Displays and Image Processing Flashcards
determines range of brilliances within the displayed image
contrast
determines brilliance of displayed image
brightness
scan converters
store images (write) and display them (read)
made grayscale imaging possible
translates info from spoke format to video format
can be digital or analog
funnel shaped vacuum that shoots image info
analog scan converter
benefit of analog scan converter
GREAT spatial resolution
limitations of analog scan converters
images fade, flicker, and are unstable and deteriorate
digital scan converters
convert images into numbers and store as a series of ZEROs and ONEs
advantages of digital
uniform, stable, durable, instant speed, accurate
smallest building block of a digital picture
pixel
high pixel density has high _______ resolution
spatial
smallest amount of computer memory
bit
bits are bistable and can only have a value of
0 and 1
group of 8 bits
byte
2 bytes, or 16 bits is called
word
when we talk about pixels, we are referring to the image’s
spatial resolution
when we refer to bits, we are referring to the image’s
shades of gray
images with many shades of gray have great _____ resolution
contrast
how do we calculate number of shades of gray
2 ^ # of bits
processing of reflected signals before storage is called
preprocessing
processing after storage is called
postprocessing
Preprocessing
compensation compression WRITE magnification persistence spatial compounding edge enhancement fill-in interpolation
postprocessing
any change after freeze frame black / white inversion READ magnification contrast variation 3D rendering
a way to improve detail by enlarging a portion of an image
magnification
selected portion of image in magnification
region of interest, ROI
read magnification
occurs AFTER image data is stored in scan converter (post processing) uses old data larger pixel size same amount of pixels as original ROI unchanged resolution
write magnification
applied before storage in scan converter (preprocessing) uses new data identical pixel size more pixels than in the original ROI improved spatial and temporal resolution
method of improving image quality, creates long sound pulses containing a wide range of frequencies, occurs in the pulser, alter long reflected pulses into a form suitable for high image quality
coded excitation
coded excitation improves ____ resolution
contrast, axial, and spatial
Spatial Compounding
method of using sonographic info from several imaging angles to produce a single image
o Frames are overlapped / compounded
o Reduces speckle and minimizes shadowing artifacts
o Limitations – reduced frame rates, reduced temporal resolution
o Uses electronic steering
o Available only with phased array transducers
Frequency compounding
reduces speckle artifact and noise in US images
o All reflected sound pulses contain a large range of frequencies, with frequency compounding the reflected signal is divided into sub-bands of limited frequencies and an image is created from each sub-band
o The images from each sub-band are then combined into a single image
Edge enhancement
makes pictures look sharper by emphasizing sharp edge boundaries in the image, such as the reflecting surface between two media with different gray scale levels
o Works by increasing the contrast in the area around the edge
Temporal Compounding
also called persistence or temporal averaging
o Image processing technique that continues to display information from older images
o Several previous frames are superimposed on the most current frame
o Produces a smoother image with reduced noise, higher signal to noise ratio, and improved image quality
o Limitations – reduction in displayed frame rate which reduces temporal resolution
o Persistence/temporal compounding is the most effective with slowly moving structures and less useful in rapid moving structures such as echo because rapid motion cannot be observed acuratelly
Fill-in interpolation
2D images created from multiple ultrasound pulses into the body, with sector shaped images the scan lines separate at increasing depths, gaps/missing data exist between the scan lines and interpolation is a method of constructing new simulated data points to fill in the gaps
o Goal is to fill in the gaps of missing data in a way that cannot be detected by the observer
o Predicts grayscale levels of missing data
o A form of preprocessing
o As the line density increases with fill-in, the spatial resolution increases
Elastography
a dynamic technique that produces images from sound reflections in an entirely new way
o Images are related to the mechanical properties of tissue
o Theory of elastography – tissues will deform differently following the application of a force
o Estimates of tissue stiffness are obtained
o Stiffness data and ultrasound reflections are combined into images called elastograms
o Can be combined with anatomical images and doppler to add to the diagnostic value of the ultrasound exam
o Can differentiate between benign and malignant tumors
PACS system
picture archiving and communication system
o Describes the digital ultrasound laboratory in which images and medical info are digitized and stored on a large computer network
o 3 major advantages
1. Virtually instant access to archived studies
2. No degradation of data
3. Electronic transmit images and reports to remote sites
o Computer hard drives are the primary digital storage devices used in PACs
DICOM
digital imaging and computers in medicine
o A set of rules, or protocols, that allows imaging systems to share information on a network
o Assures current imaging modalities can communicate
o Guarantees that all devices developed in the future will easily attach to the PACs network
