Imaging modalities and physics: dose-length product: 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: dose-length product

Sample item

A CT report lists CTDIvol of 12 mGy and a dose-length product of 480 mGy-cm for an abdominal scan. How is the effective dose estimated from this?

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

The answer and the reasoning

C. Multiply the DLP by a region-specific conversion coefficient

DLP is the CTDIvol multiplied by the scanned length. Effective dose is approximated by multiplying DLP by a conversion coefficient specific to the body region, such as chest, abdomen or head.

Option by option

  • A. Multiply the CTDIvol by the patient's weight

    Patient weight does not convert CTDIvol into an effective dose.

  • B. Divide the DLP by the scan pitch

    Pitch is already included in CTDIvol, and dividing by it gives no dose estimate.

  • C. Multiply the DLP by a region-specific conversion coefficient (correct)

    Correct. The coefficient converts DLP to effective dose in mSv for a given body region.

  • D. Add the CTDIvol to the DLP

    The two quantities have different units and cannot be added.

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, Multiply the DLP by a region-specific conversion coefficient. DLP is the CTDIvol multiplied by the scanned length.

Why is "Multiply the CTDIvol by the patient's weight" not the answer?

Patient weight does not convert CTDIvol into an effective dose.

Why is "Divide the DLP by the scan pitch" not the answer?

Pitch is already included in CTDIvol, and dividing by it gives no dose estimate.

Why is "Add the CTDIvol to the DLP" not the answer?

The two quantities have different units and cannot be added.

What concept does this question test?

It tests Imaging modalities and physics: dose-length product in Radiology. Effective dose is approximated by multiplying DLP by a conversion coefficient specific to the body region, such as chest, abdomen or head.

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 modalities and physics: dose-length product?

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.