13.BIOEFFECTS Flashcards
What are Bioeffects?
Answer: The effects of ultrasound on the tissues are called bioeffects.
The bioeffects can be categorized as thermal effects, cavitation and mechanical effects.
There is no solid evidence available to support any detrimental bioeffects from the application of diagnostic ultrasound to human tissues. It is generally agreed that the value of information obtained from the procedure far overweighs the possibility of any biologic effects.
What are in vitro studies?
Answer: In vitro studies are the studies for bioeffects of ultrasound performed in non-living settings.
The meaning of in vitro is discernible in a test tube.
In vitro bioeffects may not be applicable to clinical settings.
What is the effect of increasing the output power on the patient?
Answer: Patient is exposed to higher intensity levels of ultrasound waves, when output power is increased. Exposure to higher intensity ultrasound waves increases the risk of patient exposure to bioeffects of ultrasound.
Ultrasound is generally believed to be safe; we must always try to minimize patient exposure to ultrasound energy. Sonographer should use the minimum output power necessary to create good quality images and should not expose the patient to unnecessary ultrasound energy.
Always apply the ALARA principle which is keeping the output power “as low as reasonably achievable”.
What kind of ultrasound has the greatest output intensity?
Answer: Pulsed wave ultrasound has the greatest output intensity.
What is cavitation?
Answer: Cavitation is the interaction of ultrasound waves with microscopic gas bubbles that are present in the tissue.
The interaction of ultrasound waves with gas bubbles results in the expansion and contraction of these gas bubbles and can produce severe tissue damage.
Cavitation is most likely to occur under which circumstances?
Answer: Cavitation is most likely to occur with low frequency and high signal amplitude ultrasound waves.
What is stable cavitation?
Answer: Stable cavitation occurs when ultrasound waves strike microscopic gas bubbles present in tissues and these bubbles rhythmically expand and contract. These bubbles make contact with the surrounding tissues and may cause cell injury. The micro bubbles do not burst.
What is transient cavitation?
Answer: The transient cavitation causes microscopic bubbles to contract and expand violently and burst. Transient cavitation can cause highly localized, violent effects involving increased pressures, elevated temperatures, shock waves, and mechanical stress in the surrounding tissue. These violent bioeffects are limited to the microscopic level and cause injury to only few cells.
What is the difference between stable cavitation and transient cavitation?
Answer: The difference between stable cavitation and transient cavitation is that in stable cavitation, the micro gas bubbles in soft tissue expand and contract but do not burst. In transient cavitation, the micro gas bubbles in soft tissue expand and contract violently and burst which can cause damage to the soft tissue.
What is associated with cavitation?
Answer: Mechanical index is associated with cavitation.
Mechanical Index is a number that relates to the cavitation.
What is normal cavitation?
Answer: Normal cavitation is also known as inertial cavitation and transient cavitation.
Normal cavitation is consistent with shock waves and temperatures in the thousands of degrees are created.
Only a 10% increase in pressure is needed to convert to normal cavitation from stable cavitation.
Which form of cavitation is most likely to produce micro streaming in the intracellular fluid and shear stresses?
Answer: Stable Cavitation is most likely to produce micro streaming in the intracellular fluid and shear stresses.
Micro bubbles already present in the tissue respond by expanding and contracting when pressure is applied.
What is mechanical index?
Answer: Mechanical index is a number that relates to the possibility that cavitation will occur. It is related to the power output of the ultrasound system and the frequency of the ultrasound wave emitted by the transducer.
What is thermal index?
Answer: Thermal index is a number related to the bioeffects caused by tissue heating.
The value of the thermal index indicates the number of degrees of temperature elevation that can occur based on power output of the ultrasound system.
There are three types of thermal indexes:
* TIS - Thermal index calculated in soft tissue
* TIB - Thermal index calculated when bone is located at the focus of the ultrasound beam
* TIC - Thermal index calculated when cranial bone is located in the near field
What conditions will result in the highest mechanical index while performing an ultrasound exam?
Answer: Low frequency and high signal amplitude ultrasound waves will result in the highest mechanical index.
What is the empirical approach study of bioeffects and ultrasonic safety?
Answer: The empirical approach is the study of bioeffects and ultrasonic safety surveys data. The data involves the finding of a relationship between exposure and toxic effects. The data is acquired from patients and animals to correlate exposure and effects. Empirical approach helps to identify exposure-response relationship.
Exposure-response best describes the empirical investigation of bioeffects.
What is the mechanistic approach study of bioeffects and ultrasonic safety?
Answer: True
The mechanistic approach to the study of bioeffects and safety includes the identification of a theoretical construct that could produce an effect.
It is a theoretical analysis to estimate scope of bioeffects at various exposures. It proposes a specific physical mechanism that could produce bioeffects.
Mechanistic approach helps to identify cause-effect relationship.
A bioeffect identified through the mechanistic approach rather than by the empirical approach is more likely to have clinical significance.
Answer: False
Strongest conclusions are made when mechanistic and empirical approaches are in agreement.
The AlUM considers an ultrasound-induced biologic tissue temperature rise of less than 2 degree centigrade above normal body temperature as safe for clinical studies.
Answer: True
The AIUM considers an ultrasound-induced biologic tissue temperature rise of less than 2 degree centigrade above normal body temperature as safe for clinical studies.
What kind of ultrasound beam has a characteristic that is most likely to cause temperature elevation in soft tissue?
Answer: Unfocused ultrasound beams are more likely to cause temperature elevation and thermal bioeffects in tissues. The unfocused ultrasound beam is spread on wider area of soft tissue than compared to focused ultrasound beam and causes more temperature elevation in soft tissue.
Why focused ultrasound beams with low intensities are less likely to cause bioeffects?
Answer: The reason that focused ultrasound beams with low intensities are less likely to cause bioeffects is that a focused beam is less efficient in heating a large mass of tissue to a critical temperature.
The focused ultrasound beams are narrower and smaller soft tissue area is exposed to ultrasound beam compared to unfocused ultrasound beam and therefore is less effective in increasing the soft tissue temperature.
With focused ultrasound beams, only a small area of soft tissue is heated, and the heat flows rapidly to the neighboring tissue. There is less accumulation of heat in that area and is less likely to cause critical temperature increase in that area.
According to the AlUM, what in situ tissue temperature is dangerous to a fetus?
Answer: 41° C
According to the AIUM a rise in temperature of the tissues to 41°C or above is considered dangerous to the fetus.
What is the epidemiology study?
Answer: Epidemiology is the study of the prevalence of disease in a defined population.
Epidemiology is the science related to the study of factors that determine the frequency and distribution of disease, injury, and other health related events in a defined population.
Randomized clinical studies require large data sets on each patient to account for factors which may contribute to the findings. Using this method, diagnostic ultrasound has shown no adverse effects on fetal outcome or birth weight or any other measurement.
What describes an ideal epidemiologic bioeffects study?
Answer: Randomized and prospective best describes an ideal epidemiologic bioeffects study.
Randomized clinical studies require large data sets on each patient to account for factors which may contribute to the findings. Using this method, diagnostic ultrasound has shown no adverse effects on fetal outcome or birth weight or any other measurement.
