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BONE DENSITOMETERS: LATEST ADVANCEMENT IN DETECTION OF OSTEOPOROSIS -   ANOOP DEWANI B.E. (BIO-MED.), T.S.E.C.

In layman's language osteoporosis can be referred to as a decalcification/porousness/ hollowing of the bone. It is a typical feminine disease, which occurs after menopause. In India over 61 million people have osteoporosis, of these about 48million are women.

Bone Densitometry is a totally new diagnostic concept in INDIA. It is a non-invasive detection technique through which osteoporosis can be detected early and a course of treatment can be established; this also enables to monitor response to therapy.There are various different modalities available to detect osteoporosis, which are as follows:

1. Ultrasound based Bone Sonometers: for early detection of fracture risk.

2. X-rays based Bone Densitometers: site-specific bone mineral density measurement and fracture-risk assessment.

This includes the following detection techniques:

a) SEXA b) DEXA

b) QCT d) PCT

Of all these detection modalities DEXA is the most popular and widely accepted.

DEXA: DUAL ENERGY X-RAY ABSORPTIOMETERY.

This X-ray based technique is a gold standard and is most popular amongst Radiologists, with more 10,000 installation around the world.The principle and measuring technique involves two X-ray beams of 70kV and 140kV respectively which are fired on to the site of measurement which are the hip (pelvic girdle and femur) and the lumbar spine (L1 to L4). These two beams are fired after a time lag of 4 milli - secs. The X-rays pass through the soft tissues and the bones, the detector detects the attenuation of the two beams. The total time of scan is approx. 5 minutes each for the hip and the lumber region. The data obtained is fed into the computer which is powered with a complex algorithm and calculates Bone Mineral Density (B.M.D.) in gms/cm2. This data is analysed statistically and correlation are done with the stored database, which result in two different scores.

1. T-score: the B.M.D. calculated is compared with mean B.M.D. of young normal females.

2. Z score: the B.M.D. calculated is compared with mean B.M.D of age matched normal females.

A T-score of -2.5 SD (standard deviation) is commonly used as an arbitrary cut off point for defining the disease state. Standard Deviation below -2.5 is termed as OSTEOPOROTIC condition.

ADVANTAGES OF DEXA OVER OTHER MODALITIES:

1. Precision: As the X-ray tube produces higher radiation flux this technique gives greater precision and reduces scan time.

2. Large scan area: The sites of scan are the lumbar region of the spine, pelvic girdle, and the femur bone, thus assessment of both trabecular and cortical bones is done. These areas are the fracture prone areas as they are the most weight bearing areas of the skeletal system.

It is estimated that approx. 5000 DEXA would be installed in INDIA within next 5 years, catering to an estimated 14 million Bone Densitometer tests per year.

©1999 IEEE VESIT Student Branch  Hits :

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