CT: pitch and spiral scanning: 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: pitch and spiral scanning

Sample item

In helical CT with a single detector row, increasing the pitch from 1 to 2 (other parameters unchanged) will lead to which effect?

AComplete loss of axial image reconstructionBFaster coverage and lower patient dose, with some loss of z-axis resolutionCHigher dose and better z-axis resolutionDNo change in dose or scan time

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

The answer and the reasoning

B. Faster coverage and lower patient dose, with some loss of z-axis resolution

Pitch is table travel per rotation divided by beam collimation. A higher pitch covers a given length faster and with less dose when mAs is not compensated, but the data are more sparsely sampled and z-axis resolution falls. Modern scanners often adjust mA with pitch to keep noise constant.

Option by option

A. Complete loss of axial image reconstruction
Helical data can still be reconstructed into axial images with interpolation.
B. Faster coverage and lower patient dose, with some loss of z-axis resolution (correct)
Correct. Higher pitch means quicker coverage and less dose at some cost to resolution.
C. Higher dose and better z-axis resolution
Dose does not rise and resolution does not improve with a higher pitch.
D. No change in dose or scan time
Pitch affects both scan time and dose.

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, Faster coverage and lower patient dose, with some loss of z-axis resolution. Pitch is table travel per rotation divided by beam collimation.

Why is "Complete loss of axial image reconstruction" not the answer?

Helical data can still be reconstructed into axial images with interpolation.

Why is "Higher dose and better z-axis resolution" not the answer?

Dose does not rise and resolution does not improve with a higher pitch.

Why is "No change in dose or scan time" not the answer?

Pitch affects both scan time and dose.

What concept does this question test?

It tests CT: pitch and spiral scanning in Radiology. A higher pitch covers a given length faster and with less dose when mAs is not compensated, but the data are more sparsely sampled and z-axis resolution falls. Modern scanners often adjust mA with pitch to keep noise constant.

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: pitch and spiral scanning?

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.