Incorporating a priori information into the Sheffield filtered backprojection algorithm

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Abstract
The Sheffield image reconstruction algorithm is based on the assumption that the initial conductivity distribution of the body being imaged is uniform. In many situations this assumption is violated. Previous attempts at incorporating a priori information by modifications to the backprojection matrices were ineffective. An alternative method of including a priori information became apparent following the recent reformulation of the Sheffield image reconstruction algorithm. Applying matrix algebra to the image reconstruction equations reveals that the incorporation of a priori information can be considered as either a modification to the original backprojection matrix or a component of a composite data filter. A simple two-dimensional model of the adult head was chosen to test this approach. The results of imaging studies using synthetic data derived from this model show that a priori information has been successfully incorporated into the image reconstruction process. The ability to include a priori information into the image reconstruction process may have significant implications for the more challenging applications of EIT such as imaging the adult head.