Lecture 13: Iterative Back Projection Reconstruction

Question 1

Define iterative back projection reconstruction

Answer 1

An alternative to crude or filtered back projection that uses numerical techniques. It is slow, however, it can result in better images and with the introduction of faster computers it is becoming more popular (and more viable).

Question 2

How does iterative back projection work?

Answer 2

Initially, an intelligent guess at the object is taken by producing a ‘P x q’ grid of voxel values. The guess is then used to make simulated projections. These simulated projections are then compared to the real data, and the simulated projection is systematically varied until they match.

Question 3

A key concept in iterative back projection reconstruction is _____ _______. It is the length of a ray through each voxel.

Answer 3

Path length

Question 4

What is the equation for the simulated projections in iterative back projection?

Answer 4

Question 5

Describe the algorithm used to determine the true voxel values in iterative back projection.

Answer 5

1) Take a projection at φ=0, and spread values back evenly across the voxels in each row to generate an initial guess.
2) Compute the simulated projection for the next angle and compare the result to the real data.
3) Compute the difference between the simulation and real data, and spread the difference across the rows.
4) Repeat for the next angle.