BackgroundPenetrating transmural arteries with a diameter of <500 μm are considered to be a critical vascular component that causes a transmural variation of myocardial blood flow under various pathophysiological conditions. However, the conventional coronary angiographic system is not oriented to the visualization of such small arteries as these.Methods and ResultsWe magnified and monochromatized the inherently narrow beam (3 mm along the vertical direction) of synchrotron radiation by using an asymmetrically cut silicon crystal with 311 reflecting planes to obtain a monochromatic x-ray with relatively large beam size (60×25 mm) and with an energy of just above (+130 eV) the K-absorption edge of the contrast materials (33.17 and 37.41 keV for iodine and barium, respectively). We irradiated dogs or excised hearts with the monochromatic x-ray and obtained coronary angiograms using an image intensifier and video system with a spatial resolution of 170 μm. In the anesthetized dog experiments, we visualized the transmural penetrating arteries (5 to 15 μm in length) arising every 4 to 7 mm from the epicardial branch. Visualization of these arteries filled with heavy element- loaded microspheres (15 gm in diameter) in the excised- heart experiments, in which the monochromatic x-ray was irradiated to the hearts through a 10- to 20-cm acrylic plate, indicated that this system could be used for human patients, in whom body absorption of x-ray is substantial.ConclusionsCoronary angiogram by means of monochromatic x-ray is useful for a precise evaluation of coronary circulation, both in clinical settings and in physiological animal experiments.