What is a bone scan?
Various processes in the body cause an increase in bone turnover, i.e. the breaking down and absorption of old bone and the laying down of new bone. This process is a normal or physiological process that ensures adequate strength of the bone to withstand the day-to-day stresses that are applied to the skeleton.
Some disease processes, e.g. infections, inflammation or cancers involving bones, can also cause rapid destruction of the bones. Again, as is the typical response, new bone gets deposited by specialized bone cells called osteoblasts.
At the same time, this immature bone gets reorganized into compact units predominantly made up of calcium crystals. In diseased bone, there are increased calcium crystal deposits (e.g. infections, inflammation & cancer). These deposits cover a larger surface area than normal bone since calcium is loosely deposited.
Bisphosphonate medication used in treating osteoporosis binds readily to these crystals. Since the bony crystal deposits in diseased bone also have a larger surface area, significantly more bisphosphonate will bind to these crystals than the more stable mature elsewhere.
Nuclear pharmacists have developed various diphosphonate chemicals that bind similarly but are also attached to a radioactive substance that emits specialized rays called gamma rays. While given in extremely low doses, these gamma rays (much lower radiation than conventional x-rays) can be detected by specialized detectors on a gamma camera machine. The machine itself does not cause radiation exposure.
The bisphosphonate injected is available to the whole body, which allows us to examine the body for multiple areas of increased bone turnover (e.g. in bone cancer or cancer spread).
This gives your doctor an indication of how advanced cancer or infective process is, thereby assisting them in their decision-making regarding future treatment plans.
What can be expected to happen?
You will be asked to drink plenty of water to allow for urinary clearance of any excess tracer that isn’t bound to bone. Furthermore, you will be required to empty your bladder before imaging so that the pelvic bones can be well visualized. This may need to be repeated.
Sometimes we need to perform some images immediately called “early phase” imaging. This is of importance in infection or inflammation imaging. During the 1st phase (flow phase), we assess the blood flow to the area in question. If infected acutely, the blood supply to this area will be increase and show up “hotter” than other areas in the body.
Similarly, in subacute (longer duration) infections, the 2nd phase (tissue or blood pool phase) will also be “hotter” than other areas. This infers that the tissues are leaky for the tracer. This leakiness is typical in an infective process – it allows for white blood cells and other molecules to seep through tissue spaces and make their way to the site of infection. This imaging is performed 5-10 minutes after injection of the tracer.
The 3rd, delayed, or bony phase occurs much later (3 hours later). This allows for adequate attachment to the hydroxyapatite crystals mentioned previously. Usually, a whole-body image is taken lasting 10-15 minutes. A selection of sectional views is also taken from different angles if required. Then finally, the camera detectors will be made to rotate around you at a certain level – the area of suspect infection or most likely area of cancer spread – allowing us to form a three-dimensional image of that section.
Sometimes if the location of a “hot spot” is uncertain, we can perform a CT scan and superimpose the two images to give us a more accurate answer.
The nuclear physician (specialist doctor) will then look at all these images and conclude about your condition that will benefit your doctor and ultimately for you.
How long will the whole scan take?
Approximately 3 ½ hours (including reporting time)
