Dual-energy x-ray absorptiometry (DXA) or bone densitometry also called Bone density scanning , is an enhanced and standard form of x-ray technology that is used to measure bone loss and bone mineral density, most often performed on the lower spine and hips, requires whole body scan in children and some adults

 

X ray, Ultrasound and CT scan using special software can also diagnose or monitor low bone mass but DEXA is used more common though they are accurate enough, often used to diagnose osteoporosis. The DXA 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 Test uses:

• DXA is most often used 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, as well as structural changes, causing the bones to become thinner, more fragile and more likely to break
• DXA is also effective in tracking the effects of treatment for osteoporosis and other conditions that cause bone loss
• The DXA test can also assess an individual's risk for developing fractures

Indications:

Bone density testing is done in cases such as

• Post-menopausal woman not taking estrogen
• History of hip fracture or smoking
• Clinical conditions associated with bone loss
• Usage of 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 diabetes, liver disease, kidney disease or a family history of osteoporosis
• Excessive collagen in urine samples indicating high bone turnover
• Hyperthyroidism, Hyperparathyroidism
• Fracture after mild trauma.
• Signs of osteoporosis
• Loss of Height and unexplained back pain

Preparation for the procedure:

• 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 a gown or wear loose, comfortable clothing, avoiding garments that have zippers, belts or buttons made of metal
• Objects such as keys or wallets or jewelry, eye glasses and any metal objects that would be in the area being scanned should be removed
• If you had a barium examination or have been injected with a contrast material for a computed tomography (CT) scan or radioisotope scan then should wait 10 to 14 days before undergoing a DXA test.
• 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.

Procedure:

• In the Central DXA examination, which measures bone density in the hip and spine, the patient lies on a padded table. An x-ray generator is located below the patient and an imaging device, or detector, is positioned above

To assess the spine, the patient's legs are supported on a padded box to flatten the pelvis and lower 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 must hold very 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 technologist will walk behind a wall or into the next room to activate the x-ray machine
• The finger, hand, forearm or foot is placed in a small device that obtains a bone density reading within a few minutes.
• The DXA bone density test is usually completed within 10 to 30 minutes, depending on the equipment used and the parts of the body being examined

Benefits and Risks:

Benefits:

• DXA bone densitometry is a simple, quick, convenient and noninvasive procedure.
• No anesthesia is required
• The amount of radiation used is extremely small and no radiation remains in the body
• DXA bone density testing is the most accurate method available for the diagnosis of osteoporosis and fracture

Risks:

• Chances of cancer due to radiation exposure
• Fetus may be affected in case of pregnant women undergo scan.