Lecture 3: Image reconstruction Flashcards
1
Q
Explain how FBP works. (8 marks)
A
- Acquire projections using a translate - rotate geometry with two collimators.
- These images suffer from a 1/r point spread blurring effect
- Remove this by filtering the projections (multiplying projections by a convolution kernel)
- summary:
- acquire projections
- filter images
- backproject the images
- repeat for large set of projections
Draw this process out.
2
Q
How are FBP images normally stored? What do different lines in this image correspond to? (3 marks)
A
They are usually stored as sinograms, transmission profiles which have been combined.
Different lines in the image correspond to different projection angles.
3
Q
What is meant by iterative reconstruction? (3 marks)
A
- Make a guess of what the image is using FBP reconstruction.
- Compare the guess to the actual projection data.
- Correct guess based on the comparision and repeat the process in an iterative manner…
4
Q
What advantages does iterative reconstruction offer? (3 marks)
A
Less noise, artefacts and dose.
5
Q
Sketch and describe the characteristics of fan beam CT design. (4 marks)
A
- Source to detector beam geomtry spreads out like a fan.
- High heat capacity for the anode.
- Continous rotation and a helical path.
- There is collimation after the source and before the detector.
6
Q
What is meant by pitch in a CT context? (1 mark)
A
Pitch = travel / width
7
Q
How does digital breast tomosynthesis work? (5 marks)
A
Sketch this one out…
- source moves in an arc about a pivot point
- breast and detector remain still
- creates reconstructed slices at depth
- due to pivoting the tissue at a depth, d, is clear with the over and underlying tissue out of focus, unlike regular mammo
8
Q
What are the features of a modern CT scanner? (5 marks)
A
- 3rd generation, cone-beam, multi-detector
- uses iterative reconstruction
- volume data-sets
- high heat capacity
- continuous rotation
