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The effects of the medium upon the sound wave.
Acoustic Propagation Properties
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The effects of the sound wave on biologic tissue
Biologic Effects
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Sound is what kind of wave?
Mechanical, longitudinal
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Period-
Definition?
Determined by?
Changed by sonographer?
The time required to complete a single cycle
determined by--source
changed by sonographer--no
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Frequency-
Definition?
Units?
Determined by?
Changed by sonographer?
- Definition--The number of certain events that occur in a particular time duration
- Units-- per second, hertz, Hz
- Determined by--Source
- Changed by sonographer--no
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Ultrasound Range?
Greater than 20,000Hz, not audible
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Audible Sound
20-20,000 Hz
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Infrasound?
Less than 20 Hz
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Intensity is proportional to?
Amplitude2
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Formula for wavelength?
wavelength (mm)= prop. speed (mm/us) / frequency (MHz)
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Formula for wavelength in soft tissue?
wavelength= 1.54mm/frequency (MHz)
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Wavelength is determined by?
Source and Medium
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Propagation speed is determined by?
- Medium only,
- density and stiffness
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Propagation Speed formula?
- speed= frequency x wavelength
- (m/s) =(Hz) x (m)
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In-Phase waves interfere how?
Constructively
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Pulse duration formula?
PD= number of cycles in pulse x period
or
PD=number of cycles in pulse / frequency
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Pulse Repetition Period definition?
The time from the start of one pulse to the start of the next pulse. Includes "on time" and "off time"
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PRP
Determined by?
Changed by sonographer?
- Determined by-- source
- Changed by sonographer--yes
- (amount of listening time is determined by image depth)
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PRF definition?
The number of pulses that occur in one second
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Depth and PRF are related how?
Inversely proportional
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Depth and PRP are related how?
directly proportional
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Duty Factor formula?
DF = PD/PRP x 100
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Duty Factor
Definition?
Determined by?
Changed by sonographer?
- Definition-- The percentage of time the system is transmitting sound. (% of "on time")
- Determined by-- source
- changed by sonographer--yes
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SPL formula?
SPL= number of cycles x wavelength
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SPL determines resolution?
Axial resolution
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PRP, PRF, and DF are all affected by what?
Depth of view
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What intensity is most relevant with respect to tissue heating?
SPTA
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What is the log of:
a-100?
b-10,000?
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