In this paper we present a deconvolution technique for ultrasound images based on a Maximum Likelihood (ML) estimation procedure. In our approach the ultrasonic radio-frequency (RF) signal is considered as a sequence affected by intersymbol interference (ISI) and AWGN noise. In order to reduce the computational cost, the estimation is performed with a reduced-state Viterbi algorithm. The channel effect is estimated in two different ways: either measuring the transducer response with an experimental setting or with blind homomorphic techniques. We verify an image quality enhancement with respect to different metrics. Extensive tests are made to estimate the quantization alphabet that gives the best performances.