CT physics: 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 physics

Sample item

What CT unit is assigned to water?

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

The answer and the reasoning

A. 0 Hounsfield units

Water is assigned 0 Hounsfield units on CT, providing a reference for tissues that attenuate X-rays less or more strongly.

Option by option

  • A. 0 Hounsfield units (correct)

    Correct: water defines the zero HU reference.

  • B. -1000 Hounsfield units

    Air is approximately -1000 HU.

  • C. +40 Hounsfield units

    Soft tissue is often around +40 HU.

  • D. +1000 Hounsfield units

    Dense cortical bone is near +1000 HU.

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.

More Radiology questions

Questions about this Radiology question

What is the answer to this Radiology question?

The best answer is A, 0 Hounsfield units. Water is assigned 0 Hounsfield units on CT, providing a reference for tissues that attenuate X-rays less or more strongly.

Why is "-1000 Hounsfield units" not the answer?

Air is approximately -1000 HU.

Why is "+40 Hounsfield units" not the answer?

Soft tissue is often around +40 HU.

Why is "+1000 Hounsfield units" not the answer?

Dense cortical bone is near +1000 HU.

What concept does this question test?

It tests CT physics in Radiology. The correct option holds because: Correct: water defines the zero HU reference.

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 CT physics?

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.