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51 Cards in this Set
- Front
- Back
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What is the frequency range of human hearing?
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20 Hz - 20,000 Hz (same as 20 Hz - 20 kHz)
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What is the term for frequencies < 20 Hz?
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Infrasound
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What is the term for frequencies > 20,000 Hz?
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Ultrasound
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What is the term for frequencies in the range 20 Hz - 20,000 Hz?
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Acoustic
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What range of ultrasound is useless for medical purposes?
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20,000 Hz - 2 MHz (same as 20 kHz - 2,000 kHz)
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What is the normal range of period in diagnostic ultrasound?
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.2 to .5 microseconds
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What is the normal range of frequency in diagnostic ultrasound?
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2 - 5 MHz
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What is the normal range of wavelength in diagnostic ultrasound?
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.15 mm to .8 mm
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What does sound require to travel?
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A medium (which is anything that has molecules)
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What is the range of medical ultrasound (aka "diagnostic ultrasound)?
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2 MHz - 20 MHz
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What does the "baseline" represent in a frequency diagram?
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Some kind of "resting" value, not necessarily = 0.
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In what fashion do the molecules move?
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In the direction they are "pushed" by the previous molecule.
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How does sound originate?
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By something physically moving or vibrating.
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Do the molecules move in a fashion resembling a sine wave?
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No, that is only a graphical representation of the fact that the molecules move first in one direction, then back in the other direction.
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What kind of wave is sound?
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Mechanical, longitudinal
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What is it about sound that causes it to be classified as "mechanical"?
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The fact that it requires a medium in order to propagate.
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What is the characteristic which causes some types of waves to be characterized as "electromagnetic"?
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The fact that they do not require a medium in order to propagate.
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Are the molecules which transmit sound permanently displaced?
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No, only temporarily displaced. This is "vibration".
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What is the term which represents the physical distance from one area of peak compression to the next area of peak compression?
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Wavelength
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What is the term for the time between the occurrance of one area of peak compression and the next area of peak compression?
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Period
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What is the difference between wavelength and period?
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They are measuring the same thing - the difference between areas of peak compression - but using different units. Wavelength uses units of distance. Period uses units of time.
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What term could be used in connection with either the distance or the time between areas of peak compression?
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The cycle. In practice, though, the term is nearly always used in connection with the time, not the distance, between areas of peak compression.
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What is the term for the number of cycles you can perform in a unit of time (which is always 1 second in ultrasound)?
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Frequency
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Frequency =
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1 / period
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Period =
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1 / frequency
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What is the lowest possible frequency?
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1
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What are the units of frequency?
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Hertz, or cyles/second
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What is the term for the speed at which the vibrations move from one location to another location - or in other words, the speed at which sound travels?
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Propagation speed
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Propagation speed =
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frequency x wavelength = wavelength / period
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At a given speed, how are frequency and wavelength related?
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Inversely (as one increases, the other must decrease)
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At a given speed, how are period and wavelength related?
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Directly (as one increases, the other must also increase)
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What is the term for a higher concentration of molecules than normal?
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Compression
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What is the term for a lower concentration of molecules than normal?
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Rarefaction
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What is the purpose of ultrasound gel?
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To create another medium, to minimize loss of sound between the transducer and the skin
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What is another name for gel?
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A "matching layer"
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What are examples of electromagnetic waves?
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light, x-ray, radio, infrared, and heat
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What size particles are too small to be detected by transcutaneous scanning?
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< 3 mm diameter
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What are the 2 types of mechanical waves?
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1. Longitudinal
2. Transverse |
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What is the speed of sound in air?
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330 m/s
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What is the speed of sound in fluid?
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1480 m/s
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What is the average speed of sound in tissue?
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1540 m/s
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What is the speed of sound in bone?
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3,000 - 4,000 m/s
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What determines propagation speed? Is it operator-dependent or operator-independent?
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It is determined by the medium (human tissue), and is operator-independent.
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What determines transducer frequency? Is it operator-dependent or operator-independent?
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Frequency is determined by the source (the transducer). For a particular transducer, it is fixed by the material characteristics of that transducer, and is operator-independent.
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What determines the period? Is it operator-dependent or operator-independent?
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Since it is merely the inverse of frequency, the period is determined by the source (the transducer), and is operator-independent,
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What determines the wavelength? Is it operator-dependent or operator-independent?
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Wavelength is determined by both the source and the medium, and is operator-independent
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Show the dependency variables within the formula for propagation speed
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Speed (determined by medium) = frequency (determined by source) x wavelength (determined by medium and source)
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What is pitch?
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The sensation of frequency
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What is the term for "loudness" or volume?
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Amplitude
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If sound travels 340 m/s, and a sound vibrates at 440 Hz, what is the wavelength of that sound?
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Propagation speed = frequency x wavelength
340 m/s = 440 cycles/sec x wavelength wavelength = (340 m/s / 440 cycles/s) = .77 m |
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If a bat hears an echo .01 seconds after he chirps, how far away is the object?
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Since the speed of sound in air is 330 m/s, and since the bat's chirp must spend half its time traveling to the object and half its time echoing back, set up the ratio (330 m / 1 sec = x m / .005 sec)
x m = 330 m / 1 sec x .005 sec = 1.65 m |
