Question

Many radioactive isotopes are used in medicine for imaging and treatment purposes. The specific isotopes used depends on the particular organ or body system being studied (for example, Xe-133 is used to image lung function and blood flow.) For thyroid imaging, isotopes of iodine are used, commonly I-123 and I-131, which have half-lives of 13.2 hours and 8.0 days, respectively.

Why is iodine used for thyroid imaging (as opposed to any other element)?

I-129 is an extremely rare isotope of iodine with a half-life of 15.7 million years. Assuming it was much more abundant in nature, would I-129 be a good substitute for I-123 or I-131 in thyroid imaging? Why or why not?

Although both I-123 and I-131 can be used in imaging of the thyroid, only I-131 is used in treating thyroid cancer. What difference in radioactivity between I-123 and I-131 accounts for this preference?

Sometimes non-radioactive isotopes of iodine can be preferred depending on the intended medical use. For example, many people preparing for a nuclear disaster stockpile KI tablets (non-radioactive). Why would someone consume KI during a radioactive disaster? Would you consider purchasing KI tablets as a precaution? Why or why not?

Answer 1

i) Iodine is used in the treatment of the thyroid disease. Therefore, iodine is also used for thyroid imaging among the several elements.

ii) If I-129 is much more abundant in nature, it would not be good substitute for I-123 or I-132 in thyroid imaging. This is because the half life of I-129 is 15.7 millions years which is very large than the half life of I-123 or I-132. I-129 can not be released from the body due to its larger half life.

iii) Both I-123 and I-131 are used in the imaging of the thyroid but only I-131 is used in the treating the thyroid cancer. This is because due to its mode of beta decay, I-131 causes mutation and death in thyroid cells while this type of radioactive properties is not present in the I-123.

iv) The consumption of KI during a radioactive disaster protects the thyroid gland from being harmed. This is because after consuming KI, the body does not receive radioactive iodine.