Imaging modalities and physics: opposed-phase imaging principle: 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: opposed-phase imaging principle

Sample item

On dual-echo gradient-echo MRI, an adrenal mass loses signal on the opposed-phase image compared with the in-phase image. What does this indicate about its content?

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

The answer and the reasoning

C. Fat and water protons within the same voxels

On opposed-phase images the fat and water signals in a voxel cancel, so a lipid-rich adenoma drops in signal. The finding is called chemical shift imaging and is used to confirm a benign lipid-rich adenoma.

Option by option

  • A. Haemorrhage with methaemoglobin

    Methaemoglobin is bright on T1 and does not lose signal by phase cancellation.

  • B. Pure fluid

    Pure fluid has no fat and so shows no drop in signal.

  • C. Fat and water protons within the same voxels (correct)

    Correct. Signal cancellation shows that lipid and water share the voxels.

  • D. Calcification

    Calcification is low signal on both sequences and does not change between them.

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, Fat and water protons within the same voxels. On opposed-phase images the fat and water signals in a voxel cancel, so a lipid-rich adenoma drops in signal.

Why is "Haemorrhage with methaemoglobin" not the answer?

Methaemoglobin is bright on T1 and does not lose signal by phase cancellation.

Why is "Pure fluid" not the answer?

Pure fluid has no fat and so shows no drop in signal.

Why is "Calcification" not the answer?

Calcification is low signal on both sequences and does not change between them.

What concept does this question test?

It tests Imaging modalities and physics: opposed-phase imaging principle in Radiology. The finding is called chemical shift imaging and is used to confirm a benign lipid-rich adenoma.

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 Imaging modalities and physics: opposed-phase imaging principle?

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.