Physics of Ultrasound 1-4 Flashcards
1
Q
What is A mode?
A
Amplitude Mode
2
Q
What is B-Mode?
A
Brightness Mode
3
Q
What is M-Mode?
A
Motion Mode
(B-Mode vs. Time)
4
Q
Which ultrasound mode has the best temporal resolution?
A
M-Mode
5
Q
What correlates to the strength of the echo on ultrasound?
A
Brightness of the image
6
Q
When you look at an M-mode example, what do you see on the:
X-axis?
Y-axis?
A
X-axis = Time
Y-axis = Depth
7
Q
What is seen in this M-Mode clip?
A
Early closure of the aortic leaflets
HOCM
8
Q
Draw an EKG comparing Systole and Diastole
A
9
Q
Draw what you would expect a normal Aortic Valve Appears like in M-mode in AV LAX.
A
See image
10
Q
Draw what you would expect a bicuspid Aortic Valve Appears like in M-mode in AV LAX.
A
See image
11
Q
What is the period in terms of ultrasounds?
A
Time it takes to complete a single cycle
12
Q
What is frequency?
A
Number of cycles per second
13
Q
What is the pulse duration?
A
Time to complete a single pulse
14
Q
What is the pulse repetition period?
A
Time is takes to go from pulse to pulse
15
Q
What is the pulse repetition frequency?
A
Inverse of Pulse repetition period
OR
Number of pulses per second
16
Q
What is 1/2 of the Pulse Repetition Frequency?
A
Nyquist Limit
(Max doppler shift before aliasing occurs)
17
Q
What is a spatial pulse length?
A
Length of a single pulse
18
Q
What is a wavelength
A
Length (distance of one cycle)
19
Q
What resolution correlates to spatial pulse length?
A
Axial Resolution
Axial resolution = 1/2 of the Spatial Pulse Length
20
Q
What is amplitude?
A
Difference between the average acoustic variable and the peak acoustic max variable
21
Q
What is Power?
A
Amount of Work per unit time
Measured in: Watts or (Joules / second)
Said another way…….
Rate of Energy transfer = Rate at which work is performed
22
Q
What is intensity?
A
Power per unit area (Watts/cm2)
23
Q
What resolution does the pulse repetition frequency determine?
A
Temporal Resolution
24
Q
What sound property is important for bioeffects of ultrasound?
A
Intensity
25
What is spatial resolution?
**Ability to discern the correct space (place) of a structure**
Said another way....
**Ability to accureately create images of small structures in their correct anatomic position**
26
What are the three types of spatial resolution?
1. Axial
2. Lateral
3. Elevational
27
**Axial** resolution is proportional to ...?
Pulse Length
28
**Lateral** resolution is proportional to ...?
Beam Width
29
**Elevational** resolution is proportional to ...?
Beam Height
30
What is the equation for axial resolution?
Axial resolution = 1/2 of the Pulse Length
31
What is the relationship for higher frequency ultrasound for:
*_Spatial Pulse Length*_ and _*Axial Resolution_*?
**Higher** Frequency = **Shorter** Spatial Pulse Length = **Better** Axial Resolution
32
What is Ultrasound in hertz?
**\>20,KHz**
1 KHz = 1 Kilo Hertz = 1000 Hz
33
What does increasing frequency do to attenuation?
Increased **frequency** = Increased **attenuation**
## Footnote
As the ultrasound beam travels through the body it loses energy. The intensity and amplitude of the sound wave decreases, and this process is known as **attenuation**.
The amount of **attenuation** that occurs will depend on the type of tissue the sound wave is traveling through. Where the molecules of the tissue are densely packed (such as bone), attenuation will be much greater than in less densely packed tissue (such as fat). Different tissues have different **attenuation** coefficients depending on the amount of attenuation occurring in the beam of sound.
34
How does attenuation change with increasing depth
Decreases (See image)
35
What is temporal resolution?
Abiltiy to accurately determine the position of a structure at a particular instant in time
36
What is frame rate?
The number of framees/sec = # images /sec
37
How does the pulse repetition frequency correlate to frame rate?
Proportional (Directly)
38
What are the 4 acoustic variables of a sound wave?
1. Pressure
2. Density
3. Temperature
4. Distance
39
What are the 3 mechanisms for Bioeffects?
1. Thermal Effects
2. Cavitation
3. Physical Vibration
40
What is maximal heating related to?
Spatial peak temporal average (SPTA) intensity
41
What temperature flux do we want to limit the U/S exposure to produce in local tissue temperature?
1 degree Celcius
42
What is the Maximum Spatial peak temporal average (SPTA) intensity for *_Unfocused_* beam?
\<1 Watt / cm2
43
What is the Maximum Spatial peak temporal average (SPTA) intensity for *_Focused_* beam?
\< 100 milli Watt/cm2 (0.1 Watts)
44
What is the mechanical index of an ultrasound?
Strength of Ultrasound beam and the ability of the beam to produce cavitation (Bursting of bubbles) of contrast material
45
What is the formula for mechanical index?
Peak negative pressure / (Frequency) 1/2
46
What do high mechanical index ultrasound. beams cause?
Microbubbles of contrast materal to be compressed and expand significantly and to even burst (Cavitation)
47
What does the shrinking and expanding of bubbles create?
New frequencies (Harmonic freqencies) different from the frequency of the original sound beam so the ultrasound transduce will receive echos containing the original frequency and the new harmonic frequency
48
What two variables does the mechanical index depend on?
1. Frequency
2. Pressure
49
How does the mechanical index changes given:
1. Changes in frequency?
2. Changes in pressure?
MI increases with **lower** *_frequency_*
MI increases with **stronger** (higher *_pressure_* variation)
50
When are the strongest harmonic frequencies produced under ultrasound?
Mechanical Index (MI) of \>1
51
No harmonics are seen at what Mechanical index value?
MI **\< 0.1**
Linear beahvior of bubble shrinking and expanding and this produces no harmonics but instead produces only **backscatter**
52
What are the two types of harmonics?
1. Tissue harmonics
2. Contrast harmonics
53
Tissue harmonics only exist at ... (what)?
Deeper depths
Center main axis
54
What is resonance in terms of harmonics?
Uneven shrinking and expanding of bubbles
55
When you have a MI \>1,
what is present?
**Strong resonance** and **Cavitation** (Lots of harmonics)
56
When you have a MI 0.1 0 1
what is present?
**Resonance** (harmonics generated)
57
When you have a MI \< 0.1,
what is present?
No harmonics
58
What is different from the Pulse Duation to Pulse Repetition Period?
Pulse Repititon Period = **Pulse Duration** + **Listening time**
59
What is velocity of an ultrasound determined by?
**Medium** only
| (Not the source)
60
What are main properties of the medium that determine velocity of the medium?
1. Stiffness
2. Density
61
How does **stiffness** of the medium affect **velocity**?
(Of ultrasound waves)
More stiff = higher velocity
62
How does **density** of the medium affect **velocity**?
(Of ultrasound waves)
**Increasing** density = **Decrease** velocity
(
63
Why do sound waves tend to travel faster in more dense materials?
\*Tommy Burch describes this paradox\*
Sound travels faster in higher density material **because they are more stiff** because stiffness differences among materials are usually larger than density differences
64
What is the relationship between frequency and attenuation?
Frequency increases = Attenuation increases
65
What is impedance?
Acoustic resistance to sound traveling through a medium
66
What is the formula for acoustic impedance?
**Z = P x V**
Z = Acoustic Impedance
P = Density
V = Velocity
67
What is acoustic impedance dependent on:
Source or Medium?
Medium Only
68
What does a transducer do in its simplist definition?
Convert one from of energy to another
69
What is the function of piezoelectric crystals?
Convert voltage to ultrasound
70
What is the Curie Temperature?
Threshold temperature in which the piezoelectric crystals are dead
71
What is the backing material on an ultrasound?
*_Function_*?
Backing material = Damping material = Deceases "ringing" of crytals
*_Function = Decreases spatial pulse length and improves axial resolution and decreases sensitivity to reflected echoes_*
72
What is Q factor?
Unitless number that represents the ability of the machine to emit a "clean" pulse with a narrow beam length
73
What is the formula for Q factor?
RF / Bandwidth
74
Which transducers have a low QF?
Which transducers have a high QF?
Low QF (**Imaging** transducers) i.e. high bandwidth and short SPL
High QF (**Therapeutic** transducers)
75
For **continuous** wave doppler, what is the frequency determined by?
Electrical frequency of the voltage
76
For **pulse** wave doppler, what is the frequency determined by?
U/S System
Resonant Frequency
77
What is the resonant frequency formula?
**RF (Resonant Frequency) = V / 2T**
V = Velocity
T = Thickness
78
What is the bandwidth?
Difference between highest and lowest frequency pulse
79
What phenomenon will increase your bandwidth?
Damping
80
How does SPL correlate to bandwidth?
Shorter SPL = Higher BW
81
How does QF relate to RF and Bandwidth?
QF = RF / Bandwidth
82
What is the focus of an ultrasound beam?
**Most narrow portion** of an ultrasound sound beam
said another way
**Focus = Location of the Minimum diameter of the beam**
83
What is the **near field** of a sound beam?
Space between near field and focus of a sound beam
84
What is the **far field** of an ultrasound beam?
Space between **far field** and focus of a sound beam
85
What is another name for the far field or far zone of the sound beam?
Fraunhofer Zone
86
What is the formula for the near field length?
**Ln = r2/wavelength**
Ln = Near Field Length
r = Radius of the crystal
87
What is another term for near field length?
Focal Length
88
If you have a higher frequency, how will this affect the focal length?
**Longer focal length**
| (Higher frequency = Lower wavelength)
89
What are the three types of spatial resoluation?
1. **LARD** - longitudinal, axial, radial, range, and depth resolution
2. **LATA** - Lateral, Angular, Transverse and Azimuthal.
3. Elevational
90
What is the formula for axial resolution?
1/2 Spatial Pulse Length
91
What is range resolution?
**Descibes the ability to discern the specific depth** (range ~ location) of a reflector (Describes pulsed U/S)
92
What is the doppler equation?
**Change in Frequency = v \* cos(Angle) \* 2Ftransmitted / C**
Change in Frequency = Doppler shift
v = 1540 m/s
93
What is fast fourier transform?
Current method of PW and CWD analysis
94
What are the 5 functions of a receiver?
1. Amplification
2. Compensation
3. Compression
4. Demodulation
5. Rejection
95
What does amplification of the receiver do?
Enlargement of the returning signals
AKA
Receiver gain = Overall gain
96
What does **compensation** do?
**Makes all echos from similar structures appear with similar brightness**
AKA
Time Gain Compensation
Depth Gain Compensation
Swept gain compensation
97
What does compression do?
Reduces the total rnage of signals from smallest to largest
Dynamic range.= Range of signals that can be processed by the ultrasound machine
**Compression decreases the dynamic range**
98
What is the function of demodulation?
Changes the shape of the electrical signal to make it recognizable by the image screen
99
What are the 2 steps of demodulation?
1. **Rectification** (Turn all negative voltages positive)
2. **Smoothing** - smoothes out signals
100
What is the purpose of rejection?
Low level signals are ignored (Noise)
101
What are the other two names for rejection?
1. Threshold
2. Suppression
102
What is the sound of speed in m/s?
1540 m/s
103
What is the sound of speed in mm/microsecond?
1.54 mm/microsecond
104
What are the two types of reverberation?
Ring down artifact
Comet Tail
**Image shows Ring down and comet tail artifact**
105
What is seen at the green arrow?
Reverberation artifact
## Footnote
**Comet Tail seen here**
106
Why can we not see the septal wall (Green arrows)?
Thick calcified mitral valve causes ***_Acoustic Shadowing_***
107
What is the formula for resonant frequency (RF) of a piezoelectric crystal?
RF = Velocity / (2\*Thickness)
\*\*Remember, the more thin the crystal, the higher the resonant frequency\*\*
108
Which of the following is associated with cavitation of microbubbles present in an ultrasound contrast agent?
A. High frequency ultrasound
B. Low pressure ultrasound
C. High mechanical index (MI) ultrasound
D. High velocity ultrasound
E. Low intensity ultrasound
**High mechanical index (MI) ultrasound**
## Footnote
Mechanical index is an indication of an ultrasound beam's ability to cause cavitation-related bioeffects, and this is currently thought a reasonable proxy for micromechanical damage. It is "strictly a cavitation index," but is meant to be interpreted more broadly as tissue mechanical stress/damage.
109
An ultrasound contrast agent is exposed to an ultrasound beam with a high mechanical index (MI \>1). Which is the following is more likely true?
1. The sound beam has high frequency
2. The sound beam has a low peak negative pressure
3. The strength of the sound beam is low
4. The contrast agent will experience bubble disruption and production of strong harmonic frequencies
**D = The contrast agent will experience bubble disruption and production of strong harmonic frequencies**
110
Which of the following is true with regard to harmonic imaging using contrast agents?
A. Harmonic are only produced when the mechanical index \> 0.1
B. The harmonic signals are stronger than tissue harmonics
C. Harmonic signals result from microbubble disruption
D. Harmonic signals result from microbubble resonance
E. All of the above
All of the above
111
Which of the following is true with regard to tissue harmonic imaging?
A. Tissue harmonics are created during transmission through tissues
B. Tissue harmonics are NOT present as sound leaves the transducer but are only present deeper in the tissue
C. Tissue harmonics are weaker than the harmonics created by contrast agents
E. All of the above
F. None of the above
**All of the above**
