Depends upon increased osteoblastic activity and/or increased bone blood flow. Trauma, infection, tumour, metabolic, inflammatory, degenerative diseases are associated with hypervascularity and osteoblastic activity.
Technique:
Single dose of 99m Tc methylene diphosphonate (MDP) 450-600 MBq.
Static imaging 2-4 hours later.
Whole body images and/or multiple spot views
Excreted through kidneys - kidneys and bladder and bladder seen
Triple phase:
Vascular phase 1-3 minutes; radionuclide angiogram
Blood pool phase 3-5 minutes; extracellular activity
Static phase 2-4 hours; skeletal activity
Indications:
Occult bone pain
Metastatic disease: false negative in 3%. MR more sensitive. Beware of metastatic superscan which shows absent or reduced renal activity, common in widespread osteoblastic metastases from prostate or breast.
Assessment of chemotherapy/radiotherapy response: Beware of ‘flare’ phenomenon. Re-imaging within 6 months of treatment may show increased number and increased activity
Primary bone tumours: Useful in osteoid osteomas and osteoblastomas - when suspected a normal bone scan essentially excludes the diagnosis
Bone infection:
Acute osteomyelitis: more sensitive than radiography but less sensitive than MRI. Useful for multifocal disease.
Chronic osteomyelitis: abnormal bone scan does not necessarily indicate active disease. MRI better for assessing disease activity, CT for identifying bony sequestrum.
Skeletal trauma: in occult trauma such as scaphoid or neck of femur, in rib fractures differentiated from metastatic disease, in NAI. Not useful in fracture dating. Stress fractures may be differentiated from traumatic periostitis (shin splints).
Metabolic bone disease: may lead to metabolic superscan, generalised, diffuse increase in skeletal activity with absent or reduced renal activity.
