# Shared Flashcard Set

## Details

Ultrasound Physics
Chapter 2 Sound
38
Physics
Professional
04/26/2013

Term
 What is the effects of the medium upon the sound wave called?
Definition
 Acoustic Propagation Properties
Term
 What is the effects of the sound wave upon biologic tissue called?
Definition
 Biologic Effects
Term
 What is sound?
Definition
 Sound is a mechanical, longitudinal wave that consists of compressions and rarefactions that which carries energy, not matter, from place to place.
Term
 How is sound created?
Definition
 By the vibration of a moving object.
Term
 What are compressions?
Definition
 Areas in a sound wave of increased pressure and density.
Term
 What are rarefactions?
Definition
 Areas in a sound wave of decreased pressure and density.
Term
 Define acoustic variables and what are the three types?
Definition
 Acoustic variables identify which waves are sound waves.  When an acoustic variable changes rhythmically in time, a sound wave is present.   Pressure Density Distance
Term
 Define pressure as it relates to sound and what are the units?
Definition
 Concentration of force within an area, force/area.   Units: Pascals (Pa)
Term
 Define density as it relates to sound and what are the units?
Definition
 Concentration of mass within a volume.   Units: kg/cm3
Term
 Define distance as it relates to sound and what are the units?
Definition
 Measure of particle motion.   Units: cm, ft, miles
Term
 Define Transverse Wave
Definition
 Particles move in a perpendicular direction (right angles or 90°) to the direction of the wave.
Term
 Define Longitudinal Wave
Definition
 Particles move in the same direction as the wave
Term
 Define acoustic parameters and what are the seven types?
Definition
 Acoustic parameters describe the features of a particular sound wave.   Determined by sound source                              [Period Frequency]-->inversely related to each other   [Amplitude Power                                                Intensity]-->directly related to each other   Determined by both sound and medium wavelength   Determinded by medium speed
Term
 Define Period
Definition
 The time required to complete a single cycle.   units: μsec (or any unit of time)   typical values: 0.06 to 0.5   determined by: sound source   1/f   sec/cycle
Term
 Define Frequency
Definition
 Number of certain events that occur in a particular time duration.  In diagnostic ultrasound, the frequency of a wave is the number of cycles of an acoustic variable that occur in one second.   units: Hertz (Hz)   typical values: 2 MHz to 15 MHz   Note: Frequency affects penetration and axial resolution (image quality)   determined by: sound source   1/p   cycles/sec
Term
 Define Ultrasound
Definition
 A wave with a frequency exceeding 20,000 Hz (20kHz).  This frequency is so high that the sound is not audible by man.
Term
 Define Audible Sound
Definition
 Heard by man, frequencies between 20 Hz and 20 kHz
Term
 Define Infrasound
Definition
 Sound with frequencies less than 20 Hz.  This frequency is so low that the sound is not audible by man.
Term
 How is frequency and period related to each other?
Definition
 They are reciprocals or have an inverse relationship.   frequency (Hz) X period (sec) = 1   period (sec) = 1/frequency (Hz)   frequency (Hz) = 1/period (sec)
Term
 Define Amplitude
Definition
 The difference between the average value and the maximum value of an acoustic variable.  The variation of an acoustic variable.   units: those of the acoustic variables: Pressure: Pascals Density: grams/cm3 Particle motion: cm, inches, units of distance Amplitude may be expressed in decibels (dB)   output/input
Term
 Define Peak-to-Peak Amplitude
Definition
 The difference between maximum and minimum values of an acoustic variable.  Amplitude is half of the peak-to-peak amplitude.
Term
 Define Power
Definition
 The rate that work is performed, or the rate of energy transfer   units: Watts   Power decreases as sound propagates through the body.
Term
 What is the relationship between Power and Amplitude?
Definition
 Power is proportional to the wave's amplitude squared   Power [image] (Amplitude)2
Term
 Define Intensity
Definition
 The concentration of energy in a sound beam.  Intensity depends upon both the power and the cross-sectional area of the beam.   intensity (watts/cm2) = power (watts)/beam area (cm2)   units: watts/cm2   typical values: 0.001-100 watts/cm2   Intensity decreases as sound propagates through the body   power/area
Term
 What is the relationship between Power and Intensity?
Definition
 Intensity is proportional, or directly related, to the power.  When one goes up, so does the other.
Term
 What is the relationship between Amplitude and Intensity?
Definition
 Intensity is proportional to the amplitude of the wave squared   Intensity [image] (Amplitude)2
Term
 Define Wavelength
Definition
 The length or distance of a single cycle.  Similar to the length of a single boxcar in a long train.   units: meters, mm or any unit of length   Determined by both the sourse and the medium   Typical values: 0.1-0.8 mm (in soft tissue)   wl (mm) = proagation speed (mm/μs)/frequency (MHz)   λ = C/F
Term
 What is the λ equation rule?
Definition
 In soft tissue, divide 1.54 mm by frequency in MHz
Term
 Define Propagation Speed
Definition
 The rate that sound travels through a medium.  Also called velocity or speed.   units: m/s, mm/μs   Determined by the medium   Note: All sound travels at the same speed through any specific medium regardless the frequency.   Typical values: Avg speed of all sound (regardless of frequency) in biologic or "soft tissue" is:   1540 m/s = 1.54 km/s = 1.54 mm/μs   General rule: gas (slower)
Term
 What is the propagation speed through air?
Definition
 330 m/s
Term
 What is the propagation speed through lung?
Definition
 300-1200 m/s
Term
 What is the propagation speed through fat?
Definition
 1450 m/s
Term
 What is the propagation speed through soft tissue?
Definition
 1540 m/s
Term
 What is the propagation speed through tendon?
Definition
 ~1850 m/s
Term
 What is the propagation speed through bone?
Definition
 2000-4000 m/s
Term
 What characteristics of a medium determine the speed of sound in that medium?
Definition
 Stiffness and density
Term
 How does stiffness affect speed?
Definition
 Stiffness and speed are directly related.  As materials become stiffer, the speed of sound in the material increases.   Stiffness and Speed ---> Same direction   Bulk modulus is the same as stiffness.
Term
 How does density affect speed?
Definition
 Density and speed are inversely related.  As materials become more dense (heavier), the speed of sound in the material decreases.   Density and Speed ---> opposite directions
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