Novel x-ray source for dual-energy subtraction angiography

In angiography practice an iodate contrast medium is injected in patient vessels with catheters. The absorption of x-rays raises immediately after the iodine K-edge energy (33.17 keV). In digital subtraction angiography, two images are used, acquired before and after the injection of the contrast medium, respectively. The vessels morphology results from the difference of images so obtained. This technique involves a non-negligible risk of morbidity or mortality, due to high concentration of injected contrast agent. We are investigating a new source which produces two thin parallel quasi-monochromatic beams - having peak energies centered before and after the iodine K-edge energy, respectively - by using a conventional x-ray tube and a highly oriented pyrolytic graphite mosaic crystal. The polychromatic x-rays incident on the crystal are monochromatized by Bragg diffraction and splitted in two thin parallel beams, by means of a collimating system. These two beams impinge on the phantom simulating patient vessels and are detected with solid-state array detectors. The image results as difference between the remaining intensities of two beams. We report a preliminary study of the new technique performed both with theoretical simulations and experimental measurements. Results of computer simulation give information about characteristics as size and quality of the quasi-monochromatic beams, that should be considered in detail to design a system dedicated to the clinical practice. Experimental measurements have been performed on a small-field detector in order to shows the enhancement of image contrast obtained with the application of the new technique.