A LABORATORY-BASED X-RAY PHASE CONTRAST IMAGING SCANNER WITH APPLICATIONS IN BIOMEDICAL AND NON-MEDICAL DISCIPLINES

C K Hagen,D A Olivo,R Speller,M Endrizzi,P R T Munro,M B Szafraniec,P C Diemoz,T P Millard

doi:10.1142/s2010194514601501

Abstract

X-ray phase contrast imaging (XPCi) provides a much higher visibility of low-absorbing details than conventional, attenuation-based radiography. This is due to the fact that image contrast is determined by the unit decrement of the real part of the complex refractive index of an object rather than by its imaginary part (the absorption coefficient), which can be up to 1000 times larger for energies in the X-ray regime. This finds applications in many areas, including medicine, biology, material testing, and homeland security. Until lately, XPCi has been restricted to synchrotron facilities due to its demanding coherence requirements on the radiation source. However, edge illumination XPCi, first developed by one of the authors at the ELETTRA Synchrotron in Italy, substantially relaxes these requirements and therefore provides options to overcome this problem. Our group has built a prototype scanner that adapts the edge-illumination concept to standard laboratory conditions and extends it to large fields of view. This is based on X-ray sources and detectors available off the shelf, and its use has led to impressive results in mammography, cartilage imaging, testing of composite materials and security inspection. This article presents the method and the scanner prototype, and reviews its applications in selected biomedical and non-medical disciplines.

Highlights

When X-rays traverse an object, they experience absorption and a phase shift that, if spatially non-uniform, translates into a slight deviation from their original path. This can be expressed by characterizing objects through their complex refractive index: This is an Open Access article published by World Scientific Publishing Company
The imaginary part β in Eq (1) is directly proportional to the attenuation coefficient and drives the corresponding effect, while the decrement from unity of its real part δ is responsible for phase effects such as refraction
Within the energy range of X-rays used in biomedical applications, the refractive index decrement of an object can be up to three orders of magnitude larger than its absorption term

Summary

Introduction

When X-rays traverse an object, they experience absorption and a phase shift that, if spatially non-uniform, translates into a slight deviation from their original path. The focus of research has been on developing methods that can make XPCi compatible with conventional X-ray sources and detectors, as this is the first step towards a transfer into laboratory environments and eventually into clinical practice One such approach is Talbot (“grating”) interferometry,[4] a technique making use of the Talbot self-imaging effect. This article describes a different XPCi method that is compatible with conventional X-ray equipment It originates from synchrotron experiments carried out at the SYRMEP (synchrotron radiation for medical physics) beamline at ELETTRA (Trieste, Italy) in the late nineties, in which a vertically narrow beam was aligned with the edge of a single row of detector pixels rather than with the pixel center (see Fig. 1a)). Based on the above concepts, a CA XPCi scanner prototype has been built and is fully operational in the radiation physics laboratories at UCL

Materials and Methods

Results and Discussion

Conclusions