Thyroid Scan (cont.)
How is the thyroid scan performed?
A thyroid scan is an outpatient procedure usually done
in the nuclear medicine section of a hospital. This is usually part of the
radiology
department.
If you have a thyroid scan, you will be asked to take a
drink, or swallow a pill containing the iodine. You will then wait for the iodine to be
taken up by the thyroid - usually about 4 hours. At this time you lie under a
scintography camera, and it will take pictures which correlate directly to the
amount of iodine taken up by the thyroid. This is done by counting the intensity
and location of the gamma rays emitted by the radioactively labeled iodine. You
then leave the hospital, and return in 24 hours to have a second scan performed
in the same manner.
There are no limitations during this 24 hour interval except
that you will be asked to take precautions when you urinate. This is because the
radioactive iodine is
removed from your body by the urine, and it is safer to have others avoid
contact with your urine during this time. Be sure to let the doctor performing
the test know if you have a iodine allergy, or if you have
ingested a lot of iodine-containing foods (like sushi) prior to the test.
When is thyroid scanning helpful?
A thyroid scan can provide information on
the size and shape of the gland as well as the overall activity of the gland (is
the whole thyroid gland overactive or underactive?).
For example, thyroid scanning is used to determine how
active thyroid tissue is in manufacturing
thyroid hormone. This
feature can determine whether inflammation of the thyroid
gland (thyroiditis) is present. It can also detect the presence and degree of
overactivity of the gland (hyperthyroidism ). In this case the scan reveals
increased iodine uptake by the whole gland.
In addition, a thyroid scan can provide information on
specific areas within the thyroid gland and can help to determine whether any
localized areas are hyperfunctioning or under functioning compared to the rest
of the gland. In these cases spots appear on the image
corresponding to areas that take up iodine differently from the rest of the
gland.
Thyroid scanning is especially helpful in evaluating
thyroid nodules,
particularly after a fine needle
aspiration biopsy has failed
to provide a diagnosis. A scan will reveal whether a thyroid nodule is
"functioning" or "nonfunctioning". Doctors refer to hyper functioning nodules of
the thyroid (those that are actively taking up iodine to produce thyroid hormone
more so
than surrounding thyroid tissue) as "hot" nodules, and these hyperfunctioning
areas are seen on the image of the thyroid gland. A nonfunctioning nodule does
not take up iodine and produces a localized "cold" area on the image of the
thyroid gland.
In addition, thyroid scanning can be done to help
determine if thyroid cancer has spread beyond the bed of the thyroid in the neck. For this
purpose, usually a whole body thyroid scan is performed.
Next: What is significant about whether a nodule is "hot" or "cold?" »
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