However, there are charge sharing effects between the pixels caused by the energy and impact position of incoming photons. Utilising an X-ray source, which allows magnetic stepping of the X-ray spot, several slightly shifted images can be obtained without requiring mechanical movements. Registering the shifts between individual images with sub-pixel precision allows to estimate a high-resolution image. With repeatable and equally spaced X-ray spot position patterns, sufficient information can be obtained with only a few images. In this paper, we present the application of super-resolution for X-ray imaging using a Pilatus 100K hybrid pixel detector from Dectris Ltd. and a prototype micro-focus X-ray source from Excillum AB. Moreover, we analyse the image quality for applications in X-ray radiography and tomography. Using a sufficient number of low-resolution images allows us to achieve an increase in resolution, without introducing significant blur or artefacts into the image. Here we quantify the effects on the quality of resulting super-resolution images using different methods of image interpolation, interpolation factors, shifts of the sample on the detector, and amount of low-resolution images.