IMPLEMENTATION OF A MODEL-BASED NONUNIFORM SCATTER CORRECTION SCHEME FOR SPECT

In this paper four scatter-compensation schemes are considered, The fo ur schemes are all based on a previously developed two-dimensional (2- D) scatter model, Reconstruction is achieved using the iterative expec tation-maximization maximum-likelihood (EM-ML) algorithm. The schemes consist of: 1) including the model in both the forward and hack projec tor; 2) just including the model in the forward projector; 3) and 4) i mplementing the model in a subtraction and addition scheme, respective ly, Monte Carlo simulated projection data are used to test the accurac y, convergence properties, and noise properties of the four scatter-co mpensation schemes. Data are simulated for both uniformly and nonunifo rmly attenuating objects, The results show that all four correction sc hemes yield images which are similar in terms of accuracy to that obta ined from reconstructing scatter-free data, The subtraction scheme is shown to converge faster than the other compensation schemes, both in terms of iterations and actual time required for reconstruction, The s cheme in which the model is only used in the forward-projector and the scatter-addition scheme both performs slightly better, in terms of si gnal-to-noise ratio (SNR), than the subtraction scheme, However, the f orward projector scheme requires significantly more CPU time for recon struction. The correction scheme in which the scatter model was includ ed in both the forward and backprojectors is shown to produce accurate images with SNR's higher than even a perfect scatter rejection scheme , dWhile the scatter correction scheme with the model in both the forw ard projector and backprojector has superior noise properties to the o ther algorithms, the results suggest that the faster subtraction/addit ion schemes will probably prove most useful for routine clinical scatt er compensation.