Tomographic imaging of the angular-dependent coherent-scatter cross section.

A new special-purpose computed tomographic (CT) imaging system is described which produces images based on measurements of the low-angle (0-10 degrees) x-ray diffraction properties of an object. Low-angle scatter in the diagnostic x-ray energy range is dominated by coherent scatter, and the system uses first-generation CT geometry to acquire a diffraction pattern for each pencil beam. The patterns are used to reconstruct a series of images which represent the coherent-scatter intensity at a series of scatter angles. To demonstrate the potential of coherent-scatter CT (CSCT), the scanner has been built and used to image a phantom consisting of a water-filled Lucite cylinder containing rods of polyethylene, Lucite, polycarbonate, and nylon. In this paper, the system is described and a sequence of CSCT images of this phantom is shown. Coherent-scatter cross sections of these materials are generated for each pixel from this sequence of images and compared with cross sections measured separately. The resulting excellent agreement shows that the angular-dependent coherent-scatter cross section can be accurately imaged in a tomographic slice through an object. These cross sections give material-specific information about the object. The long-term goal of this research is to make measurements of bone-mineral content for every pixel in a tomographic slice.