11 doctors weighed in:

Question on thyroid nuclear scan - do you stay radioactive for a while?

11 doctors weighed in
Dr. Gerald Mandell
Nuclear Medicine
3 doctors agree

In brief: Usually 2 days

Half life for radiotracers used to image thyroid is 6 hours for Tc99m pertechnetate and 13 hours for Iodine 123.
Usually two days after dose, no appreciable residual activity.

In brief: Usually 2 days

Half life for radiotracers used to image thyroid is 6 hours for Tc99m pertechnetate and 13 hours for Iodine 123.
Usually two days after dose, no appreciable residual activity.
Dr. Gerald Mandell
Dr. Gerald Mandell
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Dr. Susan Wingo
Internal Medicine - Endocrinology
3 doctors agree

In brief: It depends

Thyroid scans can be done with three different isotopes - most often technetium(tc-99) or iodine (i-123).
Scans done to monitor patients with a known history of thyroid cancer use iodine(i-131). Tc-99 decays quite rapidly, but i-123 takes a few days to decay, and i-131 can persist at low levels for several weeks. Low doses are used, that are safe for patients and those around them.

In brief: It depends

Thyroid scans can be done with three different isotopes - most often technetium(tc-99) or iodine (i-123).
Scans done to monitor patients with a known history of thyroid cancer use iodine(i-131). Tc-99 decays quite rapidly, but i-123 takes a few days to decay, and i-131 can persist at low levels for several weeks. Low doses are used, that are safe for patients and those around them.
Dr. Susan Wingo
Dr. Susan Wingo
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1 comment
Dr. Susan Wingo
While the doses used are considered to low to require special precautions, they could be picked up by detectors at airports. The Nuclear Medicine department doing the scan can give people receiving scans a letter if they are traveling shortly after their scan.
Dr. Thomas Namey
Internal Medicine - Rheumatology
2 doctors agree

In brief: Not really.

The half-life of the tc99m used in most scans is such that you are radiation free in 24hrs.
Also, the amount used is very small. Don't worry.

In brief: Not really.

The half-life of the tc99m used in most scans is such that you are radiation free in 24hrs.
Also, the amount used is very small. Don't worry.
Dr. Thomas Namey
Dr. Thomas Namey
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Dr. Guido Davidzon
Nuclear Medicine
1 doctor agrees

In brief: Depends on isotope

Different isotopes have different physical half-lifes.
In the us, a thyroid scan should ideally be performed using i-123 which has a half-life of 13.2 hours. Some places use a low dose of i-131which has a half-life of 8 days or tc-99m which has a half-life of 6 hours. The radioactivity used in this study is low, however the rule of thumb is 10 half-lifes for all activity to decay. Biology is also.

In brief: Depends on isotope

Different isotopes have different physical half-lifes.
In the us, a thyroid scan should ideally be performed using i-123 which has a half-life of 13.2 hours. Some places use a low dose of i-131which has a half-life of 8 days or tc-99m which has a half-life of 6 hours. The radioactivity used in this study is low, however the rule of thumb is 10 half-lifes for all activity to decay. Biology is also.
Dr. Guido Davidzon
Dr. Guido Davidzon
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