Poster — Thur Eve — 37: Incorporation of K‐Edge Materials into Dual‐Energy X‐Ray Imaging Theory
Dual‐energy x‐ray imaging is capable of enhancing the conspicuity of materials by removing extraneous contrast. Classic dual‐energy theory, however, does not encompass materials which have a K edge in the diagnostic energy range, such as iodine contrast agent. We attempt to extend dual‐energy theory to incorporate all materials. In the first approach, a third basis material is introduced to account for the discontinuity. The transmission of a human torso consisting of muscle, adipose and iodine can be represented by equivalent thicknesses of three basis materials chosen to be Lucite, aluminum and iodine. Material look‐alike unit vectors in the Lucite, aluminum and iodine space give the direction for projecting patient data to remove contrast between any two pairs of materials. This approach fails, however, if a contrast agent different from that used as a basis material is present, such as barium. A more general extension of dual‐energy theory would accommodate different K edges. In the second approach, a K‐edge material is represented by two basis materials and a Heaviside function shifted to the K edge and scaled to give the jump ratio. The scale factor is a slowly varying function of the energy shift: the jump ratio is 5.58 for iodine (Z=53) and 5.23 for barium (Z=56). This makes it possible to describe any material by three parameters. The next step will be to link the two disjoint approaches to obtain a general extension of dual‐energy theory, of which the current theory is a projection into the two‐basis plane.