The Utility of 18F-NaF-Positron Emission Tomography/Computed Tomography in Measuring the Metabolic Activity of the Aging Spine

Study Design. Cross-sectional; observational. Objectives. To determine whether sodium fluoride (NaF) positron emission tomography/computed tomography (PET/CT) can be used to monitor decreased bone turnover with aging in the spine. Background. Osteoporosis is characterized by structural changes in the bone such as decreased bone mineral density leading to an increased risk for fractures. An imaging modality capable of identifying molecular changes that precede these structural changes could be critical for the early diagnosis and monitoring of osteoporosis and other metabolic bone disorders. Materials and Methods. The potential of 18 F-sodium fluoride (NaF)–PET/CT in detecting changes in bone turnover associated with aging was examined in the lumbar spine of 88 healthy volunteers (43 females, 45 males; mean age 44.6 yr). Regions of interest equal to the trabecular body of the L1 to L4 vertebrae were used to calculate the mean standardized uptake value (SUVmean) and average Hounsfield unit (HU) values. Receiver-operating characteristic curve analysis with an area under the curve using the Wilson/Brown method was generated to assess the value of NaF uptake (SUVmean) in predicting osteoporosis as defined by HU-threshold values. To determine the correlation among global SUVmean, mean HU values, and age, the Spearman correlation test was performed on images acquired at 90 minutes postinjection. Results. There was a significant negative correlation between NaF SUVmean and age in females ( P < 0.0001, r = −0.59), and a weaker, but also significant correlation in males ( P = 0.03, r = −0.32). In females only, there was a significant correlation between NaF uptake and age at all acquisition time points. Measured NaF uptake increased by 10% to 15% with acquisition time in both sexes, from 45 to 90 minutes and from 90 to 180 minutes. Conclusions. NaF-PET/CT detects decreased vertebral bone turnover with aging, particularly in females. Measured NaF uptake increased with PET acquisition time after tracer injection, which must be considered in follow-up studies monitoring disease development and treatment effects.