The Dual Energy X-ray Absorptiometry (DXA) method of assessing bone mineral density is the gold-standard. It is the most accurate and reliable method currently used. In order to determine if you have osteoporosis we will scan both of your hips, along with your lumbar spine, as these areas are a good indication of the density of the bones in the rest of your body. On occasions, such as in cases of primary hyperparathyroidism or if the patient has left and right total hip replacements, it may be necessary to scan the distal forearm in order to support the lumbar spine BMD data.
Vertebral fracture assessment (VFA)
Additionally, we may offer a VFA to women aged 65 and over and men aged 70 and over. This will include two extra scans of the spine which take additional 5 minutes. This quick technique helps to identify potential broken bones in the back due to osteoporosis (vertebral fractures).
Features of vertebral fracture might include back pain or height loss, however many vertebral fractures are not picked up. It is very important to identify vertebral fractures, because they increase the chance of breaking more bones in the future.
How does DXA work?
The DXA scanner has two separate X-ray beams; one will be absorbed mostly by the soft tissue surrounding your bones, whilst the other X-ray will be absorbed by the bone. In order to differentiate between the two types of bone, the scanner will subtract the x-rays absorbed by the soft tissue away from the total X-rays absorbed. This will produce a good estimate of your bone mineral density.
You will be asked to lie down on the scanning couch, whilst the scanning arm passes over you. The scan does not involve going into an enclosed tunnel, you can remain dressed for the scan as long as there are no metal fastenings on your clothing, and typically only takes 10-15 minutes. The DXA scan uses a minimal level of radiation in order to produce accurate results and is approximately one tenth of a normal chest X-ray, or the equivalent of one day’s natural background radiation.
In order to have a DXA scan here at Southmead Hospital Bristol you must be able to transfer to the scanning table independently and not weigh more than 160kg in weight. Pregnant women will not be given a DXA scan as the radiation may harm the unborn child. They should ask for a referral from their GP when a scan is desired after pregnancy.