Bone scan with Tc-99m HDP
This is one of the most widely performed Nuclear Medicine tests. The principle of the test is visualisation of living bone, or more accurately, visualisation of the living molecules that make up bone tissue. This test is extraordinarily sensitive in detecting any abnormality within living bone. It is far more sensitive that x-ray, CT or even MRI in the detection of fractures and is the most sensitive means of detecting malignant tumour in bone. The entire skeleton can be surveyed easily and rapidly with modern Nuclear Medicine equipment. This test is also extremely useful for assessment of bone and joint pain following sporting activities or in the many forms of arthritis. It also has an important role in detecting infection in bones and joints.
How is the test performed?
Usually there are 3 phases to a bone scan.
- The first part requires the intravenous administration (using a very small bore needle) of what is known as a radiotracer. As the name implies, a radiotracer is a radioactive compound that is tagged to a molecule or particle that delivers the radioactive compound to a target site. In this case the target site is the cell that generates new bone tissue (osteoblast cell). The radiotracer commonly used is Technetium-99m tagged to HDP (hydroxymethylene diphosphonate). Immediately following injection imaging of the relevant part of the body is undertaken using a gamma camera. This demonstrates blood flow from the venous injection site to the heart and then through the arterial system of the region imaged. This part of the test demonstrates how well that particular part of the body is perfused with blood. Where there is inflammation, perfusion may be increased; where there is disease or trauma of an organ or blood vessels, perfusion may be reduced. This part of the scan usually takes only a minute to image.
- The second part is performed immediately after the first part. This also involves imaging with the gamma camera. Images demonstrate the pooling of blood in the veins. This too may indicate inflammation. Blood pool imaging is very useful to demonstrate inflammation in joints of patients with symptoms of arthritis, and may allow a specific diagnosis of particular types of arthritis, e.g. rheumatoid arthritis. This also allows the doctor to accurately locate and identify the source of joint or bone pain so that appropriate treatment can be started.
- The third part is performed several hours later. Each patient having a bone scan should be encouraged to be relatively mobile during the intervening period and also remain well hydrated. Imaging is again undertaken using the gamma camera. This time the images demonstrate living bone. An accumulation of radiotracer will occur where the bone is under repair. This is therefore seen in fractures, bone tumours, infection, other trauma and wear-and-tear. More diffuse accumulation is seen in arthritis, and other conditions such as Paget’s disease of bone.
Has technology changed bone scanning recently?
The principles of bone scan remain as they have over the past 40-50 years but the technology has dramatically changed as computers have become more powerful. The modern gamma camera consists of a relatively comfortable scanning bed with two detectors front and back that move along the length of the body. This is called planar imaging. This equipment can also perform what is known as SPECT imaging (Single Photon Emission Computed Tomography) that relies on computer reconstruction to show parts of the body in slices. This can be accurately attached to a CT (Computed Tomography) scan by a technique called image fusion or image co-registration. The CT scan demonstrates the bony anatomy and, when coupled with the SPECT images, allows demonstration of the exact location of bone lesions.
PLEASE BRING ANY OTHER X-RAYS, ULTRASOUNDS, CT SCANS, MRI SCANS, MEDICATION LIST OR RELEVANT MEDICAL HISTORY ON THE DAY OF NUCLEAR MEDICINE SCAN
This information sheet may be of use to patients and referring doctors.