DEXA scan is one of the most popular methods of measuring bone mineral density. It is a procedure in which certain parts of the body are exposed for a short duration to X-ray beams of different energy levels. It is possible to account separately for the capacity of the soft tissue in the body to absorb radiation and that of bone tissue to do so, which gives an accurate measure of the level of bone mineral loss that has already taken place or even to assess the chances of bone damage and corrosion in the future. The advantages DEXA scan has over other means of determining bone mineral density is that it is far more accurate in its readings and is much more effective in detecting tissue loss at a very early stage. The actual procedure involves exposure to very mild radiation compared to what a person is subjected to during a traditional X-ray reading. The readings are taken by subjecting the lumbar bones around the hips, the spine and/or the forearm to radiation for roughly half an hour, during which the patient has to simply lie motionless on a table. The scan is absolutely painless and requires no special precaution or preparation. The bone mineral density readings are taken in units of milligram per centimeter squared.
The individual's score is known as the T-score and indicates the deviation in bone density below his own average at the peak density level. This is then compared with the standard deviations of the average score for adults belonging to the same age group and sex, which is called the Z-score. This comparison is conducted in order to reduce the margin of error that may creep into the calculation because of the variations in bone mineral density that occur across factors like age, race, sex and weight. For instance, in children the bone density is naturally lower than in adults, so in the absence of a comparison between the individual T-score and the average Z-score for the same age group, the readings may be wrongly interpreted to indicate osteoporosis. Also, the readings for an overweight person might be significantly influenced by the amount of radiation absorbed by the fat deposits in his/her body. The readings for a single person may also vary depending on which part of the body is scanned. Therefore, all of these factors have to be taken into consideration before arriving at a correct diagnosis. A score greater than -1 indicates normal bone density, between -1 and -2.5 osteopenia and less than -2.5 a confirmed case of osteoporosis.
Submitted by N S on February 14, 2010 at 10:45