Imaging modalities and physics: macrocyclic gadolinium chelates: 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 · Imaging modalities and physics: macrocyclic gadolinium chelates

Sample item

A department wishes to minimise release of free gadolinium ions in patients with eGFR near 25 mL/min. Which structural type of chelate is kinetically the most stable?

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

The answer and the reasoning

D. Macrocyclic chelates

The cage-like macrocyclic structure holds gadolinium more tightly than open-chain linear molecules, so there is less transmetallation and less free gadolinium. Macrocyclic agents carry the lowest reported risk of nephrogenic systemic fibrosis.

Option by option

  • A. Linear ionic chelates

    Linear ionic agents are open-chain and release gadolinium more readily.

  • B. Linear non-ionic chelates

    Linear non-ionic agents are also open-chain and are less stable than macrocyclic ones.

  • C. Unchelated gadolinium salts

    Free gadolinium salts are toxic and are never injected as contrast agents.

  • D. Macrocyclic chelates (correct)

    Correct. The enclosed ring binds the metal ion firmly and resists release.

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 D, Macrocyclic chelates. The cage-like macrocyclic structure holds gadolinium more tightly than open-chain linear molecules, so there is less transmetallation and less free gadolinium.

Why is "Linear ionic chelates" not the answer?

Linear ionic agents are open-chain and release gadolinium more readily.

Why is "Linear non-ionic chelates" not the answer?

Linear non-ionic agents are also open-chain and are less stable than macrocyclic ones.

Why is "Unchelated gadolinium salts" not the answer?

Free gadolinium salts are toxic and are never injected as contrast agents.

What concept does this question test?

It tests Imaging modalities and physics: macrocyclic gadolinium chelates in Radiology. Macrocyclic agents carry the lowest reported risk of nephrogenic systemic fibrosis.

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 Imaging modalities and physics: macrocyclic gadolinium chelates?

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.