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ultrasound physics 1

following the edelman book, sound, pulsed sound, intensity

sound creates images by sending short bursts into the body
acoustic propagation properties the effects of the medium upon the sound wave
biologic effects the effects of the sound wave upon the biologic tissue
sound a type of wave that carries energy, not matter, from place to place
compressions areas of increased or higher pressure and density
rarefactions areas of decreased or lower pressure and density
what type of wave is sound? mechanical and longitudinal
sound travels in a straight line
acoustic variables do what identify which waves are sound waves
three acoustic variables pressure, density, distance
pressure concentration of force within an area, force/area
density concentration of mass within a volume
distance measure of particle motion
pascals (Pa) units of pressure
kg/cm^3 units of density
cm, feet, miles units of distance
transverse wave particles move in a perpendicular direction, right angles or 90 degrees, to the direction of the wave
longitudinal wave particles move back and forth in the same direction as the wave
acoustic parameters period, frequency, amplitude, power, intensity, wavelength, speed
what do acoustic parameters do? describe the features of a particular sound wave
period the time required to complete a single cycle
units of period any unit of time
what is period determined by? the sound source
typical values of period 0.06 to 0.5 microseconds
frequency number of certain events that occur in a particular time
units of frequency per second, 1/second, hertz (Hz)
typical values of frequency 2 MHz to 15 MHz
audible sound frequency is between 20 Hz and 20,000 Hz and can be heard by man
ultrasound greater than 20,000 Hz and can not be heard by man, the frequency is too high
infrasound less than 20 Hz and can not be heard by man, the frequency is too low
frequency and period are reciprocals
what type of relationship do frequency and period have? inverse relationship, when one goes up, the other goes down
equation for period and frequency frequency (Hz) x period (sec) = 1
what are the three bigness parameters? amplitude, power, and intensity
amplitude the difference between the average value and the maximum value of an acoustic variable, half the peak-to-peak amplitude
units for amplitude those of the acoustic variables, pressure - pascals, density - grams/cubic cm, particle motion - cm, inches, units of distance
peak-to-peak amplitude the difference between maximum and minimum values of an acoustic variable
power the rate that work is performed, or the rate of energy transfer
units for power watts
what is the relationship between power and amplitude? power is proportional to the wave's amplitude squared
intensity the concentration of energy in a sound beam
intensity depends upon both the power and the cross-sectional area of the beam
equation for power intensity(watts/cm^2) = power(watts) / beam area (cm^2)
what is the relationship between intensity and power? intensity is proportional, or directly related, to power (when one goes up, the other goes up)
what is the relationship between amplitude and intensity? intensity is proportional to the amplitude of the wave squared
wavelength the length of distance of a single cycle, similar to the length of a single boxcar in a long train
units for wavelength meters, mm, or any unit of length
what is wavelength is determined by? both the sound source and the medium
what is the equation for wavelength? wavelength (mm) = propagation speed (mm/us)/frequency (MHz)
wavelengths in soft tissue sound with a frequency of 1 MHz has a wavelength of 1.54mm, sound with a frequency of 2 MHz has a wavelength of 0.77mm
what is the equation for wavelength in soft tissue? wavelength(mm) = 1.54 mm/us / frequency (MHz)
propagation speed the rate that sound travels through a medium, also called velocity or speed
what is propagation speed determined by? the medium only - density and stiffness
what is the speed of sound in air? 330 m/s
what is the speed of sound in lung? 300 - 1,200 m/s
what is the speed of sound in fat? 1,450 m/s
what is the speed of sound in soft tissue? 1,540 m/s
what is the speed of sound in tendon? about 1,850 m/s
what is the speed of sound in bone? 2,000 - 4,000 m/s
stiffness and speed same direction
density and speed opposite directions
compressibility and elasticity opposites of stiffness
bulk modulus the same as stiffness
when bulk modulus increases, speed increases
interference when two waves overlap at the same location and at the same time, they combine into a single new wave
constructive interference occurs when the amplitude of the new, combined wave is greater than the original two waves, in-phase waves interfere constructively
destructive interference the amplitude of the new wave is less than one of the original waves, out-of-phase waves interfere destructively
in diagnostic imaging, what kind of pulses are used to create anatomic images? short pulses
pulse a collection of cycles that travel together
what are the two components of pulsed ultrasound? the cycles (on or transit time) and the dead time (off or receive time)
five additional parameters that describe pulsed sound pulse duration, pulse repetition period, prf, duty factor, spatial pulse length
pulse duration the time from the start of a pulse to the end of that pulse, the actual time that the pulse is on
what is the unit of pulse duration? usec - any unit of time
what is pulse duration determined by? by multiplying the number of cycles in the pulse and the period of each cycle
what are the typical values of pulse duration? in clinical imaging, pulse duration ranges from 0.5 to 3us.
equation of pulse duration pulse duration (us) = # of cycles in pulse x period (us)
spatial pulse length the length or distance that an entire pulse occupies in space, the distance from the start to the end of one pulse
what is the unit of spatial pulse length? mm - any unit of length
what are the typical values of spatial pulse length? 0.1 to 1 mm
equation of spatial pulse length spatial pulse length (mm) = # of cycles x wavelength (mm)
pulses that are short in time are ______ in distance short in distance
pulse repetition period the time from the start of one pulse to the start of the next pulse, includes one pulse duration and one listening time
what is the unit of pulse repetition period? msec or any unit of time
what are the typical values of pulse repetition period? 100 us to 1 ms
pulse repetition period is determined by? the imaging depth
as pulse repetition period increases, imaging depth _____ increases
as pulse repetition period decreases, imaging depth _____ decreases
PRF the number of pulses created by the system in one second, pulse repetition frequency
what are the units of PRF? hertz, Hz, per second
what are the typical values of PRF? from 1,000-10,000 Hz (1-10 kHz)
true or false, PRF is related to frequency false
duty factor the percentage or fraction of time that the system transmits sound
what are the units of duty factor? unitlless
what are the typical values for duty factor? from 0.1% to 1% or 0.001 to 0.01 (little talking, lots of listening)
continuous wave sound can or cannot create anatomical images? cannot
terms that have the same meaning to shallow imaging high pulse repetition frequency, short pulse repetition period, high duty factor
terms that have the same meaning to deep imaging low pulse repetition frequency, long pulse repetition period, low duty factor
intensity the concentration of power in a beam
intensity is or is not uniform across a sound beam is not uniform
spatial intensity an ultrasound beam does not have the same intensity at different locations within the beam
temporal intensity pulsed ultrasound does not have the same intensity at different times
peak the maximum value
average the mean value
spatial referring to distance or space
temporal referring to all time (transmit & receive)
pulsed referring only to the time the pulse exists (transmit only)
SPTP spatial peak, temporal peak - highest value
SATP spatial average, temporal peak
SPTA spatial peak, temporal average - most important for thermal bioeffects
SATA spatial average, temporal average - lowest value
SPPA spatial peak, pulse average
SAPA spatial average, pulsed average
Created by: arielenicole
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