Comet tail artefact in USG is seen in
**Core Concept**
The comet tail artefact in ultrasound (USG) imaging is a type of artefact that occurs due to the motion of a moving object, such as a patient's bowel or a vessel, within the ultrasound beam. This artefact is characterized by a bright, streaky pattern that extends from the moving object towards the transducer.
**Why the Correct Answer is Right**
The comet tail artefact is caused by the Doppler effect, which occurs when the ultrasound beam encounters a moving object. The moving object scatters the ultrasound waves, creating a bright, streaky pattern that extends from the object towards the transducer. This artefact is often seen in patients with bowel movements or vascular flow. The frequency shift caused by the moving object creates a high-frequency signal that is amplified by the ultrasound machine, resulting in the characteristic comet tail appearance.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not mention the Doppler effect, which is the underlying mechanism behind the comet tail artefact.
* **Option B:** This option is incorrect because it does not specify the type of artefact, and the description does not match the characteristic of the comet tail artefact.
* **Option C:** This option is incorrect because it does not describe the motion-related artefact, and the description does not match the characteristic of the comet tail artefact.
* **Option D:** This option is incorrect because it does not mention the ultrasound beam or the Doppler effect, which are the key factors in the formation of the comet tail artefact.
**Clinical Pearl / High-Yield Fact**
A key feature of the comet tail artefact is that it is highly suggestive of bowel movement or vascular flow, and it is often seen in patients with these conditions. It is essential to identify and recognize this artefact to avoid misinterpreting it as a real anatomical structure.
**Correct Answer: C. Reverberation artefact**