Ultrasound: Doppler angle: 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 · Ultrasound: Doppler angle

Sample item

During a carotid Doppler examination, no flow signal is detected even though the vessel is patent. Which technical factor best explains this?

AGel has been appliedBThe ultrasound beam is at 90 degrees to the direction of flowCThe beam is at 60 degrees to the flowDThe frequency is too high for a superficial vessel

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

The answer and the reasoning

B. The ultrasound beam is at 90 degrees to the direction of flow

Doppler shift is proportional to the cosine of the angle between beam and flow, and cos 90 is zero, so no shift is recorded. An angle of 60 degrees or less is recommended for accurate velocity measurements. Angle correction is applied to the spectral trace.

Option by option

A. Gel has been applied
Gel is needed to remove air and does not stop signals.
B. The ultrasound beam is at 90 degrees to the direction of flow (correct)
Correct. A perpendicular beam gives no Doppler shift.
C. The beam is at 60 degrees to the flow
At 60 degrees a signal is recorded and velocity can be calculated.
D. The frequency is too high for a superficial vessel
High frequency does not abolish a signal in a superficial vessel.

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, The ultrasound beam is at 90 degrees to the direction of flow. Doppler shift is proportional to the cosine of the angle between beam and flow, and cos 90 is zero, so no shift is recorded.

Why is "Gel has been applied" not the answer?

Gel is needed to remove air and does not stop signals.

Why is "The beam is at 60 degrees to the flow" not the answer?

At 60 degrees a signal is recorded and velocity can be calculated.

Why is "The frequency is too high for a superficial vessel" not the answer?

High frequency does not abolish a signal in a superficial vessel.

What concept does this question test?

It tests Ultrasound: Doppler angle in Radiology. An angle of 60 degrees or less is recommended for accurate velocity measurements. Angle correction is applied to the spectral trace.

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 Ultrasound: Doppler angle?

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.