Abstract:
A probe is connected to a probe carrier that is positioned with respect to the body of a patient. The probe is moved into or out of the body incrementally by means of a driver mechanism and flexible coupler. The flexible coupler in one embodiment comprises a flexible sheath with a flexible driver shaft that can be passed within the flexible sheath and can be rotated or pushed forward and backward with respect to the sheath by a driver element thereby causing translational movement of probe. Several forms of probes, flexible coupling elements, and driver apparatus as well as methods of applications accommodate specific objectives.

Description:
This application claims benefit of provisional application No. 60/130,867 filed Apr. 23, 1999. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to advances in medical systems and procedures for prolonging or improving human life. More particularly, this invention relates to an improved method and system for advancing a probe or an electrode into the human body in finely graded steps while detecting the position of the probe advancement. 
     BACKGROUND OF THE INVENTION 
     In the field of neurosurgical stereotaxy, electrodes and probes of various kinds may be advanced into the brain of a patient. In the case of deep brain stimulation (DBS) or radiofrequency (RF) lesion making, microelectrodes are typically advanced from a stereotactic frame into the brain in very small steps, sometimes of micron incrementation. These microelectrodes typically have tips with lengths of several microns to several hundred microns. In some applications recordings of electrical activity of brain cells deep in the brain are recorded by electrical signal monitoring from the microelectrode as it is incrementally advanced into the brain. 
     Microdrives for such brain probes may include mechanical sliding devices and mechanical screw devices that are attached to the carrier of the stereotactic frame. These devices typically are cooperatively connected to the probe so that advancement of the probe into the patient&#39;s brain, for example, can be done while visually reading a mechanical scale or digital readout. In some instances, the operation of these devices involves turning a mechanical screw or rack-and-pinion to advance the position of the electrode mechanically. 
     By reference, the stereotactc frames of Radionics, Inc., Elekta AB, and the TrentWells, Inc. stereotactic systems illustrate the use of stereotactic frames and recording probes. 
     The capability to advance an electrode in fine steps, on the order of several tens of microns (micrometers) to several hundred microns presents certain technical problems. Mechanical motions of the electrode or the advancing device can disturb the highly sensitive electrical recording measurements of electrical brain activity. For similar reasons, it may be advantageous to electrically decouple moving device from the electrode. Hydraulic microdrives have been used to provide fine verniated movements. The hydraulic microdrives comprise a flexible hydraulic tubing that advances an incompressible fluid within the tubing to drive a piston which is coupled to the electrode near the stereotactic frame. By reference, the electrode microdrive of the TrentWells, Inc. company (Los Angeles, Calif.) is an example of a hydraulically advanced microdrive for stereotactic probes. 
     Difficulties with hydraulic microdrives include fluid leaks and problems with sterilization. For example, steam autoclave sterilization disrupts the hydraulic fluids that are contained in the enclosed, flexible tubing. Furthermore, the ability to monitor the position of the electrode at the position of the probe carrier on the stereotactic frame has been difficult. By reference, the hydraulic probe microdrive of the TrentWells, Inc. company does not provide detection means at the probe end near the stereotactic frame end of the hydraulic tubing. Rather, this microdrive only provides deflection means at the side near the hydraulic piston, which is remote from the stereotactic frame. 
     It is important for a surgeon to know the actual position of the probe at the stereotactic frame for quantitative evaluation of the position of the probe. However, mechanical screw type, rack-and-pinion, or millimeter slide type probe carriers on the stereotactic frame prove relatively ineffective in achieving fine distance verniations (e.g. on the order of tens of microns) without creating electrical disturbance of the brain recordings. 
     Accordingly, an effective technique and system for stereotactic probe advancement, especially when fine advanced movements are required and electrical recording is required, is desirable for purposes of stereotactic probe placement. Particularly in the surgical setting, a need exists for a microdrive for probes which does not rely on fluid coupling and which can be readily cleaned and sterilized. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a mechanical microdrive system and method for smooth and reliable advancement of a probe with respect to a probe carrier. The present invention is different from any of the systems discussed in the Background section. Advantages of the present system and method reside in their simplicity, mechanical stability, ability to be sterilized and cleaned for surgical use, ruggedness and reliability, and clinical effectiveness. 
     In one embodiment, the mechanical microdrive includes flexible tubing that contains a flexible but longitudinally rigid push cable (push rod). The tubing is connected on its distal end to a stereotacic carrier attached to a stereotactic frame. The flexible push rod is attached independently to a microelectrode holder that advances the microelectrode stereotactically into the patient&#39;s body. On the proximal end, the flexible tubing is attached to a platform, and the flexible push rod is advanced within the tubing by an advancing mechanism. The advancing mechanism can have very fine longitudinal position gradations and have readout and display of its position. It is driven either manually or by a motor. At the stereotactic frame, the relative position of the probe is measured by a detecting system to give a position of the advancement of the probe into the patient&#39;s body. Electrical signals from the driving mechanism and the probe position mechanism can be sent to a computer or other display to control the process. 
     One embodiment of the mechanical flexible advancement device utilizes a longitudinal advancement of the push rod within the device as provided by a rotatable internal drive rod which enables a screw advancement at the proximal end by the stereotactic device. 
     The present technique avoids many of the difficulties associated with a hydraulic microdrive. For example, since a hydraulic transmission fluid is not used within the system, difficulties of autoclaving and unwanted leaks are avoided. In addition, a system conducted according to the present invention may be cleaned and sterilized by using autoclave and other means, thus simplifying the surgical preparation. Such a system has further advances of simplicity and robustness. It does not need to be filled with a hydraulic fluid and does not have problems associated with bubble formation within the hydraulic tube, as does the hydraulic microdrive described in the Background section. 
     These features and advantages, as well as others of the present method and system, will become apparent in the detailed description that follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings which constitute a part of the specification, embodiments exhibiting various forms and features hereof are set forth, specifically: 
     FIG. 1 is a schematic diagram showing one embodiment of a probe being advanced relative to a stereotactic holder by a flexible mechanical probe microdrive in accordance with the present invention. 
     FIG. 2 shows a flow chart of a process that may be performed by a system in accordance with the present invention. 
     FIG. 3 illustrates an alternative embodiment utilizing a manual device for advancing the flexible coupler. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to FIG. 1, in a system S in accordance with the present invention, a probe  1  is advanced into the body of a patient P. The patient is fixed in a stereotatiic frame which comprises a headring structure  4  that is secured firmly to the patient&#39;s head by posts such as  7 . The headring platform includes support structures  11  that support a stereotactic arc system  10  which may be slidable engaged with a probe carrier structure C. The probe carrier structure C includes a probe carrier  14  that has a probe post  17  that supports a probe drive block  20 . The probe drive block  20  moves in and out relative to the stereotactic frame as indicated by the arrow  24 . The probe drive block  20  is attached at connection  18  to the electrode  1 , and advances the electrode into or out of the brain in the directions indicated by arrow  24 . The probe  1  is guided through a guide block  30  for directional stability. By reference, the CRW stereotactic arc system of Radionics, Inc. (Burlington, Mass.) includes examples of guide carriers for probes. 
     Also shown in FIG. 1 is a flexible mechanical probe drive tube  36 , which connects at one end to a coupler  41  affixed to the stereotactic probe carrier structure C. On the other end, the tube  36  is connected to a block  44  attached to a drive apparatus base  47 . Inside the tube  36  is a mechanical and flexible internal drive structure  52 , indicated by the dashed line in FIG.  1 . The internal drive structure  52  (e.g., a cable) emanates from the tubing  36  at its distal end, as illustrated by element  56 , and may connect by connection  57  to the electrode or probe drive block  20 . 
     On the proximal end, the internal drive structure  52  emanates from the tubing  36  as illustrated by drive or driver element  61  (e.g., a push rod)  44  and connects to a drive device  70 . The drive device  70  may, for example, be a transmission or hydraulic moving device or a geared vernier translator. Examples of vernier translators are the fine movements in a vernier caliper used in mechanical measurements in machine shops (for example, supplied by the Starrett Company, Athol, Mass.). 
     Also shown in FIG. 1 is a movement encoder or detection device  78  which can provide mechanical or electrical output indicative of the position of the drive device  70 ; and henceforth, the position of element  61 . The drive device  70  (e.g., translator) can be driven by driver  84 , which can be a motor or a manual device for turning a shaft  88  or otherwise actuating the vernier translation device  70 . FIG. 3 illustrates a manual device having a rotation knob  92 . 
     A drive device  70  can be controlled or powered by a drive control element  87 . The drive device  70  also may incorporate various display elements  91  to indicate the position of the drive element, and therefore of the push rod  61 . Electronic output or control signals of elements  87  and  91  can communicate with computer  99  for automation of the system or other control aspects. Computer  99  may have stereotactic planning information in it based on CT, MR, or other image data. The computer  99  may provide an electronic readout from a microelectrode such as electrode  1  that has its tip positioned deep within the brain (e.g. position  31 ). This readout information can be correlated with the position of the encoder  78  or an encoder on the probe carrier structure C as described below. 
     The drive shaft (e.g., elements  61 ,  52 , and  56 ) may, for example, be a longitudinal push-pull type or rotational-type wire or structure. The indication of these motions are shown schematically by the translation arrow  85  and the rotation direction  86 , respectively. The drive shaft can move, for example, longitudinally with the sheath or carrier  36  or rotate within it. For example, in the first case, the drive device  70  causes linear movement of element  61 . This movement, in turn, causes drive structure  52  to move linearly within the tube  36 ; the ends of tube  36  being fixed to block  44  and coupling  41 . The movement of drive structure  52 , in turn, causes element  56  to move in a linear fashion, thereby causing drive block  20  to move as indicated by arrow  24 . It should be appreciated that, in general, the drive shaft components  61 ,  52  and  56  are constructed of material of sufficient rigidity to cause predictable linear movement of drive block  20  in response to a given linear translation by drive device  70 . 
     In the case of a rotational drive shaft, the shaft may connect to a rotational transmission within coupling  41 , which for example, may include a threaded not  114  such that rotation of the shaft and the nut corresponds to a pushing or pulling motion on the electrode or probe  1 , as indicated by arrow  24 . Thus, the coupling  41  translates the rotational movement of the drive structure  52  into linear movement of element  56 . It should be appreciated that, in general, the drive shaft components  61 ,  52  and  56  are constructed of materials of sufficient rigidity to cause predicable linear movement of drive block  20  for a given angle of rotation of drive device  70 . For example, the rotating components (element  61  and drive structure  52 ) typically would be sufficiently rigid with respect to the rotational forces to which they are subject. Element  56  would be sufficiently rigid with respect to the linear forces to which it is subjected. 
     Note that, depending upon the coupling type, the element  56  also may rotate. In this case, the connection  57  would include a rotating member that connects to the rotating element  56 . 
     Also shown in FIG. 1, in accordance with the present invention, is an apparatus to detect the actual movement of the electrode  1  with respect to its probe carrier  14  and therefore with respect to the stereotactic frame  10  and the patient&#39;s body P. For example, a probe carrier plate  42  can have connected to it a linear translation detection device  110 , which detects the movement of the drive block  20  with respect to the probe carrier plate  42 . As the drive block  20  moves in and out, as illustrated by the arrow  24 , the shaft element  111 , which is connected to the probe  1  by drive block  20 , moves with respect to the base of the detection device  110 . This combination of  110  and  111  elements could, for example, be a linear translation detection/measuring device that is used for detection of linear motions. By reference, see, for example, descriptions of Linear Variable Differential Transformer (LVDT) devices illustrated by the products of Lucas/Schaevitz Company, USA. As the probe  1  moves in and out of the patient&#39;s body, as driven by drive shaft  56 , the actual position of the probe  1  with respect to the stereotactic frame is therefore detected by the translation detection elements  110  and  111  and by sensing or detecting apparatus  120 . The apparatus  120  may, for example, translate induction, capacitor, resistance, or other electrical parameters associated with or provided by the detection device  110  into a measurement signal (e.g., representing millimeters or inches) corresponding to the advancement position of probe  1 . The position of the probe also may be visually represented on display element  124 , which may be part of a computer system, a CRT, a flat screen LCD, or other analog or digital display. The display may be cooperatively connected to computer  99  so that a comprehensive measurement and control system is integrated between the drive and measurement elements as described above. 
     In accordance with the present invention, various probes or electrodes may be used in the system shown in FIG.  1 . For example, the probe  1  may be a microrecording electrode having a conductive electrode tip exposure in the range of 1 to several microns. The probe  1  may be a semi-microelectrode where the exposed recording and stimulating tip has larger dimensions (e.g, on the order of tens to hundreds of microns). The probe  1  may be a macrostimulation, lesioning, or recording electrode having a tip adapted to do gross stimulation, recording, or heat lesioning. The probe  1  also may be part of a deep brain stimulation system. By reference, recording, stimulating, lesioning, and deep brain stimulating electrodes are represented in the product line of Radionics, Inc., Burlington, Mass., or Medtronic, Inc., Minneapolis, Minn. 
     Referring to FIG. 2, a process is shown in accordance with the present invention in which a probe is advanced into the patient&#39;s body. The probe may be held and stabilized in a stereotactc device, as shown in FIG. 1, or some other type of actuator such as a robot, image-guided system, or alternative types of stereotactic apparatus. The insertion of the probe into the holder and its attachment is illustrated by step  1  in FIG.  2 . After insertion of the probe into the stereotactic holder, connection can be made via the flexible mechanical drive structure (step  137 ). The driver on the distal end can be connected to adaptions (e.g.,  41 ) that allow advancement of the probe into the patient&#39;s body. On the proximal end, the flexible drive structure may be connected to the drive mechanism with verniated readout on the driver end (e.g.,  70 ,  78 ). After appropriate registration of the probe relative to the stereotactic frame, the probe may be advanced incrementally into the patient&#39;s body (step  140 ). The advancement may be accompanied by detection and readout of the probe position and/or the driver position, as described in the embodiment of FIG.  1 . That information can be connected to computer, control, and/or display apparatus to control monitor, and indicate the probe position relative to the stereotactic frame and/or the patient&#39;s body (step  144 ). 
     Other steps may follow the steps of FIG.  2  and may include, in the case of neurosurgery, recording, stimulating, or producing a radiofrequency lesion and displaying parameters associated with these functions on a display or computer system. Correlation of the displays of these parameters can be made with scan data or other representations of anatomy associated with the patient&#39;s body or atlases that are registered with the patient&#39;s body. 
     The system and method of the present invention has the advantage that a flexible mechanical drive coupling provides versatility of position of the proximal drive device relative to the probe and stereotactic frame. When delicate recording, stimulation, or lesioning is required from the probe, vibration isolation of the drive device through a flexible mechanical driver (e.g., driver tube  36 , as illustrated in FIG. 1, advantageously reduces electrical noise and mechanical vibration of the probe. Another advantage of the invention is that the flexible mechanical drive system, does not have the handling and sterilizing problems of a hydraulic probe microdrive, as described in the Background section. A tubing filled with incompressible fluid to drive the probe is subject to bubble lock, leaks, contamination and is difficult to autoclave and sterilize and clean. The present invention has the advantage that it is simple, robust, easy to clean and handle, poses no leak contamination risks, and can be sterilized. Another advantage of the present invention is that the mechanical driver can be electrically isolated from the probe. The flexible tubing  36  and drive shaft  52 , as shown in FIG. 1, may be made of electrical insulative material or have insulative couplings at its proximal or distal end to isolate the drive device from the probe carrier. Moreover, the driver (e.g., motor) can also be placed at a somewhat remote location, for example several inches to several feet away from the probe, to eliminate electrical noise and capacitive or inductive noise. As an example, the drive sheath  36  (tubing) in FIG. 1 can be made from a Teflon, PVC, polyurethane, or braided plastic and metal structure which is fully insulated and flexible. The inner drive element  52  can be made from a metal wire coated by an insulative and low friction material such as Teflon. At the proximal end in the bushing  44  or the distal end in the busing  41 , the drive element can be electrically insulated from the drive device  47  or from the probe carrier  42 . 
     To enable positioning of probe  1  to virtually any location in the patient&#39;s head, the probe carrier  14  may be movable with respect to the headring structure  4 . For example, probe carrier  14  may be slidably attached to arc system IO so that the probe carrier  14  moves in the direction indicated by arrow  151 . The arc system  10  may be movable with respect to the headring structure  4 . For example, member  150  (connected to structure  11 ) may move with respect to member  152  (connected to posts  7 ). Arc system  10  also could be adapted to linearly move relative to headring structure  4 , for example, as is known in the art. 
     Various devices for measuring the probe position corresponding to element  110  can be devised. LVDT, capacitive distance measurements, inductive devices, vernier calipers, digital LCD readouts, rheostat or resistive displacement devices, or other means can be used to provide accurate position and displacement, both absolute and incremental measurements. In view of these considerations, as would be apparent by persons skilled in the art, implementations and systems should be considered broadly and with reference to the claims set for below: