Chapter 3: Describing sound waves

Question 1

what do parameters describe?

Answer 1

features of a sound wave

Question 2

what is the source of a sound wave?

Answer 2

the ultrasound system and transducer

Question 3

what is another way parameters can be determined?

Answer 3

by the tissue (medium) through which the sound is traveling

Question 4

what is a period?

Answer 4

the time it takes a wave to vibrate a single cycle, or the time from the start of one cycle to the start of the next cycle

Question 5

what unit is period reported in? what is period determined by?

Answer 5

time (micro secs, secs, hrs, days); sound source only, not by the medium

Question 6

what is the typical value of period in diagnostic ultrasound? is period adjustable?

Answer 6

0.06 to 0.5 microseconds; no, not able to change the period

Question 7

what is frequency? how is the applied in diagnostic ultrasound?

Answer 7

the number of particular events that occur in a specific duration of time; the frequency of a wave is described as the number of cycles that occurs in one second

Question 8

units of frequency?

Answer 8

units per second; 1/ sec or Hertz ( 1 cycle/ sec = 1 hertz)

Question 9

what is the typical value of frequency in clinical imaging?

Answer 9

ranges from 2MHz to 15MHz (2 million to 15 million)

Question 10

what is frequency determined by? is frequency adjustable?

Answer 10

determined by the sound source only, not by the medium; No, cannot change the frequency

Question 11

what is infrasound?

Answer 11

less than 20 Hz

Question 12

what is the frequency of audible sound?

Answer 12

bw 20 and 20,000 Hz

Question 13

what is ultrasound frequncy?

Answer 13

greater than 20,000 Hz

Question 14

why is frequency important?

Answer 14

affect penetration and image quality

Question 15

what is the relationship bw period and frequency?

Answer 15

inversely related; reciprocal

Question 16

what does hertz mean?

Answer 16

events per second

Question 17

what 3 parameters describe size, magnitude, or strength of a sound wave?

Answer 17

amplitude, power, intensity

Question 18

what is amplitude? what does this measure?

Answer 18

“bigness” of a wave; diff bw max/min value and the average value of an acoustic variable

Question 19

what units are used for amplitude?

Answer 19

pressure (Pa), density (g/cm^3), particle motion (distance)

Question 20

what is the typical values of amplitude?

Answer 20

1-3 million pascalst

Question 21

what is amplitude determined by?

Answer 21

sound source only

Question 22

is amplitude adjustable?

Answer 22

yes, can alter initial amplitude of a wave

Question 23

how is amplitude measured?

Answer 23

from the middle (baseline) to the max or minimum value

Question 24

how do you measure peak-to-peak amplitude?

Answer 24

diff bw max and min values of an acoustic variable

Question 25

what is the difference bw amplitude and peak-to-peak amplitude?

Answer 25

peak-to-peak is double

Question 26

what is power? how does this compare to amplitude?

Answer 26

rate of energy transfer; rate at which work is performed; like amplitude, describes the “bigness” of a wave

Question 27

what units is power measured in?

Answer 27

watts

Question 28

what is the typical value of power?

Answer 28

0.004 to 0.090 watts (4 to 90 milliwatts)

Question 29

what determines power? how does this compare to amplitude?

Answer 29

initial power determined by sound source only, power decreases as sound propagates through the body. Rate at which power decreases as sound propagates depends on charac of the medium and wave; same

Question 30

is power adjustable?

Answer 30

yes, can alter initial power of a wave

Question 31

how are power and amplitude related?

Answer 31

power is proportional to the wave’s amplitude squared

Question 32

what is intensity? how is this calculated?

Answer 32

conc of energy in a sound beam; divide the beam’s power by the beam’s cross-sectional area

Question 33

how does intensity relate to the other bigness parameters? what does this depend on?

Answer 33

relates how the power in a wave spreads or is distributed in space. Depends on both power in beam and area over which the power is applied.

Question 34

what units is intensity measured in?

Answer 34

watts/square cm (W/cm^2)

Question 35

what are the typical values of intensity?

Answer 35

0.01 to 300 W/cm^2

Question 36

what is intensity determined by? how it this similar to power and amplitude?

Answer 36

initial intensity determined only by sound source; same, intensity changes as sound propagates through body

Question 37

is intensity adjustable?

Answer 37

yes, can alter initial intensity of a wave

Question 38

what is the formula for intensity?

Answer 38

intensity (W/cm^2)= Power(w)/area (cm^2)

Question 39

how are the 3 bigness parameters related?

Answer 39

directly related; when intensity increases, power and amplitude also increase.

Question 40

what is the relationship bw intensity and power?

Answer 40

intensity is proportional to power

Question 41

what is the relationship bw intensity and amplitude?

Answer 41

intensity is proportional to the wave’s amplitude squared

Question 42

what is true about the relationship bw amplitude, power, and intensity?

Answer 42

amplitude is always squared when compared to power or intensity