Imaging modalities and physics: BOLD functional MRI: 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: BOLD functional MRI

Sample item

During finger tapping, functional MRI shows increased T2-star signal over the contralateral motor cortex. What is the intrinsic contrast mechanism?

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

The answer and the reasoning

D. Fall in local deoxyhaemoglobin because blood flow rises more than oxygen extraction

Deoxyhaemoglobin is paramagnetic and shortens T2-star. When a cortical area is active, blood flow increases out of proportion to oxygen extraction, so deoxyhaemoglobin falls and the signal rises. This blood oxygen level dependent effect needs no contrast agent.

Option by option

  • A. Heat generated by neuronal firing

    Neuronal heat production is far too small to alter MRI signal.

  • B. Accumulation of gadolinium in active neurones

    No contrast agent is used and gadolinium does not enter neurones.

  • C. Rise in local deoxyhaemoglobin from increased oxygen extraction

    More deoxyhaemoglobin would lower the signal and is the opposite of what happens.

  • D. Fall in local deoxyhaemoglobin because blood flow rises more than oxygen extraction (correct)

    Correct. Relative washout of paramagnetic deoxyhaemoglobin raises the signal.

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, Fall in local deoxyhaemoglobin because blood flow rises more than oxygen extraction. Deoxyhaemoglobin is paramagnetic and shortens T2-star.

Why is "Heat generated by neuronal firing" not the answer?

Neuronal heat production is far too small to alter MRI signal.

Why is "Accumulation of gadolinium in active neurones" not the answer?

No contrast agent is used and gadolinium does not enter neurones.

Why is "Rise in local deoxyhaemoglobin from increased oxygen extraction" not the answer?

More deoxyhaemoglobin would lower the signal and is the opposite of what happens.

What concept does this question test?

It tests Imaging modalities and physics: BOLD functional MRI in Radiology. When a cortical area is active, blood flow increases out of proportion to oxygen extraction, so deoxyhaemoglobin falls and the signal rises. This blood oxygen level dependent effect needs no contrast agent.

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: BOLD functional MRI?

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.