Flashcards in Chapters 15-16 Deck (77):
bistable image are composed of how many shades?
2- black and white
the range of brilliancies within the displayed image.
What does low contrast mean?
many grey shades
what does high contrast mean?
bistable- white and black
What does brightness determine?
the brilliance of the displayed image
What does the scan converter do?
translates the info from the spoke format into video format
What are analog numbers?
"real world numbers"
unlimited number of choices and continuous range of values
What are digital numbers?
associated with computer numbers
they only have discrete values
How does the analog scan converter work?
funnel shaped vacuum tube with a stream of charged particles called electrons, contain the image info, and are shot out of the electron gun. the larger end of the tube contains a dielectric matrix or silicon wafer.
What are limitations of analog scan converters?
image fade-silicon wafer dissipate over time
image flicker-caused by switching between read and write modes
instability- image quality depends on many factors like length of use, room temp, and humidity
deterioration- image degrades as device ages
What is superb with analog scan converter?
spatial resolution or image detail
Digital scan converters use computer technology to convert images into numbers, a process called what?
What are the advantages for digital scan converter?
uniformity- consistent gray scale quality throughout the image
stability- does not fade or drift
durability- no affected by age or heavy use
speed- nearly instant processing
accuracy- error free
What are the two important elements of digital scan converters?
pixel and bit
What is a pixel?
smallest building block of a digital picture
What is the number of picture elements per inch?
How is pixel density and spatial resolution related?
How is higher pixel density achieved with?
smaller pixels =many pixels per in
What is a bit?
smallest amount of computer memory
What makes up a byte?
What does a word of computer memory consists of?
two bytes, or 16 bits
Images with many gray shades have better what resolution?
how is contrast resolution and bits per pixel related?
more bits per pixel improved contrast resolution
How many gray shades in a 5 bits?
What is the difference between a pixel and a bit?
What is the five step process of translating image info?
1. A-to-D converter
2. digital info is stored in the scan converter. any processing of the reflected signals before storage is preprocessing.
4. D-to-A converter
5. video display
What is an example of an A-to-D converter?
a computer mouse
What is an example of an D-to-A converter?
What is preprocessing?
the manipulation of image data before storage in the scan converter.
cant be undone or reversed
What is postprocessing?
manipulation of image data after storage in the scan converter
can be reversed
When does postprocessing occur?
occurs after A-to-D conversion (digitization) and storage
What are examples of preprocessing?
What are examples of post processing?
any change after freeze frame
What is it called when you enlarge a portion of an image to fill the entire screen?
What are the two types of magnification?
When does the read magnification occur?
after the image is stored in the scan converter
When does write magnification occur?
before the storage in the scan converter
What are some characteristics of read magnification?
uses old data
larger pixel size
same # of pixels as the original ROI
unchanged spatial resolution
unchanged temporal resolution
What are some characteristics of write magnification?
acquires new data
identical pixel size
more pixels than the original ROI
improved spatial resolution
may improve temporal resolution
When does temporal resolution improve with write magnification?
if the bottom of the region of interest is shallower than the original images depth of view.
What is a sophisticated method of improving image quality?
Where does coded excitation occur?
in the pulser
What does coded excitation provide?
higher signal to noise ration
improved axial resolution
improved spatial resolution
improved contrast resolution
What does compound imaging do?
reduces speckle and minimizes shadowing artifacts
What are limitations of spatial compounding?
reduced frame rates and reduced temporal resolution
What type of steering is used in spatial compounding?
only available with phased array transducers
What is an advanced technique that reduces speckle artifact and noise in ultrasound images?
What imaging process make pictures looks sharper?
create subtle bright and dark highlights on either side of these boundaries to make them appear more defined.
What is it called when reflected sound wave is divided into parts with different freq ranges with frequency compounding?
What are other names for temporal compounding?
persistence or temporal averaging
What is the process technique that continues to display info from older imaging?
What is a limitation of persistence?
reduction in displayed frame rate, which reduces temporal resolution.
What is persistence more effective with?
slow moving structures.
cannot display rapid moving structures accurately
What is the purpose of fill in interpolation?
to fill in the gaps of missing data in a way that cannot be detected by the observer
What does fill in interpolation increase?
line density, which improves spatial resolution
What does PACS stand for?
picture archiving and communications system
What are three advantages for PACS?
virtually instant access to archived studies
no degradation of data-which happens with analog archiving
store and forward telemedicine
What are the primary digital storage devices used in PACS?
computer hard drives
What does DICOM stand for?
digital imaging and computers in medicine
is the set of rule that allows the components of network to communicate
Define dynamic range
a method of describing the extent to which a signal can vary and still maintain accuracy
"number of available choices"
Weak signals are below the systems ____
What are the units for dynamic range?
What is dynamic range?
a comparison, a relative measurement, or a ratio between the largest and smallest signals that are measured accurately.
The strong signals ____the system
The dynamic range of info ___(increases or decreases) the more it is processed?
What eliminates inaccuracies in the dynamic range?
the process of compression
What is the technique that reduces the dynamic range of a signal without introducing errors?
What are the requirements of compression?
the largest signal remains the largest
the smallest signal remains the smallest
the range of signals is reduced
What is an alternative description of dynamic range?
number of choices
What does a narrow dynamic range?
fewer gray shades. bistable image, only contains black and white, has the narrowest dynamic range.
Images that display few shades of gray are also called what?
What does wide dynamic range?
many shades of gray, a gray scale image- contains many shades of gray has the widest dynamic range
Images that display many shades of gray are also called what?
Few choices have a ____ dynamic range
many choices have a ____ dynamic range
What do fewer shades have?
black and white (bistable)
narrow dynamic range