Scansione DEXA

Nota: le informazioni di seguito sono solo una guida generale. Le disposizioni e il modo in cui vengono eseguiti i test possono variare tra i diversi ospedali. Segui sempre le istruzioni fornite dal tuo medico o dall'ospedale locale.

Che cos'è una scansione DEXA?

DEXA stands for 'dual-energy X-ray absorptiometry'. DEXA (also sometimes known as DXA) is a test that measures the density of bones. Density means how much of something there is in a certain amount of space. The denser the tissue, the less X-rays pass through.

Air and water are less dense than solid things such as bone. This is because the particles which make air and water are not held closely together. In general, the more dense the bone, the stronger it is, and the less likely it is to break (fracture).

There are two different types of DEXA scanning devices:

• Central DEXA devices are large machines that can measure bone density in the centre of your skeleton, such as your hip and spine.

• Peripheral DEXA devices are smaller, portable machines that are used to measure bone density on the periphery of your skeleton, such as your wrist, heel or finger. These are mainly to get an idea about whether further tests are needed, as they are not as accurate as the larger DEXA machines.

A DEXA scan uses low-energy X-rays. A machine sends X-rays from two different sources through the bone being tested. Bone blocks a certain amount of the X-rays. The more dense the bone is, the less X-rays get through to the detector. By using two different X-ray sources rather than one it greatly improves the accuracy in measuring the bone density.

The amount of X-rays that comes through the bone from each of the two X-ray sources is measured by a detector. This information is sent to a computer which calculates a score of the average density of the bone. A low score indicates that the bone is less dense than it should be, some material of the bone has been lost and it is more prone to fracture.

You lie on your back on a couch and are asked to keep still while an X-ray detector (the 'scanner') comes over the area to be tested. An X-ray machine fires X-rays towards the detector. The bones commonly scanned are the bones of the back (the vertebrae), hip and wrist.

Smaller peripheral scanners are available in some places and can be used to check the bone mass density of the heel, wrist or finger.

Quanto dura una scansione DEXA?

La scansione di solito richiede tra i 5 e i 20 minuti, a seconda della parte del corpo che viene esaminata e se viene utilizzato uno scanner centrale o periferico. Non c'è un 'tunnel' da attraversare come in altri tipi di scansioni come una risonanza magnetica o una TAC, quindi non dovrebbe influenzare le persone che non amano stare in spazi chiusi.

Scanner DXA

© Nick Smith photography (ALSPAC website), via Wikimedia Commons

Are DEXA scans safe?

Le scansioni DEXA utilizzano un livello molto basso di radiazioni a raggi X. Ciò significa che è sicuro per il tecnico che esegue la scansione rimanere nella stanza con te. (Nei test a raggi X standard, il tecnico deve rimanere dietro uno schermo protettivo.)

Preparing for a DEXA scan

You do not need to do any special preparation prior to a DEXA scan. You can normally remain fully clothed, although you will need to avoid or remove clothes with metal in them (for example, zips, belts, buttons). You may also be asked to remove jewellery for the scan. In some places, you may be given a gown to wear.

Una scansione DEXA può essere consigliata se hai avuto una frattura ossea dopo un lieve infortunio. Può anche essere consigliata se sei considerato a rischio aumentato di 'assottigliamento' delle ossa (osteoporosi) e quindi a rischio aumentato di avere una frattura in futuro.

If your doctor thinks you have risk factors for osteoporosis, they may use un calcolatore del rischio come uno chiamato FRAX® o QFracture®. Questo fornisce un'idea di quanto sia probabile che tu possa fratturarti le ossa dopo un piccolo urto. Se il tuo rischio è a un livello medio, il tuo medico organizzerà una scansione DEXA. Questo consente loro di ottenere un quadro più chiaro del tuo rischio e quindi di decidere se hai bisogno di un trattamento.

DEXA scans are also used to monitor whether treatment for osteoporosis is working.

DEXA scans are not advised for women who are pregnant. You should also not have a DEXA scan within two weeks of certain other types of scans - for example, those using contrast dye.

For further information, see the separate leaflet called Osteoporosi.