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# SPI Chapter 3

### Describing Sound Waves

Question | Answer |
---|---|

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 |