DEXA scanning, an enhanced form of x-ray technology, is today's established standard for measuring bone mineral density and body composition. In simple terms, it is capable of creating a map of your body's bone mass, fat mass, and lean mass, and bone mass.
What is a DEXA scan?
Bone density scanning, also called DEXA (short for dual-energy x-ray absorptiometry) or bone densitometry, is an enhanced form of x-ray technology that is used to measure bone loss by measuring bone mineral density (BMD). By measuring the amount of bone in areas such as your hip and spine, the results of the DEXA scan can tell you if you have normal or abnormal bone density, and can determine your risk for fractures.DEXA scanning can also register fat and lean mass distribution throughout the entire body. In simple terms, it is capable of detailing overall and regional measures of fat mass, lean mass, and bone mass. This can serve as a powerful motivational tool for people tracking weight loss, nutrition, exercise, rehabilitation and overall health. Armed with the information gained from these scans, you can take measures to improve your overall health or measure the progress you have made.
DEXA is most often used to diagnose osteoporosis, a condition that often affects women after menopause but may also be found in men (and rarely in children). Osteoporosis involves a gradual loss of calcium, as well as structural changes, causing the bones to become thinner, more fragile and more likely to break. By examining the bone mineral density at key points, DEXA scanning can accurately assist in diagnosing this condition.
DEXA is also effective in tracking the effects of treatment for osteoporosis and other conditions that cause bone loss, as well as assessing an individual's risk for developing fractures. The risk of fracture is affected by several factors, including age, body weight, history of prior fracture, family history of osteoporotic fractures and life style issues such as cigarette smoking and excessive alcohol consumption. These factors are taken into consideration when deciding if a patient needs therapy.
For those seeking knowledge of their body’s composition, there is no better way than through the use of a DEXA scan. Think of every time you’ve used a scale to track your progress – while this number is a good way to track progress, it doesn’t tell you what type of weight your losing or gaining. Is it fat? Muscle? Both? While there are ways of calculating your body composition, none are more accurate and definitive as a DEXA scan. Once the scan is complete, your technician will review your results with you, including a colored map of your body and charts showing your exact composition.
So who needs a bone density DEXA scan?
People who should consider having a DEXA scan to determine their bone density fall into 3 categories: 1. All women 65 years and older, and all men 70 years and older
2. Women under the age of 65 with any of the following risk factors:
Low body mass (less than 127 pounds)
History of amenorrhea before the age of 42, or early menopause
3. Men and women of any age with any of the following risk factors:
Family history of osteoporosis
Vitamin D deficiency
Loss of height
Alcohol or cigarette use
Long term use of steroids
Eating disorder, malnutrition or recent unexplained weight loss
Broken bone from little or no trauma
Hyperthyroidism or hyperparathyroidism
And who needs a body composition DEXA scan?
People who should consider having a DEXA scan to determine their body composition fall into 4 categories:
If you are trying to lose weight & want to monitor body fat loss and muscle growth from exercise, DEXA is an accurate measure of weight management and fitness programs.
If you are proactive in your health and want to reduce the risks of heart disease, diabetes, high blood pressure, high cholesterol, cancer and obesity – a DEXA scan is a positive first step.
If you are an athlete or bodybuilder and you’re trying to achieve a low ratio of fat to lean tissue mass, you can use DEXA to track muscle atrophy from injury, as well as muscle gain during rehabilitation.
If you are interested in weight training and you want to monitor muscle mass, and want to get a fat scan and analysis for your health, DEXA scanning provides insight into your body’s measurements.
What about the alternative methods of measuring body composition?
Essentially, you get the accuracy you pay for. Other popular methods like hydrostatic weighing, the Bod Pod, and calipers rely on calculated measurements of body fat that are influenced by uncontrollable environmental variables and accidental, or intentional, human error.
Underwater weighing, the pre-DEXA body composition gold standard, assumes that densities of fat mass and fat-free mass are constant. However, this doesn’t take into account a few important and potentially conflicting variables that strongly influence the equations used to calculate body density. For example, athletes typically have denser bones and muscles than non-athletes. Thus, their measurements often underestimate body fat percentage. Conversely, the body fat of elderly patients, especially those with osteoporosis, may be overestimated due to these body density assumptions.
Other popular calculated measurements have similar limitations. Subjective variables are inherent to any calculated measurement of body fat. Therefore, any discrepancy between DEXA and another method is not due to an overestimate of the DEXA, but rather inconsistencies inherent in other measurement methods. Of these, measurements by caliper (skin fold) and electrical impedance testing have proven to be the most wildly inaccurate. In fact, measurement by caliper significantly underestimated body fat percentage by 3.2–5.6% in women when compared to a DEXA scan.
In a recent Texas A&M study, the body composition and bone mineral density of elite female college athletes was observed and tracked over competitive seasons. Although not the intent of the study, an interesting juxtaposition emerged between popularly reported body fat percentages, and those measured in elite athletes. For example, the DEXA-measured average body fat percentage of female swimmers was measured at 22.2%, and 15% for track sprint athletes. These numbers differ vastly to what we would assume they would have, due in part to the popular notions of single-digit leanness.
While body mass index (BMI) can be helpful to track your progress, body fat percentage is superior as a measure of healthy weight. Over the long haul, weight means nothing unless you can accurately assess whether that weight you’re trying valiantly to lose or gain actually consists of fat or muscle. Think your diet and training regimen is really working? The DEXA is a simple and sure-fire way of letting you know.
How should I prepare for the scan?
On the day of the exam you may eat normally. You should not take calcium supplements for at least 24 hours before your exam. You should wear loose, comfortable clothing, avoiding garments that have zippers, belts or buttons made of metal. Objects such as keys or wallets that would be in the area being scanned should be removed. You may be asked to remove some or all of your clothes and to wear a gown during the exam. You may also be asked to remove jewelry, removable dental appliances, eye glasses and any metal objects or clothing that might interfere with the x-ray images.
Inform your physician if you recently had a barium examination or have been injected with a contrast material for a computed tomography (CT) scan or radioisotope scan. You may have to wait 10 to 14 days before undergoing a DEXA test.
Women should always inform their physician and x-ray technologist if there is any possibility that they are pregnant. Many imaging tests are not performed during pregnancy so as not to expose the fetus to radiation. If an x-ray is necessary, precautions will be taken to minimize radiation exposure to the baby.
How is the DEXA scan performed?
The x-ray technician will help you lie on your back on a padded table. An x-ray generator is located below this table, with the imaging device attached to it. The scanner, which is positioned above you, will move back and forth as it measures your bone density or body composition. The machine is very open and does not feel “closed in” (see above photo).
To assess the spine, the patient's legs are supported on a padded box to flatten the pelvis and lower (lumbar) spine. To assess the hip, the patient's foot is placed in a brace that rotates the hip inward. In both cases, the detector is slowly passed over the area, generating images on a computer monitor.
You will be asked to hold still and may be asked to keep from breathing for a few seconds while the x-ray picture is taken to reduce the possibility of a blurred image.
The DEXA machine sends a thin, invisible beam of low-dose x-rays with two distinct energy peaks through the bones being examined. One peak is absorbed mainly by soft tissue and the other by bone. The soft tissue amount can be subtracted from the total and what remains is a patient's bone mineral density. DEXA machines feature special software that compute and display the bone density measurements on a computer monitor.
Is a DEXA scan safe?
A DEXA scan uses an extremely low dose of radiation and is considered safe for patients of any age. Radiation exposure from DEXA is less than one-tenth the dose of a standard chest x-ray, and is comparable to being in the sun for 2-3 hours. The benefits of an accurate diagnosis far outweigh the risks of exposure.
If you are interested in having a DEXA scan performed, we invite you to call us at 703.444.5000 to schedule an appointment with us here at Arthritis & Sports. To stay up-to-date on the latest news and tips from us, like us on Facebook and follow us on Twitter by clicking below.