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10 Cards in this Set
- Front
- Back
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What is sound?
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Sound is a wave that travels through a medium and carries energy from one place to another. A sound wave consists of a series of orderly oscillations of particles within the medium. These oscillations produce regions of compression and rarefaction (high and low pressures) throughout the medium.
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What is ultrasound?
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Ultrasound is described as a sound wave with a frequency above 20,000 cycles per second or hertz. One hertz means one event per second. The frequency of an ultrasonic wave is so high that it is inaudible to humans.
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What is audible sound?
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Audible sound is defined as a sound wave that can be heard by man. The frequency range of audible sound is from 20Hz to 20,000Hz.
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What is infrasound?
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Infrasound is defined as a sound wave with a frequency less than 20 hertz. The frequency of infrasound is so low that it is inaudible to the human ear.
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Two sound waves are traveling through an opera house. One wave was produced by a soprano, while a baritone produced the other. Which sound wave travels faster?
At what speed does sound travel through the body? |
Both waves travel at exactly the same speed. Only the characteristics of the medium through which sound travels determines the speed of sound. The speed of sound is not affected by the characteristics of the wave. Since both waves are traveling through the same medium (i.e., the air), they must have identical speeds.
It is important to know that the speed of sound in soft tissue is 1540 meters per sec. That is, all sound travels nearly one mile per sec through the body. |
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While traveling through the body, ultrasound waves encounter many different media, including bone, fat, lung nad soft tissue. Rank these 4 media according to their propagation speed (i.e., how fast sound travels through them), in increasing order.
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1) lung
2) fat 3) soft tissue 4) bone The propagation speed of sound is slowest in the air-filled lungs, then fat, soft tissue, and fastest in bone. It is important to remember that all sound waves travel through soft tissue at exactly 1540 meters per second. |
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What is the frequency of a sound wave?
What units are used to report frequency? What is the frequency range of the ultrasound waves used in diagnostic imaging? |
Frequancy refers to the number of times per second that the particles in a medium oscillate back and forth as a sound wave propagates through the medium.
Frequency is reported in the following units: per second, or hertz (Hz). The sound waves used in diagnostic imaging have a frequency range of 2 million to 10 million cycles per second (2 to 10 MHz). |
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What is the definition of wavelength?
What units are used to report wavelength? How is the wavelength determined? What is the importance of wavelength in diagnostic imaging? What is the wavelength of 1 MHz sound in soft tissue? |
Wavelength is the distance occupied by a single cycle in a wave.
Wavelength is measured in units of distance, most commonly in millimeters. Wavelength is determined both by the frequency of sound and the medium through which the sound is traveling. Wavelength is important in diagnostic imaging because it helps to determine image quality. Shorter wavelengths produce higher quality images. The wavelengths of ultrasound traveling through soft tissue range from 0.2 to 0.8mm. There is an inverse relationship between frequency and wavelength. Higher frequency sound waves have shorter wavelengths, while lower frequency waves have longer wavelengths. The wavelength of 1 MHz sound in soft tissue is 1.54mm. |
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Three specific terms are used to describe the size or magnitude of a sound beam: pressure, power, and intensity.
What is the meaning of the term pressure? Which units are used to measure pressure? What is the meaning of the term power? Which units are used to measure power? What is the meaning of the term intensity? Which units are used to measure intensity? |
As a sound wave travels through medium, the molecules of the medium are rhythmically compressed and expanded. This compression and rarefaction creates a pressure wave. Pressure is defined as the concentration of force within a particular area, and is reported in untis called Pascals (Pa).
Power is the amount of energy per second that is delivered by an ultrasound beam. Power is measured watts. Intensity is the concentration of power within a particular area of a sound beam. Intensity is measured in watts per square centimeter (watts/cm2). |
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What is a decibel?
What is the meaning of 3dB? What is the meaning of -3dB? What is the meaning of 10dB? What is the meaning of -10dB? |
A decibel (dB) is a unit that is used to measure the relative change in the intensity or power of a sound beam. A relative change compares the current intensity of the sound beam with its original intensity. For example, if a sound beam's power has increased by 50 %, compared with its original power, this is a relative change.
3 dB means that the beam's intensity has doubled. -3 dB means that the beam's intensity is only half of the original intensity. 10 dB means that the beam's intensity is 10 times greater. -10 dB means that the beam's intensity is only 1/10th of the original intenisty. |
