ultrasound physics ch 15
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What does Bistable mean?
images composed of only 2 shades: black and white
What are two user controls on the monitor that can alter characteristics of displayed images?
- 1.) Contrast
- 2.) Brightness
What does the contrast control do?
- Determines the range of brilliancies within the displayed image. Bistable images, in which only white and black appear, are high contrast.
- High contrast = bistable
- Low contrast = many gray shades
What does the brightness control do?
determines the brilliance of the displayed image.
Brightness (whiter image) or not (darker image)
What do scan converters do?
- translates the information from the spoke format into the video format.
- Changes the format of the data.
What are analog numbers?
"real world" numbers that are found in our everyday lives.
Analog numbers have...
an unlimited and continuous range of values.
What are digital numbers?
numbers associated with computer devices.
Digital numbers have...
a limited # of choices and are only discrete values
What is spatial resolution?
What resolution is great with analog scan converters?
Spatial resolution, because of the large number of storage elements within the matrix.
Analog scan converters are now obsolete because of the following limitations: (4)
- 1.) Image fade- stored charges on the silicon wafer dissipate over time.
- 2.) Image flicker - caused by switching between read and write modes.
- 3.) Instability- picture quality depends on many factors including length of use, room temperature, and humidity.
- 4.) Deterioration- image degrades as the device ages.
What do digital scan converters do?
they use computer technology to convert images into numbers called digitizing.
What are the advantages of digital scan converters? (5)
- 1.) Uniformity- consistent gray scale quality throughout the image.
- 2.) Stability- does not fade or drift.
- 3.) Durability- not affected by age or heavy use.
- 4.) Speed- nearly instant processing
- 5.) Accuracy- error free.
What are the two important elements of digital scan converters?
What is pixel density?
the number of picture elements per inch.
Higher pixel density is achived with...
Spatial resolution improves with what pixel density?
higher pixel density and creates an image with greater detail.
What is bit?
a bistable number either having a value of 0 or 1.
What is a binary number?
a group of bits and a series of zeros and ones, such as 101000100.
What is a byte?
a group of eight bits of computer memory such as 10011111.
What is a word?
computer memory that consists of 2 bytes = 16 bits.
What makes better contrast resolution?
more bits per pixel which is more shades of gray per pixel.
examples of calculating # of shades of gray
# of bits
- # of bits # of shades
- 1 2
- 3 8
What three things does pixels pertain to?
- 1.) image element
- 2.) image detail
- 3.) spatial resolution
What are three things does bits pertain to?
- 1.) computer memory
- 2.) gray shades
- 3.) contrast resolution
What form is less susceptible to contamination?
(analog or digital)
What is the five step process to translate image information?
- 1.) Analog to digital (A to D) converter
- 2.) Preprocessing- stored in scan converter's memory
- 3.) Postprocessing- Any processing after storage in the digital scan converter.
- 4.) Digital to Analog (D to A) converter
- 5.) Video display
to move information from real world to computer world requires what type of converter?
analog to digital or A to D converter
To move information from computer world to real world requires what type of converter?
digital to analog or D or A converter
What is not reverseable or undoable? (preprocessing or postprocessing)
What is reverseable or can be undone? (preprocessing or postprocessing)
WHat is magnification?
the sonographer can improve the visualization of the anatomic detail by enlarging a portion of an image to fill the entire screen.
What is the selected part of the screen called?
region of interest or ROI
What are the two different forms of magnification?
- 1.) Read magnification
- 2.) Write magnification
What is coded excitation?
it is a sophisticated method of improving image quality.
Creates a very long sound pulses containing a wide range of frequencies, so the coded pulse is strong but still keeps the peak intensity below the FDA's limit. Improving penetration results.
What is spatial compounding?
- a method of using sonographic information from several different imaging angles to produce a single image.
- 1.) starts by acquiring multiple frames from different viewing angles
- 2.) the frames are than combined (overlapped or compounded) to form a single real-time image.
What can spatial compounding imaging reduce?
reduces speckle and minimizes shadowing
What are the limitations to spatial compounding?
The frame rates and reduced temporal resolution.
What is frequency compounding?
- an advanced technique, where the reflected signal is divided into subbands of limited frequencies, and an image is created from each subband. The images from teh subbands are then combined, or compounded, into a single image.
- It creates subtle bright and dark highlights on either side of these boundaries to make them appear more defined.
What is edge enhancement?
is an image processing method that makes pictures look sharper. The computer identifies and emphasizes sharp edge boundaries in teh image, such as the reflecting surface between two media with different gray scale levels.
What are two other words for temporal compounding?
- temporal averaging
What is temporal compounding?
is an image processing technique that continues to display information from older images.
What is the limitation to temporal compounding?
reduction in the displayed frame rate, which reduces temporal resolution.
What is temporal compounding best used for?
What is temporal compounding worse used for?
best- slow moving structures
worse- fast moving structures such as valves
What is Interpolation?
is a method that predicts what information that lies between the gaps and improves the spatial resolution.
What is Elastography?
is a dynamic technique that produces images from sound reflections based on differing stiffenss.
What is PACS?
The digital ultrasound laboratory in which images and additional medical information are digitized and stored on a large computer network.
What does PACS stand for?
Picture Archiving and Communications System
What is DICOM?
Is a set of rules, or protocols, that allows imaging systems to share information on a network.
What does DICOM stand for?
Digital Imaging and Computers in Medicine
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