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Ultrasound Physics > Chapter 2 & 3 > Flashcards

Chapter 2 & 3 Flashcards

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1
Q

Sound Waves

A
  • All waves carry energy from one location to another.
  • In ultrasonography, sound pulses must travel through biologic tissue or media.
  • Sound waves are longitudinal
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2
Q

Definition of sound

A

Sound is a mechanical wave in which particles in the medium move.

  • Sound cannot travel through a vacuum; it must travel through a medium where molecules are alternately compressed and rarefied.
  • Sound travels in a straight line
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3
Q

Sound waves are also known as _____

A

Acoustic Waves

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4
Q

Acoustic variables

A

Pressure, density, distance, & temp (PDDT)

  • Are used to identify a sound wave. If one of these variables has a rhythmic oscillation, then the wave is a sound wave.
  • These make sound waves, sound waves
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5
Q

Pressure

A

Concentration of force onan area

  • Unit: Pa
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6
Q

Density

A

Concentration of mass in a volume

  • Unit: kg/cm3
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7
Q

Distance

A

Measure of particle motion

  • Unit: cm, feet, mile…
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8
Q

Temperature

A

Warming of particles from absorption of wave energy

Unit: °C

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9
Q

Compression

A

Molecules are squeezed together creating…
- High pressure and density
- Small distance between molecules

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10
Q

Rarefaction

A

Molecules are stretched apart creating…
- Low pressure & density
- Larger distance between molecules

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11
Q

Acoustic Parameters

A

Period, frequency, amplitude, power, intensity, wavelength, and propagation speed.

  • Acoustic parameters are used to describe the characteristics of a sound wave.
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12
Q

Transverse waves

A

Particles move (oscillate) perpendicular to the direction of a wave.

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13
Q

Longitudinal waves

A

Particles move (oscillate) parallel to the direction of a wave. Sound is a longitudinal wave.

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14
Q

In-phase

A

A pair of waves are considered in-phase when their peaks occur at the same time and at the same location.

  • Result in the formation of a single wave of greater amplitude. This is called constructive interference.
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15
Q

Out-of-phase

A

Two waves are out-of-phase when their peaks occur at different times.

  • Result in the formation of a single wave of lesser amplitude. This is called destructive interference.
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16
Q

Interference

A

When waves combine to form a single wave and lose their individual characteristics.

  • Interference can be constructive or destructive.
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17
Q

Interference of Waves with Different Frequencies

A

When the frequency of the waves differ, both constructive and destructive interference occurs

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18
Q

Source

A

The source of a sound wave is the ultrasound system and transducer.

19
Q

Medium

A

Medium is another name for the tissue the sound is traveling through.

20
Q

Period

A

The time it takes to complete one cycle

  • Units: seconds, ms
  • Determined by: sound source
  • Adjustable: NO!
21
Q

Cycle

A

One positive and one negative half of a wave.

22
Q

Frequency

A

The number of cycles per second

  • Units: – 1/second, Hertz (Hz)
  • Determined by: sound source
  • Adjustable: NO
23
Q

Infrasound

A
  • Less than 20 Hz.
  • Cannot be heard by humans
24
Q

Audible Sound

A
  • Between 20 Hz & 20 kHz.
  • Can be heard by humans
25
Q

Ultrasound

A
  • Greater than 20 kHz.
  • Cannot be heard by humans.
  • This is what we use in sonography.
26
Q

Relationship Between Frequency and Period

A

Period and frequency are inversely related to each other. (As frequency increases, period decreases and vice versa)

Period and frequency are reciprocals of each other. (Period x Frequency = 1)

27
Q

The Three “Bigness” Parameters

A

The three parameters that describe the size, or magnitude, or strength of a sound wave are

  • Amplitude
  • Power
  • Intensity
28
Q

Amplitude

A

The difference between the maximum value and the mean value

  • Units: can be any of the acoustic variables such as pressure (Pa) or density (kg/cm3)
  • Determined by: sound source and
    medium
  • Adjustable: Yes
29
Q

Amplitude vs. Peak to peak amplitude

A

Amplitude is measured from the middle (baseline) to the maximum value

Peak to peak amplitude is the difference between the maximum and minimum values to an acoustic variable

30
Q

Power

A

The rate at which energy is transferred

  • Units: watts
  • Determined by: sound source
  • Adjustable: Yes
31
Q

Relationship Between Amplitude and Power

A

Amplitude and power are directly related to each other.
- When power increases, so does amplitude
- When power decreases, amplitude decreases

Power is proportional to the wave’s amplitude squared.
- Power ∝ Amplitude2

32
Q

Intensity

A

The concentration of energy in a sound beam

  • Units: W/cm2
  • Determined by: sound source
  • Adjustable: Yes
33
Q

Relationship Between Intensity and Power

A

Intensity and power are proportional to each other.
- When intensity increases, so does power
- When power increases, so does intensity
- Intensity ∝ Power

If a waves power is doubled, the intensity is also doubled.

34
Q

Relationship Between Intensity and Amplitude

A

Intensity and amplitude are directly related to each other.

Intensity is proportional to the wave’s amplitude squared. (Intensity ∝ Amplitude^2)

35
Q

Wavelength

A

The distance or length of one complete cycle

  • Units: meters, mm, cm
  • Determined by: both the source and the medium
  • Adjustable: not by the sonographer

Shorter wavelength sound usually produces higher quality images with greater detail.

36
Q

Relationship Between Wavelength and Frequency

A

Wavelength and frequency are inversely related to each other.

If a waves frequency is doubled, the wavelength is halved.

In soft tissue, sound with a frequency of 1 MHz has a wavelength of 1.54 mm

Wavelength (mm) = 1.54 mm/μs (prop. speed/frequency (MHz)

37
Q

Propagation Speed

A

The distance that a sound wave travels through a medium in one second.

  • Units: meters/sec., mm/μs
  • Determined by: medium
  • Adjustable: not by sonographer
38
Q

Speed of Sound in Soft Tissue

A

The speed of sound in soft tissue is 1,540 m/s, or 1.54 mm/μs

Speed (m/s) = frequency (Hz) x wavelength (m)

39
Q

Speed of Sound in Other Tissues

A

Tissue Type Speed (m/s)

Lung - 500
Fat - 1,450
Soft Tissue - 1,540
Liver - 1,560
Blood - 1,560
Muscle - 1,600
Tendon - 1,700
Bone - 3,500

40
Q

Speed of Sound in Other Media

A

Material Speed (m/s)
Air 330
Water 1,480
Metals 2,000 to 7,000

As a general rule, sound travels fastest in solids, slower in liquids, and slowest in gasses.

41
Q

Stiffness

A

The ability of an object to resist compression

42
Q

Density

A

the mass per unit volume

43
Q

The Relationship Between Stiffness and Speed

A

Stiffness and speed are directly related to each other.

44
Q

The Relationship Between Density and Speed

A

Density and speed are inversely related to each other

If two media are equally stiff, the denser medium will have a lower speed.

Ultrasound Physics (11 decks)

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