Limitations to iodine isolation using a dual beam non�K�edge approach

S. J. Riederer, R. A. Kruger, C. A. Mistretta

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


In dual�beam selective iodine imaging, images of an object are made with each of two spectrally different x�ray beams. The mean beam energies may either straddle the 33 keV iodine K�edge or both lie above the K�edge. Both patient exposure considerations and the availability of sufficient x�ray flux make the latter approach favorable for tissue thicknesses exceeding 5 cm. Consider such an approach in which image contrast from tissue is suppressed in the difference image. It is proven theoretically that the residual bone–to–iodine contrast is a constant independent of the two mean beam energies used. This invariance principle is demonstrated experimentally by comparing images made from different pairs of x�ray spectra. Observed contrast ratios match the predicted value very well. In dual�beam imaging, contrast from only one material may be suppressed. Other substances yield residual signals which compete with the iodine. Subtleties of this incomplete cancellation are demonstrated, discussed, and quantitated. A contrast enhancement factor (CEF) is defined as the factor by which iodine contrast is enhanced in a multiple beam subtraction technique relative to monoenergetic imaging at 40 keV. CEFs are determined for tissue and bone cancellation separately and their limits are discussed. Images of a simulated artery containing iodine superimposed over a Rando head and neck phantom show that the CEF limitation for dual beam imaging is quite severe compared to a time dependent mask mode imaging approach. Finally, optimum energies for dual beam images are discussed.

Original languageEnglish (US)
Pages (from-to)54-61
Number of pages8
JournalMedical physics
Issue number1
StatePublished - Jan 1981



ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging


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