Phase–contrast X–ray computed tomography for observing biological soft tissues

Abstract

Biological soft tissues are almost transparent to hard X rays and therefore cannot be investigated without enhancement with a contrast medium, such as iodine. On the other hand, phase–contrast X–ray imaging is sensitive to light elements^1–8. This is because the X–ray phase shift cross section is almost a thousand times larger than the X–ray absorption cross section for light elements such as hydrogen, carbon, nitrogen and oxygen^4,5. Hence, phase–contrast X–ray imaging is a promising technique for observing the structure inside biological soft tissues without the need for staining and without serious radiation exposure. We have devised a means of observing biological tissues in three dimensions using a novel X–ray computed tomography (CT) by modifying the phase–contrast technique. To generate appropriate CT input data, we used phase–mapping images obtained using an X–ray interferometer⁶ and computer analysis of interference patterns⁹. Now, we present a three–dimensional observation result of a nonstained sample of a cancerous rabbit liver, using a synchrotron X–ray source. Phase–contrast X–ray CT was able to clearly differentiate the cancer lesion from the normal tissue. Moreover, fine structures corresponding to cancerous degeneration and fibrous tissues were clearly depicted.