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136 Cards in this Set
- Front
- Back
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DEFINE SOUND
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A DISTURBANCE OF MECHANICAL ENERGY THAT PROPAGATES THROUGH MATTER AS A WAVE; USED TO CREATE IMAGES
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WHAT DOES SOUND NEED TO EXIST?
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It must travel through a MEDIUM
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What are some examples of a medium?
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air, fluid, soft tissue
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What is the medium that carries our voice when we talk?
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Air
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What is the medium used in ultrasound?
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Imaging travels through the gel and the patient's body
SOFT TISSUE IS THE MEDIUM |
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How is sound used in ultrasound?
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It is used to create images by sending a short burst into the body, traveling as a wave.
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Define sound...
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A mechanical longitudinal wave that travels in a straight line (ex: ultrasound)
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What are waves?
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* a repetitive phenomenom
* energy |
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What are 4 types of waves?
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1. heat
2. sound 3. magnetic 4. light |
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How are sound waves created?
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By the vibration of a moving object & transfer its energy (no matter) from source to the receiver.
All waves carry energy from 1 location to another. |
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"TYPES OF WAVES"
Define mechanical wave. |
It is just a disturbance that propagates through a medium.
(Longitudinal) |
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Give some examples of a mechanical wave.
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* sound
* water waves * a pulse traveling on a spring * earthquakes * a 'people wave' in a stadium |
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"TYPES OF WAVES"
Define a electromagnetic wave. |
It is simply light of a visible or invisible wavelength.
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Give some examples of electromagnetic waves.
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* light
* radio waves * x-rays * infrared |
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What is light made of?
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Oscillating intertwined electric and magnetic fields. Light can travel without a medium.
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What can electromagnetic waves travel through and mechanical waves cannot?
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a vacuum or empty space
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What are the 2 ways particles move in a mechanical wave medium?
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Either perpendicular or parallel to the direction of the wave itself.
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What is a surface wave?
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*a combination of perpendicular and parallel movements
* typically a circular or elliptical movement/path at the surface of a medium |
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Give an example of a mechanical transverse wave.
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water waves
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What is a sine wave?
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Sound waves that reoccur.
A cyclical event that travels in a straight line. |
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What type of wave is sound?
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A mechanical longitudinal wave, in which particles in the medium move.
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What causes the molecules of the medium to vibrate/oscillate?
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The mechanical pressure waves of the sound beam.
*The molecules vibrate back and forth from a fixed position. * passes the energy to neighboring molecules by causing them to vibrate * no permanent displacement of the molecule * molecules return to resting state |
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Define sound.
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A mechanical compressional wave in which back and forth particle motion is parallel to the direction of the wave travel (longitudinal wave)
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Define Acoustic Variables and name 4
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They are parameters that change rhythmically throughout time.
1. Pressure 2. Density 3. Temperature (not any more) 4. Distance (particle motion) They inform us of which waves are sound waves. |
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Define Pressure and name its unit of measurement.
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It is a concentration of force within an area
Units: Pascal (Pa) |
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Define Density and name its unit of measurement.
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It is a concentration of mass within a volume.
Units: kg/cm cubed |
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Define Distance and name its unit measurement.
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It is a measure of particle motion or displacement.
Units: cm, feet, miles |
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Define Temperature and name its unit measurement.
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The measure of relative warmth or coolness of an object.
Units: grades: centrigade or fahrenheit |
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What happens when sound moves through a medium?
(related to pressure and density) |
Pressure and density go through cycles of increase and decrease and particles of the medium oscillate back and forth.
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What is a cycle?
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One complete variation in pressure or another acoustic variable.
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What is a sound wave?
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A recurring, cyclical event that travels in a straight line.
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What are compressions?
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Regions of high pressure & density.
* a crest * travels through a medium with a soundwave |
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What are rarefactions?
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Regions of low pressure and density.
* a trough * travels through a medium with a soundwave |
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What are the crests of a wave?
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compressions
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What are the troughs of a wave?
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rarefactions
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Define a pair of in-phase waves.
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Their peaks and troughs occur at the same time and at the same location.
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Define a pair of out-of -phase waves.
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Their peaks and troughs occur at different times and at different locations.
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What is wave interference?
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* When 2 waves overlap at the same time & place.
* Their combination forms a single wave. |
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What is constructive interference?
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When 2 or more waves are in-phase and combine to create a new wave with a greater amplitude.
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What is destructive interference?
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When 2 or more waves are out-of-phase and combine to form a new wave with a smaller amplitude.
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Name 7 parameters used to describe sound waves.
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* frequency
* period * wavelength * propogation speed * amplitude * power * intensity |
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What do acoustic parameters describe?
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The particular features of sound waves.
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What is frequency?
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The number of certain events that occur in a particular time duration.
- In ultrasound, it is a count of how many complete variations (cycles) of pressure (or any acoustic variable) goes through in 1 second of time *Determined by: sound source *Changed by Sonographer: No |
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1 cycle per second =
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1 Hertz per second
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What is hertz?
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* a unit of frequency Hz
* the number of cycles that occur in one second 1 Hertz = 1 cycle per second |
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What is a period?
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The time it takes to complete one cycle... or
The time from start of one cycle to start of next cycle. |
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What are the units of period?
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*seconds
*msec *hours |
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What is the relationship of period and frequency?
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They have an inverse/reciprocal relationship.
When one goes up, the other goes down. frequency = 1/period or period = 1/frequency |
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What are the units of a period?
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Time or seconds
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What is the unit of frequency?
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Hertz or Hz
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What determines ultrasound wavelength?
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The transducer and the medium.
Can sonographer change: NO |
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What are the units of wavelength?
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* meters
* cm * mm |
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What is the distance between the beginning of a compression and the beginning of the next compression?
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a wavelength
It is the distance it takes for one cycle to occur Determined by sound source and medium Can sonographer change: NO |
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What is the equation for wavelength?
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Wavelength = propogation of speed / frequency
An inverse relationship. If frequency increase, the wavelength is shorter. If frequency decrease, the wavelength is longer. |
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Define propagation speed.
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Speed at which sound moves through a medium.
AKA: sound's speed velocity of sound acoustic velocity Determined by: medium only Can sonographer change: NO |
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What two acoustic variables measure the same exact area on a wave but in different units of measure?
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Period and wavelength
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Give examples of propagation speed in mm/microsec
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Bone = 4.0
Soft tissue = 1.54 Fat = 1.45 Lung = 0.5 Air = 0.33 Lung (air) < fat < soft tissue < bone |
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Is frequency related with propogation speed?
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No.
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What is the typical value of propogation of speed in soft tissue (regardless of frequency)?
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1540m/s = 1.54 mm/microsecond
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Give examples of material in Velocity (m/s)
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air = 330
water = 1480 soft tissue avg = 1540 liver = 1550 muscle =1580 fat = 1459 kidney = 1560 lung = 650 bone = 4080 |
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What is propagation speed determined by?
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Density of the medium
Stiffness of the medium/Compressibility |
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How much does the speed of sound vary with the temperature of the medium through which it travels?
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0.1% of 1% change in speed per degree centigrade change
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What is the relationship between density and velocity?
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INVERSE
As density increases, more mass is contained within a given volume. |
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What is stiffness?
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The ability of a material to maintain its shape even when pressure is applied.
It is the opposite of compressibility and elasticity. |
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Is air compressible?
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Yes
*gas molecules are far apart *low density *high compressiblity |
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What is compressibility?
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The ability to squeeze molecules of a material closer together.
It indicates the fractional decrease in volume when pressure is applied. The easier a medium is to reduce in volume, the higher its compressibility. |
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What is the relationship between compressibility and bone?
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lower compressibility = faster speed
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What combination determines propogation speed?
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Density and stiffness
Stiffness and speed are directly related. The greater the stiffness, the higher the speed |
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What is the relationship between compressibility and air?
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Greater compressibility = lower speed
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Define amplitude.
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The strength of a pressure in a wave.
The maximum value of the wave function * the greater the amplitude, the louder the sound |
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Name 3 units of measurement for amplitude.
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*acoustic pressure - Pa (Paschal)
*density - grams/cubic cm. *particle motion - distance - cm, ft |
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What is the maximum variation from normal resting or baseline level to the peak?
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AMPLITUDE
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What is peak to peak amplitude?
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The difference between maximum and minimum values of an acoustic variable.
More amplitude = More strength/power |
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Can sonographer change the amplitude?
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Yes - use power control or output power control
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What causes the amplitude of the wave to decrease?
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propagating through tissue
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What is the difference between ordinary sound we hear and ultra sound?
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ultrasound has higher frequency than human ears can hear
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Define power.
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the rate at which work is done or
the rate at which energy is transmitted by the transducer into the body *Power decreases as sound propagates through the body. |
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What is the equation for power?
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Power - work/time
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What is power determined by?
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the sound source
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What are the units of power?
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Watts
(amplitude) squared - an increase power * If amp changes in 2 power changes (2) squared = 4 * If amp changes in 3 power changes (3) squared = 9 |
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Define intensity.
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The concentration of energy in the sound beam.
The smaller the area, the greater the intensity. |
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What is the equation for intensity?
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Intensity = power/area
An increase in power = an increase in intensity Power = watts Intensity = watts/cubic cm. |
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What are 3 parameters that describe magnitude or strength of the sound wave?
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Amplitude
Power Intensity An increase in intensity will increase power and amplitude. |
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What are decibels?
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* a unit used to compare the ratio of intensities/amps. of 2 sound waves or 2 points along the wave path
* decibels don't represent absolute values * logarithms |
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What are positive decibels?
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An increase in values.
* Final intensity > original intensity * An increase in gain = > decibels = > echoes |
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What are negative decibels?
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A decrease in value
* Final intensity < original intensity * The signal is weakened. |
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What is attenuation?
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A weakening of the sound beam as it passes through soft tissue.
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What is the decibel scale?
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Illustrations of sounds of different volume.
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Megahertz =
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1,000,000 of Hz
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Kilohertz =
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1,000 of Hz
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How do acoustic variables affect sound?
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* Sound waves are identified by the oscillation in acoustic variables
* When an acoustic variable changes rhythmically in time, a sound wave is present. |
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What is the Hz range of DIAGNOSTIC ultrasound?
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200 KHz or 2 MHz to 15 MHz
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Medium is anything that has________.
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molecules
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In a cycle, what is the baseline equivalent to?
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the resting value
NOT zero |
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The frequency is _______not the velocity of motion.
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changes
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Molecules vibrate in the ______axis.
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same
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Define frequency.
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how many times each molecule vibrate per second
* it is non perceivable to us |
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___________ and ____________ are part of each cycle or each vibration.
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Compressions and rarefactions
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Baseline represents ___________air pressure.
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normal
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Define electromagnetic waves.
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* Waves which have an electric and magnetic nature and are capable of traveling through a vacuum.
* they do not require a medium in order to transport their energy |
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Define mechanical waves.
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* waves which require a medium in order to transport their energy from one location to another
* they rely on particle interaction in order to transport their energy, they cannot travel through regions of space which are devoid of particles ( a vacuum) |
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Diagnostic ultrasound chart
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Wave type: longitudinal mechanical waves
Transmission requirements: elastic medium Generation: stressing the medium Velocity: depends on the medium through which it propagates |
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Name 2 similar waves similar to the waves used in ultrasound.
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seismic, acoustic
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Understanding the basic principles, ex:
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When 2 sounds with a frequency difference of greater than 7 Hz are played simultaneously, most people are capable of detecting the presence of a complex wave pattern.
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Define consonant.
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Certain sound waves when played (& heard) simultaneously will produce a pleasant sensation when heard.
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Define Intervals in music.
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Consonant sound waves form the basis of intervals in music. Any 2 sounds whose frequencies make a 2:1 ratio are separated by an octave.
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Two sound waves sound good when played together if one sound has ____the frequency of the other.
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2x
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Propagation speed =
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frequency x wavelength
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Define baseline.
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the resting value of a molecule
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T/F Molecules are not transient but are stationary.
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True
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T/F Molecules are never permanently displaced.
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True
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Graphing is ________to molecule movement.
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perpendicular
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Molecules vibrate in
a. the same axis b. multiple axises |
the same axis
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What decides the number of cycles?
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The source
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Time =
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period
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Length =
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wavelength
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What is the purpose of gel when scanning?
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* creates another medium between transducer and the skin
* minimizes loss of sound * propagates sound * gives a "matching layer" |
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Transcutaneous scanning won't pick up ____mm with transducer.
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< 3 mm
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What type of ultrasound is non-invasive without cutting?
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Transrectal ultrasound
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Propagation is determined by
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medium
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Frequency is determined by
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the sound source (Transducer has a specific range.)
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Wavelength is determined by
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medium
* or the patient (can't change the patient) |
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Period is determined by
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the source
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WL = ps/f, therefore if PS is decided by medium and frequency is determined by the sound source then WL is or isn't operator dependant?
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Is not
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The normal range of wavelength in diagnostic ultrasound is
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0.15 to 0.8 mm OR
.00015 to 0.0008 meters |
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Wavelength is determined by
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source (transducer) and medium (tissue)
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The normal range of period in diagnostic ultrasound is
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0.1 to 0.5 microseconds OR
0.0000001 to 0.0000005 seconds |
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1 million cycles per second means
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you do 1 cycle in 1/millionth of a second
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Giga
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billion = 10 to 9th
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hecto
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hundred = 10 to 2nd
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deca
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ten
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deci
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tenth = 1/10 = 10 to -1
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centi
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hundredth = 1/100 = 10 to -2
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milli
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thousandth = 1/1000 = 10 to -3
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micro
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millionth = 10 to -6
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nano
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billionth = 10 to -9
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