Flexible Retrospective Phase Stepping in X-Ray Scatter Correction and Phase Contrast Imaging Using Structured Illumination

Han Wen,Nick M Adamo,Lei Chen,Houxun Miao,Eric E Bennett,Ge Wang

doi:10.1371/journal.pone.0078276

Abstract

The development of phase contrast methods for diagnostic x-ray imaging is inspired by the potential of seeing the internal structures of the human body without the need to deposit any harmful radiation. An efficient class of x-ray phase contrast imaging and scatter correction methods share the idea of using structured illumination in the form of a periodic fringe pattern created with gratings or grids. They measure the scatter and distortion of the x-ray wavefront through the attenuation and deformation of the fringe pattern via a phase stepping process. Phase stepping describes image acquisition at regular phase intervals by shifting a grating in uniform steps. However, in practical conditions the actual phase intervals can vary from step to step and also spatially. Particularly with the advent of electromagnetic phase stepping without physical movement of a grating, the phase intervals are dependent upon the focal plane of interest. We describe a demodulation algorithm for phase stepping at arbitrary and position-dependent (APD) phase intervals without assuming a priori knowledge of the phase steps. The algorithm retrospectively determines the spatial distribution of the phase intervals by a Fourier transform method. With this ability, grating-based x-ray imaging becomes more adaptable and robust for broader applications.

Highlights

X-ray phase contrast imaging and scatter correction are both being developed for the benefit of medical diagnosis, where x-ray modalities account for 70% of the diagnostic imaging procedures in the US [1]
We demonstrate its use in x-ray phase contrast imaging of biological samples using electromagnetic phase stepping
By introducing a high-spatial-frequency modulation into the propagating wave of an x-ray imaging system using grids or gratings, both the scattering and refraction of the wave can be quantified at the full resolution of the detector through the phase stepping procedure

Summary

Introduction

X-ray phase contrast imaging and scatter correction are both being developed for the benefit of medical diagnosis, where x-ray modalities account for 70% of the diagnostic imaging procedures in the US [1]. Phase contrast relates to the distortion of the periodic fringes by refractive bending of the x-rays in the imaged object, while scattering in the object causes a loss of the fringe amplitudes in excess of the conventional intensity attenuation [5,7]. The quickest method requires just a single image, where the phase value is measured by the displacement of the fringes, and the amplitude is measured by the intensity oscillation in a fringe period. Such measurements can be made efficiently over the entire image through Fourier analysis [5,8,9], or directly in the real space [10]. A limitation of single image analysis is that the spatial resolution of the measurements is no finer than the fringe period, which is at least 3 times the resolution of the imaging device in order for the fringes to be clearly resolved

Methods

Results

Conclusion