Bone Density Scan - Dual-Energy x-ray absorptiometry (DXA)

General Info:

Bone density scanning, also called dual-energy x-ray absorptiometry (DXA) or bone densitometry, is an enhanced form of x-ray technology that is used to measure bone loss. DXA is today's established standard for measuring bone mineral density (BMD).

An x-ray (radiograph) is a noninvasive medical test that helps physicians diagnose and treat medical conditions. Imaging with x-rays involves exposing a part of the body to a small dose of ionizing radiation to produce pictures of the inside of the body. X-rays are the oldest and most frequently used form of medical imaging.

DXA is most often performed on the lower spine and hips. In children and some adults, the whole body is sometimes scanned. Peripheral devices that use x-ray or ultrasound are sometimes used to screen for low bone mass. In some communities, a CT scan with special software can also be used to diagnose or monitor low bone mass (QCT). This is accurate but less commonly used than DXA scanning.

Scan Summary

A DXA scan is a non-invasive test. The test requires that subjects put on a hospital gown and lie on an x-ray bed. Subjects cannot be wearing anything metal and are therefore asked to remove all jewellery. Please note that the DXA table cannot accommodate subjects > 300 lbs, and therefore we are unable to perform body composition scans on subjects > 300 lbs. The dimensions of the DXA table are 197.5 x 60 cm.

Pregnancy is the major exclusion criteria for having a DXA scan. Pregnancy tests will be performed to ensure there is no chance of pregnancy at the time of the scan. Additionally, individuals who have recently undergone barium tests/exams (within 2 weeks), or who have had a nuclear medicine scan or injection with an x-ray dye (within 1 week) cannot have a DXA scan.

A Word About Minimizing Radiation Exposure

Special care is taken during x-ray examinations to use the lowest radiation dose possible while producing the best images for evaluation. National and international radiology protection councils continually review and update the technique standards used by radiology professionals.

State-of-the-art x-ray systems have tightly controlled x-ray beams with significant filtration and dose control methods to minimize stray or scatter radiation. This ensures that those parts of a patient's body not being imaged receive minimal radiation exposure.

What are the limitations of DXA Bone Densitometry?

A DXA test cannot predict who will experience a fracture but can provide indications of relative risk.

Despite its effectiveness as a method of measuring bone density, DXA is of limited use in people with a spinal deformity or those who have had previous spinal surgery. The presence of vertebral compression fractures or osteoarthritis may interfere with the accuracy of the test; in such instances, CT scans may be more useful.

Central DXA devices are more sensitive than pDXA devices but they are also somewhat more expensive.

A test done on a peripheral location, such as the heel or wrist, may help predict the risk of fracture in the spine or hip. These tests are not helpful in following response to treatment, however, and if they indicate that drug therapy is needed, a baseline central DXA scan should be obtained.

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