Abstract:
A method is disclosed for substantially cutting and cauterizing tissue during a surgical procedure. The method involves using a first laser beam to irradiate a first area. The first laser beam is configured in intensity and duration to cut the tissue within the first area, and further causes a temporary increase in an absorptivity of tissue in a second area in proximity to the first area. A second laser beam is used to irradiate the second area while the temporary increase in absorptivity is occurring. The second laser beam has a different intensity than the first laser beam and cauterizes tissue within the second area substantially simultaneously with the cutting of the tissue in the first area.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/798,154, filed on Mar. 15, 2013. The entire disclosure of the above application is incorporated herein by reference. 
     
    
     STATEMENT OF GOVERNMENT RIGHTS 
       [0002]    The United States Government has rights in this invention pursuant to Contract No. DE-AC52-07NA27344, between the U.S. Department of Energy and Lawrence Livermore National Security, LLC, for the operation of Lawrence Livermore National Laboratory. 
     
    
     FIELD 
       [0003]    The present disclosure relates to laser systems, and more particularly to a laser system that enables virtually simultaneous cutting and cauterization of tissue. 
       BACKGROUND 
       [0004]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0005]    Laser surgery is a well-established technique that enables cutting of soft or hard tissue. Usage of lasers has become ubiquitous in wide ranging surgical and microsurgical applications. Laser surgery involves using a laser pulse (or pulses) to cut soft or hard tissue. In simple terms, the pulse laser beam deposits locally, to a well-defined area of tissue, sufficient energy to vaporize small sections of tissue with each pulse. Currently laser surgery is commonly used on the eye to correct near and far-sightedness in vision, and permanently reshapes the cornea. Lasers are also used for the treatment/reduction of enlarged prostates. The use of lasers in dentistry is also expanding. 
         [0006]    The potential of laser surgery to expand into various other medical applications is tremendous but there are a number of limitations that need to be resolved. Some of these limitations are technical, while still others relate to the cost and training of using a laser for a medical or dental application. However, a significant limitation of present day laser systems used in medical applications is the inability of the laser to simultaneously cut and cauterize tissue. Cauterization is associated with the “burning” (raising temperature of tissue above a certain threshold) of part of a tissue structure in an attempt to mitigate damage to surrounding tissues, to remove an undesired growth or tumor, or to minimize other potential medical harmful possibilities such as infections or bleeding. 
         [0007]    When performing surgical procedures, cauterization of tissue during surgery is associated with depositing heat to the tissue to stop bleeding or for other therapeutic purposes. The main forms of cauterization used today are electrocautery and chemical cautery. Cauterization requires an increase of the tissue temperature to induce permanent alterations with clinically desirable properties. Cauterization must also be “localized,” meaning it must be applied to a small region of tissue around the tissue being cut. Cauterization is typically performed by placing a heated metal object in contact with the tissue to be cauterized to deposit energy into a localized region of tissue via heat conduction. Using a laser to achieve such a process would require a very short penetration depth and relatively low energy deposition rate from the laser to the tissue over relatively long periods of time. However, cutting tissue with a laser is typically associated with depositing a pulse of laser energy to a location which is sufficiently high to cause what may be termed a “micro-explosion.” The micro-explosion tears apart, over small spatial scales, a highly localized region of the tissue where the laser energy is being deposited. But the laser-induced micro-explosion, while serving to cut tissue, is not able to deposit sufficient energy to achieve cauterization of the tissue in surrounding areas of tissue which are in close proximity to the tissue being cut. 
         [0008]    The cauterization process, from a technical standpoint, is the complete opposite of the laser cutting process. In the latter case the tissue is quickly brought above the boiling temperature so that there is an explosive reaction (i.e., evaporation, fragmentation and tearing) of the tissue. This can be done over small-localized regions by focusing the laser beam as needed. For example, if using a pulsed laser, the energy coupling from the laser into the tissue leads to a cascade increase of the localized tissue absorptivity, which leads to formation of plasma and localized temperatures on the order of 1 eV or higher, depending on the laser pulse length. This energy leads to the launching of a shockwave (i.e., pressure wave) and heating of the surrounding tissue via heat diffusion. However this heating, although extremely high at the cutting (laser focal) point, is very quickly diminished via heat diffusion. Thus it is not able to cause cauterization over a sufficiently deep surrounding tissue layer. 
         [0009]    The above discussion highlights two issues. First, that laser cutting and laser cauterization are completely different processes and that they are applied over different time scales and require completely different laser energy deposition mechanisms. In simple terms, the cutting of tissue requires a short laser pulse of high peak intensity while the cauterization of tissue requires a long laser pulse of low peak intensity. The technology of the laser tissue “cutting” is well developed. The technology of laser heating of a tissue is also in the research/developmental stage of research and development and is often found under the “laser welding” developmental effort. The later process is slow as it requires temperature controlled heating of large areas. Increase of the laser energy to increase the speed leads to adverse effects as the laser energy expands and heats larger than desired areas to higher temperatures. An effective cauterization process needs to be able to provide highly localized, “slow” heating at the area of tissue exposed to the laser cutting micro-explosion. 
         [0010]    Accordingly, with presently available technology, typically a separate instrument is required to perform the cauterization of tissue. As one can appreciate, this complicates the performance of any medical procedure, and especially a surgical procedure. 
       SUMMARY 
       [0011]    In one aspect the present disclosure relates to a method for substantially cutting and cauterizing tissue during a surgical procedure. The method may comprise using a first laser beam to irradiate a first area, the first laser beam being configured in intensity and duration to cut the tissue within the first area, the first laser beam further causing a temporary increase in an absorptivity of tissue in a second area which is in proximity to the first area. A second laser beam is used to irradiate the second area while the temporary increase in absorptivity is occurring. The second laser beam has a different intensity than the first laser beam to cauterize tissue within the second area substantially simultaneously with the cutting of the tissue in the first area. 
         [0012]    In another aspect the present disclosure relates to a method for substantially cutting and cauterizing tissue during a surgical procedure. The method may comprise using a first laser beam having a first series of laser pulses to irradiate a first area. The first laser pulses may be configured in intensity and duration to cut the tissue within the first area. The first laser beam may further cause a temporary increase in an absorptivity of tissue in a second area which is in proximity to the first area. A second laser beam may be used which comprises a second series of laser pulses to irradiate the second area while the temporary increase in absorptivity is occurring. The second series of laser pulses is made up of pulses that each have a lower intensity than the pulses of the first series laser pulses, and each may be longer in duration than those of the first series of laser pulses. The second series of laser pulses cauterizes tissue within the second area substantially simultaneously with the cutting of the tissue in the first area. 
         [0013]    In still another aspect the present disclosure relates to a system for substantially cutting and cauterizing tissue during a surgical procedure. The system may comprise at least one laser configured to generate a first laser beam and a second laser beam. The first laser beam may be configured in intensity and duration to cut tissue within a first area. The first laser beam further causes a temporary increase in an absorptivity of tissue in a second area which is in proximity to the first area. The second laser beam may be configured in intensity and duration to irradiate the second area while the temporary increase in absorptivity is occurring, the second laser beam having laser pulses which are of a different intensity and a different duration than laser pulses forming the first laser beam, to cauterize tissue within the second area substantially simultaneously with the cutting of the tissue in the first area. 
         [0014]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0016]      FIG. 1  is a high level block diagram of a system laser system for both cutting and cauterizing tissue which makes use of two computer controller lasers, or optionally one computer controller laser; 
           [0017]      FIG. 2  is a high level block diagram of a system for both cutting and cauterizing tissue which makes use of a single lasing system to generate two distinct types of laser pulses that are used for simultaneous, or virtual simultaneous, cutting and cauterizing of tissue; 
           [0018]      FIG. 3  is a high level flowchart setting forth various operations that may be performed using either of the systems of  FIG. 1  or  2  to perform both laser cutting and laser cauterizing of tissue; and 
           [0019]      FIG. 4  is a graph illustrating one laser pulse shape that may be emitted by a single lasing device or the sum of the emitted light by separate laser devises to produce the two distinct intensity/duration profiles needed for both cutting and cauterizing. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The various embodiments and methodologies of the present disclosure teach rapid cutting and localized cauterization of the tissue immediately after cutting. The system and method takes advantage of distinct processes associated with the material (i.e., tissue) response to the localized heating that can be utilized and integrated into a single instrument that offers the aforementioned capability. 
         [0021]    The process of tissue cutting with a laser utilizes a single laser pulse or a train of laser pulses to deliver energy at localized regions, thus increasing the localized temperature on the order of 1 eV (10000 K) or higher, depending on the laser pulse characteristics. The energy deposition is followed by a micro explosion, material evaporation and/or ejection and localized heating of the surrounding region. A key to this invention is the recently improved understanding of transient material changes after exposure to laser-induced high temperatures and pressures. More particularly, it has been discovered that materials (including tissues) experience transient changes relative to their optical properties. More specifically, the affected tissue exhibits increased absorption over periods of time that can extend to 10 to 100 microseconds or longer. This relatively short time of increased absorptivity is localized in the tissue volume around the site of micro-explosion, thus in the region that must be cauterized after laser cutting. For ease of explanation, this modified, localized region of the tissue that exhibits the increased absorptivity due to its exposure, via secondary mechanisms (not from direct exposure), to the laser cutting pulse energy may be termed the “surrounding modified tissue.” The recognition of this transient modification of the absorptive property of the surrounding modified tissue is highly important to the present disclosure. This is because the recognition of particular absorptive property of the surrounding modified tissue, during the relatively small time “window” that laser cutting of the tissue is occurring, enables cauterization of the surrounding modified tissue if a secondary delivery of laser energy is applied to the surrounding modified tissue using a lower intensity laser beam. Accordingly, cauterization of the surrounding modified tissue may be effected simultaneously, or virtually simultaneously, by using a laser beam of a second (i.e., lower) intensity pulse immediately following culling of the tissue using a first (i.e., higher intensity) laser pulse. 
         [0022]    Referring to  FIG. 1  a system  10  is illustrated for performing both laser cutting and cauterization simultaneously or virtually simultaneously. The system  10  may include a lasing system  12  that is controlled by a suitable computer  14  or other type of suitable electronics. The lasing system  12  in this embodiment makes use of two lasers  12   a  and  12   b . Laser  12   a  is used to generate a first laser beam comprising laser pulses  16  having a first intensity and a first duration. Laser  12   b  is used to generate a second laser beam having laser pulses  18  with a second intensity and a second duration. The laser pulses  16  may be in the duration of typically less than 1 microsecond but more optimally on the order of 10 picoseconds to 10 nanoseconds. The laser pulses  18  may be for durations of between about 10-100 microseconds or longer, but otherwise generally in accordance with the duration of the enhanced absorptivity of the surrounding modified tissue. The two pulses  16  and  18  can have the same operational wavelength or they may have different operational wavelengths. In either event the two pulses  16  and  18  will be focused on the same approximate region of tissue. While only a single one of each of the pulses  16  and  18  is shown in  FIG. 1 , it will be appreciated that in practice a series of pulses  16  followed by a series of pulses  18  may be applied by the lasers  12   a  and  12   b . The pulses  16  and  18  may be applied alternately or they may overlap at times. 
         [0023]    It is also important to note that the enhanced absorptivity of the surrounding modified tissue is well above the level of a “background” absorptivity of the “unmodified” tissue. The unmodified tissue will be understood as that tissue which is not being irradiated or otherwise affected/influenced by the first laser pulses  16 . 
         [0024]    The energy density deposited by the laser pulse  16  in the tissue depends on a multiplicity of parameters but in general it is proportional to the laser intensity and material density. The energy deposited by the laser pulse  18  of the second laser beam is proportional to the laser intensity and the transient tissue absorptivity. However, the intensity of the laser pulse  18  is kept well below the intensity level that could significantly increase the temperature of the surrounding unaffected normal tissue but, due to the increased absorptivity of the surrounding modified tissue, the intensity will still be sufficient to deposit a much higher energy density into the surrounding modified tissue. The laser pulse  18  of the second laser beam may be generated (initiated) before or during each pulse  16  of the first laser beam. The pulse  18  may also be generated (initiated) after the first pulse  16  occurs, but the pulse  18  still needs to be generated within the relatively narrow time window when the enhanced absorption of the surrounding modified tissue is occurring. 
         [0025]      FIG. 2  shows a system  100  in accordance with another embodiment of the present disclosure in which a lasing system  102  is controlled by a suitable computer  104 . The lasing system  102 , however, may generate a laser beam having pulses  106  that each have a shape that accomplishes both the required high intensity, short duration heating for a cutting action on tissue, as well as the lower intensity, longer duration heating required for cauterization. A single one of the pulses  106  is shown in greater detail in  FIG. 4 . In  FIG. 4  pulse  106  has a first portion  106   a  which forms a spike having a high intensity and short duration, and a second portion  106   b  that forms a “tail.” The second portion (i.e., tail)  106   b  is of significantly lower intensity and longer duration than the first portion. The pulse  106  may be applied repeatedly at a desired frequency as needed to accomplish both cutting and cauterization of tissue. As with the system  10 , the pulses  106  need to be applied within the narrow time window when the enhanced absorptivity is occurring in the surrounding modified tissue. This time window may be represented as the period  106   c  of the pulse  106 . The pulse  106  may also represent the sum of laser energy emitted by pulses  16  and  18  of the two lasers  12   a  and  12   b  of  FIG. 1 . 
         [0026]    It will be appreciated that a method performed using either of the systems  10  or  100  will deliver increased laser energy on the tissue region that requires cauterization (i.e., the area/region in close proximity to the area being cut) while it will minimally affect other tissue areas. This provides a number of important benefits. For one, it enables energy to be deposited in the target tissue region that requires cauterization while the background tissue is not exposed to any potentially harmful level of laser radiation. It also enables the rate of energy deposition to be controlled by the laser intensity, which in turn allows one to control the cauterization process. Still further, the energy deposition by the second laser beam will delay the relaxation of the enhanced, transient absorption that is occurring in the surrounding modified tissue, which in turn can be used to achieve the desired level of cauterization. 
         [0027]    Referring to  FIG. 3  a flowchart is presented showing a method  200  which may be used to perform simultaneous, or virtually simultaneous, cutting and cauterization of tissue. At operation  202  a first laser beam is generated having a pulse of a first intensity and a first duration, and then applied to an area of tissue to be cut. At operation  204  either prior to, concurrently with, or subsequent to application of the pulse using the first laser beam, a pulse from a second laser beam is applied to the modified surrounding tissue region during the enhanced absorptivity time window of the modified surrounding tissue region to thus cauterize the modified surrounding tissue region. The pulse from the second laser beam is lower in intensity than the pulse from the first laser beam but longer in duration than the pulse from the first laser beam. At operation  206  pulses using both the first and second laser beams are controllably applied as needed to continue the simultaneous cutting of tissue and the cauterization of the surrounding modified tissue region. As explained above, if a single laser is used, the pulse type  106  shown in  FIG. 4  may be used in which case both the cutting and the cauterizing may be accomplished with a single laser. It can be appreciated that the time durations of the first and second pulses are relatively short compared to laser beam stability from the handling of the operator. Thus, the pointing stability on the target region of the second laser pulse is almost ideal in all possible practical cases. 
         [0028]    It will be appreciated that control over the intensity of the second laser pulses  18  or  106  needs to be closely maintained to be able to effectively achieve the desired cauterization. This intensity may need to be varied for different tissue types. The intensity of the second pulse may also be temporally modulated with parts of the pulse requiring higher intensities than other parts of the pulse during the duration of the pulse. In other words the pulse shape maybe more complex than the hat-top intensity profile shown in the  FIG. 4 . 
         [0029]    Still further, it will be appreciated that the first and second laser beams described herein may be delivered using a fiber optic system. The above can be combined with other diagnostic instrumentation such as with spectroscopic characterization and/or imaging. Also, while the tissue has been described herein as human tissue, the systems and methods described herein are expected to have the same utility when applied to tissue from animals. 
         [0030]    While various embodiments have been described, those skilled in the art will recognize modifications or variations which might be made without departing from the present disclosure. The examples illustrate the various embodiments and are not intended to limit the present disclosure. Therefore, the description and claims should be interpreted liberally with only such limitation as is necessary in view of the pertinent prior art.