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Nonuniqueness in dual‐energy CT
Author(s) -
Levine Zachary H.
Publication year - 2017
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.12298
Subject(s) - basis (linear algebra) , photon , exponential function , voxel , physics , dual energy , tomography , computational physics , mathematical analysis , mathematics , optics , computer science , geometry , artificial intelligence , medicine , bone mineral , osteoporosis , endocrinology
Purpose The goal is to determine whether dual‐energy computed tomography ( CT ) leads to a unique reconstruction using two basis materials. Methods The beam‐hardening equation is simplified to the single‐voxel case. The simplified equation is rewritten to show that the solution can be considered to be linear operations in a vector space followed by a measurement model which is the sum of the exponential of the coordinates. The case of finding the concentrations of two materials from measurements of two spectra with three photon energies is the simplest non‐trivial case and is considered in detail. Results Using a material basis of water and bone, with photon energies of 30 keV, 60 keV, and 100 keV, a case with two solutions is demonstrated. Conclusions Dual‐energy reconstruction using two materials is not unique as shown by an example. Algorithms for dual‐energy, dual‐material reconstructions need to be aware of this potential ambiguity in the solution.