Particle Motion and Wave Propagation Flashcards
5 steps of getting an image
- operator control: decide preset/transdcer
- transducer activation (sending): electrical current to sound; reverse piezoelectric effect
- sound interaction: sound waves travel through tissue and produce echoes
- transducer activation (receiving): sound waves converted to electrical current; piezoelectric effect
- image display: electrical current processed through machine and converted to image on monitor
3 reason why preset is important
- get you in the neighborhood
- gives you labels/calculations
- safety
acoustic
refers to sound
propagation
refers to travel
acoustic propagation
refers to the effects tissue cause on sound
bioeffects
refers to the effects of ultrasound on tissue (can be good or bad)
acoustic variables
pressure
density (rarefactions/compressions)
particle motion
temperature
pressure represented by
sine wave where crests=increased pressure and troughs=decreased pressure
density
concentration of particles or mass per unit volume
low=rarefaction
high=compressions
what kind of wave is a sound wave
mechanical wave (needs a medium to travel through)
what kind of wave is an ultrasound machine using
longitudinal mechanical wave
longitudinal vs transverse sound waves
L: back and forth particle motion parallel to wave travel direction
T: perpendicular to wave travel (swinging rope up and down but waves travel sideways)
mode conversion
when one type of wave is converted to another form (ex. long waves until hit bone then trans waves)
wave terms (6)
frequency
period
wavelength
propagation speed
amplitude
intensity
frequency (what/equation)
number of complete variations an acoustic variable goes through in one second (how many cycles per second)
f=1/T
period (what/equation)
time it takes for once cycle to occur
T=1/f
wavelength
length of space one cycle takes up
λ=C/f
speed of sound in tissue
1540 m/s
1.54 mm/microsecond
an increase in frequency affects the period and wavelength how
it will result in a decrease in period and wavelength
what determines the propagation speed
the medium
amplitude
max variation of an acoustic variable
strength of wave determined by the source of sound
intensity (what/equation)
power of wave divided by the area
I= P/a
power
total energy over the entire cross-sectional area
how are intensity and amplitude related
I = Amp^2
this means a small change in amplitude results in a large change in intensity
spatial peak (what/where)
greatest intensity found across beam
where focus is
spatial average (what/where)
average intensity over entire beam
right where probe first makes contact
SP and SA related by what and what does the equation look like
related by beam uniformity ratio
BUR= SP/SA
Temporal peak
greatest intensity found in the pulse
pulse average
average for all values found in a pulse (average of peak on 3 cycles if pulse has 3 cycles)
TP and PA relation
TP always higher than PA but in ultrasound its so close they are used interchangeably
temporal average
includes the dead time between pulses where there is no intensity
TP and TA related by (equation)
related by duty factor
DF=TA/TP
highest intensity
SPTP
biological considerations intensity
SPTA
lowest intesnity
SATA
modes of ultrasound from lowest to highest intensity
M mode
real time b mode
doppler
continuous wave (no dead time=SPTP)
SPTA values are dependent on
the depth (changes shape of beam=changes SP)
propagation speed in air, fat, bone, soft tissue
330m/s
1460m/s
4080m/s
1540m/s
range equation
D=Cxt
what do we do differently in an equation of we want distance to a reflector (interface) vs G-R
for reflector we divide by 2
for G-R we dont
1cm rule
it takes 13 microseconds to travel 1cm to reflector and back to probe (2cm total)
If the intensity of the emitted sound is doubled what will happen to the power?
it will also double
If you scanned with frequencies of 3 MHz, 5 MHZ, and 7.5 MHZ to scan through the same section of liver tissue, which one would reflect back to the surface first?
all at the same time as speed of sound is constant
