System and method for dynamic background subtraction

• US 4,448,200 A
• Filed: 04/27/1981
• Issued: 05/15/1984
• Est. Priority Date: 03/27/1978
• Status: Expired due to Fees

• Current Assignee: University of Southern California
• Original Assignee: University of Southern California
• Inventors: Blankenhorn, David H., Selzer, Robert H., Brooks, Samuel H., Crawford, Donald W.
• Primary Examiner(s): Howell, Kyle L.
• Assistant Examiner(s): Jaworski, Francis J.
• Application Number:
  US06/258,132
• Time in Patent Office: 1,114 Days
• Field of Search: 128/653, 128/660-663, 378/20, 378/151, 364/414, 358/111-112
• US Class Current: 600/425
• CPC Class Codes: A61B 6/481 involving the use of contrast agents
• CPC Class Codes: A61B 6/504 for diagnosis of blood vessels, e.g. by angiography
• CPC Class Codes: A61B 8/06 Measuring blood flow measuring volume flow in general G01F, e.g. G01F1/66, G01F1/72; measuring speed of fluids in general G01P5/00

Abstract

An image acquisition system and method for generating a subtracted image motion picture as an imaging device moves relative to a subject includes an imaging device for first generating a sequence of first image frames as the imaging device moves along an imaging path under operator control and later generating a sequence of second image frames as the imaging device automatically moves along the same imaging path under processor control. Motion along the imaging path can be duplicated by sensing and storing information indicative of the position of the imaging device relative to the subject as a function of time and later commanding servo motors connected to the imaging device using that position information. Each frame in the first and second sequence of frames has position information stored therewith identifying the location along the imaging path at which each frame was generated. The first and second sequence of frames may then be aligned using the position information and subtracted on a frame-by-frame basis to obtain a subtraction image motion picture essentially free of background interference to detect change over time. The first and second motion pictures may be made at different points of time under similar circumstances either with or without the use of a contrast medium, and subtracted to obtain a difference picture to highlight changes over time.

Claims

1. An image acquisition system for generating a subtracted image motion picture of a selected feature of a biological subject comprising:

imaging means including an illumination source, a support for the subject and an illumination receiver, for generating an image of the selected subject feature, at least one of the illumination source, the support and the illumination receiver being movable by an operator whereby there is relative movement between the subject and the illumination receiver along an imaging path selected by the operator;

means for causing at least one of the illumination source, support and illumination receiver to move so that the relative movement between the subject and the illumination receiver is along the imaging path to duplicate said imaging path;

means for generating and storing a sequence of first frames of the image to define a first motion picture as the operator causes relative movement between the subject and the illumination receiver to define the imaging path and a sequence of second frames of the image to define a second motion picture as the relative movement between the subject and the illuminating receiver along the imaging path is duplicated;

means for aligning and registering the first motion picture and the second motion picture on a frame-by-frame basis; and

means for subtracting the aligned second motion picture from the first motion picture on a frame-by-frame basis for generating a subtracted image motion picture of the subject as the relative movement between the illumination receiver and the subject occurs along the imaging path.

2. The system of claim 1 wherein the illumination source is an X-ray generator and the illumination receiver is sensitive to X-ray energy.

3. The system of claim 1 wherein the illumination source is an ultrasound generator and the illumination receiver is sensitive to ultrasound energy.

4. The system of claim 1 further comprising means for maintaining a constant illumination source exposure level during the generation of the first motion picture and the generation of the second motion picture.

5. The system of claim 1 wherein the first motion picture is generated photographically, the second motion picture is generated photographically, and the means for subtracting comprises apparatus for performing frame-by-frame photographic subtraction.

6. The system of claim 1 wherein the support for the subject is stationary and the illumination receiver is movable to define the relative movement along the imaging path.

7. The system of claim 1 wherein the illumination receiver is stationary and the support for the subject is movable to define the relative movement along the imaging path.

8. The system of claim 1 wherein each first frame and each second frame is digitized to define a plurality of first frame pixels for each first frame and a plurality of second frame pixels for each second frame, each first frame pixel and each second frame pixel defined by an address specifying its position in the frame and an illumination energy density value for defining the density of the illuminating energy impinging on the pixel, the means for generating and storing further comprising:

memory means for storing the illuminating energy density values of each pixel; and

the subtracting means further comprising;

means for repeatedly selecting a first frame generated at a selected position along the imaging path and a corresponding second frame generated at substantially the same position along the imaging path, and,

pixel differencing means for subtracting the pixel illumination energy density value of each pixel in the selected second motion picture frame from the pixel illumination energy density value of the pixel in the selected first motion picture frame having a corresponding pixel address.

9. The system of claims 1 or 5 and 8 wherein the means for generating a sequence of first frames and second frames further comprises:

means for generating a sequence of unprocessed first frames;

means for registering at least two of the unprocessed first frames; and

means for averaging the registered unprocessed first frames to define each first frame.

10. The system of claim 1 or 5 or 8 wherein the means for generating a sequence of first frames and second frames further comprises:

means for generating a sequence of unprocessed second frames;

means for registering at least two of the unprocessed second frames; and

means for averaging the registered unprocessed second frames to define each second frame.

11. The system of claim 9 wherein the means for generating a sequence of first frames and second frames further comprises:

means for generating a sequence of unprocessed second frames;

means for registering at least two of the unprocessed second frames; and

means for averaging the registered unprocessed second frames to define each second frame.

12. An image acquisition system for generating a subtracted variable density motion picture of a biological subject wherein there is relative movement of the subject while the motion picture is being taken, comprising:

a source of illuminating energy for illuminating the subject;

means for receiving the illuminating energy and generating a variable density image;

a support for positioning the subject between the source of illuminating energy and the receiving means;

means for selectively changing the relative position between the support and the means for receiving for defining a first relative movement path;

position sensing means for sensing the relative position between the support and the receiving means for generating sensed position signals representative of the relative position between the subject and the receiving means along the first relative movement path;

means for storing the sensed position signals;

means for generating position control signals from the stored position signals;

means for subsequently driving at least a selected one of the support and the receiving means to vary the relative position between the support and the receiving means in response to the position control signals for defining a second relative movement path substantially duplicative of the first relative movement path;

means for generating a first motion picture of the variable density image of the subject during the relative movement along the first relative movement path, and generating a second motion picture of the variable density image of the subject during the relative movement along the second relative movement path wherein the first motion picture has a plurality of first frames, each first frame defining a picture at a specific geometric position along the first relative movement path and the second motion picture has a plurality of second frames, each second frame defining a picture at a specific geometric position along the second relative movement path;

means for aligning the first frames in the first motion picture and the second frames in the second motion picture whereby each first frame and second frame which is aligned represent variable density images at substantially corresponding geometric positions relative to the subject along the respective first and second relative movement paths; and

means for subtracting each second frame from each corresponding aligned first frame for defining a plurality of subtracted variable density frames to define the subtracted variable density motion picture.

13. The system of claim 12 wherein the source of illuminating energy is an X-ray generator and the receiving means is sensitive to X-ray energy.

14. An image acquisition system for generating a subtracted image motion picture of a biological subject comprising:

imaging means for periodically generating a motion picture frame wherein the received illumination at a plurality of predefined locations in the frame is sensed and digitized, to define an array of digitized pixel densities, the array defining a digitized motion picture frame;

means for selectively moving the imaging means along an imaging path whereby there is relative movement between the subject and the imaging means;

means for periodically generating digitized position information representative of the position of the imaging means relative to the subject;

means for storing the digitized position information;

means for subsequently automatically moving the imaging means in response to the stored digitized position information for substantially retracing the relative movement between the subject and the imaging means along the imaging path whereby a first sequence of digitized first frames is generated during the selective movement along the imaging path and a second sequence of digitized second frames is generated during the subsequent retrace along the imaging path;

means for storing the first sequence of digitized first frames and the second sequence of digitized second frame;

means for sampling the digitized position information after each digitized first frame and digitized second frame is generated and storing the sampled digitized position information with each digitized picture frame and each digitized second frame respectively for indicating the position along the imaging path whereat each first frame and each second frame was generated; and

means for aligning the first frames with the second frames in accordance with the correspondence between the sampled digitized position information stored and associated with each first frame and second frame.

15. The system of claim 14 wherein the imaging means is an X-ray imaging device.

16. The system of claim 14 wherein the imaging means is an ultrasound imaging device.

17. A method for generating a subtracted image motion picture of a selected feature of a biological subject comprising the steps of:

generating an image of the selected subject feature, using an imaging device including an illuminating source, a support for the subject and an illumination receiver, as at least one of the illuminating source, the support and the illumination receiver is moved by an operator whereby there is relative movement between the subject and the illumination receiver along an imaging path;

causing at least one of the illuminating source, support and illumination receiver to move so that the relative movement between the subject and the illumination receiver is along the imaging path to duplicate said imaging path;

generating and storing a sequence of first frames of the image to define a first motion picture as the operator causes relative movement between the subject and the illumination receiver to define the imaging path and a sequence of second frames of the image to define a second motion picture as the relative movement between the subject and the illuminating receiver along the imaging path is duplicated;

aligning and registering the first motion picture and the second motion picture on a frame-by-frame basis; and

subtracting the aligned second motion picture from the first motion picture on a frame-by-frame basis for generating a subtracted image motion picture of the subject as the relative movement between the illumination receiver and the subject occurs along the imaging path.

18. The method of claim 17 further comprising the step of maintaining a constant illuminating source exposure level during the generation of the first motion picture and the generation of the second motion picture.

19. The method of claim 17 wherein the first motion picture is generated photographically, the second motion picture is generated photographically, and the step of subtracting comprises frame-by-frame photographic subtraction.

20. The method of claim 17 wherein the step of generating an image comprises the further steps of keeping the support for the subject stationary and moving the illumination receiver to define the relative movement along the imaging path.

21. The system of claim 17 wherein the step of generating an image comprises the further steps of keeping the illumination receiver stationary and moving the support table for the subject to define the relative movement along the imaging path.

22. The method of claim 17 comprising the further steps of digitizing each first motion picture frame and each second motion picture frame to define a plurality of first frame pixels for each first frame and a plurality of second frame pixels for each second frame, each first frame pixel and each second frame pixel defined by an address specifying its position in the frame and a light density value for defining the density of the illuminating energy from the illumination source impinging on the pixel, step of generating and storing further comprising the steps of:

storing the illuminating energy density values of each pixel; and

the step of subtracting further comprising;

repeatedly selecting a first frame generated at a selected position along the imaging path and a corresponding second frame generated at substantially the same position along the imaging path; and

subtracting the pixel illumination energy density value of each pixel in the selected second motion picture frame from the pixel illumination energy density value of the pixel in the selected second motion picture frame having a corresponding pixel address.

23. The method of claim 17 or 19 or 21 wherein the step of generating a sequence of first frames and second frames further comprises:

generating a sequence of unprocessed first frames;

registering at least two of the unprocessed first frames; and

averaging the registered unprocessed first frames to define each first frame.

24. The method of claim 17 or 19 or 21 wherein the step of generating a sequence of first frames and second frames further comprises:

generating a sequence of unprocessed second frames;

registering at least two of the unprocessed second frames; and

means for averaging the registered unprocessed second frames to define each second frame.

25. The method of claim 23 wherein the step of generating a sequence of first frames and second frames further comprises:

generating a sequence of unprocessed second frames;

registering at least two of the unprocessed second frames; and

means for averaging the registered unprocessed second frames to define each second frame.

26. The method of claim 17 in which the subject is a biological vessel capable of accepting the injection of a contrast medium the method comprising the further steps of:

injecting a contrast medium material into the subject immediately prior to generating the first motion picture whereby the first motion picture is a motion picture of the contrast medium as it flows through the subject; and

generating the second motion picture after the contrast medium is dissipated from the subject whereby the second motion picture is taken when there is substantially no detectible contrast medium in the subject.

27. The method of claim 17 wherein the step of generating and storing the second motion picture generated occurs an extended length of time after performing the step of generating and storing the first motion picture whereby the resultant subtracted image motion picture shows only image differences which have occurred during the extended length of time.

28. The method of claim 27 comprising the further steps of injecting a contrast medium into the subject immediately before generating both the first motion picture and the second motion picture.

29. The method of claim 17 wherein the illumination source is an X-ray generator so that the first and second motion pictures are generated by X-rays interacting with the selected feature of the subject.

30. The method of claim 17 wherein the illumination source is an ultrasonic wave generator so that the first and second motion pictures are generated from ultrasonic waves interacting with the selected feature of the subject.

31. An image acquisition system for generating a subtracted image motion picture of a selected feature of a subject comprising:

imaging means including an illumination source, a support for the subject and an illumination receiver, for generating an image of the selected subject feature, at least one of the illumination source, the support and the illumination receiver being movable by an operator whereby there is relative movement between the subject and the illumination receiver along an imaging path selected by the operator;

means for causing the at least one of the illumination source, support and illumination receiver to move so that the relative movement between the subject and the illumination receiver is along the imaging path to duplicate said imaging path;

means for generating and storing a sequence of first frames of the image to define a first motion picture as the operator causes relative movement between the subject and the illumination receiver to define the imaging path and a sequence of second frames of the image to define a second motion picture as the relative movement between the subject and the illuminating receiver along the imaging path is duplicated;

means for aligning and registering the first motion picture and the second motion picture on a frame-by-frame basis; and

means for subtracting the aligned second motion picture from the first motion picture on a frame-by-frame basis for generating a subtracted image motion picture of the subject as the relative movement between the illumination receiver and the subject occurs along the imaging path.