Dual-energy x-ray absorptiometry (DEXA)

Dr Henry Knipe et al.

Dual-energy x-ray absorptiometry (DEXA) is a technique used to aid in the diagnosis of osteopaenia 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, history of hyperparathyroidism) the forearm can be used 1.

Bone mineral density is calculated in grams/cm2, and then compared against two reference population giving two scores 1-3:

  • 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)
    • ≥ -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)
    • < -2.0: below expected range, 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)
  • scores in the lumbar spine can be increased in setting of degenerative sclerotic change, ankylosing spondylitis, etc
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Article Information

rID: 43367
Section: Radiography
Tag: snippet
Synonyms or Alternate Spellings:

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    Case 1: osteopaenia
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    Case 2: osteoporosis
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    Case 3: osteopaenia with forearm measurement
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