Diagnostic Challenge of Staging Metastatic Bone Disease in the Morbidly Obese Patients: A Primary Study Evaluating the Usefulness of 18F-Sodium Fluoride (NaF) PET-CT

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Optimizing diagnostic imaging may be challenging in obese patients. The quality of conventional bone scintigraphy can be poor in the morbidly obese due to a combination of factors including high background soft tissue activity. In comparison, sodium fluoride (18F-NaF PET-CT) has a better target-to-background ratio attributed to rapid single-pass extraction and fast clearance from the soft tissues. The aim of the present study is to assess the diagnostic efficacy of 18F-NaF PET-CT in the evaluation of bone metastases in obese cancer patients.

Patients and Methods

Two hundred twelve morbidly obese patients (body mass index, 45 ± 5.1 kg/m2; mean age, 57 years; range, 32–81 years) with body mass index greater than 40 kg/m2 referred for NaF PET-CT for osseous staging of malignancy were retrospectively analyzed. All patients underwent PET-CT scan by injecting 2.2 MBq/kg (0.06 mCi/kg) of 18F-NaF.


18F-NaF PET-CT was definitely benign in 145, possibly benign in 3, equivocal in 4, possibly malignant in 13, and definitely malignant in 47 patients. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of 18F-NaF PET-CT were 93.1%, 96.1%, 90%, 97.3%, and 95.2%, respectively (95% confidence interval).


The results of the present study indicate that 18F-NaF PET-CT retains its high diagnostic accuracy in morbidly obese patients and, by inference, can be a preferred functional modality in these patients.

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