Final answer:
Thyroid nodules that spread through the bloodstream typically indicate metastatic thyroid cancer, which is diagnosed and treated using radioisotopes like Iodine-131 for imaging and irradiating affected thyroid tissue.
Step-by-step explanation:
A thyroid nodule that spreads via blood usually refers to metastatic thyroid cancer. The primary mode by which cancer cells travel from the original tumor to other parts of the body is called metastasis. In diagnostic imaging, radioisotope scans can be exceptionally useful for locating thyroid nodules and identifying metastases. Isotopes such as Iodine-131 (I-131) or Iodine-123 are utilized because the thyroid gland concentrates iodine, allowing it to be imaged for diagnostic purposes and irradiated for treatment. I-131, in particular, is used not only for imaging thyroid nodules but also for treating conditions like hyperthyroidism and thyroid cancer, as it destroys excess or cancerous thyroid tissue. Another diagnostic tool is a PET scan, which uses isotopes like fluorine-18 incorporated into glucose molecules to trace metabolic processes in body organs, helping identify areas with rapid cell growth like tumors.