Method and Apparatus for Enhanced Vascular or Other Growth

The invention relates to the use of laser radiation to promote or enhance vascular or other growth in a thus-irradiated local area of living body tissue.

In their paper, "Some New Findings on Retinal Irradiation by Krypton and Argon Lasers",* J. Marshall, et al. review the histopathology of the acute effects of krypton and argon laser radiation on the human retina, and these effects are related to their long-term pathology by observations on diabetics. Emphasis was on laser photocoagulation but some "surprising findings" were reported involving proliferation of vascular endothelial cells adjacent the reaction site. And in a later paper, "He-Ne Laser Stimulation of Human Fibroblast Proliferation and Attachment in Vitro",** coauthored by J. Marshall, laboratory studies are reported for laser-irradiated cultures of excised human tissues, wherein the irradiation source was a 1 mW helium-neon laser providing a coherent source at 633 nm, wherein the irradiation was chopped at 100 Hz, to provide a 50 percent duty cycle; for each experiment, a comparative run was made involving monochromatic incoherent light via a 640-nm interference filter (bandwidth 9 nm), adjusted for intensity comparable with that of laser delivery to an identical culture. The reported result was that, at 24 and at 48 hours after 15-minute exposure, the particular laser-irradiated cultures exhibited a significant increase in the number of cells in comparison with their respective non-irradiated controls, while no significant change in cell counts was observed between irradiated and control cultures in experiments with the incoherent source.

It is an object of the invention to provide an improved method and means for in-vivo laser irradiation of living-body tissue.

It is a specific object to achieve the above object using perturbation effects induced by multiple beams of laser irradiation delivered to affected body tissue.

Another specific object is to achieve the above objects without inducing photocoagulation, photonoptical-tissue breakdown, photovaporization, or photoablative decomposition of the affected body tissue and/or cells.

The invention achieves the foregoing objects by directing at least two beams of laser irradiation at an affected area of body tissue, wherein the irradiation (a) is of low intensity at tissue impingement and (b) is also of spectral wavelength that is preferably in the visible red or in the infrared. Perturbations result in the affected cells either directly by reason of differences in the physical properties of the respective beams or indirectly by reason of interaction between the two beams at or near the situs of delivery to the affected body tissue.

The invention will be described in detail for presently preferred apparatus, in conjunction with the accompanying drawings, in which:

FIG. 1 is an optical diagram schematically indicating components of apparatus of the invention;

FIG. 2 is an enlarged diagram indicative of a beam-delivery embodiment;

FIG. 3 is a diagram similar to FIG. 1 to show a modification; and

FIG. 4 is a simplified fragmentary optical diagram of one technique of laser-beam delivery within an eye, for either of the embodiments of FIG. 1 or FIG. 3; and

FIG. 5 is a diagram similar to FIG. 4 to show another technique of laser-beam delivery within an eye, for either of the embodiments of FIG. 1 or FIG. 3.

In FIG. 1, a first laser A delivers an output beam on a first optical axis 10, and a second laser B delivers an output beam on a second optical axis 11 which is orthogonally oriented for intersection and folded merger with axis 10 at a beam splitter 12. As a consequence, both laser beams utilize a common axis 13 of therapeutic energy delivery which, in the form shown, employs a dichroic filter 14 to fold projected laser energy onto a delivery axis 15. The delivered energy may be in the form of a collimated beam, producing a circular or otherwise configured spot at impact with living tissue to be irradiated; alternatively, as suggested by converging-lens means 16, the laser energy may be converged to a lesser area for coupling to a fiber-optic delivery system 17, as in the case of an endoscope utilization.

Each of the lasers A, B preferably emits in the visible red or in the infrared and at extremely low power, in terms of energy delivered to body tissue, thus avoiding local heating or coagulation of tissues and/or cells. Suitable and reasonably priced helium-neon, krypton and diode lasers are available for present purposes, and modes of use will determine particular selection.

To further facilitate particular desired modes of use, optical elements on axis 10 are shown to include attenuator means 20 (which may be selectively variable), shutter means 21 (which may be mechanical and electromagnetically actuated, or electro-optical and electronically actuated), a beam expander 22 (with manual means 23 for adjusting expansion), a field stop 24, and a beam-displacement optic 25 (having provision for its adjustable tilt with respect to axis 10, as suggested by double-headed arcuate symbolism). In similar fashion, optical elements on axis 11 are shown to include attenuator means 30, shutter means 31, a beam expander 32 (with adjustment means 33), a field stop 34, and an adjustable-tilt beam-displacement optic 35; in addition , the optical elements on axis 11 are seen to include adjustable phase-shifter means 36 to enable selective phase offset of the axis 11 beam with respect to the axis 10 beam (in the event that lasers A and B are identical), and means 37 for selective angular shifting of the polarization of one with respect to the other of beams 10-11. A suitable polarization-rotator product of Newport Corporation is identified by Catalog Number PR-550 for use in the visible spectrum, or by Catalog Number PR-950 for use in the near-infrared (700 to 1200 nm).

To complete the description of components shown in FIG. 1, a field-illumination system 40 projects light onto the delivery axis 15, via a folding reflector 41 and a beam splitter 42, and a viewing device such as a stereo-observing biomicroscope 43 has a direct line of sight along axis 15. With both field stops 24, 34 adjusted to confine their respective beams to the same circular section, and with the two beam-displacement optics 25, 35 set for zero tilt (i.e., with their plane-parallel surfaces oriented normal to their respective optical axis 10, 11), the described system will deliver equal and coincident areas of radiation from both lasers A, B; if, on the other hand, one of stops 24, 34 is set for a larger beam-limiting section than the other, then delivered concentric overlap of radiation from the two lasers will be as depicted in FIG. 2, namely, with a central area 44 of concurrent response to both lasers, surrounded by a fringe annulus 45 of response to but one of the two lasers. The latter situation will be seen to have utility for a case wherein a buffer zone 45 of less-exposed tissue is desired between a central maximally treated zone and externally adjacent areas of untreated tissue.

As indicated generally above, it is the intention and purpose of the present invention to employ interaction between concurrent, or effectively concurrent, but dissimilar, laser beams of the character indicated to induce perturbations in affected tissue whereby vascular or like growth is enhanced beyond what may be achievable with emanations from a single laser. With the described apparatus, such dissimilarities are achieved through one or more of various combinations of beams on axes 10 and 11, as follows:

A. With identical lasers at A and B, as for example two He-Ne lasers, one on each of the axes 10, 11:

(1) Adjust phase shifter 36, so that combined output on delivery axis 15 is sum of two spatially and temporally coherent radiations at identical wavelength, but phase-displaced with respect to each other.

(2) Adjust polarization rotator 37, so that combined output on delivery axis 15 is the product of a predetermined difference in polarization-plane orientation for each of two spatially and temporally coherent radiations of identical wavelength.

(3) Adjust the beam-displacement optics 25, 35 for equal and opposite offsetting displacements of their respective axes (from 10 to 10', and from 11 to 11', respectively) so that the beam 13a (15a) for laser-A radiation may be converged on a first axis 18a to treated tissue, and so that the beam 13b (15b) for laser-B radiation may be converged on a second axis 18b to the same area of treated tissue.

(4) With a selected one of the modes (1), (2) or (3) above, operate the shutters (choppers) 21, 31 in synchronism, in accordance with a selected one of the following mode refinements:

(a) shutter-open/shutter-closed, in coincident synchronism on both axes 10, 11.

(b) shutter-open/shutter-closed, in time interlaced relation on the respective axes 10, 11.

(c) shutter-open action on one axis (1) in only partial cyclical overlap with shutter-open action on the other axis (11).

(d) cyclical rate of less than 15 Hz, to allow affected-cell recovery between shutter-open exposures.

(e) cyclical rate greater than 15 Hz, to suppress affected-cell recovery during period of treatment.

B. With non-identical lasers at A and B, as for example, a He-Ne laser on axis 10 and a krypton laser on axis 11:

(5) Adjust attenuator 20 or 30 such that beam intensity at one wavelength on one axis (1) is equal to or greater than beam intensity at the other wavelength on the other axis (11).

(6) Adjust polarization rotator 37, so that the combined output on delivery axis 15 is the product of a predetermined difference in polarization-plane orientation for each of two spatially and temporally coherent radiations of different wavelengths.

(7) Adjust the beam-displacement optics 25, 35, for equal and opposite offsetting displacements of their respective axes (from 10 to 10', and from 11 to 11', respectively) so that the beam 13a (15a) for laser-A radiation may be converged on a first axis 18a to treated tissue, and so that the beam 13b (15b) for laser-B radiation may be converged on a second axis 18b to the same area of treated tissue.

(8) With a selected one of the modes (5), (6), or (7) above, operate the shutters (choppers) 21, 31 in synchronism in accordance with one of the mode refinements recited in mode A (4) above.

Whatever the selected variety of laser at A or B, it is recommended that the combined intensity of beam energy deliverable to the affected area of body tissue be in the order of microwatts/cm.sup.2, as and preferably in the range of 100 to 150 microwatts/cm.sup.2.

In the embodiment of FIG. 3, the output beam from a single laser 49 is divided by a beam splitter 50 into beams 51, 52 on separate paths, which are thereafter recombined by beam-splitter means 53 to a single axis 54, before folding at a dichroic filter 55, to the delivery axis 56. Instrumentalities operative upon beam 52 are as described for the beam 10 from laser A in FIG. 1, and those operative upon beam 51 are as described for the beam 11 from laser B in FIG. 1; these instrumentalities, as well as illumination and viewing instrumentalities, have therefore been given the same reference numbers as in FIG. 1.

It will be seen that the single-laser embodiment of FIG. 3 is essentially the functional equivalent of the identical-laser situation mentioned above in connection with FIG. 1. The dissimilarities that may be produced in the divided beams 51, 52 of FIG. 3 may therefore include those tabulated under category A above for identical lasers on axes 10 and 11 of FIG. 1

As to body-tissue application, the presently described multiple-beam exposures may be delivered either directly as a collimated beam wherein field-stop openings determine size and shape of a delivered spot or spots, or via a fiber-optic endoscope to an internal body-tissue region. For delivery within an eye 54, FIG. 4 illustrates use of a converging optic 55 to develop a relatively large area of exposure to the retina, while FIG. 5 illustrates use of a contact-lens element 56 in conjunction with a converging optic 57 to effect exposure over a more restricted area of the retina. It will be understood that beam cross-sectional areas delivered to the optic element 55 (or 56) will be determined by field-stop dimensional limitation, at legend-identified components of FIG. 1 or FIG. 3, as the case may be.

Parenthetic reference has been made above to choppers as having equivalence to shutters, for present purposes, with electrical or electronic control for their particular synchronized coordination; such controls are well understood and therefore need not now be described. It will also be understood that time-interlaced chopper action, as between two differently characterized laser beams delivered to body tissue, may be achieved by a rotary chopper having a flat mirror surface (1) that is inclined 45.degree. to the one beam which is to be folded into axis alignment with that of the other beam, and (2) that the mirror surface is interrupted to provide an open sector space for non-reflected direct delivery of said other beam in interlace with reflected delivery of said one beam. In FIG. 1, such a mirror chopper is to be understood as symbolized by the 45.degree.-inclined plane-parallel device called out as beam-splitter 12 in FIG. 1 or as beam-splitter 53 in FIG. 3.

It will further be understood that the operative limited spectral band of reflectivity at each of the dichroic filters 14 (55) will depend upon the particular selected lasers at A, B and 49. Thus, for HeNe and krypton lasers, the limited band of dichroic-filter reflectivity is suitably 610 to 660 nm, thereby allowing for field illumination (from 40) and viewing (from 43) via a generous remainder of the visible spectrum.