A method of tracking motion of an object with an imaging system comprising the steps of: obtaining at least two images of a region of interest containing at least a portion of the object with the imaging system, the at least two images lying in intersecting two-dimensional planes that also intersect the object; defining a plurality of fiducial regions in the region of interest with a controller of the imaging system, wherein defining the plurality of fiducial regions comprises selecting a plurality of points in the at least one image; defining a fingerprint point within each fiducial region with the controller, wherein the fingerprint point represents an area smaller than any detail resolvable by the imaging system and comprises a machine-recognizable signature representing a portion of a fiducial region, and wherein defining the fingerprint point comprises defining a first fingerprint point at an intersection between the two-dimensional planes and the object, defining a second fingerprint point in a first of the at least two images, and defining a third fingerprint point in a second image not at the intersection; transmitting a series of unfocused ultrasound pings into the region of interest from a transducer array of the imaging system; receiving echoes from the series of transmitted unfocused ultrasound pings with a plurality of transducer elements of the transducer array; storing echo data received by each of the plurality of transducer elements in a separate memory string; detecting movement of at least one fingerprint point with the controller; and communicating a signal with the controller to an external device indicating that movement of the object relative to the transducer array has occurred. obtaining at least two images of a region of interest containing at least a portion of the object with the imaging system, the at least two images lying in intersecting two-dimensional planes that also intersect the object; defining a plurality of fiducial regions in the region of interest with a controller of the imaging system, wherein defining the plurality of fiducial regions comprises selecting a plurality of points in the at least one image; defining a fingerprint point within each fiducial region with the controller, wherein the fingerprint point represents an area smaller than any detail resolvable by the imaging system and comprises a machine-recognizable signature representing a portion of a fiducial region, and wherein defining the fingerprint point comprises defining a first fingerprint point at an intersection between the two-dimensional planes and the object, defining a second fingerprint point in a first of the at least two images, and defining a third fingerprint point in a second image not at the intersection; transmitting a series of unfocused ultrasound pings into the region of interest from a transducer array of the imaging system; receiving echoes from the series of transmitted unfocused ultrasound pings with a plurality of transducer elements of the transducer array; storing echo data received by each of the plurality of transducer elements in a separate memory string; detecting movement of at least one fingerprint point with the controller; and communicating a signal with the controller to an external device indicating that movement of the object relative to the transducer array has occurred. <EOS>