Bone metabolism at the spine and hip measured using 18F-PET

Introduction: The imaging technique of ¹⁸F-fluoride positron emission tomography (¹⁸F-PET) allows the non-invasive assessment of regional bone metabolism at clinically important sites such as the hip and lumbar spine and allows the measurement of a number of parameters relating to bone metabolism, for example, regional bone turnover (K_i) and bone blood flow (K₁). Purpose: To compare the differences between the K_i, K₁ and standardized uptake values (SUV) at the hip and lumbar spine. Methods: Twelve healthy postmenopausal women had age ranging from 52.3 to 70.6 years, bone mineral density (BMD) T-score ranging from − 2.9 to 1.4 at the lumbar spine and from − 2.4 to 1.7 at the hip. None had any history of metabolic bone disorder or had taken any medications that affected skeletal metabolism. Dynamic ¹⁸F-PET scans at the lumbar spine and hip were performed on two separate occasions. The K_i and K₁ values obtained using the Hawkins 3-compartment model were compared using Wilcoxon paired signed rank test. Results: The Ki values at the lumber spine vertebral bodies (mean of L1-L4), total hip outer (including the trabecular and cortical bone), total hip inner (including only the trabecular bone), femoral neck, and cortical shaft (including only cortical bone) were 0.042 ± 0.008, 0.013 ± 0.005, 0.015 ± 0.006, 0.015 ± 0.005, and 0.009 ± 0.002 ml.min− 1.ml− 1 respectively. The K1 values were 0.15 ± 0.01, 0.044 ± 0.013, 0.048 ± 0.018, 0.048 ± 0.017 and 0.036 ± 0.009 ml.min− 1.ml− 1 respectively. The SUVs were 6.0 ± 1.5, 2.3 ± 0.7, 2.6 ± 1.0, 2.7 ± 1.1 and 1.8 ± 0.4 respectively. The differences for K_i at spine and any other hip region were significant (p = 0.005). The differences among hip regions were also significant (p < 0.05) except between femoral neck and total hip (p > 0.05). The differences for K₁ were significant between lumbar spine and any other hip regain (p = 0.005) with no-significant differences among the hip regions (p > 0.05). Conclusion: This is the first study presenting the dynamic quantification of bone turnover and bone blood flow at the hip. We conclude that the bone turnover, perfusion and SUVs are higher in trabecular bone than in cortical bone.