Chapter 15 Flashcards
scan converter
stores echo data signals in preparation for display
writing
The process of putting echo data signals into the scan converter/storage
reading
The process of taking the echo data signals from the scan converter/storage to display
Analog Scan Converters
They made gray scale display possible
Analog Signals consist of an unlimited continuous stream of values
dielectric storage matrix
a checkerboard of silicon wafers i.e., “electron buckets”
Limitations of dielectric storage matrix on the display:
Image fade: stored charges dissipate over time
Image flicker: caused from switching between read and write modes
Instability: image quality effected by heat and humidity
Deterioration: image degrades as device ages
digital scan converters
amplitude of the analogue voltage signal is determined, converted to digital (binary digit), and stored
“Digitizing”
analogue to digital conversion
Advantages to digital scan converters
Uniformity: consistent grayscale quality
Stability: image does not fade or drift
Durability: performance not affected by age or heavy use
Speed and Accuracy: nearly instant and error free processing
Digital data is less susceptible to contamination
Digital Scan Converter (memory board)
is set up in a computer monitor scan format (a matrix/checkerboard set up)
Rectangular series of columns and rows
Each square is a “Pixel” (picture element)
Pixels are at least
1024 x 768
bits
0 and 1 are binary digits
element at each pixel location can only operate in two conditions
1 = “on”
0 = “off”
bistable display
black and white imaging
A bit
is the smallest amount of computer memory
byte
A group of 8 bits
Two bytes or 16 bits
is a word of computer memory
A kilobyte
1000 bytes (1024) or 8000 (8192) bits
Preprocessing
Manipulation of the data during the “writing” process
Postprocessing
Manipulation of the data during the “reading” process
Types of Processing
Time gain compensation (generally pre)
Compression (generally pre)
Grayscale Maps (pre or post)
Magnification known as “zoom”
Write Magnification
the ROI is rescanned, and all pixels are devoted to the region of interest = preprocessing
Known as “RES”
Read Magnification
The system reads and displays the data pertaining to the ROI
post processing
Edge enhancement (generally pre)
Boundaries in memory are identified and the contrast between the adjacent pixels is enhanced (one slightly brightened while the other is slightly darkened)
Fill-in Interpolation (pre)
assigns an amplitude value to a missed pixel based on an average of amplitudes of adjacent pixels
Temporal Compounding/Averaging (pre)
AKA: Persistence
Averaging of sequential frames to produce one frame that is entered into the scan converter
Disadvantage = reduced frame rate and temporal resolution; therefore, most effective with static or slow-moving structures
Speckle
grainy tissue texture caused when small wavelets interfere
Panoramic imaging (pre)
Produces an image that has a wider field of view than what is available on an individual frame
done on static organs
Spatial Compounding/Compound Imaging (pre)
Averaging of sequential frames to produce one frame that is entered into scan converter
Three-Dimensional Imaging
Many 2D scans are built into a 3D volume of echo information stored in sophisticated memory = preprocessing
Black white inversion (generally post)
a white on black image is turned into a black on white
B color/colorize/ tinting/chromatization (typically post)
assigns a color instead of a shade or gray to amplitudes pulled from scan converter to display
Frequency Compounding (pre)
Reflected signal is divided into sub bands of limited frequencies
A frame is created from each sub band
The frames are then averaged and entered in the scan converter
Coded Excitation in Pulser /Beam Former (pre)
Pulse is made into an “ensemble pulse”
a decoder rebuilds or “stacks” the ensemble parts into one short high intensity pulse (“pulse compression”)
B-flow imaging
grey scale imaging of blood flow
Elastography/Elastogram = emerging modality
The stiffness data as well as the ultrasound reflections are represented in
Strain
When hit by a force (sound wave) tissue deforms relative to its stiffness
Fusion Tool in Volumetric Imaging
Allows you to merge real time ultrasound with a previously acquired CT, PET, MR or US Data Set
Computer CRT
cathode ray tube
digital to analog conversion takes place
a glass vacuum tube shaped like a funnel
Color Computer CRTs include
three cathodes and thousands of groups of tiny red, green, and blue phosphor dots inside the face of the screen
Liquid Crystal Displays (LCD)
Most common flat panel ultrasound system display
Can operate with analog or digital signals
A rectangular matrix of thousands of liquid crystal elements
Advantages: lighter, slimmer, less power consumption and heat generation
Display controls
Display needs to be calibrated in each new ambient light or the recorded study will present differently than when the images were acquired
The contrast button
sets monitor gray scale range
Adjust it to achieve graduation of gray shades
The brightness button
sets monitor brightness
adjust to ensure only the 16th gray scale bar is black – melting into or non distinguishable from the background
May have one monitor control knob
offers various contrast/brightness combinations
Settle on one that achieves appropriate contrast and brightness
Paper (stored static)
Images written on paper by automated pen writers
Images exposed onto photographic paper
Magnetic Media
Dynamic and static images stored on video tape
Optical Media
Standard: floppy disks (early) then CD, DVD, Flash drive
Limited capacity
Loss of echo data (highly compressed)
Specialized Disks specific to the ultrasound system
Limited capacity
Maintain echo data (less compression)
Require special reader for playback
Ultrasound System Hard Drive
Capacity for several weeks of studies
Maintained echo data (no compression)
Physician would have to read and interpret study on the ultrasound system – impractical
PACS System – solved all problems
Stands for Picture Archiving and Communication System
-a digital ultrasound lab in which images and reports are digitized and stored on a large specialized computer network
Advantages:
Instant access to archived studies
Studies viewed quickly
Practical high-capacity long term storage (servers)
Maintained echo data (minimal compression)
Store and forward telemedicine = the ability to view from remote sites
DICOM = Digital Imaging and Communication (not computer) in Medicine
is a set of rules that describes the means of formatting and exchanging medical images and associated information.
It ensures that all devices on the network will work together to share, manage, and distribute images regardless of the manufacturer
Lossless compression
eliminates redundant data only and does not alter the image (ideal)
Lossy compression
eliminates redundant and similar data and does alter the image (more practical)
