injection of a bone seeking compound attached to a radioisotope. The material is laid down in the hydroxyapatite crystal
resultant radiation is picked up by a gamma camera, consisting of a circular sodium iodide crystal 40cm in diameter coupled to a number of photomultiplier tubes.
Bone scanning relies on osteoblastic activity. If there is no osteoblastic activity (e.g. in multiple myeloma) there will be no tracer uptake
Other tumours with little or no uptake include
- some lymphomas
- anaplastic tumours
- high grade renal & thyroid tumours.
most commonly used material is technetium 99m phosphate
- half life of 6 hours
- decays by emitting photons with an energy of 140keV, which is ideal for imaging with a gamma camera

Phases

A bone scan has three phases

Blood flow
- taken in the first 30 seconds, with images every 5 seconds providing an angiogram like image
Blood pool
- taken minutes afterwards. This is a reflection of soft tissue distribution
Delayed
- shows accumulation of tracer at 3-4 hours post injection. Increase bone activity.Note: the tracer accumulates in bone within one hour, but the delayed views are taken at 3-4 hours to allow elimination of the tracer. Patients on dialysis should have their dialysis after the injection of tracer but before the delayed images to allow for elimination, or resolution of bony structures will be difficult

Other tracers

incorporated into hydroxyapatite crystals
but is also an iron analog & is thus incorporated into bacterial siderophores & leucocyte lactoferrins, thus accumulating as a result of hyperaemia & chemotaxis
Gallium is more effective than technetium in diagnosing spinal infections

tracer is normally taken up in areas of red marrow (the axial skeleton). Uptake of the labeled leucocytes isn’t related to bone turnover so this marker is more specific for infection than technetium or gallium. The labeling doesn’t work as well in chronic infections (lymphocytes rather than leucocytes present) or in neutropenic patients

is being used in the evaluation of osteosarcomas. Thallium is taken up by viable parts of the tumour, so repeated scans may be useful in assessing response to chemotherapy