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

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.

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.

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.

X-ray phase-contrast microCT is becoming a valuable tool for studies of organic samples in medicine and biology.