Nuclear medicine: effective half-life: 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 · Nuclear medicine: effective half-life

Sample item

A radiopharmaceutical has a physical half-life of 6 hours and a biological half-life of 6 hours. What is its effective half-life?

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

The answer and the reasoning

C. 3 hours

Effective half-life equals the product of the physical and biological half-lives divided by their sum. Here (6 x 6) divided by (6 + 6) gives 3 hours, and it is always shorter than either component.

Option by option

  • A. 36 hours

    Multiplying the half-lives gives a meaningless unit.

  • B. 12 hours

    Adding the two half-lives is wrong because it ignores the combined removal.

  • C. 3 hours (correct)

    Correct. 36 / 12 = 3 hours.

  • D. 6 hours

    The effective half-life must be shorter than both components when both processes act.

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.

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Questions about this Radiology question

What is the answer to this Radiology question?

The best answer is C, 3 hours. Effective half-life equals the product of the physical and biological half-lives divided by their sum.

Why is "36 hours" not the answer?

Multiplying the half-lives gives a meaningless unit.

Why is "12 hours" not the answer?

Adding the two half-lives is wrong because it ignores the combined removal.

Why is "6 hours" not the answer?

The effective half-life must be shorter than both components when both processes act.

What concept does this question test?

It tests Nuclear medicine: effective half-life in Radiology. Here (6 x 6) divided by (6 + 6) gives 3 hours, and it is always shorter than either component.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Nuclear medicine: effective half-life?

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.