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The method DEXA ( Dual energy X-ray absorptiometry , or Bi-photonic absorption with x-rays ) is a means of measuring the osseous Densité. It is very much used in Ostéodensitométrie because powerful in term of exactitude, reproducibility, and linearity, even for mineral weak densities. Its use for early detection of the Ostéoporose is essential, because the traditional Radiologie offers only one late detection.

Principle

It is a question of measuring the attenuation of two beams of x-ray of different energy through fabrics (soft and hard: bodies and bone). Once the known attenuation, one can solve a system with two equations and two unknown factors, by using the equation of the attenuation (law of Beer-Lambert):

{I = I_ {0}} e^ {u.d} \;

with:

I_ {0}

emitted energy,

I waste heat

U the linear absorption coefficient

D the thickness of the fabric

To obtain two beams X of different average energy, one can is to use a tension of different acceleration, that is to say to use filters. To obtain two images types (high and low energy), one can also use systems of detection able to discriminate the photons according to their energy, which makes it possible to avoid making two irradiations.

Advantages

the method is not very irradiant.
Good performances in term of precision and reproducibility.
very fast Time of examination.
the examination does not require particular preparation (one should be with jeun, no catch oral or INTER-F of an unspecified product is used)

Disadvantage

the examination studies at the same time the cortical bone and trabéculaire.
Material.
Examination not refunded in certain countries.

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