Novel digital K-edge imaging system with transition radiation from an 855-MeV electron beam

A novel K-edge imaging method has been developed at the Mainz Microtron MAM I aiming at a very efficient use of the transition radiation (TR) flux gene rated by the external 855-MeV electron beam in a foil stack. A fan-like qua si-monochromatic hard X-ray beam is produced from the +/-1-mrad-wide TR con e with a highly oriented pyrolytic graphite (HOPG) crystal. The absorption of the object in front of a 30 mm x 10 min pn charge-coupled device (pn-CCD ) photon detector is measured at every pixel by a broad-band energy scan ar ound the K-absorption edge. This is accomplished by a synchronous variation of the lateral crystal position and the electron beam direction which defi nes also the direction of the TR cone. The system has been checked with a p hantom consisting of a 2.5-mum thick molybdenum sample embedded in a 136- o r 272-mum-thick copper bulk foil. A numerical analysis of the energy spectr um for every pixel demonstrates that data as far as +/- 0.75 keV away from the K edge of molybdenum at 20 keV still improve the signal-to-noise ratio (SNR). Prospects are discussed to investigate the human lungs with xenon as a contrast agent at the available total primary photon flux of 2 x 10(10) / (s . 0.1% band-width (BW)) only.