Answer #53

The correct answer is D:PZT crystal>matching layer> ultrasound gel>skin.

The PZT crystal is very dense and has the highest impedance followed by the matching layer which is an intermediary layer that has an impedance inbetween that of gel and the crystal so as increase the amount of transmission that occurs. Gel has the same function and has an impedance in between that of the matching layer and the skin in order to increase ultrasound transmission/penetrance to the body. This is because the larger the difference in impedance between two surfaces, the more signal that will reflect and the less that will penetrate. Gel and the matching layer aim to decrease these large inherent differences in impedances.