Tissue analysis using dual energy CT

A new dual-energy x-ray CT algorithm is presented which makes use of both pre- and post-reconstruction data in an iterative manner to achieve accurate beam hardening correction and decomposition into basis materials. The technique does not require a calibration phantom and also does not require accurate estimation of the effective energies of the polyenergetic x-ray beams. It does however, require a knowledge of the incident x-ray spectra. For the situation where the incident spectra are unknown, a method is given whereby sufficiently accurate approximations to the spectra can be determined from attenuation measurements. Decomposition into basis materials makes use of spatial and energy information and an 'a priori' knowledge of the composition and attenuating properties of various tissue types. Any total number of basis materials may be used within the limitation that a subset containing a maximum of three materials is used for any individual pixel. Results of a computer simulation show that the algorithm produces accurate measurements of the concentrations of both high and low atomic number materials such as bone mineral, collagen, fat and air. However the results of a phantom study show that the measurement of the concentrations of low atomic number basis materials may be subject to systematic errors arising from uncertainties in the published values of linear attenuation coefficients.