Liver SUL_mean at FDG PET/CT: Interreader agreement and impact of placement of volume of interest

Purpose: To evaluate how interreader agreement and the site of the volume of interest (VOI) affect the agreement and variability of liver mean standardized uptake value normalized to lean body mass (SUL_mean) at fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT). Materials and Methods: Institutional review board approval was obtained for this HIPAA-compliant retrospective review of PET/CT images and patient records. PET/CT images were reviewed in 116 randomly selected patients who had undergone a baseline PET/CT examination and who had normal livers according to imaging and biochemical test results. A 30-mmdiameter spherical VOI was placed within the right lobe of the liver above, below, and at the level of the main portal vein. Two readers performed all measurements independently. Analysis of variance, intraclass correlation coefficient (ICC) analysis, and Bland-Altman analysis were performed. Results: The mean SUL_mean was between 2.11 and 2.17 at the upper, portal, and lower levels of the right lobe of the liver. The coefficient of variance was between 21.0% and 23.1%, without significant differences for location, with the least variance in the upper level. The ICC of the two readers varied between 0.98 and 0.99 (95% confidence interval [CI]: 0.97, 0.99; P = .0001) at each level. The greatest precision (narrowest CI) was also in the upper level. Bias was 0.025±0.10 (standard deviation) at the upper level, was 0.004±0.14 at the lower level, and was 0.047±0.10 at the portal vein (P = .02). For each reader, there was almost perfect reliability between the SUL_mean measurements made at the three levels, with an ICC of 0.98 (95% CI: 0.98, 0.99; P = .0001). Conclusion: Liver SUL_mean at FDG PET/CT has excellent interreader agreement, with similar values and variance whether measured at the upper, lower, or portal vein levels within the right lobe of the liver.