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densitometry is an examination for measuring bone mass. It is a sensitive
screening method to detect loss of bone in the early stages. This is
usually done with the use of low doses of X-rays to scan the spine, hip
and wrist. As a narrow beam of X-ray passes through the area to be
examined, the machine calculates the amount of bone. The most widely used
method is called DEXA i.e. dual energy X-ray absorptiometry. The dose of
radiation involved in one examination is 1/10th that which is received by
a patient having a chest X-ray. Therefore this examination is quite safe.
The other methods using X-rays are the single photon absorptiometry and
quantitative CT. There are also other methods which use Radioisotope and
ultrasound.
Bone
densitometry will be able to detect a decrease in the amount of bone
before it fractures, predict the risk of fracture, as well as diagnose
osteoporosis (a decrease in the amount of bone) following fractures.
It may also be useful in studying the effects of treatment.
Thus bone densitometry is recommended for those who are
trying to decide on starting oestrogen therapy. It is recommended for
menopausal and perimenopausal women as they are prone to
osteoporosis, which may require treatment. Patients on long-term steroid
treatment (e.g. for joint diseases or asthma) and patients who have
metabolic bone disease would also benefit from this examination, as
osteoporosis occurs in these conditions.
No special
preparation is required. There is no need to fast. The possibility of
pregnancy should be alerted to the radiographer. There are a few tests
which may have been done recently that may interfere with the examination
results and these include any nuclear medicine examination or barium
studies. The patient should bring along any previous X-rays of the spine
or hips for the doctor to review. This will be helpful in planning the
examination. The patient will have to change into a hospital gown as
metallic objects on clothes would interfere with the examination. All that
is required is for the patient to lie on the examination table for less
than 5 minutes. There are no injections involved.
The following examinations are available:
(a) Lumbar spine
(b) Hip Region
(c) Wrist
(d) Whole body scan
The
longest scan is the whole body scan and will take about 4 minutes.
Scanning time for each of the other regions is less than one minute. Scans
(a), (b) and (c) are most useful and widely used. The total examination
time, including positioning and scanning is 15-20 minutes. After scanning
is completed, the computer processes the images before it is printed. This
will usually take about 15 minutes for a 3-part study.
The results of the test will be compared with standards
already available. This will help decide where the patient stands within
the normal range and what the risks of fractures are. If the values are
low, it indicates bone loss but blood tests are needed to determine if the
process of bone loss is ongoing. There are effective treatments available
to reduce bone loss.
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