MRI: contrast agent: 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 · MRI: contrast agent

Sample item

Gadolinium chelates enhance MR images mainly by which mechanism?

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

The answer and the reasoning

C. Paramagnetic effect that shortens T1 relaxation time

Gadolinium is paramagnetic and shortens T1 of nearby water protons, so enhancing tissue turns bright on T1 images. It does not attenuate X-rays like iodine. In severe renal failure, linear agents carry a risk of nephrogenic systemic fibrosis.

Option by option

  • A. Absorbing X-rays

    X-ray attenuation is the principle of iodinated contrast.

  • B. Emitting positrons

    Positron emission is the principle of PET tracers.

  • C. Paramagnetic effect that shortens T1 relaxation time (correct)

    Correct. T1 shortening produces signal increase.

  • D. Increasing proton density in tissue

    Gadolinium does not change proton density.

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, Paramagnetic effect that shortens T1 relaxation time. Gadolinium is paramagnetic and shortens T1 of nearby water protons, so enhancing tissue turns bright on T1 images.

Why is "Absorbing X-rays" not the answer?

X-ray attenuation is the principle of iodinated contrast.

Why is "Emitting positrons" not the answer?

Positron emission is the principle of PET tracers.

Why is "Increasing proton density in tissue" not the answer?

Gadolinium does not change proton density.

What concept does this question test?

It tests MRI: contrast agent in Radiology. It does not attenuate X-rays like iodine. In severe renal failure, linear agents carry a 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 MRI: contrast agent?

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.