Ch 7 Performance & Safety Flashcards
No confirmed adverse effect in mammals exposed in vivo:
Below 1 W/cm2 SPTA
W/ low megahertz range
And
Focused beam
Typical output intensity (SPTA) for US
1 mW/cm2
Hydrophone membrane made of
Polyvinylidene fluoride (PVDF)
Temp rises significant if
Exceed 2 degrees C
Tissue phantoms simulate tissue properties and assess:
Detail/contrast resolution, penetration, dynamic range, and TGC
Tissues w/ well-defined gas (like lungs) have been observed for in situ peak rare factional pressures
Below 0.4 MPa or MI less than 0.4
Highest acoustic pressure output
Spectral Doppler
Lowest outputs
Gray-scale
Attenuation due to
Absorption (conversion of US to heat)
Test objects contain _____ and ______ to evaluate _______ and ________. They do not _______.
Nylon lines; scattering layers
Detail resolution; beam profiles
Simulate tissue characteristics
Regular quality control testing required by ___ at a minimum _____.
ACR
Semiannually
Bio effects have not occurred below ___. Above that bio effects depend on ___and ___.
39*C
Temp, time
Temp increases in tissues close to transducer surface significantly caused by
Transducer self-heating
Bio effects of hyperthermia:
Fetal absorption/abortion, IUGR, microphthalmia, cataract production, abdominal wall defects, renal agenesis, palatal defects, reduced brain waves, microencephaly, anencephaly, spinal cord defects, renal amyoplasia, forefoot hypoplasia, tibial/fibular deformities, abnormal tooth genesis
Phantoms and test objects can be used by
Service personnel and instrument operators.
Manufacturers must submit ___ to the ___ before _________.
Pre market notifications
FDA
marketing a device for a specific application in the U.S.
No significant adverse bio effects have been observed for exposure duration up to ____ from temp increases ____ above normal.
50 hours
Less than or equal to 2*C
Doppler test objects useful for testing:
Effective penetration of Doppler beam
Ability to distinguish different flow directions
Accuracy of sample volume (gate) location
Accuracy of measured flow speed
Sonography requires application of _____ principle which requires _______________.
ALARA
medical indication and using minimum output and exposure time necessary
Output of some current US machines can generate levels that _____.
Produce hemorrhage in lungs and intestines of lab animals.
2007 statement by AIUM:
Required medical indication for diagnostic examinations.
Greatest risk from cracked transducer housing:
Electric shock
____ regulates outputs
____ evaluates research
FDA
AIUM
Freq = 1/?
Period
PRF=
1/PRP
DF=
PD/PRP
Wavelength=
Prop speed/Freq
SPL=
cycles X wavelength
MI=
Peak rarefaction pressure (MPA) /
sq root of Freq
Types of bioeffect studies
- Experimental observation in cells
- Epidemiologic studies on humans
- Studies of interaction mechanisms (heating & cavitation)
Hydrophone aka Microprobe measures…
Pressure in a sound wave
Calculates Period, PRP, and PD, PRF, DF, freq, pressure amp, wavelength, SPL, intensity
Cavitation
Production/behavior of bubbles in liquid.
Cavitation types
Stable- oscillates and may cause streaming/stresses
Transient- oscillates and collapses; shockwave may cause local extreme high temp and light emission
TI Thermal Indices
Real-time display of thermal injury likelihood.
Either overestimate or very close
TIS- soft tissue
TIB- bone
TIC- cranial
MI Mechanical Index
Likelihood of cavitation effects
No effects confirmed
Output Intensities
Highest- Spectral
Lowest- Grey scale
Color and M mode in between
SPTA intensity- Spatial Peak Temporal Average
Most commonly used;
Includes listening time
Heat and fetal tissues/bones:
Absorption coefficient _______ in bone; Fetal tissue less ____; Most effects in ___ trimester during _____. If temperature is elevated > ____ for ___ min or more it can cause developmental effects.
higher
tolerant
1st; organogenesis
4*C; 5
In vivo
In living
In vitro
In glass
Focused beams
less likely to cause temp rise in tissue
Max I= 1,000 mW/cm2 or 1 W/cm2
Unfocused beams
more likely to cause temp rise in tissue
Max I= 100 mW/cm2
Bioeffect study technique
Mechanistic Approach
Theoretical
Cause and Effect
Bioeffect study technique
Empirical Approach
Based on review of info
Relationship btwn exposure and effects
Both mechanistic and empirical have merits but…
Strongest argument when both approaches are in agreement
Attenuation
Caused by 1)Reflection 2) Scattering 3) Absorption
Increases w/ longer distance and higher frequency
Rayleigh Scattering
Scattering that occurs when structure’s dimensions are much smaller than the beam’s wavelength.
Redirects sound equally in all directions.
Ex: US and RBCs
It increases dramatically w/ increased Freq.:
Rayleigh Scatter= Freq^4
Contrast Agents
Bioeffects confirmed w/diagnostic US and MI of >0.4 and gas body contrast agent present in circulation.
Output Power vs. Receiver Gain
Overall brightness- BOTH Alters signal-to-noise ratio- OP Alters patient exposure- OP Bioeffect concerns- OP Decrease OP if image too BRIGHT Increase RG if image too DARK
Therapeutic US
Many uses (chemo, break of calculi, etc.) Long duration US increases blood flow to area and speed healing of MSK injuries
