True or False
Cavitation describes the interaction between sound waves and small gas bubbles that exist in tissues.
What is: TRUE
Cavitation is the main cause of mechanical bio effects. Ultrasound waves can heat the tissues slightly. In some cases, it can also produce small pockets of gas in body fluids or tissues (cavitation). The long-term consequences of these effects are still unknown.
What is the most relevant intensity with respect to tissue heating?
a. SATP
b. SPTA
c. SPTP
d. SATA
What is B: SPTA
SPTA (Spatial Peak Temporal Average) is important when measuring bioeffects because it is the only intensity that tell us the highest intensity that a tissue is exposed to over time. This measures both the Peak intensity in the beam and the average intensity across the pulse duration.
This is why SPTA will be the most important measure in determining potential bio-effects like heating and tissue damage.
What is the ALARA principle?
What is: As low as reasonably achievable
Adjust output power to the lowest possible without affecting the exam. The less output power the the less potential harm from bio-effects
Output power will affect the brightness and change the strength of the sound pulse.
What is the cause of thermal bio-effects?
What is: Absorption
Absorption is the conversion of ultrasound to heat energy. Thermal effects happen as the result of absorption of ultrasound waves within tissue, resulting in heating in the tissue.
There are two forms of cavitation:
Inertial and Normal
What is: FALSE
Inertial, transient, and normal cavitation are considered the same. They describe the bursting of micro bubbles.
Which of the following ultrasound beams has a characteristic that is most likely to cause temperature elevation in soft tissue?
a. Strongly focused
b. Medium focused
c. Unfocused
What is C: unfocused
An unfocused beam is most likely to cause temperature elevation in soft tissues. The overall volume of tissue exposed to a potentially damaging level of energy is greater compared to a focused beam which concentrates the energy in a smaller focal point. Although the peak intensity at the focal point might be lower in an unfocused beam compared to a focused one, the overall energy in the tissue can still be significant due to the larger area affected.
If the image is too dark, first increase the ____________ ______, which does not increase patient exposure to bio-effects.
What is: Receiver gain
Receiver gain is also called amplification, it changes the strength of the voltage in the receiver created during reception. Receiver gain will make your image brighter without increasing patients exposure, unlike output power.
Which component of an ultrasound system exposes a patient to greatest risk of bio-effects?
What is: The transducer
The transducer is the main point of contact with the patients skin and is where the ultrasound waves are emitted and absorbed, meaning any potential heating or bio-effects would occur at this surface and can cause superficial burns on the skin. This is the case with Continuous wave transducers, you have to constantly be moving the transducer head so that it is not touching one spot for more than a second.
Continuous Wave transducers have a greater risk of thermal Bioeffects than Pulsed Wave transducers?
What is: TRUE
Continuous Wave transducers transmit repeatedly in the same direction, allowing for heat to build up and increasing the risk of thermal bio-effects. CW transducers offer the greatest potential risk of thermal effects with 100% Duty Factor
Of the following choices, which is considered the most important for the sonographer with regard to bio-effects?
a. Pulse repetition frequency
b. Frequency
c. Duration of the study
d. Imaging mode
What is C: Duration of the study
The longer the exposure to ultrasound waves, the greater the potential for heating of the tissue, which can lead to potential biological effects, even at low intensities.
This is why minimizing exposure time is crucial to maintain safety
If the image is too bright, first decrease the __________ ________.
What is: Output power
Which is then decreasing the exposure of thermal bio-effects to your patient and making your image a little darker.
The US Food and Drug Administration (FDA) is the main regulator for diagnostic ultrasound in the United States. It provides guidelines for the output power that are set into the machines.
Thermal bio-effects are directly proportional to:
(there are 2)
What is: Intensity and Frequency
Intensity is the power of an ultrasound wave per unit area, while Frequency refers to the number of wave cycles passing a point per second, and both influence the potential bio-effects of ultrasound.
Higher intensities and frequencies lead to greater potential for tissue damage.
One reason focused ultrasound beams with low intensities are less likely to cause bio-effects is that a focus beam is less efficient in heating a large mass of tissue to a critical temperature.
What is: TRUE
With focus beams, only a small mass of tissue is heated, and the heat blows rapidly to cooler neighboring tissues. There is limited accumulation of heat energy and the temperatures tend to stay below critical levels.
When studying bio effects, which research approach is more important?
a. Empirical
b. Mechanistic
c. Neither is important
d. Both a and b
What is D: Empirical and Mechanistic
Both the empirical (in living tissue) and mechanistic approaches are important. The strongest bio-effects conclusions are reached when both results come to an agreement.
Empirical is relying on experimental data and observation
Mechanistic is how ultrasound waves interact with biological tissue on a cellular and molecular level and how our bodies react to ultrasound waves.
By understanding how ultrasound interacts with tissue, sonographers can minimize the risk of bio-effects by adjusting ultrasound parameters like intensity and pulse duration.
Patient exposure to sound energy is affected by changes in output power, but not by changes in ______________.
What is: Amplification or Reciever gain
When adjusting the gain on an ultrasound machine, you are essentially increasing the strength of the returning echo signals, allowing for a better image quality without necessarily increasing the transmitted sound wave power.
What is TI?
What is: Thermal index
The thermal index is a measurement that tells you approximately how much a tissue temperature will increase during an ultrasound. The TI is the ratio of the power produced by the transducer to the power needed to raise tissue temperature by 1°C
TI is a unitless numberAbsorption rates are the same, no matter the type of tissue?
What is: FALSE
Absorption rates vary, depending on the medium. Absorption is the main way that attenuation occurs. It is the process in which electrical energy is converted into heat energy as it passes through tissues.
Which of the following is related to cavitation bio effects?
a. TIS
b. MI
c. Cavitation index
d. Pulsatility index
What is B: Mechanical index or MI
Mechanical index is the measurement of the power of the ultrasound beam and is related to cavitation. It indicates the likelihood of cavitation. Higher values of mechanical index are associated with more exposure and an increased chance of cavitation.
Under which condition is it permissible to perform a diagnostic ultrasound exam?
What is: When the benefits outweigh the risks.
While ultrasound is considered a safe imaging modality, there is a very small potential for harm and should only be used when medically necessary.
Since ultrasound uses sound waves instead of radiation, it is considers safer than
X-rays, PET scans, MRI’s, or CT scans.
What is the maximum beam intensity allowed in an unfocused beam?
What is: 100 mW/centimeters squared
According to most safety guidelines any more intense of a beam could cause damage to soft tissue.