DEXA scan Dual energy X-ray absorptiometry Imaging An imaging system to assess bone mineral density; commonly used to screen perimenopausal and menopausal ♀ before beginning HRT, to evaluate Pts with 1º or 2º osteoporosis or metabolic diseases affecting the skeleton and monitor treatment and progression of osteoporosis. Bone Density (DEXA) scan. A simple scan can help diagnose osteoporosis before a fracture happens. Osteoporosis mainly affects women after menopause and can cause a loss of bone mass, which makes your bones prone to breaking and fracturing easily. A DEXA scan is a quick, painless test that helps diagnose osteoporosis and can help assess your.
Dual-energy X-ray absorptiometry ( DXA, previously DEXA ) is a means of measuring (BMD) using. Two beams, with different, are aimed at the patient's. When absorption is subtracted out, the (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, as contrasted to the nuclear, which is sensitive to certain metabolic diseases of bones in which bones are attempting to heal from infections, fractures, or tumors. Contents.Physics Soft tissue and bone have different to X-rays. A single X-ray beam passing through the body will be attenuated by both soft tissue and bone, and it is not possible to determine, from a single beam, how much attenuation was attributable to the bone. However, the attenuation coefficients vary with the energy of the X-rays, and, crucially, the ratio of the attenuation coefficients also varies.
DXA uses two energies of X-ray. The difference in total absorption between the two can be used, by suitable weighting, to subtract out the absorption by soft tissue, leaving just the absorption by bone, which is related to bone density.One type of DXA scanner uses a filter with a of 80, resulting in effective photon energies of about 40 and 70. There is also a DXA scanner type using a filter with a tube voltage of 100 kV, resulting in effective energies of 47 and 80 keV. Also, the tube voltage can be continuously switched between a low (for example 70 kV) and high (for example 140 kV) value in synchronism with thefrequency of the electrical mains, resulting in effective energies alternating between 45 and 100 keV.The combination of uses the laser to measure the thickness of the region scanned, allowing for varying proportions of lean soft tissue and within the soft tissue to be controlled for and improving the accuracy.Bone density measurement.
Main article:The recommends that women over the age of 65 should get a DXA scan. The date at which men should be tested is uncertain but some sources recommend age 70. At risk women should consider getting a scan when their risk is equal to that of a normal 65-year-old woman.A person's risk can be measured using the 's calculator, which includes many different clinical risk factors including prior fragility fracture, use of, heavy smoking, excess alcohol intake, rheumatoid arthritis, history of parental hip fracture, chronic renal and liver disease, chronic respiratory disease, long-term use of phenobarbital or phenytoin, celiac disease, inflammatory bowel disease, and other risks. DEXA assessment of bone mineral density of the femoral neck (A) and the lumbar spine (B): T scores of - 4.2 and - 4.3 were found at the hip (A) and lumbar spine (B), respectively in a 53-year-old male patient affected with.The World Health Organization has defined the following categories based on bone density in white women:Severe (established) osteoporosisA T-score more than -2.5 standard deviations below the young adult female reference mean in the presence of one or more fragility fractures.Bone densities are often given to patients as a T score or a Z score. A T score tells the patient what their bone mineral density is in comparison to a young adult of the same gender with peak bone mineral density. A normal T score is -1.0 and above, low bone density is between -1.0 and -2.5, and osteoporosis is -2.5 and lower.
A Z score is just a comparison of what a patient’s bone mineral density is in comparison to the average bone mineral density of a male or female of their age and weight.The WHO committee did not have enough data to create definitions for men or other ethnic groups.Special considerations are involved in the use of DXA to assess bone mass in children. Specifically, comparing the bone mineral density of children to the reference data of adults (to calculate a T-score) will underestimate the BMD of children, because children have less bone mass than fully developed adults. This would lead to an over-diagnosis of for children. To avoid an overestimation of bone mineral deficits, BMD scores are commonly compared to reference data for the same gender and age (by calculating a ).Also, there are other variables in addition to age that are suggested to confound the interpretation of BMD as measured by DXA. One important confounding variable is bone size.
DXA has been shown to overestimate the bone mineral density of taller subjects and underestimate the bone mineral density of smaller subjects. This error is due to the way by which DXA calculates BMD. In DXA, bone mineral content (measured as the attenuation of the X-ray by the bones being scanned) is divided by the area (also measured by the machine) of the site being scanned.Because DXA calculates BMD using area (aBMD: areal Bone Mineral Density), it is not an accurate measurement of true bone mineral density, which is divided by a. In order to distinguish DXA BMD from bone-mineral density, researchers sometimes refer to DXA BMD as an areal bone mineral density (aBMD). The confounding effect of differences in bone size is due to the missing depth value in the calculation of bone mineral density.
Despite DXA technology's problems with estimating volume, it is still a fairly accurate measure of bone mineral content. Methods to correct for this shortcoming include the calculation of a volume that is approximated from the projected area measure by DXA. DXA BMD results adjusted in this manner are referred to as the bone mineral apparent density (BMAD) and are a of the bone mineral content versus a estimation of the volume of bone. Like the results for aBMD, BMAD results do not accurately represent true bone mineral density, since they use approximations of the bone's volume. BMAD is used primarily for research purposes and is not yet used in clinical settings.Other imaging technologies such as (QCT) are capable of measuring the bone's volume, and are, therefore, not susceptible to the confounding effect of bone-size in the way that DXA results are susceptible.It is important for patients to get repeat BMD measurements done on the same machine each time, or at least a machine from the same manufacturer.
Error between machines, or trying to convert measurements from one manufacturer's standard to another can introduce errors large enough to wipe out the sensitivity of the measurements. DXA results need to be adjusted if the patient is taking supplements. Current clinical practice in pediatrics DXA is, by far, the most widely used technique for bone measurements, since it is considered to be cheap, accessible, easy to use, and able to provide an accurate estimation of bone mineral density in adults.The official position of the (ISCD) is that a patient may be tested for BMD if he suffers from a condition that could precipitate bone loss, is going to be prescribed pharmaceuticals known to cause bone loss, or is being treated and needs to be monitored. The ISCD states that there is no clearly understood correlation between BMD and the risk of a child's suffering a fracture; the diagnosis of osteoporosis in children cannot be made using the basis of a densitometry criteria. T-scores are prohibited with children and should not even appear on DXA reports. Thus, the WHO classification of osteoporosis and osteopenia in adults cannot be applied to children, but Z-scores can be used to assist diagnosis.Some clinics may routinely carry out DXA scans on pediatric patients with conditions such as nutritional,. DXA has been demonstrated to measure skeletal maturity and body fat composition and has been used to evaluate the effects of pharmaceutical therapy.
It may also aid pediatricians in diagnosing and monitoring treatment of disorders of bone mass acquisition in childhood.However, it seems that DXA is still in its early days in pediatrics, and there are widely acknowledged limitations and disadvantages with DXA. A view exists that DXA scans for diagnostic purposes should not even be performed outside specialist centers, and, if a scan is done outside one of these centers, it should not be interpreted without consultation with an expert in the field.
Furthermore, most of the pharmaceuticals given to adults with low bone mass can be given to children only in strictly monitored clinical trials.Whole-body measured by DXA has been validated in adults using of total body calcium but this is not suitable for paediatric subjects and studies have been carried out on paediatric-sized animals. Body composition measurement DXA scans can also be used to measure total and with a high degree of accuracy comparable to with a few important caveats. From the DXA scans, a low resolution 'fat shadow' image can also be generated, which gives an overall impression of fat distribution throughout the body While it has been suggested that, while very accurately measuring minerals and lean soft tissue (LST), DXA may provide skewed results due to its method of indirectly calculating fat mass by subtracting it from the LST and/or body cell mass (BCM) that DXA actually measures.DXA scans have been suggested as useful tools to diagnose conditions with an abnormal fat distribution, such as, but its use in this context is yet to be approved. They are also used to assess adiposity in children, especially to conduct clinical research.
Radiation exposure DXA uses X-rays to measure bone mineral density. The dose of current DEXA systems is small, as low as 0.001, much less than a standard chest or dental x-ray.
However, the dose delivered by older DEXA radiation sources (that used rather than ) could be as high as 35 mGy, considered a significant dose by standards.Regulation United States The quality of DXA operators varies widely. DXA is not regulated like other radiation-based imaging techniques because of its low dosage. Each US state has a different policy as to what certifications are needed to operate a DXA machine., for example, requires coursework and a state-run test, whereas has no requirements for DXA technicians. Many states require a training course and certificate from the International Society of Clinical Densitometry (ISCD).Australia In Australia, regulation differs according to the applicable state or territory. For example, in Victoria, an individual performing DXA scans is required to be a qualified radiographer. This contrasts to NSW and QLD whereby a DXA technician only requires prior study in science, nursing or other related undergraduate study.
The Environmental Protection Agency (EPA) oversees licensing of technicians, however, this is far from rigorous and regulation is non-existent.References.