A radiotracer (bone-seeking radionuclide) is injected into the bloodstream through a vein. As it decays, the radiotracer emits gamma radiation, which is detected by a camera that slowly scans your body. The camera captures images of how much radiotracer collects in the bones. Several bone-seeking radiopharmaceutical have been used:
- Calcium analogues
- Strontium 85
- Strontium 87
- Hydroxyl group analogues
- Fluorine 18
- Phosphonate Analogues
- Pyrophosphate
- Methylen dyphosphonate (MDP)
- Methylen hydroxidyphosphonate (MHDP)
Dyphosphonates (MDP and MHDP) are the most common used. The advantages of dyphosphonates include:
- Rapid bone uptake
- 50% of activity in bone at 2-3 hours
- Rapid urinary clearance
- 35% excreted by kidneys within 3 hours
- High bone / soft tissue ration
- Only 10-15% of activity remain in soft tissues
Bone uptake depends on several factors:
- Blood supply
- Capillary permeability
- Fluid pressure within bone
- Quantity of mineralized bone
- Bone turnover
- Hormones
- Vitamins
Non-osseous structures normally seen on bone scintigrams are kidneys and bladder, as technetium-99m diphosphonates are excreted primarily via the urinary tract.