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Dexa Scan

Dual energy X-ray absorptiometry (DEXA), also called bone densitometry uses a very low dose of X-ray to measure bone mineral density (BMD) which is the amount of calcium and other minerals present in the bones. The DEXA scan is a quick, non-invasive, and painless method and is most often done to get the images of lower spine and hip region.

Types

There are two different types of DEXA scanning devices:

  • Central DEXA: The central DEXA scanner is passed over lower part of your spine and hip when you are lying on the X-ray table. It is the most reliable test to predict the risk of fractures.
  • Peripheral DEXA (p-DEXA): The peripheral DEXA device is a smaller machine that is used to measure bone density of the bones in periphery, such as the wrist, heel or finger.

Indications

A DEXA scan is used to diagnose osteoporosis, a disease in which bones become fragile and more likely to get fractured. It is highly recommended to undergo a DEXA scan in individuals who are at risk of developing osteoporosis. The risk factors for osteoporosis include:

  • Women  aged above 65 and men aged above 70 years
  • A fracture following a minor fall or injury
  • Other disorders such as rheumatoid arthritis, chronic kidney disease, and eating disorders
  • An early menopause
  • Prolonged use of corticosteroid therapy for more than three months
  • Cigarette smoking
  • Previous hormonal treatment for prostate cancer or breast cancer
  • Loss of height due to vertebral compression fracture
  • Family history of osteoporosis
  • Excessive alcohol intake

The DEXA machine transmits two X-ray beams with different energy levels through the bone being tested. Soft tissues absorb one of the energy level and the remaining is absorbed by the bone. The bone mineral density is measured based on the difference between the soft tissue absorption and the total amount.

Procedure

Normally, there are no restrictions on eating prior to the test. Calcium supplements should be discontinued 24 hours before the test. Women who are pregnant should always inform their physician or X-ray technologist.

During the central DEXA examination, you will be asked to lie still on your back on an X-ray table. The scan usually takes between 10 to 30 minutes. A detector arm of the device will slowly pass over the region of your body being measured. Generally, central DEXA scan measures bone density in the hip and spine region.

Peripheral DEXA scans are more simple in which your finger, hand or foot is kept in a small device that gives the bone density reading instantly.

Test results will be in the form of two scores:

  • T score: It is the comparison of your bone density with that of a young healthy adult. A T score of -1.0 or above is considered normal. A score between -1 and -2.5 indicates osteopenia (low bone mass). A score below -2.5 indicates osteoporosis.
  • Z score: It is the comparison of your bone density with that of other people of same age, sex, and race.

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