Dual energy x-ray absorptiometry (DEXA)

Dual-energy
x-ray absorptiometry • Osteoporosis on DXA and vertebral fractures on VFA - Ganzer Fall bei Radiopaedia
Powrie N, Osteoporosis on DXA and vertebral fractures on VFA. Case study, Radiopaedia.org (Accessed on 03 Dec 2022) https://doi.org/10.53347/rID-59194 • CC by-nc-sa 3.0 (modified)
Dual-energy
X-ray absorptiometry (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 Fabry disease. Courtesy: Dr Caroline LEBRETON, CHU Raymond Poincaré, Garches, France.
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Dual-energy x-ray absorptiometry (DEXA or DXA) is a technique used to aid in the diagnosis of osteopenia and osteoporosis.

Radiographic features

Values are calculated for the lumbar vertebrae and femur preferentially, and if one of those sites is not suitable (e.g. artifact, patient mobility), or if there is a history of hyperparathyroidism, the forearm can be used .

Bone mineral density is calculated in g/cm, and then compared against two reference population giving two scores :

  • T-score: comparison by standard deviation (SD) to a young adult population, matched for sex and ethnicity (used for postmenopausal women and men >50 years) and classified by WHO criteria
    • ≥-1.0: normal
    • <-1.0 to >-2.5: osteopaenia
    • ≤-2.5: osteoporosis
    • ≤-2.5 plus fragility fracture: severe osteoporosis
  • Z-score: compared by SD to an age, sex, and ethnicity population (used for premenopausal women, men <50 years, and children instead of T-score WHO criteria )
    • <-2.0: below expected range/low bone density for age, and a cause should be sought

Practical points

  • if automatic segmentation is performed, ensure that it has been performed correctly (i.e. not including ilium on lumbar spine or ischium on hip calculations)
  • similarly, ensure the bone edges have been accurately detected (this is a particular problem in individuals with very low BMD, where software can not detect a clear density difference between soft tissue and bone)
  • valid comparison to reference data requires adequate positioning - deviations from optimum positioning may falsely decrease (e.g. spinal rotation) or increase (e.g. insufficient internal rotation of the femur) measured BMD
  • scores in the lumbar spine can be increased in the setting of degenerative sclerotic change, ankylosing spondylitis, osteoporotic spinal compression fracture, etc. (where there is a focal abnormality, e.g. a vertebral fracture at L2, the affected level should be excluded from the analysis)
  • for diagnosis, the region with the lowest T-score from the lumbar spine (L1-L4 or L2-L4), hip (lowest value at the femoral neck or total hip) or radius (mid-third/33% radius) is used to classify bone mineral density per WHO criteria
Siehe auch:
und weiter:
Assoziationen und Differentialdiagnosen zu Dual-Röntgen-Absorptiometrie (DXA/DEXA):
Osteoporose
 
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