Payne Dual-energy X-ray absorptiometry benefits Dual-ennergy of error in the assessment of body composition is, therefore, the means by which the composition of soft tissue over-and underlying bone is estimated. Medically reviewed by Brenda B.

Dual-energy X-ray absorptiometry benefits -

It exposes you to a small dose of ionizing radiation to produce pictures of the inside of the body. X-rays are the oldest and most often 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, mostly at the forearm. 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.

DXA is most often used to diagnose osteoporosis , a condition that often affects women after menopause but may also be found in men and rarely in children.

Osteoporosis involves a gradual loss of bone, 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.

The risk of fracture is affected by age, body weight, history of prior fracture, family history of osteoporotic fractures and life style issues such as cigarette smoking and excessive alcohol consumption.

These factors are taken into consideration when deciding if a patient needs therapy. The Vertebral Fracture Assessment VFA , a low-dose x-ray examination of the spine to screen for vertebral fractures that is performed on the DXA machine, may be recommended for older patients, especially if:.

On the day of the exam you may eat normally. You should wear loose, comfortable clothing, avoiding garments that have zippers, belts or buttons made of metal. Objects such as keys or wallets that would be in the area being scanned should be removed. Remove jewelry, removable dental appliances, eyeglasses, and any metal objects or clothing that might interfere with the x-ray images.

Inform your physician if you recently had a barium examination or have been injected with a contrast material for a computed tomography CT scan or radioisotope scan. You may have to wait 10 to 14 days before undergoing a DXA test. Women should always tell their doctor and technologist if they are pregnant.

Doctors will not perform many tests during pregnancy to avoid exposing the fetus to radiation. If an x-ray is necessary, the doctor will take precautions to minimize radiation exposure to the baby. See the Radiation Safety page for more information about pregnancy and x-rays.

Most of the devices used for DXA are central devices, which are used to measure bone density in the hip and spine. They are usually located in hospitals and medical offices. Central devices have a large, flat table and an "arm" suspended overhead. Peripheral devices measure bone density in the wrist, heel or finger and are often available in drugstores and on mobile health vans in the community.

The pDXA devices are smaller than the central DXA devices, weighing only about 60 pounds. They may have a portable box-like structure with a space for the foot or forearm to be placed for imaging.

Other portable technologies such as specially designed ultrasound machines, are also sometimes used for screening. However, central DXA is the standard technique. 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. DXA machines feature special software that compute and display the bone density measurements on a computer monitor.

In the central DXA examination, which measures bone density of 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 lumbar 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 need to hold your breath for a few seconds while the technologist takes the x-ray. This helps 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 peripheral tests are simpler. The finger, hand, forearm or foot is placed in a small device that obtains a bone density reading within a few minutes.

An additional procedure called Vertebral Fracture Assessment VFA is now being done at many centers. VFA is a low-dose x-ray examination of the spine to screen for vertebral fractures that is performed on the DXA machine. 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.

You will probably be asked to fill out a questionnaire that will help the doctor determine if you have medical conditions or take certain medications that either increase or decrease your risk of a fracture.

The World Health Organization has recently released an online survey that combines the DXA results and a few basic questions and can be used to predict year risk of hip fracture or other major osteoporotic fractures for post-menopausal women. Routine evaluations every two years may be needed to see a significant change in bone mineral density, decrease or increase.

Few patients, such as patients on high dose steroid medication, may need follow-up at six months. A radiologist , a doctor trained to supervise and interpret radiology examinations, will analyze the images.

The radiologist will send a signed report to your primary care or referring physician who will discuss the results with you. DXA scans are also interpreted by other physicians such as rheumatologists and endocrinologists. A clinician should review your DXA scan while assessing the presence of clinical risk factors such as:.

T score — This number shows the amount of bone you have compared with a young adult of the same gender with peak bone mass. A score of -1 and above is considered normal. A score between A score of The T score is used to estimate your risk of developing a fracture and also to determine if treatment is required.

Z score — This number reflects the amount of bone you have compared with other people in your age group and of the same size and gender. If this score is unusually high or low, it may indicate a need for further medical tests. Small changes may normally be observed between scans due to differences in positioning and usually are not significant.

Doctors take special care during x-ray exams to use the lowest radiation dose possible while producing the best images for evaluation. National and international radiology protection organizations continually review and update the technique standards radiology professionals use.

Modern x-ray systems minimize stray scatter radiation by using controlled x-ray beams and dose control methods. This ensures that the areas of your body not being imaged receive minimal radiation exposure.

Please type your comment or suggestion into the text box below. Note: we are unable to answer specific questions or offer individual medical advice or opinions. org is not a medical facility.

Please contact your physician with specific medical questions or for a referral to a radiologist or other physician. To locate a medical imaging or radiation oncology provider in your community, you can search the ACR-accredited facilities database.

This website does not provide cost information. The costs for specific medical imaging tests, treatments and procedures may vary by geographic region. Web page review process: This Web page is reviewed regularly by a physician with expertise in the medical area presented and is further reviewed by committees from the Radiological Society of North America RSNA and the American College of Radiology ACR , comprising physicians with expertise in several radiologic areas.

Outside links: For the convenience of our users, RadiologyInfo. org provides links to relevant websites. One last vertical line should be placed between legs to separate them 4 , See Figure 1 for a detailed explanation of DXA analysis. In addition, Figure 2 shows some examples of inaccuracies in positioning and analysing a whole body DXA scan.

Sarcopenia is a disease typically associated with advancing age, characterized by a progressive and generalized loss of skeletal muscle mass and strength 13 , 26 - There is increasing awareness of the medical community for this condition, as it has been estimated a consistent increase of the prevalence of sarcopenia due to advancing age, as well as for its association with several negative outcomes such as physical disability, falls, hospitalization 30 - The disease is costly to healthcare systems, as it has been shown that the cost of care during hospitalization is increased in subject with sarcopenia In , the EWGSOP revised its operational definition of sarcopenia, giving primary importance to muscle strength as the most important parameter for predicting adverse outcomes More practically, according to EWGSOP definition, a diagnosis of sarcopenia is probable when low muscle strength is detected.

When also low physical performance is present, the diagnosis of sarcopenia is considered severe Each of these parameters can be measured: muscle strength and physical performance are typically measured by means of different tests such as grip strength, chair stand, gait speed or the Short Physical Performance Battery; on the contrary, the evaluation of muscle quantity or quality needs the use of imaging or non-imaging techniques, such as DXA, MRI, CT or Bioelectrical impedance analysis BIA 15 , 34 , Among the different imaging techniques available to quantify muscle mass, DXA is currently favoured by clinicians and working groups DXA is capable of determining regional and total body muscle quantity, providing both absolute values of LM as well as LM indices, such as the appendicular skeletal muscle mass ASMM.

Nevertheless, it has to be taken into account that muscle mass correlates to body size. As a consequence, values from DXA are typically adjusted to body parameters such as height 2 , weight, or body mass index BMI In fact, such diagnosis needs the concurrent presence of low muscle strength detected at functional tests.

In addition to this, the medical community is debating about the clinical value of combining the use of ASMMI and femoral neck BMD to predict fracture risk, similarly to what is commonly performed in the Fracture Risk Assessment Tool FRAX ® To date, literature evidence suggests that DXA-derived ASMMI has a limited role in the prediction of incident fractures Despite the well-known link between bone and muscle, fracture is just one outcome resulting from sarcopenia, and ASMMI may have better value for identifying other adverse outcomes such as falls.

In their editorial, Harvey concludes that the use of DXA-derived lean mass indices still does not provide additional risk information when BMD is also considered; further studies are warranted to understand the role of possible use of ASMMI in the FRAX.

The possible introduction of newer DXA based tools for evaluating bone strain together with body composition may even provide additional information for fracture risk prediction A possible DXA drawback is related to the fact that densitometers of different brands may not give the same results 36 , A practical suggestion is to perform the follow-up scan always with the same densitometer, to remove such source of variability.

Several adipose indices can be obtained with whole body DXA, some of them being similar to lean indices. These values help in providing additional data about whole body and regional FM distribution. FMI is calculated as the total body fat mass with height 2 adjustment.

The use of FMI has been advocated to diagnose obesity, similarly to what done by BMI. The rationale of using FMI is based on the assumption that BMI, despite its ease of use, is not a direct adiposity measurement parameter On the contrary, despite the use of FMI which is a direct measurement of adiposity has its rationale, there is an ongoing debate about what cut-off point should be used to better diagnose obesity.

Figure 3 compares BMI thresholds to a list of FMI cut-off points proposed for defining obesity categories both for male and female subjects using FMI, according to the National Health and Nutrition Examination Survey NHANES reference values Nevertheless, it is still unclear which associations exist between such thresholds and obesity related negative outcomes.

Regarding obesity, several studies clearly showed that DXA measurements of FM including FMI are strongly correlated with negative cardiovascular and metabolic outcomes, independent of BMI 44 , A recent study from Vasan et al. evaluated the associations between DXA values and conventional anthropometry measurements of fat waist and hip circumference , together with cardiovascular disease CVD risk markers The result of this study confirmed that conventional anthropometry underestimated the associations of regional adiposity subcutaneous and visceral fat with diabetes and CVD risk markers.

Another parameter that can be used for evaluating the CVD risk is the AG fat mass ratio, which is analogue to the more commonly used anthropomorphic measurement of waist-to-hip ratio DXA machines obtain this value as the ratio between the android and gynoid region of interest ROI.

Android ROI is typically defined as the region between the last thoracic rib and the upper part of iliac wings. Gynoid ROI is located below the android ROI, and includes the gluteo-femoral region with an upper horizontal line placed caudally to the pelvis line, and a lower horizontal line identified by measuring twice the height of the android ROI 4.

It has been shown that an increase in the android fat distribution with values of AG ratio greater than 1 is associated with conditions such as dyslipidemia and insulin resistance, as well as other cardiovascular risk factors such as impaired glucose tolerance, hypercholesterolemia, hypertriglyceridemia, and hypertension 47 - Unfortunately, as for FMI, despite the evidence of a strong correlation between the increasing amount of android fat and CVD risk, there is still no consensus on the possible cut-off points to be used for defining a specific high-risk patient.

As a matter of fact, DXA is currently the only technique which is capable of identifying all these conditions at the same time, by evaluating the presence of low ASMMI together with adipose indices such as FMI and BMD with DXA performed at lumbar spine and femur.

Figure 4 compares two subjects with reduced muscle mass according to ASMMI values, but with different percentage of fat mass as evaluated with FMI. In fact, the association of lipodystrophy with agents such as zidovudine and stavudine has been extensively reported, being confirmed in a systematic review of randomized controlled trials Nevertheless, the ISCD Reporting guideline of clearly specified that a consensus about the values to be accepted has never been reached Recently in a study by Alikhani et al.

evaluated the prevalence of lipodystrophy in HIV patients and the association to cumulative exposure of newer antiretroviral drugs agents Surprisingly, lipodystrophy resulted still very common in HIV infected patients, being correlated with the duration of some new antiretroviral drugs such as raltegravir.

Such results keep open the possibility to still use DXA for the evaluation of suspected lipodystrophy, and probably suggests additional investigations are required to understand the utility of such adipose indices. One of the most recent developments for whole body DXA is the possibility to evaluate visceral adipose tissue VAT.

This can be done with both GE and Hologic densitometers, thanks to new software which are called CoreScan TM for GE-Lunar and InnerCore TM for Hologic 4. This software firstly estimates the amount of subcutaneous fat SAT in the android ROI of DXA scan, by detecting the fat located on both sides of the abdominal cavity.

This estimate of SAT is then subtracted from the total FM in the android ROI, thus providing the final amount of VAT. Figure 5 explains the working principle beyond VAT estimation by DXA. DXA VAT measurements have several advantages over CT, first and foremost related to lower radiation dose provided to patients.

The clinical importance of VAT is widely recognized, as it has been showed that VAT is a better predictor of mortality than SAT or AG ratio Thus, it is possible that VAT will replace the AG ratio as a risk factor for the assessment of CVD risk with DXA It is important to consider that even subjects with normal values of BMI may have an increased amount of VAT accumulation, thus being at higher risk than that estimated by only conventional anthropometry measurements Regarding thresholds, VAT is typically expressed as a real measurement in cm 2.

Cross-sectional studies suggested that VAT levels exceeding — cm 2 were associated with adverse metabolic profile in women On CT measurements of VAT, Pickhardt et al.

found that a threshold of 70 cm 2 yielded a sensitivity, specificity, and accuracy of The analysis of body composition with DXA is becoming more and more popular among physicians, as DXA has the potentiality to evaluate LM and FM with an accuracy that is close to that of CT and MRI, but with some advantages compared to cross-sectional techniques.

As a consequence, whole body DXA is increasingly used for different potential applications, such as the investigation of low lean mass in the setting of suspected sarcopenia. The possible combination of LM and FM values with that of BMD obtained with DXA at central site open the possibility for a more comprehensive evaluation of osteometabolic disorders, such as osteosarcopenia and sarcopenic obesity.

There is still a lot that has to be done, and further research studies are warranted to provide clear cutoff values for adipose indices in cardiovascular disease, as well as to understand the role of ASMMI in the possible prediction of fracture risk in patients with sarcopenia.

The article was sent for external peer review organized by the Guest Editors and the editorial office. GG served as the unpaid Guest Editor of the special issue and serves as an unpaid editorial board member of Quantitative Imaging in Medicine and Surgery.

AB served as the unpaid Guest Editor of the special issue. The authors have no other conflicts of interest to declare. Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.

Figure 1 Two examples of proper positioned and post-processed whole body DXA scan, according to Hologic manufacturer guidelines. The visual comparison of a young man first two images on the left side with a middle-aged woman the last two images on the right side clearly depict differences in fat distribution represented in yellow , with the woman showing the typical gynoid distribution around the hips and thighs.

Head line number 1 is placed below the jaw; pelvis line number 2 has to be placed just above the iliac crests; two groin lines number 3, in green have to bisect the femoral neck on each side; trunk lines number 4, in blue separate the arm regions from the trunk android regions, and they should pass through the gleno-humeral joints along each side of the trunk.

A, android region; G, gynoid region; VAT, visceral adipose tissue region. Figure 2 Examples of common positioning and postprocessing artifacts that may limit the accuracy of whole body DXA scan.

Dual-energj X-ray absorptkometry DXAor DEXA ahsorptiometry is a means of absorptimetry bone mineral density BMD using spectral imaging. Two X-ray beams, abslrptiometry Dual-energy X-ray absorptiometry benefits energy Dual-energy X-ray absorptiometry benefitsare aimed at Dual-energy X-ray absorptiometry benefits patient's bones. When soft tissue absorption Organic energy supplements subtracted out, the bone mineral density BMD can be determined from the absorption of each beam by bone. Dual-energy X-ray absorptiometry is the most widely used and most thoroughly studied bone density measurement technology. The DXA scan is typically used to diagnose and follow osteoporosisas contrasted to the nuclear bone scanwhich is sensitive to certain metabolic diseases of bones in which bones are attempting to heal from infections, fractures, or tumors. You may want to have a say Dual-energy X-ray absorptiometry benefits this decision, or you Dual-energgy simply want Dual-energy X-ray absorptiometry benefits follow your doctor's recommendation. Benefis way, this Duale-nergy will help you Diabetic ketoacidosis diet what your choices are Dual-energy X-ray absorptiometry benefits Dual-fnergy you Dual-energy X-ray absorptiometry benefits talk to your doctor about them. Osteoporosis is a disease that affects your bones. It means that your bones are thin and brittle, with lots of holes inside them like a sponge. This makes them easy to break. Osteoporosis can lead to broken bones fractures in the hip, spine, wrist, and other parts of your body. These fractures can be disabling and may make it hard for you to live on your own.