X-ray monochromator for divergent beam radiography using conventional and laser produced X-ray sources

摘要

We discuss technology that will produce a wide angle monochromatic beam of X-rays that appears to diverge from a virtual point source. Although our ideas are discussed in the context of dual energy subtraction angiography (DESA) that we are developing to operate in a clinical setting, they are widely adaptable to all applications of x-ray radiography. The best DESA analysis is obtained from X-ray images made in narrow energy bands just below and just above the I K-absorption edge. Our monochromator will be used to isolate these narrow bands to produce high contrast, high spatial resolution, ECG gated angiographic images. Emission lines, that have X-ray energies below (E~-) and above (E~+) the I K-absorption edge at 33.2 keV, are readily available. We have deposited variable d-spacing artificial crystals, called multilayers, on optically flat, very smooth substrates, to create narrow pass band X-ray monochromators centered on La and Ba K-emission lines. We will record (E~-) and (E~+) exposures on either photographic plates or, in the future, with energy sensitive pixelated arrays of solid state detectors. After a suitable normalization, the exposures will be subtracted to yield a high resolution, high contrast image of the I filled arteries. Although initial results will be obtained with conventional X-ray tubes, our goal is to couple the monochromators to a high intensity, laser produced, X-ray plasma. We will present early test data that shows the multilayer performance.