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Phase contrast imaging core
Core Director: Prof. Giorgio Margaritondo
Since the discovery of x-rays over one century ago, radiology is one of the major research and diagnostics techniques for materials science, the life sciences and medical applications. Until recently, however, it was only based on the absorption of x-rays by the specimen, that is very weak: this makes it possible to explore the inside of the object but at the same time limits the contrast. It is well known, for example, that this limitation has an important impact on issues such as the mass screening of the population for breast cancer or cardiovascular diseases.
The advanced x-ray sources based on synchrotron radiation - such as the Swiss Light Source (SLS) at the Paul-Scherrer Institute (PSI) in Villigen - change this picture by producing x-rays with a high level of spatial coherence. This opens the way to radiology based on refraction, diffraction and other phase-related phenomena characterized by the refractive index. The results are quite spectacular: radiology was extended to the microscopic scale (space resolution better than 1 micron) with real-time monitoring (below 1 millisecond) and excellent image/movie quality, without contrast agents. This approach is already used to solve a variety of problems in the life sciences and in materials science.
Our team was involved in phase contrast imaging research since the very beginning of this domain, approximately ten years ago. It produced some of the key results such as simple theoretical models to assess the necessary levels of space and time coherence, the first images on live specimens, the first images at the cellular and subcellular level, the first applications to angiography without contrast agents and several others. We are also actively involved in the development of the tomographic mode of this technique, with reconstruction of sophisticated three-dimensional images on the microscopic scale and in real time.
The objectives of this core are to improve the characteristics of the techniques and of the corresponding instrumentation as well as to test the results for practical experiments. More specifically, we are developing - in collaboration with the team of PSI led by Dr. Marco Stampanoni - a beamline at SLS exclusively dedicated to microradiology and microtomography, with the capability to perform quantitative analysis. The beamline, called "TOMCAT", is in advanced state -- and will be available for experiments and tests to all members of the CIBM and of the Swiss and international research community in general.
In addition to the partnership with PSI, our phase contrast research is also conducted in cooperation with colleagues from Taiwan, Korea, Singapore, the USA and Italy. We participate to the Korean-Swiss-Taiwanese beamline at the Pohang Accelerator Laboratory of POSTECH in Korea, enhancing our experimental capabilities with access to very advanced instrumentation. In Taiwan, we have access to one of the top systems in the world for microradiology and x-ray microscopy in general, at the Synchrotron Radiation Research Center of Hsinchu. All these facilities are also routinely used for collaboration porograms involving other members of CIBM.
The medium-term objectives of our efforts are to push to new limits the time and space resolution, to improve the performances of microtomography, to couple synchrotron-radiation-assisted nanofabrication (both for the life sciences and for materials science) and characterization of the products with phase contrast radiology. In the long term, the objective is diagnostics for human patients in domains like angiography and microangiography.
The figure on the right illustrates one of our results: different microtomographic reconstructions of the head of a fly.
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