Bioeffects

Question 1

Acoustic Variable

Answer 1

Pressure, Temperature, particle displacement, density

Question 2

Attenuation

Answer 2

sound is absorbed by tissue (heat), non-linear frequency dependent absorption

Question 3

Pulsed Wave Operation

Answer 3

Scanned vs non-scanned modality (M-mode vs B-mode)

Duty factor, frame rates

Question 4

Transudcers

Answer 4

Focal point of beam, highest intensity,

Question 5

System Operation

Answer 5

Output power, SNR

Question 6

Doppler

Answer 6

Spectral Doppler and Continuous Doppler

Question 7

Contributions to Bioeffects

Answer 7

Heating and Cavitation Mechanisms

Epidemiologic studies in human beings

Observation based research in cells, cultures, plants, and experimental animal studies.

Question 8

Studies for bioeffects

Answer 8

Begin at the cellular level which provides information on interaction of mechanisms to guide

Question 9

In animal studies…..

Answer 9

Information on thermal and non-thermal bio effects is provided

Question 10

In epidemiology studies…..

Answer 10

Long term effects on patients with a history of previous ultrasound examinations are studied

Question 11

Bioeffect

Answer 11

Refers to an undesired biological change to tissues as a result of interaction with the insonating beam

Question 12

Sound beam is a

Answer 12

Transportation of energy

Energy is work with the possibility of work performed within the body can indicate a potential of adverse biological situations

Question 13

Mechanisms of bioeffects

Answer 13

Thermal

Mechanical

Question 14

What are the two principle mechanisms for bioeffects

Answer 14

Thermal effects

Mechanical bioeffects

Question 15

Thermal bioeffects

Answer 15

Temperature rise related to: 
temporal average intensity
 duty factor
 scan time
 scanned vs. non-scanned modalities

Question 16

mechanical bioeffects

Answer 16

Cavitation related to :

peak rarefactional pressure

Question 17

What occurs with thermal bioeffects

Answer 17

Temperature in a region rises too high metabolic breakdown occurs and cellular damage can occur

Question 18

What occurs with Mechanical bioeffects

Answer 18

Risk involves mechanical damage from interaction between the wave and the tissues within the body

This should not be surprising since sound is a mechanical wave

Question 19

What are possible forms of mechanical bioeffects

Answer 19

Inertial / Transient Cavitation

Stable Cavitation

Radiation Force

Question 20

Cavitation

Answer 20

Hollow space

Question 21

Cavitation is when….

Answer 21

Bubbles are produced, vibrate or oscillate; bubbles burst or implode and a potential for biological effects is present

Question 22

Stable Cavitation

Answer 22

• When oscillation of the microbubbles does not lead to collapse
• Bubbles oscillate with the varying acoustic pressure field in a stable manner
• Fluids surrounding the bubbles may begin to flow or stream
• Flow is the result of eddy currents which develop as energy is imparted to the fluid through the oscillating bubbles
• Referred to as micro-streaming
• Momentum of flow is potentially capable of inducing cellular wall stresses that can cause cellular harm

Question 23

Inertial/Transient Cavitation

Answer 23

Unlike stable cavitation, this results in implosion of the microbubbles
The microbubbles may completely fragment or the ‘destruction’ may lead to a collection of smaller microbubbles
The likelihood of implosion is related to the peak rarefactional pressure
During this rarefaction phase, the pressure within the bubble relative to the lower decreasing pressure external to the bubble causes the bubble to expand
Clearly during the compression, the increasing external pressure causes the bubble to contract
With increasing ‘negative’ pressure of rarefaction, the bubble expands more and more

Question 24

Inertial Transient Cavitation (Con’t)

Answer 24

Eventually the bubble expands so much that when compression begins, there is so much inertia from the surrounding fluid, that the bubble collapses inwardly (implodes)
This collapse can be extremely violent generating high amplitude shock waves and producing extremely high temperatures (as high as 10,000 Kelvin)
These shock waves and localized high temporature increases can cause damage to surrounding regions

Question 25

Inertial Transient Cavitation Con't 2

Answer 25

This can lead to cellular death Fortunately the affected region is small, potentially only a few cells The term transient is also used synonymously with the term inertial cavitation The term transient is indicative of the fact that there is a change in “state” of the bubble The word inertial is indicative of the fact that the dramatic change in state is the result of inertia

Question 26

Radiation force

Answer 26

Is the force exerted by a sound beam on an absorber or a reflector This force cab deform or disrupt structures Can cause flow in an absorbing fluid This flow can cause shear stresses that can deform or disrupt structures Noncavitational mechanical interaction

Question 27

Radiation force or direct force

Answer 27

is the interaction force of an ultrasound beam on an absorber or a reflector. Basically when the ultrasound wave propagates through the medium it interacts between particles in the tissues Target particles are pushed away from the transducer which causes acoustic streaming This produces shear stresses that can disrupt or deform structures

Question 28

Threshold Effect

Answer 28

limit or boundary It implies that there is a limit above which a specific outcome is achieved, and below which a different outcome is occurs

Question 29

Threshold effect-bioeffects

Answer 29

threshold bioeffects will force different behaviour and protocols than non-threshold effects

Question 30

cavitation is stable up to...

Answer 30

A certain threshold, above which inertial cavitation occur

Question 31

Long periods of time at lower refratctional pressures

Answer 31

will not produce inertial cavitation

Question 32

There is no specific point...

Answer 32

at which a slight increase in power or scan duration will cause a dramatic increase in tissue temperature Instead, the temperature change tends to be gradual over periods of time This behavior is in stark contrast to the threshold behavior of cavitation

Question 33

Mechanical bioeffects ehixibit

Answer 33

Threshold behaviour

Question 34

What are mechanical bioeffects are related to ?

Answer 34

short-term event during the transmit burst and are not related to longer periods of time

Question 35

Intensity

Answer 35

Power/Area

Question 36

What is used to measure the risk of bioeffects

Answer 36

Common intensities

Question 37

Common intensities: Concept 1

Answer 37

A peak is always greater than or equal to an average

Question 38

Therefore an.....

Answer 38

SP is greater than an SA and | a TP is greater than a TA.

Question 39

Common intensities: Concept 2

Answer 39

The first letter (S) refers to how the beam is distributed over physical space

Question 40

Common Intensities: Concept 3

Answer 40

Pulse measurements

Question 41

Common intensities: Concept 4

Answer 41

Temporal (PRP) measuremnts

Question 42

Spatial Distribution

Answer 42

Refers to how the beam energy is distributed over physical space in the body. The beam parameters principally determine the spatial distribution of the beam.

Question 43

Temporal Distribution

Answer 43

Refers to how the energy is distributed over time.