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54 Cards in this Set
- Front
- Back
In ultrasound, how is "loudness" (aka volume, aka amplitude) controlled?
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By the "power" button on the machine.
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Is amplitude operator-dependent or operator-independent?
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Operator-dependent
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What are the two types of ultrasound?
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1. Diagnostic
2. Theraputic |
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What are two typical uses of theraputic ultrasound?
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1. To destroy kidney stones
2. To remove fat |
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In diagnostic ultrasound, the power level we use is about what fraction of the maximum potential destructive force which ultrasound is capable of?
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1 / 1,000
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What are 2 ways of improving an ultrasound image?
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1. By transmitting the signals at higher power
2. By manipulating the received (echoed) signals |
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What principle is used to govern the power setting using in ultrasound?
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The ALARA Principle (As Low As Reasonably Achievable)
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To be consistent with the ALARA principle, a good sonographer manipulates ____ signals, not ____ signals.
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1. Received
2. Transmitted |
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An example of a received signal which the sonographer can manipulate is ____.
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Gain (including the TGC slider controls)
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An example of a transmitted signal (which the sonographer should not manipulate to a significant extent) is _____.
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Power
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What are the units of power?
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Watts
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What additional information is needed for us to place a particular level of power in perspective?
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The size of the area over which that power is being applied
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Intensity =
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Power / Area
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What is the "sector"?
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The imaging area - the area being exposed to the ultrasound beam
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What are typical units for intensity?
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Watts / sq. cm
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At a constant power, decreasing the area of the sector will have the effect of increasing the _____.
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Intensity
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When 2 sounds have a frequency difference of less than _ Hz, most people hear it as one sound
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7
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Frequencies in certain ratios create _____ sensations.
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pleasing
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What is stated by Huygen's Principle?
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When 2 waves meet in a medium, the resulting interference causes the medium to take on a shape resulting from the effect of each individual wave.
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What is interference?
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A reaction to 2 or more waves
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What type of interference occurs if two waves meet in such a fashion that their crests (or troughs) coincide?
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Constructive interference
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What type of interference occurs if two waves meet in such a fashion that the crest of one coincides with the trough of the other?
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Destructive interference
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When two waves engage in "constructive interference", they are said to be _____.
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In phase
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When two waves engage in "destructive interference", they are said to be _____.
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Out of phase
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What is sound?
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A traveling variation of acoustic variables.
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What is an "acoustic variable"?
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The acoustic variables are pressure, density, and particle motion. These undergo transient cyclic changes when a sound occurs.
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What technology is used to eliminate the potential for constructive or destructive interference between the transmitted and received signals?
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Pulse technology, which involves pausing between sets of transmitted signals to allow time for the echoes to return without encountering interference from the next set of transmitted signals.
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A region of high acoustic variables is called an area of _____.
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Compression
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A region of low acoustic variables is called an area of ______.
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Rarefaction
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What is amplitude (in terms of actual physical conditions)?
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The amount of change in a varying quantity over time. The quantity in question can be any of pressure, density, or particle motion.
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What is amplitude (in terms of graphic representation)?
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The maximum variation from normal resting or baseline level (of pressure, density, or particle motion) to the peak
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The units used to measure amplitude depend on which ______ is being measured.
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acoustic variable
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Amount of pressure increase or decrease is called ________.
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Pressure amplitude
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What are the units of pressure, or pressure amplitude?
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pascals (Pa) or megapascals (MPa)
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What are the units of density, or density amplitude?
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grams / cubic cm
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The difference between maximum and minimum (peak to trough) values of an acoustic variable is called the ______.
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Peak to peak amplitude
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What are the units of motion (distance), or motion (distance) amplitude?
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cm
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Peak to peak amplitude =
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2 x amplitude
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Half of the peak to peak amplitude is simply called ______.
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Amplitude
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If the "resting" value is 5, the "compressed" value is 15, and the "rarefied" value is -5, then the amplitude is _1_, and the peak to peak amplitude is _2_.
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1. 10
2. 20 |
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The more power used, the higher the _____.
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Amplitude
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As sound passes through a medium, the _____ of the sound decreases.
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Amplitude
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Weakening of a wave is called _____.
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Attenuation
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The rate at which work is done is called _____.
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Power
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As sound propagates through the body, power ______.
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Decreases
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How is power related to amplitude?
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Power is proportional to (Amplitude) ** 2
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What determines the power?
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Initially, by the sound source (the ultrasound machine), which is controlled by the operator - then, as it propagates, by the body tissues
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Can the sonographer change the power?
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Yes, but (s)he should refrain from setting it to 100%
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How are intensity and area related?
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Inversely. Since Intensity = Power / Area, as area decreases, intensity increases.
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How are power and intensity related?
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Directly. Since Intensity = Power / Area, as power increases, so does intensity.
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Who determines intensity?
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The source (the ultrasound machine) and the imaging area
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How are amplitude, power, and intensity related?
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Directly, since Power = Amplitude **2, and Intensity = Power / Area
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What are acoustic parameters?
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"Acoustic parameter" is a more general term than "acoustic variable". It includes the acoustic variables, and any other variable involved in making sound, including frequency, wavelength, period, power, intensity, propagation speed, etc.
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How is intensity related to amplitude?
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Intensity is proportional to amplitude **2.
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