1. A method for imaging an image field, comprising: transmitting a plurality of laterally spaced transmit beams from a probe including an array of transducer elements, each transmit beam encompassing a plurality of laterally spaced line positions; producing, using a multiline receive beamformer, a plurality of receive lines of the image field at the line positions in response to one transmit beam; using a multiline combining circuit, responsive to a plurality of r.f. receive line signals which relate to a common line position produced by the multiline receive beamformer in response to a plurality of transmit beams, to delay r.f. receive line signals of a receive line with a phase characteristic which varies as a function of depth and to combine the plurality of r.f. receive line signals to produce transmit refocused image data; detecting a presence of motion in the image field; and displaying an image utilizing the transmit refocused image data, wherein a number of the plurality of r.f. receive line signals combined by the multiline combining circuit is a function of the presence of motion.