A bone scan is a two-part imaging test that takes about five hours total. You receive an injection of a mildly radioactive tracer into a vein, wait two to four hours while it travels through your bloodstream and absorbs into your bones, then lie on a table while a specialized camera photographs your entire skeleton. The tracer collects in areas where bone is actively repairing or changing, making those spots visible on the images.
Why Bone Scans Are Ordered
Bone scans detect problems that regular X-rays can miss. X-rays mainly reveal late-stage bone injuries like visible fractures and healing calluses, with a sensitivity of only about 56% for stress injuries. A bone scan picks up changes much earlier because it tracks biological activity in the bone rather than structural damage. This makes it especially useful for finding stress fractures, cancer that has spread to bone, infections, and unexplained bone pain.
Your doctor may also order a bone scan to monitor how well a known bone condition is responding to treatment, or to evaluate abnormal lab results that suggest bone disease.
How to Prepare
Preparation is straightforward. Most facilities ask you to drink plenty of water before and after your appointment, which helps the tracer circulate and later flush from your body. You typically don’t need to fast for a standard bone scan, though some specialized bone studies do require overnight fasting and temporarily stopping calcium, vitamin D, or certain medications. Your imaging center will give you specific instructions when you schedule the appointment.
Wear comfortable clothing without metal snaps or zippers if possible. You may be asked to change into a gown. Remove jewelry and metal objects before the scan.
The Tracer Injection
The appointment starts with a small injection into a vein in your arm, similar to a routine blood draw. The tracer is a radioactive compound called technetium-99m attached to a bone-seeking molecule. Once in your bloodstream, it naturally gravitates toward areas of high bone activity, the places where your skeleton is actively rebuilding or remodeling itself.
The injection itself takes just a few seconds and feels like any other needle stick. Some people notice a cool sensation as the fluid enters the vein. In certain cases, the imaging team takes a quick set of pictures immediately after the injection to capture blood flow patterns, which can help evaluate inflammation or blood supply problems near the bone.
The Waiting Period
After the injection, you wait about two to four hours. Memorial Sloan Kettering puts the typical wait at around three hours. During this time, the tracer circulates through your body and gradually binds to bone tissue. Areas with higher metabolic activity absorb more tracer than healthy bone does.
You’re free to leave the imaging area during this wait. Most facilities encourage you to drink several glasses of water and urinate frequently, which helps clear excess tracer from soft tissues and improves image quality. You’ll return to the imaging department at a scheduled time for the actual scan.
What the Scan Feels Like
You lie flat on a padded table while a large camera (called a gamma camera) passes slowly over your body. The camera detects the tiny amount of radiation emitted by the tracer in your bones and converts it into images. It does not emit radiation itself, so there’s no buzzing, heat, or discomfort. The camera moves close to your body but doesn’t touch you.
You need to lie still during the scan, which typically takes 30 to 60 minutes depending on whether your doctor requested images of your whole body or just a specific area. The room is quiet, and the process is painless. If lying flat for that long is uncomfortable due to back pain or other issues, let the technologist know. They can often make small adjustments with pillows or positioning aids.
How Results Are Interpreted
The images show your skeleton in shades of gray. Areas where the tracer concentrated heavily appear as bright spots, often called “hot spots.” These indicate places where bone cells are unusually active, which can result from fractures, infections, arthritis, or tumors. Areas with unusually low tracer uptake, called “cold spots,” suggest reduced blood supply or certain types of cancer that destroy bone rather than stimulate it.
A hot spot alone doesn’t confirm a specific diagnosis. Many different conditions cause increased bone activity, so your doctor interprets the results alongside your symptoms, medical history, and sometimes additional imaging like CT or MRI. Results are typically available within a few days, though some facilities provide preliminary findings sooner.
Radiation Exposure
A bone scan delivers an effective radiation dose of about 6.3 millisieverts (mSv). For context, a standard chest X-ray delivers about 0.1 mSv, and the average person absorbs roughly 3 mSv per year from natural background sources like radon, cosmic rays, and the earth’s soil. So a bone scan exposes you to roughly two years’ worth of natural background radiation in a single session.
The tracer has a half-life of just six hours, meaning half of its radioactivity disappears every six hours. Within a day or two, virtually all of it has decayed or been flushed from your body through urine.
Safety During Pregnancy and Breastfeeding
If you’re pregnant, the fetal radiation dose from a bone scan is generally under 5 milligray, which the American College of Obstetricians and Gynecologists considers safe. Ultrasound and MRI are preferred when they can answer the clinical question, but ACOG’s guidelines state that a bone scan should not be withheld from a pregnant patient if it’s the best available test for the situation.
If you’re breastfeeding, some radioactive materials can pass into breast milk. Your nuclear medicine team can advise whether you need to temporarily pause nursing and pump and discard milk for a specific window after the scan.
After the Scan
There’s no recovery period. You can drive, eat, and return to normal activities immediately. The main recommendation is to keep drinking extra water for the rest of the day to help your kidneys flush the remaining tracer. Each time you urinate, you’re eliminating more of it. Washing your hands thoroughly after using the bathroom is a reasonable precaution for the first 24 hours, since the tracer leaves your body through urine.
The small amount of radiation still in your body after the scan is not a risk to the people around you, including children. No isolation or special contact precautions are needed.