Particle Motion and Wave Propagation Flashcards
1
Q
Describe how an ultrasound image is produced in 5 steps
A
- Sonographer selects a probe and preset based on the requisition 2. An electrical current is sent to the transducer and is converted into sound by the “reverse piezoelectric effect” - (the crystals vibrate causing sound waves) 3. The sound waves travel through the tissue and produce echoes 4. The returning sound waves are converted back to an electrical current by way of the “piezoelectric effect”. 5. The electrical current is processed though the machine and converted into an image one monitor
2
Q
What does ‘acoustic’ mean?
A
Refers to sound
3
Q
What does ‘propagation’ mean?
A
Refers to travel
4
Q
What does ‘acoustic propagation’ mean?
A
Refers to the effects tissue cause on sound
5
Q
What are ‘bioeffects’?
A
Refers to the effects of ultrasound on tissue
6
Q
What is sound?
A
A propagating variation (a wave)
7
Q
What do waves carry?
A
Energy, not matter.
8
Q
What do sound waves require to travel?
A
A medium
9
Q
What is the term for the quality of waves?
A
Variables
10
Q
What variables apply when sound travels through a medium?
A
- Pressure2. Density —> Rarefactions - low density —> Compressions - high density 3. Particle motion4. Temperature
11
Q
What does ‘Rarefaction’ indicate?
A
Low density
12
Q
What does compression indicate?
A
High density
13
Q
How are pressure variations represented?
A
By a sine wave
14
Q
What is a sine wave?
A
Motion over time
15
Q
What do the crests represent in a sine wave?
A
Increased pressure
16
Q
What do the troughs represent in a sine wave?
A
Decreased pressure
17
Q
What is density?
A
The concentration of particles or mass per unit volume.
18
Q
Does a change in pressure effect the density?
A
Yes.A change in pressure = a change in density.
19
Q
When sound travels through a medium how do the particles inside the medium move or vibrate?
A
They oscillate.
20
Q
How is temperature related to sound waves?
A
Sound is an energy.Energy creates heat (friction).
21
Q
What is attenuation?
A
Weakening of sounds as it travels.
22
Q
What type of wave is sound?
A
Mechanical
23
Q
What do mechanical waves require to travel?
A
A medium
24
Q
Can sound travel in a vacuum? Why or why not?
A
No.Because there is no medium in a vacuum.
25
What type of wave is ultrasound?
Mechanical longitudinal
26
What is the partial motion in longitudinal waves?
Back and forth parallel to the direction of travel.
27
What is the partial motion in transverse waves?
Up and down perpendicular to wave travel.
28
Can transverse waves exist in the body? Why or why not?
No, transverse waves cannot exist in liquids and soft tissue is considered a liquid.
29
Can solids, liquids and gases support longitudinal waves?
Yes.
30
Can solids, liquids and gases support transverse waves?
No.Only solids support transverse waves.
31
What is mode conversion?
When one type of wave is converted to another form.Ex. When a UT wave hits a bone, the longitudinal wave is converted to a transverse wave that travels along the bone and therefore isn't reflected back to the transducer. (Shadows appear).
32
What is the simple definition of frequency?
A measurement of how often something happens.
33
What is frequency related to sound?
One cycle per second.(It is the number of complete variations an acoustic variable goes through in one second.)
34
How is frequency represented?
By a sine wave.
35
What is the unit of frequency?
Herts (Hz) which represents cycles per second.Ex. Something repeating 100 times per second so 100 Hz
36
What is the unit for frequency in ultrasound?
Megahertz (MHz)
37
What is the unit of frequency in our probes?
Megahertz (MHz)
38
What is the abbreviation for period?
T
39
What is period?
The time it takes for one cycle to occur.
40
What is the unit of period? Is it the same as the unit used in ultrasound?
No, period is measured in seconds (s) but in ultrasound it is measured in millionths of seconds or μs (microseconds)
41
What is the abbreviation for wavelength?
λ
42
What is wavelength?
The length of space one cycle takes up.(Distance)
43
What unit is wavelength expressed in?
Usually millimetres.
44
Frequency = ?
f = 1/T(One over period)
45
Wavelength =
λ = c/f
46
What is does 'C' mean?
Propagation speed (the speed with which a wave moves through a medium). In UT, the medium is soft tissue therefore C = the speed of sound in soft tissue.
47
What is the constant value for 'c'?
1540 m/s
| 1.54 mm/μs
48
λ is a measure of?
Distance (mm)
49
An increase/decrease in frequency effects period and wavelength how?
If frequency increases, period and wavelength decrease. If frequency decreases, period and wavelength increase.(They have an inverse relationship)
50
What factor determines the propagation speed?
The medium
51
What is 'amplitude'?
The maximum variation (displacement) of a wave. (The strength of the wave determined by the UT machine)
52
What is 'intensity'?
The power of wave divided by the area
53
What is 'power'?
The total energy over the entire cross sectional area.
54
How does a higher amplitude affect the sound?
A higher amplitude = louder.
55
What is intensity?
The concentration of energy in a sound beam.
56
What is the relationship between amplitude and intensity?
I α Amp^2
Doubling the amplitude quadruples the intensity.
(Therefore a small change in amp results in a large change in intensity).
57
Intensity = ?
I = P/a
```
a = area
P = power
```
58
As the area of a beam increases the intensity?
Decreases
Ex. Flashlight beam on a wall example.
59
If intensity doubles, power?
Doubles.
60
In space, where is the intensity of a sound beam the greatest?
The centre.
| It falls off near the periphery.
61
Within a pulse how does the intensity vary?
Starts off high at the beginning and then falls off.
62
What is the intensity during the listening phase of a pulse?
No intensity.
63
What part of the beam is the most intense?
The narrowest part at the centre.
64
What is the 'TP'?
Temporal Peak
| The greatest intensity found in one pulse.
65
What is the 'PA'?
Pulse Average
| The average for all values found in a pulse.
66
Are TP and PA the same?
Almost, TP is slightly greater.
67
What is the 'TA'?
Temporal Average
| Includes the dead time between pulses where there is no intensity (ringing and listening).
68
How are TP and TA related?
| What is the equation?
By the Duty Factor (DF).
DF = TA/TP
69
What is DF?
Duty Factor is the amount of ringing time.
70
What is the SPTP?
The highest intensity (but a very small portion of exposure, only happens for a fraction of a second during an exam).
71
What is SPTA?
What we use in UT for biological considerations because it is the most fair (it takes the average over an entire exam).
72
What is SATA?
The lowest intensity.
73
What is BUR?
Beam Uniformity Ratio.
74
What does BUR relate?
Relates the Spatial Peak and the Spatial Average
75
What is DF?
Duty Factor
76
What does DF relate?
Relates the Temporal Peak and Temporal Average.
77
What is the unit of BUR?
Unitless
78
What is the unit of DF?
Unitless
79
To convert SP to the SA?
Divide by BUR
80
To convert SA to SP?
Multiply by BUR
81
To convert TP to TA?
Multiply by DF
82
To convert TA to TP?
Divide by DF
83
Considering SPTA, what are the different modes of UT from lowest to highest? Give an example of each mode.
1. M mode (lowest) - baby's heartbeat & echo
2. Real time B-mode - normal everyday mode
3. Doppler - colour
4. Continuous wave - vascular & echo (no image)
84
What factor/s are SPTA values dependant on?
Depth.
| As the depth changes the shape changes.
85
What is an artifact?
Something that isn't real on the screen.
86
What is an example of an artifact?
Shadow from a bone.
87
Why do artifacts occur?
Because our UT machines are calibrated to the average speed in soft tissue (1540 m/s) but velocities actually differ in different types of tissue and as a result artifacts may appear.
88
What is the velocity of fat?
1460 m/s
89
What is the velocity of bone?
4080 m/s
90
What happens when sound travels through fat?
Things may appear deeper than they actually are because it takes sound longer to travel through fat than regular tissue.
91
What is the range equation?
D = C x t OR t = D/C
```
D = distance to the reflector and back
C = average speed of sound in soft tissue
t = time for the round trip
```
92
What is the range equation used to calculate?
The distance of a reflector from the probe.
93
To find the distance to the reflector using the range equation what do we do?
Divide the answer by two.
| Equals one way trip
94
How long does it take for sound to travel out and back to a depth of 1 cm?
13 μ/s to get to 1 cm and back.
95
What does D(gr) mean?
Go return distance
