Ch 2a Sound Wave Principles Flashcards
Is sound a traveling variation of acoustic variables?
Yes!
What are compressions?
Areas of high pressure + density
What are rarefactions?
Areas of low pressure + density
Differentiate b/w a mechanical + electromagnetic wave?
Mechanical: requires a medium to transport energy
(ex. sound waves are longitudinal mechanical waves)
Electromagnetic: can transfer energy through empty space or a medium
What are acoustic variables? List them all.
Quantities that vary in a sound wave:
-Pressure
-Density
-Particle motion
-Temperature
Do sound waves require a medium to travel through?
Yes!
(sound waves are longitudinal mechanical waves - meaning they travel parallel to wave motion + require a medium)
Differentiate b/w TRV (shear) waves + longitudinal waves?
TRV: particle motion is perpendicular to wave motion (ex. water ripples)
Long: particle motion is parallel to wave motion (ex. sound, u/s)
List 6 sound wave terms?
-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)
What is frequency?
-How often something happens
-# of cycles per second
What is a cycle?
1 complete variation in pressure or acoustic variable
(1 Hz = 1 cycle per sec)
How many Hz are in 1 kHz + 1 mHz?
1 kHz = 1000 Hz
1 mHz = 1,000,000 Hz
How many Hz is u/s?
> 20,000 Hz (20kHz)
How many Hz is human hearing?
20-20,000 Hz
U/s ranges b/w how many mHz for most applications?
B/w 2-20 mHz
What is the period?
Time it takes for 1 cycle to occur
(in microseconds)
What is wavelength?
Length of space 1 cycle takes up
(in mm)
What is propagation speed?
-Speed at which a wave moves through a medium
-Determined by stiffness of the medium
(in m/s or mm/microsec)
The average propagation speed in soft tissue is what?
1540 m/s (1.54 mm/microsec)
How would the propagation speed be in gases, liquids + solids?
Gases: lowest
Liquids: middle
Solids: highest
Do soft or stiff media have higher sound speeds?
Stiff media
What is bulk modulus?
The measure of how resistant a material (solid or fluid) is to compression
Mediums that are more stiff (ex. bone) will contribute higher or lower propagation speeds?
Higher
Mediums that have low stiffness (ex. liquid) will contribute higher or lower propagation speeds?
Lower
Is pulsed u/s continuously on?
No - a pulse is a few cycles of u/s that gets separated in time with gaps of no u/s (ringing + listening period)
Explain what the ringing + listening period is with pulsed u/s?
Ringing (transmission): periods of pulses of sound
Listening (receiving): gaps of no u/s
(1 scan line = 1 pulse transmitted/ringing + received/listening)
Describe PRF, PRP, pulse duration, duty factor, spatial pulse length + bandwidth?
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
If PRF decreases, what happens to the PRP?
It increases
(inversely proportionate: PRF = 1/PRP)
Can PRF + PRP be adjusted by the sonographer?
Yes - by changing depth
Does a shallow image have a high or low PRF?
High PRF
Does a deep image have a high or low PRF?
Low PRF
If PRP increases, what happens to the imaging depth?
It increases - more listening time
(proportionate)
If PRP decreases, what happens to the imaging depth?
It decreases - less listening time
(proportionate)
What 2 things control PRP?
-Depth
-Speed of sound in soft tissue
Is PRP or PRF the ringing + listening time?
PRP
Explain pulse duration?
-Time for pulse to occur + actual time pulse is ON
-Is the ringing (transmission) of pulse
Explain the variables in the following formula: PD = n x T
PD: pulse duration
n: # of cycles in pulse
T: period
U/s pulses are typically how many cycles long?
2 or 3 cycles long
(shorter pulses improve quality of images)
Doppler pulses are typically how many cycles long?
5-30 cycles long
Can PD be changed by the sonographer?
Nope
List the pulse duration for B-mode imaging, 3D imaging, PW + CW doppler?
B-mode: 2-5 cycles
3D: 3-5 cycles
PW: 5-30 cycles
CW: non stop
What is the typical duty factor for sonography + for doppler u/s?
Sono: 0.1-1%
Doppler: 0.5-5%
Does duty factor have a unit?
No, unitless
SPL increases when what increases?
Number of cycles in a pulse increases
SPL decreases when what increases?
Frequency
(inversely related)
Do shorter or longer pulses create higher image quality?
Shorter
As frequency increases what happens to the wavelength, penetration + spatial resolution?
Wavelength: decreases
Penetration: decreases
Resolution: increases
Higher frequency = shorter wavelength = less penetration
As frequency decreases what happens to the wavelength, penetration + spatial resolution?
Wavelength: increases
Penetration: increases
Resolution: decreases
Lower frequency = longer wavelength = greater penetration
What is frequency?
Number of cycles in a wave per second
Do pulsed u/s gaps exist b/w pulses with CW or PW doppler?
PW - meaning there are cycles missing
The shorter the pulse, the broader or smaller the bandwidth?
Broader
Amplitude + intensity are indicators of what?
The strength of the sound
Define amplitude, power + intensity of sound in simple terms?
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
What is amplitude?
-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
Amplitude of a pulse is determined by what?
How hard the crystals of the probe are struck
(displayed as a % or in dB)
What is power?
The rate of energy transfer over time from 1 location to another (energy that travels along the u/s beam)
Other terms for amplitude?
-Transmit voltage
-Output power (shown on our u/s machines)
If the amplitude is doubled, what will happen to the power?
Quadrupled
(power is 2x amplitude)
How can we change beam intensity?
By changing our focus
If amplitude is halved, what happens to the intensity?
It decreases by a factor of 4
If amplitude is doubled + power is quadrupled, what happens to intensity?
It is also quadrupled
