Chapter 24 Flashcards
is similar to a small hypodermic needle with a tiny piece of PZT material attached to its end; small transducer that measures the characteristics of a sound beam
Hydrophone (or microprobe)
The hydrophone also measures the:
-period
-PRP
-PRF
-pulse duration
measures the total power in a sound beam through the process of absorption
Calorimeter
tiny electric thermometer; inserted into the sound beam and temperature is measured
Thermocouple
change color based on their temperature; energy is absorbed when a sound beam strikes
ex: mood rings
Liquid crystals
T/F: Low intensity ultrasound has no known bioeffects.
True
T/F: Extremely high ultrasound intensities damage biologic tissues.
True
science of identifying and measuring the characteristics of an ultrasound beam that are relevant to its potential for producing biological effects
Dosimetry
research preformed within the living body of an animal or plant; “in the living”
In vivo
research performed outside of the living body and in an artificial environment; “in glass”
-provide the opportunity to perform research that would be impossible with live, human subjects
-indicated that very high intensities can cause genetic damage and cell death
In vitro
2 study techniques used to study bioeffects
- mechanistic approach
- empirical approach
-begins as a proposal
-theoretical analysis is performed based on proposal
-cause & effect relationship
Mechanistic approach
-based on acquisition and review of info from patients/animals exposed to ultrasound
-relationship b/w exposure and response
Empirical approach
What are the (+) and (-) of mechanistic approach?
(+): broad exposure
(-): uncertainty about assumptions; are other mechanisms involved?; is the bioeffect clinically significant?
What are the (+) and (-) of empirical approach?
(+): no need to understand mechanism; obvious biological significance
(-): no need to understand mechanism; species differences may alter results
Which of the study techniques, mechanistic or empirical, is the best w/ regard to ultrasound bioeffects?
The strongest conclusions are made when the mechanistic and empirical conclusions are in agreement.
2 important mechanism of bioeffects
- thermal
- cavitation (nonthermal)
proposes that bioeffects result from tissue temperature elevation
-as sound propagates in body, energy is converted into heat
-core temp of 37C; life processes do not function normally at other temps
-tissue temps are elevated through exercising, sunbathing, fever, etc.
Thermal mechanism
- TIS (soft tissue thermal index): assumes that sound is traveling in soft tissue
- TIB (bone thermal index): assumes that bone is at or near focus of sound beam
- TIC (cranial bone thermal index): assumes that cranial bone is in the sound beam’s near field
3 forms of thermal index (TI)
useful predictor of max temp increase under most clinically relevant conditions; 3 forms: TIS, TIB, and TIC
Thermal index (TI)
T/F: Tissue heating is related to the output characteristics of transducer and the properties of the tissues.
True
A combination of _________ and __________ determine the likelihood of harmful bioeffects. With higher temps, harmful effects can occur with shorter exposure times.
temperature; exposure time
T/F: Adult tissues appear less tolerant of tissue heating than fetal and neonatal tissues.
False
Fetal and neonatal tissues appear less tolerant of tissue heating than adult tissues.
Numerous fetal defects have resulted from temp elevation.
T/F: The temperature rise in soft tissues near bone is significantly higher than in other locations.
True
Bone absorbs more acoustic energy than soft tissue. Ultrasound that strikes fetal bone deserve special attention.
interaction of sound waves with microscopic, stabilized, gas bubbles* in tissue; also describes the creation of gaseous nuclei from dissolved gasses in a fluid
*gaseous nuclei
2 forms:
1. stable
2. transient
Cavitation
-gaseous nuclei tend to expand and contract (at lower MI levels)
-do not burst
-intercept and absorb acoustic energy
-fluids surrounding the cells undergo microstreaming and the cells are exposed to shear stresses
Stable cavitation
-higher MI levels
-bursting bubble
-also called normal or inertial
-shock waves and very high temp
Transient cavitation
calculated number that indicates the harmful bioeffects from cavitation
lower:
-less cavitation
-less pressure
-higher frequency
higher:
-more cavitation
-more pressure
-lower frequency
Mechanical index (MI)
T/F: A health care professional may proceed when the benefits surpass the risks.
True
What are three devices that measure the output of ultrasound transducers by absorption?
- Calorimeter
- Thermocouple
- Liquid Crystal
How is the best epidemiological study taken?
By prospective and randomized.
What is the most important patient precaution?
To minimize the patient ultrasound exposure. Use ALARA (as low as reasonably achievable) the minimum output power and maximum amplification to optimize image quality.
What are two mechanisms that are likely to induce bioeffects?
Two. Most important mechanism associated with ultrasound induced, bioeffects are thermal and non-thermal (mechanical).
Which type of Doppler imaging is associated with the highest tissue temperature elevation?
Pulsed Doppler
