Week 1

Question 1

What is mechanical index?

Answer 1

Relative potential for ultrasound to induce an adverse biotech by a nonthermal mechanism (cavitation)

Question 2

What is thermal index?

Answer 2

Indicator of the relative potential for a tissue temperature rise

Question 3

What threshold should the MI and TI be kept under?

Answer 3

1

Question 4

What are some ways of keeping the MI and TI under threshold?

Answer 4

• Begin at a low power output and increase power only if necessary
• Incorporate ALARA

Question 5

What are the safety considerations with Doppler ultrasound during first trimester scans?

Answer 5

• Pulsed Doppler (spectral, power and colour) should not be used routinely
• Pulsed Doppler may be used for clinical indications to refine risks for trisomies
• The thermal index should be less than, or equal to 1 and exposure time should be kept as short as possible (usually no longer than 5-10mins) and not exceed 60 mins.
• Can implement ALARA which means ‘as low as reasonably achievable’

Question 6

What is the purpose of first, second and third trimester scans?

Answer 6

First is to ensure fetal viability, dating, localisation and number of fetus’, second is for fetal anatomy scanning and third is fetal well-being.

Question 7

What are the three important parameters under end-user control?

Answer 7

• Dwell time
• System setup and output control
• Scanning/operation mode
• Transducer choice

Question 8

ASUM policy states that diagnostic exposure to ultrasound should not produce what?

Answer 8

1.5°C increase in temperature

Question 9

Why is choice of scanning mode important?

Answer 9

Different modes offer varying levels of detail, image quality, and energy exposure, which can impact the accuracy and safety of the scan.

Spatial peak temporal average intensity (ISPTA) increases from B-mode (34 mW/cm2) to over 1180 mW/cm2 in Doppler and spectral Doppler

Question 10

Why does colour Doppler have higher intensities than b-mode?

Answer 10

Because it needs to detect and process more information about blood flow which involves analyzing subtle changes in frequency due to the Doppler effect. Due to of mode of operation: sequences of pulses, scanned through the area of interest (“box”).

Question 11

Why is transducer choice important in regards to ultrasound safety?

Answer 11

Transducer choice is important because it will determine frequency, penetration, resolution, and field of view