Introduction

A considerable development in X-ray imaging techniques has taken place over the last few years at the ESRF. This has associated optimal source characteristics with new detectors and computers. These developments may be characterised using keywords such as "high spatial resolution", "three-dimensional", "coherent beams", "in situ", "real-time", and "combination of techniques". The main aims of the X-ray Imaging Group are to enhance imaging techniques and to apply these techniques to a range of topics, including physical, biomedical, materials and engineering science. New subject areas such as geophysics, the environment, archaeology and biology are constantly appearing.

Three short general papers introduce important aspects of the development of these techniques and their applications. The first highlights the increasing use of microtomography for the investigation of a wide variety of problems. Microtomography provides three-dimensional information and, by making full use of the ESRF's capabilities, can also provide high spatial resolution and quantitative measurement. The second describes how synchrotron radiation is currently being used in state-of-the-art medical applications. The main themes of this research are the combination of imaging for diagnosis with radiation therapy in its various forms coupled with work on small animals. The third paper shows the importance of microanalysis to environmental studies.

These general papers are supported by short illustrative contributions. The in situ visualisation by diffraction imaging (X-ray topography) of the migration of a grain boundary provided the data required to determine the basic characteristics of this process (Polcarova et al.). The high spatial resolution now available in microtomography allowed the investigation of an important but complex problem, the quantification of fatigue crack closure (Khor et al.).

Fiedler et al. present the latest developments at the ESRF of Diffraction Enhanced Imaging (DEI), which could constitute an important diagnostic tool for mammography. The first in vivo assessment of cerebral blood volume and blood flow was made using highly-accurate synchrotron radiation tomography: this new tool to investigate cerebral physiopathology, coupled with radiotherapy, could help to treat brain tumours (Adam et al.).

Microanalysis has been used to study the role of metals in processes leading to neurodegenerative disorders, such as Parkinson's disease (Lankosz et al.), and to extract information about the sulphur-metabolising activities in archeen bacteria, which could give clues about the mechanisms involved in the origin of life (Philippot et al.). Two technical enhancements open new scientific possibilities. First the standing-waves technique coupled with a microbeam permitted the identification of polarity-inverted regions of a GaN film (Drakopoulos et al.) and second, Zernike-type phase contrast was used to improve the possibilities of X-ray microscopy at energies of about 4 keV (Neuhausler et al.).