Bone densitometry uses a low dose of ionizing radiation to render pictures of the inside of the body to assess bone loss. The use of a bone density scan is commonly used to determine osteoporosis and to evaluate an individual’s risk for developing bone fractures. DEXA, a dual-energy x-ray absorptiometry and another name for bone densitometry, is fast, easy, noninvasive and the most accurate procedure for diagnosing osteoporosis.
The exam does not require much special preparation. If you may be pregnant, have recently had a barium exam, been given an injection of contrast medium for a CT scan or radioisotope scan be sure to tell your doctor and the technologist before your test. Make sure to wear comfortable loose fitting clothing, and leave any jewelry at home. It is advised not to take any calcium supplements for at least 24 hours before you have your exam.
- What is a Bone Density Scan (DEXA)?
- What are some common uses of the procedure?
- How should I prepare?
- What does the equipment look like?
- How does the procedure work?
- How is the procedure performed?
- What will I experience during and after the procedure?
- Who interprets the results and how will I get them?
- What the benefits and risks of a DEXA scan?
- What are the limitations of DEXA Bone Densitometry?
- Why is a Bone Density Test done?
What is a Bone Density Scan?
A bone density scan, also known as DEXA, is a type of x-ray technology used to evaluate bone loss. DEXA has become an established standard to measure bone mineral density (BMD).
An x-ray is a medical test that aids physicians to treat and diagnose medical conditions in the body. When imaging with x-rays it exposes the part of the body being examined with a tiny dose of ionizing radiation in order to produce the images of the inside of the body. X-rays are the form of medical imaging used the most.
DEXA is mainly performed on the lower hips and spine. Often times in adults and children, the whole body is scanned.
What are some common uses of the procedure?
A bone density scan is commonly used to diagnose osteoporosis. Osteoporosis is a condition that affects women after menopause but can also be found in men and very rarely in children. Osteoporosis is a medical condition in which the bones become brittle and fragile because of the loss of tissue. The bone becomes more likely to break.
DEXA is beneficial in tracking the results of treatment for osteoporosis and alternative conditions that create bone loss. The DEXA exam also assesses someone’s risk for developing any fractures. Several factors that contribute to the risk of fracture are body weight, family history of osteoporotic fractures, age, history of prior fracture, and other possible lifestyle problems such as smoking and alcohol consumption. All of these are into consideration when deciding if a patient will need therapy.
Bone density tests are recommended if you:
- have already had an x-ray showing vertebral fracture or signs of osteoporosis
- have a fracture after a small trauma
- have hyperparathyroidism or other parathyroid condition
- have hyperthyroidism or a thyroid condition
- have a high-rise bone turnover
- have type 1 diabetes, kidney disease, liver disease, or a family history of osteoporosis
- have a history of hip fracture or smoking
- take medication which can cause bone loss, such as the corticosteroid Prednisone, some anti-seizure medications like Dilantin and certain barbiturates, or thyroid replacement drugs
- are a man whom has history of clinical conditions associated with bone loss
- are a thin (less than 125lbs) or tall (over 5ft. 7in.) post-menopausal woman
- are a post-menopausal woman who is not taking estrogen
A Lateral Vertebral Assessment (LVA), is a low-dose x-ray examination for the spine to check for any vertebral fractures which are performed on the DEXA machine recommended for older patients if:
- you have lost more than one inch of height
- you have back pain
- a DEXA scan gives borderline readings
How should I prepare?
Before you take the exam women should let their physician and x-ray technologist if they may be pregnant. Numerous imaging tests may not be done during pregnancy in order for there not to be any exposure of radiation to the fetus. IF you have to get an x-ray, precautions will be taken in order to reduce the radiation exposure to the baby.
If you have recently received a barium examination or received an injection with a contrast material for a CT scan or radiosotope scan, then you may have to wait 10 to 14 days before you can get a DEXA test.
Now the day of the exam you can eat normally. You should wear comfortable loose fitting clothing that do not have zippers, buttons, or belts made from metal. You will be asked to wear a gown during the exam and remove some of your clothes. You might be asked to take off any jewelry, eye glasses, any metal objects, jewelry, keys, and wallets.
Please, do not take any calcium supplements for at least 24 hours before your exam.
What does the equipment look like?
2 Types of DEXA equipment:
- Central Device
- Peripheral Device
Central DEXA Device: measures hip and spine bone density and are typically located in hospitals and several medical offices. They have a large, flat table, with a suspended overhead.
Peripheral Device: measures heel, finger, and wrist bone density. They are often found in drugstores or on mobile health vans. The pDEXA device is smaller compared to the Central DEXA device. The pDEXA is a portable box-like device that has space for the foot or forearm imaging.
How does the procedure work?
DEXA machines use a special software to evaluate and present the bone density measurements on the computer screen. It sends a narrow, invisible bean of low-dose x-rays with two different energy peaks through bones examined. One peak is absorbed by the bone and the other by the soft tissue. The soft tissue will be taken from the total and the remaining is the patient’s bone mineral density result.
How is the procedure performed?
When doing a central DEXA examination, the patient will lie down on a padded table. The x-ray generator is positioned under the patient and an imaging device is placed above. The exam is mostly done on an outpatient basis.
While assessing the spine, the legs of the patient are supported on a padded box to make flat the lower spine and pelvis. While assessing the hip, the foot of the patient will be placed in a brace which will rotate the hip toward the inside. In both assessments, the detector passes slowly above the area, producing images on the computer screen.
You must make sure to be very still and perhaps will be asked to keep from breathing a few short seconds while the x-ray image is taken to decrease the chances of having a blurry image.
When doing a peripheral test, the hand, forearm, finger, or foot is put in a small device that has a bone density reading in a couple minutes.
The Lateral Vertebral Assessment (LVA) is currently being done at several centers. LVA is a small-dose x-ray analysis of the spine to monitor for vertebral fracture which is conducted on the DEXA machine. LVA tests only add a couple minutes to the DEXA procedure.
A DEXA bone density test takes sometime between 10 to 30 minutes. The length of the test will depend on the equipment used and the part of the body that will be examined.
What will I experience during and after the procedure?
A bone density test is fast and pain free procedure. A routine evaluation every two years might be needed to check on the increase or decrease change in bone mineral density. Some patients, those who take a high dose steroid medication, might need to follow up in six months.
Who interprets the results and how will I get them?
Someone who is precisely trained to oversee and interpret radiology examinations, such as a radiologist, will review the images and send a signed report of the bone density test to your physician. Your physician or primary care will review the results and discuss them with you.
DEXA scan results may also be interpreted by a rheumatologist and endocrinologist. A clinician might review the results of your DEXA scan to assess the existence of clinical factors like:
- inflammatory bowel disease
- respiratory disease
- rheumatoid arthritis
- chronic renal and liver disease
The results of the test will be in two types of scores:
Z score – A Z score shows the number of bone you have in comparison with other people in your age group, gender, and of the same size. Depending on the score being high or low, it may show a need for more medical tests.
T score – A T score shows the number of bone you have in comparison with a same gender, young adult with peak bone mass. If you get a score more than -1 it is considered normal. If you get a score somewhere in between -1 and -2.5 it’s classified as osteopenia (low bone mass). If you get a score lower than -2.5 it is classified as osteoporosis. Your T score will determine your risk of getting a fracture.
What the benefits and risks of a DEXA scan?
- X-rays typically don’t have side effects for this exam.
- Radiation will not remain in a patient’s body after the x-ray exam.
- Only an extremely small amount of radiation will be used – less than one-tenth of the dose of a standard chest x-ray and less than the amount of radiation you are exposed to naturally in a day.
- No anesthesia is necessary.
- Equipment for a DEXA bone density is easily available which makes this testing convenient for physicians and patients.
- DEXA bone density testing is a highly accurate method to diagnose osteoporosis and an accurate estimator of fracture risks.
- DEXA bone densitometry is a easy, fast and noninvasive procedure.
- If you are or might be pregnant you should always inform your physician or x-ray technologist.
- There’s always a minimal chance of cancer from extreme exposure to radiation.
- The correct radiation dos for this procedure differs.
- Complications are no expected with the DEXA procedure.
What are the limitations of DEXA Bone Densitometry?
- DEXA tests cannot determine who might experience a fracture but can supply indications of relative risk.
- In spite of its effective rate as a method to measure bone density, DEXA is of insufficient use in people who have a spinal deformity or anyone who has had spinal surgery. The existence of vertebral compression fractures or osteoarthritis could hinder the accuracy of the test; in these cases, CT scans could be of better use.
- Central DEXA devices are further more sensitive than pDEXA devices but are slightly more expensive.
- A test performed on a peripheral location, like the wrist or heel, could aid in predicting the risk of fracture in the hip or spine. These tests may not be helpful in succeeding a response to treatment and if they show that drug therapy may be needed, a baseline central DEXA exam should be performed.
Why is a bone density test done?
Bone density tests are done to determine decreases in bone density prior to breaking a bone, your risk of fractures, diagnose osteoporosis, and monitoring osteoporosis treatments.
Bone density tests are different from bone scans. A bone scan requires an injection before the test and is performed to detect cancer, fractures, infections, and other abnormalities in the bone.
View example of bone density scan here