Signal-to-noise-ratio (SNR) images were constructed by a sliding window technique. Theoretical derivations of the first order statistical properties of SNR images are given for the case of intensity coding of the original images for low number densities and for the limit case of fully developed speckle. The original images were obtained by realistic simulations of backscattering by homogeneous media, while using a range of number densities of the scatterers (isotropic scattering). The SNR imaging method is illustrated by results obtained from simulated scattering media containing a lesion that is contrasting in reflectivity level or in number density of the scatterers. A considerable improvement in lesion detection is obtained if the primary difference from the background speckle is due to a different number density of the scatterers within the lesion.