Evolving Role of Molecular Imaging with 18F-Sodium Fluoride PET as a Biomarker for Calcium Metabolism

¹⁸F-sodium fluoride (NaF) as an imaging tracer portrays calcium metabolic activity either in the osseous structures or in soft tissue. Currently, clinical use of NaF-PET is confined to detecting metastasis to the bone, but this approach reveals indirect evidence for disease activity and will have limited use in the future in favor of more direct approaches that visualize cancer cells in the read marrow where they reside. This has proven to be the case with FDG-PET imaging in most cancers. However, a variety of studies support the application of NaF-PET to assess benign osseous diseases. In particular, bone turnover can be measured from NaF uptake to diagnose osteoporosis. Several studies have evaluated the efficacy of bisphosphonates and their lasting effects as treatment for osteoporosis using bone turnover measured by NaF-PET. Additionally, NaF uptake in vessels tracks calcification in the plaques at the molecular level, which is relevant to coronary artery disease. Also, NaF-PET imaging of diseased joints is able to project disease progression in osteoarthritis, rheumatoid arthritis, and ankylosing spondylitis. Further studies suggest potential use of NaF-PET in domains such as back pain, osteosarcoma, stress-related fracture, and bisphosphonate-induced osteonecrosis of the jaw. The critical role of NaF-PET in disease detection and characterization of many musculoskeletal disorders has been clearly demonstrated in the literature, and these methods will become more widespread in the future. The data from PET imaging are quantitative in nature, and as such, it adds a major dimension to assessing disease activity.