METHOD AND APPARATUS FOR EXTERNAL
CONTROL OF SURGICAL LASERS
REFERENCE TO RELATED APPLICATION 5
This application is a continuation-in-part of application Ser. No. 07/523,473, filed May 14, 1990, now U.S. Pat. No. 5,057,099 which is a continuation-in-part of application Ser. No. 07/265,565, filed Nov. 1,1988, now U.S. Pat. No. 4,950,268, issued Aug. 21, 1990 to John 10 Rink, which is a continuation-in-part of application Ser. No. 07/019,755, filed Feb. 27,1987, for which priority is claimed.
BACKGROUND OF THE INVENTION 15
In recent years the field of medicine has witnessed the application of lasers for therapeutic treatment of a variety of diseases and conditions. Laser energy conducted through a flexible waveguide such as an optical fiber has been used successfully for hemostasis, photody- 20 namic destruction of some forms of tumors, removal of epidermal growths and abnormalities, and the like.
Lasers have also been adapted for use in surgical procedures, and surgical devices have been built, tested, and sold commercially. However, some drawbacks in 25 laser devices for surgical use have been noted in the prior art. Surgical lasers are generally controlled grossly by presetting an output power level which is deemed appropriate for a particular surgical procedure and laser surgical tool, based on empirical knowledge. 30 This preset power approach achieves results that are far less than optimal for many types of laser tools and procedures. For example, U.S. Pat. Nos. 4,693,244 and 4,736,743 discuss the use of a bare optical fiber connected to a laser and used to cut tissue. It is noted that 35 if the bare fiber end contacts the tissue being cut, the fiber becomes fouled, the transmission efficiency decreases, more heat is generated in the fiber, thermal runaway ensues, and the fiber quickly heats to the point of material failure. One attempted solution to this prob- 40 lem in the prior art is to use the fiber end in a non-contact mode, thereby avoiding contamination of the fiber output end. However, contamination is difficult to avoid in practice, due to the fact that the fiber must be held very close to the tissue target, and tissue contact is 45 unavoidable. A single contact with tissue will often result in fiber failure. Also, the smoke and vapor arising from the laser beam impact site can contaminate the fiber end without any contact with the tissue itself.
Another attempt to solve this problem has been the 50 provision of a transparent tip secured to the output end of the optical fiber, the tip being formed of a material such as sapphire that is tolerant of extremely high temperatures. If the tip becomes fouled or coated with carbonized material, it will not be heated to the point of 55 material failure. Several manufacturers make available surgical optical tips having differing cutting configurations. However, even sapphire can be fractured by the high temperatures and temperature transitions experienced at the optical fiber output end. Moreover, sap- 60 phire or any similar material is expensive and difficult to manufacture, and the surgical tips can be reused only a few times.
A surgical tip, as well as a bare optical fiber end, may be provided with a constant flow of gas or liquid to 65 prevent overheating and to remove some of the inevitable contamination. However, in some procedures gas cooling can create the risk of embolism in the patient;
liquid cooling can cause such problems as fluid distension, fluid absorption through the surgical wound, and the like.
The simplest practical solution available in state of the art surgical lasers is to limit the laser power to a level that cannot damage the optical fiber. Ironically, this approach requires that a laser capable of delivering high power; e.g., 120 watts of beam energy, must often be limited to 30 or 40 watts output or less to preserve the optical fiber integrity. Alternatively, the optical fiber output end must be constantly immersed in a lasertransparent liquid, such as water, during operation, or the tip must remain in contact with the tissue during operation so that the tissue cools the fiber tip. These conditions are difficult to achieve in practice.
It should be noted that there are thousands of surgical lasers installed in hospitals and medical institutions, and that many of them are unable to control the temperature of the delivery system which utilizes the laser output. Furthermore, there are no devices available in the prior art that could be easily retrofitted to existing surgical lasers to enhance their effectiveness by adding a temperature control function to the lasers to protect the delivery systems.
Another drawback to the use of lasers in general is that laser safety eyewear (filter goggles and shielded filter spectacles) is required to protect the eyes of all personnel in the operating area. Failure to use such protection can result in permanent eye damage. However, goggles and shielded spectacles often interfere with ophthalmic spectacles worn by personnel, and severely narrow the field of vision. Moreover, in surgical procedures, where sterile conditions must be maintained, the surgeon and assistant cannot touch the unsterile laser safety eyewear to remove or put them on, nor to adjust them when necessary. Because of this annoyance, some surgeons abrogate the safety rules and refuse to wear the safety eyewear. There is no laser safety feature available in the prior art to alleviate the need for laser safety eyewear.
SUMMARY OF THE PRESENT INVENTION
The present invention generally comprises a method and apparatus for adding a temperature control function to existing surgical lasers. A salient feature of the invention is the provision of an external temperature control device coupled between the output of the laser and the optical fiber delivery system to monitor the temperature of the optical fiber delivery system and attenuate the laser output power to achieve a desired temperature level. The temperature control device may be used to prevent heating of the optical fiber beyond its structural tolerance or a preset limit. Thus the problems known in the prior art associated with contamination of the optical fiber output end, and the resulting thermal runaway, are obviated, and the use of expensive laser surgical cutting tips is eliminated. The optical fiber output end may also be maintained at a predetermined temperature level which is optimized for a particular surgical or medical procedure. Moreover, most existing surgical lasers can be retrofitted with the invention to realize the enhanced surgical cutting effects that are provided by a temperature control system.
The temperature control device may comprise housing having an input connector to receive the laser beam output, and an output connector to secure an optical fiber delivery system. A beam path is established be