Week 11 biosafety Flashcards
What are epidemiology studies?
what have they shown about US?
Epidemiology studies follow a group of people over time
To date, have never proven any bad effects from US
What are in vitro and in vivo studies?
What have they shown about US?
in vitro = in glass (cells)
in vivo = on plants or animals
Have proven that, at higher power levels than used in medical US, cell tissue damage will occur
What are the 3 main bioeffects from US?
- Tissue heating - mech wave E is absorbed by tissue and turned into heat. In addition, the transducer itself heats up (TEEs have temp gauge)
- Cavitation - generation of tiny gas bubbles that expand and contract with pressure variations of beam. 2 types: stable and transient. Happens at low freq and high intensity.
- Non-cavitation mechanical forces - exact cause not understood
Stable cavitation
- already have small bubbles in fluid
- US causes bubbles to grow
- when bubbles reach a certain size they can resonate and cause damage
Transient cavitation
- bubbles develop during rarefraction and burst when pressures rise in compression
- large E release can cause damage
What is the overall risk of bioeffects for non-obstetrical and obstetrical exams
non-obstetrical
- very safe
- can scan for educational reasons
- precise limit not known and need more research
obstetrical
- fetal temp can rise by up to 4°C, bone will absorb most of the heat
- only do scans for med reasons
Power - defn and units
Power is rate of transmission of E into a medium (tissue)
mW
rank the 4 different scanning types that we use in order of increasing power
in order of increasing power:
M-mode
B-mode
PW and CW
Colour
Intensity - defn and units
Intensity is amount of power in a given area
mW/cm^2
- is US focused in 1 area? or spread out?
What is insonation? what measures it?
Insonation is amount of exposure to US
it is measured by intensity
Amplitude - defn
Amplitude is the height of compression or rarefaction
In terms of bioeffects, what happens when you incr intensity? or Amplitude?
incr intensity = incr risk of heating
incr amplitude = incr risk of cavitation
When you increase power output, what happens to intensity and amplitude?
increase power = increase intensity and increase amplitude
What are 4 ways to measure acoustical power?
- Radiation force balance - a scale that measures power
- hydrophone - put probe in water with a very sensitive senser. Oscilloscope detects Press and other data. (ie measures power and intensity)
- Spectrum analyzer - breaks sound wave down into its components such as freq and bandwidth (often used with hydrophone)
- Calorimeter - measures temp
Duty Factor - defn and formula
Duty factor is percent of time spent actively sending pulse
DF = PD/PRF
Intensity - temporal values
I-(TP) vs I-(PA) vs I-(TA)
I-(TP)
Temporal Peak - measures intensity over halve the pulse
I-(PA)
Pulse Ave - intensity of the pulse
I-(TA)
Temporal Ave - intensity of pulse and waiting time
I(TA) = I(PA) x DF
Intensity - spatial values
I-(SP) vs I-(SA)
I-(SP)
Spatial Peak - highest intensity, often in the center of the beam
I-(SA)
Spatial ave - ave intensity along the entire beam
There are 6 combination of spatial and temporal intensity values…
how do you rank them from lowest to highest intensity
SA is first, SP is second
TA < PA < TP
so
SA TA
SA PA
SA TP
SP TA*
SP PA
SP TP
What is the most commonly used intensity value? why?
SPTA
SP bc it is best indicator for cavitation (cavitation can occur in a single pulse)
TA bc it is best indicator for heating
(heating occurs over time)
How does increasing PRF affect SPTA?
SP no change
TA increases bc more pulses and less wait time
so SPTA increases
rank the 4 different scanning types that we use in order of increasing overall intensity
B- mode
M- mode
Colour doppler
PW and CW
order of increasing intensity is same as order of increasing risk of heating
What does it mean if an intensity value is derated
Water value - as measured in hydrophone
Derated value - converts to tissue (not perfect but accounts for incr attenuation of tissue)
Who created the TI and MI system?
AIUM = American Institute of US in Med
NEMA = National Electrical Manufacturing Assoc.
created the output display system that shows real time power levels (TI and MI)
Thermal Index (TI) - defn
What does TIS 1.1 mean?
TI indicates the likelihood of heating
it can range from 0 to 4
eg. TIS 1.1 means Thermal Index Soft tissue - the amt of energy transmitted could increase the temp of tissue by 1.1 degrees
What are the safe values for TI? AIUM and Health Canada
AIUM:
Non obstetrical < 1.5 is safe (>= 1.5 follow ALARA)
Ob < 0.7 is safe
Health Canada
Non ob < 1.0 is safe
Ob - use extra caution
What does the 3rd letter mean?
TIS
TIB
TIC
TIS - Soft tissue (cardiac)
TIB - Bone (fetal femur - bone near focal zone)
TIC - Cranial (fetal transcranial - bone near skin surface)
TIB > TIS for same transducer and situation, since bone absorbs more E than soft tissue
Mechanical Index (MI) - defn
MI is likelihood of cavitation forming
it can range from 0 to 2
Safe values for MI?
MI <= 1 very low potential for cavitation
MI > 1 potential for cavitation (follow ALARA)
How does MI relate to peak rarefraction pressure and probe freq?
formulas
MI proportional to Pr
incr peak rarefractional press = incr MI
MI proportional to 1/√f
Incr freq = decr MI a little bit
How can you decr TI and MI
if TI and/or MI is above 2…. try to decr by
- decr overall power (and incr gain)
- decr scan time
Contrast agents - what are they and what are the risks
Contrast agents are microbubbles stabilized by proteins that are injected into patient
looks grey (vs blood is black) bc of impedance diff btw blood and contrast agent
risks are PVCs
QA - Quality Assurance
QA is the plan and policies you follow to ensure patient safety
eg. cleaning, maintain machines, records, patient privacy
QC - Quality Control
QC is the inspection phase of QA
eg. check machine cables, clean air filters = RECORD THIS (sonographers job)
QC also involves preventative maintenance 2x per year
- biomed or manufacturer comes and cleans, checks, and calibrate machine (using phantums)
What are phantoms and what are they used for?
phantoms are gel like substances filled with scatterers that mimic tissue (c=1540 exactly)
used to calibrate machine
- pins in different arrangements to check for axial res, lat res, near field dead zone, penetration…
Doppler phantoms: string phantom vs tissue mimicking material
string phantom - string attached to motor and put in a box of water (moves at known vel)
tissue mimicking material - 2D phantom but with tubes of fluid (fluid is pushed through tubes at known vel)
used for Doppler calibration
What are the 3 levels of reprocessing?
- cleaning
- remove dirt but doesn’t kill microbes
- for contact with skin (normal probe) - Disinfection
- kills most microbs but not bacterial spores
- for contact with mucous membranes (TEE) - Sterilization
- kills all microbs
- for if penetrate skin or tissue (biopsy)
- Reprocessing department (autoclave)
Spaulding classification system:
Critical
Semi-critical
Non-critical
give an example for each
What do you need to do for echo for each?
what do you need to do for reprocessing for each?
- Critical
- probe contacts sterile tissue (eg. biopsy)
- use sterile probe cover and sterile gel package
- requires cleaning and sterilization - Semi-critical
- probe contacts mucous mem or non intact skin (TEE or TTE with open wounds)
- use probe cover (sterile or non-sterile) and sterile gel package
- requires cleaning and disinfection - Non-critical
- probe contacts intact skin (normal TTE)
- requires cleaning
*after exam, inspect probe cover and probe for damage
