Dual Energy X-ray Absorptiometry for Bone Densitometry

Osteodensitometry (bone densitometry) using dual-energy X-ray absorptiometry (DXA), DEXA; dual X-ray absorptiometry; radiographic method) is used for early diagnosis and follow-up of osteoporosis (bone loss). Only the DEXA method can determine whether osteoporosis as defined by the WHO is present. The measurement is taken in the area of the lumbar spine (L1 to L 5) and the proximal femur (thigh bone close to the hip joint; total femur region “total hip”). Similarly, the distal radius (near wrist bone of the forearm) is also internationally accepted as a measurement site.

Indications (areas of application)

• Osteoporosis:
  • Early detection of osteoporosis (bone loss).
  • Early detection of osteopenia (reduction in bone density).
  • Fracture risk assessment (bone fracture risk assessment).
  • Stage classification of manifest osteoporosis.
  • Follow-up of the progression
  • Follow-up of the (drug) therapy.
• Patients over 65 years of age without risk factors for bone density reduction.
• Patients over 65 years of age with the following risk factors:
  • Family history of osteoporosis – at least two family members with osteoporosis.
  • Family history of diseases associated with bone density reduction.
  • Hypogonadism – gonadal insufficiency (testes/ovaries) of male and female, respectively.
  • Early climacteric (menopause, menopause)
  • Fracture (bone fracture) after menopause.
  • Age-related, significant loss of body size.
  • Consumption of stimulants: alcohol (woman: > 20 g/day; man: > 30 g/day); tobacco (smoking – in osteoporosis after menopause).
  • Lack of exercise
  • BMI (body mass index) < 20 kg/m²
  • Unintentional weight loss of more than 10 kg or of more than 10% in the last few years
  • No estrogen substitution in the postmenopausal period.
• Other indications:
  • Hormonal factors – estrogen deficiency in girls and young women, e.g., late menarche (delayed puberty, > 15 years of age).
  • Early onset of menopause (< 45 years of age) or early ovariectomy (removal of the ovaries).
  • Menopause (menopause in women)
  • Andropause (menopause of the male)
  • Anorexia nervosa (anorexia)
  • Chronic diseases or surgeries that can trigger bone loss, e.g., small intestine diseases and stomach surgery
  • Chronic renal insufficiency (chronic renal failure).
  • Increased risk of falls (more than 2 falls in 6 months).
  • Previously occurred fractures (bone fractures)
  • Joint diseases with restricted movement
  • Hyperthyroidism (hyperthyroidism)
  • Hyperparathyroidism (parathyroid hyperfunction).
  • Osteopathies (bone diseases)
  • Glucocorticoid long-term therapy – cortisol intake.
  • Systemic long-term therapy with the following other drugs: Antiepileptic drugs, glucocorticoids, heparin, Marcumar.
  • Therapy with immunosuppressants after organ transplantation.
  • Patients after transplantation, especially of kidney, liver and heart.
  • Condition after surgery in the gastrointestinal tract (gastrointestinal tract).

In elderly persons (> 75 years of age), the measurement should not be performed on the spine due to possible metrological problems.

The procedure

This procedure is used to determine bone density (mineral salt content of bone). This is measured using dual X-ray absorptiometry on two different areas of the body, usually the lumbar spine and the thigh. In principle, it can be measured at any point on the body, but then the results may vary due to different measurement protocols. The principle of the measurement is that rays penetrate the bone at different intensities depending on the bone density. This intensity is measured and compared to a standard value. The decrease in mineral content by one standard deviation (STD) is referred to as t-score – 1.0. The following is an explanation of the terms used in osteodensitometry:

• Absorption describes the intensity attenuation of incident radiation per unit mass of the body being penetrated, which electromagnetic radiation experiences when passing through a body.
• Density is the ratio of mass to volume and is expressed in units of mg/cm3 in computed tomographic osteodensitometric techniques.
• Bone mass is the bone mineral mass plus bone matrix mass.
• Bone Mineral Content (BMC) is the mineral mass of the corresponding bone, expressed in g.
• Bone Mineral Density (BMD – Bone Mineral Density) – expressed in the unit of measurement mg/cm3 – is the bone mineral content per measured volume.
• T-score (T-value) is a statistical measure that indicates the difference of measurement results from the mean value of bone density of young adults (25 – 40 years) of the same sex. The T-score is expressed in standard deviations (SD) and is crucial for the assessment of fracture risk.
• Z-score is a statistical measure that describes the difference of measurement results from the mean value of bone density of same-aged and same-sex reference subjects. This is also expressed in standard deviations (SD).

Densitometric classification of osteoporosis.

The following examination findings suggest an increased risk of vertebral body or femoral fractures even without the presence of other risk factors.

Therapy should be initiated when DXA values are < -2.0. Follow-up examinations should be performed no earlier than two years after the last measurement or after the end of therapy. Bone density measurement may not be necessary if more than one fracture (bone fracture) of a vertebral body typical of osteoporosis is already present. Addendum: In addition to the above-mentioned determination of the T-score, which is decisive for the classification of osteoporosis, a structural analysis of the trabecular bone is increasingly carried out in parallel with the creation of the trabecular bone score. This trabecular bone score consists of structural parameters [e. g. E.g., bone volume fraction (BV/TV), trabecular number (Tr.N. ), trabecular thickness (Tr.Th.), and trabecular distance (Tr.Sp.)].

Utility

Osteodensitometry using dual X-ray absorptiometry (DXA/DEXA) is a powerful diagnostic technique for assessing bone density and bone composition of the entire skeletal system. The most important field of application is the diagnosis, staging and follow-up of osteoporosis with regard to fracture risk. Regular check-ups will significantly reduce your risk of fracture and improve your quality of life.