Surgery – Instruments – Light application
Reexamination Certificate
1995-08-04
2002-03-19
Shay, David M. (Department: 3739)
Surgery
Instruments
Light application
C606S003000, C606S013000
Reexamination Certificate
active
06358243
ABSTRACT:
1. FIELD OF THE INVENTION
The present invention relates to lasers and particularly to a dual wavelength surgical laser system that would inflict significantly less collateral tissue damage during surgery than currently available scalpels or medical lasers.
2. DESCRIPTION OF THE RELATED ART
Lasers are currently employed in a wide variety of surgical applications. A major disadvantage encountered in laser surgery is collateral tissue damage. Such damage frequently results in longer healing times, accompanied by an increase in scarring. It has been fairly well established that collateral damage is caused by thermal diffusion and/or shock waves, and efforts have been made to reduce the damage by judicious selection of laser wavelength and pulse width. Until very recently, tissue ablation models employed in that selection process were based on a detailed understanding of the properties of water. Although water is the principal constituent of all biological tissue, it does not determine all the physical properties involved in the tissue ablation mechanism. Mechanical properties in particular are determined primarily by protein constituents such as collagen, lipoproteins and proteoglycans. With the availability of the medical free electron laser (FEL) at Vanderbilt University Medical Center (VUMC) it has now become possible to investigate the role played by the protein constituents in the laser tissue ablation process. This is accomplished by irradiating into known amide absorption bands in the spectral region between 5.9 &mgr;m and 6.6 &mgr;m, which have varying degrees of overlap with the absorption due to the bending mode of water. In a most recent FEL study of corneal, dermal and neural tissue, which covered the spectral range between 2.5 &mgr;m and 6.85 &mgr;m, VUMC scientists observed maximum ablation rate and minimum collateral damage when they tuned to the amide-II band near 6.45 &mgr;m.
These exciting new FEL results have raised several basic questions about the fundamental mechanism of laser ablation, and they suggest the possibility of designing a surgical laser which could inflict significantly less collateral tissue damage during surgery. VUMC scientists have proposed a dual-mechanism model to explain their FEL results. Qualitatively, their model assumes that laser energy absorbed into the protein and into the water perform two separate functions. The former serves to weaken the mechanical structure of the irradiated tissue volume, and the latter provides the “thermal explosion” to blow out the structurally weakened material. The highly favorable results obtained for FEL ablation of corneal tissue were tentatively attributed to the approximately equal partition of absorbed 6.45 &mgr;m radiation between the protein and the water. If this interpretation is correct, then it may also be possible to obtain even more favorable results by optimizing the partition of the absorbed energy. There has not yet been any clear indication that equipartition is optimal, nor that one specific partition of the energy will be favorable for all tissue types.
At the present time, applicants know of no prior art dual wavelength surgical laser used for precision surgery.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a surgical laser that would inflict significantly less collateral tissue damage during surgery than currently available scalpels or medical lasers.
Another object of the invention is to provide a dual wavelength surgical laser system for performing laser surgery on living tissue with a minimum amount of collateral tissue damage.
Another object of the invention is to provide a tunable dual wavelength surgical laser system for producing a sequence of protein and water absorption light pulse pairs, with each protein absorption light pulse softening the tissue and the following water absorption light pulse in a pulse pair acting to remove the softened tissue.
Another object of the invention is to provide a dual wavelength surgical laser system for producing a sequence of protein and water absorption light pulse pairs in which the ratio of light amplitudes in each pulse pair can be changed to compensate for a different type of living tissue having laser surgery performed thereon.
A further object of the invention is to provide a tunable, amplitude-variable, dual wavelength surgical laser system for performing laser surgery on different types of living tissue with a minimum of collateral tissue damage.
These and other objects of this invention are achieved by providing a dual wavelength surgical laser system comprising: a pump laser for emitting pump laser pulses of light at a preselected pump wavelength; an optical parametric oscillator responsive to each pump pulse from the pump laser for producing a first wavelength pulse of light in a water absorption band of the tissue and a second wavelength pulse of light in a protein absorption band of the tissue; a first set of optics for only passing therethrough each first wavelength pulse from the optical parametric oscillator; an optical delay line for delaying each first wavelength pulse from the first set of optics by a predetermined period of time; a second set of optics for only passing therethrough each second wavelength pulse from the optical parametric oscillator; and a beam combiner for combining each second wavelength pulse with the following delayed first wavelength pulse to form a stream of consecutive second and delayed first pulse pairs for application to the tissue.
REFERENCES:
patent: 5312396 (1994-05-01), Feld et al.
Esterowitz Leon
Marquardt Charles L.
Shay David M.
The United States of America as represented by the Secretary of
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