This study presents a geometric model for

segmentation of ultrasound images. A partial differential

equation based flow is designed in order to achieve a

maximum likelihood segmentation of the target in the

scene. The flow is derived as the steepest descent of an

energy functional taking into account the density

probability distribution of the gray levels of the image as

well as smoothness constraints. To model gray level

behavior of ultrasound images the classic Rayleigh

probability distribution is considered. The steady state of

the flow presents a maximum likelihood