Liver Fat and Iron Quantification With Spectral Localizer Radiographs From Photon-counting Detector CT

Objectives: Quantification of liver fat on computed tomography (CT) is often confounded by hepatic iron deposition and the use of iodinated contrast agents. This phantom study aimed to evaluate the feasibility and accuracy of quantifying liver fat content (LFC) in the presence of iron using spectral localizer radiographs acquired with photon-counting detector CT (PCD-CT). Materials and Methods: Sixteen liver phantoms were constructed using mixtures of liver tissue, fat, and iron to simulate 4 levels of LFC (0%, 10%, 30%, and 50%) and 4 levels of liver iron concentration (LIC: 0, 1.5, 3, and 6 mg/mL). Five additional reference phantoms (containing fat only, water only, or water–iron solutions) were included. All phantoms were scanned on a clinical PCD-CT system using 3 tube current settings (10, 50, 300 mA) to acquire spectral localizer radiography data. Material decomposition of high- and low-energy bin data yielded water and hydroxyapatite (HA) maps. HA values were analyzed as a function of LFC and LIC, and water values were correlated with corresponding HA values. Results: Increasing LFC resulted in a linear decrease in HA values, consistent across all LIC levels (slopes=−0.0016 to −0.0023; mean=−0.0019; r=0.997 to 1.0). Conversely, increasing LIC caused a linear increase in HA values, independent of LFC (slopes=0.0147 to 0.017; mean=0.0156; r=0.978 to 1.0). When combined with water values in a 2-dimensional material space, these stable linear relationships enabled estimation of LFC irrespective of LIC. Findings were reproducible across all tube current settings. Conclusion: Spectral localizer radiographs from PCD-CT allow quantification of liver fat content even in the presence of iron deposition. If validated in vivo, this technique may enable low-threshold opportunistic screening for hepatic steatosis and iron overload from precontrast localizer scans.