Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
14 Cards in this Set
- Front
- Back
- 3rd side (hint)
|
What is the purpose of a filter?
|
1. enhance contrast
2. minimize the effect of noise without significantly degrading resolution when are filters applied? |
post acquisition
|
|
|
What is noise?
|
The statistical variations in the signal due to the random nature of the emission and detection of radiation
|
|
|
|
How can noise be described mathematically?
|
The square root of the mean of all events
|
|
|
|
What is the signal to noise ratio?
|
The mean of all events divided by the square root of those events
|
|
|
|
When is noise most significant?
|
when the counts are low, as in spect imaging.
what greatly improves the SNR? |
increasing the count in low count images because the signal increases greater than noise, increasing counts in a high count image does little to increase SNR
|
|
|
How is a planar image filtered?
|
using a kernel, also called smoothing convolution.
what does this result in and how does this work? |
decreased noise and increased blurring
it works by a calculation in each pixel in an image matrix based on a small area around each pixel |
|
|
What is the industry standard in smoothing kernels?
|
a nine point kernel
how does it work? |
the nearest 8 neighboring pixels are averaged resulting in a more visually appealing image, though more blurry
|
|
|
What is the difference between a smoothing kernel and a sharpening one?
|
a smoothing takes away information from the noise while the sharpening one adds to it creating a sharper image
|
|
|
|
What are the 3 general areas of frequency to be considered in SPECT filtering?
|
1. low frequency background
2. middle frequency information 3. high frequency noise |
|
|
|
What are the 2 main parameters in SPECT filtering?
|
1. cutoff frequency
2. order explain each |
a lower frequency cutoff makes for a smoother image but degrades resolution while a higher frequency cutoff makes for higher resolution but the image looks noiser
the order is the steepness of the signal slope |
|
|
What is a RAMP filter?
|
common in all SPECT reconstruction, it is filtered backprojection, it suppresses the star artifact by eliminating low frequency background and some high frequency noise, it sharpens the image by improving SNR
|
|
|
|
How does a RAMP filter work?
|
unfiltered back projection over emphasizes low frequencies making for a blurred image lacking in details. the RAMP filter assigns a weighting factor and multiplies it, giving the low frequencies the smallest correction and the higher the larger
|
|
|
|
Why can't RAMP filters be used alone for SPECT?
|
because it does not remove much noise, so it must be used in combination with another low pass filter
|
|
|
|
What is the most common low pass filter used in SPECT reconstruction?
|
butterworth
what are its two parameters? |
cutoff and order
|
