A method for calibrating the CT-based attenuation correction of PET in human tissue

The use of CT-based attenuation correction for PET in PET/CT systems requires the transformation of CT Hounsfield units (HU) to linear attenuation coefficients at 511 keV (LAC₅₁₁). This cannot be done perfectly from a single kVp CT scan due to variability in Compton and photoelectric composition, and thus an approximate transformation must be employed. One difficulty in this lies in accurately determining the LAC in actual human tissue. Typically, phantoms consisting of synthetic materials thought to be approximate human tissue equivalents are employed instead. A potentially more accurate approach would be to use dual kVp CT scans to estimate LAC₅₁₁ in actual human tissue, and then base the single kVp transformation on these data. This approach would also permit an assessment of the dispersion of actual tissue values about the two-component trend lines typically used for the single kVp transformation. In this paper we develop and assess this methodology.