What is a Bone Density Study?
Every day, physicians use radiography, or x-rays, to view and evaluate bone fractures and other injuries of the musculoskeletal system. However, a plain x-ray test is not the best way to assess bone density. A Bone Mineral Density test is the only way to diagnose osteoporosis and determine your risk for a future fracture. Since osteoporosis can develop undetected for decades until a fracture occurs, early diagnosis is important. There are several different machines that measure bone density with DEXA and QCT (Quantitative Computed Tomography) being the most accurate. DEXA is more widespread because it is a stand-alone machine which can be purchased by any physician and set up in an exam room in his/her office. QCT is a three-dimensional method obtained on a CT scanner. Both DEXA and QCT are good exams, but based on recent data, QCT is more accurate at determining true bone density of the spine and hip. QCT is a three-dimensional method that can target the trabecular bone (the first to show changes of bone loss) and measure it separate from the surrounding cortical bone, degenerative/arthritic changes, bone spurs and aortic calcifications. QCT is also superb at monitoring the response to therapy, demonstrating changes months to years before other methods. At Methodist Diagnostic Center, we perform the QCT, because we understand that it is considered to be the “gold-standard” in testing.
What are some common uses of the procedure?
CT Bone Density testing is used most often to diagnose osteoporosis, a condition that often affects women after menopause, but may also be found in men. Osteoporosis involves a gradual loss of calcium, causing the bones to become thinner, more fragile, and more likely to break. The CT Bone Density test can also assess your risk for developing fractures. If your bone density is found to be low, you and your physician can work together on a treatment plan to help prevent fractures before they occur. CT Bone Density testing is also effective in tracking the effects of treatment for osteoporosis or for other conditions that cause bone loss. CT Bone Density testing is strongly recommended if you:
- are a post-menopausal woman and not taking estrogen.
- have a personal or maternal history of hip fracture or smoking.
- are a post-menopausal woman who is tall (over 5 feet 7 inches) or thin (less than 125 pounds).
- are a man with clinical conditions associated with bone loss.
use medications that are known to cause bone loss, including corticosteroids such as Prednisone, various anti-seizure medications such as Dilantin and certain barbiturates, or high-dose thyroid replacement drugs.
- have type 1 (formerly called juvenile or insulin-dependent) diabetes, liver disease, kidney disease, or a family history of osteoporosis.
- have high bone turnover, which shows up in the form of excessive collagen in urine samples.
- have a thyroid condition, such as hyperthyroidism.
- have experienced a fracture after only mild trauma.
- have had x-ray evidence of vertebral fracture or other signs of osteoporosis.
How should I prepare for the procedure?
- On the day of the exam, eat normally.
- Do not take over-the-counter or prescription medication such as calcium, multivitamins or Tums for 48 hours.
- If you currently Fosamax, Actonel or Miacalcin these medications will need to be discontinued within 7 days of the test.
- The bone density study should not be scheduled within 7 days of the following:
- Barium enema
- Barium swallow
- Upper GI series
- CT scan with contrast
- Any nuclear medicine study
- Angiogram/heart catheterization
- MRI with contrast
- Wear loose, comfortable clothing, avoiding garments that have zippers, belts, or buttons made of metal.
- Women should always inform their physician or x-ray technologist if there is a possibility they are pregnant.
What does the equipment look like?
The CT scanner is a large, square machine with a hole in the center, something like a doughnut. The patient lies still on a table that can move up or down, and slide into and out from the center of the hole. Within the machine, an x-ray tube on a rotating gantry moves around the patient's body to produce the images, making clicking and whirring noises as the table moves. Though the technologist will be able to see and speak to you, you will be alone in the room during the CT scan.
How is the procedure performed?
The technologist begins by positioning the patient on the CT table. The patient's body may be supported by pillows to help hold it still and in the proper position during the scan. As the study proceeds, the table will move slowly into the CT scanner "doughnut." Depending on the area of the body being examined, the increments of movement may be so small that they are almost undetectable, or large enough that the patient feels the sensation of motion. A CT examination usually takes from five minutes to half an hour. When the exam is over, the patient may be asked to wait until the images are examined to determine if more images are needed.
What will I experience during the procedure?
CT Bone Density testing is a simple, non-invasive procedure. CT scanning causes no pain, and with spiral CT, the need to lie still for any length of time is reduced. No anesthesia is required and radiation exposure is minimal.
Who interprets the results and how do I get them?
The results of a CT Bone Density test are interpreted by our radiologist, who is a physician specially trained to diagnose conditions and diseases by obtaining and interpreting medical images. Our radiologist will send an interpretation of your results and a signed report to your primary care physician, who will work with you to develop a treatment plan.
Usually available within a few days, your test results will be in the form of a T score. This number shows the amount of bone you have compared to a young adult of the same gender with peak bone mass. A score above -1 is considered normal. A score between -1 and -2.5 is classified as osteopenia, the first stage of bone loss. A score below -2.5 is defined as osteoporosis. It is used to estimate your risk of developing a fracture.
What are the benefits of Bone Density Scans?
CT Bone Density testing is the most accurate method available for the diagnosis of osteoporosis. It is also considered an accurate estimator of fracture risk. It will not tell whether you will or will not have a fracture, but gives relative risk of suffering a fracture, just as cholesterol and blood pressure help determine risk for heart disease. A low reading should not cause you to be anxious, but may help you set healthy goals. As with other diseases and conditions, early detection is the key to prevention of further bone loss and eventual fractures.
What are the limitations of CT Bone Densitometry?
CT Bone Density tests cannot predict who will experience a fracture, but can provide indications of relative risk. Osteoporosis is not part of normal aging, although many people continue to believe this is true. With the information obtained from a CT Bone Density test, you and your doctor can decide what prevention or treatment steps are right for you.