System Operations Flashcards
What are the 6 main components of the ultrasound system?
Transducer Pulser and beam former Receiver Display Storage Master synchronizer
What does the master synchronizer do?
It organizes and maintains the timing and interaction of the different components of the ultrasound system by use of communication
What does the pulser do?
Creates and controls electrical signals that are sent to PZT crystals to create sound beams or pulses
What is another term for the pulser?
Transmitter
What does the transducer do?
Transmission: to transform electrical energy to acoustic
Reception: to transform acoustic energy back to electrical
What does the receiver do?
Changes the electronic components from the transducer (that are created by reflected sound) and transforms them to a form suitable for display
What does the display do?
Presents the processed data from the machine
Flat screen monitor, transparency, audio speaker
What does the storage do?
Stores or archives the ultrasound studies produced by that machine
Form of hard drive, CD or DVD, videotape, USB
What determines the transducer output magnitude?
It is determined by the excitation voltage that comes from the transducer
Increased voltage means increased magnitude of PZT vibration
What are other terms used to describe transducer output?
Output gain Acoustic power Pulser power Energy output Transmitter output Power Gain
How is the image affected when the transducer output changes?
When there is lower output, the entire image is darker
When there is higher output, the entire image is brighter
What is ultrasound “signal”?
The meaningful portion of the data that we want to have
What is ultrasound “noise”?
The inaccurate portion of the data that has random or persistent disturbance, reducing the signal clarity
Signal contamination
What is signal to noise ratio?
The comparison of the meaningful information to the amount of contamination
Is a high or low signal to noise ratio desirable?
High S/N ratio
This means that the signal is stronger than the noise, producing a high quality image
What is the primary method for improving S/N ratio?
Increasing output power
Improves image quality as signal dominates noise
What component of the US system determines the PRP (and PRF)?
The pulser
What is the beam former?
Transmission: creates and distributes the delay patterns for array transducers
Reception: dynamic receive focusing to establish correct time delays
What is adopization?
A process of adjustments to the electrical spike voltages to reduce lobe artifact
What is the receiver?
The electronic components of the machine that boosts the strength of the electric signals and converts them for display on the monitor?
What is the order of functions performed by the receiver?
Amplification Compensation Compression Demodulation Reject
What is amplification?
Increases the strength of all electronic signals equally
Needed when electronic signals are too low
What is the synonym for receiver gain?
Amplification
How does receiver gain affect the received signals?
It increases the strength of all signals identically
How does receiver gain affect the entire image?
It makes the entire image brighter or darker
Does the receiver gain create an image of uniform brightness top to bottom?
No, because it affects signals equally
What is the preamplifier?
The process of improving the signal quality before it is amplified and occurs as close to the PZT as possible
What is the purpose of compensation?
To create an image with uniform brightness from top to bottom
What are other terms used to describe compensation?
Time gain compensation (TGC)
Depth compensation (DGC)
Swept gain
Do higher or lower frequencies require more or less compensation?
Higher frequencies
They attenuate more quickly and need compensation at shallower depths
What does compression do?
It reduces the total range of signals
It keeps the signals within accuracy range for system
It keeps the gray scale within human eye
What are other terms used to describe compression?
Log compression
Dynamic range
What is demodulation?
A two-part process that changes the signal to a form suitable for display
Rectification turns the negative voltages positive
Smoothing evens out the bumps by wrapping an envelope around them
What does reject do?
It eliminates the low-level noise in images
Displays only meaningful low-level signals
What signals are affected by reject?
All low-level echoes
No bright echoes
What effect does reject have on an image?
It affects all low level echoes equally while not changing the bright echoes, causing weaker reflections to be eliminated from display
How does output power affect the brightness of an image?
By altering the strength of the sound pulse that the transducer sends into the body
When the pulse is more powerful, the entire image becomes brighter
How does receiver gain affect the brightness of an image?
It alters the strength of the voltages in the receiver created by the transducer during transmission
Higher amplification creates a brighter image
Lower amplification creates a darker image
If an image is too bright should power or gain be reduced first?
Output power because it decreases patient exposure
ALARA
If an image is too dark should power or gain be increased first?
Gain because it does not increase patient exposure
ALARA
If you have insufficient penetration should you increase power or use a lower frequency transducer?
Use a lower frequency transducer because increasing power would alter patient exposure
What is bistable?
Images that are only composed of black or white shades
What is gray scale?
Images that are composed of many shades of gray to show multiple levels of contrast
What is contrast?
The range of brilliances in the displayed image
Bistable are high contrast images
What is brightness?
It determines the specific brilliance of the image
What does the scan converter do?
It changes the format of stored data from spoke format to display format (horizontal lines)
What are analog numbers?
Real world numbers that we use in our everyday lives
Continuous range of values
Not rounded
What are digital numbers?
Numbers that are associated with computer devices
Can only have discrete values
Rounded
What is spatial resolution?
Image detail
Great spatial resolution in analog scan converters
What does the digital scan convertor do?
It uses the technology of the computer to convert images to numbers (digitizing)
What is computer memory called?
Random Access Memory
RAM
What is a pixel?
The smallest building block or element of a digital picture
Individual square boxes on the grid
How are pixels related to spatial resolution?
Smaller pixels create higher pixel density, which improves spatial resolution
What is a bit?
The smallest amount of digital storage of a computer’s memory
What is a byte?
A group of 8 bits of computer memory
In the form of 1s and 0s
How are the number of bits per pixel related to contrast resolution?
Fewer bits per pixel causes degraded contrast resolution with fewer shades of gray
More bits per pixel causes improved contrast resolution with more shades of gray
If you know the number of bits per pixel how can you determine how many shades of gray will be presented?
By multiplying the number 2 times itself the same number of times as the number of bits
4 bits = 2x2x2x2 = 16 shades
What does the analog-to-digital converter do?
It converts the electrical signals made by the transducer during reception from analog to digital
What is preprocessing and when does it occur?
It is the processing of reflected signals that occurs before storage
What is post-processing and when does it occur?
It is the processing of reflected signals that occurs after storage and in the digital scan converter
What is read magnification and is it pre or post processing?
It is when the system reads the original stored image data and displays only the original data
Post processing
What is write magnification and is it pre or post processing?
It is when the system rescans the area of interest and writes or provides new data to the scan converter
Preprocessing
How does the magnification affect spatial resolution?
Improves spatial resolution because it has an increased number of pixels in the area of interest
How does write magnification affect temporal resolution?
Improves temporal resolution when the area of interest is shallower than the original depth of view
Where does coded excitation take place?
In the pulser
What does coded excitation improve?
Image quality
Higher S/N
Better axial, spatial, temporal res
Deeper penetration
What is spatial compounding?
When scan lines are steered by the transducer to image structures with multiple pulses from different angles
What transducers perform spatial compounding?
Phased array transducers because electronic steering is necessary
What are the benefits of spatial compounding?
Averages the frames by
Improving S/N ratio
Reducing speckle and clutter artifacts and shadowing
What is frequency compounding?
When frequency ranges are divided into sub-bands are combined to make a single image
What are the benefits of frequency compounding?
Reduces speckle artifact and noise
What does edge enhancement do?
Increases the image contrast immediately around the edge of an area
Makes the image sharper with better defined boundaries
What is temporal compounding?
When previous frames are superimposed over the most recent frame to create an image made of displayed information from past images
What are synonyms for temporal compounding?
Persistence
Temporal averaging
How does temporal compounding affect temporal resolution?
It reduces temporal resolution because it causes reduced frame rate
What are the benefits of temporal compounding?
It creates a smooth image with
Higher S/N
Reduced noise
Improved image quality
What is fill-in interpolation?
A method of filling in the gaps or missing data between scan lines
Is fill-in interpolation pre or post-processing?
Preprocessing
What is elastography?
A technique used to create an image based on the tissue’s mechanical properties
What is dynamic range?
A method of describing the extent of signal variation that can occur while still maintaining accuracy
