Imaging modalities and physics: off-level grid cutoff: 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: off-level grid cutoff

Sample item

A radiograph taken with a focused grid shows an even loss of density across the entire film. The tube was angled slightly across the grid lines, and the focus-grid distance was correct. Which fault is this?

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

The answer and the reasoning

C. Off-level grid cutoff

When the central ray is not perpendicular to the grid plane (a tilted tube or tilted grid), the lead strips absorb primary photons across the whole field, giving uniform density loss. Off-focus cutoff, in contrast, darkens the centre and loses density towards the periphery.

Option by option

  • A. Moire pattern

    Moire patterns arise when a stationary grid interacts with the scanning frequency of a computed radiography reader.

  • B. Grid line artefact from a stationary grid

    A stationary grid leaves fine parallel lines on the image and does not cause an even loss of density.

  • C. Off-level grid cutoff (correct)

    Correct. A tilt of the grid relative to the beam causes uniform loss of density across the film.

  • D. Off-focus grid cutoff

    Off-focus cutoff arises from the wrong focus-grid distance and loses density mainly towards the edges.

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, Off-level grid cutoff. When the central ray is not perpendicular to the grid plane (a tilted tube or tilted grid), the lead strips absorb primary photons across the whole field, giving uniform density loss.

Why is "Moire pattern" not the answer?

Moire patterns arise when a stationary grid interacts with the scanning frequency of a computed radiography reader.

Why is "Grid line artefact from a stationary grid" not the answer?

A stationary grid leaves fine parallel lines on the image and does not cause an even loss of density.

Why is "Off-focus grid cutoff" not the answer?

Off-focus cutoff arises from the wrong focus-grid distance and loses density mainly towards the edges.

What concept does this question test?

It tests Imaging modalities and physics: off-level grid cutoff in Radiology. Off-focus cutoff, in contrast, darkens the centre and loses density towards the periphery.

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: off-level grid cutoff?

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.