SPI 3 Flashcards
Far field
Region distal to focal point where sound beam diverges
Intensity of beam more uniform
Far field relationship
Inversely related to operating frequency and diameter of element
(Increasing frequency decreases angle of divergence)
Focal length determined by
Operating frequency and diameter of element
Focal length directly related to
Operating frequency and diameter of element
Focal length inversely related to
Divergence of beam in far field
Focal point is also called
Focus
Area of maximum intensity in the beam
Focal Zone is located
1/2 in near field
1/2 in far field
Near field length directly related to
Frequency of the transducer and diameter of element
Focusing if the sound beam improves
Lateral resolution
Focusing accomplished where?
Within near field
Focusing creates
A narrower sound beam over a specific area
Beam diameter in near field does what toward the focal point
Decreases in size
Beam diameter in far field
Increases in size after focal point
Increasing frequency or diameter of the element
Produces a narrower beam
Longer focal length
Less divergence in far field
External focus
Lens placed in front of crystal to focus sound beam
Internal focus
Beam diameter is reduced in the focal point
Piezoelectric element shaped concavely to focus the sound beam
Steering sound beam
Created by beam former
Used to sweep sound wave over specific area
System alters electronic excitation of elements steering beam in various directions
Returning echoes delayed
Axial Resolution characteristics
Does not vary with distance
Always better than lateral resolution
Improves with transducer dampening
Axial resolution is equal to
1/2 SPL
Smaller is better
Axial resolution is directly related to?
Frequency
Axial resolution is inversely related to
SPL and depth
Contrast resolution
Ability to differentiate. Between echoes of slightly different amplitude
High contrast
Fewer shades of gray
Low contrast
More shares of gray
Contrast resolution is directly related to
Axial and lateral resolution
Elevational resolution is related to
Beam width
Thinner slice thickness produces better image quality
Lateral resolution improves with
Focusing
Lateral resolution is directly related to
Beam diameter, frequency, focus, and distance
Spatial resolution
Ability to see detail on image
Spatial resolution is directly related to
Number of scan lines
Spatial resolution is indirectly related to
Temporal resolution
Temporal resolution
Ability to position moving structures precisely
Ability to separate two points in time
Temporal resolution determined by
Frame rate
Temporal resolution is directly related to
Frame rate
Temporal resolution is indirectly related to
Number of focal zones depth and spatial resolution
Optimizing axial resolution
Increase frequency
Increase focal zones
Decrease imaging depth
Optimizing contrast resolution
Increase compression (dynamic range)
Increase frequency
Decrease beam width
Post process mapping
Optimizing lateral resolution
Proper focal placement
Decrease beam width
Decrease depth
Optimizing temporal resolution
Decrease focal zones
Decrease depth
Decrease beam width
Decrease persistence
Artifact
Anything not properly indicative of anatomy or motion imaged
Binary number
Group of bits
Bit
Binary digit; smallest amount of computer memory
Byte
Group of 8 bits of computer memory
Channel
An independent signal path consisting of a transducer element delay and other electronic components
Code excitation
Series of pulses and gaps allowing multiple focal zones and harmonic frequencies
Comet tail
Series of closely spaced reverberation echoes behind a strong reflector
Dynamic range
Ratio of the largest to the smallest amplitude that the ultrasound system can handle
Edge shadow
Loss of intensity from bending of the sound beam at a curved surface
Enhancement
Increase in reflection amplitude from structures that lie behind a weakly attenuating structure
Field of view
Displayed image of of returning echoes
Frame rate
The number of complete scans (images) displayed per second
Gain
Ratio of amplifier output to input of electric power
Grating lobes
Secondary sound beams produced by a multi element transducer
Line density
Number of scan lines per frame; scan line density
Matrix
Denotes the rows and columns of pixels in a digital image
Mirror image
Artifact gray scale, color Flow, or Doppler signal appearing on the opposite side of a strong reflector
Multipath
Path toward and away from a reflector are different
Noise
Disturbance that reduces the clarity of the signal
Nyquist limit
Minimum number of samples required to avoid aliasing; Doppler shift frequency above which aliasing occurs
Pixel
Smallest portion of digital image
Pixel density
Number of picture elements per inch
Pulse repetition frequency
Number of voltage pulses sent to transducer each second
Pulse repetition period
time from beginning of one voltage pulse to the start of the next voltage pulse
RAM (random-access memory)
allows access of stored data in an unsystematic order
Range ambiguity
Produces when echoes are placed too superficially because a second pulse was emitted before all reflections have returned from the first pulse
ROM (read-only memory)
Stored data cannot be modified
Real time imaging
Two dimensional imaging of the motion of moving structures
Reflection
Portion of sound reflected from the boundary of a medium
Refraction
Change of sound direction on passing from one medium to another
Reverberation
Multiple reflections between a structure and the transducer or within a structure
Scattering
Redirection of sound in several directions on encountering a rough surface
Shadowing
Reduction of reflective amplitude from reflectors that lie behind a strongly reflecting or attenuating structure
Signal to noise ratio
Comparison of meaningful information in an image (signal) to the amount of signal disturbance (noise)
Spatial compounding
Averaging of frames that view anatomy from different angles
Specular
Large flat smooth surface
Voxel
Smallest distinguishable part of a 3-D image
A-Mode
Amplitude mode
Y axis- amplitude
X-axis- distance
Single sound beam one dimentional
B-Mode
Brightness mode
2-D image cross-sectional using multiple sound beams
Displays strength of returning echoes as pixels in various shades of gray
Y-axis- depth
X-axis- side to side or superior to inferior aspects of body
Stronger the reflection brighter the pixel
M-mode
Motion mode
Y axis- reflector depth
X axis- time
Advantages of real time imaging
Rapid location of anatomy
Movement can be observed
Structures or vessels can be followed
Limitations of real time imaging
Penetration depth is limited by propagation speed of the medium
Exact imaging plane cannot be systematically reproduced
Measurement of structures larger than the field of view is estimated
Field of View is directly related to
PRF
Field of view is inversely related to
Frame rate and temporal resolution
Field of view is adjusted using
Depth and region of interest settings
Frame rate determines
Temporal resolution
Frame rate is determined by
Propagation speed of the medium and imaging depth
Frame rate is proportional to
PRF
Frame rate is inversely related to
Number of focal zones used, imaging depth, and lines per frame (beam width)
Frame rate adjusted by
Using depth and PRF settings
Line density is directly related to
PRF and spatial resolution
Line density inversely related to
frame rate and temporal resolution
Max imaging depth dependent on
Frame rate, number of lines per frame, and number of focal zones used
Pulse repetition frequency inversely related to
Frequency and depth
Pulse repetition frequency indirectly adjusted by
Imaging depth setting
Coded excitation improves
Contrast, axial, and spatial resolution
Coded excitation occurs where
Pulser
4-D imaging
Real time presentation of 3-D image
Harmonic frequencies relationships
Improves lateral resolution
Decreases contrast resolution
Reduces grating lobes
Harmonics frequency generated
At a deeper imaging depth (reduces reverberation)
And in the highest intensity and narrowest portion of the beam
Multifocal imaging directly related to
Lateral resolution and PRF
Multifocal imaging inversely related to
Frame rate and temporal resolution
Spatial compounding does what
Improves visualization of structures beneath a highly attenuating structure and smooths specular surfaces
Spatial compounding reduces
Speckle and noise
Spatial compounding uses
Phasing to interrogate the structures more than once
Functions of pulses echo instrumentation
Prepare and transmit electronic signals to the transducer to produce a sound wave
Receive electronic signals from reflections
Process reflected info for display
Power
Output control
Controls the amplitude of transmitted sound beam and the amplitude of the received echoes
Power is directly related to
Signal to noise ratio and the intensity of acoustic exposure of patient
Acoustic exposure measured by
Mechanical index and thermal index
Master synchronizer
Instructs pulser to send electrical signal to transducer
Coordinates all the components of the US system
Manager of US system
Pulser (transmitter)
Generates pulses to crystal producing pulsed US waves
Drives transducer through pulse delays with one voltage pulse per scan line
Adjusts PRF for imaging depth
Communicates with receiver the moment the crystal is excited to help determine distance to reflector
Pulser determines what?
PRF PRP and pulse amplitude
Digital beam former
Part of pulser
Determines firing delay for array systems
What happens to beam former during reception
Establishes time delays used in dynamic focusing
Advantages of beam former
Software programming and extremely stable with wide range of frequencies
Receiver
Amplifies and modifies echo information returning from the transducer
5 functions of receiver
Amplification Compression Compensation Demodulation Rejection
Amplification
dB
Increases small electric voltages received from the transducer to a level suitable for processing
Amplification adjusted how?
Using overall gain setting
Compensation
TGC
compensates for the loss of echo strength caused by the depth of the reflector
Areas of compensation
Near field- minimum amplification Delay- depth where compensation begins Slope-region for depth compensation Knee-deepest region attenuation compensation can occur Far field- max amplification
