Final answer:
Iodine is used as a contrast agent in X-rays, particularly for imaging the thyroid gland and for treating thyroid cancer, as it is selectively taken up by thyroid cells. Small doses allow for imaging and have a short half-life, ensuring the iodine doesn't stay in the body for an extended period.
Step-by-step explanation:
Iodine is used intravenously in X-rays as a contrast agent due to its ability to be concentrated by the thyroid gland. This is particularly useful in medical diagnostics where imaging of the thyroid and other organs are necessary. By replacing a stable element with a radioactive isotope like iodine-131, doctors can image many organs, including the thyroid. Once iodine is administered, it is absorbed by the thyroid cells that are most active, often including cancerous cells, which then allows for imaging or therapeutic purposes.
Small doses of I-131 are utilized for imaging and have a half-life of approximately 8 days, which means that it does not remain in the patient's system for long. Larger doses can be used to treat thyroid cancer, as the radioactive iodine is taken up by and destroys thyroid cells. During diagnostic or therapeutic use, this process permits medical professionals to obtain clear images for assessment or to deliver targeted radiation therapy to the thyroid.