A matrix inversion algorithm based on the Sherman-Morrison formula is analyzed and compared with the classical Gauss-Jordan algorithm. In particular the results obtained in a Cray T3-E by the parallel versions of both algorithms are compared. Key-Words:Sherman-Morrison formula, matrix inversion, Parallel algorithms, Cray T3-E

This paper presents an alternative formulation for the cone-beam projections given an arbitrary source trajectory and detector orientation. This formulation leads to a new inversion formula. As a special case, the inversion formula for the spiral source trajectory is derived.