Efficacy of 18F-FDG and 18F-NaF PET/CT imaging: A novel semi-quantitative assessment of the effects of age and obesity on hip joint inflammation and bone degeneration

Objective: Osteoarthritis (OA) is characterized by synovial tissue inflammation and underlying bone degeneration in the joints. Aging and obesity are among the major risk factors. This study evaluated the effects of aging and body mass index (BMI) on hip joint inflammation and bone degeneration using fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography ( ¹⁸F-FDG PET/CT) and fluorine-18 sodium fluoride (F-NaF) PET/CT imaging, respectively. Subjects and Methods: In this retrospective study, a total of 116 subjects (58 males and 58 females) who had undergone both ¹⁸F-FDG and ¹⁸F-NaF PET/CT imaging were analyzed. The mean age of these subjects was 48.6±14.5 with an age range of 21-75 years. Fluorine-18-FDG and ¹⁸F-NaF PET/CT imaging was conducted 180min and 90min (respectively) after intravenous administration of the appropriate tracer. The hip joint was segmented on fused PET/CT images using OsiriX MD v.9.5 (DICOM viewer and image-analysis program, Pixmeo SARL; Bernex, Switzerland). The region of interest (ROI) for the hip joint was indicated by using a 3D-growing region algorithm with upper/lower Hounsfield Units (HU) followed by a morphological closing algorithm. The metabolic activity for the left and right side of the joint was measured and correlated with age and BMI. Results: Fluorine-18-FDG uptake in the hip was 0.83±0.22 (right side: 0.83±0.23, left side: 0.83±0.22, P=0.82). Fluorine-18-NaF uptake in the hip was 3.20±1.07 (right side: 3.25±1.14, left side: 3.15±1.04, P= 0.02). Body mass index positively correlated with both ¹⁸F-FDG (r=0.29, P=0.001) and NaF (r=0.26, P=0.005) uptake. No significant correlation was seen between age and either ¹⁸F-FDG (r=0.12, P=0.19) or ¹⁸F-NaF (r= 0.03, P=0.78) uptake. Conclusion: Body mass index had a significant impact on ¹⁸F-FDG and ¹⁸F-NaF uptake, whereas age had no correlation with either tracer uptake. Obesity increases the mechanical forces applied on weight-bearing joints such as the hip. Body mass index was related to increased joint inflammation and bone degeneration. These findings further support the studies explaining the role of adipose tissue in promoting OA.