Surgery – Instruments – Light application
Reexamination Certificate
2000-04-11
2002-02-26
Gibson, Roy (Department: 3739)
Surgery
Instruments
Light application
C606S009000
Reexamination Certificate
active
06350261
ABSTRACT:
BACKGROUND OF THE INVENTION
Lasers are useful in medical, materials processing, and other applications to cause ablation, i.e., substance removal, within a substrate, e.g., a biological tissue. In many cases, lasers cause such ablation by rapidly and locally heating a target substance until the target substance vaporizes.
Selective laser ablation can be accomplished by using laser wavelengths that are strongly absorbed by the target tissue and only weakly absorbed by other tissue. Thus, the target tissue absorbs an amount of laser energy above a threshold for laser ablation and is removed, whereas the other tissue absorbs an amount of laser energy below the threshold and remains. However, few medical lasers and delivery systems currently available operate at wavelengths that are absorbed substantially more by some types of tissue and not by other types of tissue.
SUMMARY OF THE INVENTION
The invention features a system for selectively delivering or coupling laser radiation into a first material or substrate, e.g., a first biological tissue, having a first index of refraction and not into a second material or substrate, e.g., a second biological tissue, having a second index of refraction. The system determines whether a target area corresponds to the first material or the second material by monitoring the reflection of a probe beam incident on the target area through an optical coupler at a non-normal incident angle. For example, the incident angle can be less than the critical angle for total internal reflection for an interface between the optical coupler and the first material, and greater than the critical angle for total internal reflection for an interface between the optical coupler and the second material, in which case transmission of the probe beam is much greater when the optical coupler contacts the first material than when the optical coupler contacts the second material, and similarly, reflection of the probe beam is much greater when the optical coupler contacts the second material than when the optical coupler contacts the first material, with respect to reflection. The monitored reflection of the probe beam is the control signal for a feedback controller that causes a treatment beam to be delivered to the target area based on the monitored reflection. Thus, the control system selectively delivers the treatment beam to the target area when the optical coupler for the probe beam contacts the first material, but not the second material, or vice versa.
The treatment beam is at a wavelength and has sufficient energy to cause photophysical or photochemical change at the target area. For example, the treatment beam can be used to selectively remove fat-containing tissue from a target area. Fat-removal can be important in procedures such as laser liposuction, laser angioplasty, and dissection of fat. The laser energy delivered to the selected tissue by the treatment beam can rapidly heat the selected tissue until it vaporizes, thereby removing, ablating, or killing the selected tissue. Alternatively, the laser radiation delivered to the selected tissue can rapidly heat the selected tissue until it melts. Thereafter, the melted tissue is removed using suction or other methods.
Furthermore, rather than having an active feedback control system in which reflection of a probe beam incident on the target area at a non-normal angle controls the delivery of a treatment beam to the target area, the treatment beam itself can be delivered to the target area (though an optical coupler) at a non-normal incident angle. The incident angle is selected such that the treatment beam substantially reflects from the target area if the tissue therein is a first type of material (e.g., muscle-containing tissue) having a first refractive index and substantially couples into the target area if the tissue therein is a second type of material (e.g., fat-containing tissue) having a second refractive index greater than the first refractive index. In such examples, the treatment beam functions as both a probe beam selectively coupling into one type of material and not another, and a treatment beam causing photophysical or photochemical change when coupling into a material. Thus, the invention features both active and passive control systems for selectively delivering or coupling laser radiation into a first material or substrate and not a second material or substrate.
In general, in one aspect, the invention features a method for selectively delivering a treatment beam to portions of a substrate having a first index of refraction and not to other portions of the substrate having a second index of refraction less than the first index. The method includes: providing an optical coupler having an index of refraction greater than the second index of refraction; contacting the substrate with the optical coupler to deliver a probe beam from the optical coupler to the substrate at an incident angle; and selectively delivering the treatment beam to the region based on the reflectance of the probe beam from the substrate or the transmission of the probe beam through the substrate.
The method can include any of the following features.
The incident angle can be less than the critical angle for an interface between the optical coupler and a material having the first index of refraction and greater than the critical angle for an interface between the optical coupler and a material having the second index of refraction. The incident angle can be greater than about 10°, 20°, 30°, or 40°. The incident angle can be selected such that when the probe beam is incident on the substrate at the incident angle, the reflectance of the probe beam from an interface between the optical coupler and the portions of the substrate having the first index is at least twice, or at least four times, the reflectance of the probe beam from an interface between the optical coupler and the portions of the substrate having the second index. The optical coupler can have an index of refraction greater than the first index of refraction.
The treatment beam can have a wavelength different than that of the probe beam. The treatment beam can have a power greater than that of the probe beam. The substrate can absorb more strongly at the wavelength of the treatment beam than at the wavelength of the probe beam. The treatment beam can be delivered to the substrate through the optical coupler. The treatment beam can be selectively delivered to the region based on the reflectance of the probe beam from the substrate. For example, the treatment beam can be delivered to the region when the reflectance is less than about 0.95, less than about 0.9, less than about 0.8, or less than about 0.7.
The substrate can be biological tissue. For example, the portions of the substrate having the first index can include fat, e.g., they can consist essentially of fat. Alternatively, or in addition, portions of the substrate having the second index can include one or more of muscle, blood vessels, and skin, e.g., they can consist essentially of one of muscle, blood vessels, and skin. The power of the treatment beam can be sufficient to melt or ablate the portions of the substrate having the first index, and it can be delivered to the substrate at normal incidence. Each of the probe and treatment beams can be derived from a Nd:YAG laser, CTE:YAG laser, ErCr:YSGG laser, holmium laser, erbium laser, CO
2
laser, diode laser, or dye laser. The probe beam can also be derived from a light emitting diode. The optical coupler can be made from one of sapphire, fused silica, BK-7 glass, fint glass, germanium, and zinc selenide.
In another aspect, the invention features a system for selectively delivering a treatment beam to portions of a substrate having a first index of refraction and not to other portions of the substrate having a second index of refraction less than the first index. The system includes: an optical coupler having a surface configured to contact the substrate and a refractive index greater than the second index; a probe beam source configured to direct a pro
Anderson R. Rox
Domankevitz Yacov
Fish & Richardson P.C.
The General Hospital Corporation
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