Chap 9: Bioeffects

Question 1

What are the two principal mechanisms for bio effects?

Answer 1

Thermal and mechanical

Question 2

What is the relationship between temperature rise and thermal bio effects?

Answer 2

Related to temporal average intensity, duty factor, scan time, scanned versus non-scan modalities

Question 3

What is cavitation related to in mechanical bio effects?

Answer 3

Peak fractional pressure

Question 4

How does temperature affect enzyme activity?

Answer 4

As temperatures rise, so does the reaction rate

Question 5

What happens to protein activity when temperature increases beyond 45°C?

Answer 5

Denaturing decreases activity

Question 6

At what temperature is the reaction rate of enzymes at its peak?

Answer 6

40°C

Question 7

What is stable cavitation?

Answer 7

When the oscillation of the micro bubbles does not lead to collapse

Question 8

What is initial transient cavitation?

Answer 8

When the oscillation of the micro bubbles leads to an implosion of the micro bubbles

Question 9

What is the formula for intensity in bio effects?

Answer 9

Intensity = power/area

Question 10

What does ISPTP stand for?

Answer 10

Spatial peak, temporal peak

Question 11

What does ISPPA represent?

Answer 11

Spatial peak, pulse average

Question 12

What does ISPTA stand for?

Answer 12

Spatial peak, temporal average

Question 13

What is ISATP?

Answer 13

Spatial average, temporal peak

Question 14

What does ISAPA represent?

Answer 14

Spatial average, pulse average

Question 15

What is ISATA?

Answer 15

Spatial average, temporal average

Question 16

What is the relationship between peak and average in bio effects?

Answer 16

A peak is always greater than or equal to an average

Question 17

What does the first letter ‘S’ in intensity measurements refer to?

Answer 17

How the beam is distributed over physical space

Question 18

What is the definition of pulse intensity measurements?

Answer 18

Measurements made during the shorter period referred to as the pulse duration

Question 19

What is the pulse peak?

Answer 19

The highest intensity that occurs during the pulse duration

Question 20

What is the pulse average?

Answer 20

The average intensity over the pulse duration

Question 21

What are temporal intensity measurements made during?

Answer 21

The longer period of time referred to as the pulse repetition

Question 22

What are the pulse peak (pp) and temporal peak (tp) measurements?

Answer 22

They are the same measurement; therefore, the pulse peak is not used

Question 23

What is the duty factor in relation to temporal intensity measurements?

Answer 23

The ratio of the temporal average (TA) to the pulse average (PA)

Question 24

What does spatial distribution refer to?

Answer 24

How the beam energy is distributed over physical space in the body

Question 25

What primarily determines the spatial distribution of the beam?

Answer 25

The beam parameters

Question 26

What does temporal distribution refer to?

Answer 26

How the energy is distributed over time

Question 27

In intensity measurements, what does the first set of two letters refer to?

Answer 27

The spatial distribution of energy

Question 28

In intensity measurements, what does the second set of two letters refer to?

Answer 28

The temporal distribution of energy

Question 29

What does the beam uniformity factor (BUF) measure?

Answer 29

The BUF measures the uniformity of a beam. A completely uniform beam would have a BUF equal to one.

Question 30

What is the typical BUF value for most beams?

Answer 30

Normally the BUF is greater than one.

Question 31

How is the beam uniformity factor (BUF) calculated?

Answer 31

BUF equals spatial peak divided by spatial average or BUF = sp/sa.

Question 32

Which modalities have a greater risk of thermal bio effects?

Answer 32

Non-scan modalities have a greater risk of thermal bio effects than scan modalities.

Question 33

What are examples of scan modalities?

Answer 33

* 2-D * Color Doppler

Question 34

What are examples of non-scan modalities?

Answer 34

* Continuous Wave (CW) * Pulsed Wave (PW) * M mode * A mode

Question 35

What is the primary difference between scanned and non-scanned modalities?

Answer 35

Non-scanned modalities transmit repeatedly in the same direction, allowing heat to build up, increasing the risk of thermal bio effects.

Question 36

How do scan modalities help mitigate thermal bio effects?

Answer 36

Scan modalities have time between transmits, allowing heat to dissipate.

Question 37

What is the typical transmit voltage for a 2D pulse?

Answer 37

Typical 2D pulse is 150 volts.

Question 38

What is the typical transmit voltage for an M mode pulse?

Answer 38

M mode pulse is 60 volts.

Question 39

What is the typical transmit voltage for a Color Doppler pulse?

Answer 39

Color Doppler pulse is 40 volts.

Question 40

What is the typical transmit voltage for a Pulsed Wave (PW) Doppler pulse?

Answer 40

PW Doppler pulse is 30 volts.

Question 41

What is the typical transmit voltage for a Continuous Wave (CW) Doppler?

Answer 41

CW Doppler transmit is 8 volts.

Question 42

What is the relationship between transmit voltage and duty factor?

Answer 42

Higher transmit voltage equals lower duty factor. Lower transmit voltage equals higher duty factor.

Question 43

What is the risk associated with higher transmit voltage?

Answer 43

Greater risk of mechanical bio effects, but a lower risk of thermal bio effects.

Question 44

What is the risk associated with lower transmit voltage?

Answer 44

Lower risk of mechanical bio effects, but higher risk of thermal bio effects.

Question 45

What are the characteristics of Ultra fast Doppler?

Answer 45

* Non-scanned * Entire field of view scanned at once * Relatively high duty factor from multiple cycles per pulse * Transmit power set low * Limited scan duration * Beam not focused * Predominant risk is thermal bio effects.

Question 46

What are the characteristics of CW Doppler?

Answer 46

* Non-scanned * Duty factor of 100% * Focused beam * Transmit power set very low * Predominant risk is thermal bio effects.

Question 47

What are the characteristics of PW Doppler?

Answer 47

* Non-scanned * Very high duty factor * Focused beam * Transmit power set low * Predominant risk is thermal bio effects.

Question 48

What are the characteristics of M mode?

Answer 48

* Non-scanned * High duty factor * Focused beam * Transmit power lower than for 2-D * Predominant risk is thermal bio effects.

Question 49

What are the characteristics of Color Doppler?

Answer 49

* Non-scanned color packets * High duty factor * Focused beam * Transmit power lower than 2D * Packets scanned sequentially * Predominant risk is thermal and mechanical bio effects.

Question 50

What are the characteristics of 2-D imaging?

Answer 50

* Very high transmit power * Low duty factor * Scanned * Predominant risk is mechanical bio effects.

Question 51

What is the best indicator for the risk of mechanical bio effects?

Answer 51

The mechanical index.

Question 52

What is the formula for mechanical index?

Answer 52

MI = peak rarefactional pressure / square root of operating frequency.

Question 53

What do thermal indices TIS, TIB, and TIC stand for?

Answer 53

* TIS = thermal index in soft tissue * TIB = thermal index in bone * TIC = thermal index in cranial bone.

Question 54

What do TI values indicate?

Answer 54

Predicted worst case temperature rise based on the imaging parameters in use.

Question 55

What does prudent use imply?

Answer 55

* Minimizing the risk of bio effects to patients * Not performing needless scans * Not extending scan times needlessly * Using the minimum amount of power to achieve good clinical results.

Question 56

Fill in the blank: The principle of _______ emphasizes minimizing bio effects to patients.

Answer 56

[ALARA principal]