Midterm Review Flashcards
What is the function of the image processor
Converts digital scan line data into frames
Frames are processed, stored in the image memory, retrieved and can be processed again
Converts this digital information into analog form for the display
6 examples of preprocessing
Pixel interpolation, persistence, panoramic, 3D/4D imaging Spatial compounding Write zoom
What is pixel interpolation
Assigns a brightness value to a missing pixel based on the average of the brightness of adjacent pixels
What is persistence
Averaging of sequential frames in time, can reduce artifact
When speckle is reduced, how is the image affected
The image is smoother
What is panoramic imaging? Give an example of when it would be used
• This allows an image with a larger field of view than the transducer will normally allow on a single frame. This is done by compiling an image as the transducer is slid longitudinally along the target structure. For example, for a long thrombus, you could follow the vein with the panoramic view, showing the extent of the vein
How are 3d images created? What are their useful applications?
• Assembles multiple 2D slices into a 3D volume of echo information in voxels, which are stored in the image memory. This can be used for obstetrics, imaging of masses in the liver, breast, etc.
What is put into the image memory
Frames comprised of a matrix of pixels, each dot representing echo information from a particular location
How does the read magnification work?
This is a post processing function that involves retrieving a frame from memory, and displaying a smaller group of pixels from it by expanding them
How does write magnification work
Aka write zoom
Involves writing a smaller anatomic field of view to the entire frame. Can involve depth/scan area. But can also be an independent function
Why is B colour used
Human eye can distinguish more shade of colour than shades of grey
Why is digital analog required
Display will require analog voltages so the digital signals need to be converted
What is stored in the image memory
The 100-130 frames before you hit the freeze button
What are you really doing when you hit the freeze button
Retrieving and displaying the last frame from the image memory
What is cine loop
Involves reviewing the frames stored within the image memory
What is a pixel
A square in the grid (matrix) of a frame
What is a matrix
A grid of pixels that will contain the information to be displayed on the screen
What does the number stored in a pixel represent
Correspond to the shade of grey at a particular location
What is a bit
Binary digit
A unit of memory
The shades of grey assigned to an echo are based on
Echo amplitude
What happens to the spatial resolution in memory as there is increase in dpeth
Degrades because pixels/cm decreases
Spatial resolution in memory is a limiting factor to
Image display resolution
What is contrast resolution
The ability to distinguish two separate objects as different intensities/shades of gray
What units is contrast resolution represented as
DB/shade
What affects the contrast resolution
Dynamic range and bits/pixel
