Week 11 biosafety

Question 1

What are epidemiology studies?

what have they shown about US?

Answer 1

Epidemiology studies follow a group of people over time

To date, have never proven any bad effects from US

Question 2

What are in vitro and in vivo studies?

What have they shown about US?

Answer 2

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

Question 3

What are the 3 main bioeffects from US?

Answer 3

1. Tissue heating - mech wave E is absorbed by tissue and turned into heat. In addition, the transducer itself heats up (TEEs have temp gauge)
2. 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.
3. Non-cavitation mechanical forces - exact cause not understood

Question 4

Stable cavitation

Answer 4

• already have small bubbles in fluid
• US causes bubbles to grow
• when bubbles reach a certain size they can resonate and cause damage

Question 5

Transient cavitation

Answer 5

• bubbles develop during rarefraction and burst when pressures rise in compression
• large E release can cause damage

Question 6

What is the overall risk of bioeffects for non-obstetrical and obstetrical exams

Answer 6

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

Question 7

Power - defn and units

Answer 7

Power is rate of transmission of E into a medium (tissue)

mW

Question 8

rank the 4 different scanning types that we use in order of increasing power

Answer 8

in order of increasing power:

M-mode
B-mode
PW and CW
Colour

Question 9

Intensity - defn and units

Answer 9

Intensity is amount of power in a given area

mW/cm^2

• is US focused in 1 area? or spread out?

Question 10

What is insonation? what measures it?

Answer 10

Insonation is amount of exposure to US

it is measured by intensity

Question 11

Amplitude - defn

Answer 11

Amplitude is the height of compression or rarefaction

Question 12

In terms of bioeffects, what happens when you incr intensity? or Amplitude?

Answer 12

incr intensity = incr risk of heating

incr amplitude = incr risk of cavitation

Question 13

When you increase power output, what happens to intensity and amplitude?

Answer 13

increase power = increase intensity and increase amplitude

Question 14

What are 4 ways to measure acoustical power?

Answer 14

1. Radiation force balance - a scale that measures power
2. hydrophone - put probe in water with a very sensitive senser. Oscilloscope detects Press and other data. (ie measures power and intensity)
3. Spectrum analyzer - breaks sound wave down into its components such as freq and bandwidth (often used with hydrophone)
4. Calorimeter - measures temp

Question 15

Duty Factor - defn and formula

Answer 15

Duty factor is percent of time spent actively sending pulse

DF = PD/PRF

Question 16

Intensity - temporal values

I-(TP) vs I-(PA) vs I-(TA)

Answer 16

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

Question 17

Intensity - spatial values

I-(SP) vs I-(SA)

Answer 17

I-(SP)
Spatial Peak - highest intensity, often in the center of the beam

I-(SA)
Spatial ave - ave intensity along the entire beam

Question 18

There are 6 combination of spatial and temporal intensity values…

how do you rank them from lowest to highest intensity

Answer 18

SA is first, SP is second

TA < PA < TP

so

SA TA
SA PA
SA TP
SP TA*
SP PA
SP TP

Question 19

What is the most commonly used intensity value? why?

Answer 19

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)

Question 20

How does increasing PRF affect SPTA?

Answer 20

SP no change
TA increases bc more pulses and less wait time

so SPTA increases

Question 21

rank the 4 different scanning types that we use in order of increasing overall intensity

Answer 21

B- mode
M- mode
Colour doppler
PW and CW

order of increasing intensity is same as order of increasing risk of heating

Question 22

What does it mean if an intensity value is derated

Answer 22

Water value - as measured in hydrophone

Derated value - converts to tissue (not perfect but accounts for incr attenuation of tissue)

Question 22

Who created the TI and MI system?

Answer 22

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)

Question 23

Thermal Index (TI) - defn

What does TIS 1.1 mean?

Answer 23

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

Question 24

What are the safe values for TI? AIUM and Health Canada

Answer 24

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

Question 24

What does the 3rd letter mean? TIS TIB TIC

Answer 24

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

Question 25

Mechanical Index (MI) - defn

Answer 25

MI is likelihood of cavitation forming it can range from 0 to 2

Question 26

Safe values for MI?

Answer 26

MI <= 1 very low potential for cavitation MI > 1 potential for cavitation (follow ALARA)

Question 27

How does MI relate to peak rarefraction pressure and probe freq? formulas

Answer 27

MI proportional to Pr incr peak rarefractional press = incr MI MI proportional to 1/√f Incr freq = decr MI a little bit

Question 28

How can you decr TI and MI

Answer 28

if TI and/or MI is above 2.... try to decr by 1. decr overall power (and incr gain) 2. decr scan time

Question 29

Contrast agents - what are they and what are the risks

Answer 29

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

Question 30

QA - Quality Assurance

Answer 30

QA is the plan and policies you follow to ensure patient safety eg. cleaning, maintain machines, records, patient privacy

Question 31

QC - Quality Control

Answer 31

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)

Question 32

What are phantoms and what are they used for?

Answer 32

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...

Question 33

Doppler phantoms: string phantom vs tissue mimicking material

Answer 33

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

Question 34

What are the 3 levels of reprocessing?

Answer 34

1. cleaning - remove dirt but doesn't kill microbes - for contact with skin (normal probe) 2. Disinfection - kills most microbs but not bacterial spores - for contact with mucous membranes (TEE) 3. Sterilization - kills all microbs - for if penetrate skin or tissue (biopsy) - Reprocessing department (autoclave)

Question 35

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?

Answer 35

1. Critical - probe contacts sterile tissue (eg. biopsy) - use sterile probe cover and sterile gel package - requires cleaning and sterilization 2. 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 3. Non-critical - probe contacts intact skin (normal TTE) - requires cleaning *after exam, inspect probe cover and probe for damage