How DEXA (BMD Scans) Work
The scan measures bone mineral content and will provide information as to whether you have lost some bone (osteoporosis) as well as information about your risk of having a fracture due to loss of bone. Osteoporosis is a major cause of fractures.
A BMD scan is usually taken of the spine and one hip. The forearm may also be scanned although less often. It assists your doctor in planning any prevention therapy or medical treatment.
Bone Mineral Density Scan (Bone Densitometry or DEXA Scan) generally has no required preparation. You will only need to fill out a simple questionnaire.
Please inform the radiographer if you have had any surgery on your spine or hips such as a hip replacement.
No preparation is required for this procedure. You do not need to fast and you may take all your medications as usual. There are no tunnels or confined spaces, no injections and the procedure is not painful.
It is helpful, but not essential, to wear loose fitting, comfortable clothing without metal buttons, buckles or zippers. Metal objects interfere with the X-rays and make the results inaccurate. A gown or sheet is usually provided if clothing needs to be removed.
On arrival for your BMD Scan your height and weight will be measured. This allows the computer to generate information about your bone density in comparison to general population statistics. It also assesses any height loss over time which also gives information about bone loss.
You will be asked to lie on your back on the scanning table or bed. A cushioned box will be placed under your knees to scan the spine. The boxed cushion enables the small of your back or lower spine to lie flat on the table and improves the accuracy and reproducibility of the test images.
A frame will be placed between your feet to scan the hip. The frame is made up of a flat sheet of Perspex with a triangle at one end.
The triangular end is placed between your feet so that the leg being scanned can be turned slightly inwards and the foot is strapped to the triangle by a Velcro strap.
The knee can also be held in place by a Velcro strap to keep the leg still. This also allows more accurate results that are reproducible in follow-up scans. Generally, neither of these is uncomfortable or painful.
There are no after effects of a BMD Scan.
The duration of a DEXA / BMD Scan varies between individual scanning machines and can range from 15 minutes to 30 minutes. The time varies because newer scanners are able to obtain information more quickly. Different manufacturers and slightly different techniques may add to, or subtract from, scanning time.
Generally, the risks of a BMD Scan with DEXA are very small. At the radiation dose levels that are used in diagnostic radiography there is little or no evidence of health effects.
It does involve a very small dose of radiation which makes this test unsuitable for women who are, or may be, pregnant.
If you have had spinal surgery, particularly with metallic implants, or hip surgery (hip replacements, screws or pins) you will need to inform the medical imaging technologist performing the scan who may decide to avoid that area.
BMD scans are best performed at least a week after having other radiological procedures or investigations such as barium meals or enemas, IVPs (intravenous pyelograms), CT scans or nuclear medicine studies. All forms of contrast medium or agents enhance the information obtained for that test. Since a BMD scan is an X-ray, these agents may be misread by the scanner as bone and falsely affect the result.
A BMD Scan is currently the best test for assessing the skeleton for bone loss.
The amount of bone lost, compared to the young normal population (of the same sex and ethnic background), provides an estimate of your risk of fracture or broken bones in the future.
The result may guide the doctor in deciding on a course of treatment to prevent further bone loss or fracture.
If your bone density is found to be lower than normal and you receive medical treatment, a BMD scan can be performed at intervals as the medical benefits scheme allows screening and review annually in some cases to check if the bone loss is improving or worsening in response to treatment or therapy. Bone mineral content can actually improve with treatment.
You will be scanned by a radiographer skilled in BMD scans who will ensure you are positioned correctly and you are comfortable. In most instances the technologist will remain in the room with you for the duration of the scan.
The technologist will analyse the scan and a radiologist (specialist doctor), or another medical specialist trained in bone densitometry, will interpret the scan and provide a written report to your referring doctor.
Many BMD scanning machines are located at many of our sites.
The time that it takes your doctor to receive a written report on the test or procedure you have had will vary, depending on:
- The urgency with which the result is needed
- The complexity of the examination
- Whether more information is needed from your doctor before the examination can be interpreted by the radiologist
- Whether you have had previous x-rays or other medical imaging that needs to be compared with this new test or procedure (this is commonly the case if you have a disease or condition that is being followed to assess your progress)
- How the report is conveyed from the practice or hospital to your doctor (in other words, email, fax or mail)
Please feel free to ask the radiographer when your doctor is likely to have the written report.