Accurate Hepatic Fat Fraction Quantification Across Body Sizes Using Photon-Counting CT
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Objective
To identify common photon-counting CT (PCCT) virtual monochromatic imaging (VMI) settings for accurate hepatic fat fraction (FF) quantification across different body sizes, including large body habitus.
Methods
Six non-iodinated fat lesions (FF 5%–40%) were embedded in anthropomorphic liver phantoms representing medium-sized (25×32.5 cm 2 ) and large (31×39 cm 2 ) abdomens. Phantoms were scanned on a PCCT system (NAEOTOM Alpha) at 120 and 140 kV. CT numbers were measured in VMIs at 40–190 keV in 1-keV increments. Linear regression between the ground-truth FF and measured Hounsfield units (HU) was used to estimate FF. Common optimal VMI settings yielding the minimum relative root-mean-square error (rRMSE) in both phantoms were identified.
Results
A single VMI setting of 70 keV at 140 kV demonstrated the best overall performance across body sizes, with FF (%) = −0.689HU + 36.51 (R 2 > 0.996), achieving rRMSE ≤ 3.4% and absolute RMSE ≤ 0.7% in both phantoms. Robust performance (rRMSE ≤ 5%) was consistently maintained across 69–71 keV using identical calibration parameters for both phantoms. These results represented a substantial improvement over previously reported dual-energy CT (DECT) performance, while enabling accurate quantification on PCCT at radiation doses approximately 40% lower than those used in prior DECT protocols.
Conclusion
PCCT enables accurate and robust hepatic fat fraction quantification independent of body size. A single protocol at 140 kV with VMIs of 69–71 keV consistently achieved low quantification errors, demonstrating strong potential for opportunistic liver fat assessment using PCCT, especially in obese patients.
