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X-ray imaging techniques at the best spatial resolution and using synchrotron facilities are put forth as powerful techniques for the search of small life forms in extraterrestrial rocks under quarantine conditions. Absorption and fluorescence X-ray microtomographies on sub-millimeter silicate assemblages inside a container reveal the mineralogical microenvironments were life should be looked for in priority. Limitations with respect to bacterial detection are due to the difficulties to obtain information about light elements (Z less than or equal to 14), major constituents of biological and silicate samples. The X-ray signature of a "present" bacteria on a silicate surface was defined by X-ray mapping, out of a container, as coincident micrometer and oval zones having strong P and S fluorescence lines (S-fluorescence being slightly lower than P-fluorescence) and an amino-linked sulfur redox speciation. The detection of a single cell along with new procedures to calculate tomographic views will allow considerable improvements of 3D detection of life by X-ray techniques.

The goal of this work is to present the current state of the X-ray Fluorescence Computed Microtomography. The advantages of both the experimental techniques and the data processing (the ESRF ID22 beamline facilities [1]) are considered. The latter one includes the spectra treatment, reconstruction of the atomic density distribution function of the element under consideration and/or calculation of the element effective concentration map and calculation of the element ratio maps. Possible ways of estimating the space resolution and the accuracy are discussed. Results of the tomographic investigation of the NWA817 meteorite micro-grain are presented.

The combination of synchrotron-based X-ray absorption and fluorescence computed tomographies (CT) is a new method allowing a noninvasive and nondestructive determination of the three-dimensional (3D) mineralogy with micrometer resolution of sub-millimeter silicate grains, possibly stored in a silica holder. These CT were performed with beams of a few tens of keV from a third-generation synchrotron source on one olivine grain of the NWA817 Martian meteorite presenting a reddish alteration phase. The reconstructed sections show a network of fractures and a few micrometer-thick layers formed on one grain. The 3D facet orientation and the X-ray attenuation coefficient indicate that this grain is an Fo(44+/-9) olivine crystal. The fluorescence section reveals rims enriched in Fe (a major element) or depleted in Ca (a minor element). This CT combination shows that the micrometer-thick layer is preferentially formed on the (010) olivine face and has a lower density (3.5 +/- 0.4 g/cm(3)) than the olivine, even though it is enriched in Fe. Its complex nano-petrography and the distributions of nanometer-sized voids and fractures in such a micrometer thick layer, first observed by scanning electron microscopy on focused ion-beam cuts, is not shown by CT. The precision presently achieved, although moderate, is sufficient to obtain a 3D semi-quantitative view of the mineralogy consistent with the one previously established by electron probe microanalyses (Sautter et al. 2002).

A crucial issue in the development of therapies to treat pathologies of the central nervous system is represented by the availability of non-invasive methods to study the threedimensional morphology of spinal cord, with a resolution able to characterize its complex vascular and neuronal organization. X-ray phase contrast micro-tomography enables a highquality, 3D visualization of both the vascular and neuronal network simultaneously without the need of contrast agents, destructive sample preparations or sectioning. Until now, high resolution investigations of the post-mortem spinal cord in murine models have mostly been performed in spinal cords removed from the spinal canal. We present here post-mortem phase contrast micro-tomography images reconstructed using advanced computational tools to obtain high-resolution and high-contrast 3D images of the fixed spinal cord without removing the bones and preserving the richness of micro-details available when measuring exposed spinal cords. We believe that it represents a significant step toward the in-vivo application. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement