X-ray phase contrast imaging (XPCI) is an exciting X-ray modality that can capture images that cannot be obtained with conventional radiography. The latter relies on absorption of X-ray photons whereas XPCI is based on a different physical principle: refraction. XPCI uses the phase shift experienced by an electromagnetic wave when it passes through a material. XPCI images provide higher contrast for features in low density materials such as human soft tissues, e.g., breast tissue, and composite materials such as carbon fibre-reinforced polymers. XPCI allows the detection and quantification of features of objects that are invisible in conventional radiography.
XPCI began with the extremely bright X-ray beams produced by large synchrotron radiation sources, such as those at the Diamond Light Source, the UK's national synchrotron science facility, located at the Harwell Science and Innovation Campus in Oxfordshire or the European Synchrotron Radiation Facility (ESRF) in France. Techniques were then developed to allow XPCI to be performed using conventional X-ray sources of the type used in medical and industrial radiography. One such technique is edge illumination XPCI. This achieves a relatively low dose exposure for the object and a relatively large field of view. It uses two masks that produce a structured X-ray beam by blocking part of the beam. The first mask is placed between the object and the X-ray source and the other is placed between the object and the detector and in contact with the detector.
A newly published paper in the Journal of Applied Physics ‘Replacing the detector mask with a structured scintillator in edge-illumination X-ray phase contrast imaging’ presents a proof-of-concept Edge Illumination XPCI system in which the second mask that is normally external to the detector has been replaced by a specially designed indirect conversion X-ray detector with sensitive and insensitive regions obtained by using a custom structured scintillator attached to a fibre optic faceplate. The project was led by Professor Alessandro Olivo from the Department of Medical Physics and Biomedical Engineering at University College London. Ed Bullard of Spectrum Logic was an author on the paper. The proof-of-concept detector was built by filling the apertures of a free-standing grid with fine P43 phosphor (terbium doped Gadolinium oxysulfide Gd2O2S:Tb). The period and aperture of the grid matched those of the detector mask normally used in Edge Illumination XPCI.
The paper presents images acquired with the original edge illumination technique using two masks and images of the same objects taken using the proof-of-concept edge illumination XPCI system. The novel system successfully allowed the visualization of features such as cartilage. Cartilage cannot be imaged using conventional absorption-based radiography and is normally imaged using expensive MRI systems.
The paper shows that edge illumination XPCI using a structured scintillator integrated into a high-resolution X-ray detector holds the potential to image soft tissue. It may even be possible to retrofit conventional X-ray systems for edge illumination XPCI.
For more information about XPCI contact the team at Spectrum Logic
For an overview of XPCI watch this UCL Lunchtime lecture by Prof. Alessandro Olivo: