Catheter system for controlled removal by radiant energy of biological obstructions

Having thus described the invention what we desire to claim and secure by letters patent is:

1. A method for recanalizing an obstructed lumen by removing successive layers of biological obstructing material so as to form a hole through said material by application of radiant energy comprising:

providing a catheter having waveguide means, the catheter having a distally located emission aperture for emission of said radiant energy in a beam propagating along a beam axis, said emission aperture having cross-sectional dimensions corresponding substantially to cross-sectional dimension of the catheter;

inserting said catheter into said lumen to locate the emission aperture in proximity to the obstruction;

directing said radiant energy through the waveguide means to cause emission of said beam from said emission aperture;

controlling said emitted beam to define an unfocused working region extending distally from said emission aperture and around said axis in which the density of said energy is sufficient to cause said removal and so that portion of the beam which propagates distally beyond the working region will have insufficient energy density to cause said removal;

said working region defining a cross-section substantially large enough to enable the catheter to be passed through a hole formed by the working region, the working region having an axially depth not substantially greater than about cross-sectional dimension of the catheter;

applying the working region of the beam to the obstructing material thereby to form a hole by removal of said material to a depth no greater than about the axial extent of said working region; and

advancing said catheter through said hole.

2. A method as defined in claim 1 further comprising:

providing said beam so that it has a pattern wherein the radiation diverges from said axis as it propagates along said axis beyond said working region.

3. A method as defined in claim 2 further comprising:

providing said beam so that it has substantially uniform energy distribution around said axis.

4. A method as defined in each of claims 1 to 3 wherein said radiant energy comprises laser energy.

5. A method according to claim 1 wherein the properties of said energy are selected with respect to energy absorption properties of said obstructing material to provide that substantially all the energy in said working portion is consumed in causing said removal.

6. A method according to claim 5 wherein the frequency range of said energy is selected with respect to the predominant molecular constitution of said obstructing material so as to form said hole by ablative photo-decomposition of said obstructing material.

7. A method according to claim 1 in which said energy forms said hole by thermal vaporization of said obstructing material.

8. A method according to claim 1 in which the radiation is supplied to said obstructing material via an optical conductor.

9. A method according to claim 8 in which said radiation is supplied via a net-negative optical system.

10. A method according to claim 2 in which said radiant energy is applied to said working region through a net-negative optical system.

11. A method according to claim 1 in which said working region extends up to approximately 1.5 mm. along said axis.

12. A method according to claim 1 wherein said step of providing said beam of radiant energy comprises causing said beam to be emitted from an emission aperture in which said working region has a diameter at least as great as that of said emission aperture.

13. A method according to claim 2 in which said beam diverges to about 20.degree. from said axis when said beam is propagated in a saline solution.

14. A method according to claim 8 for application to forming a hole through plaque in a vascular obstruction wherein said optical conductor is guided to said obstruction in a catheter having said optical system fixed at the distal end thereof.

15. A method according to claim 1 including the step of pulsing said radiant energy and adjusting the pulse parameters for forming said hole.

16. A method as defined in claim 8 further comprising:

flouoroscopically locating and positioning the optical conductor with respect to the biological material.

17. A method of removing a biological obstruction by radiant energy comprising:

providing a catheter having waveguide means for guiding said radiant energy from a source thereof, said catheter having a distally located emission aperture for emission of said radiant energy in a beam propagating along beam axis;

forming said beam into a geometrically expanding pattern in which the energy distribution around said beam axis is substantially uniform whereby the energy density of said beam along said beam axis when applied to said obstruction decreases both exponentially and geometrically in a distally extending direction;

the energy density in a working region of the beam within a first isothermal zone being sufficient to effect removal of the material forming the obstruction when said material is located in said region, the portion of the beam extending distally of said working region having insufficient energy density to effect said removal;

said working region defining cross sectional dimensions large enough to enable the catheter to be passed therethrough, the working region having an axially extending depth not substantially greater than about the cross-sectional dimension of the catheter;

whereby when said beam of energy is applied to the biological material said radiant energy will be effective to remove said material to a depth no greater than about the axial depth of said working region, thereby limiting said removal to a layer approximating the axial depth of said working region, and minimizing perforation of tissue located distal or radial to the isothermal boundary of said working region.

18. A method as defined in claim 17 wherein the properties of said energy are selected with respect to properties of said obstruction to provide that substantially all the energy in said working portion is consumed in causing said removal.

19. A method as defined in claim 18 wherein said step of forming said radiant energy into said beam pattern comprises:

providing net-negative optical sensing means at the distal end of the waveguide means to shape the beam.

20. A method as defined in claim 19 wherein said step of providing lens means for shaping the beam comprises:

passing the beam from the exit surface of an optical fiber conductor through an exit lens having a concave output surface.

21. A catheter for recanalizing an obstructed lumen by selectively removing sequential layers of biological obstructing material by radiant energy comprising:

an elongate catheter body containing a flexible optical conductor;

the proximal end of the catheter having means to enable said radiant energy to enter the flexible optical conductor;

the distal end of the catheter having an emission aperture from which a beam of said radiant energy may be emitted, said emission aperture having a cross-sectional dimension which substantially corresponds to that of the distal end of the catheter;

said catheter and emission aperture being constructed and arranged to shape the radiant energy beam emitted from the emission aperture to define an unfocused beam having a working region in which the density of energy is sufficient to cause said removal, and so that the portion of the beam extending distal to the working region has insufficient energy density to cause said removal; and

the cross-sectional dimensions of the beam in the working region being no smaller than about the diameter of the distal end of the catheter thereby to enable the catheter to be passed through a recanalized hole formed by said working region, the axial depth of the working region being not substantially greater than the cross-sectional dimension of the distal end of the catheter.

22. A catheter as defined in claim 21 wherein said means for shaping the beam further comprises net-negative optical means at the distal end of the catheter.

23. A catheter as defined in claim 21 or 22 wherein said optical means encloses and isolates the exit end of the optical conductor to preclude contact of the exit end of the optical conductor with the biological material.

24. A catheter as defined in claim 21 or 22 wherein said optical means is constructed and arranged so that the beam emitted from the emission aperture will have substantially uniform energy distribution in a plane transverse to the direction of propagation of said energy.

25. A catheter as defined in claim 24 further comprising:

means for holding said exit end of the optical conductor and said optical means in a prescribed spatial relationship.

26. An optical system as defined in claim 25 in which the optical means includes an exit lens and in which a concave surface of said exit lens confronts said transverse plane.

27. A catheter as defined in claim 22 in further combination with a laser source of said radiant energy.

28. An optical system as defined in claim 25 further comprising:

the optical means including an exit lens means having net negative optical power; and

a spherical object lens between said exit end of said optical conductor and the exit lens means.

29. An optical system as defined in claim 28 in which said exit lens is bi-concave.

30. An optical system as defined in claim 28 in which said exit lens is plano-concave.

31. An optical system as defined in claim 25 including a tubular housing for holding said end and said lens means in said spatial relationship.

32. An optical system as defined in claim 31 including a radiopaque tubular spacer within said housing.

33. An optical system as defined in claim 31 in which the aperture of said exit lens means is substantially equal to the outer diameter of said tubular housing.

34. An optical system as defined in claim 28 including a plano-concave lens between said object lens and said exit lens, a first tubular spacer within said housing between said object lens and said plano-concave lens, and a second tubular spacer within said housing between said plano-concave lens and said exit lens.

35. An optical system as defined in claim 31 in which said exit lens means and said housing are made of glass capable of being fused together.

36. An optical system as defined in claim 35 in which said glass is a predominantly borosilicate glass.

37. An optical system as defined in claim 25 in which said holding means includes a part which is radiopaque.

38. An optical system as defined in claim 26 in which said holding means includes a rigid holder for said exit end of said optical conductor and spacer means for fixing the distance between said holder and said exit lens means.

39. An optical system as defined in claim 38 including a tubular housing enclosing said exit lens means, said spacer means and a part of said receiver.

40. An optical system as defined in claim 31 in which said housing is radio-transparent and includes a part which is radiopaque.

41. An optical system as defined in claim 40 in which said part is a tubular spacer for an optical component of said system.

42. An optical system as defined in claim 25 including a tubular housing made of a glass that is fusible to said exit lens means, in which the edge of said housing at the periphery of said lens means is rounded to form a smooth boundary with said lens means.

43. A catheter as defined in claim 21 wherein the catheter body has a lumen extending there through from its proximal to its distal portions, the catheter body having aperture means at its distal portion in communication with the lumen and means at the proximal end of the catheter for making a fluid connection to the lumen.

44. A catheter as defined in claim 43 wherein the optical conductor extends through the lumen.

45. A catheter as defined in claim 23 further comprising means for holding the exit end of the optical conductor and lens means in prescribed spatial relation, said holding means comprising:

a rigid tubular holder having a proximal end and distal end, the holder having a bore extending therethrough to receive the distal end of the optical conductor, said optical conductor being secured rigidly within the bore of the holder;

the exit end of the optical conductor being flush with the distal end of the holder;

a tubular housing for receiving at least a portion of the holder and the proximal end of the housing and for receiving the lens means at the more distal regions of the housing;

spacer means within the tubular housing and in engagement with the lens means and the distal end of the holder to space precisely the holder and conductor carried thereby with respect to the lens means; and

means for securing holder to the tubular housing.

46. A catheter as defined in claim 45 further comprising:

the holder having a shouldered portion between its ends;

said tubular holder being formed to engage the shoulder to secure the holding means to the tubular holder.

47. A catheter as defined in claim 46 further comprising:

the proximal end of the holding means being received in the lumen at the distal end of the catheter body, the juncture region between the distal end of the catheter body and the proximal end of the tubular housing being filled to present a smooth and continuous outer surface along said catheter.

48. A catheter as defined in claim 21 wherein the length of the working region along the axis is no greater than approximately 1.5 millimeters.

49. A method of removing a biological obstruction by radiant energy comprising:

providing a catheter having waveguide means for guiding said radiant energy from a source thereof, said catheter having a distally located emission aperture for emission of said radiant energy in a pattern propagating along an axis;

forming said emitted radiant energy into a geometrically expanding pattern in which the energy distribution around said axis is substantially uniform whereby the energy density of said emitted energy along said axis when applied to said obstruction decreases both exponentially and geometrically in a distally extending direction;

the energy density in a working region of the emitted energy within a first isothermal zone being sufficient to effect removal of the material forming the obstruction when said material is located in said region, the portion of the emitted energy extending distally of said working region having insufficient energy density to effect said removal;

said working region defining cross-section dimensions large enough to enable the catheter to be passed therethrough, the working region having an axially extending depth not substantially greater than about the cross-sectional dimension of the catheter;

whereby when said emitted energy is applied to the biological material said radiant energy will be effective to remove said material to a depth no greater than about the axial depth of said working region, thereby limiting said removal to a layer approximating the axial depth of said working region, and minimizing perforation of tissue located distal or radial to the isothermal boundary of said working region.

50. A catheter for recanalizing an obstructed lumen by selectively removing sequential layers of biological obstructing material by radiant energy comprising:

an elongate catheter body containing a flexible optical conductor;

the proximal end of the catheter having means to enable said radiant energy to enter the flexible optical conductor;

the distal end of the catheter having an emission aperture from which said radiant energy may be emitted, said emission aperture having a cross-sectional dimension which substantially corresponds to that of the distal end of the catheter;

said catheter and emission aperture being constructed and arranged to shape the radiant energy emitted from the emission aperture to define an unfocused pattern having a working region in which the density of energy is sufficient to cause said removal, and so that the portion of the emitted energy extending distal to the working region has insufficient energy density to cause said removal; and

the cross-sectional dimensions of the emitted energy in the working region being no smaller than about the diameter of the distal end of the catheter thereby to enable the catheter to be passed through a recanalized hole formed by said working region, the axial depth of the working region being not substantially greater than the cross-sectional dimension of the distal end of the catheter.

Description Submit all comments and votes

FIELD OF THE INVENTION

This invention relates to catheters and techniques for delivering and applying radiant energy, such as in the form of a laser beam, to the human body for controlled and selective removal of tissue, plaque and other biological material.

BACKGROUND OF THE INVENTION

This invention relates to the use and application of radiant energy within the human body for the controlled removal or etching away, for example, by ablation, of tissue or other biological material, in particular the removal of a vascular obstruction. The treatment of vascular obstructions including peripheral as well as coronary vascular obstructions, has been the subject of much investigation in recent years. Vascular surgery in which a diseased vessel is removed and replaced with a graft, or in which the blocked region of the vessel is bypassed with a graft, has become relatively common. Nevertheless, it is desirable that procedures and techniques be improved to reduce the level of trauma to a patient so as to simplify the procedure and treatment for the patient but without sacrificing effectiveness. While procedures for surgical removal and by-passing of vascular obstructions have become well developed, it clearly is desirable to provide alternatives to such non-conventional surgical procedures.

Among the alternatives which have been developed is the angioplasty procedure in which devices such as the balloon dilatation catheter of the type illustrated in Gruntzig U.S. Pat. No. 4,195,637, are used to open a passage through a vascular obstruction. In the balloon dilatation technique a catheter having a special balloon at its distal end is advanced through the patient's blood vessels until the balloon is placed within the obstruction. The balloon then is expanded under substantial pressure to forcibly enlarge the lumen within the blood vessel. When the procedure is successful the lumen of the blood vessel remains open after the balloon has been deflated and removed. The material which caused the obstruction, typically arterial plaque, is compressed radially outwardly. Those patients who can be treated successfully with the dilatation technique are spared the trauma, time and expense of traditional vascular surgery. However, the angioplasty technique cannot be used to treat all vascular obstructions and, indeed, the majority of obstructions cannot be treated in that manner.

When an obstructed vessel is treated surgically by replacement or bypass of the vessel, the diseased portion of the vessel either is removed in its entirety or is permitted to remain, in its obstructed condition, in the patient but with a bypass vessel grafted across the blocked regions. In the angioplasty technique the plaque which formed the obstruction remains in the artery although in a compressed condition. In some instances the plaque and vessel wall may rearrange themselves after some time to begin to obstruct the vessel again.

Although the general desirability of recanalizing an obstructed blood vessel by removal of the vascular obstructions from the vessel has long been recognized, no effective system or treatment technique has yet been discovered or developed for that purpose. The possibility of using laser energy for that purpose also has been recognized for some time. While recent availability of laser sources of controllable radiant energy have been found useful for some surgical operations, such as in certain kinds of eye surgery, no suitable device and technique have been developed by which a beam of radiant energy such as laser energy can be applied to a vascular obstruction to selectively and controllably remove that obstruction without causing trauma to the vessel, so as to leave the natural vessel in a healthy, unblocked, recanalized and functioning condition.

Proposals and efforts to apply laser energy to remove a vascular obstruction have encountered numerous difficulties. Prior efforts to deliver a beam of laser energy typically have involved the use of various configurations of catheters having arrangements of fiber optical conductors to conduct the radiant energy into the patient's vessel in an effort to direct the beam to the obstruction so as to destroy the obstruction. No devices or techniques have been developed by which it was possible to control effectively the beam. If the beam is not aligned properly in the blood vessel it can impinge against the lining of the blood vessel thereby damaging the vessel wall and possibly puncture the wall. Even if the beam is aligned properly in the blood vessel, the lining of the vessel can be damaged or the vessel can be punctured if there is a bend in the vessel just distal of the location of the obstruction.

Also among the significant difficulties encountered in trying to use laser energy to clear vascular obstructions is the tendency of the laser beam to cause biological material to char in the region surrounding the target. Such charring results, at least in part, from poor control over the manner and amount of energy applied. In the context of a delicate blood vessel, charring can present very serious problems, possibly doing severe damage to the surrounding tissue. Additionally, any biological material which becomes charred and adheres to the distal tip of the optical fiber conductor prevents emission of the beam from the distal tip of the conductor. In that case, the material at the end of the conductor becomes highly heated which, in turn, causes overheating and destruction of the optical fiber.

Other difficulties relate to the manner of positioning and locating the distal end of the catheter so that it is positioned properly with respect to the obstruction. Prior proposals which have included the use of supplemental optical fibers to transmit illuminating light into the blood vessel in conjunction with other groups of fibers to permit visual observation of the interior of the blood vessel are not practical because they are too large and too stiff for use in coronary arteries. Another difficulty is that there often may be material such as blood in the region between the emission point of the laser beam at the end of the fiber and the obstruction. Such material may obstruct the optical path. The blood may become charred at the distal emitting tip of the fiber which, as described above, can result in overheating and destruction of the optical fiber.

All of the foregoing difficulties have been complicated by the dimensional limitations imposed on any catheter which is to be inserted into a blood vessel, particularly narrow blood vessels such as coronary arteries which can have lumens of the order of 1.5 to 4.5 millimeters diameter.

The present invention relates to new catheter systems for delivering radiant energy to a selected site within a blood vessel in a manner which enables the radiant energy to be applied controllably to an obstruction and in a manner which avoids the foregoing and other difficulties.

SUMMARY OF THE INVENTION

The invention relates to new methods and means for delivering radiant energy from a source to a site within a patient's blood vessel where the energy is to be applied. More particularly, the invention concerns new methods and devices including a new catheter having a fiber optics conductor to deliver radiant energy (e.g., from a laser) to the site to be treated. The catheter has, at its distal end, a miniature optical system to controllably apply the radiant energy at the site. The optical system and catheter are arranged so that the radiant energy is distributed substantially uniformly in a beam which combines an exponentially decaying energy level with a geometrically expanding beam pattern. The optical system controls the beam to define a working region surrounding the axis of the propagation direction of the energy in which the removal of biological material takes place in a very limited layer-like region transverse to that axis.

A system for practising the invention includes an elongate, small diameter catheter having a lumen which carries an optical fiber. The proximal end of the catheter has a connector by which the optical fiber may be connected to receive the radiant energy output from a laser. The distal end of the catheter has an optical housing which incorporates a net negative optical power lens system arranged to emit a beam of radiant energy in an expanding (divergent), unfocused pattern. The energy distribution is substantially uniform Over the cross-section of the expanding beam. The beam has a short segment which extends a short distance from the distal emission aperture of the optical system and defines the working region in which the radiant energy is at a high enough level to remove the biological material. Depending on the frequency of the radiant energy and the absorption properties of the biological material, thermal disassociation or ablative photo-decomposition may be employed as the dominant etching or eroding mechanism. Distally beyond the working region the exponentially decaying beam diverges to a lower, safe energy density which will minimize damage to the biological material.

The depth of the working region as measured along the optical axis of the projected beam varies somewhat depending on the index of refraction of a light-propagating medium into which the beam is projected; up to about 1 to 1.5 mm is preferred. A medium having a greater index of refraction will tend to decrease the divergence of the beam thereby increasing the depth of the working region in the direction of the optical axis. The optical system is arranged so that the maximum depth of the working region is relatively short, of the order of 1.5 millimeters maximum depth, so that a distally propagated segment of the beam will not have sufficient energy level to puncture the vessel wall. The maximum diameter of the working region is not smaller than and may be slightly greater than the catheter diameter to enable the catheter to advance through the hole which the beam will form through the obstructing material.

The optical system at the distal end of the catheter includes a housing which contains one or more lenses spaced from each other by radiopaque spacers. The use of radiopaque spacers enables the catheter to be positioned in the blood vessel accurately by fluoroscopy. A special internal holder is provided to receive and securely position the distal end of the optical fiber rigidly with respect to the optical components in the housing. The manner in which the optical fiber is mounted isolates completely the distal end of the optical fiber from the blood vessel. That completely avoids the possibility of biological material contacting the distal tip of the optical fiber which might result in formation of a char on the tip with resulting destruction of the optical fiber.

The spacers and the housing cooperate to provide optical precision in a miniature environment. The catheter is arranged so that the distal tip of the optical housing may be advanced into direct contact with the vascular obstruction. This assures that there will be little or no optically obstructing material between the distal tip of the catheter and the vascular obstruction and also assures that the distal tip of the catheter will be positioned properly with respect to the obstruction.

The catheter may be provided with a lumen by which liquid may be flushed into and aspirated from the operative site in the blood vessel to draw away debris which may be developed during the removal procedure.

It is among the objects of the invention to provide a catheter adapted to deliver radiant energy into a blood vessel to enable forming a hole in vascular obstructions, and the effective removal of such obstructions.

Another object of the invention is to provide a catheter of the type described which is arranged to emit the radiant energy from an emission aperture at the distal end of the catheter in a pattern which minimizes the risk of undue injury to or puncture of the wall of the blood vessel.

Another object of the invention is to provide a device of the type described in which the distal end of the catheter may be placed and oriented accurately with respect to the targeted obstruction by fluoroscopic means, and without requiring the use of endoscopic visualization systems.

A further object of the invention is to provide a device of the type described in which the pattern Of the beam emitted from the distal tip Of the catheter is arranged to form an aperture in an Obstruction not substantially greater than the catheter diameter but large enough to permit the catheter to be advanced through the obstruction.

Another object of the invention is to provide a device of the type described in which the distal tip of the optical fiber is completely isolated from biological material.

A further object of the invention is to provide a catheter of the type described having a miniature optical system at the distal end of the catheter.

Another object of the invention is to achieve the foregoing and other objects within a catheter of very small diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and advantages of the invention will be appreciated more fully from the following further description thereof, with reference to the accompanying drawings wherein:

FIG. 1 illustrates generally a catheter according to the invention;

FIG. 2 is a section taken on line 2--2 in FIG. 1;

FIG. 3 is a diagrammatic illustration of the distal tip of the catheter showing the divergent beam pattern emitted from the optical housing; FIG. 3A schematically illustrates the thermal profile of a heat pattern created in an absorbing medium in response to the combined exponentially decaying energy and geometrically expanding beam pattern which is provided by the invention;

FIG. 3B is a graphic representation comparing energy distribution according to the invention with a Gaussian energy distribution;

FIG. 4 is an optical-schematic view, greatly enlarged, of an optical system of the invention and its relation to the distal end of the optical fiber;

FIG. 5 is an optical-schematic view similar to that of FIG. 3 illustrating another embodiment of the optical system;

FIGS. 6A and 6B are energy distribution plots illustrating substantially uniform energy distribution in the working portion of the energy beam for the system illustrated in FIG. 4;

FIGS. 7A and 7B are energy distribution plots illustrating substantially uniform energy distribution at the working portion of the energy beam for the optical system illustrated in FIG. 5;

FIG. 8 is a greatly enlarged sectional side view of the distal end of the catheter including an optical system assembly according to the invention;

FIG. 9 illustrates in further detail, the fiber holder and distal tip of the fiber shown in the assembly of FIG. 8;

FIG. 10 illustrates dimensional details of the fiber optics conductor;

FIG. 11 is a diagrammatic illustration of the distal end of the catheter in a partially stenosed blood vessel;

FIG. 12 is another diagrammatic illustration of the distal end of the catheter in abutment with the stenosis in a fully obstructed blood vessel; and

FIG. 13 is an axial-sectional view of another embodiment of an optical system.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

As is shown generally in FIGS. 1 and 2, the catheter is formed from an elongate flexible body 10 and, for example, may be extruded from an appropriate plastic material such as Teflon (trade name for polytetrafluoroethylene). The body 10 has a lumen 12 for enclosing a fiber optic light conductor 14. The distal end of the catheter is provided with an optical housing indicated generally at 16 which contains a net-negative optical lens system. The optical system in the housing receives radiant energy from the distal tip of the fiber optic light conductor 14. The radiant energy is emitted from the optical system in a controlled predetermined pattern from an emission aperture 18.

The proximal end of the catheter includes a molded fitting 20 which is secured to the catheter body 10. Projecting from the proximal end of the fitting 20 are a pair of flexible tubes 22, 24. The tube 22 is adapted to receive the fiber optic light conductor 14, which extends through the fitting 20. The proximal end of the tube 22 is provided with a connector 26 which is connected to the proximal end of the fiber optic light conductor 14. Connector 26 is adapted to be mounted with respect to the source of radiant energy, such as a laser (illustrated diagrammatically at 27) so that the proximal end of the light conductor 14 may receive the radiant energy and conduct it along its length to the optical system 16. The ot