A2 Daily A Level Physics question
In medical ultrasound imaging, a coupling gel is applied between the transducer and the patient's skin. What is the primary purpose of this gel?
Answer
The correct answer is A.
Correct: A — To reduce the large reflection of ultrasound that would otherwise occur at the air-skin boundary. The gel displaces air and provides a medium with an acoustic impedance similar to skin, which maximises the transmission of ultrasound into the body. B is incorrect because ultrasound imaging uses sound waves, not X-rays. C is incorrect because the frequency of the ultrasound is determined by the transducer, not the coupling gel. D is incorrect because the primary function of the gel is acoustic, not thermal, as significant heating is not a primary issue with diagnostic ultrasound.