If a 5.0 MHz transducer operates in soft tissue (c ≈ 1540 m/s), what is the wavelength of the ultrasound wave in tissue?

• A. Approximately 3.08 mm.
• B. Approximately 0.308 mm.
• C. Approximately 0.0308 mm.
• D. Approximately 0.154 mm.

Answer: (B)

Wavelength in a medium equals the speed of sound in that medium divided by the frequency: λ = c / f. In soft tissue, the speed is about 1540 m/s. With a transducer frequency of 5.0 MHz (5.0 x 10^6 Hz), the wavelength is λ = 1540 / 5,000,000 = 0.000308 m, which is 0.308 mm. So the ultrasound wave in tissue has a wavelength of roughly 0.308 mm.

The other values would imply speeds or frequencies that don’t match tissue properties (for example, a wavelength of about 3.08 mm would correspond to a much higher c than tissue provides, etc.), whereas 0.308 mm aligns with the familiar tissue speed and the given frequency.