Imaging physics: CT attenuation of blood: 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 physics: CT attenuation of blood

Sample item

A non-contrast CT head shows a crescentic extra-axial collection of 65 HU. Which characteristic does this attenuation most suggest?

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

The answer and the reasoning

C. Acute haemorrhage

Fresh clotted blood is hyperdense because of its high protein (haemoglobin) content, with values around 50 to 80 HU. CSF is near 0 to 15 HU, fat is about -100 HU and calcium is far higher. As blood ages, its density falls and becomes isodense and then hypodense.

Option by option

  • A. Cerebrospinal fluid

    CSF measures close to water, about 0 to 15 HU.

  • B. Fat

    Fat is markedly negative, near -100 HU.

  • C. Acute haemorrhage (correct)

    Correct. 50 to 80 HU is typical of acute clotted blood.

  • D. Calcification

    Calcification generally exceeds 100 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.

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Questions about this Radiology question

What is the answer to this Radiology question?

The best answer is C, Acute haemorrhage. Fresh clotted blood is hyperdense because of its high protein (haemoglobin) content, with values around 50 to 80 HU.

Why is "Cerebrospinal fluid" not the answer?

CSF measures close to water, about 0 to 15 HU.

Why is "Fat" not the answer?

Fat is markedly negative, near -100 HU.

Why is "Calcification" not the answer?

Calcification generally exceeds 100 HU.

What concept does this question test?

It tests Imaging physics: CT attenuation of blood in Radiology. CSF is near 0 to 15 HU, fat is about -100 HU and calcium is far higher. As blood ages, its density falls and becomes isodense and then hypodense.

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 Imaging physics: CT attenuation of blood?

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.