Well there is not a definitive answer as this depends on the quality of the dataset, and this could vary from one image to another. However, a recent work approaches this problem from a different perspective, by providing an improved characterisation of ultrasound tissue images. An adaptive method terminates automatically the wavelet packet decomposition at the optimal level by assessing the fractal characteristics of the subbands at each resolution level. The open access paper "Quantification of ultrasonic texture intra-heterogeneity via volumetric stochastic modeling for tissue characterization" can be accessed by the following url: http://dx.doi.org/10.1016/j.media.2014.12.004