ULTRASOUND COPY Flashcards
1
Q
mechanical energy that propagates thru a continuous elastic medium by the compression and rarefaction of particles
A
Sound
2
Q
energy propagation occurs as a wavefront in the direction of energy travel
A
longitudinal wave
3
Q
distance (mm) bet compressions and rarefactions or bet any 2 points that repeat on the sinusoidal wave of pressure amplitude
A
wavelength (λ)
4
Q
of times the wave oscillates thru one cycle each second
A
frequency (f)
5
Q
infrasound Hz
A
<15 Hz
6
Q
Audible acoustic spectrume Hz
A
15-20kHz
7
Q
Ultrasound Hz
A
> 20 kHz
8
Q
Medical Ultrasound Hz
A
2-100 mHz
9
Q
occurs at tissue boundaries where there is a difference in acoustic impedance of adjacent materials
A
Reflection
10
Q
describes the change in direction of the transmitted US energy w/ non perpendicular incidence
A
Refraction
11
Q
occurs by reflection or refraction usually by small particles w/in the tissue medium
A
Scattering
12
Q
gives rise to the characteristic texture and gray-scale in the image
A
Scattering
13
Q
: loss of intensity of beam from absorption and scattering in the medium
A
Attenuation
14
Q
process whereby acoustic energy is converted to heat energy –> sound energy is lost and cannot be recovered
A
Absortpion
15
Q
Can be likened to the stiffness and flexibility of a compressible medium
A
Acoustic impedance (z)
16
Q
Acoustic impedance (z) unit
A
Rayl
17
Q
Large difference in acoustic impedance results to
A
Large Reflection
18
Q
means for producing an image using pulse echo technique
A
Acoustic impedance (z)
19
Q
Type of Transducer
converts electrical energy to mechanical energy by physical deformation of crystal structure
A
Piezoelectric materials
20
Q
Type of Transducer
mechanical pressure applied to its surface creates electrical energy
A
Piezoelectric materials
21
Q
Type of Transducer
characterized by a well defined molecular arrangement of electrical dipoles
A
Piezoelectric materials
22
Q
molecular entities containing (+) and (-) electrical charge w/ overall neutral charge
A
Electric dipole
23
Q
Piezoelectric materials are often mad of ?
A
PZT
Plumbum
Zicornate
Titanate
24
Q
Type of Transducer
voltage is applied to PZT => PZT initially contract then subsequently vibrates at a natural resonance frequency
A
Resonance Transducer
25
higher frequencies are achieved w/ thinner/thicker? elements and lower frequencies w/ thinner/thicker? elements
high frequency - thinner
| low frequency - thicker
26
layered on the back of the PZT and absorbs the backward directed US energy and attenuates stray US signals from the housing
Damping block
27
creates an US pulse w/ a short spatial pulse length necessary to preserve detail along the beam axis (axial resolution)
Damping block
28
bandwidth of sound from a transducer
Q factor
29
Q factor: narrow bandwidth, long SPL
High Q transducer
30
Q factor: broad bandwidth, short SPL
Low Q transducer
31
requires a relatively narrow band transducer response to preserve velocity information encoded by changes in the echo frequency relative to the incident frequency
Doppler
32
Provides the interface bet the raw transducer element and the tissue
Minimizes acoustic impedance difference bet the transducer and the patient
Consists of layers of materials w/ acoustic impedance intermediate to soft tissue and transducer material
Matching layer
33
is used to eliminate air pockets w/c could attenuate and reflect sound beam
Acoustic coupling gel (acoustic impedance is similar to soft tissue)
34
Center of frequency can be adjusted in the transmit mode
Piezo element is machined into a large # of small rods and filled w/epoxy resin for smooth surface
Provides greater transmission efficiency w/o multiple matching layers because its acoustic properties are closer to tissue
Non-resonance (broad bandwidth) multifrequency transducer
35
Sound pulse can be produced at low frequency and echoes received at higher frequency
HARMONIC IMAGING
36
Greater depth of penetration
Noise and clutter removal
Improved lateral spatial resolution
Native tissue harmonic imaging
37
Rectangular FOV is produced
Linear arrays
38
trapezoidal FOV is produced
Curvilinear array
39
occurs by firing another group of transducer elements
Subsequent A line acquisition
40
Echoes are detected in the receive mode by acquiring signals from most of the transducer elements
Linear arrays
41
Simultaneous firing of approx 20 adjacent elements produce the beam adjacent elements produce a synthetic aperture
Linear arrays
42
256-512 elements – largest
Linear arrays
43
64-128 elements – smaller
Phased arrays
44
All elements are activated nearly simultaneously to produce a single beam
Phased arrays
45
Beam can be steered electronically w/o physically moving the transducer
Phased arrays
46
All elements detect the returning echoes
Phased arrays
47
US beams exhibit 2 distinct patterns:
Near field
| Far field
48
Slightly converging beam out to a distance determined by geometry and frequency of the transducer
Near field
49
Fresnel zone
Near field
50
Converging
Near field
51
Occurs due to multiple constructive/destructive interference patterns of US waves from the transducer surface causes the beam profile to be tightly collimated
Near field
52
Near field length is dependent on
Transducer diameter
Propagation wavelength (thus, frequency)
NFL increases if frequency and diameter are increased
53
NFL (near field length) increases if __ and __ are increased
frequency and diameter
54
NEAR FIELD
___ is dependent on the beam diameter and is best at the end of the near field for a single element transducer
Lateral resolution
55
Ability of the system to resolve objects in a direction perpendicular to the beam direction
Poor in areas close to and far from the transducer surface
Lateral resolution
56
occurs at the end of the near field
Peak US pressure
57
Beam is divergent
Far Field
58
Fraunhofer zone
Far field
59
US intensity decreases monotonically with distance
Far field
60
the major factor that limits spatial resolution and visibility of detail is the volume of the acoustic pulse
Spatial resolution
61
Linear, range, longitudinal or depth resolution
Axial resolution
62
Ability to discern 2 closely spaced objects in the direction of the beam
Requires that returning echoes be distinct without overlapping
Axial resolution
63
aka azimuthal resolution
Lateral resolution
64
Ability to discern as separate 2 closely spaced objects perpendicular to beam direction
Lateral Resolution
65
Determines lateral resolution
Beam diamter
66
Depth dependent resolution
Lateral resolution
67
Far field, beam diverges substantially reduced ____ resolution
Lateral resolution
68
____ --> improved overall in focus lateral resolution w/ depth --> decrease frame rate
increase # of focal zone
69
Resolution perpendicular to image plane
Elevational resolution
70
dependent on transducer element height
Elevational resolution
71
Display of processed info from the receiver vs time
A mode
72
Seldom used (ophtha applications for precise distance measurements of the eye)
A mode
73
Electronic conversion of A mode and A line info into brightness-modulated dots along the A line trajectory
B mode
74
Brightness of dot is proportional to echo signal amplitude
| Used for M mode and 2D gray scale imaging
B mode
75
Uses B mode info to display echoes from a moving organ
M mode
76
Provides excellent temporal resolution of motion patterns
M mode
77
difference between incident and reflected frequency
Doppler shift
78
Proportional to velocity of the blood cells
Doppler shift
79
angle bet direction of blood flow and direction of sound
Doppler angle
80
Without correction, Doppler shift will be less and there will be an underestimate of ___
blood velocity
81
Doppler Angle: measured Doppler frequency is ½ the actual
>60 degrees
82
Doppler angle: measured frequency is 0
At 90 degrees
83
preferred doppler angle
30-60 degrees
84
apparent Doppler shift is small
> 60 degrees
85
Doppler angle
refraction and critical angle interactions can cause problems as can aliasing
< 20 degrees
86
Provides a 2D visual display of moving blood in the vasculature superimposed upon the conventional gray-scale image
Color flow imaging
87
determines the processing time necessary to evaluate the color flow data
FOV
88
Smaller/bigger? FOV delivers a faster frame rate but sacrifices area evaluated
smaller
89
Error caused by insufficient sampling rate relative to the high frequency Doppler signals generated by fast moving blood
Velocity aliasing
90
How to eliminate velocity aliasing?
Adjust the velocity scale to a wider range
91
wraps around to negative amplitude masquerading a reversed flow
Velocity aliasing
92
Relies on the total strength of the Doppler signal (amplitude)
Ignores directional information
Dependent on amplitude of Doppler regardless of frequency shift
Improves sensitivity to motion at the expense of directional and quantitative information
Not dependent as much to Doppler angle
Aliasing is not a problem
Allows detection of very subtle low blood flow
Slower frame rates
Significant amount of flash artifacts from moving tissue, pt motion or transducer motion
Power doppler
93
Arise from the incorrect display of anatomy or noise during imaging
Artifacts
94
Hypointense signal area distal to an object or interface
Shadowing
95
Caused by objects w/ high attenuation or reflection of the incident beam no return of echoes
Shadowing
96
Highly attenuating objects (bone/kidney stone) can induce low intensity streaks in the image
Shadowing
97
Occurs distal to objects having very low US attenuation
Enhancement
98
Hyperintense signals arise from increased transmission of sound by these structures
Enhancement
99
Arise from multiple echoes generated bet 2 closely spaced interfaces reflecting US energy back and forth during acquisition of the signal and before the next pulse
Reverberation
100
Often caused by reflections bet a highly reflective interface and the transducer or bet reflective interface such as metallic objects, calcified tissues or air pockets
Reverberation
101
Typically manifested as multiple equally spaced boundaries w/ decreasing amplitude along a straight line from the transducer
Reverberation
102
Arise from resonant vibrations w/in fluid trapped bet a tetrahedron of air bubbles => creates a continuous sound wave that is transmitted back to the transducer => displayed as a series of parallel bands extending posterior to a collection of gas
Ring down artifact
103
The echoes bounce back and forth between the two
| boundaries and produce equally spaced signals of diminishing amplitude in the image
Comet tail artifact
104
Artifact represented by a rapidly changing mixture of colors
Twinkling
105
Artifact typically seen distal to a strong reflector (calculus)
Twinkling
106
Artifact possibly due to echoes from the strong reflector w/ frequency changes due to wide bandwidth of the initial pulse and narrow band ringing caused by the structure
Twinkling
107
highest instantaneous intensity in the beam
Temporal peak
108
time averaged intensity over the PRP
Temporal average
109
highest intensity spatially in the beam
Spatial peak
110
good indicator of thermal US effects
Spatial peak-temporal average intensity
111
Indicator of potential mechanical bioeffects and cavitation
Spatial peak-pulse average intensity
112
the accepted methods of determining power levels
Thermal index (TI) and mechanical index (MI)
