Apparatus for and method of utilizing energy to excise pathological tissue

I claim:

1. An instrument for excising pathological tissue from a living animal organism comprising means for emitting a beam of coherent optical radiation, collimating means responsive to the beam for reducing the beam cross sectional area, a pyrolytic graphite cannula having an optically transparent interior responsive to the reduced diameter beam, said cannula coupling the reduced diameter beam onto the tissue so the tissue is irradiated by the beam, said reduced diameter beam having sufficient energy to vaporize the irradiated tissue, the graphite of the cannula having a crystalline structure orieinted whereby heating of the cannula interior by radiation from the beam is not substantially transferred by conduction to the exterior of the cannula.

2. The instrument of claim 1 wherein the transparent cannula interior is an air filled bore extending longitudinally through the cannula, said bore having a reflecting wall.

3. The instrument of claim 1 wherein the transparent cannula interior comprises a dielectric filled bore extending longitudinally through the cannula.

4. The instrument of claim 1, or 2 or 3 wherein the collimator includes means for variably reducing the beam cross section.

5. A method of excising pathological tissue from a heart without mechanically cutting the pericardial sac surrounding the heart comprising inserting a cannula through an opening in the body cavity and into proximity with a region of the sac above a site from which the tissue is to be removed, then propagating a beam of coherent optical radiation through the cannula to burn a hole in the sac, the hole having sufficient area to enable the cannula to be inserted through it, then inserting the cannula through the hole in the sac and positioning the cannula so its longitudinal axis is aligned with the site, then maintaining the cannula stationary and irradiating the site with a beam of coherent optical radiation propagated through the cannula to remove the tissue.

6. The method of claim 5 wherein the irradiating beam is gyrated about the longitudinal axis while the cannula is maintained stationary to forma frusto-conical removed region in the tissue, the frusto-conical region having a base adjacent the tissue surface smaller than a base removed from the tissue surface.

7. The method of claim 6 wherein the irradiating beam is gyrated by being stepwise directed to adjacent, overlapping subregions in the tissue so the beam is stationary as it irradiates each of the subregions and is not propagated to the tissue while it is gyrated between the subregions.

8. The method of claim 5, or 6, or 7 further including monitoring characteristics of the heart after the tissue has been removed, then repeating the irradiation step while maintaining the cannula stationary to remove additional tissue from the irradiated site, and then repeating the monitoring step.

9. The method of claim 8 further including monitoring characteristics of the heart after the tissue has been removed, then moving the cannula into proximity with a different region of the sac above another site which the monitoring indicated to contain pathological lesions, then repeating the propagating, inserting, irradiating and monitoring steps for tissue at another site.

10. The method of claim 5, or 6, or 7 comprising the step of reducing the cross sectional area of the irradiating beam relative to the area of the beam that burns a hole in the pericardial sac.

11. A method of excising pathological tissue from an organism comprising positioning a cannula through an opening in the organism into proximity with the tissue to be excised so the longitudinal axis of the cannula is aligned with a site of the tissue, then maintaining the cannula stationary while irradiating the site with a beam of coherent optical radiation propagated longitudinally through the cannula to remove the tissue, peripheral portions of the site being irradiated by gyrating the beam about the cannula axis, a central portion of the site being irradiated by propagating the beam along the cannula axis and not gyrating it about the cannula axis.

12. The method of claim 11 wherein the gyration of the beam is controlled by coupling the beam to an electronically controlled optical crystal deflector having a fixed position, and applying deflecting voltages to the crystal deflector to provide the gyration.

13. A method of excising pathological tissue from an organism comprising positioning a cannula through an opening in the organism into proximity with the tissue to be excised so the longitudinal axis of the cannula is aligned with a site of the tissue, then maintaining the cannula stationary while irradiating the site with a beam of coherent optical radiation propagated longitudinally through the cannula to remove the tissue, the site being irradiated by gyrating the beam about the cannula axis, the irradiating beam being gyrated by being stepwise directed to adjacent, overlapping subregions in the tissue so the beam is stationary as it irradiates each of the subregions and is not propagated to the tissue while it is gyrated between the subregions.

14. The method of claim 11 or 13 further including monitoring characteristics of the organism after the tissue has been removed, then repeating the irradiation step while maintaining the cannula stationary to remove additional tissue from the irradiated site and then repeating the monitoring step.

15. An instrument for excising pathological tissue from an organism comprising a laser for deriving a beam of coherent optical energy, an optical waveguide responsive to the beam, a collimator responsive to the beam exiting the waveguide for reducing the beam cross sectional area, and a graphite cannula responsive to the beam exiting the collimator, said cannula having a longitudinal optically transparent bore sight axis for coupling the reduced cross section area beam to the tissue, the graphite of the cannula having a crystalline structure oriented whereby heating of the cannula interior by radiation from the beam is not substantially transferred by conduction to the exterior of the cannula.

16. The instrument of claim 15 further including means for mounting the cannula so the cannula bore sight axis is coincident with an axis extending at substantially right angles through an exterior surface of the tissue, and motor means for moving the cannula so its bore sight axis moves in a plane at right angles to a plane on an exterior surface containing the tissue.

17. The instrument of claim 15 or claim 16 further including means for translating the cannula along its bore sight axis.

18. The instrument of claim 17 further including an electrically responsive optical deflector fixedly positioned with respect to the cannula for coupling the reduced cross sectional beam exiting the collimator to the cannula bore sight axis and for gyrating the reduced cross sectional area beam about the bore sight axis.

19. The instrument of claim 15 or 16 further including an electrically responsive optical deflector fixedly positioned with respect to the cannula for coupling the reduced cross sectional beam exiting the collimator to the cannula bore sight axis and for gyrating the reduced cross sectional area beam about the bore sight axis.

20. A method of excising pathological tissue from an organism comprising (a) directing a bore sight axis of a beam source of radiation capable of excising the tissue at the tissue so the bore sight axis is substantially at right angles to a first region of the tissue, (b) pulsing the beam on while it is directed at the first region, the beam irradiating the tissue having a predetermined cross sectional area to excise tissue in the first region, the first region having a center coincident with the bore sight axis and an extent away from the center equal to the area of irradiation, (c) deflecting the beam propagation axis by a predetermined axis off the bore sight axis while the beam is off, so the beam is directed at a second region of the tissue, the second region having a center substantially coincident with the deflected propagation axis and a peripheral portion overlapping a peripheral portion of the first region, (d) pulsing the beam on while it is directed at the second region to excise tissue in the second region, repeating steps (c) and (d) for a sufficient number of positions about the bore sight axis to excise tissue from all regions of the organism abutting the periphery of the first region, whereby an excision having a substantially frusto-conical cross section at right angles to the surface of the organism is provided in the organism, said frusto-conical cross section having a smaller base on the surface of the organism than within the organism.

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FIELD OF THE INVENTION

The present invention relates generally to a method of and apparatus for excising pathological tissue from living animal and, more particularly, to such an apparatus and method wherein high intensity coherent, optical radiation is coupled to the tissue through a cannula.

BACKGROUND OF THE INVENTION

Lasers have been extensively utilized for excising pathological, exterior tissues, such as skin, and have been suggested for excising interior pathological tissues, by utilizing invasive techniques. The pathological tissue is excised in response to the laser producing high intensity electromagnetic fields that vaporize and damage the tissue lattice. The laser damage field coincides with the electromagnetic, optical field so that the size or volume of excised tissue can be very accurately controlled. The laser beam creates holes or cuts in the tissue by disrupting bonds in the chemical network of tissue. The problems involved in invasive, rather than noninvasive, laser surgery are well known and have been dealt with, to a certain extent, by others. For example, invasive laser systems, or laser systems which appear to be adaptable to invasive applications, are disclosed in the following United States Patents:

______________________________________ Snitzer 3,471,215 Bredemeir 3,659,613 Ayres 3,467,098 Bredemeir 3,710,798 Bredemeir 3,804,095 Sharan 3,865,114 Wallace et al. 3,906,953 ______________________________________

A particular problem involved in invasive laser surgery is propagating the beam to the pathological tissue to be excised without damaging intermediate tissue between the pathological tissue and an opening in the body cavity through which the beam must enter. High intensity, coherent, optical radiation derived from the laser has a tendency to heat guiding structures through which it propagates. If the guiding structure contacts the intermediate tissue, there is a tendency for the intermediate tissue to be excessively heated and possibly burned to a serious extent. An instrument that contacts the intermediate tissue must be chemically inert with the tissue so that it does not cause any infection, thermal burns or other deleterious effects on that tissue. In addition, it is desirable for the cross sectional, circular area of the irradiating beam to be small in certain instances and larger in other instances. It is also frequently desirable to excise the pathological tissue so that the cross section of the excised tissue, in a plane at right angles to the exterior surface of the tissue, is frusto-conical, with the largest face of the frusto-conical section being below the surface to reduce blood flow from the tissue and promote faster healing of the treated area of the organ.

It is accordingly, an object of the present invention to provide a new and improved apparatus for and method of excising pathological tissue with a laser beam.

A further object of the invention is to provide a new and improved instrument for and method of excising pathological tissue from the interior of a living animal with a laser beam that is introduced into the body cavity without causing any substantial adverse effects on tissue within the body cavity between the entrance to the body cavity and the pathological tissue.

A further object of the invention is to provide a laser instrument for and method of excising pathological tissue wherein laser energy is coupled to the pathological tissue without substantially heating intermediate tissue between an opening in the body cavity and the site of the pathological tissue.

An additional object of the invention is to provide a laser instrument for excising pathological tissue within the body cavity wherein energy from the laser source irradiates the pathological tissue with an optical wave guiding cannula that is chemically inert with intermediate tissue between the opening to the body cavity and the pathological tissue.

Still another object of the invention is to provide a new and improved apparatus for and method of excising pathological tissue from the interior of a living organism by forming relatively small diameter, substantially frusto-conical cross sectioned excised regions in the tissue, wherein the conical cross section increases as a function of depth from the surface to the tissue.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with one aspect of the invention, a laser beam is invasively coupled to pathological tissue via an optically transparent interior portion of a pyrolytic graphite cannula that is inserted through an opening in a body cavity into proximity with the tissue. The pyrolytic graphite cannula has a crystalline axis disposed so that there is minimum heat transfer from the interior, optically transparent portion thereof to the exterior wall thereof. Thereby, any heat radiated to the cannula internal wall by the laser beam is substantially decoupled from healthy tissue through which the cannula is inserted, and the healthy tissue is not overheated and damaged in response to heat radiating from the laser propagating through the cannula. In addition, the pyrolytic graphite is chemically inert with tissue in contact with it, whereby the intermediate tissue does not become infected through the use of the cannula.

The cross sectional area of the cannula transparent portion determines, to a large extent, the cross sectional area of the laser beam irradiating the pathological tissue. To control the resolution of the excised tissue, cannulas having different transparent cross sectional areas and outside diameters are employed by being inserted into a holding chuck that is maintained outside of the body cavity.

For certain beam diameters, the cannula interior transparent region is formed as an air filled bore extending along the longitudinal axis of the cannula. The wall of the bore is plated with a relatively thin metal, preferably gold, optically reflective film that is covered by a protective, dielectric film. The gold film reflects any stray, disbursive laser beam energy that impinges on the internal wall of the bore, to minimize heating of the interior diameter of the cannula and to increase the energy of the beam exiting the cannula and irradiating the pathological tissue. For other applications, where the transparent cross section of the cannula is very small, in situations where it would be difficult to coat the inner diameter of the cannula with a metal, the entire bore is filled with a polycrystalline dielectric that is transparent to the laser energy.

The laser beam coupled to the input of the cannula, outside of the body cavity, is derived from a collimator that reduces the beam diameter relative to the diameter of the beam coupled to an input aperture of the collimator from a flexible, optical, wave guide that is responsive to the laser source. The collimator is adjustable to vary the cross sectional area of the beam exiting it and coupled to the inlet of the cannula. By varying the diameter of the beam exiting the collimator and coupled to the cannula, the resolution of the beam irradiating the pathological tissue is controlled. The energy density in the beam is also controlled by the collimator assist in determining the depth of excised tissue.

In accordance with another aspect of the invention, the excised tissue has a substantially frusto-conical volume having its smaller base on the initially irradiated, exterior surface of the organ being irradiated. The larger base within the organ has a concave configuration. The frusto-conical volume is desirable in many instances because the pathological tissue is usually in the interior of the organ, rather than on its surface, whereby a minimum amount of healthy tissue is removed.

The frusto-conical excision is provided by deflecting the beam coupled to the entrance aperture of the cannula an electrically responsive optical deflecting crystal. The crystal selectively deflects the beam relative to the cannula bore sight axis, so that for each position of the cannula the beam is gyrated about the cannula bore sight axis. The beam is preferably pulsed by employing either a pulsed laser source or a continuous wave laser source that is mechanically coupled to the cannula by a shutter in the collimator. For each laser energy pulse passing through the cannula at a fixed cannula position, a different beam deflection angle is provided by the electrically responsive optical deflector, whereby a series of beam pulses irradiate differing, but overlapping areas of pathological tissues to be excised. The beam deflector can either be electro-optic or acousto-optic, depending upon the wavelength of the laser beam; both types of deflectors are preferably driven in a step-wise manner.

To position the cannula so that differing regions of the pathological tissue can be excised, the cannula is mounted so that its bore sight axis is coincident with an axis extending at substantially right angles through an exterior surface of the tissue, the cannula is driven so its bore sight axis moves in a plane substantially at right angles to a plane on the exterior surface of the organ containing the tissue. Preferably, the cannula is moved so its bore sight axis moves in a plane at right angles to the exterior surface of the tissue in response to a position servo feedback control system responsive to input position control signals and an encoded signal indicative of the cannula position relative to its mounting. The cannula is also moved on its mounting so that it is translated along its bore sight axis. Thereby, different discrete and separate tissue layers can be excised by inserting the cannula to different positions within the body cavity. For example, if it is desired to remove pathological tissue from a portion of an organ, such as the heart, the cannula can first be inserted into the body cavity and the laser activated to pierce the pericardial sac. Then the cannula is inserted through the hole in the sac into proximity with a wall of the heart and the laser is reactivated to remove pathological tissue from the wall of chambers of the heart. In such an instance, it would also be frequently desirable to change the cannula to provide increased resolution for excising tissue within the wall of the chambers of the heart, relative to tissue in the pericardial sac. For heart muscle repair (as is appropriate in the treatment of rhythm disturbances and conduction abnormalities), the instrument would be utilized with a heart monitoring apparatus, such as an EKG and an array of electrodes placed on the epicardial surface of the heart, to determine if the pathological tissue removal resulted in the restoration of normal function.

One particular application of the instrument is for the treatment of cardiac myopathies due to structural and functional abnormalities. Some examples of cardiac myopathies are (1) the Wolff-Parkinson-White syndrome (WPW syndrome), (2) supra-ventricular, (3) ventricular tachycardias, (4) nodal tachycardias due to failure of pacemakers below the AV node, (5) firing of an ectopic foci due to myocardial change such as atrial flutter or fibrillation and other reentry mechanisms and/or circus pathways (where two areas of the heart are inhomogeneous).

The Wolff-Parkinson-White syndrome is a classic reentrant mechanism and is characterized by the following electrocardiographic features: (1) abnormally short P-R intervals, (2) distortion of QRS complex, resulting from the appearance of a delta wave due to accessory pathways of conduction from the atrium to the ventricle (due to the presence of anamolous Kent bundles. The interruption of the anamolous Kent bundles is a treatment for WPW syndrome. The location of Kent bundles is done by epicardial mapping in combination with lasing and excision procedures in accordance with an aspect of the invention. The invention can also be utilized in connection with neural disorders, with the assistance of electro-cortical mapping. Other applications of the apparatus include selective excision of tissue from bone marrow and other internal organs. Hence, the invention has particular utility in connection with surgical procedures that involve excision of pathological tissues in areas that are not easily accessible. These procedures are performed without extensive dissection and/or trauma to normal tissues in the cannula path leading to the pathological lesion. In contrast, prior techniques for excising pathological tissue from the heart have involved opening the pericardial sac by mechanically cutting a relatively lengthy slit in the sac and then removing the pathological tissue by mechanical cutting surgical instruments such as a scalpel. With the present invention, it is merely necessary to make a relatively small diameter circular hole in the sac and a smaller diameter circular cavity in the heart or other organs in question.

It is, accordingly, a further object of the invention to provide a new and improved method of and apparatus for excising pathological tissues at areas that are not readily accessible in a body cavity, without extensive dissection and trauma.

A further object of the invention is to provide a new and improved method of excising pathological tissue from the heart without mechanically opening the pericardial sac.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following