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;
15 Cards in this Set
- Front
- Back
- 3rd side (hint)
|
How is the 3rd image plane created in SPECT?
|
Through computer generated algorithms
|
|
|
|
Creating medical images from radiation around the body of a patient is what type of problem?
|
Inverse problems
What does this mean? |
Inverse problems are characterized by the fact that the information of interest is not directly available
|
|
|
Why can't we recreate an exact anatomical image in SPECT?
|
measurements are incomplete (sampling) and inaccurate (noise)
|
|
|
|
What is a representation of the distribution of the tracer in a single slice at every angle of the acquisition?
|
sinogram
|
|
|
|
What are the 2 methods of reconstruction of the 3rd plane in SPECT?
|
1. Analytical
2. Iterative Give the most popular application of each? |
1. Analytical - FBP - filtered back projection
2. Iterative - OSEM - ordered subset expectation maximization |
|
|
What was the 1st and simplest reconstruction method for SPECT?
|
Back projection
How is it used today? |
Used in combination with filtering, called filtered backprojection, most common filter is Butterworth
|
|
|
What is back projection?
|
The ray sums of a series of 2 dimensional images acquired around an object are added together. The overlapping images represents a cross sectional image of the object
|
|
|
|
What causes a "star" artifact?
|
It is the result of simple back projection
What helps diminish it? |
acquiring numerous ray sums, which then need to be filtered
|
|
|
What is the TYPE of filter used with SPECT imaging reconstruction?
|
It is called a Ramp filter
What does it correct for? |
sudden density changes or sudden changed in detected radioactivity
eliminates frequencies which are responsible for the blurring of the image |
|
|
How does iterative reconstruction work?
|
It is repetitive correlation between an assumed and measured matrix. It is assumed that all points in the matrix are the same value, which is then compared with measured value. the two are brought into agreement by repetitive processing until acceptable criterion is met
|
|
|
|
What iterative method is better, MLEM or OSEM? and why?
|
OSEM because it is a newer mathematical reconstruction method and it is faster
|
|
|
|
What are the advantages of iterative methods over filtered backprojection?
|
1. it "knows" the physics of SPECT/PET
2. Attenuation correction 3. reduction of "star" artifact 4. overall quality is better What is its one big disadvantage? |
it is slow as it requires tens of hundreds of iterations to arrive at a good image (however better and faster computers is making this a non-issue)
|
|
|
How is spatial and time domains interpreted in the frequency domain as it is read by the computer?
|
time and spatial domains are converted into a series of sine waves that are more easily read by the computer. (changing slopes of count profiles represent frequency; steep slope is high frequency and flat portion is low)
give the 3 general categories of spatial frequency and how they relate to images: |
1. low frequencies include components of an object that are large and homogeneous, depicts the general shape of an object
2. middle frequencies refers to the area where counts are moderately changing, this is where the desired object information is. 3. high frequency refers to areas where counts are changing quickly, small objects and sharp edges as well as noise are found here |
|
|
What is the problem with partial volume in SPECT reconstruction?
|
thickness of the slice we are viewing is actually larger because counts have bled over from adjoining slices, giving only partial volume of the slice
|
|
|
|
What happens when there is no attenuation correction?
|
The center of the image will be darker, since it has less counts
|
|
