Ultrasound imaging systems and methods for detecting object motion
Ping-based imaging systems may be used for tracking motion of hard or soft objects within an imaged medium. Motion detection and motion tracking may be performed by defining fingerprint points and tracking the position of each fingerprint point based on the echoes of multiple transmitted pings.
1. A method of tracking motion of an object with an imaging system comprising the steps of:
defining a fiducial region in a region of interest with a controller of the imaging system;
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;
identifying a fingerprint within the fiducial region, wherein the fingerprint comprises a pattern of data in the received echoes that is identifiable as a data string;
storing echo data received by each of the plurality of transducer elements in a separate memory string;
detecting movement of the fingerprint with the controller; and
communicating a signal with the controller indicating that movement of the object relative to the transducer array has occurred.
2. The method of claim 1 , further comprising obtaining at least one image of the region of interest with the imaging system, and wherein defining the fiducial region comprises selecting at least one point in the at least one image.
3. The method of claim 1 , wherein detecting movement of the fingerprint comprises identifying a fingerprint point in each memory string, and detecting a shift in a position of the fingerprint point in each memory string.
4. The method of claim 3 , wherein the fingerprint comprises at least one machine-identifiable peak.
5. The method of claim 1 , further comprising combining memory strings from two or more unfocused ultrasound pings to form a combined memory string before detecting a shift in a position of the fingerprint in the combined memory string.
6. The method of claim 1 , further comprising combining memory strings from two or more transducer elements of the transducer array to form a combined memory string before detecting a shift in a position of the fingerprint in the combined memory string.
7. The method of claim 1 , wherein detecting movement of the fingerprint comprises identifying a fingerprint pattern with the controller in a location other than an original location.
8. The method of claim 1 , further comprising tracking motion of the object with the controller, comprising:
obtaining a pre-movement fingerprint pattern with the controller corresponding to the fingerprint contained within the fiducial region;
defining a search region surrounding the fingerprint with the controller;
obtaining a plurality of post-movement search images with the controller by retrieving post-movement data corresponding to the search region surrounding the fingerprint and beamforming the search region;
searching the search region with the controller for a new position of the pre-movement fingerprint pattern;
determining a new position for the fingerprint with the controller based on finding a fingerprint pattern in the search region; and
communicating a signal with the controller indicating a new position of the fingerprint or a new position of the object.
9. The method of claim 8 , wherein only the search region is beamformed and echo data that does not correspond to the search region is not beamformed during the step of tracking motion of the object.
10. The method of claim 1 , further comprising detecting a shift in a position of the fingerprint based on data in a plurality of the memory strings corresponding to a plurality of receiving transducer elements.
11. The method of claim 10 , wherein the plurality of receiving transducer elements are closer to opposite ends of the transducer array from one another than they are to one another.
12. The method of claim 1 , wherein the fingerprint has an area of between 1 square nanometer and 100 square micrometers.
13. The method of claim 1 , wherein the fiducial region lies within a free depth range defined as a range of distance from each transducer element in which returning echoes result from only a single transmitted ping, and transmitting pings at a rate greater than an inverse of a maximum round-trip travel time between a transmitting transducer element, a furthest reflector, and a receive element furthest from the transmitting element.
14. The method of claim 1 , wherein the transducer array comprises a first plurality of one-dimensional linear transducer elements aligned with a first image plane and a second plurality of one-dimensional linear transducer elements aligned with a second image plane that intersects the first image plane, and wherein transmitting a series of unfocused pings into the region of interest comprises transmitting a first series of pings from a first single element of the first plurality of one-dimensional transducer elements and transmitting a second series of pings from a second single element of the second plurality of one-dimensional transducer elements.
15. The method of claim 1 , wherein the transducer array comprises a first plurality of one-dimensional linear transducer elements aligned with a first image plane extending into the region of interest, a second plurality of one-dimensional linear transducer elements aligned with a second image plane extending into the region of interest, the second image plane intersecting the first image plane, and a point source transmitter element; and wherein transmitting a series of unfocused pings into the region of interest comprises transmitting a series of unfocused pings from the point source transmitter element.
16. The method of claim 15 , wherein the point source transmitter element is positioned at an intersection of the first image plane and the second image plane.