Abstract: An energy substraction medical imaging system which is used for imaging a body part impregnated with a radio-opaque dye such as iodine is provided. The system includes an electron beam target having a target surface which, when excited by a high-energy electron beam, generates radiation having strong K.sub..alpha. at energy levels slightly above and slightly below the K-edge energy level of the dye. The target surface is preferably formed of a compound containing lanthanum, such as lanthanum oxide. The target may also be formed of a compound containing a material having a K.sub..alpha. line at an energy level slightly above the dye K-edge and a material with K.sub..alpha. line slightly below the dye K-edge or with separate sections containing such materials which are alternately excited. The target is excited by a high-energy electron beam from a suitable source, the electron beam having sufficient energy to provide a high photon yield at the K.sub..alpha.