1. A method of collecting ultrasound imaging data at an adjustable collection image frame rate, the method comprising: (a) processing echoes produced from transmission of ultrasound energy into a subject's body by an image frame acquisition device to produce a series of image frames, each image frame comprising data representing an image of a portion of the subject's body at a given time, the image frames including (i) collection image frames, and (ii) interrogation image frames for sampling the subject's body between collection of at least some collection image frames; (b) determining the difference between the current image frame and at least one preceding image frame and outputting a frame correlation coefficient based upon the difference; and (c) adjusting the collection image frame rate of the image frame acquisition device in inverse proportion to the most recent frame correlation coefficient.