Physics Mod 9

Question 1

Parameters that increase risk of thermal bioeffects

Answer 1

1) higher transmit power
2) non-scanned modality (spectral, M-mode)
3) higher duty factor (PD/PRP)
4) Greater absorption rate (collagen content)
5) longer scan time
6) below fluid-filled structures

Question 2

Mechanical index

Answer 2

measurement of US bioeffects

MI = peak rarefactional pressure / SQRT (operating frequency)

Question 3

Two types of cavitation

Answer 3

1) inertial (transient)

2) stable

Question 4

Typical transmit voltages for different modalities

Answer 4

2-D pulse = 150V
M-mode pulse = 60V
Color doppler = 40V
PW doppler = 30
CW doppler = 8

Question 5

Duty factor

Answer 5

Pulse duration / PRP

Question 6

Mechanical vs thermal risk in different modes

Answer 6

Mechanical risk highest in B mode with highest voltage

Thermal risk highest in CW doppler with highest duty factor