What is the wavelength in soft tissue for an ultrasound transducer operating at 5 MHz if the speed of sound is approximately 1540 m/s?

• A. 0.308 mm
• B. 3.08 mm
• C. 0.031 mm
• D. 1.54 mm

Answer: (A)

Wavelength in a medium comes from dividing the speed of sound by the frequency: lambda = c / f. In soft tissue, c ≈ 1540 m/s, and the transducer operates at 5 MHz, which is 5 × 10^6 Hz. So lambda = 1540 / (5 × 10^6) = 3.08 × 10^-4 m, which is 0.308 mm. This matches 0.308 mm, the correct value.

If you check the other numbers, they'd correspond to different frequencies: 3.08 mm would need about 0.514 MHz, 0.031 mm would need around 50 MHz, and 1.54 mm would need about 1 MHz.