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System Matrix Calculation for 2D Image Reconstruction Algorithms for the Clear-PEM Scanner

N. Matela, M. V. Martins, N. Oliveira, P. Rodrigues, A. Trindade, J. Varela, P.D. Almeida


The Clear-PEM system is a prototype scanner for Positron Emission Mammography (PEM), currently under development. In the scope of this project, we have implemented three iterative algorithms for 2D image reconstruction, using linograms: the Algebraic Reconstruction Technique (ART), the Maximum Likelihood – Expectation Maximization (ML-EM) and the Ordered Subsets – Expectation Maximization (OS-EM) algorithms. All these algorithms require the calculation of a system matrix, which contains the information about the probability of a pair of photons being the product of an annihilation occurred in a certain voxel of the object.
In this paper, we present three different methods that we have developed (the pixel-driven, the ray-driven and the tube-driven method) to calculate the system matrix. The comparison of these methods was done with the help of Monte Carlo simulated data, which allowed evaluating image spatial resolution, convergence speed and image uniformity.
The results showed that the tube-driven method allowed the best image spatial resolution and the best values of the homogeneous index calculated, with any of the image reconstruction algorithm. These results strongly recommend the use of this system matrix in future works in which we will compare the image reconstruction algorithms regarding the lesion detectability with data simulated using a digital breast phantom.


Positron Emission Mammography (PEM), 2D Iterative Image Reconstruction, System Matrix Calculation

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