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 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 interferometer (6) and computer analysis of interference patterns (9). 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.

Low-dose, simple, and fast grating-based X-ray phase-contrast imaging

“…For propagation-based phase imaging, where the measured quantity corresponds to the second derivative of the phase (ΔΦ), the in-line method is often used, where the effects of phase contrast become evident-due to the intrinsic coherent nature of the beam-as the sample-detector distance is increased. Although some of them yield excellent results for specific problems (4,6,11), none of them has so far found wide applications in medical or industrial areas, which typically require the use of a laboratory X-ray source, a large field of view (up to several centimeters), and a reasonably compact setup.…”

“…In addition, because grating interferometry is particularly sensitive to shallow phase gradients, it is ideal technique for soft tissue studies in the fields of medical and biological imaging. These characteristics make grating interferometry superior to other phase-contrast approaches (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) and set the prerequisites for a broad use of phase-contrast X-ray radiography and tomography.…”

Direct Observations of Cracks and Voids in Structural Materials by X-ray Imaging Using Ultra-bright Synchrotron Radiation

“…It is thought that such ultra-bright synchrotron radiation source could provide us, in principle, completely different information from conventional methods such as absorption contrast X-ray imaging, because much highly directional property is also available. That is why, based on the fact that the phase shift cross section for light element is almost a thousand times larger than the absorption one, especially in a hard X-ray region, new X-ray imaging techniques such as refraction method, [10][11][12][13][14][15] diffraction method, 15,16) inter-ferometric method 4,9,18) have recently been studied and proposed actively.…”

“…different information from conventional methods such as absorption contrast X-ray imaging, because much highly directional property is also available. That is why, based on the fact that the phase shift cross section for light element is almost a thousand times larger than the absorption one, especially in a hard X-ray region, new X-ray imaging techniques such as refraction method, 10-15) diffraction method, 15,16) inter-ferometric method 4,9,18) have recently been studied and proposed actively.The principle of refraction contrast X-ray imaging is shown in Fig. 2, as compared with conventional absorption X-ray imaging, illustrating the X-ray intensity profiles of the absorption contrast and refraction contrast for a void in material.…”

“…20) So, such phase contrast imaging has been intensively and successfully applied as a high resolution medical diagnosis method to observe the internal structure of biological materials such as the respiratory organ, cancers, capillaries, blood vessel in tumors, and so on. [18][19][20] For example, in SPring-8, efforts are being made in the field of medical diagnosis, and the development of cancer diagnosis is being actively carried out at the experimental station of BL20B2. These observations utilize a high spatial resolution of 10 mm imaging method, confirming that the accurate diagnosis of tumors using synchrotron radiation is possible.…”