Comparison of propagation- and grating-based x-ray phase-contrast imaging techniques with a liquid-metal-jet source T. Zhou * a , U. Lundström a , T. Thüring b,c , S. Rutishauser b,c , D. H. Larsson a , M. Stampanoni b,c , C. David b , H. M. Hertz a , and A. Burvall a a Biomedical and X-ray Physics, KTH Royal Institute of Technology, Albanova, SE-10691, Stockholm, Sweden; b Paul Scherrer Institut, Villigen PSI, Switzerland; c Institute for Biomedical Engineering, Swiss Federal Institute of Technology, Zurich, Switzerland ABSTRACT X-ray phase-contrast imaging has been developed as an alternative to conventional absorption imaging, partly for its dose advantage over absorption imaging at high resolution. Grating-based imaging (GBI) and propagation-based imaging (PBI) are two phase-contrast techniques used with polychromatic laboratory sources. We compare the two methods by experiments and simulations with respect to required dose. A simulation method based on the projection approximation is designed and verified with experiments. A comparison based on simulations of the doses required for detection of an object with respect to its diameter is presented, showing that for monochromatic radiation, there is a dose advantage for PBI for small features but an advantage for GBI at larger features. However, GBI suffers more from the introduction of polychromatic radiation, in this case so much that PBI gives lower dose for all investigated feature sizes. Furthermore, we present and compare experimental images of biomedical samples. While those support the dose advantage of PBI, they also highlight the GBI advantage of quantitative reconstruction of multimaterial samples. For all experiments a liquid-metal-jet source was used. Liquid-metal-jet sources are a promising option for laboratory-based phase-contrast imaging due to the relatively high brightness and small spot size. Keywords: X-ray imaging, phase-contrast, propagation-based, grating-based 1. INTRODUCTION 1.1 Phase-contrast methods Conventional x-ray imaging registers the attenuation of the intensity after passage through an object. This attenuation is primarily caused by absorption in the object, and usually called absorption imaging. Phase-contrast imaging, on the other hand, utilizes the phase information which can be orders of magnitudes more sensitive than absorption information for some materials such as soft tissue. There are different methods of phase-contrast imaging, among which the propagation- and the grating-based methods are discussed and compared here. PBI utilizes the propagation of the wavefront in free space and obtains the phase information as the edge enhancements [1]. GBI uses a Talbot grating interferometer and captures a series of images when the two gratings are at different relative positions of each other [2]. Source gratings are used when using an extended source [3]. The variance of the intensities of each pixel can be approximately analyzed with Fourier series, from which absorption, phase and scattering information can be obtained simultaneously [4]. Image quality has been studied in different ways for GBI differential phase contrast (DPC) images [5-13]. Comparisons with absorption imaging [14, 15] show that GBI and PBI give higher SNR at higher spatial resolution while absorption imaging gives higher SNR at lower spatial resolution. Here we compare PBI and GBI to each other in a direct way with respect to dose [16], which is an important issue for medical imaging, to investigate the detectability of the two methods for different object feature sizes. 1.2 Liquid-metal-jet source PBI and GBI both have the advantages of robust experimental arrangements and good compatibility with polychromatic sources, which are needed for more practical applications. If aiming at small-animal imaging with high resolution, a microfocus source would be needed. For the sake of better dose efficiency, a larger source-to-object distance would be preferred, if keeping the same magnification. For a microfocus source which has relatively low flux compared to other sources such as synchrotron radiation sources, a larger distance can lead to a much longer exposure time to obtain good Medical Imaging 2014: Physics of Medical Imaging, edited by Bruce R. Whiting, Christoph Hoeschen, Despina Kontos, Proc. of SPIE Vol. 9033, 903353 · © 2014 SPIE · CCC code: 1605-7422/14/$18 · doi: 10.1117/12.2043417 Proc. of SPIE Vol. 9033 903353-1 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 19 Apr 2019 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use