A novel analyzer control system for diffraction enhanced imaging

Abstract

Diffraction Enhanced Imaging is an imaging modality that derives contrast from X-ray refraction, an extreme form of scatter rejection (extinction) and absorption which is common to conventional radiography. A critical part of the imaging system is the «analyzer crystal» which is used to re-diffract the beam after passing through the object being imaged. The analyzer and monochromator crystals form a matched parallel crystal set. This analyzer needs to be accurately aligned and that alignment maintained over the course of an imaging session. Typically, the analyzer needs to remain at a specific angle within a few tens of nanoradians to prevent problems with image interpretation. Ideally, the analyzer would be set to a specific angle and would remain at that angle over the course of an imaging session which might be from a fraction of a second to several minutes or longer. In many instances, this requirement is well beyond what is possible by relying on mechanical stability alone and some form of feedback to control the analyzer setting is required. We describe a novel analyzer control system that allows the analyzer to be set at any location in the analyzer rocking curve, including the peak location. The method described is extensible to include methods to extend the range of analyzer control to several Darwin widths away from the analyzer peaked location. Such a system is necessary for the accurate implementation of the method and is intended to make the use of the method simpler without relying on repeated alignment during the imaging session. © 2013 IOP Publishing Ltd.