US20010027271A1 - Instrument guidance for stereotactic surgery - Google Patents

Abstract

A method and apparatus for positioning a surgical instrument during stereotactic surgery using a guidance fixture. The guidance fixture includes an upper portion, which includes an instrument guide for moving the surgical instrument along a constrained trajectory relative to the upper portion, and includes an adjustable base supporting the upper portion, which includes a mounting base and an adjustment mechanism. The adjustable base can include a rotating collar attached to the mounting base and a pivoting collar coupling the rotating collar to the upper portion. A remote sensing device, such as a camera array sensing LEDs on the fixture, is used to determine the orientation of the upper portion of the guidance assembly in relation to the body.

Description

RELATED APPLICATION
• This application is a continuation and claims the benefit of priority under 35 USC 120 of U.S. application Ser. No. 09/063,658, filed Apr. 21, 1998. The disclosure of the prior application is considered part of (and is incorporated by reference in) the disclosure of this application.[0001]
BACKGROUND
• This invention relates to guidance of surgical instruments using stereotactic localization.[0002]
• Stereotactic localization is a method for locating a target within a three-dimensional object. This method is used in the medical arts and sciences to locate a target in the human body, in particular in the brain or spine, for medical and surgical treatment. Stereotactic surgery has a history dating back to the turn of the century, when the Horsely-Clark Apparatus was described as a mechanical frame system in which an animal was immobilized. This frame system permitted reproducible targeting within the animal's brain for physiological experiments. This and similar technology found application in 1948 in the work of Wycis and Speigel. In their work, a frame was attached to a human skull. The frame permitted targeting of sites within the human brain for neurosurgical treatment. A detailed survey of the field of stereotactic surgery can be found in[0003]Textbook of Stereotactic and Functional Neurosurgery,P. L. Gildenberg and R. R. Tasker (eds.), McGraw-Hill, June 1997 (ISBN: 0070236046).
• One approach to stereotactic surgery involves the following steps. Fiducial scanning markers are attached to the body in one of a variety of manners, including using an attachable frame or attaching the markers to the skin with an adhesive. A scan is then taken of a body, for example of the head, to produce a three-dimensional image of the body.[0004]
• Scanning can be done using a variety of techniques including CT, MRI, PET, and SPECT. Images of the fiducial scanning markers that are located around the body are then located in the three-dimensional image at fiducial image points. Points of interest, such as the location of a tumor, are located in the three-dimensional image with reference to these fiducial image points. The body and the image are registered by matching the locations of the scanning markers and the coordinates of the fiducial image points. In an approach to stereotactic brain surgery, a three-dimensional frame is screwed to the patient's skull prior to scanning the head. This frame serves as a mechanical reference mechanism that supports scanning fiducial markers at fiducial points around the body. The frame remains attached to the patient's skull from before scanning until after surgery is complete. Prior to surgery, a mechanical guide assembly is attached to the frame. The relative location in the image of the point of interest with respect to the fiducial image points is determined, and this relationship is used to adjust the mechanical guide assembly with respect to the fiducial points on the frame. Using the adjusted mechanical guide assembly, a surgical instrument is then guided to a location in the body that corresponds to the point of interest in the image.[0005]
• In another form of stereotactic surgery, known generally as “image-guided” stereotactic surgery, rather than relying on mechanical adjustment of a guide assembly, visual feedback is provided to a surgeon by displaying a composite image formed from the scanned three-dimensional image and a synthesized image of a hand-held surgical instrument. The surgeon guides the hand-held instrument into the body using the visual feedback. In this form of surgery, a frame is attached to the patient and a scan is taken as described above. After scanning, the head and frame are secured in a fixed position, for example, fixed to an operating table. In order to display the image of the surgical instrument in a proper relationship to the scanned image, the position and orientation of the instrument is sensed using a localization apparatus that remains in a fixed position relative to the body. The localization apparatus can be coupled to the surgical instrument using an articulated mechanical arm on which the surgical instrument is attached. Sensors in the joints of the arm provide signals that are used to determine the location and orientation of the instrument relative to a fixed base of the mechanical arm. Some more recent systems do not use mechanical coupling between the surgical instrument and the localization apparatus and instead rely on remote sensing of small localized energy emitters (e.g., sources or transducers of energy) fixed to the instrument. For example, a camera array is used to locate light-emitting diodes (LEDs) that are attached to the instrument. The locations of the LED images in the camera images are used to determine the three-dimensional physical locations of the LEDs relative to the camera array. The locations of multiple LEDs attached to the instrument are then used to determine the location and orientation of the instrument. Another example of remote sensing uses sound generators and a microphone array and relies on the relative time of arrival of acoustical signals to determine the three-dimensional locations of the sound generators.[0006]
• Before a synthesized image of the instrument can be combined with the scanned image in a proper relationship, some form of registration is required. For example, the tip of the surgical instrument can be placed at each of several fiducial markers for which corresponding images have been located in the three-dimensional scanned image. Registration of the synthesized image of the instrument and the scanned image can thereby be established.[0007]
• In a variant of image-guided stereotactic surgery, generally known as “dynamic referencing,” the head and frame are secured in a fixed position, as in the image-guided approach. However, unlike other image-guided techniques, the sensors (e.g., cameras) of the localization apparatus are not at a fixed location. In order to compensate for the motion of the sensors, energy emitters are fixed to the frame as well as to the instrument. At any point in time, the location and orientation of the frame relative to the sensors as well as the location and orientation of the instrument relative to the sensors are both determined, and the differences in their locations and orientations are used to compute the location and orientation of the instrument relative to the frame. This computed location of the instrument is then used to display the synthesized image of the surgical instrument in an appropriate relationship to the scanned image.[0008]
• Still another approach to stereotactic surgery, generally known as “frameless image-guided” stereotactic surgery, does not rely on attaching a frame to the body before scanning. Instead, adhesive fiducial scanning markers are applied to the scalp, or small screws are inserted into the skull, and the patient is scanned as in the techniques described above. During surgery, the patient is immobilized and locked in place using a head clamp or a frame. The image-guided stereotactic approach described above is then followed, including the registration procedure described above to establish the locations of the fiducial scanning markers relative to the instrument.[0009]
• In image-guided techniques, a surgeon can rely on a variety of views of a three dimensional scanned image. These views can include a three-dimensional surface view with an adjustable point of view (e.g., a perspective view with surface shading). In addition, planar (i.e., two-dimensional) views of the image can be displayed. In particular, three two-dimension “slices” through orthogonal planes of the image are typically displayed, with the orientations of the planes being sagittal (dividing a head into a left and a right part), coronal (dividing a head into a front and a back part), and axial (dividing a head into an upper and lower part). As the orientations of the planes are predetermined, the particular planes that are displayed can be determined by the point of intersection of the three planes. A point, such as the tip of a probe, can be displayed in a three-dimensional surface view as a point in a appropriate geometric relationship. The point can be displayed in a planer view by orthogonally projecting the point onto the associated plane. A line can be displayed in a planar view as an orthogonal projection onto the associated plane, or as the point of intersection of the line and the associated plane. Note that if a first point, such as a surgical entry point is used to determine which planes are displayed, a second point, such as a surgical target point, does not in general fall in any of the displayed planes.[0010]
• Planar views of a three-dimensional scan can also use alternative orientations than the standard sagittal, coronal, and axial orientations described above, allowing two points to lie in two orthogonal planes, and one of the two points to additionally lie in a third orthogonal plane.[0011]
• In particular, a “navigational” view can be determined according to two points in an image, such as an entry point at the surface of a body and a target point within the body.[0012]
• The line joining the entry point and the target point is chosen as the intersection of two orthogonal planes,[0013]navigation planes1 and2. The orientation ofnavigational planes1 and2 is arbitrary (that is, the two planes can be rotated together around their intersecting line). A third plane, orthogonal tonavigation planes1 and2, provides a “bird's eye” view looking from the entry point to the target point. This bird's eye plane is typically chosen to pass through the target point. (Such a navigational view is shown in FIG. 14a). Using a navigational view, the orientation of a surgical instrument is typically shown as a line projected orthogonally onto the two navigational planes, and as the point of intersection of the line and the bird's eye plane. Manipulating an instrument using such a navigational view for feedback requires considerable practice and is not intuitive for many people.
• Image-guided frameless stereotaxy has also been applied to spine surgery. A reference frame is attached to an exposed spinous process during open spine surgery, and a probe is used to register the patient's spine with scanned image of the spine. Anatomical landmarks are used as fiducial points which are located in the scanned image. Visual feedback is provided to manually guide placement of instruments, such as insertion of pedicle screws into the spinal structures.[0014]
SUMMARY
• In one aspect, in general, the invention is a method for positioning a surgical instrument during stereotactic surgery by providing a guidance fixture that includes an upper portion, including an instrument guide for moving the surgical instrument along a constrained trajectory relative to the upper portion, and also includes an adjustable base supporting the upper portion, including a mounting base and an adjustment mechanism. The method includes attaching the guidance fixture to a body, including attaching the mounting base to the body. The method also includes determining, using a remote sensing device, the orientation of the upper portion of the guidance assembly in relation to the body, and displaying a representation of a relationship of the constrained trajectory and a target point in the body. The method also includes aligning the guidance fixture, including aligning the orientation of the upper portion to achieve a desired relation between the constrained trajectory and the target point.[0015]
• The invention can include one or more of the following features.[0016]
• Aligning the orientation of the upper portion includes rotating the upper portion about a central axis of the mounting base and pivoting the upper portion to adjust an angle between the upper portion and the central axis.[0017]
• Determining the orientation of the upper portion includes determining the locations of a first set of tracking markers affixed to the upper portion, determining the locations of a second set of tracking markers affixed to the body, and computing the orientation using the locations of the first and the second sets of tracking markers.[0018]
• The method can include locking the adjustment mechanism to fix the orientation of the upper portion in relation to the body, and then determining a displacement of the surgical instrument along the constrained trajectory. For example, a remote sensing device can be used to locate a tracking marker affixed in a fixed relationship to the surgical instrument, and used to locate a set of tracking markers affixed to the guidance assembly. The displacement can then be computed using the location of the marker affixed in a fixed relationship to the surgical instrument and the locations of the set of tracking markers affixed to the guidance assembly. The method can also include displaying a representation of a location of the surgical instrument in relation to the body, and guiding the surgical instrument into the body along the constrained trajectory.[0019]
• The method can also include attaching to the body a scanning frame that includes a set of scanning markers and then scanning a three-dimensional image of the body, including locating images of the scanning markers in the three-dimensional image. The method then includes attaching to the body a tracking frame that includes a set of tracking markers, and registering the body and the three-dimensional image, including tracking the tracking markers in the tracking frame and locating points on the body corresponding to the scanning markers. The tracking frame can be attached in a predetermined location in relation to the attachment location of the scanning frame. Locating points on the body can be done by tracking the location of a point on a probe using the remote sensing device, and positioning the point on the probe at each of the points on the body corresponding to the scanning markers.[0020]
• Aligning the orientation of the upper portion can include rotating the upper portion about a central axis of the mounting base, and pivoting the upper portion to adjust an angle between the upper portion and the central axis. Displaying the representation of the relationship of the constrained trajectory and the target point then includes displaying a representation of the target point, displaying a representation of the range of possible orientations of the guidance fixture, displaying a first line segment corresponding to possible orientations of the guidance fixture that could result from pivoting the upper portion at a current degree of rotation of the upper portion, and displaying an indication of a current degree of pivoting of the upper portion.[0021]
• In another aspect, in general, the invention is a guidance fixture for guiding a surgical instrument into a body during stereotactic surgery. The fixture includes an upper portion including an instrument guide for moving the surgical instrument along a constrained trajectory relative to the upper portion, and an adjustable base supporting the upper portion, including a mounting base for attaching the guidance fixture to a body, the mounting base having central opening and a central axis passing through the central opening, and an orientation adjustment mechanism coupled between the mounting base and the upper portion, configuration of the adjustment mechanism determine the orientation of the upper portion relative to the mounting base. The guidance fixture can include a set of tracking markers, such as light emitting diodes, that can be located by a remote sensing device, such as an array of camera.[0022]
• The orientation adjustment mechanism of the guidance fixture can include a rotation adjustment mechanism and a pivoting adjustment mechanism, wherein adjustment of the rotation adjustment mechanism rotates the upper portion about the central axis, and adjustment of the pivoting adjustment mechanism adjusts an angle between the upper portion and the central axis. The rotation adjustment mechanism can include a rotating collar attached to the mounting base and the pivoting adjustment mechanism includes a pivoting collar coupling the rotating collar to the upper portion. The adjustable base can further include a rotation locking screw for preventing rotation of the rotating collar and a pivoting locking screw for preventing pivoting of the pivoting collar.[0023]
• The upper portion of the guidance fixture can include an x-y table adjustment of which displaces the constrained trajectory.[0024]
• The instrument guide of the guidance fixture can include a driving mechanism for positioning the instrument along the constrained trajectory, such as a linear trajectory.[0025]
• In another aspect, in general, the invention is a system for stereotactic surgery on a body, which includes a remote sensing device, a tracking frame, including a plurality of tracking markers for tracking a location and an orientation of the body by the remote sensing device, and a guidance fixture. The system also includes a tracking system for accepting the locations of the tracking markers on the tracking frame and the locations of the tracking markers on the guidance fixture, and computing a relationship between the constrained trajectory and the body, and a display system for presenting an image of the body and the relationship between the constrained trajectory and the body.[0026]
• The invention provides several advantages. A highly accurate and reproducible way of guiding a surgical instrument deep into a body is provided without requiring a frame to be fixed to the body for the entire interval from scanning through subsequent surgery. Not requiring the frame to be fixed for this time avoids the inconvenience, discomfort, and inefficiency of placement of a fiducial frame on a patient. Inaccuracy imparted to an MRI scan by electromagnetic interaction with a reference frame or to a CT scan by x-ray interaction with the frame is also improved. Furthermore, by providing a compact and relatively lightweight guidance fixture, the patient is not required to the be immobilized during surgery and therefore may not require general anesthesia or heavy sedation. This can allow immediate determination of the response to a surgical intervention in behavioral or physiological terms without interference of general anesthesia or heavy sedation. In addition, both the patient and the sensors used to locate a patient and a surgical instrument can be mobile providing further flexibility in operating procedures.[0027]
• An additional advantage is that the invention does not require immobilizing (i.e., clamping in a fixed position) the patient. This contributes to patient comfort which can extend the time a surgical procedure can be carried out. Furthermore, since a guidance fixture is not attached until a scan has been made, surgical time is further extended as discomfort generally relates to having a guidance fixture attached. Also, alignment of the guidance fixture is made easier with this invention, and therefore, less time can be spent on alignment, thereby leaving more time for the actual surgical procedure.[0028]
• Another advantage of the invention is that alignment of the guidance fixture is performed using motions, each of which is constrained to one degree of freedom (e.g., rotation or pivoting). When the two motions are clamped in position, this arrangement provides a relatively stable alignment compared to alternative arrangements in which a two degree of freedom motion (such as alignment of a ball and socket arrangement) is clamped.[0029]
• Yet another advantage of the invention is that the constrained motions of the guidance fixture, that is, the rotation and pivoting motions, are directly reflected in the computer displayed navigational view, thereby greatly simplifying targeting.[0030]
• Other features and advantages of the invention will be apparent from the following description, and from the claims.[0031]
DESCRIPTION OF THE DRAWING
• FIG. 1 is a flowchart of a stereotactic brain surgery procedure;[0032]
• FIG. 2 is a head with threaded inserts implanted including a cross-sectional view of the skull and a threaded insert;[0033]
• FIG. 3 is a head with a scanning MIRRF attached including a detailed exploded view of the attachment of the MIRRF to the implanted threaded inserts;[0034]
• FIG. 4 illustrates scanning of a head on which a scanning MIRRF is attached;[0035]
• FIG. 5 is a head with a tracking MIRRF attached and a cranial probe being tracked using a camera array;[0036]
• FIG. 6 is a dataflow diagram for computation of a composite image including a synthesized image of a probe;[0037]
• FIG. 7 illustrates locating a planned entry point using the tracked cranial probe and a computer display;[0038]
• FIG. 8 is a display of a virtual burr hole and accessible cone of orientations;[0039]
• FIG. 9 is a head with a tracking MIRRF and a guidance fixture attached being tracked using a camera array;[0040]
• FIG. 10 is a view of a base platter and an adjustable base of a guidance fixture;[0041]
• FIG. 11 is an exploded view of the adjustable base of a guidance fixture;[0042]
• FIG. 12 is a dataflow diagram for computation of a composite image including a synthesized image of a surgical instrument;[0043]
• FIG. 13 is a detailed flowchart of trajectory replanning and fixture alignment;[0044]
• FIGS. 14[0045]a-cillustrate a navigational view display and corresponding planar segments through a body;
• FIGS. 15[0046]a-fillustrate a “field of view” display and corresponding conical section through a body;
• FIG. 16 is a guidance fixture including an adjustable base and an instrument drive attached to a base platter;[0047]
• FIG. 17 is a retractor in a guidance fixture;[0048]
• FIG. 18 is a calibration jig;[0049]
• FIG. 19 is a phantom jig and a guidance fixture and a tracking MIRRF attached to the jig;[0050]
• FIG. 20 is an arc shaped MIRRF attached to a head including a view of a threaded insert and mounting bolt;[0051]
• FIG. 21 is a scanning marker and a tracking marker attached to a threaded insert;[0052]
• FIG. 22 is a guidance fixture and a tracking MIRRF attached to a conventional stereotactic frame; and[0053]
• FIG. 23 is a tracking MIRRF attached directly to a guidance fixture.[0054]
DESCRIPTION
• Referring to FIG. 1, an aspect of the invention relates to stereotactic brain surgery. This approach to brain surgery involves a series of steps, shown in FIG. 1, from[0055]start100 prior to scanning throughfinish199 after the surgical phase of a procedure is completed. There are generally two phases to the approach. The first phase involves creating a three-dimensional image of the head (steps105,110,115,120), planning a surgical trajectory based on the image (step125), and validating the guidance fixture (step130) that will be used during the surgical procedure. The second phase involves the remaining steps (steps135 through195) that are used to carry out the actual surgical procedure. The steps of the first phase can be carried out quite some time before those of the second phase. For example, creating the three-dimensional image of the head can be done on one day, and the steps used to carry out the actual surgery can be done on a subsequent day. Also, the steps of the second phase may be repeated, for example on several different days, illustrated bytransition192 betweensteps195 and135.
• One to three days prior to surgery, the patient is seen in a post anesthesia care unit (PACU) or other suitable location. Referring to FIG. 1, the first step of the procedure is to attach anchors to which scanning, registration, and tracking markers will be subsequently attached (step[0056]105). Referring to FIG. 2, the anchors include two threadedinserts220 that are surgically implanted into the patient'sskull210 using a template (described below). The template precisely determines the separation and parallel orientation ofinserts220.
• Referring to FIG. 3, a rigid cross-shaped device, a scanning “miniature removable reference frame” (scanning MIRRF)[0057]310, is next attached to threadedinserts220 using screws320 (FIG. 1, step110). Aretention plate330 is used to aid precise reattachment of scanningMIRRF310 to the skull.Retention plate330 is also used as the template during insertion of threaded inserts220. ScanningMIRRF310 includes fourfiducial scanning markers340 that will be visible in the scanned image. ScanningMIRRF310 is made from a material that is chosen to interfere as little as possible with the type of scan that will be performed. For example, for MRI and CT scans, the chosen material can be polycarbonate, which results in scanningMIRRF310 being almost invisible in the scanned image.Fiducial scanning markers340 are mounted in spherical cavities in scanningMIRRF310. The design of the cavities is such that the “press-in” marker inserts can be removed for cleaning. The star-shaped design ofscanning MIRRF310 is such that, when attached, the elongated part of the star extends behind or in front of the ear so that mountingscrews320 are located toward the top of the skull where soft tissue thickness is minimal and skull thickness is maximal. This minimal tissue thickness allows threadedinserts220 to be implanted easily under local anesthetic by making a small incision. As an alternative to attaching a single MIRRF as shown in FIG. 3, multiple MIRRFs can be attached in a similar manner to increase the number or separation of the scanning markers.
• Referring to FIG. 4, MRI or[0058]CT scanner400 is used to obtain a three-dimensionaldigitized image410 of the head, for example, as a series of two-dimensional “slices” (step115 in FIG. 1). In addition, a model or map of the surface of the skull can be made allowing, for instance, subsequent three-dimensional surface display of the skull. Thefiducial scanning markers340 producefiducial images420 at inimage410. Fiducial coordinates421 offiducial images420 in the coordinate system ofimage410 are determined, for example, by manually positioning a cursor atfiducial images420 on a computer display.Image410, along with thefiducial coordinates421, are stored on a computerreadable storage medium430 for use during the subsequent surgical phase of the approach. Typically the image is stored as a series of two-dimensional images, each corresponding to a horizontal “slice” of the head.
• After scanning, scanning[0059]MIRRF310 is removed (FIG. 1, step120), and threadedinserts220 are left in place. Antibiotic ointment can be applied and the patient is either discharged or sent to the operating room.
• Also after scanning, a surgeon determines the location of a target point within the brain and an entry point through the skull (FIG. 1, step[0060]125). A planned surgical trajectory is then determined as the line joining the entry point and the target point. The surgeon plans the trajectory using a computer display ofimage410 which provides, for example, a three-dimensional surface view, and sagittal, coronal, and axial planar views. This allows the surgeon, for example, to plan a trajectory that avoids critical structures in the brain. The target and entry points, and the trajectory are stored along with the image onstorage medium430.
• Other than an optional fixture validation (FIG. 1, step[0061]130), all the preoperative steps are complete at this point.
• Referring to FIG. 5, the surgical phase of the procedure begins by attaching a tracking[0062]MIRRF510 to threaded inserts220 (not shown) that remained implanted in the patient's skull after scanningMIRRF310 was previously removed.Tracking MIRRF510 has a very similar structure to scanningMIRRF310.Tracking MIRRF510 includesfiducial divots540 at the centers of locations corresponding to fiducial markers340 (shown in FIGS. 3 and 4). Four trackingLEDs550 are also attached to trackingMIRRF510. Since trackingMIRRF510 is rigid, the geometric relationship between trackingLEDs550 andfiducial divots540 is fixed and can be determined beforehand and verified in a subsequent verification step, or can be unknown and determined in a subsequent registration step. Preferably, trackingMIRRF510 is made of a material that is lightweight and can be autoclaved, such as Radel.
• After attaching tracking[0063]MIRRF510 to the patient's skull, the patient can be comfortably placed in an awake, possibly lightly sedated, state in an operating room chair, which is similar to a dental chair. The patient is allowed to recline in an essentially unrestrained manner in the operating room chair in a semi-sitting position. Alternatively, at the surgeon's prerogative and if appropriate, general anesthesia can be administered to the patient.
• Referring still to FIG. 5, a[0064]camera array560 provides time-varyingdigitized images586 to alocalization application588 executing on acomputer workstation580. The patient can be free to move relative tocamera array560 and relative to the operating room chair, andcamera array560 can be free to move relative to the patient and relative to the operating room chair.Camera array560 includes threeCCD cameras562 positioned in a fixed configuration relative to one another. Alternatively, two cameras, which are sufficient for three dimensional localization, or more than three cameras, which may provide greater accuracy, can be used. Eachcamera562 incamera array560 produces one time-varying image. Each trackingLED550 on trackingMIRRF510 is powered and emits infra-red illumination which is seen as a bright point in each of time-varyingdigitized images586. Based on the relative coordinates of the bright points inimages586 from eachcamera562 ofcamera array560localization application588 computes the position (i.e., the coordinates) of trackingLEDs550 in the coordinate system ofcamera array560. Using the positions ofmultiple tracking LEDs550, the location and orientation of trackingMIRRF510 can be computed bylocalization application588. Tracking of MIRRF coordinates510 is illustrated schematically byline564.
• A[0065]cranial probe570, including threeprobe LEDs572 attached along its length, is also tracked usingcamera array560 andlocalization application588. Based on the coordinates of the images ofprobe LEDs572 inimages586 andprobe geometry584,localization application588 computes the position and orientation ofprobe570 in the coordinate system ofcamera array560.
• Using[0066]cranial probe570, the surgeon then carries out a registration step (FIG. 1, step140). In this registration step, the surgeon first locates the fiducial points in the image. Then he touches the tip ofprobe570 to each offiducial divots540 in trackingMIRRF510 in turn, indicating tolocalization application588 when he is touching each of the divots.Localization application588 then computes a three-dimensional conformal registration (map) betweenimage410 and the coordinate system of trackingMIRRF510.
• Note that if the geometric relationship of tracking[0067]LEDs550 andfiducial divots540 is known tolocalization application588, for example using a previously calibrated MIRRF, the coordinates of the fiducial divots can be computed from the coordinates of the tracking LEDs, which in turn can be computed from the locations of the fiducial images in the camera images. The step of touching the divots can be omitted in this case, or used to verify the computed coordinates of fiducial divots.
• Having computed the conformal mapping,[0068]localization application588 continuously combinesimage410 and a synthesized image ofprobe570 to form acomposite image599 that combines the scanned image with the synthesized image of the probe.Composite image599 is shown on acomputer display610 which includes a three-dimensional surface display.
• Referring to FIG. 6, the registration and image composition functions performed by[0069]localization application588 involves a series of data processing stages. As shown in FIG. 5, time-varyingdigitized images586 are provided tolocalization application588 fromcamera array560. Referring to FIG. 6, time-varyingdigitized images586 are input to MIRRF tracking591, a processing stage oflocalization application588, which tracks trackingLEDs550 on trackingMIRRF510 and produces “MIRRF/cam”593, an orientation and location of trackingMIRRF510 in the coordinate system ofcamera array560. At the same time, probe tracking590tracks probe570 and produces “probe/cam”592, an orientation and location ofprobe570 in the coordinate system ofcamera array560. Probe tracking590 makes use ofprobe geometry584 which specifies the geometric relationship between the tip of theprobe570 and probeLEDs572. The next stage oflocalization application588,relative positioning594 inputs MIRRF/cam593 and probe/cam592 and produces “probe/MIRRF”595, the position and orientation ofprobe570 in the coordinate system of trackingMIRRF510. When the surgeon touchesfiducial divots540,registration581 takes the location information from probe/MIRRF595 and records it in “fids/MIRRF”582, the coordinates offiducial divots540 in the coordinate system of trackingMIRRF510. Fiducial coordinates421, the coordinates offiducial images420 in the coordinate system ofimage410, are provided tolocalization application588, along withimage410, fromstorage medium430.Mapping587 includes matching of corresponding coordinates in fids/MIRRF582 andfiducial coordinates421 and forming aconformal map589 between the coordinate system ofimage410 and the coordinate system of trackingMIRRF510.Conformal map589 includes the quantities required to transform any three-dimensional coordinate in the coordinate system of trackingMIRRF510 into a three-dimensional coordinate in the coordinate system ofimage410. These quantities correspond, in general, to a rotation, scaling, and translation of points in the coordinate system of trackingMIRRF510 to determine the corresponding points in the coordinate system ofimage410.
• Referring still to FIG. 6, the next stage of[0070]localization application588,probe mapping596, takes the continually updated probe coordinates, probe/MIRRF595, andconformal map589, and computes probe/image597, the coordinates ofprobe570 in the coordinate system ofimage410. Then,image composition598 combinesimage410 and a synthesized image ofprobe570 to formcomposite image599.
• [0071]Composite image599 typically includes a three-dimensional surface view and three orthogonal planar views.
• The orthogonal planar views can correspond to the three standard orientations, sagittal, coronal, and axial planes, for instance passing through the planned target point. More typically, three planar views of a navigational view that is determined by the planned entry and target points are included in[0072]composite image599. The tip of the probe is displayed as an orthogonal projection onto the planes of the planar views, and as a point in an appropriate geometric relationship in the three-dimensional surface view. The orientation of the probe can be displayed using a line passing through the tip of the probe and displayed as a orthogonal projection ontonavigational planes1 and2 of the navigational view, and as a point of intersection on the bird's eye view of the navigational view.
• If the geometric relationships of the fiducial points, fids/[0073]MIRRF582, the coordinates offiducial divots540 does not match the geometric relationships offiducial coordinates421, then an error in placingprobe570 during the registration procedure may have occurred. If such an error is detected,conformal mapping589 is not computed, a warning is provided to the surgeon, and the surgeon must perform the registration procedure again. Furthermore, if the geometric relationships betweenfiducial divots540 is known through prior measurement or calibration, registration errors and errors locatingfiducial points420 inimage410 can also be detected.
• Referring to FIG. 7, a[0074]cranial probe570 is used to determine an actual entry point. Acomputer display610 showscomposite image599, which includes a three-dimensional surface view and three planar views of a navigational view determined by the planned entry and target points.
• Referring to FIG. 8, a[0075]virtual burr hole640 is displayed in the planar views of navigational view at theprobe location642 ofcranial probe570. In addition, the range of adjustable orientations of a guidance fixture that would be attached atprobe location642 is displayed as acone644, and the extent of effects of x-y adjustment of the guidance fixture is displayed as asecond cone646. Display ofcones644 and646 allows the surgeon to verify that plannedtarget point650 is accessible in the range of adjustments of a guidance fixture attached atprobe location642.
• When the surgeon has located an[0076]entry point620 on the skull, he marks the entry point as the desired center point of attachment of a guidance fixture that will be used during the surgical phase of the procedure.
• The patient then has a small area of the head shaved and draped off. A 2 to 4 cm linear incision is made over[0077]entry point620 after local anesthesia is administered. The location ofentry point620 is then reconfirmed usingcranial probe570 after the incision is made. An approximately 1 cm burr hole (not shown in FIG. 7) is then drilled through the skull at entry point620 (FIG. 1, step150). The surgeon opens the dura under the burr hole and visually inspects the area to determine that no critical structures, such as a blood vessel, are located directly under the burr hole. If the location of the burr hole is found to be unacceptable, a new entry point can be planned and return to the step of locating the entry point (FIG. 1, step145).
• Referring to FIG. 9, having drilled the burr hole, the surgeon next attaches a[0078]guidance fixture710 to the skull (FIG. 1, step155). (Note that an optional instrument drive can also included in the guidance fixture but is not shown in FIG. 9.) As is described more fully below,guidance fixture710 includes abase platter720 on whichplatter LEDs730 are attached.Base platter720 is attached to anadjustable base715, which is in turn attached to the skull. The orientation of a line normal tobase platter720 is adjustable within a cone forming a solid angle of approximately 45 degrees. After attachingguidance fixture710 the surgeon adjusts the orientation of base platter720 (FIG. 1,step170; note thatoptional steps160 and165 are described below). Asurgical instrument740, including aninstrument LED742 fixed relative to the instrument, passes throughguidance fixture710.Surgical instrument740 is constrained to follow a fixed trajectory perpendicular to and through a central opening through adjustedbase platter720.Workstation580 tracks the location and orientation ofbase platter720, and the displacement ofsurgical instrument740, indicated schematically bylines564 and750 respectively, and computes the position ofsurgical instrument740 in the coordinate system ofimage410.Workstation580 continually displays on display610 acomposite image750 including a navigational view ofimage410 showing the position and orientation ofsurgical instrument740. The surgeon uses the visual feedback ondisplay610 to positionsurgical instrument740 along the constrained trajectory. Note that during this time, the patient is not necessarily immobilized. Both the patient andcamera array560 can move and, as long asplatter LEDs730 andinstrument LED742 are visible tocamera array560 at an appropriate distance and orientation,workstation580 can maintain a continuously updated display.
• Referring to FIG. 10,[0079]guidance fixture710 includesbase platter720 andadjustable base715. In use,base platter720 is attached to an entry column850 (through an x-y positioning table1150, described fully below) which is held inadjustable base715. The orientation ofentry column850 can be adjusted relative toskull210 using separate rotation and pivoting motions, as described below.
• Referring also to the exploded view of[0080]adjustable base715 shown in FIG. 11,guidance base715 includes a mountingbase820, which is rigidly attached to the skull during an operation using screws through mountingholes822. Mountingholes822 pass through mountingtabs723 as well as through the inside of the mountingbase820. Mounting tabs823 are pliable to allow them to conform to the skull. As mountingbase820 may be distorted in being mounted to the skull, it can be designed to be disposable. Mountingbase820 has a cylindrical opening which accepts arotating collar830. Arotation locking screw824 in mountingbase820, when tightened,locks rotating collar830 in place and prevents its movement within the mounting base.Entry column850 is held withinrotating collar830 by apivoting collar840. Pivotingcollar840 slides in an arc-shapedpivoting guide841 withinrotating collar830. When rotated, apivoting locking knob846 prevents pivotingcollar840 from sliding by drawing acollar clamp842 against pivotingcollar840 using a threadedrod920. When rotated, a pivotingadjustment knob844slides pivoting collar840 along pivotingguide841.
• Referring again to FIG. 11, mounting[0081]base820 includes mountingholes822 drilled through mounting tabs723 (one tab is not visible on the side opposite the visible one), as well as through the inside of mountingbase820. Mountingbase820 includes a threadedhole922 within whichrotation locking screw824 turns.Rotation locking screw824 mates with a recessedchannel923 inrotating collar830, thereby preventing rotation ofrotating collar830 and also preventingrotating collar830 from lifting off mountingbase820.
• [0082]Entry column850 includes acylindrical portion913 and aspherical portion914 at one end.Spherical portion914 mates with aspherical socket916 in the bottom ofrotating collar830. When mated,entry column850 can pivot withinrotating collar830.Entry column850 also has opposinggroves910 which mate withprotrusions912 on the inside of the circular opening in pivotingcollar840.Entry column850 passes through the circular opening, andprotrusions912 mate withgroves910. When assembled, the mated groves and protrusions hold thespherical portion914 ofentry column850 againstspherical socket916 in the bottom ofrotating collar830.
• The position of pivoting[0083]collar840 within pivotingguide841 is adjusted by turning pivotingadjustment knob844 and tightened in place by rotatingpivoting tightening knob846. Pivotingadjustment knob844 attaches to a pivotingadjustment rod930 which passes throughcollar clamp842 and the main portion of pivotingcollar840 to a rack and pinion mechanism. Apinion931 is attached to the end pivotingadjustment rod930.Pinion931 mates with an arc-shapedrack932 which attaches torotating collar830 using threescrews934. Rotation of pivotingadjustment knob844 rotates pivotingadjustment rod930 andpinion931, which then slides pivotingcollar840 in pivotingguide841.
• Rotating[0084]pivoting locking knob846locks pivoting collar840 rigidly torotating collar830. Tightening bothrotation locking screw824 and pivotinglocking knob846 fixes the orientation ofentry column850 relative to mountingbase820.
• Referring to FIG. 10, the procedure for attaching and adjusting guidance fixture[0085]710 (FIG. 1,steps155 through170) is carried out as follows. Mountingbase820 is attached in a temporary fashion overburr hole625. While attaching the base, mountingtabs723 are conformed to the shape of theskull210 and secured to the skull an orientation generally directed towards the target using three or more titanium bone screws724 passing through mountingholes822 through mountingtabs723 and through the interior of the mounting base.
• After mounting[0086]base820 is attached toskull210, the remainder ofguidance base715 is attached to mountingbase820. In particular, rotatingcollar830, withentry column850 already attached, and adjusted to be centered (oriented along the central axis of guidance base715) is inserted in mountingbase820 androtation locking screw824 is tightened to mate with recessedchannel923.
• After[0087]guidance base715 is attached toskull210, the remainder ofguidance fixture710 is attached toguidance base715. In FIG. 10, the drive assembly, which is already attached tobase platter720 at thetime base platter720 is attached toguidance base715 is not shown.Base platter720 is attached toentry column850 via an x-y positioning table1150 (described below). During the alignment phase in which the orientation ofguidance base715 is adjusted, x-y positioning table1150 remains centered.
• During a surgical procedure,[0088]surgical instrument740 is passed through acentral opening721 ofbase platter720 and throughentry column850 into the brain. During the alignment phase in which x-y table1150 is centered, a line along the trajectorysurgical instrument740 would follow passes along the central axis ofentry column850. Adjusting the orientation ofguidance base715 adjusts this trajectory. In all orientations, the trajectory passes through a single point on the central axis ofguidance base715 near the surface of the skull. If the guidance base is exactly mounted over the planned entry point, this single point is the planned entry point. More typically, the point is slightly displaced from the planned entry point due to mounting inaccuracies.
• Referring again to FIG. 9,[0089]platter LEDs730 onbase platter720 are sensed bycamera array560, and the location and orientation ofbase platter720 in the coordinate system ofimage410 is computed bylocalization application588 executing oncomputer workstation580.Localization application588 computes the location and orientation ofbase platter720 using the known geometry of the base platter relative toplatter LEDs730.
• Referring to FIG. 12,[0090]localization application588 computes composite image750 (FIG. 9) in a series of data transformations. Time-varyingdigitized images586 are passed to MIRRF tracking591 as well as platter tracking7010 and instrument tracking7012. MIRRF tracking591 produces “MIRRF/cam”592, the position and orientation of trackingMIRRF510 in the coordinate system ofcamera array560.Platter tracking7010 produces “platter/cam”7020, the position and orientation ofbase platter720. The instrument trajectory is at a known location and orientation relative toplatter LEDs730 onbase platter720, therefore the location and orientation of the instrument trajectory in the coordinate system ofcamera array560 is also known.Instrument tracking7012 produces instrument/cam7022, the location ofinstrument LED742 in the coordinate system ofcamera array560.Platter localization7030 usesconformal map589, MIRRF/cam593, and platter/cam7020 to compute platter/image7040, the location and orientation ofbase platter720 in the coordinate system ofimage410. Note that onceguidance fixture710 is attached and aligned, thenbase platter720 no longer moves relative to the skull (other than due to adjustment of x-y table1150) and therefore, platter/image7040 can be fixed rather than continuously recomputed.Instrument depth measurement7032 combines platter/cam7020 and instrument/cam7022 to compute instrument/platter7042, the depth of penetration of the surgical instrument relative to the plane ofbase platter720.Instrument depth measurement7032 makes use of the known displacement of the tip of the instrument frominstrument LED742.Instrument localization7050 takes platter/image7040 and instrument/platter7042 and computes instrument/image7060, the location and orientation of the surgical instrument in the coordinate system ofimage410. Finally,image composition7070 combinesimage410 with a synthesized image of the surgical instrument to generate acomposite image750.
• Referring to FIG. 13, before aligning[0091]guidance fixture710, the surgical trajectory is optionally replanned to go through the center of the actual mounted position of the guidance fixture, rather than the planned entry point (FIG. 1, step165).
• The surgeon aligns[0092]guidance fixture710 using visual feedback. Referring to FIGS. 14a-c,a navigational view indicating the trajectory of the surgical instrument is used. Referring to FIG. 14a,navigational planes1020 and1022 correspond to navigationalplanar views1030 and1032 respectively.Navigational planes1020 and1022 are orthogonal and their intersection forms a line passing through anentry point1010 and atarget point1012. Bird'seye plane1024, the third plane of the navigational view, is orthogonal toplanes1020 and1024 and passes throughtarget point1012.
• Referring to FIG. 14[0093]b-c,navigational planes1020 and1024 are shown schematically, along with aline1040 corresponding to the orientation ofguidance fixture710. The goal of the alignment procedure is to makeline1040 coincident with the intersection ofplanes1020 and1022. The alignment procedure is carried out in a series of two motions each of which is constrained to one degree of freedom. Initially,line1040 is not generally coincident with either navigational plane. Prior to beginning the alignment procedure, the orientation ofline1040 is displayed as orthogonal projections,lines1041 and1042, onplanes1020 and1022, respectively.
• In the first alignment motion, rotating[0094]collar830 is rotated within mounting base820 (FIGS. 10 and 11). Referring to FIG. 14b,this rotation causesline1040 to sweep out a portion of a cone, indicated diagrammatically by dashedarrow1050. After rotation through an angle ö₁,orientation line1040 is in the direction ofline1043, which is coincident withplane1022. During the rotation, theorthogonal projection line1041 ofline1040 inplane1020 forms a smaller and smaller angle è₁with the desired orientation inplane1020, while the angle è₂between theorthogonal projection line1042 inplane1022 and the desired orientation inplane1022 increases, ultimately to ö₂whenline1040 is coincident withplane1022.
• Referring to FIG. 14[0095]c,the second alignment motion reduces the angle ö₂while maintaining the coincidence of the orientation line andplane1022. This motion corresponds to slidingpivoting collar840 within rotating collar830 (FIGS. 8 and 9). Alignment is achieved when angle ö₂is zero, that is, theorientation line1040 is coincident with the intersection ofplanes1020 and1022.
• At this point, after tightening the locking knobs on[0096]guidance fixture710,base platter720 is firmly fixed to the skull, in an orientation and location that constrains a surgical instrument passing through it to pass along the replanned trajectory to the planned target point in the head.
• In addition to, or as an alternative to, using a navigational view to provide visual feedback during the alignment procedure, a “field of view” display can be provided. Referring to FIGS. 15[0097]a-f,the field of view display uses a representation of a cross-section of a cone extending below the entry point. Referring to FIG. 15a,the central axis of acone1061 is coincident with the central axis of the mounting base of a guidance fixture mounted at anentry point1010. That is, the central axis of the cone is generally perpendicular to the surface of the skull at the entry point. The angle of the cone corresponds to the range of possible alignments of a guidance fixture mounted at the entry point. In this embodiment, this is a 45 degree angle. The cross-section is normal to the central axis of the cone, and passes through atarget point1012. Referring to FIG. 15b,the corresponding display shows acircular section1070 of the scanned image. Thecenter1011 and thetarget point1012 are indicated. Also indicated are two orthogonal axes. Anaxis1072 corresponds to the achievable orientations of the guidance fixture as its pivoting collar is moved in the rotating collar. Anotheraxis1074 is orthogonal toaxis1072. Motion of the rotating collar rotates the orientation ofaxes1072 and1074. These axes can be thought of as intersections of the navigational planes with the bird's eye plane of a navigational view, although here, the intersecting lines rotate with the rotation of the guidance fixture while in the navigational view, the navigation planes remain fixed as the guidance fixture is rotated. Referring to FIG. 15c,after an appropriate rotation,axis1072 passes throughtarget point1012. FIG. 15dshows the display after this rotation. Motion of the pivoting collar is indicated by aline1076, parallel toaxis1074. If the pivoting collar is centered, thenline1076 is aligned withaxis1074, as is shown in FIG. 15d.When the guidance fixture is aligned with the target point,line1076 passes through target point1064, as doesaxis1072. FIG. 15f,corresponding to FIG. 15e,shows the display after alignment is achieved. This circular field of view display provides intuitive visual feedback to the surgeon who is aligning the guidance fixture. Furthermore, displacement of the x-y table can also be shown in such a field of view display, by indicating the intersection of the resulting instrument trajectory on the circular display.
• Referring to FIG. 16, an[0098]instrument drive1110 is attached tobase platter720 prior to attaching the combination ofinstrument drive1110,base platter720, and x-y table1150 toguidance base715. In FIG. 16,instrument drive1110 is shown partially mounted onto adrive post1120. Prior to attachment toguidance base715,drive post1120 is fully inserted intoinstrument drive1110 so thatinstrument drive1110 is in contact withbase platter720.Base platter720 can be displaced relative toguidance base715 in a plane orthogonal toentry column850 using twoperpendicular adjustment screws1060, and1062 turned by x-ytable adjustment knobs1061, and1063. Note that prior to alignment (FIG. 1, step170) the x-y table is adjusted so thatcentral opening721 inbase platter720 is centered overentry column850.
• [0099]Instrument drive1110 includes adrive platform1130 that moves within adrive mechanism1125 along a threadedrod1132. Threadedrod1132 is oriented parallel to drivepost1120 and perpendicular tobase platter720. In this embodiment, rotation of threadedrod1132, which causes displacement ofdrive platform1130, is manual using a mechanism that is not shown. Alternative embodiments can use an electronic stepper motor or a manual hydraulic drive to rotate threadedrod1132 and thereby displacedrive platform1130.
• In operation, a surgical instrument, such as a micro-electrode, is passed into the brain through a guidance tube. After alignment of[0100]guidance fixture710, the guidance tube is manually inserted into the brain throughcentral opening721 inbase platter720. The guidance tube is then secured inclamp1135 that is fixed relative to drivemechanism1125. The instrument is passed into the guidance tube and is secured in aclamp1133, which is fixed relative to driveplatform1130.
• [0101]Instrument LED742 is attached to driveplatform1130. The displacement of the end of the surgical instrument frominstrument LED742 is known tolocalization application588 which executes onworkstation580. By tracking the position ofinstrument LED742, as well asplatter LEDs730, the position of the end of a surgical instrument onworkstation580 and displayed on display610 (FIG. 9) to the surgeon. The surgeon then uses this visual feedback in adjusting the depth of the instrument.
• Various types of surgical probes or instruments can be attached to drive[0102]mechanism1110 shown in FIG. 16. One type of instrument is an electrode, such as a recording micro-electrode or a stimulating electrode or lesioning electrode. The electrode is introduced into a rigid insertion (guidance) tube that is attached to drivemechanism1110. Another type of instrument is a hypothermia cold probe.
• In cases of movement disorder or pain surgery, a chronically implanted stimulating electrode can be placed utilizing an insertion tube. The lead, being of a smaller diameter than the insertion tube, can be slipped through the insertion tube upon removal of the drive and guide assembly, to allow fixation of the chronically implanted electrode into the brain. The electrode is secured to the skull using a compression-fitting. A chronically implanted recording electrode can similarly be placed during epilepsy surgery to monitor abnormal activity within the deep brain utilizing similar techniques.[0103]
• In cases of hydrocephalus or other situations where chronic drainage of intracranial cavities is necessary, a shunt tube, such as a ventricular shunt, can be applied through the insertion tube into the target such as the ventricles of the brain. The shunt tube will have a stylet and be slipped into the insertion tube.[0104]
• The insertion tube structure and its retention ring will have varying diameters, depending on the diameters of the various objects that can be placed in the insertion tube, such as the shunt tube, in this application, or micro-electrodes, in the prior application. The insertion tube, therefore, will be connected to the drive mechanism using varying sized retention rings. The shunt will be directed towards the target established by the software mechanism alluded to above. The shunt tube will then be secured to the skull via mechanisms described in prior art, or via a compression fitting described above.[0105]
• Alternatively, a biopsy probe can be inserted into the insertion tube by first placing a biopsy tube with a trocar/obturator through the insertion tube. The mechanism would then be directed down towards the appropriate target using the drive mechanism. The obturator would be removed, and a cutting blade will then be inserted into the biopsy tube.[0106]
• In applications in which a radioactive seed for brachytherapy, a targeting nodule with a radio sensitizing, chemotherapeutic agent for external beam radiation, or a sustained release polymer drug or microdialysis capsule for local drug administration, are required for placement in a deep brain target, a different insertion tube can be connected to the[0107]drive mechanism1110. A delivery catheter can be placed through the insertion tube. The whole mechanism can be directed towards the deep target using the software system as alluded to above. An insertion plunger can be used to insert the object of delivery and the system is then be removed after insertion of the object. A micro-endoscope can also be inserted through the insertion tube mechanism described above and deep brain structures can be visualized prior to excision or lesioning.
• In certain surgical procedures, it is desirable to drive a surgical instrument along several parallel tracks. This is facilitated using x-y table[0108]1150. Before an instrument is driven toward the target, an offset is adjusted usingadjustment knobs1061, and1063. These knobs include markings that allow precise adjustment.
• An example of a procedure using penetration of an instrument along parallel tracks involves mapping the electrical activity of a region of the brain. The surgical instrument in this case is a thin electrode that is repeatedly inserted to points on a two- or three-dimensional grid. At each point, electrical activity is monitored.[0109]
• Referring to FIG. 17, when larger masses within the brain, such as brain tumors, have to be removed with precision, the drive mechanism has a localizing[0110]surgical retractor1210 mounted in place of the insertion tube, andbase platter1220 has a large central opening through which the retractor passes.Retractor1210 includes three ormore spatulas1212 inserted throughbase platter1220 and the entry column. Eachspatula1212 includes atracking LED1214 attached to it. The relationship of the spatulas is controlled by ascrew assembly1216 that allows the relative distance between the spatulas to be modified. Relatively small movement at the screw assembly results in a larger movement at the other ends of the spatulas due to the pivoting of the spatulas within the retractor.Tracking LEDs1214 are tracked by the camera array and the localization application computes the depth ofspatulas1212 and their displacement from the central axis. Using the tracking approach described above,surgical localizing retractor1210 is directed towards the brain target. Upon acquiring the target,screw assembly1216 is adjusted to expand localizingretractor1210 to allow visualization of the underlying brain. A variety of surgical instruments can be attached toretractor1210 in addition to using the retractor with more conventional manual techniques. These instruments can include an endoscope, an ultrasonic aspirator, an electronic coagulation/evaporator/ablator, or a laser.
• An optional fixture validation step (FIG. 1, step[0111]130) can be used to confirm that the position of the tip of the surgical instrument is accurately tracked. Two types of validation can be performed. Referring to FIG. 18,guidance fixture710 is attached to anupper mounting plate1334 of acalibration jig1330. Prior to attachingguidance fixture710 tocalibration jig1330, pivoting locking knob846 (FIG. 10) is loosened allowing pivotingcollar840 to pivot. Afterguidance fixture710 is attached, pivotingcollar840 is centered and pivotinglocking knob846 is tightened. Aguidance tube1340 is clamped into the guidance fixture, and asurgical instrument1342 is passed through the guidance tube.Guidance tube1340 protrudes below upper mountingplate1334. Aruler1335 can then be used to measure the depth of penetration of the guidance tube. Similarly,ruler1335 can be used to measure the penetration ofsurgical instrument1342.
• Referring to FIG. 19, a validation (or “phantom”)[0112]jig1312 can also be used.Tracking MIRRF510 is attached tovalidation jig1312.Guidance fixture710 is be mounted onvalidation jig1312. Aphantom target point1320 at a known position relative tovalidation jig1312, and therefore at a known position relative to the fiducial points on trackingMIRRF510, is chosen. Thelocalization application588 is programmed with the phantom target position. Using the procedure that will be used during the surgical phase, the surgeon performs the registration and alignment steps and then drives the instrument throughguidance fixture710. If the tip of the instrument is coincident with the phantom target point, thenguidance fixture710 is validated. If for some reason the instrument is not coincident with the phantom target point, for example, due to improper attachment of the instrument to the drive assembly resulting in an incorrect depth calibration, the surgeon readjusts the instrument and attempts the validation step again.
• Other embodiments of the invention use alternative scanning, registration, and tracking markers, and methods of scanning and registration.[0113]
• In the first embodiment, scanning[0114]MIRRF310 and trackingMIRRF510 are star-shaped. Other alternative shapes of MIRRFs can be used. Referring to FIG. 20, an arc-shapedMIRRF1410 is attached to threadedinserts1420 usingbolts1430, and marking and locking nuts1432. Arc-shapedMIRRF1410 includes scanningfiducial markers1412. The fiducial markers are more widely spaced than in star-shapedMIRRFs310, and510, resulting in a more accurate tracing of the MIRRF. During insertion of threadedinserts1420, arc-shapedMIRRF1410 acts as a template for accurate positioning of the threaded inserts.
• In embodiments described above, threaded inserts are inserted into the skull to provide the fixed points of attachment for MIRRFs. Alternative embodiments use other types of anchors or forms of mechanical attachment. Protruding posts can be attached to the skull. A MIRRF is then attached to the posts. Also, inserts can be implanted in the skull which provide precisely positioned “divots.” These divots are used to mate clamping posts on a MIRRF, which hold the MIRRF in place. Such implanted divots can be covered by the skin and remain in place for an extended period of time.[0115]
• An alternative to use of a MIRRF is to attach markers directly to anchors in the skull. Referring to FIG. 21, each such anchor, shown as threaded[0116]insert1440, can support asingle scanning marker1444 on apost1442, subsequently support asingle registration divot1450 on asecond post1451, and then support a single tracking marker,LED1448, on athird post1446. The geometric relationship of the anchor to the scanning marker is the same as the geometric relationship of the anchor to the tracking marker thereby allowing a localization application to directly track the fiducial points by tracking the location of the tracking marker.
• Using any of the MIRRF structures described, multiple MIRRFs can be used to provide increased accuracy in registration and tracking. For example, two star-shaped MIRRFs can be used, one on each side of the head.[0117]
• In other embodiments, alternative attachment methods can be used to secure a guidance fixture to the skull. For instance, the mounting base can be relatively small and have extended “legs” extending radically and secured to the skin or skull with sharp points. These legs provide stabilization that may not be achievable using mounting screws through the smaller mounting base. The mounting base can alternatively include an insert that fits into the burr hole. This insert can also be threaded to allow direct attachment of the mounting base to the burr hole.[0118]
• In other embodiments, threaded inserts are used to attach, and subsequently accurately reattach, conventional stereotactic frames. This allows the conventional stereotactic frame to be removed and then accurately reattached to the skull. Procedures, such as fractionated multi-day stereotactic radiation treatments could then be performed with the stereotactic frame being reattached for each treatment.[0119]
• Referring to FIG. 22, a modified[0120]guidance fixture1510 is used in combination with a conventionalstereotactic frame1520.Guidance fixture1510 includes an x-y positioning table withLEDs1512 and an instrument drive with anLED1514 for tracking the depth of the surgical instrument. The guidance assembly is positioned onframe1520 to align with the planned surgical trajectory. A trackingMIRRF1530 is attached to frame1520 to allow dynamic tracking.
• Rather than using a scanning MIRRF with scanning fiducial markers, or scanning fiducial markers attached directly to anchors embedded in the skull, alternative embodiments can use other features for registration. In one alternative embodiment, paste-on scanning markers are attached to the skin. During the registration phase, the cranial probe is positioned at each of the paste-on markers in turn, rather than at the fiducial points on a MIRRF. Tracking LEDs are attached in a fixed position relative to the skull in some other way than using a MIRRF, for example, using an elastic headband. Rather than using pasted on fiducial markers, another alternative embodiment uses accessible anatomical features. These features are located in the scanned image, and the probe is positioned at these features during the registration phase. Still another alternative does not use discrete fiducial points, but rather makes use of the surface shape of the skull in a “surface merge” approach. The surface of the skull is located in the three-dimensional image. During registration, the cranial probe touches a large number of points on the skull. The locations of these points is matched to the shape of the skull to determine the conformal mapping from the physical coordinate system to the image coordinate system.[0121]
• In yet another embodiment, referring to FIG. 23, a tracking[0122]MIRRF1610 can be attached directly to the base of aguidance fixture710. TrackingMIRRF1610 is only useful for tracking afterguidance fixture710 has been attached to the skull. In this approach, registration is based on fiducial points elsewhere on the skull than trackingMIRRF1610.
• Locating the entry point, over which[0123]guidance fixture710 is attached can be accomplished using one of a variety of alternative techniques. For example, the entry point may be known-for some standardized procedures. Alternatively, the entry point may be determined by registration of the skull and the three-dimensional image based on fiducial markers attached to the head, for example using adhesive pads, anatomical markers, or a “surface merge” technique as described above.
• Once the guidance fixture and tracking[0124]MIRRF1610 are attached to the skull,LEDs1620 on trackingMIRRF1610 are used to track the location of the skull, and thereby track the location of the surgical instrument. A reregistration step (FIG. 1, step160) can be performed to determine the relative position of the fiducial points toLEDs1620.
• Various mechanical adjustments of[0125]guidance fixture710, if performed when an guidance tube is inserted in the brain, would potentially damage the brain tissue. The guidance fixture optionally includes a feature that the various locking knobs and x-y adjustment knobs are rotated using a removable knob (or key). When not in use, this knob is stowed on the drive assembly. Whenever the removable knob is removed from its stowed position, the signal from an electrical sensor on the drive assembly that is connected to the workstation causes a warning, for example on the computer display, to be provided to the surgeon.
• Alternative related embodiments can make use of known geometric relationships of points on various devices.[0126]
• For instance, the relationship between the tip of a probe and the location of tracking LEDs can be calibrated and used by a localization application to compute the location of tip using the computed location the LEDs. Similarly, the relationship between the location of fiducial points on a MIRRF and tracking LEDs can be calibrated, thereby allowing a localization application to compute the coordinates of fiducial points from the coordinates of the tracking LEDs without using the registration procedure described above.[0127]
• In the above embodiments, tracking LEDs are tracked using a camera. Other alternative embodiments can use other three-dimensional sensing and tracking approaches. Rather than LEDs, other tracking markers that are active emitters of electromagnetic-or mechanical energy such as electronic sparks, heat, magnetic energy, or sound can be used. Appropriate three-dimensional tracking approaches, for example, using imaging or triangulation techniques determine the three-dimensional coordinates of the emitters. Alternatively, tracking markers that are passive reflectors or transducers of externally applied localizing energy, such as infrared light, sound, magnetism, can be used.[0128]
• The devices described above can be made of a variety of materials. One alternative is to use a material, such as carbon fiber, which does not interfere with MRI scanning. This allows use of the devices during intraoperative MRI scanning. Also, use of hydraulic drive mechanisms rather than electrical motors avoids interference with MRI scanning.[0129]
• In the surgical procedures described above, the patient is not necessary immobilized. It may be desirable, however, to immobilize the patient, for example by clamping the guidance fixture to an operating table, at some times during the surgery.[0130]
• It is to be understood that the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.[0131]

Claims (32)

What is claimed is:

1. A method for positioning a surgical instrument during stereotactic surgery, comprising:

providing a guidance fixture that includes an upper portion, including an instrument guide for moving the surgical instrument along a constrained trajectory relative to the upper portion, and includes an adjustable base supporting the upper portion, including a mounting base and an adjustment mechanism;

attaching the guidance fixture to a body, including attaching the mounting base to the body;

determining using a remote sensing device the orientation of the upper portion of the guidance fixture in relation to the body;

displaying a representation of a relationship of the constrained trajectory and a target point in the body; and

aligning the guidance fixture, including aligning the orientation of the upper portion to achieve a desired relation between the constrained trajectory and the target point, including rotating the upper portion about a central axis of the mounting base and pivoting the upper portion to adjust an angle between the upper portion and the central axis.

2. The method of

claim 1

wherein determining the orientation of the upper portion includes:

determining the locations of a first plurality of tracking markers affixed to the upper portion;

determining the locations of a second plurality of tracking markers affixed to the body; and

computing the orientation using the locations of the first and the second pluralities of tracking markers.

3. The method of

claim 1

further comprising:

locking the adjustment mechanism to fix the orientation of the upper portion in relation to the body;

determining a displacement of the surgical instrument along the constrained trajectory;

displaying a representation of a location of the surgical instrument in relation to the body;

guiding the surgical instrument into the body along the constrained trajectory.

4. The method of

claim 3

wherein determining the displacement of the surgical instrument includes:

determining using a remote sensing device a location of a tracking marker affixed in a fixed relationship to the surgical instrument;

determining the locations of a plurality of tracking markers affixed to the guidance assembly; and

computing the displacement using the location of the marker affixed in a fixed relationship to the surgical instrument and the locations of the plurality of tracking markers affixed to the guidance assembly.

5. A method for positioning a surgical instrument during stereotactic surgery comprising:

providing a guidance fixture that includes an upper portion, including an instrument guide for moving the surgical instrument along a constrained trajectory relative to the upper portion, and includes an adjustable base supporting the upper portion, including a mounting base and an adjustment mechanism;

attaching the guidance fixture to a body, including attaching the mounting base to the body;

determining using a remote sensing device the orientation of the upper portion of the guidance assembly in relation to the body;

displaying a representation of a relationship of the constrained trajectory and a target point in the body; and aligning the guidance fixture, including aligning the orientation of the upper portion to achieve a desired relation between the constrained trajectory and the target point;

attaching at an attachment location on the body a scanning frame that includes a plurality of scanning markers;

scanning a three-dimensional image of the body, including locating images of the scanning markers in the three-dimensional image;

attaching to the body a tracking frame that includes a plurality of tracking markers; and

registering the body and the three-dimensional image, including tracking the tracking markers in the tracking frame, and locating points relative to the body which correspond to the locations of the scanning markers.

6. The method of

claim 5

wherein attaching the tracking frame includes attaching the tracking frame in a predetermined location in relation to the attachment location of the scanning frame.

7. The method of

claim 5

wherein locating points relative to the body which correspond to the locations of the scanning markers includes:

tracking the location of a point on a probe using the remote sensing device;

positioning the point on the probe at each of the points on the body corresponding to the scanning markers.

8. The method of

claim 5

wherein locating points on the body includes computing the locations of points relative to the body which correspond to the locations of the scanning markers using a known geometry relationship of the locations of the scanning markers on the attached scanning frame and the locations of the tracking markers on the attached tracking frame.

9. The method of

claim 1

wherein displaying the representation of the relationship of the constrained trajectory and the target point includes

displaying a representation of the target point,

displaying a representation of the range of possible orientations of the guidance fixture,

displaying a first line segment corresponding to possible orientations of the guidance fixture that could result from pivoting the upper portion at a current degree of rotation of the upper portion, and

displaying an indication of a current degree of pivoting of the upper portion.

10. A guidance fixture for guiding a surgical instrument into a body during stereotactic surgery, comprising:

an upper portion including an instrument guide for moving the surgical instrument along a constrained trajectory relative to the upper portion;

an adjustable base supporting the upper portion, including a mounting base for attaching the guidance fixture to a body, the mounting base having central opening and a central axis passing through the central opening, and an orientation adjustment mechanism coupled between the mounting base and the upper portion, a configuration of the adjustment mechanism determining the orientation of the upper portion relative to the mounting base; and

a plurality of tracking markers for tracking with a remote sensing device.

11. The guidance fixture of

claim 10

wherein the plurality of tracking markers includes a plurality of light emitting diodes and the remote sensing device includes a plurality of cameras.

12. A guidance fixture for guiding a surgical instrument into a body during stereotactic surgery, comprising:

an upper portion including an instrument guide for moving the surgical instrument along a constrained trajectory relative to the upper portion;

an adjustable base supporting the upper portion, including a mounting base for attaching the guidance fixture to a body, the mounting base having central opening and a central axis passing through the central opening, and an orientation adjustment mechanism coupled between the mounting base and the upper portion, a configuration of the adjustment mechanism determining the orientation of the upper portion relative to the mounting base;

wherein the orientation adjustment mechanism includes a rotation adjustment mechanism and a pivoting adjustment mechanism, wherein adjustment of the rotation adjustment mechanism rotates the upper portion about the central axis, and adjustment of the pivoting adjustment mechanism adjusts an angle between the upper portion and the central axis.

13. The guidance fixture of

claim 12

wherein the rotation adjustment mechanism includes a rotating collar attached to the mounting base and the pivoting adjustment mechanism includes a pivoting collar coupling the rotating collar to the upper portion.

14. The guidance fixture of

claim 13

wherein the adjustable base further includes a rotation locking screw for preventing rotation of the rotating collar and a pivoting locking screw for preventing pivoting of the pivoting collar.

15. The guidance fixture of

claim 14

wherein the upper portion includes an x-y table adjustment of which displaces the constrained trajectory.

16. A guidance fixture for guiding a surgical instrument into a body during stereotactic surgery, comprising:

an upper portion including an instrument guide for moving the surgical instrument along a constrained trajectory relative to the upper portion wherein the instrument guide includes a driving mechanism for positioning the instrument along the constrained trajectory; and

an adjustable base supporting the upper portion, including a mounting base for attaching the guidance fixture to a body, the mounting base having central opening and a central axis passing through the central opening, and an orientation adjustment mechanism coupled between the mounting base and the upper portion, a configuration of the adjustment mechanism determining the orientation of the upper portion relative to the mounting base.

17. The guidance fixture of

claim 16

wherein the constrained trajectory is a linear trajectory.

18. The guidance fixture of

claim 16

wherein the upper portion includes a plurality of tracking markers and the driving mechanism includes an instrument tracking marker for tracking a location of the instrument using a remote sensing device.

19. A system for stereotactic surgery on a body, comprising:

a remote sensing device;

a tracking frame for attachment to the body, including a plurality of tracking markers for tracking a location and an orientation of the body by using the remote sensing device;

a guidance fixture including

an upper portion including an instrument guide for moving the a surgical instrument along a constrained trajectory relative to the upper portion,

an adjustable base supporting the upper portion, including a mounting base for attaching the guidance fixture to a body, the mounting base having central opening and a central axis passing through the central opening, and an orientation adjustment mechanism coupled between the mounting base and the upper portion, configuration of the adjustment mechanism determine the orientation of the upper portion relative to the mounting base, and

a plurality of tracking markers for tracking a location of the upper portion of the guidance fixture; a tracking system for accepting the locations of the tracking markers on the tracking frame and the locations of the tracking markers on the guidance fixture, and computing a geometric relationship between the constrained trajectory and the body; and

a display system for presenting an image of the body and the geometric relationship between the constrained trajectory and the body.

20. The system of

claim 19

wherein the remote sensing device includes a plurality of cameras, and the tracking markers are light emitting diodes.

21. A method for positioning a surgical instrument during stereotactic surgery, comprising:

providing a guidance fixture that includes an upper portion, including an instrument guide for moving the surgical instrument along a constrained trajectory relative to the upper portion, and includes an adjustable base supporting the upper portion, including a mounting base and an adjustment mechanism;

attaching the guidance fixture to a body, including attaching the mounting base to the body;

sensing using a remote sensing device locations of a plurality of tracking markers affixed to the upper portion of the guidance fixture;

determining a location and an orientation of the upper portion using the plurality of sensed locations of the tracking markers;

sensing using the remote sensing device a location of a tracking marker affixed to the instrument guide; determining a location of the instrument using the determined location and orientation of the upper portion and the sensed location of the tracking marker affixed to the instrument guide.

22. An adjustable guidance fixture for stereotactic surgery comprising:

an upper portion including an instrument guide for moving a surgical instrument along a constrained trajectory relative to the upper portion;

an adjustable base, including a mounting base for attaching the guidance fixture to a body, and an orientation adjustment mechanism coupled between the mounting base and the upper portion;

a plurality of tracking markers affixed to the upper portion for tracking a location and an orientation of the upper portion using a remote sensing device; and

a tracking marker affixed to the instrument guide for tracking a motion of the surgical instrument using the remote sensing device.

23. A method for adjusting a guidance fixture for stereotactic surgery, comprising:

attaching the guidance fixture to the body at an entry point to the body, the guidance fixture having an adjustable orientation;

displaying a planar section of a three-dimensional image of the body, including displaying a representation of the orientation of the guidance fixture, the planar section containing a target point within the body;

adjusting the orientation of the guidance fixture using a first constrained motion of the guidance fixture until the orientation lies in a plane corresponding to the displayed planar section;

adjusting the orientation of the guidance fixture using a second constrained motion of the guidance fixture, such that the orientation continues to lie in the plane corresponding to the displayed planar section, until the orientation passes through the target point.

24. A guidance fixture for stereotactic surgery on a body, comprising:

an instrument guide for moving a surgical instrument along a constrained trajectory relative to the instrument guide;

an adjustable base supporting the instrument guide, including a mounting base having a central axis and an adjustment mechanism coupled between the mounting base and the instrument guide, wherein a configuration of the adjustment mechanism determines an orientation of the instrument guide relative to the central axis of the mounting base; and

a signaling device for providing a signal representation of the configuration of the adjustment mechanism;

wherein the adjustment mechanism includes a rotation adjustment mechanism and a pivoting adjustment mechanism, adjustment of the rotation adjustment mechanism rotates the instrument guide about the central axis, and adjustment of the pivoting adjustment mechanism adjusts an angle between the instrument guide and the central axis.

25. The guidance fixture of

claim 24

wherein the mounting base includes a portion for mating directly with the body.

26. A guidance fixture for stereotactic surgery on a body, comprising:

an instrument guide for moving a surgical instrument along a constrained trajectory relative to the instrument guide;

an adjustable base supporting the instrument guide, including a mounting base having a central axis and an adjustment mechanism coupled between the mounting base and the instrument guide, wherein a configuration of the adjustment mechanism determines an orientation of the instrument guide relative to the central axis of the mounting base; and

a signaling device for providing a signal representation of the configuration of the adjustment mechanism wherein the signaling device includes a plurality of tracking markers and the signal representation of the configuration includes a plurality of signals propagating from corresponding tracking markers.

27. The guidance fixture of

claim 26

wherein at least some of the plurality of tracking markers are in fixed locations relative to the instrument guide.

28. The guidance fixture of

claim 26

wherein the signals propagating from the tracking markers are electromagnetic signals.

29. The guidance fixture of

claim 26

wherein the tracking markers are light emitting diodes and the signals propagating from the tracking markers are optical signals.

30. The guidance fixture of

claim 26

wherein the signals propagating from the tracking markers are acoustic signals.

31. The guidance fixture of

claim 10

wherein the tracking markers emit signals to the remote sensing device.

32. The guidance fixture of

claim 10

wherein the tracking markers reflect signals to the remote sensing device.

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