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30 Cards in this Set
- Front
- Back
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Sound
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a type of wave that carries energy, not matter, from place to place
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Transverse Wave
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particles move in a perpendicular direction (90 degress) to the direction of the wave
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Longitudinal Wave
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particles move in the same direction as the wave
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Compressions
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regions of higher density and pressure
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Rarefactions
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regions of lower density and pressure
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Period
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time required to complete a single cycle
Inverse relationship with frequency as one goes up the other goes down |
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Frequency
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the number of cycles that occur in one second (Hertz)
frequency affects penetration and axial resolution |
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Amplitude
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the difference between the average value and the maximum value of an acoustic variable.
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Power
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the rate that work is performed, or the rate of energy transfer (Watts)
Power is proportional to the wave's amplitude squared Power= (amplitude) |
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Intensity
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the concentration of energy in a sound beam
it depends upon both the power and cross-sectional area of the beam |
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Wavelength
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the length or distance of a single cycle
higher frequency=shorter wavelength |
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Propagation Speed
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the rate that sound travels through a medium
all sound regardless of the frequency travels at the same speed through any specific medium |
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Pulse Duration
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the time from the start of a pulse to the end of that pulse, the actual time that the pulse is "on"
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Pulse Repetition Period
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the time from the start of one pulse to the start of the next pulse
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Pulse Repetition Frequency (PRF)
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the number of pulses that occur in one second
PRF is determined by depth of view only |
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Duty Factor
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the percentage or fraction of time that the system transmits sound.
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Shallow imaging
High PRF High duty factor Short pulse repetition period |
Deep imaging
Low PRF Low duty factor Long pulse repetition period |
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Spatial Pulse Length
(Shorter pulses create higher quality images) |
the length or distance that a pulse occupies in space. the distance from the start to the end of one pulse
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Reflection
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when sound energy strikes a boundary between two media and some returns to the transducer
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Specular Reflection
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reflections from a smooth reflector(mirror) and return on one direction
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Diffuse Reflection or Backscatter
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when a boundary is rough reflected sound is disorganized and random
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Rayleigh Scattering
(Red Blood Cell) |
if a reflector is much smaller than the wavelength of sound, sound is uniformly distributed in all directions. Higher frequency undergoes more Rayleigh scattering
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Attenuation Coefficient
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the amount of attenuation per centimeter.
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Incident Intensity
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the intensity of the sound wave at the instant prior to striking a boundary
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Reflected Intensity
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the portion of the incident intensity that after striking a boundary changes direction and returns back from where it came
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Transmitted Intensity
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the portion of the incident intensity after striking a boundary continues on in the same general direction
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Refraction
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the transmission with a bend. A change in direction as sound transmits from one medium to another
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Time-of-flight
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the time needed for a pulse to travel to and from the transducer and reflector
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The 13 Microsecond Rule
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In soft tissue every 13 microseconds of go-return time means the reflector is 1 cm deeper in the body
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Snell's Law
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the physics of refraction
2 sines + 2 speeds= that's all |
