USING A BONE SCAN TO DIAGNOSE BONE INFECTIONS
Bone infections are uncommon, only affecting about two in 10,000 people. However, they can cause serious bone damage if left untreated.
Also called osteomyelitis, infection and inflammation of the bone or bone marrow can be caused by bacteria or fungus that enters bone tissue from the bloodstream, due to injury or surgery. Most cases develop because of an open wound.
Commonly affecting the long bones in the feet, leg, pelvis, upper arm, and spine, the signs and symptoms of osteomyelitis depend on the type. Symptoms often include:
- Pain, swelling, redness, and tenderness in the affected area.
- Irritability, lethargy, or fatigue.
- Fever, chills, and sweating.
- Drainage from an open wound near the infection site or through the skin.
- Swelling of the ankles, feet, and legs, or changes in walking pattern/limping.
For unexplained bone pain, your doctor might order a bone scan to help determine the cause. This test is sensitive to differences in bone metabolism.
HOW DOES A BONE SCAN DETECT INFECTION?
Bone scans, also known as bone scintigraphy, use a small amount of radioactive material (called a radiopharmaceutical) injected into a vein that travels through your bloodstream into your bones. A gamma camera detects the radiation emitted from your body, which is put together by a computer that creates images of the bones.
Areas that take up little or no amount of the radiopharmaceutical appear as "cold" spots, and could show a lack of blood supply to the bone. Areas which take up more radiopharmaceutical show up as "hot" spots, indicating increased blood flow or bone turnover, and could point to problems like arthritis, a tumour, a fracture, or an infection.
Depending on the area of concern, a bone scan can image the entire body or pay particular attention to certain parts. It is useful in surveying areas with many small bones and joints like the spine, foot, and ankle because it can provide detailed, localized information about bone metabolism.
WHAT HAPPENS DURING A BONE SCAN?
A bone scan involves two separate appointments booked on the same day. The first appointment will take approximately 15 minutes. During this time, the radiopharmaceutical is injected into an arm vein and travels throughout the body. You will be asked to lie on your back on the imaging bed while a gamma camera is placed over your body. The first set of images documents increased or decreased flow to the areas of concern. Afterwards, you will be able to go about your normal daily activities until the second appointment (2-5 hours after the first).
During the second appointment, imaging will be performed without any additional injections, to document uptake in the bones. It will take approximately 30-45 minutes. You will be asked to hold as still as possible, while breathing normally – movement can blur the images and make them more difficult to interpret. If required, additional imaging called “SPECT/CT” may also be performed towards the end of this second appointment.
SPECT/CT (Single Photon Emission Computed Tomography/Computed Tomography) imaging combines two imaging types to help localize the area of abnormal activity that may be present on the planar bone scan image. For the "SPECT" part, the nuclear medicine gamma camera rotates 360 degrees around the body and acquires measurements of the radiation being emitted, which the system reconstructs into a 3D image. For the "CT" portion, a low-dose CT image is taken, similar to those from a classic diagnostic CT scan, but using limited radiation. In this case, they are fused electronically with the SPECT images to get the SPECT/CT image.
IS A BONE SCAN SAFE?
The radiopharmaceutical is excreted from the body through your urine and will decay within the body over the 48 hours following your exam. Keeping hydrated and voiding frequently will help eliminate it from your body.
A bone scan involves a small dose of ionizing radiation from the radiopharmaceutical injected into your vein, and also from the CT scan during the CT portion of SPECT/CT imaging. CT imaging is a form of X-ray and the exposure to radiation from this scan is slightly higher than that of standard X-rays, but the associated risk is still small. Overall, the radiation exposure from a bone scan with SPECT/CT is about the equivalent of exposure to the earth's natural background radiation over two years. In most cases, the benefits, such as the early detection of a serious illness, outweigh the small increased risk from radiation exposure.
Mayfair Diagnostics complies with policies and has procedures in place for nuclear medicine radiation safety, including a Radiation Safety Officer who ensures we follow all policies and procedures. If you are pregnant, or if there is a chance you are pregnant, we will not perform the exam. If you are breastfeeding, please inform the technologist. The exam will still be performed, but you will be advised to pump and discard breast milk, or store it for a specific period of time before using.
HOW DO I GET A BONE SCAN?
This exam is covered under your Alberta Health Care Insurance Plan and must be requested by a health care practitioner. To determine whether it is appropriate for you, your doctor will often review your medical and family history, risk factors, how long symptoms have been present, and how they affect daily activities. If this exam is indicated as a best next course of action, your doctor will provide you with a requisition and the appointment can be booked.
Lee, Y. J., et al. (2016) “The imaging of osteomyelitis.” Quantitative Imaging in Medicine and Surgery. 2016 Apr; 6(2): 184–198. Accessed July 21, 2021.