Iterative image enhancement algorithms for multi-layer specimens in scanning tomographic acoustic microscopy

A performance evaluation of three iterative enhancement techniques is presented. The reconstruction obtained with the backward propagation algorithm is used as the initial estimate for these recursive procedures. The results indicate that the estimates can be improved consistently by using Newton´s method, the conjugate gradient method, or pixel-by-pixel optimization. In addition to simulated data, experimental data samples have been applied to this analysis to demonstrate the capability, effectiveness, and convergence properties of these techniques. In the computer simulations at low signal-to-noise ratios (SNRs), the conjugate gradient method was the best, and at high SNRs Newton´s method was superior