System and method for controlling force applied to and manipulation of medical instruments

[0001] This application is a divisional of and claims the benefit of pending U.S. application Ser. No. 09/811,358, filed Mar. 16, 2001 and U.S. Provisional Application No. 60/189,838, filed Mar. 16, 2000 by Merril et al., both of which are entitled System and Method for Controlling Force Applied to and Manipulation of Medical Instruments, both disclosures of which are incorporated herein by reference in their entirety.

[0002] Minimally invasive techniques for providing medical examinations and therapies frequently employ endoscopes, such as a bronchoscope, ureteroscope, or flexible sigmoidoscope. Endoscopes such as these typically employ fiber optic or CCD imaging devices to enable the practitioner to visually inspect otherwise inaccessible areas of the anatomy such as the lungs, the ureter and kidneys, the colon, etc. These endoscopes also typically contain a tube, called the working channel, through which solutions such as anesthetics can be administered and bodily materials such as mucus can be withdrawn, typically via suction. In addition to use in administering and removing liquids or other material, the working channel of an endoscope is used to pass slender instruments to perform other functions at the distal end of the scope, under visual guidance through the endoscope.

[0003] Instruments typically used in this manner include forceps for grasping objects or for pinching and removing small tissue samples, biopsy needles for removing deep tissue samples in the lumen of a needle, snares or baskets for capturing and withdrawing objects such as an aspirated peanut from the lungs or a kidney stone from the calyxes of the kidney, and a wide variety of other tools.

[0004] Manipulation of these tools requires simultaneous manipulation or stabilization of the endoscope, along with manipulation of the working channel tool itself. The endoscope can typically be maneuvered along three, four or more degrees of freedom, including insertion and withdrawal, rotation, and tip flexion in one or two dimensions (up/down and/or left/right). The working channel tool is maneuvered along an additional two or more degrees of freedom, including insertion/withdrawal, rotation, and tool actuation, etc. Tool actuation can include, for example, opening and closing the jaws of a biopsy forceps, controlling the plunge of a biopsy needle, actuating a cauterization or ablation tool, pulsing a laser, or opening and closing a snare or basket. The tasks of manipulating and stabilizing the three or more degrees of freedom of the endoscope, while simultaneously manipulating the multiple degrees of freedom of the working channel tool are difficult to perform, and frequently the practitioner uses an assistant to manipulate one or more of the degrees of freedom, such as working channel tool actuation.

[0005] The present invention relates to a device or system that extends the functionality of the working channel of an endoscope by adding devices for sensing motion of the working channel tool and r for application of motive force to assist the practitioner in manipulation of the instrument in the working channel.

[0006] In one mode of use, the system uses drive wheels driven by a motor or other device to permit the, practitioner to quickly exchange working channel tools, by smoothly moving the current tool out of the working channel, and then quickly moving in the new tool to a point just short of exiting the working channel. At this point the practitioner takes over and performs the fine motor skills necessary to move the tool out of the endoscope and into a position to interact with the anatomy. In another mode of operation the physician manipulates tools manually and is provided with tactile guidance via a set of driven or braked drive wheels. One form of guidance is the provision of notification that the tool is approaching the end of the endoscope and is about to emerge from the endoscope. A braking or other tactile force would signal nearing the end of the working channel, enabling the user to move the tool quickly within the working channel without Manger of moving the tool too rapidly out of the working channel, thereby reducing the risk of damage or injury to tissue adjacent the distal end of the endoscope.

[0007] In another embodiment, the sensor and drive assembly is coupled to a catheter through which instruments and tools are passed into the vascular system. For instance, in the process of implantation of a heart pacing lead, the cardiologist must make a number of fine adjustments in the position of a guide catheter; then attempt to stabilize it while inserting an additional element through the lumen of the stabilized catheter. In one mode, the sensor/drive assembly is commanded to maintain a position using passive or active braking force. In another mode, the tip of the catheter is instrumented and an active mechanism commands insertion/retraction and roll increments to stabilize the actual position of the distal end.

[0008] In yet another embodiment, the sensor and drive assembly is instrumented with strain gauges or other devices to detect forces encountered at the distal end of the catheter or working channel tool. These forces are then amplified and displayed to the user via a motor or other motive mechanism.

[0009] In another embodiment, the sensor and drive assembly detect and modify motions, for example, detecting and filtering, out high frequency jitter caused by the user. This superstabilization mode is useful in situations where fine motor control is required.

[0010] In another embodiment, signals from a device inserted in the working channel are used to command the motive device to maintain a particular quality of electrical contact with the anatomy. In this situation, electrical impedance is changed by the force of contact. A desired quality of contact is initially attained by the physician, then the device is commanded to control contact force automatically to maintain the particular quality of contact.

[0011] The above and still further features and advantages of the present invention will become apparent upon consideration of the following detailed description of specific embodiments thereof, particularly when taken in conjunction with the accompanying drawings wherein like reference numerals in the various figures are utilized to designate like components.

[0012] FIG. 1a illustrates an unmodified endoscope with working channel and working channel tool.

[0013] FIG. 1b illustrates an endoscope modified to provide a sensor and control element in accordance with the present invention.

[0014] FIG. 2 illustrates an endovascular tool inserted into the vascular anatomy, combined with a sensor and control element in accordance with the present invention.

[0015] FIG. 3 illustrates an axial motion sensor control element in accordance with the present invention.

[0016] FIG. 4 illustrates addition of a rotational motion sensor and control element to the device in FIG. 3.

[0017] FIG. 1a illustrates an unmodified endoscope, showing the endoscope body 2 attached to the endoscope tube assembly 3. Working channel tool 4 is inserted into working channel orifice 6 in endoscope body 2. Working channel tool 4 slides through working channel tube 1 and exits the distal end of endoscope tube assembly 3 through working channel orifice 5.

[0018] FIG. 1b illustrates motion sensor and control element 10 affixed to the working channel orifice 6. Working channel tool 4 passes through motion sensor and control element 10 and through working channel orifice 6. Normal manipulation and operation of the working channel tool is possible through the body of motion sensor and control element 10.

[0019] FIG. 2 illustrates an endovascular application of the motion sensor and control element of the present invention. Motion sensor and control element 10 is coupled to introducer sheath 7 which pierces skin 8 and the wall of blood vessel 9. Elongated endovascular tool 4 passes through motion sensor and control unit 10, through introducer sheath 7, and into the lumen of blood vessel 9.

[0020] In one mode of the present invention, the total distance of insertion of the working channel tool is measured and controlled by the motion sensor and control element. In FIG. 3, motion sensor and control element 10 contains a device for measuring translational motion of the body of working channel tool 4. As the elongated portion of working channel tool 4, passes between motion sensing and control wheel 18 and idler wheel 13, it causes rotation of each wheel. Wheel 18 is affixed to shaft 15 of motor 12. In turn, transparent optical encoder disk 14 is affixed to the opposite end of motor shaft 15. Encoder reader 16 passes light through transparent encoder disk 14. As transparent encoder disk 14 rotates, marks imprinted on the surface pass in front of the light source, occluding alternately light passing through the disk. A plurality of light sensors in encoder reader 16 measure the varying light and dark patterns and determine the amount and direction of rotational motion of encoder disk 14. Control unit 24 receives motion signals from encoder reader 16 corresponding to translational motion of working channel tool 4. Control unit 24 measures total insertion distance of working channel tool 4 and, for example, when a preset limit is approached, produces control signals transmitted to motor 12 to produce torque necessary to slow and then halt farther motion of motion sensing and control wheel 18, thereby slowing and then halting further insertion of working channel tool 4.

[0021] In another mode of the invention, motion sensing and control unit 10 amplifies or reduces forces applied by the user to working channel tool 4. In FIG. 3, handle 17 is disposed adjacent force-torque sensor 19 which in turn is disposed adjacent working channel tool 4 such that translational force applied by the user to working channel tool 4 via handle 17 is sensed by force-torque sensor 19. A control algorithm described below and residing in control unit 24 receives signals resulting from applied force measured by force-torque sensor 19 and in response produces control signals which are transmitted to motor 12 to control the motion of wheel 18. Wheel 18 can be moved either by force applied by motor 12 or by frictional forces applied via working channel tool 4. When working channel tool 4 is held motionless by the user, force applied to wheel 18 via shaft 15 of motor 12 is opposed by, and therefore sensed by torque sensor 22 which is attached to bracket 20 which is in turn fastened to base 11 of sensing and control element 10. Force applied to working channel tool 4 by control wheel 18 is sensed by torque sensor 22 and denoted F_W. This force is added to force applied by the user (F_U) to produce the effective force at the distal end of the working channel tool F_WC, as expressed in the following equation of equilibrium:

[0022] The control algorithm described below and contained in controller 24 dynamically modifies the force applied by the wheel 18, F_W, to control working channel tool force, F_WC, in response to force applied by the user F_U. In particular, if the desired relationship between user applied forces and working tool forces is expressed by function f( ) as:

[0023] Combining these equations and solving for F_W provides the following control algorithm:

[0024] Control unit 24 receives signals corresponding to user applied force F_U and control wheel force F_W and adjusts control signals transmitted to motor 12 to implement the control algorithm of equation 3.

[0025] The sensing and control unit of FIG. 3 can be extended to sense and control rotation and torque as well as translation and axial force. In FIG. 4, as the elongated portion of working channel tool 4 rotates between motion sensing and control wheel 28 and idler wheel 26, it causes rotation of each wheel. Wheel 28 is affixed to shaft 29 of motor 30. In turn, transparent optical encoder disk 34, is affixed to the opposite end of motor shaft 29. Encoder reader 38 passes light through transparent encoder disk 34. As transparent encoder disk 34 rotates, marks imprinted on the surface pass in front of the light source, occluding alternately light passing through the disk. A plurality of light sensors in encoder reader 38 measure the varying light and dark patterns and determine the amount and direction of rotational motion of encoder disk 34. Control unit 24 receives motion signals from encoder reader 38 corresponding to rotational motion of working channel tool 4. Control unit 24 measures total rotation of working channel tool 4 and, for example, when a preset limit is approached, produces control signals transmitted to motor 30 to produce torque necessary to slow and then halt further motion of motion sensing and control wheel 28, thereby slowing and then halting further rotation of working channel tool 4.

[0026] Likewise, motion sensing and control unit 10 in FIG. 4 amplifies or reduces torques applied by the user to working channel tool 4. In FIG. 4, handle 17 is disposed adjacent force-torque sensor 19 which in turn is disposed adjacent working channel tool 4 such that rotational force applied by the user to working channel tool 4 via handle 17 is sensed by force-torque sensor 19. A control algorithm described below and residing in control unit 24 receives signals resulting from applied force measured by force-torque sensor 19 and in response produces control signals which are transmitted to motor 30 to control the motion of wheel 28. Wheel 28 can be moved either by force applied by motor 12 or by frictional forces applied via working channel tool 4. When working channel tool 4 is held motionless by the user, force applied to wheel 28 via shaft 29 of motor 30,is opposed by, and therefore sensed by torque sensor 32 which is attached to bracket 36 which is in turn fastened to base 11 of sensing and control element 10. Torque applied to working channel tool 4 by control wheel 28 is sensed by torque sensor 32 and denoted T_W. This torque is added to torque applied by the user (T_U) to produce the effective torque at the distal end of the working channel tool T_WC, as expressed in the following equation of equilibrium:

[0027] The control algorithm described below and contained in controller 24 dynamically modifies the torque applied by the wheel 28, T_W, to control working channel tool torque, T_WC, in response to force applied by the user T_u. In particular, if the desired relationship between user applied torque 10 and working tool torque is expressed by function q( ) as:

[0028] Combining these equations and solving for T_W provides the following control algorithm:

[0029] Control unit 24 receives signals corresponding to user applied torque T_U and control wheel torque T_W and adjusts control signals transmitted to motor 30 to implement the control algorithm of equation 6.

[0030] Thus, sensing and control unit 10 as shown in FIG. 4 can provide rotational or translational position control, as well as translational force and rotational torque control to working channel tools. As shown in FIG. 2, sensing and control unit 10 can be used to control any elongated medical instrument, such as a catheter used in interventional radiology.

[0031] While this invention has been described in terms of several preferred embodiments, it is contemplated that alterations, permutations, and equivalents thereof will become apparent to those skilled in the art upon a reading of the specification and study of the drawings. For example, many different types of sensors and actuators can be used to sense tool position or motion and to output tactile sensations to the user. Furthermore, many of the features described in one embodiment can be used interchangeably with other embodiments. Furthermore, certain terminology has been used for the purposes of descriptive clarity, and not to limit the present invention.