Iterative image reconstruction for positron emission tomography: a study of convergence and quantitation problems

Iterative reconstruction techniques have been shown to have superior noise characteristics compared to conventional filtered backprojection (FB). The main drawbacks of the iterative methods are the increased computational burden and the difficulty in establishing a stopping criterion and ensuring proper quantitation in different imaging situations. Using a combination of techniques, it has been possible to reduce the time required for iterative reconstruction to a few times that of FB. The quantitation properties of FB have been compared to those of additive and multiplicative iteration formulas, including the maximum likelihood method. Without acceleration, all three tested methods gave quantitative results after 40 iterations, regardless of the number of counts in the data. However, with noisy data, the best images in a least-squares sense were typically obtained after 10-20 iterations