Ch 2a Sound Wave Principles

Question 1

Is sound a traveling variation of acoustic variables?

Answer 1

Yes!

Question 2

What are compressions?

Answer 2

Areas of high pressure + density

Question 3

What are rarefactions?

Answer 3

Areas of low pressure + density

Question 4

Differentiate b/w a mechanical + electromagnetic wave?

Answer 4

Mechanical: requires a medium to transport energy
(ex. sound waves are longitudinal mechanical waves)

Electromagnetic: can transfer energy through empty space or a medium

Question 5

What are acoustic variables? List them all.

Answer 5

Quantities that vary in a sound wave:

-Pressure
-Density
-Particle motion
-Temperature

Question 6

Do sound waves require a medium to travel through?

Answer 6

Yes!

(sound waves are longitudinal mechanical waves - meaning they travel parallel to wave motion + require a medium)

Question 7

Differentiate b/w TRV (shear) waves + longitudinal waves?

Answer 7

TRV: particle motion is perpendicular to wave motion (ex. water ripples)

Long: particle motion is parallel to wave motion (ex. sound, u/s)

Question 8

List 6 sound wave terms?

Answer 8

-Frequency (# cycles per sec)
-Period (time for 1 cycle to occur)
-Wavelength (length 1 cycle takes up)
-Propagation speed (speed wave moves through medium)
-Amplitude (how loud)
-Intensity (rate energy passes through area)

Question 9

What is frequency?

Answer 9

-How often something happens
-# of cycles per second

Question 10

What is a cycle?

Answer 10

1 complete variation in pressure or acoustic variable

(1 Hz = 1 cycle per sec)

Question 11

How many Hz are in 1 kHz + 1 mHz?

Answer 11

1 kHz = 1000 Hz
1 mHz = 1,000,000 Hz

Question 12

How many Hz is u/s?

Answer 12

> 20,000 Hz (20kHz)

Question 13

How many Hz is human hearing?

Answer 13

20-20,000 Hz

Question 14

U/s ranges b/w how many mHz for most applications?

Answer 14

B/w 2-20 mHz

Question 15

What is the period?

Answer 15

Time it takes for 1 cycle to occur

(in microseconds)

Question 16

What is wavelength?

Answer 16

Length of space 1 cycle takes up

(in mm)

Question 17

What is propagation speed?

Answer 17

-Speed at which a wave moves through a medium
-Determined by stiffness of the medium

(in m/s or mm/microsec)

Question 18

The average propagation speed in soft tissue is what?

Answer 18

1540 m/s (1.54 mm/microsec)

Question 19

How would the propagation speed be in gases, liquids + solids?

Answer 19

Gases: lowest
Liquids: middle
Solids: highest

Question 20

Do soft or stiff media have higher sound speeds?

Answer 20

Stiff media

Question 21

What is bulk modulus?

Answer 21

The measure of how resistant a material (solid or fluid) is to compression

Question 22

Mediums that are more stiff (ex. bone) will contribute higher or lower propagation speeds?

Answer 22

Higher

Question 23

Mediums that have low stiffness (ex. liquid) will contribute higher or lower propagation speeds?

Answer 23

Lower

Question 24

Is pulsed u/s continuously on?

Answer 24

No - a pulse is a few cycles of u/s that gets separated in time with gaps of no u/s (ringing + listening period)

Question 25

Explain what the ringing + listening period is with pulsed u/s?

Answer 25

Ringing (transmission): periods of pulses of sound Listening (receiving): gaps of no u/s (1 scan line = 1 pulse transmitted/ringing + received/listening)

Question 26

Describe PRF, PRP, pulse duration, duty factor, spatial pulse length + bandwidth?

Answer 26

PRF: # of pulses occurring in 1 sec PRP: time from start of 1 pulse to start of next PD: actual time pulse is on DF: fraction of time that pulsed u/s is on SPL: length of space occupied by a pulse Bandwidth: range of frequencies contained within a pulse

Question 27

If PRF decreases, what happens to the PRP?

Answer 27

It increases (inversely proportionate: PRF = 1/PRP)

Question 28

Can PRF + PRP be adjusted by the sonographer?

Answer 28

Yes - by changing depth

Question 29

Does a shallow image have a high or low PRF?

Answer 29

High PRF

Question 30

Does a deep image have a high or low PRF?

Answer 30

Low PRF

Question 31

If PRP increases, what happens to the imaging depth?

Answer 31

It increases - more listening time (proportionate)

Question 32

If PRP decreases, what happens to the imaging depth?

Answer 32

It decreases - less listening time (proportionate)

Question 33

What 2 things control PRP?

Answer 33

-Depth -Speed of sound in soft tissue

Question 34

Is PRP or PRF the ringing + listening time?

Answer 34

PRP

Question 35

Explain pulse duration?

Answer 35

-Time for pulse to occur + actual time pulse is ON -Is the ringing (transmission) of pulse

Question 36

Explain the variables in the following formula: PD = n x T

Answer 36

PD: pulse duration n: # of cycles in pulse T: period

Question 37

U/s pulses are typically how many cycles long?

Answer 37

2 or 3 cycles long (shorter pulses improve quality of images)

Question 38

Doppler pulses are typically how many cycles long?

Answer 38

5-30 cycles long

Question 39

Can PD be changed by the sonographer?

Answer 39

Nope

Question 40

List the pulse duration for B-mode imaging, 3D imaging, PW + CW doppler?

Answer 40

B-mode: 2-5 cycles 3D: 3-5 cycles PW: 5-30 cycles CW: non stop

Question 41

What is the typical duty factor for sonography + for doppler u/s?

Answer 41

Sono: 0.1-1% Doppler: 0.5-5%

Question 42

Does duty factor have a unit?

Answer 42

No, unitless

Question 43

SPL increases when what increases?

Answer 43

Number of cycles in a pulse increases

Question 44

SPL decreases when what increases?

Answer 44

Frequency (inversely related)

Question 45

Do shorter or longer pulses create higher image quality?

Answer 45

Shorter

Question 46

As frequency increases what happens to the wavelength, penetration + spatial resolution?

Answer 46

Wavelength: decreases Penetration: decreases Resolution: increases Higher frequency = shorter wavelength = less penetration

Question 47

As frequency decreases what happens to the wavelength, penetration + spatial resolution?

Answer 47

Wavelength: increases Penetration: increases Resolution: decreases Lower frequency = longer wavelength = greater penetration

Question 48

What is frequency?

Answer 48

Number of cycles in a wave per second

Question 49

Do pulsed u/s gaps exist b/w pulses with CW or PW doppler?

Answer 49

PW - meaning there are cycles missing

Question 50

The shorter the pulse, the broader or smaller the bandwidth?

Answer 50

Broader

Question 51

Amplitude + intensity are indicators of what?

Answer 51

The strength of the sound

Question 52

Define amplitude, power + intensity of sound in simple terms?

Answer 52

Amplitude: how loud (represented by the height of the wave) Power: time required to transfer energy Intensity: rate that energy passes through a unit area

Question 53

What is amplitude?

Answer 53

-Max variation that occurs in an acoustic variable (pressure, density, particle motion, temp) -How much the acoustic variable changes as the sound wave travels through a medium

Question 54

Amplitude of a pulse is determined by what?

Answer 54

How hard the crystals of the probe are struck (displayed as a % or in dB)

Question 55

What is power?

Answer 55

The rate of energy transfer over time from 1 location to another (energy that travels along the u/s beam)

Question 56

Other terms for amplitude?

Answer 56

-Transmit voltage -Output power (shown on our u/s machines)

Question 57

If the amplitude is doubled, what will happen to the power?

Answer 57

Quadrupled (power is 2x amplitude)

Question 58

How can we change beam intensity?

Answer 58

By changing our focus

Question 59

If amplitude is halved, what happens to the intensity?

Answer 59

It decreases by a factor of 4

Question 60

If amplitude is doubled + power is quadrupled, what happens to intensity?

Answer 60

It is also quadrupled