Bone imaging uses technetium-labeled MDP, free technetium is unavoidable during the labeling process, and the thyroid gland will show up when the technetium is ingested, especially when the quality of the drug labeling is not good and the free technetium is relatively high. But compared with bone imaging thyroid imaging peak time is earlier, bone metabolism is a little slower, so bone imaging to do scanning in 2-4h after injection, thyroid is usually within 1h.
So if the thyroid gland is visualized in bone imaging, either the acquisition time is too early, or the thyroid gland is hyperfunctional with more uptake and slower excretion.