Power law spectral photon-counting CT for quantitative effective atomic number and electron density imaging.

Objective.To develop and evaluate a scanner-specific power law method for voxelwise effective atomic number () and electron density () imaging on a commercial spectral photon-counting CT (SPCCT) system, and to demonstrate its applicability to tissue characterization in heterogeneous samples.Approach.The x-ray linear attenuation coefficientwas modeled as a power law sum of photoelectric, Compton and empirical correction terms. Model coefficients were fitted to NIST cross sections for-21 over the scanner energy range from 7 to 115 keV. A QRM spectral-computed tomography (CT) phantom containing soft-tissue-equivalent, hydroxyapatite and iodine inserts was scanned on a MARS Microlab 5120 SPCCT system in five detector energy bins. For each bin, reconstructed SPCCTimages were linearly calibrated to NIST, and the calibratedserved as input to four-window and dual-energy models to estimate voxelwiseand. The same calibration and model were applied, without retuning, to a meat sample with embedded iodine vials.Main results.Using NISTas input, the four-window formalism gave mean absolute errors of approximately 1% for bothand. On calibrated SPCCT images, errors were 4.9% and 2.1% forandwith the four-window model, and 3.6% and 1.7% with the best dual-energy pair (50-60 / 60-79 keV). The same framework, applied without retuning, separated fat, muscle, bone and iodine in the heterogeneous meat sample.Significance.A scanner-specific power law model ofcombined with bin-wise linear calibration can deliver accurateandfrom a single SPCCT acquisition. Optimized dual-energy windows achieve near-percentaccuracy for clinically relevant materials, providing a quantitative basis for tissue characterization with photon-counting CT.