CT: beam hardening artefact: 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 · CT: beam hardening artefact

Sample item

A CT of the head shows dark streaks running between the two petrous temporal bones in the posterior fossa. What is the usual cause?

ADetector overload from a very low tube currentBFailure of the contrast injectorCBeam hardening, as the polychromatic beam loses low-energy photons while crossing dense boneDPatient motion during the scan

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

The answer and the reasoning

C. Beam hardening, as the polychromatic beam loses low-energy photons while crossing dense bone

A polychromatic beam becomes harder as it passes through dense bone because low-energy photons are preferentially absorbed. The reconstruction then underestimates attenuation along paths between dense structures, giving dark bands, and cupping in uniform objects.

Option by option

A. Detector overload from a very low tube current
Low tube current causes noise rather than structured streaks.
B. Failure of the contrast injector
This is a non-contrast head CT, so the injector is irrelevant.
C. Beam hardening, as the polychromatic beam loses low-energy photons while crossing dense bone (correct)
Correct. Beam hardening between dense bones produces dark streaks.
D. Patient motion during the scan
Motion gives blurring or ghosting rather than fixed dark bands between the petrous bones.

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 C, Beam hardening, as the polychromatic beam loses low-energy photons while crossing dense bone. A polychromatic beam becomes harder as it passes through dense bone because low-energy photons are preferentially absorbed.

Why is "Detector overload from a very low tube current" not the answer?

Low tube current causes noise rather than structured streaks.

Why is "Failure of the contrast injector" not the answer?

This is a non-contrast head CT, so the injector is irrelevant.

Why is "Patient motion during the scan" not the answer?

Motion gives blurring or ghosting rather than fixed dark bands between the petrous bones.

What concept does this question test?

It tests CT: beam hardening artefact in Radiology. The reconstruction then underestimates attenuation along paths between dense structures, giving dark bands, and cupping in uniform objects.

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 CT: beam hardening artefact?

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.