Effect of Hepatic Steatosis on Liver FDG Uptake Measured in Mean Standard Uptake Values1

Purpose: To evaluate the association between diffuse fatty infiltration of the liver and average fluorine 18 fluorodeoxyglucose (FDG) uptake in the liver. Materials and Methods: Institutional review board approval was obtained for this study; the requirement for informed patient consent was waived. Consecutive nonenhanced whole-body hybrid FDG positron emission tomographic (PET)-computed tomographic (CT) scans obtained in 142 patients (mean age, 63.6 years; age range, 19–94 years) from October 1, 2008, to November 28, 2008, were retrospectively reviewed. Mean attenuation (in Hounsfield units) and standardized uptake value (SUV) measurements for the liver and spleen were obtained, with identical regions of interest used for the CT and PET examinations. The patients were assigned to three study groups: a control group—119 patients with a mean liver attenuation value greater than or equal to the mean spleen attenuation value, a diffuse fatty liver disease group—23 patients in whom the mean liver attenuation value was less than the mean spleen attenuation value, and a more strictly defined fatty liver disease group—a subset of 10 patients from the diffuse fatty liver disease group with a mean liver attenuation value minus mean spleen attenuation value difference of less than or equal to −10 HU. Mean SUV (SUV m ) values were compared between the groups by using a two-sample t test for means. The association between mean liver attenuation and average FDG uptake was assessed with linear regression analysis. Results: The average SUV m for the control group was 2.18 (standard deviation [SD], 0.36; 95% confidence interval [CI]: 2.12, 2.24). No significant difference was identified when the average SUV m for the control group was compared with those for the fatty liver disease (SUV m , 2.03; SD, 0.36; 95% CI: 1.90, 2.16) ( P >.05) and more strictly defined fatty liver disease (SUV m , 2.07; SD, 0.24; 95% CI: 1.92, 2.22) groups ( P >.05). Linear regression analysis of liver SUV m as a function of mean liver attenuation revealed a mean slope of 0.005 (SD, 0.04; 95% CI: −0.005, 0.015) and a correlation coefficient of 0.02. Conclusion: No association between liver attenuation and FDG uptake measured in terms of SUV m was observed. On the basis of these data, it is acceptable to use the liver as a comparator for extrahepatic foci of equivocal increased FDG activity in patients with fatty liver disease. © RSNA, 2010