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

(18)F-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.

Impact of Personal Characteristics and Technical Factors on Quantification of Sodium 18F-Fluoride Uptake in Human Arteries: Prospective Evaluation of Healthy Subjects

Sodium 18F-fluoride (18F-NaF) PET/CT imaging is a promising imaging technique for the assessment of atherosclerosis but is hampered by a lack of validated quantification protocols. Both personal characteristics and technical factors can affect quantification of arterial 18F-NaF uptake. This study investigated whether blood activity, renal function, injected dose, circulating time, and PET/CT system affect quantification of arterial 18F-NaF uptake.

METHODS

Eighty-nine healthy subjects were prospectively examined by 18F-NaF PET/CT imaging. Arterial 18F-NaF uptake was quantified at the level of the ascending aorta, aortic arch, descending thoracic aorta, and coronary arteries by calculating the maximum 18F-NaF activity (NaFmax), the maximum/mean target-to-background ratio (TBRmax/mean), and the maximum blood-subtracted 18F-NaF activity (bsNaFmax). Multivariable linear regression assessed the effect of personal characteristics and technical factors on quantification of arterial 18F-NaF uptake.

RESULTS

NaFmax and TBRmax/mean were dependent on blood activity (β=0.34 to 0.44, P<0.001, and β=-0.68 to -0.58, P<0.001, respectively) and PET/CT system (β=-0.80 to -0.53, P<0.001, and β=-0.80 to -0.23, P<0.031, respectively). bsNaFmax depended on PET/CT system (β=-0.91 to -0.57, P<0.001) but not blood activity. This finding was observed at the level of the ascending aorta, aortic arch, descending thoracic aorta, and the coronary arteries. In addition to blood activity and PET/CT system, injected dose affected quantification of arterial 18F-NaF uptake, whereas renal function and circulating time did not.

CONCLUSION

The prospective evaluation of 89 healthy subjects demonstrated that quantification of arterial 18F-NaF uptake is affected by blood activity, injected dose, and PET/CT system. Therefore, blood activity, injected dose, and PET/CT system should be considered to generate accurate estimates of arterial 18F-NaF uptake.

FDG-PET/CT can rule out malignancy in patients with vocal cord palsy

The aim was to investigate the performance of (18)F-fluorodeoxyglucose PET/CT to rule out malignancy in patients with confirmed vocal cord palsy (VCP). Between January 2011 and June 2013, we retrospectively included consecutive patients referred to PET/CT with paresis or paralysis of one or both vocal cords. PET/CT results were compared to clinical workup and histopathology. The study comprised 65 patients (32 females) with a mean age of 66±12 years (range 37-89). Eleven patients (17%) had antecedent cancer. Twenty-seven (42%) were diagnosed with cancer during follow-up. The palsy was right-sided in 24 patients, left-sided in 37, and bilateral in 4. Median follow-up was 7 months (interquartile range 4-11 months). Patients without cancer were followed for at least three months. PET/CT suggested a malignancy in 35 patients (27 true positives, 8 false positives) and showed none in 30 (30 true negatives, 0 false negatives). Thus, the sensitivity, specificity, positive and negative predictive values, and accuracy were (95% confidence intervals in parenthesis): 100% (88%-100%), 79% (64%-89%), 77% (61%-88%), 100% (89%-100%), and 88% (78%-94%), respectively. Sixteen patients had palliative treatment, while 11 were treated with curative intent, emphasising the severity of VCP and the need for a rapid and accurate diagnostic work-up. In this retrospective survey, biopsy proven malignancy (whether newly diagnosed or relapsed) was the cause of VCP in almost half of patients (42%). PET/CT had a high sensitivity (100%) with a relatively high false positive rate, but was excellent in ruling out malignancy (negative predictive value 100%).