According to the National Institutes of Health (NIH), a bone density scan is used to measure the density of bone in a person. When bone density is low, there is a greater likelihood of fracture. A bone scan, along with a patient's medical history, is a valuable tool in predicting the chance of a fracture and whether any preventative treatment would be beneficial.
Bone Scan vs. Bone Density Test
A bone scan, also called dual-energy X-ray absorptiometry (DXA), differs from a bone density test. A bone scan requires the patient to be injected with a dye prior to the exam, which allows a scanner to identify differences in the conditions of various areas of bone tissue.
A bone density test, also called densitometry (DEXA), uses special X-rays to calculate how many grams of calcium and other bone minerals are grouped together into a segment of bone.
Bone Scan Benefits
DXA is most commonly used to diagnose osteoporosis (thinning and weakening of the bones) that frequently affects postmenopausal women. A DXA test can also gauge a person's risk for developing fractures.
A bone scan can show changes in bone tissue that may be a sign of cancer, bone lesions, inflammation, infections or other irregularities in the bone.
Postmenopausal women who are not taking estrogen replacement and people who use medications that have been found to cause bone loss are among those who are strongly encouraged to have a bone density scan.
Preparation
According to the NIH, a bone density scan is painless and exposes the patient to a minimal dose of radiation. The scan uses a low-energy X-ray similar to what is used in a chest X-ray. You do not have to limit or restrict food and/or beverage intake prior to undergoing the scan.
It's important that you have not recently had oral contrast (improves CT images of the abdomen and pelvis) or nuclear medicine (small amounts of radioactive materials used to diagnose and treat disease) prior to a bone density scan.
Tell your doctor if you are pregnant or suspect you may be pregnant. Because of the radioactivity used in a bone scan, it is not performed on pregnant women.
Procedure
As the bone density scan gets under way, you will lie on your back on an exam table. Support will be provided to the specific area of the body that is to be scanned. These are most frequently the lower back, left hip or lower arm.
X-rays will move from under the exam table up through the body area to the scanner above the table. The X-rays are recorded and used by the scanner to establish your bone density. The scan takes about 30 minutes from start to finish.
Scan Results
According to the American College of Radiology and the Radiological Society of North America, the results of a bone density scan will have two scores.
The T-score number shows the amount of bone you have in comparison to a young adult of the same sex with optimal bone mass. A score above 1 is normal, while a score below -2.5 is considered to be osteoporosis.
The Z-score number indicates the amount of bone you have compared with other people in your age group and of the same size and sex. If the Z-score is abnormally high or low, additional tests may be necessary.
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