A bone scan is used to find problems that are not able to be diagnosed by viewing an ordinary x-ray. It is used in combination with a radioactive tracer, which is a radioactive dye that is injected into the blood stream. The dye collects in your bones, leaving behind a radioactive marker, or "hot spot" that can alert your physician of any abnormalities that need to be addressed.
What is a Hot Spot?
Hot spots are small amounts of radioactive material that is left behind after the injected dye travels through your entire skeletal system. American Cancer Society explains that the scientific name for a hot spot is "technetium diphosphonate," which has no known side effects. The hot spots will show up on scanned images, black or grey in colour.
The amount of radioactive dye that is absorbed by the bones depends on the degree of illness or injury. The pattern of absorption varies from illness to illness. For instance, the hot spot pattern that is indicative of cancer is different than that of an infection. According to John Hopkins Medicine, a normal bone scan would show no black hot spots. Instead, each bone would show an equal amount of grey which shows even absorption.
According to the Cleveland Clinic, osteomyelitis is a bone infection that is usually caused by "Staphylococcus aureus," which is a bacterium that is also responsible for the methicillin resistant Staphylococcus aureus, or MRSA, infection. On a bone scan image, hot spots are revealed along the outer areas of bones, indicating areas of infected bone tissue. Sepsis can also be seen as hot spots on a bone scan, showing bones that have become infected by other illnesses such as a bladder infection.
Arthritis and Bone Trauma
In some patients, hot spots are a sign that somewhere along the line there has been a trauma or injury to one or several bones. Bones that have been fractured will show signs of new growth and active cells that are highly absorbent and attracted to the radioactive dye. Roswell Park Cancer Institute reports that arthritis will also show up in a bone scan.
Cancer is another condition that can be seen in bone scan images. Hot spots that appear throughout the body may indicate that cancer has spread or "metastasized" to the bones. Merck.com explains that the most common types of cancer to spread to the bones are carcinomas. When there are multiple hot spots throughout the body of a patient with a known cancer, bone infiltration is often suspected. Treatments for such a scenario would most often include a combination of radiation therapy and chemotherapy.