Chapter 7: Viscous Absorption

Question 1

Viscous absorption

Answer 1

Viscosity leads to shear forces within the tissue as the sound wave passes through and some energy is converted via friction to heat.

Question 2

Molecular relaxation absorption

Answer 2

the transfer of energy to the molecular storage - translational, rotational and vibrational. (vrt)

Question 3

what does the equipartition theorem state?

Answer 3

that at thermal equilibrium the energy of the molecules will be shared equally among these various modes.

Question 4

Time gain compensation: The increase in absorption with both frequency and distance has two important consequences for ultrasound imaging,

Answer 4

1. Lower frequencies are better for deep tissue imaging as the reduced absorption improves the signal to noise ratio of the reflected signals.
2. Because the amount of the signal that has been absorbed is greater the longer the signal has traveled ultrasound pulses reflecting back from deep within the tissue are much more strongly attenuated than pulses reflected from structures close to the surface.

Question 5

Time gain compensation is what?

Answer 5

An approximate way to correct for this attenuation deeper down