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Taking x-ray phase contrast imaging into mainstream applications

Event

Starts:

February
112013

09:00

Ends:

February
122013

17:00

Location

The Royal Society, London, 6-9 Carlton House Terrace, London, SW1Y 5AG

Overview

Mouse brain- copyright- F. Pfeiffer et al, Technical University Munich

Scientific discussion meeting organised by Dr Alessandro Olivo and Professor Ian Robinson

Event details

X-ray phase contrast imaging (XPCi) emerged in the mid-90s at synchrotrons, showing potential to revolutionize all applications of x-ray imaging. Recently methods have emerged that could take XPCi out of the synchrotrons and deploy it into hospitals, industries, etc. This meeting brings together the leading experts in the area to discuss what is still needed to achieve this important goal.

Biographies of the organisers and speakers are available below. Recorded audio of the presentations are available by clicking on the names of the speakers below. 

Papers of these talks are now available in Philosophical Transactions A.

Schedule of talks

Organisers and Chairs

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Dr Alberto Bravin, European Synchrotron Radiation Facility (ESRF)

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Dr Alessandro Olivo, University College London, UK

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Professor Ian Robinson, University College London, UK

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Professor Philip Withers, University of Manchester, UK

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Session-1

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Crystal-based methods: from synchrotron to x-ray tube

Dr Zhong Zhong, Brookhaven National Laboratories

Abstract

Crystal-based phase contrast imaging introduces fine selectivity for the angular deviation of x rays traversing the subject. Experiments at the NSLS to investigate Diffraction Enhanced Imaging (DEI), also called Analyzer Based Imaging (ABI) in areas of radiology of clinical relevance, including breast, lung, and cartilage imaging will be introduced. Recent advancement in DEI instrumentation using an x-ray tube as the source of x-rays will be discussed. From the measurement and simulations, it will be argued that DEI with x-ray tube is possible in a clinical setting. DEI is extremely simple both in theory and in practice, making it rewarding to implement DEI for solving scientific and technical problems. The goal as envisioned over a decade ago, only more reachable today, remains the translation of DEI to clinical utilization.

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Development and recent applications of grating-based X-ray phase contrast for biomedical imaging

Professor Franz Pfeiffer, Technischen Universität München

Abstract

The basic principles of x-ray image formation in radiography have remained essentially unchanged since Röntgen first discovered x-rays over a hundred years ago. The conventional approach relies on x-ray attenuation as the sole source of contrast and draws exclusively on ray or geometrical optics to describe and interpret image formation. This approach ignores another, potentially more useful source of contrast, namely the phase information. Phase-contrast imaging techniques, which can be understood using wave optics rather than ray optics, offer ways to augment or complement standard attenuation contrast by incorporating phase information. This presentation will review the recent development of phase-contrast imaging in general, and focus particularly on our contributions to the development of grating-based x-ray phase-contrast computed tomography. A variety of experimental results will be shown that highlight the potential of this novel method for biomedical, clinical, and industrial applications. The presentation concludes with an outlook concerning the translation to pre-clincial and finally clinical practice.

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On the genesis of XPCI – free space propagation and other implementations

Dr Stephen Wilkins, The Commonwealth Scientific and Industrial Research Council (CSIRO)

Abstract

Undoubtedly, the simplest form of X-ray phase-contrast imaging to implement is that based on free-space propagation (i.e. Fresnel diffraction). Such phenomena have been known in the case of conventional light optics (but not necessarily understood) going back to antiquity. In the case of X-rays, the effects of phase contrast appear to have been initially considered a nuisance in the context of X-ray imaging and termed “blurring” or “defocus”. However, more recently, the method of propagation-based X-ray phase-contrast imaging has been exploited with great effect to obtain improved contrast on weakly absorbing features in a wide class of objects, in many cases at high spatial resolution [1-4]. 

The present lecture will briefly outline some of the different modes of X-ray phase-contrast imaging and their specific features, including some of their relative merits. From this more general viewpoint, it will then focus on some of the principal practical outcomes of XPCI to date as well as the prospects for translation to even wider areas of practice in X-ray imaging.

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X-ray phase imaging - from synchrotron to hospital

Professor Atsushi Momose, Tohoku University

Abstract

In 1990s, X-ray phase imaging was extensively studied at synchrotron facilities. Its sensitivity to weakly absorbing objects, such as biological soft tissue and polymers, was excellent, and therefore practical application of X-ray phase imaging was strongly expected especially to medicine. However, the technology available at synchrotron facility limits its usage, and clinical diagnosis with X-ray phase imaging is not straightforward. In order to benefit patients, X-ray phase imaging technology should be realized outside of a synchrotron facility. X-ray grating interferometry developed in 2000s gives us a solution, because it functions with polychromatic cone-beam X-rays. X-ray phase imaging is attainable with a practical exposure time with a conventional X-ray source. I conducted a project to develop clinical machines that can be used by radiologists in hospitals. A system based on X-ray Talbot-Lau interferometer was constructed, aiming at diagnosis of rheumatoid arthritis and breast cancer. The former is now used for patients. The current status of this project will be reported.

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Session-2

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Boosting phase contrast with two-arm interferometers using sub-micron period gratings

Dr Han Wen, National Institute of Health, USA

Abstract

Grating interferometers of very high line density operate in the far field regime, where the incident beam is split into widely separated beams, which are then redirected to coherently interfere with each other. Because of the wide separation of the interfering beams, far field interferometers can provide high levels of phase contrast. They also provide absolute phase images in some cases. We report on imaging experiments using a symmetric three-grating interferometer of 200 nm period, operating at 22.5 keV and 1.5% spectral bandwidth on the 2-BM beamline of APS. The gratings consist of arrays of multi-layer stacks on a staircase substrate, which are fabricated in a thin-film deposition process. Using a slitted incident beam we acquired absolute phase images of lightly absorbing samples. Visible light versions of the interferometer have been shown to work with polychromatic sources. Our future aim is to adapt the method to compact x-ray sources.

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Clinical XPCi-based mammography with synchrotron radiation

Dr Maura Tonutti, Cattinara Hospital, Italy

Abstract

The first clinical study in phase contrast mammography has been completed in Trieste (Italy): the study has involved 71 patients with questionable or suspicious breast abnormalities identified at the hospital by means of standard digital mammography together with ultrasonography. The final results of this study are now available and can be regarded as the starting point of further investigations. Moreover, this first clinical experience was characterized by the use of a screen-film system. As digital detectors with high spatial resolution (pixel size of ∼50μm) have recently become commercially available, they have been considered for future clinical experiments: a second clinical study, which utilizes a computed radiology system on a limited number of patients, has already been undertaken. 
Both qualitative and quantitative (diagnostic) analysis of the results will be presented and the possible role of the XPCi-based mammography will be discussed considering all the new imaging techniques available for breast imaging.

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Medicine, material science and security: the versatility of the coded-aperture approach

Dr Peter Munro, The University of Western Australia

Abstract

The principal limitation to the widespread deployment of X-ray phase imaging in a variety of applications is probably versatility. A versatile X-ray phase imaging system must be able to work with polychromatic and non-microfocus sources such as those currently used in medical and industrial applications, have physical dimensions sufficiently large to accommodate samples of interest, be insensitive to environmental disturbances such as vibrations and temperature variations, require only simple system setup and maintenance and be able to perform quantitative imaging. The coded aperture technique, based upon the edge illumination principle, satisfies each of these criteria. To date we have applied the technique to mammography, materials science, small animal imaging, non-destructive testing and security. In this talk we will outline the theory of coded aperture phase imaging and show several examples of where the technique has been applied to practical problems.

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Phase contrast X-ray imaging in the clinic: a first mammography study

Professor Marco Stampanoni, ETH Zurich, and Paul Scherrer Institut, Switzerland

Abstract

Phase-contrast and scattering-based x-ray imaging are known to provide additional and complementary information to conventional, absorption-based methods. We present the results of a multicenter, international reader study aiming at the evaluation of the clinical relevance of phase contrast mammography. Freshly dissected whole breast specimens of 33 patients with histo-pathologically proven breast cancer were imaged using a Talbot-Lau interferometer equipped with a conventional x- ray tube (40 kVp, 28 keV, 25 mA). Absorption, differential phase and small-angle scattering signals were combined into novel, high-frequency-enhanced radiographic images and compared to digital mammography images. Six expert breast radiologists evaluated clinically relevant parameters such as general image quality, presence of artifacts, and visibility of diagnostic features (i.e. lesion conspicuity and skin infiltration) on a 5-point-scale. The study indicates that phase contrast enhanced mammograms show a better image quality concerning sharpness, lesions delineation, and visibility of microcalcifications, resulting in a general improvement of their clinical relevance.

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Clinical XPCi-based mammography with synchrotron radiation

Professor Renata Longo, University of Trieste

Abstract

The first clinical study in phase contrast mammography has been completed in Trieste (Italy): the study has involved 71 patients with questionable or suspicious breast abnormalities identified at the hospital by means of standard digital mammography together with ultrasonography. The final results of this study are now available and can be regarded as the starting point of further investigations. Moreover, this first clinical experience was characterized by the use of a screen-film system. As digital detectors with high spatial resolution (pixel size of ∼50μm) have recently become commercially available, they have been considered for future clinical experiments: a second clinical study, which utilizes a computed radiology system on a limited number of patients, has already been undertaken. 
Both qualitative and quantitative (diagnostic) analysis of the results will be presented and the possible role of the XPCi-based mammography will be discussed considering all the new imaging techniques available for breast imaging.

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Session-3

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Liquid-metal-jet sources for high-resolution phase-contrast bio-imaging

Professor Hans Hertz, KTH Royal Institute of Technology, Stockholm

Abstract

We have introduced a new anode concept for electron-impact sources, liquid-metal jets. This regenerative anode allows operation of microfocus tubes with an electron-beam power density several orders of magnitude higher than present stationary or rotating anodes. The source has been demonstrated for a wide range of liquid anodes and x-ray emission energies. Present systems rely on room-temperature liquid-metal alloys and typically operate with a 5-20 m spot size in the 10-50 kV range with up to one order of magnitude higher brightness than present state-of-the-art x-ray micro-focus tubes. 

The high brightness makes the source suitable for a wide range of diffraction, scattering, and imaging applications. For bio-imaging, in-line phase contrast with high spatial resolution is of particular interest. Present small-animal imaging applications include high-resolution CT, improved tumour demarcation, and micro-angiography. In the latter we employ CO2-gas as contrast agent and have demonstrated 3D tomography of rat-kidney blood-vessel network and 2D imaging of <8 m diam blood vessels in mouse ear, all at acceptable dose levels.

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Phase contrast imaging with compact plasma based accelerators

Professor Zulfikar Najmudin, Imperial College London

Abstract

Ever increasing developments in x-ray brightness and usability are requested to satiate the demands of novel x-ray imaging techniques. The most sought after properties of these sources include high spatial resolution, high temporal resolution and both spatial and temporal coherence. Optical lasers excel in all of these properties but without the penetration of normal materials that makes x-rays ideal for investigating optically non-transparent materials. 
However high intensity optical lasers can be used produce x-ray beams with many of these sought after properties, and so can be used indirectly for imaging opaque matter. 
In this talk, we discuss methods of generating high quality x-ray beams derived from intense laser sources. In particular, we discuss our work in developing laser driven betatron sources. In this method, a high energy electron beam, similar to those used in conventional light sources, is generated by a high power laser beam but in a fraction of the distance as compared to a conventional accelerator. The same laser driven accelerating structure can also ‘wiggle’ the electrons to produce a bright, ultrashort pulse, collimated synchrotron x-ray beam that can be used for numerous x-ray applications. In particular, we highlight our recent work trialling this source for phase contrast imaging.

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poster session

Poster Session

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Rotating anode X-ray sources and their applications

Dr Joseph Ferrara, Rigaku Woodlands Labs

Abstract

Rigaku is a manufacturer of X-ray sources for the home laboratory and has been responsible for the introduction of many technologies used in such sources, for example the turbomolecular pump and the ferrofluidic vacuum seal. 
In this talk, Dr Ferrara will review the current state-of-the-art in X-ray generation and take a look forward to future technologies for X-ray generation in the home laboratory.

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Session-4

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Clinical boundary conditions for differential phase contrast mammography

Dr Ewald Roessl, Philips Innovative Technologies, Research Laboratories

Abstract

Research in gratings-based differential phase contrast imaging (DPCI) has gained increasing momentum in the past couple of years. First results on the potential clinical benefits of the technique for x-ray mammography are becoming available and indicate improvements in terms of general image quality, the delineation of lesions versus the background tissue, and the visibility of micro-calcifications.  In this talk Dr Roessl will investigate some aspects related to the technical feasibility of DPCI for human x-ray mammography. After a short introduction to state-of-the-art full-field digital mammographic (FFDM) imaging in terms of technical aspects as well as clinical aspects, we put together boundary conditions within which a new DPCI modality would likely need to operate. He will then discuss the implications on system design in a comparative manner for systems with 2D detectors versus slit-scanning systems, stating advantages and disadvantages of the two designs. Finally, focusing on a slit-scan system, he will outline a possible concept for phase-acquisition.

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Investigation of the application of Phase Contrast Imaging using a point X-ray source to industrial Non Destructive Testing (NDT)

Mr Ian Haig, X-Tek, Nikon Metrology

Abstract

X-Tek Systems, a division of Nikon Metrology UK, designs, develops and manufactures microfocus X-ray radiography and CT systems for industrial non-destructive testing. The range of X-ray acceleration voltage of its current standard products is 130kV – 450kV. 

It is widely known that x-ray images can be created using phase contrast formed by the natural propagation of X-ray; results were reported in 1996. The short study which is the subject of this presentation, investigated the practical application of phase contrast imaging in an X-Tek tool which has a point X-ray source and has an acceleration voltage greater than 100kV. The study also included modeling and simulation 

Simulation of the natural propagation of x-ray through a cylindrical test sample predicted a small contrast peak at the boundary between the cylinder material and the air. Comparison data was obtained using a microfocus X-ray source with acceleration voltage above 100kV. The simulation results correlated well with the experimental data. A further practical example in which we detected intensity variation including the effect of phase contrast in the >100kV operating region is introduced and discussed 

In summary, phase contrast was observed in the radiographic images from a standard point X-ray source with acceleration voltages exceeding 100kV.

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Is clinical grating-based CT possible?

Dr Rainer Raupach, Siemens Healthcare

Abstract

The phase information provided by phase contrast CT (PCT) represents the local electron density which can also be obtained by multi-energy absorption measurements. In this sense, PCT visualizes material properties that are already accessible but based on an alternative physical effect and measurement principle. 
Standard CT and PCT show fundamentally different noise propagation implicating that spatial resolution plays an essential role. A clinically meaningful comparison has to evaluate the imaging performance per radiation dose. PCT outperforms CT only at high spatial resolution. The break-even spatial resolution at available x-ray source coherence of compact PCT setups is significantly higher than typically used in CT. The dose necessary in order to achieve a required CT contrast-to-noise ratio scales with resolution to the power of four. Although a relative advantage of PCT can be realized it will necessarily be related to increased radiation dose. PCT will not be beneficial for clinical CT as long as compact sources with much better spatial coherence are routinely available.

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Investigation of the application of Phase Contrast Imaging using a point X-ray source to industrial Non Destructive Testing (NDT)

Mr Kazuaki Suzuki, Nikon Metrology

Abstract

X-Tek Systems, a division of Nikon Metrology UK, designs, develops and manufactures microfocus X-ray radiography and CT systems for industrial non-destructive testing. The range of X-ray acceleration voltage of its current standard products is 130kV – 450kV. 

It is widely known that x-ray images can be created using phase contrast formed by the natural propagation of X-ray; results were reported in 1996. The short study which is the subject of this presentation, investigated the practical application of phase contrast imaging in an X-Tek tool which has a point X-ray source and has an acceleration voltage greater than 100kV. The study also included modeling and simulation 

Simulation of the natural propagation of x-ray through a cylindrical test sample predicted a small contrast peak at the boundary between the cylinder material and the air. Comparison data was obtained using a microfocus X-ray source with acceleration voltage above 100kV. The simulation results correlated well with the experimental data. A further practical example in which we detected intensity variation including the effect of phase contrast in the >100kV operating region is introduced and discussed 

In summary, phase contrast was observed in the radiographic images from a standard point X-ray source with acceleration voltages exceeding 100kV.

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Phase demodulation methods for two-dimensional grating-based X-ray interferometry

Dr Kentaro Nagai, Canon Inc

Abstract

We present two new high spatial resolution approaches to the demodulation of images produced by a two-dimensional X-ray Talbot Imaging (2D XTI) system. Demodulation of XTI images is currently achieved either by phase stepping (PS) or Fourier transform (FT) methods. 
However, the PS method for 2D XTI requires more complicated control process than that of one-dimensional XTI. On the other hand, the FT method achieves lower spatial resolution than the PS method. For practical application of 2D XTI, a simpler exposure process with high spatial resolution is required. The first approach described is a hybrid of the PS method and the FT method. The exposure process is simpler than PS while the spatial resolution of the demodulated images is improved. 
The second approach is a spectral analysis process using a windowed Fourier transform. The process improves the spatial resolution of the FT method by isolating the required spectral term from other information carrying terms. The demonstration test results show that these proposed methods can achieve high spatial resolution for both the x- and y- differential phase components.

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Taking x-ray phase contrast imaging into mainstream applications The Royal Society, London 6-9 Carlton House Terrace London SW1Y 5AG UK