Hydrophone
aka microprobe
is a small transducer that measures the characteristics of a sound beam.
Radiation Force
sound beam creates a small but measurable force on any target it strikes
Acoustic-optics
are based on the interaction of sound and light.
shock eaves from a fighter jet are examples of acoustic-optics
Absorption
converting sound energy into heat
What three devices measure absorption?
caloriemeter
thermocouple
liquid crystals
caloriemeter
measures the total power in a sound beam through the process of absorption
like a thermos sound beam is directed into the caloriemeter and converted into heat.
the temperture rise and time of heating is measured.
thermocouple
tiny electric thermometer
absorbing material is placed on the thermocouple and then placed in the sound beam.
temperture is measured
the temperture rise is related to the power of the sound beam at the particular location the device is positioned.
liquid crystals
certain liquid crystals change color based on temperature when a sound beam strikes it
this provides insight into the shape and strength of the sound beam
What is the first mandate reguarding clinical ultrasound?
the benefits must out weigh the risks of the exam.
Are there any known biologic effects of ultrasound?
Yes
Extremely high ultrasound intensities damage biologic tissues.
**There are no known cases of diagnostic imaging at standard intensities resulting in biological effects and tissue injury.
Dosimetry
the science of identifying and measuring the characteristics of an ultrasound beam that are relevant to its potential for producing biological effects.
In vivo
in the living
performed within a living body of a plant or animal.
In vitro
in glass
performed outside the living body, in an artificial enviroment.
AIUM Statement on In vitro bioeffects
in vitro bioeffects research is important
in vitro bioeffects are real even through they may not apply to clinical settings
in vitro bioeffects which claim direct clinical signifigance should be viewed with caution
Mechanistic Approach
technique used to study bioeffects
seaches for the relationship between cause and effect
Empirical Aproach
technique used to study bioeffects
seaches for the relationship between exposure and response.
Which of the study techniques, mechanistic or empirical, is best with reguard to ultrasound bioeffects?
Both, Strongest conclusions are made when there is agreement between the mechanistic and empirical conclusions.
Thermal Mechanism.
proposes that bioeffects result from tissue temperature elevation.
The rationale for studying thermal effects are
* As sound propagates through the body energy is converted into heat.
* Body core is regulated at 37 degrees C. Life processes do not function at other temperatures.
Thermal Index
TI
a useful predictor of maximum temperature increases under most clinically relevant conditions.
TIS
Soft Tissue Thermal Index
Assumes sound is traveling in soft tissue
TIB
Bone Thermal Index
Assumes sound is traveling in bone
TIC
Cranial Bone Thermal Index
Assumes sound is traveling in Cranial bone.
Thermal Mechanisms - Empirical Findings
* Serious tissue damage occurs from prolonged elevation of body temperature
* Tissue heating is related to the ouput characteristics of the transducer and the properties of the tissue
* A 2 to 4 degree rise in testicular temperature can cause infertility
* A combination of temperature and exposure time determine the likelihood of harmful bioeffects. With higher temperatures, shorter exposure times will produce harmful effects.
* No confirmed bioeffects have been reported for temperature elevations of up to 2 degrees C above normal exposures of less than 50 hours
* Maximal heating is related to the beam's SPTA intenisty
* Fetal tissue appear less tolerant of tissue heating than adult tissues. Numerous fetal defects resulting from temperatures elevation have been documented. None have been observed at temperatures less than 39 degrees C
* A greater amount of acoustic energy is absorbed by bone than by soft tissue. Circumstances wherein ultrasound strikes fetal bone deserves special attention.
Thermal Mechanisms - Mechanistic Findings
Theoretical models appear to correlate with experimental data even though:
* the ultrasound beam is quite complex
* diagnostic equipment is diverse
* tissue characteristics are different
Cavitation Mechanism
the interaction of sound waves with microscopic, stabilized, gas bubbles in the tissue.
What are the gas bubbles in cavitation called
Gaseous nuclei
Stable Cavitation
At low MI levels, stable cavitation occur.
gaseous nuclei tend to oscillate. Bibbles that are a few millimeters might double in size. The bubbles DO NOT burst.
The bubbles intercept and absorb muchof the acoustic energy.
The fluid around the bubbles undergo microstreaming and the cells are exposed to shear stress.
Transient Cavitation
AKA inertial or normal cavitation
At high MI levels, transient cavitation occur.
The bubbles burst.
Highly localized, violent effects
*colossal temperatures
*shock waves
The destructive effects of transient cavitation are not considered clinically important since they are highly localized and affect few cells.
The pressure threshold for transient cavitaion is only 10% higher than that required for stable cavitation
Mechanical Index
MI is related to the likelihood of harmful bioeffects from cavitation and it the best indicator of these effects
What two things are related to MI
peak negative pressure
frequency
What two things is there a greater likelihood of cavitation with:
additional negative pressure
lower frequency
Epidemiology
branch of medicine associated with population studies
empirical - exposure vs response
Why do many epidemiology studies deal with in utero fetal exposure to ultrasound?
* a large percetage of pregnant women in the U.S. are scanned
* ultrasound is routinely used during normal pregnancies, thereby skewing the risk-benefit relationship
*harmful effects, if present have the potential to affect the fetus for life.
Three linitations of epidemiologic studies
* often retrospective
* Ambiguities may exist in data - justification of exam, gestational age, etc
* Risk factors other than exposure to ultrasound may precipotate.
What are the characteristics of the best epidiologic studies?
prospective - forward looking
randomized - on group is exposed, one is not
Clinical Safety and Prudent Use
* No confirmed harmful bioeffects from exposure to diagnostic ultrasound has been reported
* It is possible that bioeffects may be identified in the future
* the benefit to patient outwieghs the risk
* It is appropriate to use diagnostic ultrasound prudently to provide benefit to the patient
* It is inappropriate to use diagnostic ultrasound in a non-medical setting fro entertainement
Training and Research
* No confirmed harmful bioeffects on patients or sonographers have been found with the use of diagnostic ultrasound.
* Experience with diagnostic ultrasound may differ from research ans training, due to to longer research exams and greater exposure
* When used without medical benefit, the subject should be informed how the research differs from standard diagnostic procedures.
Electrical Safety
system should be be inspected to assure proper physical status.
Overall Safely considerations
* Do not perform studies without valid medical justification
* Do not prolong studies without valid medical justification
* Minimize patient exposure
-use minimum output power and maximum amplification
-ALARA - As low as reasonably achievable
A bioeffect report claims that obstetrical scanning may be harmful to a particular group of patients. WHat should be the response of the medical community?
A) Perform the exams on all patients when the benefits are outwieghed by the risk.
B) Stop all diagnostic exams
C) ignore the report
D) Halt all exams on this patient group
E) perform exams on all patients when the benefit outweigh the risk.
E) perform exams on all patients when the benefit outweigh the risk.
The study of the characteristics, attributes, and quantities of a substance that induces bioeffect is called ___________
Dosimetry
True or False?
There are no bioeffects associated with ultrasound
False
True or False?
There are no bioeffects associated with ultrasound with characteristics typical of those in diagnostic medicine
False
True or False?
There are no harmful bioeffects associated with ultrasound with characteristics typical of those in diagnostic medicine
True
True or False?
Cavitation describes the interaction between sound waves and small gas bubbles that inhabit the tissue
True
True or False?
There are two forms of cavitation: inertial and normal
False
Normal, transient and inertial are the same
True or False?
Normal, transient or inertial cavitation describes the birsting of microbubbles
True
Which of the following is not assciated witht he mechanistic approach?
A) Identifying a cause and effect relationship
B) proposing a specific means that could produce a bioeffect
C) studying charts of patients who have been exposed to ultrasound
D) analyzing the mechanism using theoretical methods
E) Reaching a valis scientific conclusion
C) studying charts of patients who have been exposed to ultrasound
Veterans of "Operation Iraqi Freedom"
suspect that they have been exposed to chemical warefare agents. The veterans Administration Hospital surveyed these soldiers to identify the presence of prevalence. What form of medical investigations is this?
Empirical approach
Bioeffects are being investigated in an "exposure-response" context
Name the two important mechanisms likely to induce bioeffects associated with ultrasound
thermal and cavitation
Which staement allows us to concluse the diagnostic ultrasound does not injure tissues via temperature elevation?
A) Death resulting from ultrasound exam has bnever been reported
B) Mechanistic data indicates that diagnostic ultrasound is safe
C) conclusions from empirical data and mechanicalistic data are consistant, that is, diagnostic ultrasound is inlikely to cause thermally induced bioeffects
D) Patients so not complain of burning during ultrasound exams
C) conclusions from empirical data and mechanicalistic data are consistant, that is, diagnostic ultrasound is inlikely to cause thermally induced bioeffects
True or False?
Stable cavitation describes the rhythmical selling and shrinking of gaseous nuclei
True
Stable cavitation - the microbubbles do not burst
The primary investigative technique of epidemiology is:
A) computer modeling
B) library research
C) reviewing data from patients
D) performing animal expiriments
C) reviewing data from patients
Which of the following is not a limitation of epidemiological studies?
A) Medical charts are sometimes incomplete or inacurate
B) other factors, unrelated to the study's ultimate goal, must be accounted for
C) When the bioeffects rate is small, numerous patients must be studied
D) Even when bioeffect is identified, the investigator is still unsire of the specific reason for its occurance
E) it does not provide greater understanding of the biologic signifigance of bioeffects
E) it does not provide greater understanding of the biologic signifigance of bioeffects
True or False?
The intensity limit established for diagnostic ultrasound is higher for focused sound beams than for broad, unfocused beams
True
True or False?
In vetro studies are performed exclusively on living animals
False
True or False?
Bioeffects identified through in vitro research are not considered real
False
Which measure of intensity is related most closely to tissue heating?
A) Im
B) SATA
C) SPPA
D) SPTA
E) SPTP
D) SPTA
The next step following the identification of an in vitro bioeffect is:
A) Propose in vivo research to evaluate the clinical significance of the bioeffect
B) Cease performing clinical studies that may induce bioeffects in vivo
C) ignore the results: it's only in vitro research
D) continue with in vitro research
E) obtain an informed consent reguarding this report from all patients
A) Propose in vivo research to evaluate the clinical significance of the bioeffect
True or False?
Exposing an individual to ultrasound from a diagnostic imaging system is never appropriate when there is absilutely no clinical benefit to that individual
False
research and training would be appropriate
Which component of an ulrasound system is most likely to expose a patient to danger?
A) CRT
B) transducer
C) scan converter
D) pulser
B) transducer
Which is generally true of diagnostic ultrasound?
A) Harmful bioeffects do not occur, and it is unnecessary to discuss them
B) Harmful bioeffects do not occur, but it is irresponsible to ignore the possibility that they may
C) Harmful bioeffects are often seen, but the benefit to patients still outweighs the risk
D) Only new technologies such as 3-D ot intravascular ultrasound need to be evaluated fro bioeffects
B) Harmful bioeffects do not occur, but it is irresponsible to ignore the possibility that they may