MRI: Larmor frequency and field strength: 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: Larmor frequency and field strength

Sample item

A technologist moves a patient from a 1.5 tesla to a 3 tesla scanner. How does the proton resonance (Larmor) frequency change?

AIt doubles, because it is proportional to field strengthBIt halvesCIt remains the sameDIt becomes proportional to the square of field strength

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

The answer and the reasoning

A. It doubles, because it is proportional to field strength

The Larmor frequency of hydrogen is directly proportional to magnetic field strength, about 64 MHz at 1.5 tesla and 128 MHz at 3 tesla. Higher field gives greater signal but also more susceptibility artefact and heating. Radiofrequency coils must be matched to the frequency.

Option by option

A. It doubles, because it is proportional to field strength (correct)
Correct. Frequency scales linearly with field strength.
B. It halves
Halving would occur if the field halved.
C. It remains the same
The frequency changes with the field.
D. It becomes proportional to the square of field strength
The relationship is linear, not quadratic.

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.

Questions about this Radiology question

What is the answer to this Radiology question?

The best answer is A, It doubles, because it is proportional to field strength. The Larmor frequency of hydrogen is directly proportional to magnetic field strength, about 64 MHz at 1.

Why is "It halves" not the answer?

Halving would occur if the field halved.

Why is "It remains the same" not the answer?

The frequency changes with the field.

Why is "It becomes proportional to the square of field strength" not the answer?

The relationship is linear, not quadratic.

What concept does this question test?

It tests MRI: Larmor frequency and field strength in Radiology. 5 tesla and 128 MHz at 3 tesla. Higher field gives greater signal but also more susceptibility artefact and heating. Radiofrequency coils must be matched to the frequency.

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: Larmor frequency and field strength?

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.