Abstract:
Apparatuses and methods for the haptic sensation of forces at a remote location. Groups of MEMS-based pressure sensors are combined into sensor arrays. In some embodiments, the pressure sensors are encased in silicone or other elastomeric substance to allow for routine use in the aqueous environment of the body. The sensor arrays may be housed in a No-compatible material (e.g., stainless steel, plastic) and may be attached to a printed circuit board to allow the electrical signal generated by the sensors to be communicated to a user. The sensor arrays may be used with faceplates that directly interact with the target tissue or object. The faceplates may be rough, smooth, serrated, or any other texture. The present apparatuses and methods are particularly well suited for robotic surgery and may be used in wherever haptic sensing of forces at a remote location is desired.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §119(e) of the earlier filing date of U.S. Provisional Application Ser. No. 61/531,266 filed on Sep. 6, 2011. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the field of surgery and specifically to methods and systems for robotic and laparoscopic surgery providing improved tactile sensation to the surgeon. 
     2. Description of the Background 
     Surgical robots with complex maneuvering capabilities are able to perform surgery by entering the body through tiny incisions. This less invasive approach results in decreased blood loss, significantly reduced recovery time, and lower overall healthcare costs when compared with traditional open surgery. For these reasons, robotic surgical systems are becoming a valuable asset to most major surgical centers. However, the use of surgical robots is currently limited to a small number of simple procedures because of one constraint: the design of current surgical robotic tools fails to provide the surgeon with an adequate sense of the forces being exerted on the tissue by the surgical instruments. This sensory input, termed tactile perception, is vitally important to medical professionals during surgical manipulation of tissue. 
     In traditional surgery, surgeons use the tactile perception of their fingertips to ascertain how hard to pull and grasp tissue without causing unwanted damage. Surgeons also use their tactile perception to assess the stiffness, density, or texture of different tissues to determine what type of tissue it is. In minimally invasive robotic surgery, this tactile perception is lost and surgeons are left “blind” as to touch. This lack of haptic sensation poses the risk of unnecessary tissue damage and loss of valuable tactile information, and in many surgeries this risk outweighs the benefits that accompany robotic surgery. Thus, robotic surgery is excluded from use in many surgical procedures where it would prove extremely useful. 
     Ideally, a surgical tool for use in minimally invasive surgery would satisfy several criteria. Such a tool may include sensors capable of providing accurate and physiologically relevant information to the surgeon at appropriate spatial resolution. Sensors should be able to provide accurate measurements within the large range of pressures experienced at the tip of the graspers which range from very low levels up to pressures of 900 kPa. Further, the tool would possess a tissue-tool interface that allows appropriate grasping and manipulation of tissues and a profile that does not damage surrounding, non-target tissue. 
     Many research groups have attempted the design of surgical instruments that provide improved force and tactile perception to the surgeon; however, these efforts have not generated an appropriate tool for surgical use. One group attached strain gauges on the grasper jaws that bend with the grasper jaws and output a voltage signal corresponding to the amount of force exerted. Dargahi J, Najarian S. “An endoscopic force position grasper and minimum sensors.”  Canadian Journal of Electrical and Computer Engineering , (2004) 28:151-166. The design disclosed therein is able to determine the magnitude and location of a force within the jaws but does not provide force distribution maps that may be beneficial to a user. 
     Rosen et al. disclosed design of a remote control handle coupled to as pair of graspers, Rosen, J., Hannaford, B., MacFarlane, M., and Sinanan, M., “Force controlled and teleoperated endoscopic grasper for minimally invasive surgery—Experimental performance evaluation,”  IEEE Transactions on Biomedical Engineering , (1999) 46:1212-1221. Using optical encoders and actuators, the apparatus relays forces exerted at the instrument&#39;s jaws to the teleoperated unit. This design can potentially provide valuable information about local tissue compliance but utilizes only one bulk measurement that lacks adequate spatial resolution, potentially causing the surgeon to generalize inappropriately to a large tissue region. 
     Other groups have used microelectromechanical systems (MEMS) technology to develop sensor arrays to provide pressure distribution maps. Dargahi J, Najarian S. “Theorhetical and experimental analysis of a piezoelectric tactile sensor for use in endoscopic surgery”  Sensor Review , (2004)24:74-83; Heo J, Chung J, Lee J, “Tactile sensor arrays using fiber Bragg grating sensors”  Sensors and Actuators A: Physical , (2006)126:312-327; Peng P. Sezen A, Rajamani R, Erdman A, “Novel MEMS stiffness sensor for force and elasticity measurements”  Sensors and Actuators A , (2010) 158:10-17. However, these designs have limited utility due to a lack of functional integration into endoscopic tools (i.e., they are unable to adequately manipulate tissue), inadequate resolution due to the size of the force transducers, and/or possess low upper limits of pressure ranges that are inappropriate for surgical application. 
     King et al. reported on an innovative design to be used with the Da Vinci robot which provides a low-resolution force distribution via an array of piezoresistive force sensors, King C. Cuijat M, Franco M, Bisley, J, Carman G, Dutson F, Grundfest W, “A multielement tactile feedback system for robot-assisted minimally invasive surgery”  IEEE Transactions on Haptics , (2009)2:52-56. Information from these sensors is then transmitted to 2×3 tactile display placed on the Da Vinci control unit at the surgeon&#39;s fingertips. The limitations of this design are spatial resolution and certain inaccuracies associated with the use of piezoresistive force sensors. Their system also lacked a functional grasping surface. 
     Thus, there remains a long-standing, unresolved need in the medical community for surgical tools used in minimally invasive surgery that have an effective dynamic range of force measurement and sufficient spatial resolution to selectively and effectively manipulate the target tissue, while at the same time minimizing damage to surrounding non-target tissue. Further, the profile of such surgical tools should be such that it has minimal impact on the tissue through which it passes en route to the target tissue. The present invention addresses these needs. 
     SUMMARY OF THE INVENTION 
     The present invention provides a novel system capable of providing a user with accurate information about the magnitude and spatial distribution of forces at the interface between a surgical tool and a target tissue. The present invention further allows those forces to be sensed by the user through an interface that allows the surgical tool to be used during minimally invasive surgery. The present invention may include two main components: (1) A set of surgical instruments having pressure sensors at strategic locations within the tool, and (2) a user interface and control system that employs electromechanical actuation to “push back” at the user&#39;s fingertips to allow remote sensation of pressure being applied to the tissue by the surgical tool. Additionally, the profile of the presently claimed surgical devices provides for minimal damage to the tissue through which the surgical tools must pass en route to the target tissue. 
     The apparatuses, systems, and methods of the present invention may employ sensor arrays for sensing forces at a surface, comprising a plurality of pressure sensors, wherein said plurality of pressure sensors are arranged in an array, wherein said pressure sensors are surrounded by an elastomeric substance; a printed circuit board, wherein said pressure sensors are operably connected to said printed circuit board; and a housing, wherein said housing includes said plurality of pressure sensors, said elastomeric substance, and said printed circuit board. The pressure sensors may be microelectromechanical system-based pressure sensors. The elastomeric substance is preferably corrosive-resistant and may be silicone, non-reactive gel, or non-reactive fluid. The sensors may be placed in a housing that is fabricated from a non-corrosive substance such as metal or plastic. In some embodiments, the pressure sensors possess a linear response to force. When used a surgical tool, the sensor arrays of the present invention may include a faceplate that may be smooth, textured or serrated, depending on the application in which the present invention is employed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For the present invention to be clearly understood and readily practiced, the present invention will be described in conjunction with the following figures, wherein like reference characters designate the same or similar elements, which figures are incorporated into and constitute a part of the specification, wherein: 
         FIG. 1  provides a profile and cross-sectional view of a sensor array of the present invention; 
         FIG. 2  displays the response profile of the sensors of the present invention; 
         FIG. 3  shows the spatial sensitivity of the sensor arrays of the present invention; 
         FIG. 4  demonstrates the limited crosstalk of the sensor arrays of the present invention; 
         FIG. 5  provides a profile and cross-sectional view of a grasper embodiment of the present invention; 
         FIG. 6  shows a cross-sectional view of a grasper embodiment of the present invention with a face plate; 
         FIG. 7  displays an interface through which a user may utilize the grasper embodiments of the present invention; 
         FIG. 8  depicts a cross-section view of an interface through which a user may utilize the grasper embodiments of the present invention; and 
         FIG. 9  depicts two physiologic scenarios in which a grasper embodiment of the present invention may be used. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the invention, while eliminating for purposes of clarity, other elements that may be well known. 
     The systems and methods of the present invention provide surgeons with an accurate and sensitive perception of the tissue that is being manipulated during robotic or laparoscopic surgery. The present invention employs sensors that allow for an improved spatial resolution and responsiveness over a broad range of relevant pressures when compared to prior art surgical tools. 
     The surgical instrument embodiments of the present invention preferably include a plurality of micro-pressure sensors located within the base of jaws used to manipulate tissue. In some embodiments, the micro-pressure sensors are MEMS-based sensors. When chosen appropriately, the MEMS sensor arrays are capable of providing a linear response to force stimuli over the relevant physiological range. A representative micro-pressure sensor is the cubic micro-pressure sensor pat number SM5108 obtainable from Silicon Microstructures. In some embodiments, the individual MEMS sensors are cubic and may be secured to the circuit board. The micro-pressure sensors may also implemented by imprinting on a thin circuit board. The sensors may be coated with a protective silicone elastomer layer to allow the surgical tool to operate in the water-based environment of the body. For embodiments where the sensor arrays of the present invention are used in other types of corrosive environments, the protective elastomeric layer may be formed from a substance from that is resistant to whatever corrosive substances are in the environment. 
     In some embodiments, the sensor element size resolution is approximately 1.6 mm×1.7 mm, though this resolution may be altered by changing the size of the sensors with resolutions of approximately 0.65 mm×0.65 mm achievable. While the present invention is described in the context of a grasping embodiment, the invention is not so limited. The sensor arrays of the present invention may be used in graspers, forceps, scissors, trocars, and instrument shafts (to monitor lateral displacement of instruments against patient anatomy) within the context of the present invention. 
     The limited circuitry used in implementing the sensing systems of the present invention allows the housing of the surgical tool in which they are placed to be relatively small compared to prior art surgical tools. The physical profile of the devices employing the sensing arrays of the present invention are thus reduced in size compared to prior art apparatuses and provide a concomitant reduction in ancillary tissue damage during surgery. 
     One embodiment of the sensing arrays of the present invention is shown in  FIG. 1A . The sensing array displayed has a 2×4 sensor array  100 . The number and geometry of sensors may be varied to provide for appropriate sensory assessment of the surgical site. Broad ranges of both number and geometry of sensors are contemplated within the scope of the present invention. 
     A cross-section of sensor array  100  is shown in  FIG. 18 . In this embodiment, the micro-pressure sensor is a MEMS sensor die  112 . The sensor die  112  is attached to a printed circuit board  116  at the base of the sensor array  100 . To preserve the integrity of the sensor dice during surgery, they are coated in silicone  108 , though other non-reactive elastomers, gels, or fluids may be used to surround the sensor  112 . The silicone  108  in this embodiment is in turn surrounded by a plastic housing  104  in the shape of a grid as shown in  FIG. 1A . The plastic housing provides structure to the sensing array and allows it to be manipulated routinely by medical professionals. 
     A sensing array that is appropriate for surgical use should have both a linear response to force and the ability to acutely discern and isolate force input to the array. To assess the response profile of typical sensing arrays of the present invention, a set of experiments were in run in which a load was applied to the top of each element within the array. Specifically, a mounted linear bearing was used to deliver a range of forces to an individual pad of the sensor array of  FIG. 1  such that eight elements were tested. Each sensor element was characterized by measuring voltage output from each sensor die as the load was applied to the top of the element. As shown in  FIG. 2 , each sensor was found to have a linear response up to 400 grams. The use of deformable silicone raises the question of hysteresis, but the present sensory array design displays minimal hysteresis effects while providing a reproducible response to the load (error bars are standard deviation, N=5). The data are summarized in the table below. 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Hysteresis (%) 
                 Sensitivity  
                 Linear 
               
             
          
           
               
                   
                 Average 
                 Std. Dev. 
                 (Mv/V/g) 
                 Regression 
               
               
                   
               
             
          
           
               
                 Element 1 
                 1.25% 
                 0.71% 
                 0.0346 
                 0.988 
               
               
                 Element 2 
                 1.44% 
                 0.84% 
                 0.0352 
                 0.990 
               
               
                 Element 3 
                 1.62% 
                 0.43% 
                 0.0359 
                 0.988 
               
               
                 Element 4 
                 0.00% 
                 0.46% 
                 0.0314 
                 0.983 
               
               
                 Element 5 
                 1.04% 
                 1.07% 
                 0.0443 
                 0.966 
               
               
                 Element 6 
                 −0.32%  
                 1.14% 
                 0.0807 
                 0.991 
               
               
                 Element 7 
                 1.49% 
                 1.37% 
                 0.0421 
                 0.990 
               
               
                 Element 8 
                 4.31% 
                 1.87% 
                 0.200 
                 0.990 
               
               
                   
               
             
          
         
       
     
     To assess whether the present sensor array was capable of discerning force stimulation of a single element, a separate test was performed. Force was applied to a single element of the sensor array and the force measured by all sensors was assessed.  FIG. 3  shows the results of two such experiments in which two different elements were sequentially tested. As is clear from the figure, the sensor arrays of the present invention display minimal cross-talk such that the force output of individual sensors accurately represent the forces sensed at that specific point on the sensor array. 
     Finally, the ability of the sensor arrays of the present invention to discern a varied force stimulus was assessed. A synthetic tissue pad  404  was constructed in which two materials were employed to stimulate a 2×4 sensor array  400  of the present invention as shown in  FIG. 4A . On the top of the pad, a firm material  408  was placed to allow force to be distributed to the materials below. The lower portion of the pad included two distinct synthetic materials that differed in compliance, i.e., firmness or deformability. As shown in  FIG. 4A , the portion on the left  412  is a less compliant silicone material and the portion on the right  416  is more compliant synthetic fat material. The three mm-thick tissue pad  404  was placed on top of the sensor array  400  so that the border between the two materials laid along the D-D plane, as shown in  FIG. 4B . The pad  404  was depressed 0.5 mm and the output of the sensor arrays was measured. The sensor array detected increased forces at the sensor elements compressing the stiffer silicone element  404  compared to the elements compressing the more compliant synthetic fat pad  416  as shown in  FIG. 4C . 
     As a result of these experiments, it has been demonstrated that the sensor arrays of the present invention possess a linear response to applied forces and additionally display a high level of spatial acuity. Thus, the sensor arrays of the present invention possess the desired properties for an effective surgical tool. 
       FIG. 5  shows one grasper embodiment  500  of the present invention that utilizes sensor arrays as described above. As shown in profile in  FIG. 5A , this embodiment is a surgical tool includes a base  504  in which the sensor array  508  and the accompanying electronic components are found. The top portion includes a grasping jaw  512  that is adapted to open and close onto the sensor array  508  to grasp an object or tissue. This embodiment also includes an arm  516  that is capable of opening and closing the grasping jaw  512  when manipulated by a user during surgery. A face view of the base  508  and sensor array  504  is shown in  FIG. 5B . The sensor array  504  is shown as a series of pads in this embodiment. The tool may be fabricated from a wide variety of bio-compatible materials such as stainless steel, plastic, or various composites. 
     In other embodiments, such as shown in cross-section in  FIG. 6 , a faceplate  604  may be included in the surgical device and placed on top of the elastomer layer  608  and sensor die  612 . As shown in  FIG. 6 , the sensor die is attached to a printed circuit board  616  and the over all sensor array is housed in a stainless steel or plastic frame  620 . The faceplate  604  shown in this embodiment is serrated such as may be employed in grasping and resecting a piece of tissue. The faceplate may, however, possess an appropriate surface for the specific task to be performed by the medical professional utilizing the device. For example, a serrated surface may be preferred for surgical interventions such as grasping or retraction of tissue. Similarly, the faceplate may be modified to be a sharp surface (for scissors or trocar), a flat surface (for simple probing or palpation), or a round surface (such as around the cylindrical shaft of a laparoscopic instrument) for different surgical processes. The micro-pressure sensors included in the present embodiments provide for accurate, repeatable pressure distribution data across the face of the tool, and the faceplate allows for selective and delicate manipulation of tissue. 
     In some embodiments, measurements obtained through the micro-sensors are sent to an interface to be employed by the user. In one embodiment, the signals can be sent to a graphical display that will inform the user of the pressure being applied to each sensor element. The graphical display may represent the surface of the sensor array and provide information about the forces being sensed at the surface of the surgical tool. The present invention may also be implemented, either independently or in combination with a graphical display, as a finger/joystick interface. 
     During use, the surgeon may manipulate the grasper joystick by pressing his or her finger  704  against a pad  708 , as shown in  FIG. 7 . The pad  708  may rotate on a pivot  712  and the angle of displacement corresponds to the angle of displacement of the jaws of the tool. When the surgical tool face begins to experience the normal forces of tissue pressing at the jaws, the pivot  712  can lock into place. The pad  708  may also employ spatially mapped pins  804  driven by electrical induction to push on the user&#39;s finger proportionally to the pressure distribution measured at the device&#39;s jaw, thus providing the user with an accurate haptic representation of the forces measured at the tool face, as shown in  FIG. 8 . Once the pivot  712  is locked, the solenoid pins  804  may be actuated to press at the user&#39;s fingertips with forces proportional to the pressure distribution at the tool jaw ( FIG. 4 ). In some embodiments, the forces at pressure sensors implanted at the tip of the solenoid pins  804  manipulated by the user will correlate with the forces sensed the elastomer at the tool face. The arrangement of solenoid “spring” mechanisms will mimic the compliance properties of the tissue to give the surgeon the feel of the tissue he is grasping. 
     For example, if the tool were being used during an operation to remove neoplastic tissue ( FIG. 9 ), the surgeon would be able to identify the neoplastic tissue  904  as being harder than the surrounding healthy tissue  908  by employing the present invention. Alternatively, the interface of the present invention may pulse to indicate an underlying artery  912  as also shown in  FIG. 9 . Furthermore, the present invention may also be used to detect structures within fascia or tissue such as underlying non-compliant nerves. In some embodiments, sensor arrays of the present invention could be placed onto a probe which could be used to assess firmness of tissue. 
     Through use of the present invention, surgeons and other users will be provided with an accurate haptic sensation of important surgical cues such as the pulsation of an artery, the stiffness of different tissues, and the force with which they are grasping or pulling tissue. 
     While described in the context of surgical procedures, the present invention may also be employed in a variety of circumstances where remote haptic sensing of forces is desirable. Examples of such scenarios include virtual reality or simulation situations as well. Additionally, the sensor arrays of the present invention may also be useful in harsh environment where exposure to humans is detrimental (e.g., corrosive environments) or at locations that are difficult for humans to access. 
     Nothing in the above description and attached figures is meant to limit the present invention to any specific materials, geometry, or orientation of elements. Many modifications are contemplated within the scope of the present invention and will be apparent to those skilled in the art. The embodiments disclosed herein were presented by way of example only and should not be used to limit the scope of the invention.