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"What is a bone densitometry scan? A bone densitometry scan is a special type of X-ray test used to measure the calcium content of the bone. The examination is also called a dual energy X-ray absorptiometry (DEXA) scan or QDR scan. The DEXA scan is the established standard for measuring bone mineral density (BMD).  This is a simple, quick and non-invasive medical test, which involves exposing particular parts of the body to very small amounts of ionisation radiation. This is then used to produce images of the insides of the body.  DEXA scans are used to measure and therefore diagnose low bone density and also to monitor patients where a diagnosis of low bone density has been made.  DEXA scans are usually performed on the lower spine and the hips.  In children and also some adults, the whole body may be scanned. For very low bone densities, devices which target the extremities of the body and use either X-rays or ultrasound may be used instead of the traditional DEXA scan.  Similarly there&amp;#039;s a CT scan with special software can also be used as an alternative method for measuring very low bone densities. This is known as a QCT, and although it can be very accurate, it&amp;#039;s much less commonly used that a DECA scan,  How does a bone densitometry scan differ from an X-ray? Like all X-rays, a DEXA scan is relatively easy to perform.  The scanner itself differs in that it produces two X-ray beams, each beam with a different energy level. One beam is high energy, whilst the other is low energy.  The amount of energy that is able to pass through the bone is measured separately for each beam. The amount of energy that can pass through is dependent on the thickness of the bone.  By looking at the difference between the two beams concerning the amount of energy able to pass through the bone, the bone density can be calculated.  The density is directly related to the calcium content of the bone. Therefore thicker bones will have a greater calcium content than thinner bones.  Ordinary X-ray scanners are unable to accurately measure the calcium content in bone, and therefore someone with osteoporosis may have perfectly normal X-rays.  This is why, in order to get accurate bone density measurements, we use a bone densitometry scan. An ordinary x-ray is far more reliable when it comes to detecting a recent bone fracture.  What is a bone densitometry scan used for? A scan can help a doctor who is examining a patient for osteoporosis to assess their risk of having a bone fracture within the next few years.  Osteoporosis is a condition which mainly affects women after the menopause, but it can also be found in man too.  The association between the post-menopause period and the development of osteoporosis is due to a change in the normal hormones, which usually help maintain a normal bone density. Because of this, bone mass density testing is recommended for all women over the age of 65.  Other risk factors associated with the development of osteoporosis include a family history of the disease, being of small and thin stature, an inactive lifestyle, smoking, excessive drinking, and the use of certain medications, such as steroids.  Bone density testing is also strongly recommended for patients with type 1 diabetes, liver disease, kidney disease, those who have a thyroid condition or male patients with clinical conditions associated with bone loss.  A lateral vertebral assessment, which is a low dose X-ray examination of the spine that screens for vertebral fractures and is also performed on a DEXA machine, may be recommended for older patient \u2013 particularly if there&amp;#039;s a history of unexplained back pain, if there has been a loss of more than an inch of height, or if the initial DEXA scan gives borderline readings.  In general, people with a bone mineral density significantly lower than that normal for their age and sex are more likely to break a bone, even with very minor trauma such as falling from a small height or even from violent sneezing and coughing.  Diagnosing patients with a low bone density can prevent the risk of those patients obtainging a fracture in the future.  If the patient receives medical treatment, their bone mineral density will increase and their risk of fracture will reduce.  Using DEXA scanning to monitor osteoporosis treatment is a controversial area, and there is still much debate surrounding how useful periodic DEXA scanning is for monitoring changes in bone density during treatment.  If DEXA scanning is recommended, this will usually be at one to two year intervals \u2013 although more frequent follow-up, approximately every 6 months, is recommended for those on steroid treatment. How should I prepare for a bone densitometry scan?  Unlike some other X-ray procedures, there are no specific requirements prior to undertaking a bone density scan.  You can continue to take all your regular medications. It&amp;#039;s important however that you notify the medical team performing the scan beforehand if you have recently had a barium examination or have been given some contrast material before undergoing a computer tomography (CT) scan or radioisotope scan.  Your doctor will usually recommend a wait of two weeks before a DEXA scan can be carried out following any of these procedures. Female patients should also always inform the medical team if there&amp;#039;s any possibility that they may be pregnant.  This is because sources of ionising radiation can be harmful to the fetus and therefore many imaging tests may not be performed. However, if it&amp;#039;s felt the imaging is necessary, special precautions can be taken to minimise the radiation exposure to fetus.  How is a bone densitometry scan carried out? The examination is usually done on an outpatient basis. This means the patient will come into hospital, have the scan and then leave the same day.  The scan will take between 10 and 30 minutes, depending on the equipment used and the parts of the body examined.  The patient will be asked to lie on a padded table, with the X-ray generator positioned below the patient and the imaging device positioned below.  It&amp;#039;s important that the patient stays very still and may also be asked to hold their breath for a few seconds during the time which the image is obtained.  If the doctor is checking for osteoporosis, the lumbar spine and the hips are usually examined, as well as the forearm as it will give a different calcium content from other body parts.  Patients can eat immediately before the test and remain fully dressed as long as their clothes have no metal buttons or zippers.  Recently portable scanners, which can be used in a GP&amp;#039;s surgery and check the BMD of the heel bone (calcaneum), have been growing in popularity. An example of a left-hip bone scan The blue areas on the graph show the usual bone mass for women of different ages. As illustrated, the bone mass is lower among elderly women.  A 70-year-old woman&amp;#039;s bone mass is indicated by a cross in the figure. It is estimated that 95 per cent of the population belong within the blue areas. Those in the dark blue area have a bone mass above average in relation to age, while people belonging to the light blue area are below average in relation to their age. The curve for men is similar but is higher placed on the chart and shows a smaller decline with age.  Are there any side-effects or risks associated with having a bone densitometry scan? As with any procedure that involves the use of X-rays, there&amp;#039;s always a slight chance of developing cancer in the future when excessive exposure to radiation occurs. However, the chances are small and the benefit of an accurate diagnosis usually outweighs the cancer risk.  Compared to other common X-ray procedures, the radiation dose from a DEXA scan is a lot less than that obtained from having a traditional chest X-ray.  Regarding the DEXA procedure itself, there&amp;#039;s no complications expected with this.  What do the bone mass numbers and results of my DEXA scan mean? Once the DEXA scan has been carried out, a radiologist (a doctor who is specifically trained to supervise and interpret images) will send a report to your GP or to the medical team who originally refer you for the scan.  The results will be in the form of 2 scores, the T-score and the Z-score. T-score: this compares the amount of bone you have with a young adult of the same gender with a peak bone mass density.  Any score about -1 is considered normal. A score between -1 and -2.5 is considered a low bone bone mass and is classified as osteopenia. Below -2.5 is classified as osteoporosis. The T-score gives an indication as to risk of you developing a fracture. If you score below -2.5 and therefore are diagnosed as having osteoporosis then it may be necessary to put you on treatment ie calcium tablets.  This is a preventative method of treatment which will help reduce the risk of you having a fracture in the future.  Your doctor will discuss with you which options are available to manage the condition you are diagnosed with.  Z-score: this reflects the amount of bone you have compared with other people within the same age group and of the same size and gender.  If the score is unusually high or low, then this may indicate further tests are needed  Other people also read: Osteoporosis: we look at the causes, symptoms and treatment. X-ray: staff involved in X-ray tests and treatment. Arthritis: how is arthritis treated?  Based on a text by Bo Abrahamsen, PhD, Prof. Leif Mosekilde, consultant  Last updated 30.11.2012 "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.netdoctor.co.uk/conditions/aches-and-pains/a2851/bone-densitometry-scans-general/>