Radiotherapy and nuclear medicine basics: iodine-123 for imaging: practice question

A Radiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Radiology · Radiotherapy and nuclear medicine basics: iodine-123 for imaging

Sample item

Why is iodine-123 preferred over iodine-131 for diagnostic thyroid imaging?

AIt has a half-life of eight days, giving high count ratesBIt emits beta particles that treat the gland during imagingCPure gamma emission with a shorter half-life gives a lower radiation doseDIt is trapped but not organified by the thyroid

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Pure gamma emission with a shorter half-life gives a lower radiation dose

I-123 emits only 159 keV gamma photons and has a half-life of about 13 hours, so it gives good images with a lower dose. I-131 emits beta particles and high-energy gamma photons and is used for therapy.

Option by option

A. It has a half-life of eight days, giving high count rates
A half-life of eight days belongs to I-131, not I-123.
B. It emits beta particles that treat the gland during imaging
Beta emission is a property of I-131 and is the reason for its therapeutic use.
C. Pure gamma emission with a shorter half-life gives a lower radiation dose (correct)
Correct. I-123 is a pure gamma emitter with a short half-life, giving a lower radiation dose.
D. It is trapped but not organified by the thyroid
Trapping without organification describes pertechnetate, whereas iodine is both trapped and organified.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Radiology question

What is the answer to this Radiology question?

The best answer is C, Pure gamma emission with a shorter half-life gives a lower radiation dose. I-123 emits only 159 keV gamma photons and has a half-life of about 13 hours, so it gives good images with a lower dose.

Why is "It has a half-life of eight days, giving high count rates" not the answer?

A half-life of eight days belongs to I-131, not I-123.

Why is "It emits beta particles that treat the gland during imaging" not the answer?

Beta emission is a property of I-131 and is the reason for its therapeutic use.

Why is "It is trapped but not organified by the thyroid" not the answer?

Trapping without organification describes pertechnetate, whereas iodine is both trapped and organified.

What concept does this question test?

It tests Radiotherapy and nuclear medicine basics: iodine-123 for imaging in Radiology. I-131 emits beta particles and high-energy gamma photons and is used for therapy.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Radiotherapy and nuclear medicine basics: iodine-123 for imaging?

Learn signs with the image, and the disease they point to. Then use the flashcards and the other Radiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.