Bone scans are imaging procedures that examine the skeleton. These scans identify areas of physical and chemical changes within bone tissue. They provide information about bone health and can detect various bone diseases and conditions.
What is a Bone Scan
A bone scan is a nuclear medicine procedure that involves introducing a small amount of a radioactive substance, known as a radiotracer, into the body. This radiotracer, often technetium-99m methylene diphosphonate (Tc-99m MDP), is injected intravenously. After injection, the radiotracer travels through the bloodstream and gradually accumulates in the bones over several hours, usually 2 to 4 hours.
The radiotracer is absorbed by areas of the bone undergoing active metabolism or repair. Bone areas with increased activity, such as rapid cell turnover or increased blood flow, will take up more tracer. A special camera, called a gamma camera, then detects the gamma rays emitted by the radiotracer, creating detailed images. These images reveal areas where the tracer has concentrated, providing a functional view of bone activity.
Detecting Cancer with Bone Scans
Bone scans are useful in identifying areas of abnormal bone metabolism, which can occur when cancer cells are present in the bone. When cancer spreads to the bones, it often causes changes in bone activity and repair processes. The radiotracer accumulates more in these areas of increased activity, showing up as brighter or darker spots on the scan images, commonly referred to as “hot spots.”
Bone scans differentiate between primary bone cancer, which originates in the bone, and metastatic cancer, which spreads to the bone from another part of the body. They are effective at detecting metastatic cancer, such as from breast, prostate, or lung cancer, as these often stimulate increased bone metabolism. The scattered pattern of these “hot spots” can help doctors assess the extent of cancer spread. Bone scans are sensitive for identifying bone metastases, often before they are visible on other imaging tests like X-rays.
Understanding Bone Scan Results
“Hot spots” on a bone scan indicate areas of increased radiotracer uptake, signifying elevated bone metabolic activity. While these can point to cancer, they are not specific to it. Other conditions that cause increased bone turnover, such as fractures, arthritis, or bone infections, can also appear as “hot spots.” For instance, a healing fracture or areas affected by arthritis will absorb more tracer.
Conversely, “cold spots” on a bone scan indicate areas where there is reduced or no tracer uptake, suggesting decreased bone activity or blood supply. These can be caused by conditions like certain types of cancer (e.g., multiple myeloma), bone cysts, or a lack of blood flow to the bone. Because bone scans are sensitive but not highly specific, additional diagnostic tests are often necessary to pinpoint the exact cause of any abnormalities. These further tests may include X-rays, MRI, CT scans, or a biopsy to provide a definitive diagnosis.
Bone Scans in Context
Bone scans play a role in the broader diagnostic workup for various conditions, including cancer, but they are not used as a standalone screening tool. Their utility extends to staging cancer, which involves determining how far the disease has spread within the body. They can also be used to monitor the effectiveness of cancer treatment over time, by comparing scans taken at different stages.
Additionally, bone scans are useful for investigating unexplained bone pain or detecting subtle fractures that may not be apparent on standard X-rays. Healthcare providers often integrate bone scan results with other clinical information and imaging studies to form a comprehensive diagnosis and treatment plan.