Displays, Image Processing, Dynamic Range Flashcards
What is a bistable display?
2, black and white
What is gray scale display?
- variety of grayness
- spectrum of brightness levels
- able to differentiate between amplitude differences in reflections
What is contrast?
determines the range of “brilliancies” within displayed image
What is brightness?
Determines the “brilliance” of the overall displayed image
What are the two functions of scan converters?
- store info “writing”
- display info “reading”
What is the difference in formation of transmitted/reflected pulses and monitors and displays?
transmitted/reflected: vertical lines
monitors/displays: horizontal lines
What are analog numbers?
- unlimited, continuous range of values
- weight, length
- real world values
What is an example of an analog value?
165.8 lbs
What are digital numbers?
- associated with computers
- discrete, whole values
What is an example of a digital value?
166 lbs
What is an analog scan converter?
- first type of converter, made gray scale imaging possible
- funnel shaped vacuum tube with an electron gun
How does an analog scan converter work?
- Electrons contain image info and are shot out of gun
- Other end of tube contains dielectric matrix/silicon wafer
- Electrons strike matrix/wafer, stored
How does the matrix produce an image in an analog scan converter?
- matrix is a picture of a million dots, each with storage element
- stored electron charge that hits the matrix read to retrieve image info
How is the spatial resolution of analog scan converter images?
Excellent because matrix has large storage capability
What are the limitations of analog scan converter?
- image fade
- image flicker
- instability
- deterioration
What is image fade?
Stored charges in the matrix dissipate over time
What is image flicker?
Caused by switching between write and read modes
What is instability?
Image quality depends on factors such as duration of use, room temp, humidity
What is deterioration?
Image degrades as the device ages
What is a digital scan converter?
- Use of computers to convert images into numbers
- Image is stored in a computer memory as 1s and 0s
- Numerical representation is processed and retranslated into displayed image
What are the advantages of digital scan converter?
- Uniformity: consistent gray scale quality
- Stability: does not fade
- Durability: not affected by age/use
- Speed: instantaneous processing
- Accuracy: virtually error free
What is a pixel?
- picture element
- smallest unit of digital picture
How do pixels make up an image?
- Image displayed as grid
- Each box = pixel
- Each pixel = one shade of gray
What is pixel density?
Number of picture elements per inch
What is the result of higher pixel density?
More smaller pixels, increased spatial resolution/detail
What is the result of lower pixel density?
Less larger pixels, decreased spatial resolution/detail
What is a bit?
- binary digit
- smallest unit of computer memory
- value of 0 or 1
What is a binary number?
- Group of bits
- Series of zeros and ones
What is a byte?
Group of 8 bits
What is a word?
Two bytes or 16 bits
How is grayness determined?
- The cluster of bits assigned
- More bits/pixel = more shades of gray
What does more bits per pixel result in?
Increased contrast resolution
How are gray shades calculated?
- 2^n (number of bits)
- results in max number of gray shades
How many possible shades of gray will 5 bits of memory display?
2^5 = 32
How is image data converted for display?
Analog to digital back into analog for display
Why does image data need to be converted to digital form?
To reduce susceptibility to noise contamination
How are electrical signals created by the transducer converted?
Using analog-to-digital converter, digital info is string of 1s & 0s
Where is digital info stored after being converted from analog?
Scan converter’s computer memory
What is preprocessing?
Any processing of the reflected signals before storage
What is postprocessing?
Any processing of the reflected signals after storage in the digital scan converter
How are digital signals converted for display on an analog display device?
Using the digital-to-analog converter
What controls are used in preprocessing?
- TGC
- gain
- write magnification
- compression
- temporal compounding
- spatial compounding
- edge enhancement
- fill-in interpolation
What happens when an image is preprocessed?
The image data is permanently altered and cannot be reversed once saved
What can be controlled in postprocessing?
- black/white inversion
- read magnification
- contrast
- 3D rendering
What happens when an image is postprocessed?
All postprocessing changes can be reversed which will restore the image to original values
What are the 3 steps of read magnification?
- system scans anatomy
- image converted A-D, stored in scan converter
- tech picks ROI, system reads & displays on original data for that area
How are the number of pixels affected with read magnification? Spatial resolution?
Same number of pixels, same spatial resolution
What are the 4 steps of write magnification?
- system scans anatomy
- image converted from A-D, stored in scan converter
- tech picks ROI, system discards all existing data in scan converter
- system rescans only the ROI and writes new data
How are the number of pixels affected with write magnification? Spatial resolution?
Greater number of pixels, better spatial resolution
Summarize the 6 characteristics of read magnification.
- Uses old data
- Postprocessing
- Larger pixel size
- Same # pixels as orig ROI
- Same spatial resolution
- Same temporal resolution
Summarize the 6 characteristics of write magnification.
- Acquires new data
- Preprocessing
- Identical pixel size
- More pixels than orig ROI
- Improved spatial resolution
- Improved temporal resolution
What is coded excitation?
Method of improving image quality
How does coded excitation improve image quality?
- Keeps max peak intensity within specific limit
- Creates long pulses with wide freq range
- Distributes energy over broad freq range
- Strong pulse within intensity limits
- Improved penetration
What are the 5 characteristics of coded excitation?
- Higher signal to noise ratio
- Improved axial res
- Improved spatial res
- Improved contrast res
- Deeper penetration
What is spatial compounding?
Method of using info from multiple imaging angles to produce a single image
How is spatial compounding done?
- Acquires frames from multiple angles
- Frames are combined to form single image
- # of frames and steering angles varies based on transducer/clinical use
What results in better compound image quality?
More frames
What are the results of spatial compounding on an image?
- Reduces speckle and shadowing artifacts
- Lower frame rate and temporal res
What is frequency compounding?
Technique used to reduce speckle and noise artifacts
How does frequency compounding work?
- Divides reflected wave into sub-bands of limited frequencies
- Image is created from each sub-band
- Images are combined into 1
What is the result of frequency compounding?
- Mimics multiple images being created from transducer with different frequencies
- Reduces overall noise
What is edge enhancement?
Method used to make images look sharper
How is edge enhancement done?
- Computer emphasizes sharp edge boundaries w/i image
- Increases contrast in area immediately around edge
How does the computer make boundaries appear defined?
Creates subtle bright and dark highlights on either side of boundaries
What is temporal compounding?
- Technique that continues displaying info from older images
- Prev frames are superimposed on current
What is the result of temporal compounding?
- Smoother image, higher signal to noise ratio
- Improved image quality
- Lower frame rate
- Decreased temporal resolution
What is fill-in interpolation?
- With sector images, scan lines become further apart as they travel
- results in gaps
- Interpolation fills in gaps with simulated data points
How does fill-in interpolation work?
- computer programs predict gray scale levels of missing data
- uses neighboring data
What does PACS stand for?
Picture Archiving and Communications System
What is PACS?
- Digital lab where images/med info are digitized & stored
What are the benefits of PACS?
- Instant access to archived studies
- No degradation of data
- “Store & forward” info to transmit images/reports to remote locations
What does DICOM stand for?
Digital Imaging and Computers in Medicine
What is DICOM?
- Set of rules/protocols that allow imaging systems to share info on a network
- Allows a system to connect to PACS
- Allows devices to share, manage, distribute images regardless of manufacturer
What is dynamic range?
Method of describing the extent a signal can vary and still maintain accuracy
What is an example of dynamic range?
Scales weighs 30-300 lbs accurately
- Below 30 lbs, too weak for threshold, needle doesn’t move
- Above 300, too strong, saturates system, reads as 300 lbs
How is dynamic range reported?
Decibels
What kind of measurement is dynamic range?
Comparison, relative, measurement or ratio b/w largest and smallest signals within an accurate range
What happens to dynamic range of info the more it is processed?
Decreases
What processes data with the widest dynamic range?
Components earliest in imaging change
- Transducer
- Receiver
- Scan converter
- Display
- Archive
Dynamic range of a display can be reported as:
The number of possible gray shades
Narrow dynamic range results in
- Few shades of gray
- High contrast
Wide dynamic range results in
- Many shades of gray
- Low contrast
Spatial compounding can only be done with what type of transducer?
Phased array
What is temporal compounding also called?
Persistence or temporal averaging
