A research group led by Professor F. Pfeiffer (Technische Universitat Munchen, Germany) has recently reported an extremely powerful combination of X-ray tomography and ptychographic coherent imaging, which enables quantitative phase-contrast X-ray microscopy without any lenses. A refractive index in the X-ray region is usually expressed as n = 1 - d - iβ, where d and β are real and imaginary parts, and relate to the phase shift and the attenuation, respectively. The researchers developed a new method to give a 3D image of d rather than β, because d can give much higher visibility in samples based on low-Z elements, which are most likely in bio-medical applications. So far, phase-contrast X-ray imaging has had limitations in giving such quantitative information. The use of coherent X-ray diffraction is one of the most promising solutions, and ptychography is a further extension that enhances precision in recovering the phase by introducing scanning of the sample. As the spatial resolution of the computed images is no longer limited by the quality or resolving power of a lens, just a pinhole was used in the present research. By combining such image reconstruction to obtain nano-scale 2D images with other image processing based on a back-filtered projection algorithm, they have succeeded in obtaining 3D images on the 100 nm scale of bone structures such as the osteocyte lacunae and the interconnective canalicular network. The experiments were done at X12SA beamline, Swiss Light Source. For more information, see the paper, "Ptychographic X-ray computed tomography at the nanoscale", M. Dierolf et al., Nature, 467, 436 (2010). In the same issue, there is an instructive account, "A new phase for X-ray imaging", H. N. Chapman, Nature, 467, 409 (2010). For the details of ptychography, see the paper, "The Theory of Super-Resolution Electron Microscopy Via Wigner-Distribution Deconvolution", J. M. Rodenburg and R. H. T. Bates, Phil. Trans. Roy. Soc. (London) A339, 521 (1992).
