Module 13 - UltraSound

Question 1

What temperature increase is tolerable for USS?

Answer 1

<1.5C increase in tissue temperature is considered below teratogenic levels.

Question 2

What are the risks of ultrasound?

Answer 2

Tissue cavitation and formation of bioactive free radicals.

Question 3

What US most is most commonly used and considered safest?

Answer 3

B mode

Question 4

What is thermal index?

Answer 4

TI is the ratio of machine power needed to increase tissue temperature by 1C.

Question 5

What types of Thermal Index are there? When are they used?

Answer 5

TIS (soft tissue) used up to 10/40.
TIB (bone) - bone impeding view.
TIC (bone close to transducer probe) used >10/40.

Question 6

What is the difference in power output between 2D, 3D and 4D?

Answer 6

2D and 3D are the same.

4D is increased power therefore increased risks. Therefore limit time used.

Question 7

What is the theoretical risk if US is carried out in late follicular phase? (what evidence supports this?)

Answer 7

Delayed ovulation
(single trial included majority IVF patients).

Question 8

<10/40, ie the embryonic period is the most teratogenic. Why is US considered more risky in this period?

Answer 8

1. Small embryo (6mm at 6/40 to 35mm at 10/40)
2. Rapid cell devision
3. Limited foetal blood flow therefore heat is less likely to be dispersed.

Question 9

What is the evidence surrounding US and future handedness?

Answer 9

Cochrain review shows no difference.

1 meta analysis shows there is a significant association of US used in embryonic period and increased left handedness.

Question 10

Should Doppler be used <10 weeks gestation?

Answer 10

Not routinely.
But if used, then use Doppler for shortest possible time.