Quantification of Whole-Skeletal Bone Remodeling Rates with18F-NaF PET/CT Scans

184 Introduction: Throughout life, the adult skeleton is renewed through the process of remodeling. Measurement of bone turnover rate has been shown to play an important role in evaluation of localized bone health and new treatments for metabolic bone diseases, such as osteoporosis. While there are many assessments available for localized bone health, the options for assessment of health of the full skeleton are currently very limited and highly invasive. Previously, we reported on the use of fluorine 18 labeled sodium fluoride (18F-NaF) PET/CT imaging as a means of monitoring metabolic changes in the femoral neck. In the present work, we show the potential of a similar method of analyzing 18F-NaF-based PET/CT images to quantify changes in levels of bone remodeling in the full skeleton. We also demonstrate the higher fidelity of this method when compared to standard CT-based BMD measurements. Methods: In this retrospective study, 131 images from the CAMONA (Cardiovascular Molecular Calcification Assessed by 18F-NaF) study were analyzed. In this study 66 females and 65 males (ages 21 - 75, BMI 13 - 43) were injected with the radiotracer 18F-NaF and a PET/CT scan was administered. The total bone volume within the body was selected from CT image analysis using an operator-guided, semi-automatic algorithm based primarily on pixel brightness. From these imaged regions, CT-based BMD was calculated. Each CT image segmentation was superimposed onto the corresponding PET image to identify the regions of bone in these images and total NaF standardized uptake values (SUV) were calculated for each PET image. Trends in the data were evaluated using a linear model and a significance level of p=0.05. Results: The total, standardized 18F-NaF uptake calculated using the total pixel intensity was negatively correlated with age across all patients (a 6.8% drop in total SUV per decade of life, r = -0.39, p < 0.001). Among males, age-related changes in SUV include a 4.2% drop per decade of life, r = -0.25, p < 0.05. Among females, age-related changes in SUV were more prominent, with an 8.4% drop in SUV per decade of life, r = -0.51, p < 0.001. The CT-based BMD calculated using the total pixel intensity was negatively correlated with age across all patients (a 4.0% drop in total BMD per decade of life, r = -0.26, p < 0.001). Among males, age-related changes in SUV include a 0.9% drop per decade of life, r = -0.07, p = 0.28. Among females, age-related changes in SUV were more prominent, with a 5.3% drop in SUV per decade of life, r = -0.45, p < 0.001. Conclusions: This study demonstrates the capability of 18F-NaF PET scan in measuring certain factors of full body bone health. As individuals progress in age, the rate of bone metabolism and turnover begins to decline. Additionally, this rate of decrease is more prominent in females than in males. Both of these trends were illustrated within statistical significance within the set of images analyzed through 18F-NaF-based PET/CT imaging.