In the impedance reflection calculation, what unit is used for acoustic impedance?

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Multiple Choice

In the impedance reflection calculation, what unit is used for acoustic impedance?

Explanation:
The key idea is that acoustic impedance is the ratio of acoustic pressure to particle velocity, so its units are pressure times time per distance: Pa·s/m. This is commonly called a Rayl, and in ultrasound we often express tissue impedances around 1.5 x 10^6 Pa·s/m, i.e., about 1.5 MRayl. So the unit used in impedance reflection calculations for biological tissues is MRayl (mega Rayls). Pascal is only a unit of pressure, not impedance. Siemens per meter would imply an electrical-type property per length and doesn’t match the acoustic quantity. Joule per second is power, not impedance.

The key idea is that acoustic impedance is the ratio of acoustic pressure to particle velocity, so its units are pressure times time per distance: Pa·s/m. This is commonly called a Rayl, and in ultrasound we often express tissue impedances around 1.5 x 10^6 Pa·s/m, i.e., about 1.5 MRayl. So the unit used in impedance reflection calculations for biological tissues is MRayl (mega Rayls).

Pascal is only a unit of pressure, not impedance. Siemens per meter would imply an electrical-type property per length and doesn’t match the acoustic quantity. Joule per second is power, not impedance.

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