Methods and apparatus for non-uniform rotation distortion detection in an intravascular ultrasound imaging system

• US 5,921,934 A
• Filed: 11/25/1997
• Issued: 07/13/1999
• Est. Priority Date: 11/25/1997
• Status: Expired due to Term

• Current Assignee: Boston Scientific Scimed, Inc. (Boston Scientific Corporation)
• Original Assignee: Boston Scientific Limited (Boston Scientific Corporation), Scimed Life Systems Incorporated (Boston Scientific Corporation)
• Inventors: Teo, Tat-Jin
• Primary Examiner(s): Jaworski, Francis J.
• Assistant Examiner(s): PATEL, MAULIN M
• Application Number:
  US08/977,543
• Time in Patent Office: 595 Days
• Field of Search: 600/443, 600/450, 600/451, 600/454, 600/458, 600/459, 600/462, 600/466, 600/467, 600/468, 128/916
• US Class Current: 600/468
• CPC Class Codes: A61B 8/12 in body cavities or body tracts, e.g. by using catheters catheters per se A61M25/00
• CPC Class Codes: A61B 8/4461 Features of the scanning mechanism, e.g. for moving the transducer within the housing of the probe
• CPC Class Codes: A61B 8/481 involving the use of contrast agent, e.g. microbubbles introduced into the bloodstream analysis of echo signal exploiting properties of a contrast enhancer in devices for short-range imaging with acoustic waves G01S7/52039
• CPC Class Codes: G01S 15/894 by rotation about a single axis
• CPC Class Codes: G01S 7/5205 Means for monitoring or calibrating

Abstract

Methods and apparatus for non-uniform rotation distortion detection for enhanced intravascular ultrasound imaging. The present invention provides methods and apparatus which detect non-uniform rotation in an improved manner without using beacons which may create shadowing of tissue behind the beacons or other undesired artifacts in the image. In specific embodiments, the present invention may provide a particularly simple and useful solution for addressing the problem of non-uniform rotation distortion in intravascular ultrasound imaging in systems which use mechanical scanning. In specific embodiments, the present invention utilizes correlation of received signals in an image vector from reverberating ultrasound in a bubbly liquid-flushed catheter to determine non-uniform rotation of the transducer within the catheter. In other embodiments, the present invention utilizes correlation of imaging vectors within a blood speckle region given a particular beamwidth of ultrasound energy from a transducer to determine non-uniform rotation of the transducer.

Claims

1. A method for detecting non-uniform rotation distortion in an intravascular ultrasound blood vessel image, said method comprising the steps of:

providing a catheter probe within a blood vessel, said catheter probe having a sheath and a transducer substantially centrally located within said sheath, wherein said transducer is mechanically controlled and said catheter probe including a bubbly liquid between said sheath and said transducer;

emitting an ultrasonic beam to produce echoes reflected from said bubbly liquid and said sheath to obtain a given image vector;

sampling said echoes in a plurality of time windows for said given image vector;

correlating said sampled echoes in said plurality of time windows to determine existence of non-uniform rotational speed of said transducer.

2. The method of claim 1 further comprising the step of quantifying the non-uniform rotational speed of said transducer to compensate therefor.

3. The method of claim 2 wherein said bubbly liquid includes micro-bubbles having a diameter from about 1-10 μ

m.

4. The method of claim 1 wherein a time t₀ between a beginning of successive windows in said plurality is greater than the time t_S =(2 r_S)/c between said ultrasonic beam being emitted by said transducer and a first echo received by said transducer.

5. The method of claim 4 wherein a slow down in the rotational speed of said transducer has occurred if a first correlation coefficient between a first window and a second window is less than a second correlation coefficient between said second window and a third window, and an increase in the rotational speed of said transducer has occurred if the first correlation coefficient between the first window and the second window is greater than the second correlation coefficient between said second window and the third window.

6. Apparatus for detecting non-uniform rotation distortion in an intravascular ultrasound blood vessel image, said apparatus comprising:

a catheter for use within a blood vessel, said catheter including;

a sheath,

a bubbly liquid within said catheter between said transducer and said sheath, and

a transducer mechanically rotated within said catheter, wherein said transducer emits an ultrasonic beam and receives echoes of said ultrasonic beam from micro-bubbles in said bubbly liquid and said sheath; and

an image processor capable of being coupled to said transducer, said image processor including computer-readable program code fixed on tangible computer-readable medium for storing said computer-readable program, said computer-readable medium coupled to be read by said image processor, wherein said computer-readable program code performs correlation on a plurality of segments in an image vector from said echoes ultrasonic beam to detect the non-uniformity of rotation of said transducer.

7. The apparatus of claim 6 wherein said bubbly liquid includes micro-bubbles having a diameter from about 1-10 μ

m.

8. The apparatus of claim 6 wherein a time t₀ between a beginning of successive windows in said plurality is greater than the time t_S =(2 r_S)/c between said ultrasonic beam being emitted by said transducer and a first echo received by said transducer.

9. The method of claim 8 wherein a slow down in the rotational speed of said transducer has occurred if a first correlation coefficient between a first window and a second window is less than a second correlation coefficient between said second window and a third window, and an increase in the rotational speed of said transducer has occurred if the first correlation coefficient between the first window and the second window is greater than the second correlation coefficient between said second window and the third window.

10. A method for detecting non-uniform rotation distortion in an intravascular ultrasound blood vessel image, said method comprising the steps of:

providing a catheter probe within a blood vessel, said catheter probe having a transducer substantially centrally located therein, wherein said transducer is mechanically controlled;

emitting a plurality of ultrasonic beams to produce echoes reflected from a blood region within said blood vessel to obtain a plurality of successive image vectors;

sampling said echoes at a predetermined range (r_P) for each of said successive image vectors, wherein r_P for each of said successive image vectors is located within said blood region;

obtaining correlation coefficients for said sampled echoes at r_P between each of said successive image vectors to determine changes in a rotational speed of said transducer.

11. The method of claim 10 wherein said obtaining step includes determining from a decrease in correlation coefficients that said rotational speed of said transducer has increased or determining from an increase in correlation coefficients that said rotational speed of said transducer has decreased.

12. The method of claim 10 wherein said predetermined range r_P is selected to lie beyond the far-field of said transducer.

13. The method of claim 11 wherein said sampling step further includes sampling said echoes at a plurality of predetermined ranges for each of said successive image vectors, wherein said predetermined range r_P is one of said plurality and a second predetermined range r_P2 is another one of said plurality, wherein r_P2 is selected to be within said blood region at a greater distance from said transducer than said r_P, and wherein said obtaining step further includes obtaining correlation coefficients for said sampled echoes at r_P2.

14. The method of claim 13 wherein said predetermined range r_P and said second predetermined range r_P2 are each selected to lie beyond the far-field of said transducer.

15. The method of claim 14 wherein a beamwidth measured in angle of said ultrasonic beams remains constant at each of the predetermined ranges r_P and r_P 2.

16. The method of claim 15 wherein the correlation coefficients at both r_P1 and r_P2 between successive vectors should be substantially the same when said successive vectors maintain about the same angular separation.

17. The method of claim 15 wherein said successive vectors have increased their angular separation when the correlation coefficients at both r_P and r_P2 between successive vectors respectively decrease, and wherein said successive vectors have decreased their angular separation when the correlation coefficients at both r_P and r_P2 between successive vectors respectively increase.

18. The method of claim 14 wherein a beamwidth measured in angle of said ultrasonic beams increases from said predetermined range r_P to said second predetermined range r_P2.

19. The method of claim 18 wherein said successive vectors have increased their angular separation when the correlation coefficients at both r_P and r_P2 between successive vectors respectively decrease, and wherein said successive vectors have decreased their angular separation when the correlation coefficients at both r_P and r_P2 between successive vectors respectively increase.

20. Apparatus for detecting non-uniform rotation distortion in an intravascular ultrasound blood vessel image, said apparatus comprising:

a catheter for use within a blood vessel, said catheter including;

a sheath, and

a transducer mechanically rotated within said catheter, wherein said transducer emits a plurality of ultrasonic beams to produce echoes reflected from a blood region within said blood vessel to obtain a plurality of successive image vectors; and

an image processor capable of being coupled to said transducer, said image processor including computer-readable program code fixed on tangible computer-readable medium for storing said computer-readable program, said computer-readable medium coupled to be read by said image processor, wherein said computer-readable program code samples said echoes at a predetermined range (r_P) for each of said successive image vectors, wherein r_P for each of said successive image vectors is located within said blood region, and wherein said computer-readable program code also obtains correlation coefficients for said sampled echoes at r_P between each of said successive image vectors to determine changes in a rotational speed of said transducer.

21. The apparatus of claim 20 wherein said computer-readable program code determines from a decrease in correlation coefficients that said rotational speed of said transducer has increased and/or determines from an increase in correlation coefficients that said rotational speed of said transducer has decreased.