Bioeffects Flashcards
What is QA?
It is the routine, periodic evaluationg of an ultrasound system to guarantee an optimal image quality
What is the purpose of QA?
- Optimize image quality
- Assess intersystem differences
- Assess intrasystem changes over time
- Verify system specifications
- Minimize artifacts
What are the goals of QA?
- To guarantee proper operation of the system
- Detect gradual changes over time
- Minimize machine downtime
- Reduce # of non-diagnostic exams
- Reduce # of repeat scans
What is sensitivity?
It is the ability of a system to display low-level echoes.
What are 2 forms of sensitivity?
- Normal
- Maximum
What is normal?
- Uses “normal setting”
- It detects all pins
- It detects all solid masses
- It detects all cystic structures
What is maximum?
- It is evaluated with output power and amplification.
- Maximium visualization depth is used to assess sensitivity
What is the dead zone?
- It is the region closest to the transducer
- It extends from the transducer to the shallowest depth from which meaningful reflections appear (pins)
What are the characteristics to a tissue equivalent phantom?
- Similar to tissue
- Speed
- Attenuation
- Scattering
- Echogenicity
What is the Doppler phantom?
It is the device of choice for evaluating doppler systems
What is the modern doppler phantom?
It includes cirulation pumps which properl fluid through vessels embedded in a tissue phantom.
What is slice thickness phantom?
It assess the slice thickness and it effect on image quality
What does slice thickness determine?
It determines evalutional resoluton which is more likely to degrade image quality.
What is the AIUM statement?
- Valid medical reason
- Understand equipment
- Use receiver gain, ¯ output power
- ALARA
What does ALARA mean?
As Low As Reasonably Achievable
What does the AIUM limit?
- Thermal: Unfocused beam = 100 mW/cm2 ;Focused beam = 1 W/cm2
- Non-thermal: 0.4 MPa or MI =0.4 (gas bodies); 4MPa or MI = 4.0 (non-gas bodies)
What is the logic behind bioeffects?
- –Ultrasound (US) = mechanical wave
- Mechanical wave interacts with medium
- US attenuated in medium
(E is absorbed) - Modalities have different
wave characteristics - intensities at £ focus
- Understand effects of
output power vs.
receiver gain
What is dosimetry?
It is the science of idenitfying and measuring the characteristics of an ultrasound beam that are relevant to its potential for producing biological effects.
What does in vivo mean?
It is research is performed within the living body.
What does in vitro mean?
It is research that is performed outside the living body
What is thermal effect related to?
It is related to related to exposure time
What is the thermal effect?
Conversion of US to heat→ à metabolic breakdown
(Core body temperature = 37°C)
What does the thermal effect depend on?
Depends on PRF, DF, ability of body to duct heat
- Worst in non-scanned regions (narrow area, fast rate)
- Greatest risk with Doppler (DF = 100%)
- Increased with color Doppler
- Lowest risk with B-mode
What is cavitation?
It is the interaction of sound waves with microscopic, stabilized, gas bubbles in the tissue.
What are the two forms of cavitation?
- Stable
- Transient
When does stable cavitation occur?
It overs at lower MI levels
What happens om stable cavitation?
The gaseous nuclei tend to oscillate, or expand and contract.
Bubbles do not burst.
What is power?
rate energy is transferred (mWatts)
n.b. Watt = Joules / second
What is intensity?
= power / unit area (mWatts / cm2)
What does temporal refer to?
Refers to time exposure
What does spatial refer to?
Refers to physical beam area exposure
What does I SPTP mean?
highest; spatial peak, temporal peak→ Mechanical
What does I SP PA mean?
spatial peak, pulse average
What does I SP TA mean?
spatial peak, temporal average→ Thermal
What does I SA TP mean?
(spatial average, temporal peak)
What does I SA TA mean?
lowest; spatial average, temporal average
What does the temporal average equal?
(TA)
TA = PA • DF
What does the pulse average equal?
(PA)
PA = TA / DF
What does spatial average equal?
(SA)
SA = SP / BUF
What is the thermal index?
predicts max temp ↑
What is the equation for TI?
TI = 6 – (log10t / 0.6)
What does the mechanical index do?
predicts cavitation injury
What is the equation for MI?
MI = Peak Neg Press / √freq
