Evaluation of a bilinear model for attenuation correction using CT numbers generated from a parametric method

•A parametric model is used to calculate the CT number of tissues.•Only one substance, not necessarily tissue equivalent, needs to be scanned.•Attenuation coefficients of these tissues have been calculated from NIST tables.•Differences with the coefficients from the bilinear model can be 5% for soft tissues.•The different assumptions for the composition of tissues cause these differences.

A parametric model is used for the calculation of the CT number of some selected human tissues of known compositions (Hi) in two hybrid systems, one SPECT-CT and one PET-CT. Only one well characterized substance, not necessarily tissue-like, needs to be scanned with the protocol of interest. The linear attenuation coefficients of these tissues for some energies of interest (μi) have been calculated from their tabulated compositions and the NIST databases. These coefficients have been compared with those calculated with the bilinear model from the CT number (μBi). No relevant differences have been found for bones and lung. In the soft tissue region, the differences can be up to 5%. These discrepancies are attributed to the different chemical composition for the tissues assumed by both methods.