Table 1. Overview of imaging strategies in bone research.
| Nuclear imaging: Relies on pharmaceuticals that have been labeled with radionuclides | ||
| Imaging modality | Probe | Description |
| Bone scintigraphy/SPECT | 99mTc-MDP | Targets the calcium in hydroxyapatite.33 |
| PET | 18F-fluoride | Targets the hydroxyl groups in hydroxyapatite.34 |
| 18F-FDG | An indicator of cellular glucose metabolism.77 | |
| Optical imaging: Relies on the detection of photons from exogenous fluorochromes (linked to biological response) | ||
| Imaging modality | Probe | Description |
| NIRF/FMT | OsteoSense | A bisphosphonate (pamidronate) bound to a near-infrared (NIR) fluorophore (IRDye78). Targets hydroxyapatite.43 |
| Indocyanine green-alendronate conjugate | A bisphosphonate (alendronate) bound to a NIR fluorophore (indocyanine green). Targets hydroxyapatite.45 | |
| BoneTag (LI-COR Biosciences, Lincoln, NE, USA) | A tetracycline derivative bound to a NIR fluorophore (IRDye 800CW). Targets hydroxyapatite.46 | |
| Cathepsin-K | Targets cathepsin-K, which is expressed in active osteoclasts and involved in the breakdown of the bone matrix.8 | |
| BLI | OC (hOC promoter) | Targets osteocalcin, which is expressed by osteoblasts and involved in tissue mineralization.49 |
| Firefly luciferase coupled to MSCs | Targets stem cells that have the capacity to differentiate into osteoblasts and proliferate.51 | |
| Anatomical imaging: | ||
| Imaging modality | Feature | Description |
| In vivo micro-CT | Anatomical changes in bone microstructure | By using serial images, locations of bone formation and bone resorption can be visualized and morphometrically described.55 |
| MRI | Bone marrow | The trabecular bone marrow can be resolved from the relaxation rate, and the trabecular bone volume fraction from the attenuation of the spin-echo amplitude.78 |
Abbreviations: BLI, bioluminescence; CT, computed tomography; FDG, fluorodeoxyglucose; FMT, fluorescence molecular tomography; hOC, human osteocalcin; MDP, methylenediphosphonate; MSCs, mesenchymal stem cells; MRI, magnetic resonance imaging; NIRF, near-infrared fluorescence; PET, positron emission tomography; SPECT, single photon emission CT.