What is the size of the smallest feature observable in human tissue when examined with 19-MHz ultrasound?

Question

Ultrasound probes can resolve structural details with sizes approximately equal to the wavelength of the ultrasound waves themselves. What is the size of the smallest feature observable in human tissue when examined with 19-MHz ultrasound? The speed of sound in human tissue is 1,540 m/s.

Answer 1

wavelength λ, velocity v and frequency f has the relationship of:

v = λf, or λ = v/f,

so the wavelength λ = 1540 / 19×10⁶ = 8.1×10^-5 (m) = 81 (μm).