Patent Publication Number: US-2021169574-A1

Title: Medical devices and methods incorporating frustrated total internal reflection for energy-efficient sealing and cutting of tissue using light energy

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of and priority to U.S. Provisional Application Ser. No. 61/697,677, filed on Sep. 6, 2012, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Technical Field 
     The present disclosure relates to medical devices having components to treat tissue with light energy. More particularly, the present disclosure relates to open or endoscopic surgical forceps that incorporate optics to create conditions of frustrated total internal reflection to facilitate energy-efficient sealing and cutting of tissue using light energy. 
     Description of Related Art 
     In many surgical procedures, body vessels, e.g., blood vessels, ducts, adhesions, fallopian tubes, or the like are sealed to defunctionalize or close the vessels. Traditionally, staples, clips or sutures have been used to close a body vessel. However, these traditional procedures often leave foreign body material inside a patient. In an effort to reduce foreign body material left within the patient and to more effectively seal the body vessel, energy techniques that seal by heating tissue have been employed. 
     Endoscopic or open forceps are particularly useful for sealing since forceps utilize mechanical action to constrict, grasp, dissect and/or clamp tissue. Current vessel sealing procedures utilize radio frequency treatment to heat and desiccate tissue causing closure and sealing of vessels or tissue. 
     SUMMARY 
     As used herein, the term “distal” refers to that portion that is further from an operator while the term “proximal” refers to that portion that is closer to an operator. As used herein, the term “treat” refers to performing a surgical treatment to tissue including, but not limited to heating, sealing, cutting, sensing, and/or monitoring. 
     As used herein, the term “light source” broadly refers to all types of devices or elements that generate or transmit light for medical use (e.g., tissue treatment). These devices include lasers, light emitting diodes (LEDs), lamps, and other devices that generate light having a wavelength that is within the light spectrum (e.g., from infrared light to ultraviolet light). Also, the light sources described herein may be used interchangeably. For example, an LED light source may be used interchangeably with a laser light source. 
     Light sources may produce laser light having a wavelength from about 200 nm to about 15,000 nm and include but are not limited to ruby lasers, tunable titanium-sapphire lasers, copper vapor lasers, carbon dioxide lasers, alexandrite lasers, argon lasers such as argon fluoride (ArF) excimer lasers, argon-dye lasers, potassium titanyl phosphate (KTP) lasers, krypton lasers such as krypton fluoride (KrF) excimer lasers, neodymium:yttrium-aluminum-garnet (Nd:YAG) lasers, holmium:yttrium-aluminum-garnet (Ho:YAG) lasers, erbium:yttrium-aluminum-garnet (Er:YAG) lasers, diode lasers, fiber lasers, xenon chloride (XeCl) excimer lasers, tubanle thalium lasers, and any combinations of these lasers. Additional types of light sources include fiber optic light sources and deuterium light sources. 
     In some embodiments, a light source may generate light of multiple wavelengths. For example, Nd:YAG and KTP laser light may be generated by a single laser source. Nd:YAG laser light, which has a large optical depth or thickness, may be used for sealing and KTP laser light, which has a small optical depth or thickness, may be used for cutting or for sealing small vessels or thin tissue. 
     As described in more detail below with reference to the accompanying figures, the present disclosure relates to open or endoscopic surgical forceps that incorporate optics to create conditions of frustrated total internal reflection to facilitate energy-efficient sealing and cutting of tissue using light energy. In some embodiments, one or both jaw member of the surgical forceps is optically designed so that light of a therapeutic wavelength, e.g., infrared laser light having a wavelength between 800 nm and 1550 nm, is totally internally reflected from the boundary between a tissue-contacting surface of one or both jaw members and air, when tissue is not grasped by the surgical forceps. This creates an evanescent wave on the tissue-contacting surface of one or both jaw members. 
     When tissue is grasped by the surgical forceps, the tissue-contacting surface of one or both jaw members comes into contact with the tissue and the evanescent wave allows light energy to be transmitted to the tissue only through those portions of the tissue-contacting surface that are in contact with the tissue. The light energy is absorbed by the tissue resulting in heat that is used to fuse tissue (e.g., sealing) and/or separate tissue (e.g., cutting). As a result, light energy is efficiently delivered to the tissue because there is a decreased amount of wasted or lost light energy. 
     In some embodiments, the surgical devices sense and/or monitor the tissue during a surgical procedure to determine when a seal cycle is complete, to determine the efficacy of a tissue seal and/or to measure jaw pressure. In some embodiments, tissue separation may be accomplished with the same light energy device used for tissue sealing, thereby eliminating the need for a separate mechanical blade that is traditionally used for tissue separation in jaw members. 
     In aspects, the present disclosure features a medical instrument. The medical instrument includes a first jaw member including a tissue-contacting surface and a second jaw member movably coupled to the first jaw member. The first jaw member and the second jaw member cooperate to grasp tissue between the first jaw member and the second jaw member. The medical instrument also includes a light source that provides a light beam for sealing tissue. The light source is movably coupled to the first jaw member to adjust the incident angle with respect to the tissue-contacting surface of the first jaw member so that the light beam is internally reflected from the interface between the tissue-contacting surface of the first jaw member and air when tissue is not grasped between the first jaw member and the second jaw member, and at least a portion of the light beam is transmitted through that portion of the tissue-contacting surface of the first jaw member that is in contact with tissue when the tissue is grasped between the first jaw member and the second jaw member. 
     The light source may include an optical fiber, a light-emitting diode, a laser, a diode laser, a fiber laser, or any combination of these light sources. The light source may be configured to rotate and/or translate with respect to the first jaw member. The light source may also be configured to scan the tissue with the light beam. 
     The second jaw member of the medical instrument may include a light-absorbent element that absorbs light that is transmitted through the tissue. Alternatively, the second jaw member may include a reflective material that reflects light that is transmitted through the tissue. 
     The medical instrument may further include an optical element disposed in the first jaw member and having a side that forms at least a portion of the tissue-contacting surface of the first jaw member. 
     The light source may be rotatable to selectively provide a light beam having a variable angle of incidence with respect to an axis normal to the tissue-contacting surface of the optical element. The light source may further be configured to rotate to an appropriate position based on at least one optical property of the tissue to be treated. The at least one optical property of the tissue being treated may include index of refraction, absorption coefficient, scattering coefficient, anisotropy coefficient, or any combination of these optical properties. The light source may be configured to move to an appropriate position based on at least one optical property of the tissue while the tissue is in contact with at least a portion of the tissue-contacting surface of the first jaw member. 
     In other aspects, the present disclosure features a method of treating tissue with an optical energy-based medical instrument including a first jaw member and a second jaw member. The method includes directing a light beam at an incident angle with respect to a tissue-contacting surface of the first jaw member so that the light beam totally reflects from the interface between the tissue-contacting surface of the optical element and air when tissue is not grasped between the first jaw member and the second jaw member, and so that at least a portion of the light beam transmits through the tissue-contacting surface of the first jaw member to tissue when tissue is grasped between the first jaw member and the second jaw member. 
     The method may further include determining at least one optical property of the tissue, determining a desired incident angle with respect to the tissue-contacting surface of the first jaw member based upon the at least one optical property of the tissue, and adjusting the light beam to the desired incident angle with respect to the tissue-contacting surface of the first jaw member. The at least one optical property of the tissue may include index of refraction, absorption coefficient, scattering coefficient, and anisotropy coefficient, or any combination of these optical properties. Also, adjusting the light beam to the desired incident angle may include adjusting the position of a light source that generates the light beam. 
     In yet other aspects, the present disclosure features an optical-based tissue-sealing system. The optical-based tissue-sealing system may include a housing and an end effector assembly operably connected to the housing. The end effector assembly may include a first jaw member including a tissue-contacting surface and a second jaw member movably coupled to the first jaw member. The first jaw member and the second jaw member cooperate to grasp tissue between the first jaw member and the second jaw member. The first jaw member includes a movable light source that provides a light beam for sealing tissue. The movable light source is positioned with respect to the tissue-contacting surface so that the light beam is totally internally reflected from an interface between the tissue-contacting surface and air when tissue is not grasped between the first jaw member and the second jaw member, and at least a portion of the light beam is transmitted through the tissue-contacting surface to the tissue when tissue is grasped between the first jaw member and the second jaw member. 
     The optical-based tissue-sealing system also includes a sensor configured to sense at least one optical property of tissue grasped between the first jaw member and the second jaw member and a controller coupled to the movable light source and the sensor. The controller changes the position of the movable light source based upon the sensed at least one optical property of the tissue. 
     The controller may determine an incident angle at which to illuminate the tissue-contacting surface of the first jaw member with the light beam based upon the sensed at least one optical property of the tissue, and may adjust the position of the movable light source to illuminate the tissue-contacting surface of the first jaw member with the light beam at the determined incident angle. The at least one optical property of the tissue may include index of refraction, absorption coefficient, scattering coefficient, anisotropy coefficient, or any combination of these optical properties. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the subject instrument are described herein with reference to the drawings wherein: 
         FIG. 1A  is a perspective view of an optical-based surgical system including a surgical instrument having an end effector assembly that incorporates optical components for creating conditions of frustrated total internal reflection within one or more jaw members of the end effector assembly according to embodiments of the present disclosure; 
         FIG. 1B  is a perspective view of a cordless, optical-based surgical instrument having an end effector assembly that incorporates optical components for creating conditions of frustrated total internal reflection within one or more jaw members of the end effector assembly according to embodiments of the present disclosure; 
         FIGS. 2A and 2B  are schematic side, cross-sectional views of an end effector assembly according to embodiments of the present disclosure; 
         FIGS. 3A and 3B  are schematic side, cross-sectional views of jaw members according to embodiments of the present disclosure; 
         FIGS. 4A and 4B  are schematic side, cross-sectional views of jaw members incorporating fiber optic components in both jaw members according to embodiments of the present disclosure; 
         FIGS. 5A-5C  are schematic side, cross-sectional views of jaw members, one of which includes an optical element and a movable light source, according to embodiments of the present disclosure; 
         FIGS. 6A-6B  are schematic side, cross-sectional views of jaw members including an optical element that forms a portion of a jaw member according to embodiments of the present disclosure; 
         FIG. 7  is a schematic side, cross-sectional view of jaw members, one of which incorporates a light guide, according to embodiments of the present disclosure; 
         FIG. 8  is a schematic side, cross-sectional view of jaw members, one of which includes a plurality of optical elements according to embodiments of the present disclosure; and 
         FIGS. 9 and 10  are flow diagrams of methods of performing tissue sealing according to embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the presently-disclosed surgical instrument are described in detail with reference to the drawings wherein like reference numerals identify similar or identical elements. 
       FIG. 1A  shows an endoscopic surgery forceps  10  that may be used with any of the embodiments of end effector assemblies described below. In  FIG. 1A , forceps  10  is coupled to a light energy source (e.g., a generator  40 ) for generating light energy adapted to seal tissue. Light energy source (e.g., generator  40 ) is configured to output light energy having a wavelength from about 200 nm to about 11,000 nm. Forceps  10  is coupled to the generator  40  via a cable  34  that includes one or more optical fibers to transmit light energy and one or more electrical conductors to transmit control signals between the forceps  10  and the generator  40 . The generator  40  may produce light energy having one or more wavelengths. In some embodiments, Nd:Yag and KTP laser light may be produced by the same laser source. Various embodiments of the forceps  10  using the light energy are described below. 
     Forceps  10  is configured to support an end effector assembly (e.g., end effector assembly  100 ) at a distal end thereof. Forceps  10  includes various conventional features (e.g., a housing  20 , a handle assembly  22 , a trigger assembly  25 , and a rotating assembly  28 ) that enable forceps  10  and end effector assembly  100  to mutually cooperate to grasp, seal, divide and/or sense tissue. Forceps  10  generally includes housing  20  and handle assembly  22  that includes movable handle  24  and a handle  26  that is integral with housing  20 . The handle  24  is movable relative to the handle  26  to actuate end effector assembly  100  via a drive assembly (not shown) to grasp tissue. 
     In some embodiments, trigger assembly  25  may be configured to actuate a knife blade (not shown) or another component. Forceps  10  also includes shaft  12  having a distal portion  16  that mechanically engages end effector assembly  100  and a proximal portion  14  that mechanically engages housing  20  proximate rotating assembly  28  disposed on housing  20 . Rotating assembly  28  is mechanically associated with shaft  12  such that rotational movement of rotating assembly  28  imparts similar rotational movement to shaft  12  that, in turn, rotates end effector assembly  100 . 
     End effector assembly  100  includes two jaw members  110  and  120 , each having proximal ends  110   a ,  120   a  and distal ends  110   b ,  120   b , respectively (see  FIG. 1A ). One or both jaw members  110  and  120  are pivotable about a pin  19  and one or both are movable from a first position wherein jaw members  110  and  120  are spaced relative to another, to a second position wherein jaw members  110  and  120  are closed and cooperate to grasp tissue between the jaw members  110  and  120 . 
     Each jaw member  110  and  120  includes a tissue contacting surface  211  and  212 , respectively, disposed on an inner-facing surface thereof (see  FIG. 2A ). Tissue-contacting surfaces  211 ,  212  cooperate to grasp and seal tissue held between the tissue-contacting surfaces. Tissue-contacting surfaces  211 ,  212  are connected to generator  40  that can transmit light energy through the tissue held between the tissue-contacting surfaces  211 ,  212 . 
     First and second switch assemblies  30  and  32  are configured to selectively provide light energy to end effector assembly  100 . More particularly, the first switch assembly  30  may be configured to perform a first type of surgical procedure (e.g., seal, cut, and/or sense) and a second switch assembly  32  may be configured to perform a second type of surgical procedure (e.g., seal, cut, and/or sense). It should be noted that the presently-disclosed embodiments may include any number of suitable switch assemblies and are not limited to only switch assemblies  30  and  32 . It should further be noted that the presently-disclosed embodiments may be configured to perform any suitable surgical procedure and are not limited to only sealing, cutting and sensing. 
     The housing  20  further includes one or more light-transmissive elements, such as one or more optical fibers disposed within a cable  34  that connects the forceps  10  to the generator  40 . The cable  34  may include a plurality of optical fibers (not shown) that are configured to transmit light energy through various paths and ultimately to end effector assembly  100  and one or more optical elements that are configured to create conditions of total internal reflection at one or both of the tissue contacting surfaces  211  and  212 . 
     First and second switch assemblies  30  and  32  may also cooperate with a controller  42 , which may be implemented by a logic circuit, a computer, a processor, and/or a field programmable gate array. The controller  42  may automatically trigger one of the switches to change between a first mode (e.g., sealing mode) and a second mode (e.g., cutting mode) upon the detection of one or more parameters, properties, or thresholds. In some embodiments, the controller  42  is also configured to receive various sensor feedback and to control the generator  40  based on the sensor feedback. The embodiments of the present disclosure allow the jaw members  110  and  120  to seal and/or cut tissue using light energy. 
     In some embodiments, the controller  42  may include a feedback loop that indicates when a tissue seal is complete based upon one or more of the following parameters or properties: tissue temperature, change in impedance of the tissue over time, change in optical characteristics of tissue (opaqueness, clarity, etc.), rate of change of these properties, and combinations thereof. An audible or visual feedback monitor may be employed to convey information to the surgeon regarding the overall seal quality or the completion of an effective tissue seal. 
     Referring now to  FIG. 1B , forceps  10  is shown having a portable configuration and includes an internal energy source  50  for generating light energy that is operably coupled to a battery compartment  52  via one or more wires  50   a . In some embodiments, one or more battery-operated laser diodes or fiber lasers may also be used to provide a portable light energy source. Internal energy source  50  may be configured to provide light energy to the end effector assembly  100  and optical elements via one or more laser fibers  50   b  or any other suitable transmission medium. Battery compartment  52  may be configured to receive one or more batteries  54  for providing suitable energy to internal energy source  50 . In embodiments, the controller  42  may also be disposed within the forceps  10  (e.g., housing). 
     Battery compartment  52  may be defined within any suitable portion of housing  20  of forceps  10 , such as the fixed handle  26 , as shown in  FIG. 1B . Suitable batteries may include, but are not limited to a nickel-cadmium, lithium-ion, rechargeable, or any other suitable type. The location of internal energy source  50  provides an operator increased maneuverability and convenience when performing a surgical treatment with forceps  10 . 
       FIG. 2A  illustrates an end effector assembly  200  according to the present disclosure, which is configured for use with instrument  10  of  FIG. 1A , instrument  11  of  FIG. 1B , or any other suitable surgical instrument. The end effector assembly  200  includes jaw members  110  and  120  having proximal ends  110   a ,  120   a  and distal ends  110   b ,  120   b . The first jaw member  110  (e.g., a top jaw member) has a first tissue-contacting surface  211  and the second jaw member  120  (e.g., a bottom jaw member) has a second tissue-contacting surface  212 . The first jaw member  110  and the second jaw member  120  are movable with respect to each other so that tissue can be grasped between the first tissue-contacting surface  211  and the second tissue-contacting surface  212 . 
     According to the various embodiments of the present disclosure, incident light beam  214  is directed at the tissue-contacting surface  211  of the first jaw member  110  from within the first jaw member  110 . The incident light beam  214  is directed at a predetermined angle θ i  with respect to the axis  202  perpendicular to the tissue-contacting surface  211  of the first jaw member  110  so that the incident light beam  214  are totally reflected as reflected light beams  217  at the interface between the tissue-contacting surface  211  and the air  205 , e.g., when the tissue-contacting surface  211  is not in contact with tissue. The tissue-contacting surface  211  may be made of a material, e.g., coated with a material, that enables total reflection of the incident light beam  214  when the tissue-contacting surface  211  is not in contact with tissue. 
     Refraction and reflection at a planar boundary or interface between two media of different refractive indices is described by Snell&#39;s law and Fresnel&#39;s equations, which are related to Maxwell&#39;s wave equations for electromagnetic radiation at a boundary or interface. As shown in  FIG. 2A , for refraction from the tissue-contacting surface  211  of the first jaw member  110  with refractive index n 2 , to air  205  with lower refractive index n 1 , Snell&#39;s law provides the following relationship: 
         n   2  sin θ i   =n   1  sin θ r  
 
     where θ i  is the angle of incidence and Or is the angle of refraction. 
     Total internal reflection occurs at the interface or boundary  230  defined by the first tissue-contacting surface  211  and the air  205  when the angle of incidence θ i  ( 204 ) is greater than or equal to a critical angle θ c  ( 203 ), which is defined by the following equation: 
       θ c =arcsin( n   2/   /n   1 ).
 
     This reflection is “total” because a certain amount of energy is present in the air  205  in a thin layer adjacent to the boundary  230 . As shown in  FIG. 2A , this energy is in the form of evanescent waves  218 . The waves in this layer are called evanescent waves because they decay rapidly to zero. 
     When tissue  213  is not in contact with the tissue-contacting surface  211  of the first jaw member  110 , the reflected light beams  214  are contained within the first jaw member  110  so that they are not transmitted outside of the first jaw member  110 . In some embodiments, the inner or outer surfaces of the first jaw member  110  are coated with a light-reflective or a light-absorbent material to prevent the totally reflected light beam  216  from being transmitted outside of the first jaw member  110 . 
     As shown in  FIG. 2B , when tissue  213  is grasped between the first tissue-contacting surface  211  and the second tissue-contacting surface  212 , the tissue  213  comes into contact with the first tissue-contacting surface  211 , thus forming a new interface  240  between the first tissue-contacting surface  211  and the tissue  213 . Because the index of refraction of tissue  213  (e.g., 1.5) is much greater than the index of refraction of air (e.g., 1.0), the total internal reflection is “frustrated” and the evanescent wave  218  transfers light energy from the light beam  214  to the tissue  213 . 
     In other words, a new critical angle  203  is defined by the following equation: 
       θ c =arcsin( n   2/   /n   3 ),
 
     where n 2  is the index of refraction of the tissue-contacting surface  211  of the first jaw member  110  and n 3  is the index of refraction of the tissue  213 . This new critical angle  203  is greater than the angle of incidence of the light beam  214 . As a result, a transmitted portion  215  of the light beam  214  is transmitted to the tissue  213  and the remaining reflected portion  217  of the light beam  214  is reflected from the new interface between the first tissue-contacting surface  211  and the tissue  213 . 
     Thus, as illustrated in  FIGS. 2A and 2B , the incident light beam  214  passes through that portion of the tissue-contacting surface  211  that is in contact with tissue  213 . Otherwise, the incident light beam  214  is totally internally reflected. As a result, the medical device of  FIGS. 2A and 2B  saves power because light energy is transmitted to the tissue  213  only when it comes into contact with the tissue-contacting surface  211 . 
       FIG. 3A  illustrates an embodiment of a first jaw member  120  that is optically coupled to a light source  301 . The light source  301  may be an optical assembly that includes an LED (not shown) that generates light and a beam-forming optical element (not shown) that forms the light into a beam. Alternatively, the light source  301  is a light guide that carries light from an LED (not shown) to the first jaw member  110 . 
     The light source  301  directs an incident light beam  214  at the tissue contacting surface  211  of the first jaw member  110 . The light source  301  is positioned to direct the incident light beam  214  at a desired incident angle  204  with respect to the axis  202  normal to the tissue-contacting surface  211  of the first jaw member  110 . As described above, the incident angle  204  is selected so that it is greater than the critical angle to facilitate total internal reflection when air  205  is in contact with the tissue-contacting surface  211  of the first jaw member  110 . 
     The reflected light beam  216  is absorbed by a light-absorbent optical element  310  so that the reflected light beam  216  is not transmitted outside of the first jaw member  110 . In other embodiments, the light-absorbent optical element  310  is replaced with a light-reflective optical element, which may reflect the reflected light beam  216  back to the tissue-contacting surface  211  of the first jaw member  110  or to an optical element that carries the reflected light beam  216  away from the first jaw member  110 . The light-absorbent optical element  310  may be formed of a material that dissipates heat generated 
     As illustrated in  FIG. 3B , when the first jaw member  110  and the second jaw member  120  grasp the tissue  213 , at least a portion of the light beam  214 , i.e., the transmitted portion  215 , is transmitted to the tissue  213 . The transmitted portion  215  of the light beam  214  that passes through the tissue  213  is absorbed and/or reflected by optical element  320  disposed in the second jaw member  120 . 
     If the optical element  320  is light-reflective, it may be positioned at an angle with respect to the tissue-contacting surface  212  of the second jaw member  120  so that the transmitted portion  215  of the incident light beam  214  that passes through the tissue  213  is reflected back to the tissue  213 . 
       FIGS. 4A and 4B  illustrate an end effector assembly that incorporates fiber optic components  402   a ,  404   a ,  406   a ,  402   b ,  404   b , and  406   b . As shown, the fiber optic components  404   a ,  406   a  disposed in the first jaw member  110  are the same as the fiber optic components  404   b ,  406   b  disposed in the second jaw member  120 . The first jaw member  110  includes a first lens  406   a  that is optically coupled to a first light source  301   a  via an optical fiber  404   a . In this configuration, the first light source  301   a  is not disposed within the jaw members  110 ,  120 . The first light source  301   a , however, may be disposed elsewhere in the forceps  10 , the forceps  11 , the generator  40 , or the internal energy source  50 . For example, the first light source  301   a  may be disposed within the handle  26 , the housing  20 , or the shaft  12  of the forceps  10 . 
     The first light source  301   a  generates an optical signal that is transmitted to the first lens  406   a  via the optical fiber  404   a . The first lens forms a first light beam  214   a  and directs the first light beam  214   a  towards the first tissue-contacting surface  211  of the first jaw member  110  at a first incident angle  204   a  with respect to an axis  202   a  normal to the first tissue-contacting surface  211 . The first incident angle  204   a  is selected so that the first light beam  214   a  is totally reflected  216   a  from the first tissue-contacting surface  211  when tissue does not contact the first tissue-contacting surface  211 . The first jaw member  110  also includes a light-absorbent optical element  310   a  that absorbs the reflected light beam  216   a . In other embodiments, the light-absorbent optical element  310   a  may be replaced with a light-reflective optical element. 
     Like the first jaw member  110 , the second jaw member  120  includes a second lens  406   b  optically coupled to a second light source  301   b  via an optical fiber  404   a . The second light source  301   b  (which may be a different type of light source than first light source  301   a  or the same) generates an optical signal that is transmitted to the second lens  406   b  via the optical fiber  404   a . The second lens  406   b  forms a second light beam  214   b  and directs the second light beam  214   b  towards the second tissue-contacting surface  211  of the second jaw member  120  at a second incident angle  204   b  with respect to an axis  202   b  normal to the second tissue-contacting surface  212 . The second incident angle  204   b  is selected so that the second light beam  214   b  is totally reflected from the second tissue-contacting surface  212  when tissue does not contact the second tissue-contacting surface  212 . The second jaw member  120  also includes a light-absorbent optical element  310   b  that absorbs the reflected light beam  216   b . In other embodiments, the light-absorbent optical element  310   b  may be replaced with a light-reflective optical element. 
     As shown in  FIG. 4B , when tissue  213  is grasped between the first jaw member  110  and the second jaw member  120 , a portion of the first light beam  214   a  is transmitted as light beam  215   a  to the tissue and a portion of the second light beam  214   b  is transmitted as light beam  215   b  to the tissue  213 . In this manner, light can be applied to both sides of the tissue  213  to seal the tissue  213  more quickly and evenly. The transmitted light beam  215   a  is then absorbed by the light-absorbent optical element  310   b  and the transmitted light beam  215   b  is absorbed by the light-absorbent optical element  310   a.    
     In an alternative embodiment, the light sources  402   a ,  402   b  may be replaced by a single light source that emits a light beam that is split and transmitted via two different fibers to the jaw members  110 ,  120 , respectively. For example, a light source may emit a light beam that is split and transmitted via fibers  404   a  and  404   b  to the jaw members  110 ,  120 , respectively. 
       FIGS. 5A-5C  illustrate another embodiment that incorporates a movable light source  501  and a crystal  503 , e.g., a prism or other crystal structure. As shown in  FIG. 5A , the first jaw member  110  includes the crystal  503  having four surfaces: a first crystal surface  502 , a second crystal surface  504 , a third crystal surface  506 , and a fourth crystal surface  508 . The first crystal surface  502  forms a portion of the tissue-contacting surface  211  of the first jaw member  110 . The movable light source  501  is positioned to direct a light beam  512  at a first incident angle  522  with respect to an axis  302  normal to the first crystal surface  502 . The first incident angle  522  is selected so that the light beam  512  reflects from the first surface  502  as reflected light beam  514  when tissue is not in contact with the first surface  502 . 
     The first jaw member  110 , the light source  501 , and the crystal  503  are configured so that the light beam  512  also reflects off of the second crystal surface  504  as reflected light beam  516 , the third crystal surface  506  as reflected light beam  518 , and the fourth crystal surface  508 . Specifically, the first jaw member  110  may be a hollow structure that is filled with air  210  and the crystal  503  has an index of refraction much greater than the air  210 . As a result, total internal reflection can be achieved within the crystal  503  over a range of angles that are greater than the critical angle. The crystal  503  is also configured so that the incident angle of the light beam  512  with respect to the axis  302  normal to the second crystal surface  504 , the third crystal surface  506 , and the fourth crystal surface  508  is greater than the critical angle. The movable light source  501  is positioned to create an incident angle with respect to the axes (e.g., axis  302 ) normal to the crystal surfaces  502 ,  504 ,  506 ,  508  that is greater than the critical angle. 
     As shown in  FIG. 5A , the tissue-contacting surface  212  of the second jaw member  120  is coated with a light-absorbent optical material  530 . In some embodiments, the light-absorbent optical material  530  is a material that increases in temperature when it is illuminated with light. 
     Referring now to  FIG. 5B , when tissue  213  is grasped between the first jaw member  110  and the second jaw member  120 , conditions of frustrated total internal reflection are created and the light beam  512  is transmitted through the tissue  213  to the light-absorbent optical material  530 . As shown, the angle  524  of the transmitted light beam  515  with respect to the axis  302 , which is perpendicular to the tissue-contacting surface  211  of the first jaw member  110 , is greater than the incident angle  522  according to Snell&#39;s law. As a result, the transmitted light beam  515  passes through a portion of the tissue  213  at an angle  528  with respect to the axis  302 . 
     As shown in  FIG. 5C , the movable light source  501  is rotatable about a pivot point  511  and translatable. As a result, the light beam  515  can be rotated counter-clockwise or clockwise  510 , or translated right or left  513 , to direct the transmitted light beam  515  through different portions of the tissue  213 . In this way, the transmitted light beam  515  can be scanned through multiple portions of the tissue  213 . When the movable light source  501  is rotated about the pivot point  511  of the first jaw member  110 , the incident angle also changes to a second incident angle  526 . This process may allow larger tissue structures to be treated with smaller light sources, may produce varying or different surgical tissue effects (sealing versus cutting), and may provide more reliable and stronger seals. 
     In embodiments, the light source may be translatable to enable scanning of multiple portions of the tissue  213 . The light source may also be rotatable to enable changing of the incident angle with respect to the tissue-contacting surface of the optical element  503 . 
     In alternative embodiments, the movable light source  501  may be replaced by a single fixed light source that transmits light to the jaw members  110 ,  120  via a movable crystal or lens, which moves, e.g., rotates, to scan the light beam  512  over multiple portions of the tissue  213 . 
       FIGS. 6A and 6B  illustrate an embodiment in which a portion of the first jaw member  110  is a crystal structure. As shown in  FIG. 6A , the first jaw member  110  includes a crystal portion  601  and a non-crystal portion  603 . The non-crystal portion  603  contains the light source  301  and a reflective optical element  610 , e.g., a mirror, which reflects light generated by the light source  301  into the crystal portion  601 . The light source  301  is positioned so that the incident angle  304  of the light beam  612  with respect to the axis  302  is greater than the critical angle. Thus, when tissue is not in contact with the first jaw member  110 , the light beam  612  is totally internally reflected from the first crystal surface  602 . 
     The crystal portion  601  is configured so that the light beam  612  is totally internally reflected at the other crystal surfaces  604 ,  606 ,  608 . Thus, the light beam  612  propagates back and forth within the crystal portion  601  until tissue  213  contacts the first crystal surface  602 . 
     As shown in  FIG. 6B , the light beam  612  reflects from the first crystal surface  602  at a first location  621 , a second location  622 , and a third location  623  as the light beam  612  propagates back and forth within the crystal portion  601 . When the first jaw member  110  and second jaw member  120  grasp tissue  213 , the tissue  213  makes contact with the first crystal surface  602  at the first location  621  and the second location  622 . This creates conditions of frustrated total internal reflection at the first location  621  and the second location  622 . As a result, a first portion  615  of the light beam  612  is transmitted through the first location  621  of the first crystal surface  602  to the tissue  213  and a second portion  617  of the light beam  612  is transmitted through the second location  622  to the tissue  213 . In this manner, the light beam  612  can be evenly distributed through the tissue  213 . 
     For purposes of safety, the second crystal surface  604  and the third crystal surface  606  are coated with a reflective material  611  to prevent the light beam  612  from being transmitted to tissue or other objects that accidentally come into contact with the second crystal surface  604  and/or the third crystal surface  606 . In other embodiments, the second crystal surface  604  and/or the third crystal surface  606  may not be coated with the reflective material  611  to allow the user to perform surgical procedures using the second crystal surface  604  and/or the third crystal surface  606 . 
     As shown in  FIGS. 6A and 6B , the second jaw member  120  includes a light-absorbent optical element  620  that absorbs the first portion  615  of the light beam  612  and the second portion  617  of the light beam  612  that pass through the tissue. The light-absorbent optical element  620  is disposed a short distance away from the tissue-contacting surface  212  of the second jaw member  120 . In some embodiments, the second jaw member  120  may be a hollow jaw member having an optically-transparent tissue-contacting surface  212 , which allows the first portion  615  of the light beam  612  and the second portion  617  of the light beam  612  to pass through the tissue-contacting surface  212  to the light-absorbent optical element  620 . 
       FIG. 7  illustrates another embodiment of the first jaw member  110  and the second jaw member  120 . The first jaw member  110  includes a light guide  701  having a first guide surface  702  that forms a portion of the tissue-contacting surface  212  of the first jaw member  110 . The first jaw member  110  also includes multiple light sources  301   a - 301   c . The light sources  301   a - 301   c  generate multiple light beams  712   a - 712   c  that are directed into the light guide  701 . The light sources  301   a - 301   c  direct the multiple light beams  712   a - 712   c  at an appropriate angle with respect to an axis normal to the first guide surface  702  so that the multiple light beams  712   a - 712   c  are totally internally reflected off the first guide surface  702  and a second guide surface  706  when tissue does not contact the first guide surface  702 . 
     The light guide  701  includes a light-absorbent optical element  704  at the distal end of the light guide  701 . The light-absorbent optical element  704  absorbs the multiple light beams  712   a - 712   c  that propagate along the length of the light guide  701 . When the tissue  213  comes into contact with the light guide surface  702 , portions  715   a - 715   c  of the multiple light beams  712   a - 712   c  are transmitted through the tissue  213  to heat and seal the tissue  213 . In this way, light is distributed across the tissue  213 . 
     As shown in  FIG. 7 , the multiple light beams  712   a - 712   c  reflect off of different portions of the first light guide surface  702  as the multiple light beams  712   a - 712   c  propagate along the length of the light guide  701 . When the tissue  213  comes into contact with the first light guide surface  702 , portions of the multiple light beams  712   a - 712   c  are transmitted only through those portions of the first light guide surface  702  that are in contact with the tissue  213 . In some embodiments, the multiple light sources  301   a - 301   c  may be configured to generate multiple light beams  712   a - 712   c , respectively, having different wavelengths selected to produce a desired tissue affect. 
     Similar to the second jaw member  120  of  FIGS. 2A and 2B , the second jaw member  120  is made of a light-absorbent optical element  220  that absorbs the portions  715   a - 715   c  of the multiple light beams  712   a - 712   c  that are transmitted through the tissue  213 . In other embodiments, the light-absorbent optical element  220  is replaced with a light-reflective optical element, which may reflect the portions  715   a - 715   c  of the multiple light beams  712   a - 712   c  back into the light guide  701 . 
     In alternative embodiments, the multiple light sources  301   a - 301   c  may be replaced by a movable light source. For example, the light source may translate along the length of the light guide  701  to scan multiple portions of the tissue  213  (similar to the movable light source  501  in  FIG. 5C ). 
       FIG. 8  illustrates another embodiment of the first jaw member  110  that incorporates multiple crystals  802 ,  804 . The multiple crystals  802 ,  804  are distributed along a longitudinal axis of the first jaw member  110  and each crystal  802 ,  804  includes a first crystal surface that forms a portion of the tissue-contacting surface  211 . In other embodiments, the multiple crystals  802 ,  804  are also distributed in rows along a transverse axis of the first jaw member  110 . 
     The first jaw member  110  also includes multiple light sources  806 ,  808  that generate light beams  812 ,  814  and direct them into respective crystals  802 . In this embodiment, the light sources  806  direct the light beams  812  at a first angle into the crystals  802  so that the light beams  812  are totally internally reflected and circulate within the crystals  802  in a counter-clockwise direction when tissue is not in contact with the tissue-contacting surfaces of the crystals  802 . Similarly, the light sources  808  direct the light beams  814  at a second different angle into the crystals  804  so that the light beams  814  are totally internally reflected and circulate within the crystals  804  in a clockwise direction when tissue is not in contact with the tissue-contacting surfaces of the crystals  804 . 
     As shown in  FIG. 8 , the light beams  812 ,  814  are transmitted into the tissue  213  from only those crystals  802 ,  804  whose first tissue-contacting surfaces come into contact with the tissue  213 . And because the light beam  812  is circulating in a different direction from the light beam  814 , the transmitted light beams  816 ,  818  pass through the tissue  213  in different directions. 
     The optical elements described above may be formed of any material that facilitates total internal reflection. In various embodiments, the optical elements may be formed of sapphire crystal, ruby, YAG, alexandrite, flint, BK7 glass, crystal glass, or fused silica. 
       FIG. 9  is a flow diagram of a method of performing a tissue-sealing procedure with light. After the procedure starts (step  901 ), tissue is grasped between a first jaw member and a second jaw member of a medical instrument (step  902 ). Next, a tissue-contacting surface of an optical element of the first jaw member is illuminated with a light beam (step  904 ). Then, the light beam is reflected from the tissue-contacting surface when tissue does not contact the tissue-contacting surface of the optical element (step  906 ). Before the method ends (step  909 ), at least a portion of the light beam is transmitted through the tissue-contacting surface of the optical element when tissue contacts the tissue-contacting surface of the optical element (step  908 ). 
       FIG. 10  is a flow diagram of a method of performing a tissue-sealing procedure with light. After starting (step  1001 ), at least one property of the tissue to be grasped between the first jaw member and the second jaw member is determined (step  1002 ). Next, an incident angle at which to illuminate the tissue-contacting surface of the optical element of the first jaw member with the light beam is determined based upon the at least one property of the tissue (step  1004 ). Before the method ends (step  1007 ), a light source is adjusted to illuminate the tissue-contacting surface of the optical element of the first jaw member with the light beam at the incident angle (step  1006 ). 
     While several embodiments of the disclosure have been shown in the drawings and/or discussed herein, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.