154 Part II Chapter 6 routinely combined with integrated computed tomography (CT) to enhance image quality, localization and specificity of the investigation. PET/CT using Na18F (Na[18F]F- PET/CT) provides high-resolution, whole-body, 3D quantitative data on osteoblastic activity, as shown in previous studies and guidelines [6-8]. Prior published studies investigating Na18F -PET/CT mostly focused on malignant or degenerative bone diseases, or calcifications of plaques in coronary artery disease [6, 7, 9]. The use of Na18F-PET quantification in FD has been reported in only one conference abstract using Na[18F]F-PET/CT in a cohort of 16 FD patients in 2017 by Papadakis, et al., and this was followed by a full publication very recently, reporting 15 FD patients [10, 11]. The authors stated that automatic lesion demarcation was generated by the software (MIM Software Inc., Cleveland, OH, USA) and compared with the lesions’ anatomic cross-sectional images, with applied SUV threshold per subject to the entire skeleton [11]. Exclusion of non-FD-bone pathology was manually performed. Na[18F]F-PET/CT-parameters (i.e. SUV max, SUVmean, FTV and TLF, the latter two referred to as total volume and total lesions activity) were related to other clinical measures than our current study, including prognosis of fractures and necessity of surgery and to the serummarkers ALP and osteocalcin (bone formation), and N-telopeptides (bone resorption) [11]. Otherwise, only two case reports were published on Na[18F]F-PET/CT-findings in a single patient with FD in 1966 and 2015 without the use of quantification [12, 13]. Quantification of Na[18F]F-PET/CT for pathology other than FD has been performed by previous authors, starting with Rohren, et al., subsequently modified by Lapa, et al. [6, 7]. Both methods relied on subtraction in order to identify and exclude all sites of Na18F uptake not associated with the pathology of interest (i.e. bone metastases for their study), and subsequent exclusion from the final volume to be analyzed. Our current study aimed to determine the relationship between quantitative parameters of physiological and pathological Na[18F]F-PET/CT uptake and structured clinical and biochemical measures of disease in patients with FD. The primary outcome was to quantify baseline Na18F-uptake in physiological bone and in FDlocalizations in twenty patients and relate these to abovementioned biochemical parameters of FD-activity, pain score, the use of analgesic medication, and to the 36-item short form score (SF-36, RAND Corp., Santa Monica, CA, USA) on quality of life [14, 15]. Secondary aims were to relate Na[18F]F-PET/CT-parameters to classical SBS on planar bone scintigraphy and bisphosphonate treatment. Different normalization procedures to volume of distribution (VD) of the Na18F-uptake were evaluated and different parameters of normal bone uptake and FD-burden were assessed for interobserver reproducibility.