Angular-dependent coherent scatter measured with a diagnostic x-ray image intensifier-based imaging system

Low-angle scatter of x rays at diagnostic energies is primarily coherent. This coherence gives rise to interference effects resulting in x-ray diffraction patterns that are characteristic of the scattering material, A method is described of imaging these low-angle (0 degrees-10 degrees) x-ray diffraction properties of tissue specimens using a diagnostic x-ray beam and image intensifier-based system. The coherent-scatter cross sections of several materials measured this way are presented. It is shown theoretically that the measurements made with this system can be expressed as the mono-energetic cross section ''blurred'' by the x-ray spectrum using a linear superposition integral. Experimental results using aluminum powder confirm this. Using a 70 kVp x-ray beam filtered with gadolinium to reduce the spectral width, materials such as water, Lucite, and hydroxyapatite all have significantly different diffraction patterns. The cross sections determined from this analysis form the basis of a unique method of characterizing and identifying tissue samples according to their atomic structure rather than x-ray attenuation properties. (C) 1996 American Association of Physicists in Medicine.