Dual-energy imaging with brilliant x-ray beams

Brilliant x-ray sources will have great advantages over present techniques especially on regard to medical imaging. The beams are monoenergetic and pencil beam like. These two characteristics are leading to more contrasting pictures with lower beam doses. New results from simulations suggest a stimulated emission of a FEL is not necessary but a spontaneous undulator emission of laser-driven electrons would be sufficient. These incoherent beams would arise in any case as a by-product of the x-ray FEL.

Zebra fishes are convenient test objects fort he first experiments since they are not almost completely transparent in the visible range but absorb also in x-ray of only 5 keV, which would represent the first milestone. They hopefully will show whether techniques as dual-energy or scanning would allow better contrast as well as dose reduction.

One of the most important fields of application for x-ray absorption and phase contrast images by spontaneous emission is mammography. Conventional instruments deliver x-ray radiation with a very broad bandwidth, but only a part of this spectrum is making a contribution to the contrast. The exact requirements to the brilliant beam sources as exact number of photons per pulse, repetition rate, beam diameter, brilliance are not examined right now. Mammography has the additional difficulty that the testing object is three-dimensional, is moving by breathing. Simulations can help: specially prepared tissues provide virtual models, to which the expected better resolution of x-ray images at lower doses can be examined at a computer. Long before the first experiments these simulations optimize most of the beam parameters.