Assessment of bone turnover by measuring global uptake of 18F-sodium fluoride in the femoral neck, a novel method for early detection of osteoporosis

Objectives 18F-sodium fluoride (NaF) as a PET tracer reflects new bone formation and therefore has been utilized for detection of metabolic diseases of osseous structures. Over the past decade this imaging approach has been heavily employed for detection of reactive bone formation following metastasis in the skeletal system. However, it has value in measuring loss of bone formation due to aging or other disorders that result in reduced metabolic activity, particularly in the aging population. Therefore, there is a dire need to develop methodologies that will allow for accurate quantification of bone loss in structures that are prone to such processes. Attempts have been made to measure bone loss in the spine, which in our view is subject to degenerative diseases, diseases that are associated with normal aging and therefore result in erroneous measurements. By now it is established that osteoporosis is frequently noted in the femoral neck and frequently results in fractures that may lead to death in some patients.

Methods This retrospective study was carried out on 20 clinical whole-body PET scans. We selected to analyze data from 20 patients, 10 of whom were between the ages of 36 and 65 (mean = 58) and the other 10 between 76 and 86 (mean = 81). These patients were scanned 60 minutes after the intravenous administration of approximately 5.5 mCi of NaF by utilizing a time-of-flight PET-CT machine. By using a CT scan as the landmark for defining the neck region, we followed a strict region of interest for measuring NaF uptake in the neck region. The inner boundary of the neck region was defined by the epiphyseal line that was clearly identifiable on CT. The outer boundary of the neck was defined by the intertrochanteric ridge. Thereafter, this well-defined region of interest was transferred to the corresponding PET images and global NaF uptake was measured in each subject. The numbers, which reflected global bone turnover, were calculated, and correlation between the two age groups was determined.

Results Global values calculated from the study were compared between the two age groups and showed a decline with normal aging at this vulnerable anatomic location. Global activity as measured in SUV had a mean of 11826.4 and standard deviation of 7224.6 in the young population while the old population had a mean of 9719.7 and standard deviation of 4265.4. The correlation coefficient between global values and age was -0.43, which was significant (p = 0.056). SUVmax (r = -0.35, p = 0.13) and SUVmean (r = -0.27, p = 0.25) also showed promising correlation.

Conclusions By conducting this research, we have shown the potential role of assessment of global bone turnover in the femoral neck for early detection of osteoporosis in the neck region. The preliminary data generated are encouraging and a larger scale prospective study will be of great importance for defining this methodology for routine clinical use in the future.