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74 Cards in this Set
- Front
- Back
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Parameters |
describe features of a sound wave. |
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The source of a sound wave is |
the ultrasound system and transducer. |
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The quantity, or level, of some of the parameters are established by |
the ultrasound system |
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The sonographer can adjust the level of some of these parameters, whereas |
others cannot be changed |
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Period |
the time it takes a wave to vibrate a single cycle, or the time from the start of one cycle to the start of the next cycle |
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Period units |
reported in units of time, such as microseconds (us), seconds, hours, or days |
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Period typical values |
The typical value of period in diagnostic ultrasound is 0.06 to 0.5 microseconds |
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Period is determined by |
the sound source only, not by the medium |
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Period Adjustable? |
No |
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Frequency |
the number of particular events that occur in a specific duration of time; number of cycles that occurs in one second ex: frequency of presidential elections in the US is 25 times per country, 2.5 times per decade, 1 time every four years |
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Frequency units |
Hertz (Hz) = cycles/second |
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Frequency typical values |
2 MHz to 15 MHz or 2 million to 15 million per second |
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Frequency is determined by |
sound source only, not by the medium through which the sound is traveling |
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Frequency adjustable? |
No |
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Sound is classified based on the ability of |
humans to hear it |
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If the frequency of a sound wave is less than 20 Hz, it is |
below the threshold of human hearing and cannot be heard. The sound is inaudible |
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Humans can hear sound with frequencies |
between 20 Hz and 20,000 Hz. |
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Infrasonic or infrasound |
less than 20 Hz |
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Audible sound |
between 20 Hz and 20 kHz |
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Ultrasonic or ultrasound |
greater than 20 kHz |
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Why is frequency important in diagnostic sonography? |
it affects penetration and image quality. |
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What is the relationship between frequency and period? |
Inversely related to each other -frequency increases, period decreases -frequency decreases, period increases -if one remains constant, the other remains unchanged |
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Period and frequency have an even more special relationship that is called |
reciprocal |
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When two reciprocal parameters are multiplied together, the result is |
1 period x frequency = 1 |
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Three parameters describe the |
size, magnitude, or strength of a sound wave: amplitude power intensity |
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Amplitude |
"bigness" of a wave It is the difference between the maximum value and the average or undisturbed value of an acoustic variable. It is also the difference between the minimum value and the average value of the acoustic variable |
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Amplitude units |
can have units of any of the acoustic variables (pressure, Pa; density, g/cm^3; particle motion, cm or in) decibels dB |
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Amplitude typical values |
pressure amplitude ranges from 1 million pascals (1 MPa) to 3 million pascals (3 MPa) |
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Amplitude is determined by |
sound source (ultrasound system) initially Amplitude decreases as sound propagates through body. The rate at which it decreases as sound propagates depends on characteristics of both sound wave and medium |
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Amplitude adjustable? |
Yes |
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What is the difference between amplitude and peak-to-peak amplitude? |
amplitude is measured from the middle, or undisturbed, value to the max value midline to max peak or midline to min peak peak-to-peak is max to min peak value. so peak-to-peak is twice the amplitude value |
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Power
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rate of energy transfer or the rate at which work is performed like amplitude, power also describes "bigness" of a wave |
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Power units |
watts |
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Power typical values |
0.004 to 0.090 watts (4-9 milliwatts) depending on the diagnostic ultrasound technique |
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Power is determined by |
initial power determined by sound source only Power decreases as sound propagates through body and this rate depends on characteristics of medium and the wave |
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Power adjustable? |
Yes |
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When power increases |
so does amplitude |
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When power decreases |
amplitude also decreases |
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Power is |
proportional to the wave's amplitude squared |
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Intensity |
concentration of energy in a sound beam like amplitude and power, describes "bigness" |
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Intensity relates to how |
the power in a wave spreads of is distributed in space. |
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Intensity depends on |
both the power in the beam and the area over which the power is applied |
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Intensity units |
watts/square centimeter (W/cm^2) watts from power and cm^2 from beam area |
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Intensity typical values |
0.01 to 300 W/cm^2 |
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Intensity determined by |
sound source initially Intensity changes as sound propagates through the body. This rate depends on characteristics of sound wave and medium |
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Intensity adjustable? |
Yes |
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Amplitude, power, and intensity tend to be |
directly related; therefore when intensity increases, power and amplitude also increase |
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Intensity is proportional to |
power wave's amplitude squared |
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Wavelength |
the distance or length of one complete cycle. |
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Wavelength units |
units of mm, meters, or any other unit of length |
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Wavelength typical values |
in clinical imaging, wavelength in soft tissue ranges from 0.1 to 0.8 mm |
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Wavelength determined by |
both source and the medium |
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Wavelength adjustable? |
No |
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What is the difference between wavelength and period? |
Both wavelength and period describe a single cycle in a sound wave. wavelength refers to length or distance of a single cycle. Period refers to the time that it takes to complete a single cycle |
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What is the relationship between wavelength and frequency? |
As long as a wave remains in one medium, wavelength and frequency are inversely related. As frequency increases, wavelength decreases The lower the frequency, the longer the wavelength |
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What is the wavelength of 1 MHz sound i soft tissue? |
In soft tissue, sound with a frequency of 1 MHz has a wavelength of 1.54 mm. |
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Why is wavelength important is diagnostic sonography? |
Shorter wavelengths are created by high frequency sound. This usually produced higher quality images with greater detail. Therefore, monographers should try to use higher frequency transducers rather than lower frequency transducers. |
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Propagation Speed |
rate at which a sound wave travels through a medium |
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Propagation speed units |
m/s |
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Propagation speed typical values |
In the body, the speed of sound ranges from 500 m/s to 4000 m/s, depending on the tissue through which it is traveling |
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Propagation speed determined by |
medium speed is not affected by nature of sound wave |
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Propagation speed adjustable? |
No |
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The propagation speed depends on the |
density and stiffness of each medium |
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What is the speed of sound in soft tissue? |
The avg. or typical biologic medium is called soft tissue. The speed of sound in soft tissue is 1540 m/s |
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Speed of sound in different biologic media |
lung 500 fat 1450 liver 1560 blood 1560 muscle 1600 tendon 1700 bone 3500 |
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Speed of sound in other media |
air 330 water 1480 metals 2000-7000 |
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Two characteristics of a medium affect the speed of sound |
stiffness and density |
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Stiffness |
ability of an object to resist compression. a stiff material will retain its shape |
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Density |
the relative weight of a material. |
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How does stiffness affect speed? |
stiffness and speed are directly related as materials become stiffer, speed of sound in material increases. speed of sound will be higher in stiffer medium |
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What other terms describe stiffness? |
Bulk modulus |
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Terms opposite of stiffness |
elasticity and compressibility |
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How does density affect speed? |
density and speed are inversely related as materials become heavier, speed of sound in medium decreases sound travels faster in media with low density |
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Which is more important, stiffness or density? |
Stiffness has the greatest influence on speed |
