A modified perturbation method (mpm) arising from the replacement of the sensitivity matrix by the Jacobian matrix is presented. Our results have been made using an array processor board with four T-800 inmos transputers. The numerical algorithm has been matched to the new system and the procedure reached a minimum SO times faster than for a single pc/at with mathematical co-processor. Several phantoms have been reconstructed. From the results one can see the applicability of the mpm algorithm to complicated models.