19 General introduction and outline of this thesis Thus Na[18F]F-PET is able to detect changes in osteoblast activity swiftly after onset. The expression of Na[18F]F-uptake in human bone reflecting young osteoblasts is depicted in this schematic drawing (Figure 2): Figure 2. Na[18F]F and [99mTc]Tc-MDP-uptake in human bone by hydroxyapatite, reflecting young osteoblasts. After intravenous injection of Na[18F]F, the OH--ions in hydroxyapatite [Ca 10(PO4)6(OH)2] are exchanged for 18F--ions, converting hydroxyapatite to fluorapatite Source: adapted from (Creative Commons Attribution-Share Alike 3.0 Unported license). Hydroxyapetite structure adapted from: Pecheva, Emilia & Pramatarova, Lilyana. (2006). Modified Inorganic Surfaces as a Model for Hydroxyapatite Growth. 1