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

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.

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.

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.

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.