Module 3 : Particle Motion and Wave Propagation Flashcards
what are the 5 steps to create an image
- step 1 = operator control
- step 2 = transducer activation (sending)
- step 3 = sound interaction
- step 4 = transducer activation (recieving)
- step 5 = image display
what is operator control
- you decide what preset and transducer to use based on the requisition and patient history
what is transducer activation (sending)
- electrical current sent to transducer and is converted into sound
- reverse piezoelectric effect
what is sound interaction
- sound waves travel through the tissue and produce echoes that will return to the transducer
what is transducer activation (receiving)
- returning sound waves are converted back into electrical current
- piezoelectric effect
what is image display
- electrical current processed through the machine and converted into an image on a monitor
what is the piezoelectric effect
- when pressure waves are applied to a certain crystal they produce electric pulses or a voltage
what is the reverse piezoelectric effect
- when electric pulses or voltage are applied to certain crystals that will produce sound waves
what does acoustic mean
- sound
what does propagation mean
- travel
what does acoustic propagation mean
- effects tissue cause on sound
what does bio effects mean
- effects of ultrasound on tissue
what is sound
- propagating variation
doe waves carry matter
- no only energy
does sound waves require a medium to travel
- yes
what type of wave is a sound wave
- longitudinal mechanical wave
what are the 4 acoustic variables
- pressure
- density
+ rarefactions and compressions - partical motion
- temperature
characteristics of pressure as an acoustic variable
- pressure can be expressed a a sine wave
- crests = high pressure
- troughs = low pressure
what is density
- concentration of particles or mass per unit volume
what are regions of low density called
- rarefactions
what are regions of high density called
- compressions
what is the particle motion in a transverse wave
- perpendicular to travel
what is the particle motion in a longitudinal wave
- parallel to travel
characteristics of temperature as an acoustic variable
- energy creates heat
- important for attenuation and bio effects which we will discuss later
what is mode conversion
- occurs when one type of wave is converted to another form
- occurs at a tissue bone interface
what are 6 wave terms
- frequency
- period
- wavelength
- propagation speed
- amplitude
- intensity
what is frequency a measurement of
- cycles per second
- complete variations an acoustic variable goes through in one second
what is the unit of frequency
- hertz Hz
- ultrasound uses mega hertz
what is period
- time it takes for one cycle to occur
- reciprocal of frequency
what is the unit of period
- seconds or micro seconds
what is wavelength
- length of space one cycle takes up
what is the unit of wavelength
- millimeters
what is the relationship between frequency and period
- they are inverse to each other
what is the relationship between wavelength and frequency
- inverse to each other
what is the formula for determining wavelength
- wavelength = C / F
what is propagation speed (c)
- speed with which a wave moves through a medium
what is the speed of sound in soft tissue
1540 m/s
what determines the speed of sound
- the medium
what three terms are used to describe wave intensity
- amplitude
- intensity
- power
what is amplitude
- maximum variation of an acoustic variable
what is intensity
- power of wave divided by the area
what is power
- total energy over the entire cross sectional area
what is another way to describe intensity
- concentration of energy in a sound beam
how are amplitude and intensity related
- intensity is directly related to amplitude squared
how is intensity related to power and area
- directly related to power
- inversely related to area
what is the intensity equation
I = P / a
is the ultrasound beam intensity uniform in time and space
- no
where is the beam most intense in space
- greatest at eh centre and falls off near periphery
how does time change the intensity in the beam
- sound is sent in pulses which means there is no intensity during listening
- within a pulse intensity starts off high at beginning then falls off
where is the greatest intensity found across the beam
- SP at the centre
what is the average intensity
- measured over the entire beam is called the spatial average
how is the SP and SA related
- Beam Uniformity Ratio BUR
- BUR = SP/SA
what is the temporal peak found
- greatest intensity found in the pulse
- equal to the Pulse average
what is the pulse average
- average of all values found in a pulse
what is the temporal average
- includes the dead time between pulses where there is no intensity
how are the TP and TA related
- duty factor DF
- DF = TA/ TP or DF = TA/PA
what is the highest intensity
- SPTP = instantaneous peak
what is the lowest intensity
SATA
what is the intensity we use for bioconsiderations
SPTA
from lowest to highest intensity where do the ultrasound modes rank
- M Mode
- real time B mode
- doppler
- CW
what is the range equation
- used to calculate the distance to a reflector from the probe
formula for range equation
D = C x t
what does D mean in range equation
distance to REFLECTOR AND BACK
what does C represent in range equation
average speed of sound in soft tissue
what does t represent in range equation
time for round trip
- go return time
