Radiotherapy and nuclear medicine basics: limitation of brain FDG PET: 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.

Try it

Radiology · Radiotherapy and nuclear medicine basics: limitation of brain FDG PET

Sample item

A patient with a known primary tumour is suspected to have a small brain metastasis. Why is FDG PET unsuitable for excluding it?

AThe normal brain cortex takes up FDG avidly, so a small lesion is lost in the high backgroundBBrain metastases never take up glucoseCFDG cannot cross the blood-brain barrierDThe scan exposes the brain to too much radiation

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

The answer and the reasoning

A. The normal brain cortex takes up FDG avidly, so a small lesion is lost in the high background

Brain tissue relies on glucose and shows intense physiological FDG uptake, which masks small lesions. Contrast-enhanced MRI is the preferred test for brain metastases. FDG enters the brain readily and many tumours do take it up.

Option by option

A. The normal brain cortex takes up FDG avidly, so a small lesion is lost in the high background (correct)
Correct. High physiological uptake lowers lesion contrast.
B. Brain metastases never take up glucose
Many metastases take up FDG, but the background hides them.
C. FDG cannot cross the blood-brain barrier
FDG crosses the blood-brain barrier using glucose transporters.
D. The scan exposes the brain to too much radiation
Dose is not the reason the test is unsuitable.

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, The normal brain cortex takes up FDG avidly, so a small lesion is lost in the high background. Brain tissue relies on glucose and shows intense physiological FDG uptake, which masks small lesions.

Why is "Brain metastases never take up glucose" not the answer?

Many metastases take up FDG, but the background hides them.

Why is "FDG cannot cross the blood-brain barrier" not the answer?

FDG crosses the blood-brain barrier using glucose transporters.

Why is "The scan exposes the brain to too much radiation" not the answer?

Dose is not the reason the test is unsuitable.

What concept does this question test?

It tests Radiotherapy and nuclear medicine basics: limitation of brain FDG PET in Radiology. Contrast-enhanced MRI is the preferred test for brain metastases. FDG enters the brain readily and many tumours do take it up.

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 Radiotherapy and nuclear medicine basics: limitation of brain FDG PET?

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.