C Jeanguillaume

Electron energy loss spectrometry mapping

Among electron beam microanalytical techniques, electron energy loss spectrometry (EELS) offers unique advantages in terms of information content, sensitivity, limits of detection. This paper describes new methods and tools for acquiring families of spectra over many pixels on the specimen, i.e. spectrumimages, and for processing them. Applications in different fields of research, both in materials science and in life sciences, demonstrate the potential impact of the technique for characterizing nano-sized structures.

Unconventional modes for STEM imaging of biological structures.

In this paper recent developments are discussed in instrumentation and methodology associated with scanning transmission electron microscopes (STEM), which are of great potential interest for solving structural and chemical problems in biological specimens. After describing the main features of the instrument, an attempt is made to define which type of signal acquisition and processing is best suited to obtain a given type of information. Starting with a definition of cross sections of interest, a discussion follows of methods using angular selection, energy selection of the transmitted beam, and several ways of signal mixing. More specific attention is devoted to two main modes of processing signals: ratio contrast, which emphasizes slight changes in scattering factors, rather independent of thickness variations; and elemental mapping, which provides semi-quantitative information on the distribution of low Z elements of great significance in biological specimens. Data relevant to typical biological objects are presented and discussed; they allow for the definition of the capabilities and limitations of these methods. These unconventional imaging modes define a new attitude for improving the efficiency of this modern generation of electron microscopes.

Emission tomography with a large-hole collimator (CACAO): a possible new way to improve radionuclide imaging.

This work aims to improve the quality of scintigraphy. It evaluates the use of a large-hole collimator, the Computer Aided Collimation Gamma Camera Project (CACAO), in SPECT. Acquisition data from the same object were simulated for CACAO and for a conventional collimator. Better signal-to-noise ratios were found for CACAO images, whatever the number of emitted photons. This work demonstrates that high-resolution images may be obtained with large-hole collimators. The combination of CACAO and pixilated detectors may further improve radionuclide imaging.

2001 IEEE Nuclear Science Symposium Conference Record

Pixellated detectors are a fast growing area of research. However performances of such detectors will be spoiled by the poor figures of conventional collimators. The computer aided collimation gamma camera (CACAO) is a new collimation possibility for emission tomography. The CACAO system uses large hole collimator aimed at increasing the sensitivity. This article studies the possible advantages of coupling the CACAO project with pixellated detectors. Simulations of images reconstruction seem to confirm the synergistic advantages of both techniques.

CACAO a collimation means well suited for pixellated γ-camera

Pixellated detectors are a fast growing area of research. However performances of such detectors will be spoiled by the poor figures of conventional collimators. The computer aided collimation gamma camera (CACAO) is a new collimation possibility for emission tomography. The CACAO system uses large hole collimator aimed at increasing the sensitivity. This article studies the possible advantages of coupling the CACAO project with pixellated detectors. Simulations of images reconstruction seem to confirm the synergistic advantages of both techniques.

Progress in Electron Energy Loss Spectroscopic Imaging and Analysing Biological Specimens with a Field Emission Scanning Transmission Electron Microscope

A major problem raised in electron microscopy imaging and analytical studies on biological sections is the conflict between high dose requirements for getting useful signal/noise values on the different channels of information and low dose requirements for beam damage reduction. Among various solutions, our approach consists in developing a strategy which optimize the signal extraction associated to the scattering process suffered by any primary electron. The basic design of the Scanning Transmission Electron Microscope (STEM) is well adapted because it is possible, for each probe position on the specimen, to filter and simultaneously record different fractions of the transmitted beam, discriminated in scattering angle with a set of variable apertures and in energy loss with an EELS spectrometer. Electron energy loss spectroscopy constitutes then a basic component of the microscope as pointed out as early as 20 years ago by Crewe (1966). It can be used fruitfully either as a contrast-enhancement device or as a real analytical tool for chemical microanalysis, depending on the recorded fraction of the EELS spectrum. In a previous publication (Colliex et al. (1984)), we had described unconventional modes for STEM imaging of biological structures. The present paper intends to update it, covering two specific aspects: novel imaging methods and analytical microscopy. The basic methodology has not changed noticeably but the concomitant progress in detection design and in data read-out and processing have enlarged the field of applications and improved the limits of detection by at least an order of magnitude.

A fast algorithm for computer aided collimation gamma camera (CACAO)

The computer aided collimation gamma camera is aimed at breaking down the resolution sensitivity trade-off of the conventional parallel hole collimator. It uses larger and longer holes, having an added linear movement at the acquisition sequence. A dedicated algorithm including shift and sum, deconvolution, parabolic filtering and rotation is described. Examples of reconstruction are given. This work shows that a simple and fast algorithm, based on a diagonal dominant approximation of the problem can be derived. Its gives a practical solution to the CACAO reconstruction problem.

CACAO a collimation means well suited for pixellated /spl gamma/-camera

Pixellated detectors are a fast growing area of research. However performances of such detectors will be spoiled by the poor figures of conventional collimators. The computer aided collimation gamma camera (CACAO) is a new collimation possibility for emission tomography. The CACAO system uses large hole collimator aimed at increasing the sensitivity. This article studies the possible advantages of coupling the CACAO project with pixellated detectors. Simulations of images reconstruction seem to confirm the synergistic advantages of both techniques.