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SPI Chapter 3

Describing Sound Waves

QuestionAnswer
What are the 7 parameters of sound waves? period, frequency, amplitude, power, intensity, wavelength, speed
What is a source? the ultrasound system and the transducer
What is a medium? the tissue
What is period? the time it takes a wave to complete a single cycle (from start of one cycle to the start of the next cycle)
What are the units for period? microseconds, seconds, hours, days
What are the typical values of period? 0.06 to 0.5 microseconds
What is period determined by? sound source
Is period adjustable by the sonographer? No
What is frequency? the number of events that occur in a specific duration of time (once every 4 years there's a presidential election)
What are the units of frequency? 1 Hz (1 per second) 1 kHz (1,000 per second) 1 MHz (1,000,000 per second)
What are the typical values of frequency? 2 MHz to 15 MHz
What is frequency determined by? sound source
Is frequency adjustable by the sonographer? No
What is the frequency of infrasound? less than 20 Hz
What is the frequency of audible sound? between 20 Hz and 20 kHz
What is the frequency of ultrasound? greater than 20 kHz
What is the relationship between period and frequency? inversely/reciprocals (period x frequency = 1)
What is the period of the earth's rotation around the sun? 1 year
What are the 3 "Bigness Parameters?" (size and magnitude) amplitude, power, intensity
What is amplitude? measurement from the baseline to the maximum or from the baseline to the minimum
What are the units of of amplitude? Pa, density-g/cm3, or particular motion and distance
What are the typical values of amplitude? 1 million pascals ( 1MPa) to 3 million pascals (3 MPa)
What is amplitude determined by? sound source
Is amplitude adjustable by the sonographer? Yes
What is peak-to-peak amplitude? the difference between the maximum and minimum values of the amplitude
What is power? the rate of energy transferred
What are the units of power? watts
What are the typical values of power? 0.004 to 0.090 watts
What is power determined by? sound source
Is power adjustable by the sonographer? Yes
What is power proportional to? amplitude squared
What are the typical values of intensity? 0.01 to 300 W/cm squared
What is intensity determined by? sound source
Is intensity adjustable by the sonographer? Yes
What is the formula for intensity? Intensity (W/cm squared) = power (W)/area (cm squared)
What is power proportional to? intensity
What is intensity proportional to? amplitude squared
What is wavelength? distance of one complete cycle
What are the units of wavelength? mm, meters, or units of length
What are the typical values of wavelength? 0.1 to 0.8 mm in soft tissue
What is wavelength determined by? both source and medium (the only parameter determined by both)
Is wavelength adjustable by the sonographer? No
What kind of units does wavelength have? distance
What kind of units does period have? time
What relationship does wavelength and frequency have? inversely
In soft tissue, sound with a frequency of 1MHz. What is the wavelength? 1.54 mm
What is the formula for wavelength? wavelength (mm) = 1.54 mm/frequency (MHz)
Why are shorter wavelengths created by high frequency sound? this produces high quality images
What is propagation speed? rate which sound waves travel through a medium
What are the units of speed? meters per second, or any distance over time
What are the typical values of speed? 500 m/s to 4,000 m/s (depends on tissue)
What is speed determined by? the medium
Is speed adjustable for the sonographer? No
What is the speed of sound in soft tissue? 1,540 m/s
What is the speed of sound in lungs? 500 m/s
What is the speed of sound in fat? 1,450 m/s
What is the speed of sound in liver and blood? 1,560 m/s
What is the speed of sound in tendon? 1,700 m/s
What is the speed of sound in bone? 3,500 m/s
What is the speed of sound in air? 330 m/s
What is the speed of sound in water? 1,480 m/s
What is the speed of sound in metals? 2,000 to 7,000 m/s
What is the formula for speed? speed (m/s) = frequency (Hz) x wavelength (m)
From fastest to slowest, what does sound travel through? solids, liquids, and gases
What are the 2 characteristics that affects the speed of sound? stiffness and density
What is stiffness? an object that resist compression (ball vs marshmallow)
What is density? weight of a material
What relationship does stiffness and speed have? directly related (both start w/ an "S" same direction)
What is another word for stiffness? bulk modulus, elasticity, and compressibility
What relationship does density and speed have? Inversely (different letters "D" & "S" different direction)
Out of stiffness and speed, which one has the greatest influence on speed? stiffness
Does speed increases as frequency increases? No. Speed is determined by the medium only
Medium 1: Density of 9/Stiffness of 6 Medium 2: Density of 8/Stiffness of 6 Which medium will sound travel slower? Medium 1
What characteristic create the fastest speed of sound? low density, high stiffness (speed is inversely proportional to density and directly proportional to stiffness)
What characteristic create the slowest speed of sound? high density, low stiffness (speed is inversely proportional to density and directly proportional to stiffness)
If power in a beam is 1 watt and the area is 5 cm squared, what is the beam's intensity? power (1 watt) /area (5cm squared) = 1/5
If intensity remains the same while the power is doubles, what happened to the beam area? doubled
A sound beam travels a total of 10 cm in 2 sec. What is the speed? 10 cm/2 sec = 5 cm/sec
Does propagation speed increases as frequency increases? No. they are unrelated
Does propagation speed increases as frequency decreases? No. they are unrelated
Does propagation speed not change as frequency increases? True, they are unrelated
What are the effects of sound waves on tissue in the body called? Bioeffects
What is considered acoustic variables? density, particle motion, and pressure
What are the effects of tissue on sound waves called? Acoustic Propagation Properties
What are the effects of a medium on an ultrasound wave called? Acoustic Propagation Properties
Created by: Lazacha
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