Design of the angiography beamline for the Argonne Advanced Photon Source

The angiography beamline planned for the Argonne Advanced Photon Source (APS) is a very special beamline dedicated to medical imaging. It is especially designed to enhance the art of digital subtraction angiography. It is different from the angiography beamlines presently in operation that scan the X-ray picture line by line, in that it will take both the high and low energy angiography X-ray pictures simultaneously as full frame pictures. Pictures with 0.25 mm resolution and good signal to noise will be possible with 2 ms exposure times. This is possible because of the increase in flux that is available at the APS. The source of the 33 keV photons is a special high intensity wiggler. The photon beam is separated into two parts, spread out in the vertical direction, and monochromatized with two convex bent crystals. These two crystals are bent in an non-uniform way that allows one to both make the photon flux uniform over the 15 cm x 15 cm examining area and stabilize the shape of the surface of the diffraction crystal against distortion caused by the heat load on the crystal. Most of the energy of the photon beam is absorbed by a fast shutter placed in font of the crystals. The two images at the two different energies are recorded in two large position-sensitive detectors. (orig.)