Reducing Artifacts in X-Ray Interferometry using Multiple Harmonics

X-ray interferometry is a promising medical imaging modality because of its ability to simultaneously measure absorption, scatter, and refraction to produce attenuation, dark-field, and differential-phase images in a single scan. A modulated phase grating can be used to create a fringe pattern that is directly resolvable without the need for an analyzer grating. The three images are produced by analyzing phase stepping curves acquired with and without the object in place. Using an established method, we fit sinusoidal parameters to the phase stepping curves on a pixel-by-pixel basis. Currently, only one harmonic has been used in making the images, but the fringe pattern is rarely sinusoidal and has multiple harmonic components. This can negatively affect the quality of dark-field images by increasing the presence of artifacts. By considering the second harmonic we can fit more sinusoidal parameters to the phase stepping curve resulting in an image with less artifacts. We present qualitative and quantitative comparisons of images created using multiple harmonics with those created using only one harmonic. Analysis will be performed on images of PMMA, which serves as a lung tissue analogue for dark-field imaging.