1. A method for tissue border detection using ultrasonic diagnostic images, comprising: searching an initial central point of a target region in ultrasonic diagnostic images of a examined object; and detecting a border of the target region, with the initial central point being a pole, by searching positions of the target region border along polar lines across the pole, and calculating an energy function of intensity distribution based on regions on both sides of the border, wherein, in each line, the position corresponding to a minimum value of the energy function of the intensity distribution is the border of the target region.