Pilot Study to Diagnose Nonalcoholic Steatohepatitis With Dynamic ¹⁸F-FDG PET

Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are major causes of chronic liver disease characterized by steatosis, inflammation, and fibrosis. Diagnosis of inflammation is limited by the need for liver biopsy. Dynamic PET with the widely used radiotracer ¹⁸F-FDG provides a novel method for evaluating spatial and temporal changes in liver inflammation.

Patients with NAFLD or NASH underwent dynamic FDG PET and MRI within 6 months of undergoing liver biopsy. Liver time-activity curves were extracted to estimate kinetic parameters representing various rate constants of FDG transport using tracer kinetic modeling. Liver biopsy specimens were scored on the basis of NASH Clinical Research Network criteria.

This pilot study included 22 patients, 14 of whom were women. Patient age ranged from 18 to 70 years, and the mean body mass index (weight in kilograms divided by the square of height in meters) was 33.2 (range, 24-43.1). The K₁ value, which represents the rate of FDG transport from blood to hepatic tissue, was significantly correlated with inflammation (r = -0.7284; p = 0.0001) and the overall NAFLD activity score (NAS; r = -0.6750; p = 0.0006). K₁ values were inversely related to the hepatic inflammation score and NAS. Although heterogeneity in K₁ values across eight liver segments was noted, distinct segregation existed among segmental K₁ values dependent on the histologic inflammation score (p = 0.022) or NAS (p = 0.0091). K₁ had a strong association with both inflammation (ROC AUC value, 0.88) and the NAS (ROC AUC value, 0.89), with K₁ = 1.02 (mL/min/mL) corresponding to a sensitivity and specificity of 93% and 88%, respectively, for the NAS.

Dynamic FDG PET with tracer kinetic modeling has the potential to determine liver inflammation in patients with NAFLD and NASH and can fill an essential gap in diagnosis.