Particle Motion & Wave Propagation Flashcards
What are the 5 steps of a sonographers job?
1- operator control 2- transducer activation (sending) 3- sound interaction 4- transducer activation (receiving) 5- image display
Describe operators control
Operator (sonographer) decides which transducer and preset to use based on requisition and patient history
Describe transducer activation (sending)
Electrical current is sent to transducer and converted into sound through “reverse piezoelectric effect”
Describe sound interaction
Sound waves travel through tissue and produce echos that return to transducer
Describe transducer activation (receiving)
Returning sound waves are converted back into electrical current through “piezoelectric effect”
Describe image display
Electrical current is processed through the machine and converted into an image on a monitor
What is the Piezoelectric effect
Pressure waves are applied to certain crystals which produce electrical pulses (voltage)
What is the reverse piezoelectric effect
When electrical pulses (voltage) are applied to certain crystals which produce sound waves
What is Attenuation
Weakening of sound waves
What is Acoustic
Refers to sound
What is propagation
Refers to travel
What is acoustic propagation
Refers to the effects tissues cause on sound
What are bioeffects
Refers to the effects of ultrasound on tissue
Is sound a propagating variation (a wave)
Yes
Do waves carry matter or energy ?
Energy
What type of wave needs a medium to travel?
Mechanical wave
What are the qualities of waves called?
Variables
What are the 4 acoustic variables of sound when it travels through a medium?
1- pressure
2- density
3- particle motion
4- temperature
How can pressure be expressed on a sine wave?
Crests - increased pressure
Troughs - decreased pressure
In regards to pressure, when particles vibrate when is there high pressure, when is there low pressure?
High pressure - when particles are close together
Low pressure - when particles are farther apart
What is density ?
Density is the concentration of particles or mass per unit volume
Regions of low density are called?
Rarefactions
Regions of high density are called?
Compressions
List the two parts of temperature related to sound
Sound is an energy
Energy creates heat
Sound is what type of wave?
A mechanical wave
needs a medium to travel through, can’t travel through space
List some types of mechanical waves
Sound
Transverse
Rayleigh
Longitudinal
List some types of NON mechanical waves
Gamma rays
X rays
Light
Describe longitudinal waves
Particles motion is the same direction (parallel) to the direction of the wave
Describe transverse waves
Particles motion is perpendicular to waves motion
What type of wave is used in ultrasound
Longitudinal mechanical wave
Solids, liquids, gases support which type of wave?
Longitudinal
(Best in solid and liquid)
(Worst in gas)
Only solids support which type of wave?
Transverse
What is mode conversion?
One type of wave is converted into another form.
What is frequency? What is it’s units?
Cycles per second
(number of complete variations an acoustic variable goes though in one second)
Hz
(Ultrasound uses MHz)
What is period? What is it’s units?
The time it takes for something to complete one cycle
Seconds - s
Ultrasound it is measured in microseconds - us
What is a wavelength and what is it measured in?
Wavelength is the length of space one cycle takes to be completed
Usually measured in millimetres - mm
If frequency increases what happens to period and wavelength?
If frequency increases the period and wavelength decrease
If period and wavelength increase what happens to frequency?
The frequency will decrease
What is propagation speed ?
Propagation speed (c) is the speed in which a wave moves through a medium
What is the average speed of sound through soft tissue?
1.54 mm/us
1540 m/s
What determines propagation speed?
The medium in which it travels through
What ways can strength of a wave be described?
Amplitude
Intensity
Power
What is amplitude?
The maximum displacement of an acoustic variable
Strength of wave determined by source of sound
(From middle of wave to crest or trough)
What is intensity?
A way to define the strength of a wave
Is concentration of energy in a sound beam
How is intensity and amplitude related? And what does it mean?
(I) is proportional to (Amp)squared
A SMALL change in amplitude results in LARGE change in intensity
How is intensity related to power and area?
I = (P/A)
What does the relationship between intensity,power and area show?
Shows that as area increases, intensity decreases
Like a flashlight beam moved closer and further away from a surface
Intensity is not uniform in —— or ——, and we refer to intensities as these
Space and time
Describe space intensity
In sound beam the intensity is the greatest at the centre and fades towards outside. NOT UNIFORM
Describe time intensity.
Sound from the machines is sent in pulses (NO intensity during listening phase)
Within a pulse the intensity starts off high at beginning and falls off
Space and time must be considered for——
Dose (how much energy is sent into patient)
Terminology used to assess bioeffects
The greatest intensity found across the beam is called the —— and is usually found at the centre.
Spatial peak (SP)
The average intensity measured over the entire beam is what ?
Spatial average (SA)
SP and SA are related by what?
Beam uniformity ratio (BUR)
What is the equation that relates the BUR, SP and SA
BUR = (SP / SA)
What is temporal peak? (TP)
The greatest intensity found in the pulse
The average for all values found in a pulse is called?
Pulse average (PA)
Can TP and PA be used interchangeably?
Yes they can, they are almost identical
This includes the dead time between pulses (listening phase), when there is no intensity.
Temporal average (TA)
TP and TA are related by what ?
Duty factor (DF)
What is the equation that relates TA, TP and DF
TA
DF = ——
TP
What is the highest intensity about sound beam
SPTP
Not realistic it happens too quick to be able to use it for anything
What intensity do we use for biological considerations.
SPTA
Highest intensity average over total experts expect time
What is lowest intensity about sound beam
SATA
To convert possible intensities from one to another use?
SP TA
BUR = —— DF = ——
SA TP
Consider SPTA the list the different modes of ultrasound from lowest to highest values.
Lowest
M mode
Real time-B mode
Doppler
Continuous wave (no dead time SPTP)
HighestSPTA values are dependent on ?
Depth (go deeper it changes shape of beam)
Velocities differ in different tissues, and this may result in —— appearing on the monitor
Artifacts
Propagation speed in fat
1460 m/s
Propagation speed in bone
4080 m/s
Does frequency change speed?
NO
What is the range equation used to calculate?
Used to calculate the distance of a reflector from the probe
What is the range equation ?
D = C times t
D is distance there and back
C is the average speed of sound
t is time there and back
What is the 1 cm rule
Another way to calculate the distance from the probe to the reflector (interface)
Takes 13us to travel 1 cm there AND back
Can electromagnetic waves travel through space
Yes
What control on ultrasound machine can be adjusted to change the wavelength of the emitted sound?
You can adjust the frequency which will change the wavelength
What is the propagation speed for sound through air?
330 m/s
Out of 3 MHz, 5MHz, and 7MHz which has the best resolution? The best depth penetration?
3MHz for the best depth
7MHz for the best resolution
