Pseudomonoenergetic x-ray diffraction measurements using balanced filters for coherent-scatter computed tomography.

Coherent-scatter computed tomography (CSCT) is a method of "composition" imaging based on measurements of diffraction patterns from tissues. Use of an x-ray tube degrades scatter pattern angular resolution due to the x-ray spectral width, making it difficult to uniquely identify some materials. The use of two transmission filters with similar atomic numbers (balanced "Ross filters") to generate pseudomonoenergetic scatter patterns is described as it applies to CSCT. An analysis of angular-blur mechanisms reveals that focal spot size and beam width are the most important factors determining Bragg-peak width when Er-Tm filters are used. A relative RMS spectral width of 1% can be achieved in the difference spectrum and a Bragg-peak RMS angular width of approximately 0.14 degree (relative width of 3% at 5 degrees scatter angle) can be achieved with an effective energy of 58 keV.