Multiple-beam X-ray interferometry for phase-contrast microtomography.

The first successful operation of an X-ray interferometer under conditions of non-planar three-beam diffraction for phase-contrast X-ray microtomography is reported. Intrinsic phase differences of the reflections used cancel from the three-dimensional phase image of the specimen. With simultaneous hkl and hkl reflections of a synchrotron radiation beam in a side-by-side geometry, the size of the usable field of view is doubled and the investigated specimen volume is increased by a factor of four. As an example, the reconstructed slice of a mouse kidney is shown in phase contrast at 71 keV. Optimized choices of three-beam reflections and matching interferometer geometries useful for applications are presented.

Three-dimensional imaging of nerve tissue by x-ray phase-contrast microtomography.

We show that promising information about the three-dimensional (3D) structure of a peripheral nerve can be obtained by x-ray phase-contrast microtomography (p-microCT; Beckmann, F., U. Bonse, F. Busch, and O. Günnewig, 1997. J. Comp. Assist. Tomogr. 21:539-553). P-microCT measures electronic charge density, which for most substances is proportional to mass density in fairly good approximation. The true point-by-point variation of density is thus determined in 3D at presently 1 mg/cm3 standard error (SE). The intracranial part of the rat trigeminal nerve analyzed for the presence of early schwannoma "microtumors" displayed a detailed density structure on p-microCT density maps. The average density of brain and nerve tissue was measured to range from 0.990 to 0.994 g/cm3 and from 1.020 to 1.035 g/cm3, respectively. The brain-nerve interface was well delineated. Within the nerve tissue, a pattern of nerve fibers could be seen that followed the nerve axis and contrasted against the bulk by 7 to 10 mg/cm3 density modulation. Based on the fact that regions of tumor growth have an increased number density of cell nuclei, and hence of the higher z element phosphorus, it may become possible to detect very early neural "microtumors" through increases of average density on the order of 10 to 15 mg/cm3 by using this method.

X-ray microtomography (microCT) using phase contrast for the investigation of organic matter.

PURPOSE: We show that microtomography (microCT) using synchrotron radiation (SR) can be extended to include X-ray phase contrast, which is two to three orders of magnitude more sensitive than conventional attenuation contrast and better suited for the investigation of specimens consisting chiefly of light elements for photon energies ranging at least from 1 to 100 keV. METHOD: Phase contrast is generated by placing the specimen in one of the interfering beams of an X-ray interferometer. With use of 12-keV X-rays, phase projections of the specimen are recorded at 180 or 360 angular settings equally spaced between 0 and 180 degrees. One phase projection consists of four pairs of "associated" radiograms in the sense that one is taken with and the other without the specimen in the beam. Between pairs a parallel-sided phase-shifter plate is rotated for changing the relative phase of the two interfering beams by multiples of pi/2 rad. By calculating phase-weighted sums of all associated pairs of radiograms, true phase-shift projections are obtained for all angular settings of the specimen, which are then reconstructed. RESULTS: Three-dimensional images have been obtained from rat cerebrum and rat trigeminal nerve, showing cell structures at 8- to 15-micron spatial resolution. Gray and white matter of cerebrum and neurons in the trigeminal nerve are clearly visible. CONCLUSION: X-ray phase-contrast microCT is becoming a valuable tool for studies of organic samples in medicine and biology.

[New possibilities for structural analysis of bone biopsies using microcomputer tomography (muCT)]. / Neue Möglichkeiten der Strukturanalyse von Knochenbiopsien bei Anwendung der Mikrocomputertomographie (muCT).

The combined histological and microcomputed analysis of human iliac crest biopsies leads to major advances in our understanding of three-dimensional bone architecture. Microcomputed tomography avoids the time-consuming reconstruction and artifacts of serial sections. Furthermore, its high resolution allows the recording of structural differences as low as 10 microns. Thus, three-dimensional analysis in combination with histological evaluation of cellular dynamics facilitates earlier and easier recording of changes of cancellous bone.

A crystal camera for ultra-small-angle x-ray scattering using synchrotron radiation.

We describe a novel USAXS camera that combines the use of synchrotron radiation with collimation by perfect-crystal optics. The outstanding result is that high measuring intensities and extreme angular resolution are achieved even with a point-focusing geometry. Along the principles of the original design (U. Bonse and M. Hart, Z. Phys. 189, 151 (1966)) which had to be operated at an x-ray tube, we employ two sets of pairs of multiply reflecting channel-cut crystals diffracting in the horizontal and vertical planes. The collimation characteristics thus obtained are equivalent to the point-focusing geometry of conventional SAXS cameras based on slit collimation. We present results from samples of polystyrene spheres which were used for test measurements performed with synchrotron radiation of DORIS at HASYLAB/DESY in Hamburg. Taking into account the number of reflections within the channel-cut crystals, the theoretical resolution was calculated and found to agree well with that derived from measured scattering patterns. Structures as large as about 1.3 µm could easily be identified from the scattering curves. As expected with point-focusing geometry, desmearing of raw data was unnecessary.

3D computed X-ray tomography of human cancellous bone at 8 microns spatial and 10(-4) energy resolution.

Human cancellous bone was imaged and its absorptive density accurately measured in three dimensions (3D), nondestructively and at high spatial resolution by means of computerized microtomography (microCT). Essential for achieving the resolution and accuracy was the use of monoenergetic synchrotron radiation (SR) which avoided beam hardening effects, secured excellent contrast conditions including the option of energy-modulated contrast, and yet provided high intensity. To verify the resolution, we selected objects of approximately 8 micron size that could be observed on tomograms and correlated them in a unique manner to their counter images seen in histological sections prepared from the same specimen volume. Thus we have shown that the resolution expected from the voxel size of 8 microns used in the microCT process is in effect also attained in our results. In achieving the present results no X-ray-optical magnification was used. From microCT studies of composites (Bonse et al., X-ray tomographic microscopy (XTM) applied to carbon-fibre composites. In: Materlik G, ed. HASYLAB Jahresbericht 1990. Hamburg: DESY, 1990; 567-568) we know that by including X-ray magnification a resolution below 2 microns is obtained. Therefore, with foreseeable development of our microCT method, the 3D and nondestructive investigation of structures in mineralized bone on the 2 micron level is feasible. For example, it should be possible to study tomographically the 3D distribution and amount of osteoclastic resorption in the surrounding bone structure.

Scanning interferometer for the measurement of anomalous dispersion with synchrotron x rays.

We describe an x-ray interferometer optimized for operation with synchrotron radiation at the storage ring DORIS at DESY, Hamburg. Function principles, design, and manufacture are discussed. Interference fringes are created by scanning the analyzer crystal of the instrument in increments below 0.1 Å. Special attention is paid to minimize warping due to gravitational forces and disturbances from acoustic noise and ground vibration. The characteristics of two different monochromators with respect to harmonic rejection or harmonic selection and beam stability are considered. The instrument is best suited to the measurement of anomalous dispersion, for which an example is given.