System and method for determining the proximity between a medical probe and a tissue surface

• US 7,517,315 B2
• Filed: 08/26/2005
• Issued: 04/14/2009
• Est. Priority Date: 08/26/2005
• Status: Active Grant

• Current Assignee: Boston Scientific Scimed, Inc. (Boston Scientific Corporation)
• Original Assignee: Boston Scientific Scimed, Inc. (Boston Scientific Corporation)
• Inventors: Willis, N. Parker
• Primary Examiner(s): Winakur; Eric F
• Assistant Examiner(s): Laryea; Lawrence N
• Application Number:
  US11/213,020
• Publication Number:
  US 20070049826A1
• Time in Patent Office: 1,327 Days
• Field of Search: 600/449, 600/462, 600/466, 600/439, 600/459, 600/448, 600/442, 600/424, 600437-472, 606/41, 606/22, 73620-633, 367/7, 367/11, 367/130, 367/138
• US Class Current: 600/442
• CPC Class Codes: A61B 1/00147 Holding or positioning arrangements
• CPC Class Codes: A61B 5/1076 for measuring dimensions inside body cavities, e.g. using catheters A61B3/1005 takes precedence
• CPC Class Codes: A61B 5/6886 Monitoring or controlling distance between sensor and tissue
• CPC Class Codes: A61B 8/0833 involving detecting or locating foreign bodies or organic structures

Abstract

Methods and systems for determining a proximity between a medical probe (such as, e.g., the tip of the medical probe) having an ultrasound transducer and a tissue surface, is provided. The ultrasound transducer is operated in a first resonant mode to transmit a first ultrasound signal that intersects the tissue surface to create a first reflected ultrasound signal, and operating in a second different resonant mode to transmit a second ultrasound signal that intersects the tissue surface to create a second reflected ultrasound signal. The first and second reflected ultrasound signals are received, e.g., by the ultrasound transducer, and a proximity between a portion of the medical probe and the tissue surface is determined based on the received first and second reflected ultrasound signals.

Claims

1. A method of determining a proximity between a medical probe having an ultrasound transducer and a tissue surface, comprising:

operating the ultrasound transducer in a first resonant mode to transmit a first ultrasound signal that intersects the tissue surface to create a first reflected ultrasound signal;

operating the ultrasound transducer in a second different resonant mode to transmit a second ultrasound signal that intersects the tissue surface to create a second reflected ultrasound signal;

receiving the first and second reflected ultrasound signals; and

determining a proximity between a portion of the medical probe and the tissue surface based on the received first and second reflected ultrasound signals.

2. The method of claim 1, wherein the portion of the medical probe is a tip of the medical probe.

3. The method of claim 1, wherein the ultrasound transducer is cylindrically ring-shaped, the first mode is a circumferential mode, and the second mode is a thickness mode.

4. The method of claim 1, wherein the first ultrasound signal is generally isotropic, and the second ultrasound signal is anisotropic.

5. The method of claim 4, wherein the second ultrasound signal is generally focused in a plane.

6. The method of claim 1, wherein the ultrasound transducer receives the first and second reflected ultrasound signals.

7. The method of claim 1, further comprising:

measuring a first elapsed time from the transmission of the first ultrasound signal to the receipt of the first reflected ultrasound signal; and

measuring a second elapsed time from the transmission of the second ultrasound signal to the receipt of the second reflected ultrasound signal;

wherein the proximity between the medical probe portion and the tissue surface is determined based on the first and second elapsed times.

8. The method of claim 7, further comprising:

calculating a first distance between the ultrasound transducer and the tissue surface based on a function of the first elapsed time;

calculating a second distance between the ultrasound transducer and the tissue surface based on a function of the second elapsed time; and

calculating an angle formed between the medical probe and the tissue surface based on a first function of the first and second distances, wherein the proximity between the medical probe portion and the tissue surface is determined based on a second function of the angle.

9. The method of claim 8, wherein the first distance is the shortest distance between the ultrasound transducer and the tissue surface in three-dimensional space, the second distance is the shortest distance between the ultrasound transducer and the tissue surface within a plane perpendicular to an axis of the medical probe, and the first function is cos⁻

1θ

(d₁/d₂), where θ

is the angle, d₁ is the first distance, and d₂ is the second distance.

10. The method of claim 9, wherein the second function is p=d₁−

h sin θ

, where h is the distance between the medical probe portion and the ultrasound transducer.

11. The method of claim 1, further comprising:

determining contact between the medical probe and the tissue surface based on the determined proximity; and

operating the medical probe to ablate the tissue when tissue contact is determined.

12. The method of claim 1, further comprising graphically generating a representation of the tissue surface based on the determined proximity between the medical probe and the tissue surface.

13. A medical system for use with an anatomical structure, comprising:

an elongated medical probe including a shaft with a distal end and an ultrasound transducer carried by the distal probe end;

a controller configured for;

operating the ultrasound transducer in a first resonant mode to transmit a first ultrasound signal that intersects the tissue surface to create a first reflected ultrasound signal;

operating the ultrasound transducer in a second different resonant mode to transmit second ultrasound energy that intersects the tissue surface to create a second reflected ultrasound signal;

operating at least one ultrasound transducer to receive the first and second reflected ultrasound signals;

one or more processors configured for determining a proximity between a portion of the medical probe and the tissue surface based on the received first and second reflected ultrasound signals.

14. The system of claim 13, wherein the portion of the medical probe is a tip of the medical probe.

15. The system of claim 13, wherein the probe comprises an intravascular catheter.

16. The system of claim 13, wherein the ultrasound transducer is a cylindrical ring transducer, the first mode is a circumferential mode, and the second mode is a thickness mode.

17. The system of claim 13, wherein the first ultrasound signal is generally isotropic, and the second ultrasound signal is anisotropic.

18. The system of claim 17, wherein the second ultrasound signal is generally transmitted in a plane.

19. The system of claim 13, wherein the at least one ultrasound transducer comprises the ultrasound transducer that transmits the first and second ultrasound signals.

20. The system of claim 13, wherein the at least one processor is configured for:

measuring an elapsed time from the transmission of the first ultrasound signal to the receipt of the first reflected ultrasound signal; and

measuring a second elapsed time from the transmission of the second ultrasound signal to the receipt of the second reflected ultrasound signal;

wherein the proximity between the medical probe portion and the tissue surface is determined based on the first and second elapsed times.

21. The system of claim 20, wherein the at least one processor is configured for:

calculating a first distance between the ultrasound transducer and the tissue surface based on a function of the first elapsed time;

calculating a second distance between the ultrasound transducer and the tissue surface based on a function of the second elapsed time; and

calculating an angle formed between the medical probe and the tissue surface based on a first function of the first and second distances, wherein the proximity between the medical probe portion and the tissue surface is determined based on a second function of the angle.

22. The system of claim 21, wherein the first distance is the shortest distance between the ultrasound transducer and the tissue surface in three-dimensional space, the second distance is the shortest distance between the ultrasound transducer and the tissue surface within a plane perpendicular to an axis of the medical probe, and the first function is cos⁻

1 θ

(d₁/d₂), where θ

is the angle, d₁ is the first distance, and d₂ is the second distance.

23. The system of claim 22, wherein the second function is d₁−

h(sin θ

), where h is the distance between the medical probe portion and the ultrasound transducer.

24. The system of claim 13, further comprising a source of ablation energy, wherein the medical probe comprises an ablative element coupled to the source of ablation energy.

25. The system of claim 13, wherein the at least one processor is further configured for graphically generating a representation of the tissue surface based on the determined proximity between the medical probe and the tissue surface.

26. The system of claim 25, further comprising an output device configured for displaying the graphical representation.