X-RAY MICROTOMOGRAPHY (MU-CT) USING PHASE-CONTRAST FOR THE INVESTIGATION OF ORGANIC-MATTER

Purpose: We show that microtomography (mu CT) using synchrotron radiat ion (SR) can be extended to include X-ray phase contrast, which is two to three orders of magnitude more sensitive than conventional attenua tion contrast and better suited for the investigation of specimens con sisting 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 recor ded at 180 or 360 angular settings equally spaced between 0 and 180 de grees. One phase projection consists of four pairs of ''associated'' r adiograms in the sense that one is taken with and the other without th e specimen in the beam. Between pairs a parallel-sided phase-shifter p late 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 reco nstructed. Results: Three-dimensional images have been obtained from r at cerebrum and rat trigeminal nerve, showing cell structures at 8- to 15-mu m spatial resolution. Gray and white matter of cerebrum and neu rons in the trigeminal nerve are clearly visible. Conclusion: X-ray ph ase-contrast mu CT is becoming a valuable tool for studies of organic samples in medicine and biology.