Bioeffects Flashcards
What are bio effects?
The potential biological effects that can occur when ultrasound propagates through the body
What is the risk of ultrasound in terms of bio effects?
Lots of research has been done, virtually all ultrasound induced adverse bio effects occur at higher intensities than diagnostic ultrasound
What are the three ways in which we can describe the strength of the wave?
- Amplitude
- Power
- Intensity
Amplitude, power, and intensity are 3 ways to describe the strength of a wave. However, these can also express what other things?
Loudness or volume of sound
Amplitude is defined as what? 3
- Particle displacement
- Particle velocity
- Acoustic pressure of a sound wave
Amplitude indicates what?
The strength of the detected echo or the voltage induced in a crystal by a pressure wave
What is another way to describe amplitude? 2
- Maximum displacement
- Acoustic variable
What determines the initial amplitude of a pulse?
Pulser
As the pulse wave travels though the medium, what is the reduction in amplitude called?
Attenuation
What are the 5 mechanisms that cause attenuation?
- Absorption
- Reflection
- Scatter
- Refraction
- Wave front divergence
Does the amplitude of the echo decrease as the echo returns to the transducer?
Yes it does, attenuation happens on the way back
What is the measure of power?
Measurement of the total energy transmitted summed over the cross sectional area of the beam per unit time
The absolute unit of power is what?
Watt
What is the relative unit for power?
dB
Since power is another expression of strength, just like the amplitude, it is determined by what?
The Pulser
Power defaults to what amount, relative to what?
100%
Intensity is a measure of what?
The strength of sound wave and is equal to the power per unit area
What is the formula for intensity?
Intensity = power/ area
What is the absolute unit of intensity?
mW/Cm or W/cm
What is the relative units for intensity?
dB
If power increase what happens to the intensity?
It also increases
If the area decreases what happens to the intensity?
It increases (use the intensity formulas)
What is the relationship of intensity and amplitude?
what are four different expressions of intensity?
- Spatial peak
- Spatial average
- Temporal average
- Temporal peak
Where is the spatial average and peak found on the transducer?
The spatial average is found at the transducer face and the peak is found at the focal point
What is Spatial peak and average related to?
Beam uniformity ratio
What is the BUR ratio?
BUR = SP/SA
The beam uniformity ratio gives an idea of what?
How much focusing there is in a beam
Highly focused beams have what BUR value?
High
Weakly focused beams have what BUR value?
Low
Why is BUR always greater than 1?
Peaks are always higher than averages (in terms of spatial)
A perfectly uniform beam will have what BUR value?
one
The factor that effects the spatial intensities in an ultrasound system are what? 2
- Spatial peak will increase with an increase in power or focusing
- Spatial average will increase with an increase in power
Over the time a pulse is generated there is a temporal average which includes what?
Both the ringing and listening phase of the pulse and the temporal peak which is the highest amplitude in the pulse at any given time
Temporal peak and temporal average are related how?
Duty factor
What is the ratio for Duty factor?
DF = TA/TP
The factors that effect temporal intensities are what?
An increase in power or an increase in they duty factor
Duty factor is increased if what happens?
The PRF or the pulse duration is increased
The duty factor for CW is what? What does this mean?
- 100% because the crystal is constantly ringing
- CW typically has a higher SPTA value than pulsed wave applications
What is SPTP also known as?
Instantaneous peak
SPPA intensity is also known as what?
The maximum intensity, or time averaged half maximum
The information that we have on the effects of ultrasound come from multiple sources, what are three?
- Epidemiology
- In vitro cell studies
- Animal studies
What is an extensive resource for bio effects information?
American institute of ultrasound in medicine
(AIUM)
What is an epidemiological study?
Study conducted over a long term
Intensities below what value is considered safe for an unfocused probe?
100 mW/cm
Intensities below what value is considered safe for focused probes?
1000 mW/cm
Bio effects can be divided into two main categories, what are they?
- Thermal
- Non- thermal
When dealing with thermal effects, it is important to remember that attenuation is primarily due to what?
Absorption which is the conversion of sound to heat
Temperature can increase with an increase in what?
Frequency or intensity
Can temperature increase from B-mode to Colour doppler to spectral doppler?
Yes
Does adult tissues handle temperature the same as neonatal?
No, adults handle it better
How many bioeffects are attributed to hyperthermia?
Over 80 known
In terms of hyperthermia and bioeffects, there are no adverse effects when the temperature does not exceed what?
39 degrees
The temperature rise near bone is what compared to soft tissue?
Significantly higher
Temperature rise is most detrimental during what phase?
Organogenesis (first trimester)
In terms of bioeffects, there are not adverse effects when temperature index is where?
Between 1.5 - 6, depending on exposure time
The longer the exposure time the more chance of what?
Adverse effects at higher temperature
A significant rise in temperature is in excess of what?
1.5 degrees Celsius
Mechanical effects include what?
Radiation force and cavitation
Radiation force is what?
The force excreted by sound on the medium which can deform and disrupt structures
Radiation force can cause what?
Flow in absorbing fluids resulting in shear forces
Cavitation is what?
The production and behaviour of bubbles in a liquid medium
Cavitation can be divided into what categories?
Stable and transient
Stable cavitation is what?
Simple oscillation of the bubbles that can result in the streaming of liquid resulting in shear stresses
Transient cavitation is what?
When the bubble actually collapses producing shock waves
In transient cavitation, the shock waves can result in what?
Localized extremely high temperatures and has even emitted light in clear fluids
When was the standard for bioeffects created?
1992
ODS is what? What is displayed? 2
- Output display standard
- Thermal index and mechanical index
What is Thermal index?
The ratio of acoustical power produced by the transducer to the power required to raise the temperature in tissue 1 degrees Celsius
A TI value of 1, under assumed tissue conditions, could possible do what?
Raise temperature of tissue by 1 degrees Celsius
TI is further divided into 3 categories, what are they?
- TIS
- TIB
- TIC
What is TIS?
It for soft tissue and is the most common
What is TIB?
For bone near the focus ad is used for obstetrical scanning
What is TIC?
For bone near the surface as in the case of a transcranial study
Mechanical index represents what?
The likelihood that energy used will lead to cavitation
The MI is proportional to what?
The peak rarefactional pressure, so if the pressure doubles then the MI doubles as well
The MI is inversely proportional to what?
The square root of the frequency, so the frequency would have to quadruple for the MI to halve
TI max is what? And what is MI max?
6 and 1.9
What increases the possibility for MI an TI to be underestimated?
Prescience of large fluid collection, but these situation usually allows for less power
As the TI increases it is prudent to consider what?
The exposure times
What is the SPTA limits for Cardiac, peripheral vascular, ophthalmic, fetal and other?
What is the SPTA value for Pulsed doppler?
1140
The different applications of ultrasound can be divided into what different categories?
Scanned and non scanned types
The non scanned applications are what? 3
- CW
- Pulsed doppler
- M- mode
What poses the highest risk for bio effects, why?
- Non scanned applications
- Thermal effects with CW having the most potential due to the fact they transmit repeatedly in a straight line
Recent studies have concluded that adverse non-thermal effects may occur when?
When gas bodies are present in circulation
Do contrast agents in the blood stream pose any kind of concern? Why?
Yes, recent studies confirmed that at intensity below the accepted threshold, adverse non-thermal effects may occur when gas bodies are present
When MI values are below 0.4 what happens?
There is little risk
In terms of bioeffects adverses effects have included what 4 things?
- The induction of premature ventricular contraction
- Micro vascular leakage with petechiae
- Glomerular capillary hemorrhage
- Local cell killing
Medical significance is uncertain so what does this mean?
Prudent use is required
When imaging with contrast agents, practitioners should do what? 3
- Use the minimal agent dose
- MI
- Examination time consistent with efficacious acquisition of diagnostic information
Although the benefits of ultrasound outweigh the risk, one must consider the risk of using what?
Suboptimal equipment or having the exam performed by a poorly trained operator
The balance between benefit and risk comes with the prudent use of ultrasound apply to what concept?
ALARA
What does ALARA stand form?
As low as reasonably achievable
Following ALARA principles we keep ultrasound exposure what?
Minimized while optimizing diagnostic information
Who established the guidelines for the safe use of diagnostic medicine?
Heath Canada
Guidelines state that the use of ultrasound should not be used for what 3 things?
- To have a picture of a fetus, solely for non-medical reasons
- To learn the sex of the fetus, solely for non-medical reasons
- For commercial purposes, such as trade shows or producing pictures or videos of the fetus
What is the ACMDTT?
Where sonographers fall after regulation
