# Ch 3: Describing Sound Waves Flashcards

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1
Q

The source of the sound wave is the…

A

ultrasound system and transducer.

2
Q

The medium is the…

A

tissues through which the sound is traveling.

3
Q

Period is the…

A

time it takes a wave to vibrate a single cycle; the timefrom the start of one cycle to the start of the next cycle.

4
Q

Period is reported in units of…

A

time, such as microseconds, seconds, hours, or days.

5
Q

The typical value of period in diagnostic u/s is…

A

.06 to .5 microseconds.

6
Q

Period is determined by…

A

the sound source only, not by the medium.

7
Q

Is period adjustable by the sonographer?

A

No.

8
Q

Frequency is…

A

the number of particular events that occur in a specific duration of time. In u/s, the # of cycles per second.

9
Q

Frequency is reported in units of…

A

per second, 1/second, hertz, or Hz.

10
Q

In clinical imaging, the typical frequency range is…

A

from approximately 2 MHz to 15 MHz.

11
Q

Frequency is determined by…

A

the sound source only.

12
Q

Is frequency adjustable by the sonographer?

A

No.

13
Q

Sound is described as infrasonic if its frequency is…

A

less than 20 Hz.

14
Q

Sound is described as audible if its frequency is…

A

between 20 Hz and 20,000 Hz.

15
Q

Sound is described as ultrasonic if its frequency is…

A

higher than 20,000 Hz (20 kHz).

16
Q

How are period and frequency related to each other?

A

Inversely. As one increases, the other decreases.

17
Q

Period and frequency have a special inverse relationship called…

A

reciprocal. If multiplied together, the result is one.

18
Q

Amplitude is…

A

the ‘bigness’ of a wave; the difference between the maximum (or minimum) value and the baseline value.

19
Q

Amplitude is reported in units of…

A

pressure (pascals or Pa), density (g/cm^3), particle motion (any distance), or decibels (dB).

20
Q

In clinical imaging, typical amplitude ranges from…

A

1 million pascals to 3 million pascals.

21
Q

Amplitude is determined by the…

A

sound source (though it does decrease as the wave travels through the body).

22
Q

Is amplitude adjustable by the sonographer?

A

Yes.

23
Q

Peak-to-peak amplitude is…

A

the difference between the maximum and minimum values (not just between one extreme and the baseline).

24
Q

Power is the…

A

rate of energy transfer; the rate at which work is performed.

25
Q

Power is reported in units of…

A

watts (W).

26
Q

In clinical imaging, typical power ranges from…

A

.004 to .09 watts.

27
Q

Power is determined by the…

A

sound source (though the power decreases as the wave travels through the body).

28
Q

Is power adjustable by the sonographer?

A

Yes.

29
Q

The bigger the wave, the more energy is transferred. So as the amplitude changes, power changes proportionally. What is the proportion?

A

Power is proportional to amplitude SQUARED.

30
Q

Intensity is…

A

the concentration of energy in a sound beam.

31
Q

Intensity is reported in units of…

A

watts/square centimeter (W/cm^2).

32
Q

In clinical imaging, typical intensity ranges from…

A

.01 to 300 W/cm^2.

33
Q

Intensity is determined by…

A

the sound source (though the wave gets less intense as it travels through the body).

34
Q

Is intensity adjustable by the sonographer?

A

Yes.

35
Q

The ‘bigness’ parameters are all directly related. What is the proportion of intensity to power?

A

One to one. If a wave’s power is doubled, the intensity is doubled. If a wave’s power is quartered, the intensity is quartered.

36
Q

What is the proportion of intensity to amplitude?

A

Intensity is proportional to amplitude SQUARED.

37
Q

Wavelength is…

A

the length of one complete cycle.

38
Q

Wavelengh is reported in units of…

A

mm, meters, or any length.

39
Q

In clinical imaging, wavelength in soft tissue ranges from…

A

.1 to .8 mm.

40
Q

Wavelength is determined by…

A

both the sound source and the medium.

41
Q

Is wavelength adjustable by the sonographer?

A

No.

42
Q

What is the relationship between wavelength and frequency?

A

They are inversely related. As one increases, the other decreases.

43
Q

What is the wavelength of 1 MHz sound in soft tissue?

A

1.54 mm

44
Q

How do you find the wavelength of a sound wave in soft tissue?

A

wavelength (mm) = 1.54 mm per microseconds divided by frequency (MHz)

45
Q

Why is wavelength important in u/s?

A

Shorter wavelengths are created by higher frequency sound. The higher the frequency, the clearer the image.

46
Q

Propagation speed is…

A

the rate at which a sound wave travels through a medium.

47
Q

Speed is reported in units of…

A

distance divided by time (m/s, mm/microseconds, or miles per hour).

48
Q

In the body, the speed of sound ranges from…

A

500 m/s to 4,000 m/s depending on the tissue.

49
Q

Speed is determined by…

A

the medium.

50
Q

Is speed adjustable by the sonographer?

A

No.

51
Q

What is the speed of sound in soft tissue?

A

1,540 m/s

52
Q

What is the speed of sound in lung tissue?

A

500 m/s

53
Q

What is the speed of sound in bone?

A

3,500 m/s

54
Q

What two characteristics determine the speed of sound in a given medium?

A

Stiffness and density

55
Q

Stiffness describes…

A

the ability of an object to resist compression.

56
Q

How are stiffness and speed related to each other?

A

Directly. The stiffer the material, the faster the sound’s speed.

57
Q

What other terms describe stiffness?

A

Bulk modulus (same as stiff), elasticity and compressability (opposite of stiff)

58
Q

Density describes…

A

the relative weight of a material.

59
Q

How are density and speed related to each other?

A

Inversely. The denser the material, the slower the sound’s speed.

60
Q

Is stiffness or density more important to speed?

A

Stiffness has the greater influence.