AASIF MAJEED LONE ASSISTANT PROFESSOR WHAT IS DEXA SCAN Dual energy Xray absorption also called BMD Measurement is a most effective technique used to measure B one M ineral Density ID: 1014622
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1. DEXA SCAN and its applicationsAASIF MAJEED LONEASSISTANT PROFESSOR
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4. WHAT IS DEXA SCANDual energy X-ray absorption (also called BMD Measurement) is a most effective technique used to measure Bone Mineral Density .It measures the density or thickness of bones and amount of calcium content in specific area of bone, which can’t be evaluated in an ordinary XRAY. An X-ray is more reliable when it comes to detecting a recent bone fracture.DEXA is most often performed on the lower spine and hips. Portable DEXA devices ,including some that use ultrasound waves rather than X-rays measure the wrist ,fingers or heel and sometimes used for screening purposes.
5. HIstoryOsteoporosis undetected and overlooked until 1920.The first publication about bone mass appeared in 1930s.Radiographic absorptiometery Xray taken and compared to a standard radiograph.Radiogammetry introduced in the 1960s in response to the measurement of the bone loss in astronauts.In 1970 CT was used through the specialized software –Quantitative CT.In 1970s and 1980s brought the first dedicated scanners. First SPA then DPA used radioisotope as a source of radiation.First commercial DEXA scanner introduced in 1987.First used radioisotope as the XRAY source then replaced by the X-ray tube.
6. VaRIOUS WAYS TO MEASURE BMDDUAL ENERGY X-RAY ABSORPTION (DEXA)PERIPHERAL DUAL ENERGY X-RAY ABSORPTION (P-DEXA)QUANTATIVE COMPUTER TOMOGRAPHY(QCT)QUANTATIVE ULTRASOUND
7. deXA EQUIPMENTTWO TYPES:-1.Central device2.Peripheral deviceCENTRAL DEXA : are usually located in hospitals and medical offices Measure bone density in the hip and spineCentral DEXA devices have a large flat table and an arm suspended over head
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9. PERIPHERAL DEXA: are often available in drug stores and on mobile health vans.Measure bone density in the wrist , heel or fingers.Are portable units.The results are quicker than standard DEXA measurements.
10. USESDEXA bone densitometery is used to diagnose osteoporosis and to assess risk of bone fracture within the next few years.Osteoporosis or thin bones is a condition that often affects women after menopause but may also be found in men. In osteoporosis , gradual loss of calcium causing the bones to become thinner, more fragile and more likely to break.DEXA is also effective in tracking the effects of treatment for osteoporosis and other conditions that cause bone loss. IF the patient receives medical treatment for bone loss then the scan can be repeated after 2 years to assess their progress.
11. RISK FACTORS FOR OSTEOPOROSIS IN WOMENMenopause Family historySmall bone fractureAdvanced age Low calcium dietCigarette smokingCertain medication useInactive lifestyle
12. indicationsMenopausal women,all women above 60 age or older and males over 70 age.Long term steroids, hormonal therapy, vit D, calcium and low estrogen level.Lumphangiomatosis and low body weight.KyphosisPrevious history of fracture.Nutritional deficiency- rickets,lupus, Turner syndrome, rheumatoid arthritis.
13. CONTRAINDICATIONSRecent contrast studies.Weight about (120-130kg)PregnancyBilateral hip replacement.Metal implants in the area.
14. PATIENT PREPARATIONOn the day of examination eat normally. Should not take calcium supplements for atleast 24 hours before exam.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.Ask patient if recently had a barium examination or have been injected with a contrast media. If so ,may have to wait 10 to 14 days before undergoing a DEXA scan.Women should be always asked if there is any possibility that they are pregnant. If yes then precautions will be taken to minimize radiation exposure to the baby.
15. PROCEDUREIn CENTRAL DEXA examination patients lies on a padded table. An X-ray generator is located below the patient and an imaging device is positioned above.To assess the spine, the patient’s legs are supported on a padded box to flatten the pelvis and lumbar spine. To assess the hip the patients 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.
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18. The PERIPHERAL DEXA: test is simpler .The patient finger, hand, forearm or foot is placed in a small device that obtain a bone density reading within a few minutes.
19. HOW DOES THE PROCEDURE WORKDEXA machine send a thin visible beam of low dose X-ray with two distinct energy peaks through the bones being examined. One peak is absorbed 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.
20. DEXA machine feature special software that compute and display the bone density measurements on a computer monitor.One type of DXA scanner uses a cerium filter with a tube voltage of 80 kV, resulting in effective photon energies of about 40 and 70 keV .There is also a DXA scanner type using a samarium filter with a tube voltage of 100 kV, resulting in effective energies of 47 and 80 keV.
21. What Are the results OF DEXA SCANResults are reported as two values, T and Z scores.T-SCORE:-The T score compares your bone density with that of healthy young adult.A score of 0 means your BMD is equal to the standard for a healthy young adult.Differences between your BMD and that of the healthy young adult standard are measured in units called standard deviations (SDs). The more standard deviations below 0, are indicated as negative numbers, the lower your BMD and the higher your risk of fracture.
22. As shown in table ,a T score between +1 and -1 is considered normal or healthy.A T score between -1 and -2.5 indicates that patient have low bone mass.A T score of -2.5 or lower indicates that you have osteoporosis.The greater the negative number, the more severe the osteoporosisPositive T scores indicate the bone is stronger than normal , negative T scores indicate the bone is weaker than normal.
23. Z-SCORE:-The Z score compares patient bone density with that of other people of same age and gender.A low Z- score (below -2.0) is a warning sign that patient have less bone mass or that patient is losing bone more rapidly than expected for someone of same age.Z- score = T score – Reference T-score
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25. APPLICATIONSDXA scans are used to evaluate bone mineral density.DXA scans are also used to assess adiposity in children ,especially to conduct clinical research.However, it has been suggested that, while very accurately measuring minerals and lean soft tissue (LST), DXA may provide skewed results as a result of 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 familial partial lipodystrophy
26. ADVANTAGESIt is simple quick and non-invasive procedure.Low radiation dose less than 1/10th of chest X-ray.No anesthesia required.Most accurate method for the diagnosis of osteoporosis and is also considered an accurate estimator of fracture risk.Wide availability.Short scan time.Ease of use.High resolution image.Good precision.
27. LIMITATIONSCentral DEXA devices are more sensitive than pDEXA devices but they are also somewhat more expensive.A DEXA scan cannot predict who will experience a fracture but can provide indications of relative risk.A test done on a peripheral location such as wrist or heels may help predict the risk of fracture in the spine or hip. But because bone mass tends to vary from one location to the other, measuring the heel is not as accurate as measuring spine or hip.Most central DEXA machines cannot measure the hip and spine of a patient that weighs more than 300 pounds or 136kg .In this case ,a central DEXA of the radius and the calcaneous can be carried out.
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