Fibrous dysplasia related 18F-NaF activity in the spine is significantly higher in patients with scoliosis, compared to patients without spinal deformity

Objectives: Fibrous dysplasia (FD) is a benign mosaic skeletal disorder characterized by replacement of normal bone and normal marrow with abnormal fibro-osseous tissue resulting in fractures, deformity, and functional impairment. ¹⁸F-NaF PET/CT is the hybrid imaging modality of choice for functional skeletal imaging, while enabling anatomic characterization of skeletal abnormalities. Aim of the current study was to explore potential association between ¹⁸F-NaF uptake by fibrous dysplasia (FD) lesions in the spine and the presence of scoliosis. Methods: Fifteen patients with FD underwent whole-body ¹⁸F-NaF PET/CT studies at the NIH Clinical Center. The mean age ±SD at the time of the scanning was 28±12 years. PET/CT scans were obtained on dedicated PET/CT scanners, after i.v. injection of an average ±SD of 2.81±0.83mCi of ¹⁸F-NaF. PET images from the vertex of the skull to the plantar surface of the feet were acquired, 62.36±6.11 (average± SD) minutes post the radiotracer injection. A non-contrast, low dose, non-diagnostic CT scan was performed for attenuation correction and co-registration purposes. FD related activity in the spine was assessed by quantifying ¹⁸F-NaF uptake using the MIM Vista workstation (version 6.5.9). A VOI encompassing the entire spine was drawn, and subsequently a SUV-threshold based approach was applied in order to include all disease-related spinal uptake. The software enables automatic generation of separate VOIs encircling all areas above the SUVthreshold set by the user. Subsequently, an experienced nuclear medicine physician, manually excluded areas with physiologic or non-spinal FD-related activity (e.g. activity in the kidneys). Finally, the following parameters were automatically obtained: standardized uptake value of the hottest spinal lesion (SUVmax), average SUV of all ¹⁸F-NaF positive spinal lesions (SUVmean) and spinal disease indices of total volume (TV) which is the summation of the volumes of all ¹⁸F-NaF avid FD lesions in the spine and total lesions activity (TA), which is determined as the product of SUVmean multiplied by TV (TA=SUVmean × TV).

Results: Mann-Whitney-Wilcoxon test showed that TV and TA obtained from FD lesions in the spine were significantly higher (TV: P=0.01; TA: P=0.02) in patients with scoliosis in comparison to patients without spinal deformity (Fig.1). Adjusted p-value for false discovery rate equals 0.048. Spinal SUV-metrics (SUVmax and SUVmean) did not show statistical difference between patients with and without scoliosis. Conclusion: The total volume and activity of fibrous dysplasia related ¹⁸F-NaF activity in the spine correlates with the presence of scoliosis. This data indicates the capability of ¹⁸F-NaF PET/CT imaging to reflect the severity of FD clinical manifestations in a specific anatomic region of the skeleton.

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