Final answer:
The correct backing material for ultrasound in medical imaging is gel, as it facilitates the transmission of ultrasound waves by replacing air, which has a higher acoustic impedance, and thus enables clearer images.The correct option is A.
Step-by-step explanation:
The backing material for ultrasound commonly used in medical diagnostic imaging is gel. During an ultrasound exam, gel acts as a coupling medium to facilitate the transmission of ultrasonic waves from the ultrasound transducer to the patient's body. This gel is crucial because it displaces the air that would otherwise exist between the transducer and the skin, which can significantly impede the transmission of ultrasound waves due to the high acoustic impedance of air. Gel, on the other hand, has an acoustic impedance similar to human tissue and water, which allows for a lesser intensity reflection coefficient and thus a clearer image.
For example, if the acoustic impedance values indicate a high reflection coefficient when the transducer is coupled with air, there would be significant reflection of the ultrasound waves, making the diagnosis less effective. The use of gel minimizes this reflection, leading to better quality imaging. To illustrate, if we calculate the minimum frequency of ultrasound to see details as small as 0.250 mm in human tissue, and if we find the size of the smallest detail observable with 20.0-MHz ultrasound and check if its effective penetration depth is sufficient for the examination of the entire eye, knowing the right acoustic medium is essential for accurate diagnostics.