Safety and Bioeffects

Question 1

Describe the following:

TI of 1
TIS
TIB
TIC

Answer 1

TI of 1 - temperature rise of 1 degree after long exposure

TIS - soft tissues - suitable for 1st trimester

TIB - bone - suitable for 2&3rd trimester

TIC - cranial bone

Question 2

What are the TI risks of an embryo when TI < 1.5 and when TI >4 for 5minutes?

Answer 2

TI <1.5 = no risk

TI >4 for 5 minutes = increased bioeffect risk to fetus

Question 3

Thermal Index recommendations for PRE- natal exams?

Answer 3

1st trimester - TI <0.5 for extended scanning

TI >0.5 - 1 - scan less than 30 minutes

TI > 2.5 - scan less than 1 minute

Question 4

Thermal Index recommendations for POST-natal exams?

Answer 4

TI < 2 for extended time

TI 2-6 - less than 30 minutes

TI > 6 - less than 1 minute

Question 5

What is the difference in number for cavitation MI in tissues WITH and WITHOUT gas bodies? Gas bodies refer to contrast agents being introduced into the tissues (NON-THERMAL)

Answer 5

WITH gas bodies - MI <0.4

WITHOUT gas bodies / contrast - MI <1.9

Question 6

Mechanical mechanisms of interaction include? (3)

Answer 6

1. Radiation force - force exerted by the sound beam on an absorber
2. Streaming - shear stresses on suspended cells
3. Cavitation - production and behaviour of bubbles in a liquid medium

Question 7

Mechanical index recommendations for PRE vs POST natal exams?

Answer 7

PRE- natal - MI <0.4 if gas bodies are present

POST-natal - MI <0.4 WITH gas bodies and <1.9 without gas bodies

Question 8

What is temporal average vs pulse average?

Answer 8

Temporal average - peak temporal intensity averaged over PRP - intensity of the beam over the ringing and listening time

Pulse average - peak temporal intensity averaged over the PD - intensity over the ringing

Question 9

What bioeffect has high intensity for a short amount of time?

Answer 9

Mechanical

Question 10

What bioeffect has low intensity for a longer period of time?

Answer 10

Thermal

Question 11

What is the safe limit to prevent cavitation (mechanical)?

Answer 11

190 W/cm^2

Question 12

What is the safe limit to prevent heating?

Answer 12

720 mW/cm^2

Question 13

What is the order of THERMAL risk for u/s modalities?

Answer 13

1. PW
2. CW
3. Colour
4. M-mode
5. 2-D

Question 14

What is the order of MECHANICAL risk/cavitation?

Answer 14

1. 2-D
2. M-mode
3. Colour
4. PW
5. CW

Question 15

What does ALARA stand for?

Answer 15

As Low As Reasonably Achievable