Chapter 14: Ultrasound Flashcards
1
Q
A modality that uses Ultrasound Energy and the Acoustic properties of the body to produce an image from stationary and moving tissues.
A
Medical Diagnostic Ultrasound
2
Q
The type of energy delivered to the tissues of the body when performing Ultrasound.
A
Short Pulse of Mechanical Energy
3
Q
Discuss the propagation of Sound in Ultrasound.
A
Sound is a mechanical energy that propagates through a CONTINUOUS, elastic medium by COMPRESSION and RAREFRACTION of particles comprising it.
Note:
Rarefraction occurs following Compression event.
4
Q
Type of wave where energy propagation occurs as a wave front in the direction energy travel:
A
LONGITUDINAL WAVE
5
Q
This is the distance between compressions or rarefractions, or between any two points that repeat on the sinusoidal wave of pressure amplitude.
A
WAVELENGTH of Ultrasound Energy
6
Q
This refers to the number of times the wave oscillates through one cycle each second.
A
FREQUENCY
7
Q
Frequency Sound waves of INFRASOUND
A
Less than 15 cycles per second (Hz)
8
Q
Range of sound waves comprising the AUDIBLE ACOUSTIC SPECTRUM
A
15Hz to 20 kHz
9
Q
The frequency range of sound waves for Ultrasound
A
Above 20kHz
10
Q
This refers to the time duration of one wave cycle.
A
PERIOD
11
Q
This refers to the distance traveled by the wave per unit time.
=wavelength/period
A
SPEED OF SOUND
12
Q
Average speed of sound of soft tissues:
A
1540 m/s
154,000cm/s or 1.5mm/us
13
Q
Average speed of sound of fatty tissues:
A
1450 m/s
14
Q
Average speed of sound of air:
A
330 m/s
15
Q
What is the speed of sound utilized in the medical ultrasound machine in determining the localization of reflectors and creating the acoustic image?
A
1540 m/s
16
Q
Ultrasound frequencies needed for body parts requiring greater travel distance of sound waves (ABDOMEN):
A
Lower Frequency Ultrasound of 3.5 to 5.0 MHz
17
Q
Ultrasound frequencies needed for small body parts or organ closed to skin surface (THYROID and BREAST):
A
Higher Frequency Ultrasound of 7.5 to 10 MHz
18
Q
What is the ultrasound frequency range of most Medical Imaging Applications?
A
2 to 10 MHz
19
Q
This is defined as the peak maximum or peak minimum value from the average pressure on the medium in the absence of a sound wave.
A
PRESSURE AMPLITUDE
20
Q
What is the SI unit of Pressure?
A
Pascal (Pa) = Newton/m2
21
Q
This refers to the Amount of power per unit area (energy per unit).
This is proportional to the square of the pressure amplitude.
A
INTENSITY (I)
22
Q
What is the unit of Intensity?
The amount of energy per unit time per unit area.
A
Milliwatts/cm2
23
Q
The relative intensity and pressure levels are described as a logarithmic ratio:
A
DECIBEL (dB)
24
Q
Discuss the relation of Intensity ratio with the decibels.
A
Intensity ratio > 1.0 = dB values are positive
Intensity ratio < 1.0 = dB values are negative
25
This occurs between 2 tissue boundaries where there is a difference in the acoustic impedance of adjacent materials.
REFLECTION
26
A conduit of tissue that allows ultrasound transmission through structures such as the lung.
ACOUSTIC WINDOW
27
This gives rise to the differences in transmission and reflection of ultrasound energy.
which is the means of producing image using pulse echo techniques.
ACOUSTIC IMPEDANCE
28
What is the SI unit of Acoustic Impedance?
rayl
1 rayl = kg/(m2s)
29
This described the change in the direction of the transmitted ultrasound energy with nonperpendicular incidence or the beam is not perpendicular to the boundary.
REFRACTION
30
This occurs by reflection or refraction, causes the beam to diffuse in many directions, and gives rise to the characteristic texture and grayscale in the acoustic image.
SCATTERING
31
A smooth boundary between 2 media, where the dimensions of the boundary are much larger than the wavelength of the incident ultrasound energy.
SPECULAR REFLECTOR
32
Discuss echogenicity in relation ro scatter amplitude.
HYPERECHOIC - higher scatter amplitude
| HYPOECHOIC - lower scatter amplitude
33
This refers to the loss of acoustic energy with distance traveled or loss of intensity of the ultrasound beam caused by tissue absorption and scattering in the beam or medium.
ATTENUATION
34
The process whereby the acoustic energy is converted to heat energy.
ABSORPTION
35
This refers to the relative intensity loss per centimeter of travel for a given medium.
ATTENUATION COEFFICIENT
36
What is the unit of Attenuation Coefficient?
dB/cm
37
What is the Half Value Layer or Thickness of the Ultrasound?
3dB reduction in intensity
38
This material comprised of one or more ceramic elements with electrochemical properties and peripheral components used to produce and detect Ultrasound.
TRANSDUCER
39
What are the major components of Ultrasound Transducer? (STAMP-BIT)
```
Sensor Electrodes
Tuning Coil
Acoustic Absorber
Matching Layer
Piezoelectric Material
```
Backing Block
Insulating Cover
Transducer Housing
40
This is the functional component of the transducer that converts the electrical energy into mechanical energy.
PIEZOELECTRIC MATERIALS
41
A synthetic piezoelectric ceramic with a compound structure of molecular dipole most often used in Ultrasound Transducer for Medical Imaging Application.
Lead-Zirconate-Titanate (PZT)
42
This structure is layered on the back of the piezoelectric element, absorbs the backward directed ultrasound energy, and attenuates stray ultrasound signals from the housing.
DAMPING BLOCK
43
This provides the interface between the raw transducer element and the tissue.
This minimizes the acoustic impedance differences between the transducer and the patient.
MATCHING LAYER
44
Typically, 128-512 individual rectangular elements comprised of transducer assembly.
TRANSDUCER ARRAYS
45
This is the largest transducer assembly which typically contains 256-512 elements.
LINEAR ARRAY TRANSDUCER
46
This transducer assembly comprised of 64-128 individual elements in a smaller package.
PHASED ARRAY TRANSDUCER
47
This is another method of producing high frequency ultrasound which is made of silicon based electrostatic transducers. The basic element is a capacitor cell with a fixed electrode (backplate) and a free electrode (membrane).
CAPACITIVE MICROMACHINED ULTRASONIC TRANSDUCER (CMUT)
48
What is the principle of operation in CMUT?
ELECTROSTATIC TRANSDUCTION
- alternating voltage is applied between membrane and backplate, and the modulation of electrostatic force results in membrane vibration with generation of ultrasound.
49
What are the 2 distinct beam patterns of Ultrasound?
1. Near Field
| 2. Far Field
50
A beam pattern which is adjacent to the transducer and has a slightly converging beam profile out to a distance determined by the geometry and frequency of transducers.
NEAR FIELD
51
Another term for Near Field.
FRESNEL ZONE
52
This describes a large transducer surface as an infinite number of point sources of sound energy where each point is characterized as a Radial Emitter.
HUYGENS’ PRINCIPLE
53
This type of beam pattern has a diverging beam beyond that point.
It is where the beam diverges.
FAR FIELD
54
Another term for Far Field?
FRAUNHOFER ZONE
55
The function of the transducer diameter, the center of operating frequency.
FOCAL DISTANCE
56
A method to rephrase the signals by dynamically introducing electronic delays as function of depth.
DYNAMIC RECEIVE FOCUSING
57
Increases the number of active receiving elements in the array with reflector depth, so that the lateral resolution does not degrade with the depth of propagation.
DYNAMIC APERTURE
58
Unwanted emissions of ultrasound energy directed away from the main pulse, caused by radial expansion and contraction of the transducer element.
SIDE LOBES
59
Results when ultrasound energy is emitted far off axis by multielement arrays.
GRATING LOBES
60
Major factor that limits the spatial resolution and visibility of detail.
Volume of Acoustic Pulse
61
3 Components of Spatial Resolution that determines the minimal volume element.
1. Axial Dimension
2. Lateral Dimension
3. Elevational (size thickness) Dimension
62
This refers to the ability to discern 2 closely spaced objects in the DIRECTION of the beam.
Equal to 1/2 SPL - Spatial Pulse Length
AXIAL RESOLUTION
63
This refers to the number of cycles emitted per pulse by the transducer multiplied by the wavength.
Spatial Pulse Length (SPL)
64
Refers to the ability to discern as a separate 2 closely objects PERPENDICULAR to the beam direction.
LATERAL RESOLUTION.
65
Another term for Lateral Resolution.
AZIMUTHAL RESOLUTION
66
A component of spatial resolution that is perpendicular to the image plane and is dependent on the transducer element width.
ELEVATIONAL RESOLUTION
67
Another term for Elevational Resolution.
Slice Thickness Dimension
68
This is the weakest measure of resolution for array transducers.
SLICE THICKNESS
69
What are the components of the Pulse Echo Approach for Image Information? (BP-RADS)
Beam Former
Pulser
Receiver
Amplifier
Display System
Scan Converter/Image Memory
70
Responsible for generating the electronic delays for individual transducer elements.
BEAM FORMER
71
This controls the application-specific integrated circuits that provide transmit/receive switches.
DIGITAL BEAM FORMER
72
This provides the electrical voltage for exciting the piezoelectric transducer elements and control the output transmit power.
PULSER (aka Transmitter)
73
This is synchronized with the Pulser, isolates the high voltage associated with pulsing from the sensitive amplification stages during receive mode.
TRANSMIT/RECEIVE SWITCH.
74
The ultrasound pulse created with a short voltage waveform provided by the pulser of the ultrasound system.
This is also known as tye “MAIN BANG”
PULSE ECHO OPERATION
75
This refers to the number of times the transducer is pulsed per second.
PULSE REPETITION FREQUENCY (PRF)
76
This refers to the time between pulses which is equal to the inverse of PRF
PULSE REPETITION PERIOD (PRP)
77
This is determined from the product of the speed of sound and the PRP divided by 2.
MAXIMAL RANGE
78
Refers to the ratio of the number of cycles in the pulse to the transducer frequency and is equal to the instantaneous “on” time.
PULSE DURATION
79
This accepts the data from the beam former during the PRP, which represents echo information as a function of time (depth)
RECEIVER
80
The sequence of the Sequential Signal Processing:
1. Gain Adjustment and Dynamic Frequency Tuning
2. Dynamic Range (Logarithmic) Compression
3. Rectification, Demodulation, and Envelope Detection
4. Rejection
5. Processed Images
81
This defines the effective operational range of an electronic device from the threshold signal level to the saturation level.
DYNAMIC RANGE
82
This inverts the negative amplitude signals of the echo to positive values.
RECTIFICATION
83
Converts the rectified amplitudes of the echo into smoothed, single pulse.
DEMODULATION and ENVELOPE DETECTION
84
This removes a significant amount of undesirable low-level noise and clutter generated from scattered sound or by the electronics.
REJECTION
85
These are optimized for gray scale range and viewing of the limited dynamic range monitors.
PROCESSED IMAGES
86
This is the display of processed information from the receiver versus time.
A-Mode (A for Amplitude)
87
Earliest use of Ultrasound in Medicine
A-Mode
88
This type of echo display mode is used in Ophthalmology.
1. A-Mode
| 2. A Line information
89
This is electronic conversion of the A-Mode and A-Line information into brightness modulated dots along the A-Line trajectory.
B-Mode (B for Brightness)
90
This type of display mode is used for M-Mode and 2D Grayscale imaging.
B-Mode
91
Uses a B-mode information to display the echoes from a moving organ, such as Myocardium and Valve Leaflets, from a fixed transducer position and beam direction into the patient.
M-Mode (M for Motion)
92
This provide excellent temporal resolution of motion patterns, allowing the evaluation of the function of heart valves and other cardiac anatomy. (2D echo, Doppler, Color Imaging Display)
M-Mode
93
This creates a 2D images from echo information from distinct beam directions, and to perform scan conversion to enable image data to be viewed kn video display monitors.
SCAN CONVERTER
94
This image is acquired by sweeping a pulsed ultrasound beam over the volume of interest and displaying echo signals using B-mode conversion of the A-mode signals.
2D Ultrasound Image
95
These were mare with a single element transducer mounted in an articulating arm with angular position encoders to determine the location of the ultralsound beam path.
Early B-Mode Scanners
96
Transducer that produces Rectangular Image
Linear Array Transducer
97
Transducer that produces Trapezoidal Images
Curvilinear Array Transducer
98
Transducers that are typically comprised of a tightly grouped array of 64, 128, or 256 transducer elements in a 3 to 5 cm wide enclosure.
PHASED ARRAY TRANSDUCER
99
Is a metjod in which ultrasound information is obtained from several different angles of insonation and combined to produce a single image.
SPATIAL COMPOUNDING
100
Describe the image storage of Ultrasound.
Ultrasound Images are typically composed of 640 x 480 OR 512 x 512 pixels. Each pixel has a depth of 8 bits (1 byte) of digital data, providing up to 256 levels of gray scale.
101
Ultrasound that is based on the shift of FREQUENCY in an ultrasound wave caused by the moving reflector, such as blood cells in the vasculature.
DOPPLER ULTRASOUND
102
It is the difference between the incident frequency and reflected frequency.
DOPPLER (FREQUENCY) SHIFT
103
The angle between the direction of the blood flow and the direction of the sound.
DOPPLER ANGLE
104
What is the preferred Doppler Angle?
30-60 degrees
105
The simplest and least expensive device for measuring blood velocity.
CONTINUOUS WAVE DOPPLER SYSTEM
106
Advantages of Continuous Wave Dopple System.
1. High Accuracy of Doppler Shift measurement
| 2. No Aliasing
107
This measures the magnitude of the Dopple Shift but does not reveal the direction of the Doppler shift.
QUADRATURE DETECTION
108
This combines the velocity determination of continuous wave Doppler systems and the range of discrimination of pulse echo imaging.
PULSED DOPPLER OPERATION
109
Refers to the combination of 2D B mode imaging and pulsed Doppler data acquisition.
DUPLEX SCANNING
110
This providew 2D visual display of moving blood in the vasculature, superimposed upon the conventional grayscale image.
COLOR FLOW IMAGING
111
A technique to measure the similarity of one scan line measurement to another when the maximum correlation occurs.
PHASED-SHIFT AUTO CORRELATIO
112
An alternate method for Color Flow Imaging which is based upon the measurement that a reflector has moved over a time.
TIME-DOMAIN CORRELATION
113
Interpretation of frequency shifts and direction of blood flow accompanied with fast Fourier Transform, analyzes detected signals and generate amplitude versus frequency distribution profile known as Doppler Spectrum
Doppler Spectral Interpretation
114
Error caused by insufficient sampling rate (PRF) relative to high frequency doppler signals generated by fast moving blood.
VELOCITY ALIASING
115
A signal processing method that relies on the total strength of Dopple signal and ignores directional info.
POWER DOPPLER
116
Integral multiples of frequencies contained in an ultrasound pulse.
HARMONIC FREQUENCIES
117
This enhances contrast agent imaging using a low frequency incident pulse and turning the receiver to a higher frequency harmonics.
HARMONIC IMAGING
118
Acquires a 2D tomographic image data in a series of individual B-scans of a volume tissue.
3D ULTRASOUND IMAGING
119
Volume Sampling can be achieved in several ways with the following transducer arrays:
1. Linear Translation
2. Freedom Motion with External Localizers
3. Rocking Motion
4. Rotation of Scan
120
Measure of Ultrasound Image Quality includes the following: (4)
1. Spatial Resolution
2. Contrast Resolution
3. Image Uniformity
4. Noise Characteristic
121
This arises from the incorrect display of anatomy or noise during imaging which may be due to Machine or Operator related.
ARTIFACTS
122
Change in the transmitted ultrasound pulse direction at a boundary with nonperpendicular incidence, when 2 tissues support a different speed of sound.
- Misplaced anatomy ofter occurs
REFRACTION
123
Hypointense signal area distal to the object or interface caused by objects with high attenuation or reflection without return of echoes.
SHADOWING
124
Occurs distal to the objects having very low ultrasound attenuation.
ENHANCEMENT
125
Arise from multiple echoes generated between 2 closely spaced interfaces reflecting ultrasound energy back and forth during acquisition of signal and before the next pulse.
- Caused by reflection between a highly reflective interface and transducer
REVERBERATION
- manifested as Multiple equally spaced boundaries with decreasing amplitude along a straight line from transducer.
- Comet tail artifact is a form of reverberation
126
Caused by variability of speed of sound in different tissues
SPEED DISPLACEMENT
127
Nearly highly reflective surfaces, multiple beam reflections, and refractions can find their way back to the transducer.
- Anatomy involved is misplaced on beam axis
MULTIPATH REFLECTION and MIRROR IMAGE
128
Created when high PRF limits the amount of time spent listening for echoes during the PRP.
AMBIGUITY
129
Represented as rapidly changing mixture of colors in doppler, typically seen distal to a strong reflector
- due to echoes from strong reflector with frequency changes
TWINKING ARTIFACT
130
This is determined by the beam width of transducer array perpendicular to the image plane and is greater than the beam width in image plane.
- Mostly significant at distances close and far from transducers.
SLICE THICKNESS
131
Rate of energy production, absorption, flow.
POWER
132
SI unit of power
Watt (W) = 1 joule or energy/sec
133
Rate at which the sound energy flows through a unit area
ACOUSTIC INTENSITY
134
Measures ultrasound pressure amplitude with in a beam
| - A device containing a small piezoelectric element coupled to external conductors and mounted in a protective housing
HYDROPHONE
135
Highest instantaneous intensity in the beam
TEMPORAL PEAK
136
The time average intensity over the PRP
TEMPORAL AVERAGE
137
The average intensity of pulse
PULSE AVERAGE
138
Highest intensity spatially in the beam
SPATIAL PEAK
139
Average intensity over the beam area, usually taken to the area of the transducer
SPATIAL AVERAGE
140
Good indicator of thermal ultrasound effects
SPATIAL-PEAK-TEMPORAL AVERAGE INTENSITY
141
An indicator of potential mechanical bioeffects and cavitation
SPATIAL-PEAK PULSE AVERAGE INTENSITY
142
The ratio of acoustic power produced by transducer to power required to raise tissue in the beam area by 1 degree C
THERMAL INDEX (TI)
143
A value that estimates the likelihood of cavitation by ultrasound beam
MECHANICAL INDEX (MI)
144
A consequence of negative pressure that induce bubble formation from the extraction of dissolved gases in the medium
CAVITATION
145
Assumed attenuation for the logarithm that estimates MI
0.3 (dB/cm)/MHz
146
Best indicator for heat deposition
| - Measure of intensity and calculated TI value
SPATIAL PEAK TEMPORAL AVERAGE INTENSITY
147
Defined as sonically generated activity of highly compressible border composed of gas and / or vapor
CAVITATION
148
Refers to the pulsation of persistent bubbles in tissue that occue at low and intermediate ultrasound intensities
STABLE CAVITATION
149
Whereby the bubbles respond nonlinearly to the driving force, causing collapse approaching the speed of sound
TRANSIENT CAVITATION
