Imaging modalities and physics: air gap technique: 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 · Imaging modalities and physics: air gap technique

Sample item

A lateral cervical spine radiograph is taken with the patient about 15 cm from the detector and no grid. Compared with a contact exposure without a grid, what is the main effect?

AMore scatter reaches the detector, with less magnificationBLess scatter reaches the detector, with some magnificationCLower patient dose because the beam is more penetratingDLower geometric unsharpness with unchanged scatter

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

The answer and the reasoning

B. Less scatter reaches the detector, with some magnification

In the air-gap technique, scattered photons leave at an angle and miss the detector across the gap, so contrast improves without a grid. The cost is geometric magnification and some unsharpness, which is why a longer focus-to-detector distance is usually added.

Option by option

A. More scatter reaches the detector, with less magnification
The gap reduces scatter rather than increasing it, and it increases rather than decreases magnification.
B. Less scatter reaches the detector, with some magnification (correct)
Correct. The gap lets much of the scatter miss the detector, and the larger object-to-detector distance magnifies the image.
C. Lower patient dose because the beam is more penetrating
Beam penetration is set by kVp and the gap does not lower patient dose by itself.
D. Lower geometric unsharpness with unchanged scatter
A larger object-to-detector distance raises geometric unsharpness, and scatter is reduced.

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 B, Less scatter reaches the detector, with some magnification. In the air-gap technique, scattered photons leave at an angle and miss the detector across the gap, so contrast improves without a grid.

Why is "More scatter reaches the detector, with less magnification" not the answer?

The gap reduces scatter rather than increasing it, and it increases rather than decreases magnification.

Why is "Lower patient dose because the beam is more penetrating" not the answer?

Beam penetration is set by kVp and the gap does not lower patient dose by itself.

Why is "Lower geometric unsharpness with unchanged scatter" not the answer?

A larger object-to-detector distance raises geometric unsharpness, and scatter is reduced.

What concept does this question test?

It tests Imaging modalities and physics: air gap technique in Radiology. The cost is geometric magnification and some unsharpness, which is why a longer focus-to-detector distance is usually added.

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: air gap technique?

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.