1. A method for producing an image with an ultrasound system, the method comprising the steps of: a) acquiring, with the ultrasound system, a series of ultrasound image frames; b) producing a composite image by accumulating a plurality of ultrasound image frames in the acquired series of ultrasound image frames, wherein the plurality of ultrasound image frames are acquired during a time window that includes a selected ultrasound image frame; c) calculating a normalized weighting image using the selected ultrasound image frame and the composite image; d) producing a constrained image by multiplying the normalized weighting image by the composite image; and e) repeating steps b) through d) with successive different selected ultrasound image frames.