High-resolution X-ray imaging based on curved Bragg mirrors: first results

Small animal cancer imaging has drawn increased attention over the last few years due to greater availability of genetically modified mice, permitting the study of human diseases in animal models. Submillimeter resolution would be of great value to provide the fine detail needed in the imaging of small tumors traced by radio-labeled agents. Despite extensive research and improvements in instrumentation and imaging reconstruction, until now, there has been no efficient technology for this task. The limitations of scintillation cameras with pinhole collimators, currently the highest resolution devices, are fundamental in nature. They include image blurring through edge effects, scattering at the pinhole, and inelastic Compton scattering. Furthermore, such devices often yield low efficiency. In this paper, a new approach to high-resolution imaging of radio-labeled agents is introduced and first results are shown. The technique is based on curved perfect-crystal X-ray mirrors applied in a one-to-one focusing geometry. Such Bragg diffraction optics yields high reflectivity and excellent energy resolution and it has been applied in X-ray spectroscopy for many years. Today large perfect-crystal mirrors are commercially available and efficient devices covering a substantial solid angle can be envisioned. The potential advantage over conventional pinhole cameras is twofold. First, focusing diffraction optics provides a "virtual" pinhole, which can effectively be inside the object under investigation and does not suffer from edge effects. Second, Bragg optics has an energy resolution of a few eV and discriminates against Compton scattering. The fundamentals of Bragg optics are discussed and first results using ⁵⁵Fe and ^95mTc phantoms are presented. Our data show spatial resolutions of less than 1 and 2 mm, respectively. Current limitations of this new technique and possible future designs are discussed.