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.