Acoustic image system and method - Patent Review 4821731

Claims

What is claimed is:

1. Apparatus for sensing imaging information of the internal features of a living body at a preselected site, said apparatus comprising:

a catheter having a longitudinal axis, a proximal end and a distal end such that said catheter is adapted to be partially inserted into said living body so that said distal end is positioned relative to said preselected site so that said imaging information of said internal features can be acoustically sensed at said distal end;

image data sensing means, coupled to said catheter at said distal end, for acoustically sensing said imaging information of said body in the general direction of an image data sensing axis transverse to the longitudinal axis of said catheter at said distal end so that rotation of said catheter about said longitudinal axis rotates said image data sensing axis about said longitudinal axis; and

position sensing means for determining the spatial position of said image data sensing means within said body and the angular orientation of said image data sensing axis about said longitudinal axis with respect to said spatial position so that imaging information of said body sensed by said image data sensing means at each such spatial position and angular orientation can be related to a specific cylindrical coordinate position, and imaging information of said body for a plurality of said cylindrical coordinate positions can be spatially cross correlated.

2. Apparatus according to claim 1, wherein said image data sensing means includes transducer means for generating an acoustic signal in the general direction of said image data sensing axis into said body and receiving echo signals reflected by said body in the general direction of said imaging axis in response to said acoustic signal.

3. Apparatus according to claim 2, wherein said transducer means includes a transmitter transducer for generating said acoustic signal and a receiver transducer for receiving said echo signals.

4. Apparatus according to claim 2, wherein said transducer means includes (a) a single transducer operable in a transmitting mode for generating said acoustic signal and a receiving mode for receiving said echo signals, and (b) means for operating said transducer in either said transmitting or said receiving mode.

5. Apparatus according to claim 2, further including means for generating said acoustic signal as a burst of pulses.

6. Apparatus according to claim 2, further including means for generating said acoustic signal as a burst of pulses staggered with respect to one another.

7. Apparatus according to claim 1, wherein said position sensing means includes first means for determining the spatial location of said imaging means within said body and second means for determining said angular orientation.

8. Apparatus according to claim 7, wherein said first means includes (a) transducer means for generating an acoustic signal toward said distal end of said catheter, and (b) means, coupled to said catheter at said distal end, for sensing said acoustic signal.

9. Apparatus according to claim 8, wherein said transducer means for generating said acoustic signal includes means for generating said acoustic signal at a preselected frequency.

10. Apparatus according to claim 9, wherein said means for sensing said acoustic signal includes antenna means coupled to said catheter at said distal end fixed relative to said imaging axis for generating a position signal in response to and as a function of the acoustic signal.

11. Apparatus according to claim 7, wherein said second means includes (a) means for generating two magnetic fields in two respective planes generally transverse to one another and (b) means, coupled to said catheter at said distal end, for sensing said magnetic fields.

12. Apparatus according to claim 11, wherein said first means includes (a) transducer means for generating an acoustic signal toward said distal end of said catheter, and (b) means, coupled to said catheter at said distal end, for sensing said acoustic signal.

13. Apparatus according to claim 11, wherein said means for generating said two magnetic fields includes means for generating each of said magnetic fields at a predetermined frequency, and said means for sensing said magnetic fields includes antenna mean coupled to said catheter at said distal end and fixed relative to said imaging axis for generating a position signal in response to and as a function of the magnetic fields.

14. Apparatus according to claim 13, wherein said antenna means includes a wire loop secured to said catheter and dimensioned so as to sense said magnetic fields at each of said predetermined frequencies and oriented so as to lie substantially in a plane fixed relative to said image data sensing axis.

15. Apparatus according to claim 14, wherein said wire loop is oriented so as to substantially lie in a plane fixed relative to said image data sensing axis.

16. Apparatus according to claim 13 wherein said means for generating each of said magnetic field includes means for generating said magnetic fields at different frequencies from one another, and said position sensing means includes means for sensing said position signal at each of said predetermined frequencies.

17. Apparatus according to claim 13, wherein said means for generating each of said magnetic fields includes means for generating said magnetic fields at the same frequency but out of phase with one another.

18. Apparatus according to claim 17, wherein said position sensing means includes means for sensing said position signal at said frequency.

19. Apparatus according to claim 1, wherein said position sensing means includes means for compensating for rhythmic ambient motion.

20. Apparatus according to claim 19, wherein said position sensing means includes (a) means for generating at least two position signals as a function of the position of said image data sensing means within said body and the angular orientation of said image data sensing axis about said longitudinal axis, (b) means for generating at least two second signals as a function of the movement of said image data sensing means in response to said rhythmic ambient motion for at least one cycle, and (c) means for subtracting said second signals from the corresponding ones of said position signals during each subsequent cycle of said rhythmic ambient motion.

21. Apparatus according to claim 20, wherein the cycle of said rhythmic ambient motion is variable, and said means for subtracting said second signals from said corresponding position signals is adapted to correlate the values of said second signals at their respective times of said at least one cycle, with the values of said position signals at the same corresponding times of each of said subsequent cycles.

22. Apparatus according to claim 1, further including means for spatially correlating the imaging information of said body sensed at a plurality of said cylindrical coordinate positions.

23. Apparatus for imaging internal features of a living body at a preselected site, said apparatus comprising, in combination:

a catheter having a longitudinal axis, a proximal end and a distal end such that said catheter is adapted to be partially inserted into said living body so that said distal end is positioned relative to said preselected site and imaging data relating to said internal features can be acoustically provided at said distal end by moving said distal end through a plurality of positions relative to said site and generating an acoustic signal when said distal end is at each of said positions;

means for selectively generating said acoustic signal when said distal end is at each of said positions;

first sensing means for sensing acoustic energy in response to said acoustic signal at each of said positions;

second sensing means for sensing the location of said distal end of said catheter at each of said positions;

means, responsive to said first and second sensing means, for collecting a set of data derived from the acoustic energy sensed by said sensing means at each of said positions and corresponding information relative to the corresponding position from which each set of data is obtained so as to form a plurality of said sets corresponding to a plurality of said positions; and

means for relating the plurality of sets of data with respect to the plurality of positions from which the sets of data are obtained so that said plurality of sets of data can be used to create an image of said internal features at said site.

24. Apparatus according to claim 23, wherein said first and second sensing means includes transducer means for generating said acoustic signal in the general direction of an image data sensing axis into said body at each of said positions, and receiving echo signals reflected by said body in the general direction of said image data sensing axis in response to said acoustic signal.

25. Apparatus according to claim 24, wherein said transducer means includes a transmitter transducer for generating said acoustic signal and a receiver transducer for receiving said echo signals.

26. Apparatus according to claim 24, wherein said transducer means includes (a) a single transducer operable in a transmitting mode for generating said acoustic signal and a receiving mode for receiving said echo signals, and (b) means for operating said transducer in either said transmitting or said receiving mode.

27. Apparatus according to claim 24, further including means for generating said acoustic signal as a burst of pulses.

28. Apparatus according to claim 24, further including means for generating said acoustic signal as a burst of pulses staggered with respect to one another.

29. Apparatus according to claim 24, wherein said image data sensing axis is transverse to the longitudinal axis of said catheter at said distal end, and said second sensing means includes first means for determining the spatial location of said second sensing means within said body, and second means for determining the angular orientation of said image data sensing axis about said longitudinal axis at said distal end.

30. Apparatus according to claim 29, wherein said first means includes (a) transducer means for generating an acoustic signal toward said distal end of said catheter, and (b) means, coupled to said catheter at said distal end, for sensing said acoustic signal.

31. Apparatus according to claim 30, wherein said transducer means for generating said acoustic signal includes means for generating said acoustic signal at a preselected frequency.

32. Apparatus according to claim 31, wherein said means for sensing said acoustic signal includes antenna means coupled to said catheter at said distal end and fixed relative to said imaging axis for generating a position signal in response to and as a function of the acoustic signal.

33. Apparatus according to claim 29, wherein said second means includes (a) means for generating two magnetic fields in two respective planes generally transverse to one another and (b) means, coupled to said catheter at said distal end, for sensing said magnetic fields.

34. Apparatus according to claim 33, wherein said first means includes (a) transducer means for generating a second acoustic signal toward said distal end of said catheter, and (b) means, coupled to said catheter at said distal end, for sensing said second acoustic signal.

35. Apparatus according to claim 33 wherein said means for generating said magnetic fields includes means for generating each of said magnetic fields at a predetermined frequency, and said means for sensing said magnetic fields includes antenna means coupled to said catheter at said distal end and fixed relative to said imaging axis for generating a position signal in response to and as a function of the magnetic fields.

36. Apparatus according to claim 35, wherein said antenna means includes a wire loop secured to said catheter and dimensioned so as to sense said magnetic fields at each of said predetermined frequencies and oriented so as to lie substantially in a plane fixed relative to said image data sensing axis.

37. Apparatus according to claim 35, wherein said means for generating each of said magnetic fields including means for generating said magnetic fields at different frequencies from one another, and said position sensing means includes means for sensing said position signal at each of said predetermined frequencies.

38. Apparatus according to claim 35, wherein said means for generating each of said magnetic fields includes means for generating said magnetic fields at the same frequency but out of phase with one another.

39. Apparatus according to claim 38, wherein said position sensing means includes means for sensing said position signal at said frequency.

40. Apparatus according to claim 23, wherein said second sensing means includes means for compensating for rhythmic ambient motion.

41. Apparatus according to claim 40, wherein said second sensing means includes (a) means for generating at least two position signals as a function of the position and orientation of said distal end within said body, (b) means for generating at least two second signals as a function of the movement of said image data sensing means in response to said rhythmic ambient motion for at least one cycle, and (c) means for subtracting said second signals from the corresponding ones of said position signals during each subsequent cycle of said rhythmic ambient motion.

42. Apparatus according to claim 23, wherein said wire loop is oriented so as to substantially lie in a plane fixed relative to said image data sensing axis.

43. A method of imaging internal features of a living body at a preselected site, said method comprising the steps of:

(a) partially inserting a catheter into said body so that the distal end of said catheter is positioned relative to said preselected site so that data relating to an image of said internal features can be acoustically sensed at said distal end by moving said distal end through a plurality of positions;

(b) collecting a corresponding plurality of sets of data derived from acoustic signals generated from said distal end of said catheter as said distal end is moved through said plurality of positions; and

(c) relating the plurality of sets of data with respect to the plurality of positions from which the sets of data are obtained so that said plurality of sets of data can be used to create a coherent image of said internal features at said site.

44. A catheter assembly for use with a device for generating two magnetic fields in two respective planes generally transverse to one another, said assembly comprising:

a catheter including a longitudinal axis, a proximal portion and a distal portion such that said catheter is adapted to be partially inserted into a living body so that the distal portion is positioned relative to a preselected site;

means, positioned at said distal portion of said catheter, for (a) generating a beam of acoustic energy in a predetermined direction transverse to said longitudinal direction at said distal end so that the beam can be generated into said living body at said site, (b) sensing acoustic energy reflected by said body part along a image data sensing axis in response to said beam, and (c) generating an electrical signal in response to said and as a function of said sensed acoustic energy; and

antenna means, positioned at said distal end of said catheter and fixed relative to the direction of said image data sensing axis, for sensing said magnetic fields and for generating an electrical signal representative of the spatial angular orientation of the direction of said image data sensing axis about said longitudinal axis relative to said distal end.

45. A catheter assembly according to claim 44, wherein said antenna means includes a wire loop (1) positioned at said distal portion of said catheter (2) substantially disposed in a plane fixed relative to the direction of said image data sensing axis, and (3) dimensioned so as to sense said magnetic fields.

46. A catheter assembly according to claim 45, wherein said wire loop is positioned at said distal portion so that the direction of said image data sensing axis extends through said wire loop.

47. A catheter assembly according to claim 46, wherein said wire loop is substantially disposed in a plane extending substantially normal to the direction of said image data sensing axis.

48. A catheter assembly according to claim 44, further including means, coupled to said catheter, for generating an electrical signal representative of the spatial position of said distal portion of said catheter.

The present invention relates generally to acoustical imaging of internal features of a living body or the like, and more specifically to an improved device for accurately moving and positioning an image sensing device in the living body so that imaging information can be derived at a predetermined site with sufficiently high resolution.

Devices are known for using an acoustic pulse to generate echo sounds relating to internal features of various parts of a living body. Such devices, for example the one described in U.S. Pat. No. 4,576,177 (hereinafter referred to as the "Webster Patent"), include an electro-acoustical transducer device positioned on the tip section of a catheter so that the transducer device can be inserted into a liquid-filled or fillable body canal or cavity. The catheter is moved into position at the particular site of the body so that the transducer device generates each acoustic pulse in the direction of interest.

The transducer device of the Webster Patent provides an acoustic output pulse and receives return pulses, i.e., echoes, from surface discontinuies in the form of impedance mismatches (at the ultrasonic frequency) of the precise part of the body at which the pulse is directed. The temporal character of the echo pulses, in response to the initial pulse, returning from the direction of propagation of the initial pulse provides information about the tissue through which the pulses travel. More specifically, the relative timing of the return pulses corresponding to impedance discontinuities provides information on the thickness of various types of tissue (e.g., fat, arteriosclerotic plaque, etc.) at the specific location at which the initial pulse is directed. The relative strength of such echoes reflects the differences in impedance between adjacent boundaries of the different types of tissue, and therefore the difference in densities of the material. The acoustic technique can therefore be used to ascribe a signature for each type and character of tissue from which echoes are received.

As described in both the Parent Application and the Webster Patent, acoustically derived information can be particularly useful in such procedures as removing arteriosclerotic plaque deposits which restrict the flow of blood in coronary arteries. By moving the distal end of a catheter to the location of the diseased site, laser radiation can be directed through an optical fiber, provided within the catheter, onto the plaque with sufficient intensity so as to vaporize the plaque. The plaque thus can be removed without the trauma associated with open heart surgery. However, such a procedure requires specific knowledge of the location, thickness and density of the plaque to be removed in order to minimize damage to the arterial wall at the diseased site. As described in both the Webster patent and the Parent Application, the use of acoustically derived information is advantageous since it can provide such information better than other known techniques.

For example, X-ray fluoroscopy can be used to position the catheter. However, the latter technique (a) requires the injection of a radiopaque material into the occluded blood vessel, and (b) viewing the X-ray shadow images of the artery and the catheter with a fluoroscope. Although helpful in generally locating the area of interest, X-ray fluoroscopy yields images of poor resolution and incomplete information on the thickness and density of the plaque deposits. Further, real time data is difficult, if not impossible to obtain using X-ray fluoroscopy during the laser vaporization step of the procedure.

As indicated in the Webster Patent, fiberoptic scopes, having illumination and direct optical viewing capabilities which can be used to inspect the diseased site. However, such devices require the user to block the blood flow through the blood vessel and to subsequently flush the blood vessel with a clear liquid such as saline, until a clear optical viewing path is achieved. Not only does the use of fiberoptic scopes require the stoppage of blood flow, but also prevents direct viewing during the laser vaporization step and provides inadequate information on the density and thickness of the plaque. As a result the chance that the arterial wall will be damaged is greatly increased.

The system described in the Webster Patent provides at any one time only the information relating to the set of echoes received in response to a pulse transmitted in a preselected direction. There is no attempt to relate any of the information obtained from one set of echoes to any other set of echoes taken from another position of the transducer device at the site where the information is being obtained. This provides a very limited "view" of the area from which the information is being obtained (restricted by the "angle of view" of the transducer device), and prevents the surgeon from knowing the nature of the surrounding tissue which is not within the angle of view when the data is obtained in response to an acoustic pulse. As a result more time must be spent after each application of the laser at the specific location being viewed in order to try to locate another location at the site containing diseased tissue.

It is a principal object of the present invention therefore, to provide a system for and method of collecting sets of data derived from acoustic signals generated at a corresponding plurality of locations at the diseased site and to relate the sets of data with respect to the relative locations from which the sets of data are obtained so that the data can be used to create a coherent image of the diseased site.

For example, as will be more evident hereinafter, in accordance with the present invention in order to create an image of an artherosclerotic lesion on the interior wall of an artery, one can longitudinally as well as rotatably displace the catheter tip (and thus the transducer device on the catheter tip) through a predefined diseased site so that a set of return pulses is obtained from each location within the diseased site. The set of return pulses obtained for each angular and longitudinal position of the catheter then can be related to one another so as create relative spatial information of the structure of the portions of the diseased site represented by the sets of return pulses based on known signatures of various types of tissue encountered in such diseased sites. Alternatively, the sets of return pulses can be related to one another as a function of the relative spatial positions from which the sets of return pulses are obtained so as to create a three-dimensional presentation of the diseased site, as described and illustrated in the Parent Application.

Devices for determining the position of the tipsection of a catheter are known. In U.S. Pat. No. 4,173,228 (Van Steenwyk et al.) the tip of a catheter positioned in the body can be detected electromagnetically by disposing a coupling coil in the tip of the catheter coaxially with the longitudinal axis of the catheter at the tip. Leads from the coil extend along the catheter to an external receiving circuit. A "search probe" includes a pair of coils mounted perpendicular to one another. The probe is positioned outside the body. A voltage is applied to one of the probe coils so that an electromagnetic field is generated through the body and a voltage induced in the catheter coil. This voltage is sensed by the receiving circuit. The induced signal is maximized when the axes of the probe and catheter coils are parallel and the coils are laterally or axially aligned. The signal is minimized when coil axes are disposed perpendicular with respect to one another. The relative phase of the transmitted and received signals indicates whether the energized probe coil and catheter coil are facing in the same or opposite directions, and thus determines the direction in which the catheter tip is pointing.

In operation, one probe coil is energized and the probe is moved by the physician until a maximum signal is detected and the position of the probe and orientation of the energized probe coil is indicated on the patient's skin. The first probe coil is then deenergized while the second probe coil is energized with the probe positioned in the same location which produced the maximum signal in the first scan.

If the detected signal is insignificant, the catheter-tip position determined in the first scan is accurate, and the center of the catheter coil is directly below the mark, with the catheter tip pointing in a plane parallel to the plane of the first probe coil. If a significant signal is noted when the second probe coil is energized, a second scan is made to determine a new position of maximum coupling is indicated by a peak in the detected signal. The patient's skin is again marked. The position of the catheter tip will lie beneath a line connecting the first and second marks made on the skin. Both probe coils are then energized and the probe moved along the line connecting the two marks. A dip or peak in the detected signal will then indicate the position of the catheter tip. A dip in signal strength shows that the catheter tip is pointing away from the probe, and a peak shows the tip is pointing toward the probe. The procedure is repeated as many times as necessary during catheter insertion to insure that the catheter tip is following a desired path.

As described in the Van Steenwyk et al patent the tip position of a fully inserted catheter can be constantly monitored if desired by taping one or more transmission coils to the patient's skin directly over the catheter coil and then noting any change in the output reading of the catheter coil. In addition, the catheter tip can also be sensed by using sonic energy propagated through the body and sensed by an acoustic transducer at the catheter tip and wired to an external circuit. Further, three or more coils may be used in an array and driven at different frequencies for external discrimination to enable a more rapid determination of catheter tip position.

The system described by Van Steenwyk et al does not include means for imaging the internal features of a human body, for example, of a coronary artery, particularly on the detailed level required for ablating arteriosclerotic plaque from the walls of those blood vessels. For one, the device is not constructed to acquire image data relating to the thickness and types of tissue present at a diseased site, which is necessary to reliably perform the ablating procedure. The system is designed solely to locate the tip of a catheter in the body.

In order to obtain images appropriate for ablating atherosclerotic plaque, the angular orientation and position of the transducer device used for receiving the sets of acoustically derived data must be known at the time the corresponding sets are obtained. It is clear that the Van Steenwyk et al. system is incapable of determining the angular orientation of the tip end of the catheter.

Accordingly, it is another object of the present invention to provide a system for and method of acquiring ultrasonic echo data so as to create a relatively high resolution image of a predetermined site within a living body in a quick and dependable manner.

And another object of the present invention is to provide a system for and method of determining the relative position of the tip of a catheter within a living body, as well as the relative angular orientation of transducer device positioned on the tip of the catheter about the longitudinal axis of the catheter.

The foregoing and other objects will be achieved by an improved apparatus for imaging internal features of a living body within a preselected site, wherein the apparatus comprises, in combination:

a catheter having a longitudinal axis, a proximal end and a distal end such that said catheter is adapted to be partially inserted into said living body so that said distal end is positioned relative to said preselected site so that said imaging information of said internal features can be acoustically sensed at said distal end;

image data sensing means, coupled to said catheter at said distal end, for acoustically sensing said imaging information of said body in the general direction of an image data sensing axis transverse to the longitudinal axis of said catheter at said distal end so that rotation of said catheter about said longitudinal axis rotates said image data sensing axis about said longitudinal axis; and

position sensing means for determining externally of said body the position of said imaging data sensing means within said body and the angular orientation of said image data sensing axis about said longitudinal axis.

In accordance with another aspect of the present invention the apparatus comprises, in combination:

a catheter having a longitudinal axis, a proximal end and a distal end such that said catheter is adapted to be partially inserted into said living body so that said distal end is positioned relative to said preselected site and imaging data relating to said internal features can be acoustically provided at said distal end by moving said distal end through a plurality of positions relative to said site and generating an acoustic signal when said distal end is at each of said positions;

means for selectively generating said acoustic signal when said distal end is at earth of said positions;

first sensing means for sensing acoustic energy in response to said acoustic signal at each of said positions;

second sensing means for sensing the location of said distal end of said catheter at each of said positions;

means, responsive to said first and second sensing means, for collecting a set of data derived from the acoustic energy sensed by said sensing means at each of said positions and corresponding information relative to the corresponding position from which each set of data is obtained so as to form a plurality of said sets corresponding to a plurality of said positions; and

means for relating the plurality of sets of data with respect to the plurality of positions from which the sets of data are obtained so that said plurality of sets of data can be used to create an image of said internal features at said site.

In accordance with another aspect of the present invention a method of imaging internal features of a living body at a preselected site is provided. The method comprises the steps of:

(a) partially inserting a catheter into said body so that the distal end of said catheter is positioned relative to said preselected site so that data relating to an image of said internal features can be acoustically sensed at said distal end by moving said distal end through a plurality of positions;

(b) collecting a corresponding plurality of sets of data derived from acoustic signals generated from said distal end of said catheter as said distal end is moved through said plurality of positions; and

(c) relating the plurality of sets of data with respect to the plurality positions from which the sets of data are obtained so that said plurality of sets of data can be used to create a coherent image of said internal features at said site.

Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the apparatus possessing the construction, combination of elements, and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

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