Dual Energy X Ray AbsorptiometryEdit
Dual-energy X-ray absorptiometry (DEXA) is a standard medical imaging technique used to quantify bone mineral density and, in many cases, body composition. By employing two X-ray beams at different energies, DEXA differentiates mineralized bone from surrounding soft tissue, enabling precise estimates of bone density that are central to assessing skeletal strength and fracture risk. The method is fast, noninvasive, and generally associated with a low, well-controlled exposure to ionizing radiation. In clinical practice, DEXA measurements underpin the diagnosis of osteoporosis, guide treatment decisions, and contribute to longitudinal monitoring of bone health. Beyond bone assessment, the technology is also used for research and clinical purposes to estimate fat mass and lean body mass, with applications in nutrition, metabolic health, and sports science. Dual-energy X-ray absorptiometry bone mineral density areal bone mineral density X-ray
In a typical exam, the patient lies still while the scanner records how the two X-ray beams are attenuated by bone and soft tissue at standard regions of interest, most commonly the lumbar spine and hip. The results are expressed as areal bone mineral density (aBMD) in g/cm^2 and, when interpreted with reference data, as T-scores and Z-scores. The T-score compares the patient’s aBMD with a young, healthy reference population, while the Z-score compares with an age-mamed, sex-matched population. A T-score at or below −2.5 is conventionally used as a diagnostic criterion for osteoporosis in many guidelines, with higher risk thresholds informing preventive or therapeutic measures. The technology also provides bone mineral content (BMC) and regional measurements that can be tracked over time to assess response to therapy. osteoporosis T-score Z-score bone mineral density areal bone mineral density
Technology and Principles
How it works: DEXA uses two X-ray energies to distinguish materials with different atomic numbers. By comparing attenuation at the two energies, the system separates bone from soft tissue and calculates mineral content. The resulting metric is an areal density, not a true volumetric density. X-ray bone mineral density
Regions of interest: Scans commonly target the hip (proximal femur) and lumbar spine, with additional regional options such as the forearm. These sites are chosen for their relevance to fracture risk and their sensitivity to changes in bone mass. hip spine forearm areal bone mineral density
Outputs and interpretation: The primary clinical output is the aBMD value, interpreted against reference populations to yield T-scores or Z-scores. FRAX and other risk tools may incorporate DEXA results to refine fracture risk estimates. FRAX bone mineral density
Quality and standardization: Accurate DEXA assessment relies on device calibration, regular quality control with phantoms, and consistent scanning protocols. Differences among manufacturers and reference data sets can influence interpretation, underscoring the importance of site-specific standards. X-ray quality assurance
Clinical applications
Bone health and osteoporosis
DEXA is the gold standard for diagnosing osteoporosis and for monitoring response to anti-osteoporotic therapies such as bisphosphonates, denosumab, and anabolic agents like teriparatide. Its results inform treatment decisions and help stratify fracture risk beyond clinical history alone. In many guidelines, a T-score at the hip or spine guides management, while Z-scores can prompt evaluation for secondary causes of bone loss. osteoporosis bisphosphonates denosumab teriparatide
Fracture risk assessment
Beyond diagnosing osteoporosis, DEXA-derived measures contribute to fracture risk assessment when combined with clinical factors through tools like FRAX. This helps clinicians decide on preventive therapies and lifestyle interventions aimed at reducing fracture incidence. FRAX bone mineral density
Body composition and research
DEXA can be used to quantify fat mass, lean mass, and regional body composition, supporting research in obesity, metabolic health, and athletic performance. While not as precise as some dedicated body composition methods in all settings, DEXA provides a reproducible, relatively low-dose option for longitudinal tracking. body composition
Pediatric considerations
In children and adolescents, DEXA uses pediatric reference data and Z-scores rather than adult T-scores. The technique supports monitoring of peak bone mass accrual and early detection of conditions affecting bone health, with appropriate attention to growth and development. pediatrics bone mineral density
Safety, limitations, and clinical caveats
Radiation exposure: DEXA involves a small, controlled dose of ionizing radiation. Doses are typically low and are kept within the principle of ALARA (as low as reasonably achievable). Special care is taken with pregnant patients, and alternative methods may be preferred when appropriate. X-ray radiation safety
Limitations: While DEXA provides a robust measure of bone density, it does not directly assess bone quality or microarchitecture. Artifacts such as degenerative changes in the spine, vascular calcifications, or surgical hardware can influence results. The distinction between areal BMD and true volumetric density means that DEXA is best interpreted in the context of site, age, sex, and clinical risk factors. bone mineral density spine hip
Reference data and ethnicity: Population reference standards are derived from specific cohorts and may not perfectly reflect every patient group. Clinicians consider local reference data and clinical context when interpreting T-scores and Z-scores. Ongoing discussion in the field addresses how best to apply reference ranges across diverse populations. osteoporosis reference data
Use in body composition: While useful for tracking fat and lean mass, body composition measurements by DEXA can be influenced by hydration status, recent food intake, and machine calibration. Clinicians sometimes corroborate these estimates with alternative methods. body composition