Selective iodine imaging using K-edge energies in computerized x-ray tomography

Iodine is commonly used as a contrast material in computerized x-ray tomography. In some cases the determination of the iodine distribution in the image may be prevented by the presence of bone or tissue variations within the tomographic slice. This paper describes a method for quantitative selective imaging of the iodine concentration in the slice. The method employs scans using three heavily filtered x-ray beams, two having mean energies which straddle the iodine K edge (33 keV) and another at a slightly higher energy. The results are independent of tissue and bone over a broad range of projection path lengths. It is shown that, for separation of iodine from one other material, a two-beam K-edge approach requires less integral dose than a two-beam technique at conventional CT energies for slice diameters up to 30 cm. For selective iodine imaging in the presence of more than one other material, the three-spectrum K-edge technique is a necessity. Exposure requirements and beam-hardening corrections are discussed in detail and a computer-simulated CT image generated by the proposed scheme is presented.