Surgical navigation systems including reference and localization frames

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SURgICftk ΝΑΥΙΑΜΊΟΗ SYSTEMS INCLUDING RSPBRBNCB AMP LOCALIZATION FRAMES

Background of the Invention

The Invention relates generally to systems which use and generate images during medical and surgical procedures, which images assist in executing the procedures and indicate the relative position of various body parts and instruments. In particular, the invention relates to a system for generating images during medical and surgical procedures based on a scan taken prior to or during the procedure and based on the present position of the body parts and instruments during the procedure.

Image guided medical and surgical procedures comprise a technology by which scans, obtained either pre-procedurally or intra-procedurally (i.e., prior to or during a medical or surgical procedure), are used to generate images to guide a doctor during the procedure. The recent increase in interest in this field is a direct

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64725-841 result of the recent advances in scanning technology, especially in devices using computers to generate three dimensional images of parts of the body, such as computed tomography (CT) or magnetic resonance imaging (MR.I) .

The majority of the advances in diagrammatic imaging involve devices which bend to be large, encircle the body part being imaged, and are expensive. Although the scans produced by these devices depict the body part under investigation with high resolution and good spatial fidelity, their cost usually precludes the dedication of a unit to be ueed during the performance of procedures. Therefore, image guided surgery is usually performed using images taken preoperatively.

The reliance upon preoperative images has focused image guidance largely to the cranium. The skull, by encasing the brain, serves as a rigid body which largely inhibits changes in anatomy between imaging and surgery. The skull also provides a relatively easy point of reference to which fiducials or a reference system may be attached so that registration of preprocedural images to the procedural work space can be done singly at the beginning, during, or throughout the procedure. Registration is defined as the process of relating pre-procedural or intra-procedural scan of the anatomy undergoing surgery to the surgical or medical position of the corresponding anatany. For exanq>le, see U.S. Patent No. 5,383,454.

This situation of rigid fixation and absence of anatomical movement between imaging and surgery is unique to the skull and intracranial contents and permits a simple one-to-one registration process as shown in Figure

1. The position during a medical procedure or surgery is in registration with the pre-procedural image data set because of the absence of anatomical movement from the time of the scan until the time of the procedure; in

96/11624 f 2 2 0 1 8 7 7 PCT/ÜS95/12894 effect, the skull and it’s intracranial contents comprise a “rigid body,” that is, an object which does not deform internally. In almost every other part of the body there is ample opportunity for movement within the anatomy which degrades the fidelity by which the pre-procedural scans depict the intra-procedural anatomy. Therefore, additional innovations are needed to bring image guidance to the rest of the body beyond the cranium.

The accuracy of image guided surgery relies upon the ability to generate images during medical and surgical procedures based on scans taken prior to or during the procedure and based on the present position and shape of the body parts during the procedure. Two types of body parts are addressed herein: 1) structures within the body that do not change shape, do not compress, nor deform between the process of imaging and the medical procedure, which are termed rigid bodies, and are exemplified by the bones of the skeleton; and 2) structures within the body that can change shape and deform between the process of imaging and the medical procedure structures are termed semi-rigid bodies, and are exemplified by the liver or prostate. Both types of body parts are likely targets for medical or surgical procedures either for repair, fusion, resection, biopsy, or radiation treatment. Therefore, a technique is needed whereby registration can be performed between the body parts as depicted pre-procedurally on scans and the position and shape of these same body parts as detected intra-procedurally. This technique must take into account that movement can occur between portions of the body which are not rigidly joined, such as bones connected by a joint, or fragments of a broken bone, and that shape deformation can occur for semi-rigid bodies, such as the liver or prostate. In particular, the technique must be able to modify the scanned image dataset such that the modified image dataset which is

PCT/ÜS95/12894 φ

WO 96/11624 ΐ 2 201 87 7 used for localization and display, corresponds to position and/or shape of the body part(s) of interest during a medical or surgical procedure. A key to achieving this correspondence is the ability to precisely detect and track the position and/or shape of the body part(s) of interest during the medical or surgical procedure, as well as to track instruments, -------or radiation used during the said procedure.

Summary of the Invention_________

It is an object of this invention to provide a system which allows registration between a body part depicted in pre-procedural images and tracked during surgery.

It is a further object of this invention to provide a system which allows registration between a semi-rigid body such as the liver depicted in preprocedural images and detected during surgery.

It is a further object of this invention to provide a system which allows registration between multiple body parts such as skeletal elements depicted in pre-procedural images and detected during surgery.

It is a further object of this invention to provide a system which can localize a semi-rigid body that may deform between imaging and a procedure and provide a display during the procedure of the body in its deformed shape.

It is a further object of this invention to provide a system which can localize multiple rigid bodies that move with respect to each other between imaging and a procedure and provide a display during the procedure of the bodies in their displaced positions.

It is another object of this invention to provide a system for use during a medical or surgical procedure on the body, the system generating a display representing the position of one or more body elements

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2,0 1 87 7 during the procedure based on a scan generated by a scanner either prior to or during the procedure.

Tt is another object of this invention to provide a system for use during a medical or surgical procedure on a body which modifies the scan taken prior to or during a procedure according to the identified relative position of each of the elements during the procedure.

it is another object of this invention to 10 provide a system for use during a medical or surgical procedure on a body which modifies the image data set according to the identified shape of each of the element during the procedure.

It is another object of this invention to 15 provide a system which generates a display representative of the position of a medical or surgical instrument in relation to the body element(s) during a procedure.

It is a further object of this invention to 20 provide a system for use during image guided medical and surgical procedures which is easily employed by the doctor or surgeon conducting the procedure.

It is another object of this invention to provide a system which determines the relative position and/or shape of body elements during a medical or surgical procedure based on the contour of the body elements which can avoid the need for exposing the body elements.

It is still another object of this invention to provide a system which employs one or more two dimensional fluoroscopic or x-ray images of body elements to determine their relative position and/or shape in three dimensions.

It is yet a further object of this invention to describe a surgical or medical procedure which employs a display representing the position of the body element (s)

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64725-841 during the procedure based on an image data set of the body element(s) generated prior to the procedure.

It is a further object of this invention to provide a system and method for medical or surgical procedures which allows repositioning of body elements during the procedure and still permits the generation of an image showing the relative position of the body elements.

It is a further object of this invention to provide a system and method for medical or surgical procedures which allows reshaping of the body element(s) during the procedure and still permits the generation of an image showing the position and current shape of the body elements.

It is a further object of this invention to provide a system which can localize a body element and provide a display during the procedure of the position of the body element relative to an instrument, such as a forceps, microscope, or laser, so that the instrument can be precisely located relative to the body element.

Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention comprises a system for use during a procedure on a body, said system generating a display representing a position of two or more body elements during the procedure, said system comprising: a memory storing an image data set representing the position of the two or more body elements based on scans taken of the body, the image data set having a plurality of data points and corresponding to a plurality of reference points for each of the body elements, the reference points of a particular body element having a known spatial relation to the data points of the

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64725-841 particular body element; means for identifying, during the procedure, the position of the reference points of each of the body elements relative to the reference points of the other body elements; a processor modifying the spatial relation of the data points of one body element relative to the data points of another body element according to the identified relative position of the reference points during the procedure as identified by the identifying means, said processor generating a displaced image data set representing the position of the body elements during the procedure; and a display utilizing the displaced image data set generated by the processor and providing a display, illustrating the relative position of the body elements during the procedure.

The invention also comprises a method for use during a procedure, said method generating a display representing a position of two or more body elements during the procedure, said method comprising the steps of: storing an image data set in a memory, the image data set representing the position of the two or more body elements based on scans taken of the body; reading the image data set stored in the memory, said image data set having a plurality of data points and a plurality of reference points for each of the body elements, the data points of each body element having a spatial relation to the data points of another body element, the reference points of a particular body element having a known spatial relation to the data points of the particular body element; identifying, during the procedure, the position of each of the reference points of each of the body elements relative to the reference points of the other body elements; modifying the spatial relation of the data points of one body element relative to the data points of another body element according to the identified relative position of the reference points during the procedure in

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64725-841 order to generate a displaced image data set representing the relative position of the body elements during the procedure; and generating a display based on the displaced image data set illustrating the relative position of the body elements during the procedure.

The invention also comprises a system for use during a procedure on a body, said system generating a display representing a geometrical relationship of two or more body elements during the procedure, said system comprising: a memory for storing an image data set representing the position of the two or more body elements based on scans taken of the body, the image data set having a geometrical spatial relationship of the body elements and having a plurality of reference points on each of the body elements, the reference points of a particular body element having a known spatial relation on the particular body element; means for identifying, during the procedure, a position of each of the reference points of the body elements to be displayed; a processor modifying the geometrical relationship of the body elements as necessary according to the identified position of each of the reference points as identified by the identifying means, said processor generating a displaced image data set from the modified geometrical relationship of the body elements, said displaced image data set representing the geometrical relationship of the body elements during the procedure; and a display system utilizing the displaced image data set to generate the display.

The invention also comprises a system for use during a procedure on a body, said system generating a display representing a position of two or more body elements during the procedure, said system comprising: a memory configured to store an image data set representing the

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64725-841 position of the two or more body elements based on scans taken of the body, the image data set having a plurality of data points and corresponding to a plurality of reference points for each of the body elements, the reference points of a particular body element having a known spatial relation to the data points of the particular body element; means for identifying the position of the reference points; a digitizer positioned to receive a signal output by the means for identifying, said digitizer being configured to determine a three dimensional position of the reference points for the particular body element; a processor modifying the spatial relation of the data points of one body element relative to the data points of another body element according to the identified relative position of the reference points during the procedure as determined by the digitizer, said processor generating a displaced image data set representing the position of the body elements during the procedure; and a display utilizing the displaced image data set generated by the processor, illustrating the relative position of the body elements during the procedure.

The invention also comprises a system for displaying relative positions of two or more body elements during a procedure on a body, the system comprising: a memory storing an image data set, the image data set representing the position of the body elements based on scans of the body, and having a plurality of data points correlatable to a plurality of reference points for each of the body elements, the position of reference points of a particular body element relative to the data points for that particular body element being known; a reference system for identifying, during the procedure, the position of the reference points of each of the body elements relative to the reference points of the other body elements; a processor

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64725-841 modifying the relative position of the data points of one body element relative to the data points of another body element according to the identified relative position of the reference points during the procedure as identified by the reference system, the processor generating a displaced image data set representing the position of the body elements during the procedure; and a display utilizing the displaced image data set generated by the processor to display the relative position of the body elements during the procedure.

The invention also comprises a system for use during a medical or surgical procedure on a body, said system being adapted to generate a display from an image data set representing the position of one or more body elements during the procedure based on scans taken of the body, wherein at least some of the body elements are movable with respect to each other, each scan having a reference for each of the one or more body elements, the reference of a particular body element having a known spatial relation to the particular body element said system comprising: a plurality of reference frames, at least one attached to each of the movable body elements; a localizer for identifying, during the procedure, the position of the reference for each of the body elements to be displayed; a processor for modifying the image data set according to the identified position of the reference during the procedure, as identified by the localizer, said processor being adapted to generate a displaced image data set representing the position and geometry of the body elements according to the identified position of the reference frames during the procedure, as identified by the localizer; and a display utilizing the displaced image data set generated by the

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64725-841

10a processor, illustrating the position and geometry of the body elements during the procedure.

The invention also comprises a method for use during a medical or surgical procedure on a body, said method being adapted to generate a display from an image data set representing the position of one or more body elements during the procedure based on scans taken of the body, wherein at least some of the body elements are movable with respect to each other, each scan having a reference for each of the one or more body elements, the reference of a particular body element having a known spatial relation to the particular body element, wherein there is a plurality of reference frames, at least one attached to each of the movable body elements; said method comprising the steps of: identifying, during the procedure, the position of the reference for each of the body elements to be displayed; modifying the image data set according to the identified position of the reference during the procedure, as identified by the localizer; generating a displaced image data set representing the position and geometry of the body elements according to the identified position of the reference frames during the procedure; and illustrating the position and geometry of the body elements during the procedure utilizing the displaced image data set.

In addition, the invention comprises a method for displaying the relative positions of a plurality of body elements during a procedure on a body, the method comprising: storing scan images of body elements, the scan images having a plurality of data points corresponding to a plurality of reference points for each of the body elements, the position of the reference points of a particular body element relative to the data points for that particular body element being known; identifying the position of each of the

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10b reference points of each of the body elements relative to the reference points of the other body elements during a procedure; modifying the relative position of the data points of one body element relative to the data points of another body element according to the identified relative position of the reference points during the procedure; generating a displaced image data set representing the position of the body elements during the procedure; and displaying the relative position of the body elements during the procedure.

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Brief Description off the Drawings

Figure 1 is an illustration of the prior art system in which rigid fixation and absence of movement between imaging and surgery permits a one-to-one registration process between the pre-surgical scan and the position in surgery.

Figure 2A is an illustration of operation of the invention in which the pre-procedural image data set ie modified in accordance with the intra-procedural position in order to generate a displaced and/or deformed data set representative of the intra-procedural position.

Figure 2B is a block diagram of one preferred exribodiment of a system according to the invention.

Figure 3 is an illustration of the preprocedural alignment of three body elements during scanning.

Figure 4 is an illustration of the intraprocedural alignment of the three body elements of Figure 3 during surgery·

Figure 5 is an illustration of three body 25 elements, one of which has a reference frame attached thereto, in combination with a registration probe.

Figure 6 is an illustration showing ultrasound registration according to the invention in which emitters are attached to the ultrasound for a virtual reference and, optionally, the patient's body for an actual reference.

Figure 7 is an illustration of a fluoroscopic localizer according to the invention for providing projections of an image of the body elements.

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Figure 8 is an illustration of a drill guide instrument of the invention wherein the position of a drill guide relative to the body elements may be displayed.

Figures 9 and 10 illustrate a clamped reference frame and a wired reference frame, respectively.

Figure 11 is a schematic diagram of one preferred embodiment of a cranial surgical navigation system according to the invention.

Figure 11A is a top plan view of one preferred embodiment of a cranial reference arc frame according to the invention.

Figure 11B is a side plan view, partially in cross section, of one preferred embodiment of a cranial reference arc frame according to the invention.

Figure 11C is a wiring diagram of one preferred embodiment of a cranial reference arc frame according to the invention.

Figure 12A is a top plan view of one preferred embodiment of a spinal reference arc frame according to the invention.

Figure 12B is a front plan view, partially in cross section, of one preferred embodiment of a spinal reference arc frame according to the invention.

Figure 12C is a side plan view of one preferred embodiment of a spinal reference arc frame according to the invention.

Figure 12D is a top plan view of one preferred embodiment of a thoraco-lumbar mount according to the invention.

Figure 12E is a front plan view, partially in cross section, of one preferred embodiment of a thoracolumbar mount according to the invention.

Figure 12F is a side plan view of one preferred 35 embodiment of a thoraco-lumbar mount according to the invention.

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Figure 12G is a wiring diagram of one preferred embodiment of a spinal reference arc frame according to the invention.

Figure 13A is a top plan view of one preferred embodiment of a biopsy guide localization frame according to the invention.

Figure 13B is a side plan view, partially in cross section, of one preferred embodiment of a biopsy guide localization frame according to the invention.

Figure 13 C is a front plan view of one preferred embodiment of a biopsy guide localization frame according to the invention.

Figure 13D is a top plan view of one preferred embodiment of a drill guide localization frame according to the invention.

Figure 13Ξ is a side plan view, partially in cross section, of one preferred embodiment of a drill guide localization frame according to the invention.

Figure 13F is a top plan view of one preferred embodiment of a drill yoke localization frame according to the invention.

Figure 13G is a side plan view, partially in cross section, of one preferred embodiment of a drill yoke localization frame according to the invention.

Figure 13H is a top plan view of one preferred embodiment of a ventriculostomy probe including an integrated localization frame according to the invention.

Figure 131 is a side,plan view, partially in cross section, of one preferred embodiment of a ventriculostomy probe including an integral localization frame according to the invention.

Figure 13J is a wiring diagram of one preferred embodiment of a localization frame according to the invention.

Corresponding reference characters indicate corresponding parts throughout the drawings.

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Detailed Description of the Preferred Embodiments

Referring to Fig. 2, an overview of operation of one preferred embodiment of the system according to the invention is illustrated. Prior to a particular procedure, the body elements which will be part of the procedure are scanned to determine their alignment, i.e., their pre-operative position. For example, the alignment may be such as illustrated in Fig. 3 wherein body elements 10, 20, and 3 0 are more or less aligned in parallel. These body elements may be bones or other rigid bodies. In Fig. 3, three-dimensional skeletal elements 10, 20, 30 are depicted in two dimensions as highly stylized vertebral bodies, with square vertebra ll, 21, 31, small rectangular pedicles 12, 22, 32, and triangular spinous processes 13, 23, 33. During imaging, scans are taken at intervals through the body parts 10, 20, 30 as represented in Fig. 3 by nine straight lines generally referred to be reference character 40. At least one scan must be obtained through each of the body elements and the scans taken together constitute a three-dimensional pre-procedural image data set.

Fig. 2B is a block diagram of the system according to the invention. A scanner interface 102 allows a processor 104 to obtain the pre-procedural image data set generated by the scanner and store the data set in pre-procedural image data set memory 106. Preferably, after imaging, processor 104 applies a discrimination process to the pre-procedural image data set so that only the body elements 10, 20, 30 remain in memory 106. If a discrimination process is employed, processor 104 may execute the discrimination process while data is being transferred from the scanner through the scanner interface 102 for storage in memory 106. Alternatively, memory 106 may be used for storing undiscriminated data and a separate memory (not shown) may be provided for storing the discriminated data. In this alternative.

φ, WO 96/11624 É 2 θ 1 8 7 7 PCT/US95/12894 processor 104 would transfer the data set from the scanner through scanner interface 102 into memory 106 and then would discriminate the data stored in memory 106 to generate a discriminated image data set which would be stored in the separate memory.

Once the body elements 10, 20, 30 are discriminated and each defined as a single rigid body, they can be repositioned by established software algorithms to form the displaced image data set. Each rigid body element, 10, 20, 30, must have at least three recognizable reference points which are visible on the pre-procedural images. These reference points must be accurately detected during the procedure. For body part .10, reference points 10A, 10B, and 10C are located on the spinous process 13; for body part 20, reference points

20A and 20C are located on the vertebra 21 and reference point 20B is located on spinous process 23; and for body part 30, reference points 30A and 30B are located on the spinous process 33 and reference point 30C is located on the vertebra 31. More than one reference point can be selected on each scan through the bone, although the maximal accuracy of registration is achieved by separating the reference points as far as possible. For example, in the case of posterior spinal surgery, it may be preferable to select reference points 10A_f 10B, and 10C on the spinous process which is routinely exposed during such surgery. It is contemplated that system software may allow the manual or automated identification of these same points on the images of the body elements

10, 20, 30. As Fig. 3 is a two-dimensional projection of a three-dimension process, the reference points will not be limited to a perfect sagittal plane, as depicted.

After imaging, the skeletal body elements 10,

20, 30 may move with respect to each other at the joints or fracture lines. In the procedure room, such as an operating room or a room where a medical procedure will

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PCT/US95/12894 be performed, after positioning the patient the surgery, the body elements will assume a different geometry, such as the geometry depicted in Fig. 4.

As a result of this movement, the preprocedural image data set stored in memory 106, consisting of the scans through the skeletal elements, does not depict the operative position of the skeletal elements, as shown in Fig. 4. However, the shape of the skeletal elements, as depicted by the scans through the element, is consistent between imaging and procedure since they are rigid bodies, as indicated by the lines 40 through each element in Fig. 4. Therefore, the image data set must be modified to depict the intraprocedural geometry of the skeletal elements. This modification is performed by identifying the location of each reference point of each skeletal element in procedure space. As diagrammatically illustrated in Fig. 2, a localizer 108 (see Figure 13, below, for more details) identifies the location and provides this information so that the preprocedural data set may be deformed or re-positioned into the displaced data set. As a result, the displaced data set is in registration with the intra-procedural position of the elements 10, 20, 30. Once the locations of the reference points are determined by the localizer 108, processor 104, which is a part of the work station, can execute software which re-positions the images of the skeletal elements to reflect the position of the actual elements in the procedure room thus forming the displaced set and the registration between the displaced set and the intra-procedural position.

Preferably, a three-dimensional digitizer may be used as the localizer 108 to determine the position and space of the elements 10, 20, 30 during the procedure. In general, the digitizer would include a reference array 110 which receives emissions from a series of emitters. Usually, the emissions consist of

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PCT/US95/12894 some sort of energy, such as light, sound or electromagnetic radiation. The reference array 110 is distant from the emitters which are applied to and positioned in coordination with the elements being localized, determining the position of the emitters. As is apparent, the emitters may be placed distant to the elements and the reference array 110 may be attached to the elements being localized.

Referring to Fig. 2, an alternate preferred embodiment of the system according to the invention in the case where the body elements are not rigid, but rather semi-rigid such that shape deformations may occur to the body elements is described as follows. Prior to a particular procedure, the body elements which will be part of the procedure are scanned to determine their preoperative position and shape. For example, the alignment may be such as illustrated in Fig. 3 wherein body elements 10, 20, and 30 are more or less aligned in parallel and have a defined shape. These body elements may be soft tissue such as the prostate or other semirigid bodies.

After imaging, the elements 10, 20, 30 may move with respect to each other and also their shape may become deformed. In the procedure room, such as an operating room or a room where a medical procedure will be performed, after positioning the patient the surgery, the body elements may assume a different geometry, such as the geometry depicted in Fig. 4 where geometry depicts both element alignment (position) and shape.

As a result of this changed geometry, the preprocedural image data set stored in meme <y 106, does not depict the operative geometry of the boay elements, as shown in Fig. 4. Indeed, the shape of the body elements, as depicted by the scans through the element, may have changed between imaging and procedure since they are semi-rigid bodies. Therefore, the image data set must be

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PCT/US95/12894 modified to depict the current geometry of the body elements. This modification is performed by identifying the location of the reference points of each body element in procedure space. As diagrammatically illustrated in Fig. 2f a localizer 108 possibly in communication with a processor 104 identifies the location of the reference points and provides this information so that the preprocedural data set may be deformed into the displaced data set. Once the locations of the reference points are determined, processor 104, which is a part of the work station, can execute software which modifies the images of the body elements to reflect the geometry of the actual elements in the procedure room thus forming the displaced set and the registration between the displaced set and the intra-procedural position. As a result, the displaced data set is in registration with the intraprocedural geometry of the elements 10, 20, 30.

According to one preferred embodiment of the invention, a reference frame 116 is attached to one of the body elements 10 at the beginning of the procedure. Various reference frame embodiments are illustrated in more detail in Figures 11 and 12, below. Reference frame 116 is equipped with a plurality of emitters 114 which together define a three-dimensional intraprocedural coordinate system with respect to the body element 10.

In conventional terms, the reference frame 116 defines the stereotactic space with respect to the body element

10. Emitters 114 communicate with sensors 112 on a reference array 110 located in the procedure room and remote from the reference frame 116 and patient. If the body of the patient is not immobilized during surgery, then multiple reference frames may be required for each body element to define a surgical space with respect to each element. The surgical space may alternatively be defined by rigid fixation of the frame emitters 114 directly (or indirectly, for example’, to the skin) to the φ WO 96/11624 2 2 0 1 8 7 7 PCT/US95/12894 skeletal elements 10, 20, or 30. In either case, the emitters 114 emit a signal which is received by the sensors 112. The received signal is digitized to compute position, for example, by triangulation. Through such information, the localizer 108 or a digitizer which is part of the localizer 108 can determine the exact threedimensional position of the frame emitters 114 relative to the sensors 112. Thereby, localizer 108 or the processor 104 can exactly determine the position of the reference frame 116 relative to the array which is free to move except during localization, e.g., activation of the emitters 114 on the reference frame 116 and activation of the probe emitters 112. Emitters 114 of the reference frame 116 are energized to provide radiation to the sensors 112, which radiation is received and generates signals provided to the localizer 108 for determining the position of the frame 116 relative to the array 110.

Next, it is necessary to determine the position of the body element 10, which may be a skeletal element, to which the reference frame 116 is affixed or positioned with respect to. In particular, the position of the body element 10 relative to the reference frame 116 must be determined, thereby determining the position of the body element 10 in the surgical space defined by the reference frame 116. After exposure of the reference points 10A,

10B, 10C by surgical dissection, the reference points are touched by the tip of a registration probe 118 equipped with emitters 120. As each of the reference points 10A,

10B, 10C is touched by the tip of the probe 120, the emitters are energized to communicate with the sensors 112 of reference array 110. This communication permits the localizer 108 to determine the position of the registration probe 120, thereby determining the position of the tip of the probe 120, thereby determining the position of the reference point 10A on which the tip is

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PCT/US95/12894 {φ positioned. By touching each of the reference points 10A, 10B, 10C on each body element 10, 20, 30 involved in the procedure, an intra-procedural geometry data is generated and stored in memory 121. This data is related to the corresponding reference points on the preprocedural images of the same elements by processor 104 which employs software to derive a transformation which allows the determination of the exact procedural position, orientation, and shape in surgical space of each body element, and thereby modifies the preprocedural image data set stored in memory 106 to produce a displaced image data set which is stored in memory 122. The displaced image data set in memory 122 reflects the geometry of the actual elements 10, 20, 30 during the procedure. Processor 104 displays the displaced image data set on display 124 to provide a visual depiction of the geometry of the body elements 10, 20, 30 during the procedure. This image is used during the procedure to assist in the procedure. In addition, it is contemplated that an instrument, such as a forceps, a laser, a microscope, a endoscope, or a radiation delivery system, which would be used during the procedure may be modified by the addition of emitters. This modified device when moved into the area of the body elements 10, 20, 30 would be activated so that its emitters wbuld communicate with the reference array 110 thereby permitting localizer 108 to determine the instrument's position. As a result, processor 104 would modify display 124 to indicate the position of the instrument or the instruments focal point, such as by positioning a cursor, with respect to the body elements 10, 20, 30.

Further, it is contemplated that the addition of emitters on an instrument (effector) may be used with the system in order to create a closed-loop feedback for actively (in the case of robotics) or passively controlling or monitoring the instrument and its

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WO 96/11624 position. Such a control loop allows the monitoring of certain procedures such as the delivery of radiation to the body or the use of a drill where the object of the procedure is to keep the focal point of the instrument in a safe zone, i.e. a predetermined procedural plan. Such a control loop could also control the operation of a robotically controlled instrument where the robotics could be driven (directly or indirectly) by processor 104 to control the position the position of the instrument.

For example, the processor could instruct a robotic arm to control the position of a laser. The laser position could be monitored, such as by emitters on the laser.

The processor would be programmed with the control parameters for the laser so that it would precisely follow a predetermined path.

Reference frame 116 allows the patient to be moved during the procedure without the need for reregistering the position of each of the body elements 10, 20, 30. It is assumed that during the procedure, the body elements are fixed relative to each other. Since the reference frame 116 is fixed (directly or indirectly) to body element 10, movement of the patient results in corresponding movement of the reference frame 116. Periodically, or after each movement of the patient, array emitters 114 may be energized to communicate with the sensors 112 of reference array 110 in order to permit localizer 108 to determine the position of the reference frame 116. Since the reference frame 116 is in a known relative position to element 110 and since we have assumed that elements 20 and 30 are in fixed relation to element 10, localizer 108 and/or processor 104 can determine the position of the elements and thereby maintain registration.

An alternative to touching the reference points

A, B, C with the tip of the probe 118 would be to use a contour scanner 126a with emitters attached 126b. Such a

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64725-841 device, using some form of energy such as sound or light which is emitted, reflected by the contour and sensed, would allow the extraction of a contour of the body elements 10, 20, 30, thus serving as a multitude of reference points which would allow registration to occur. The registration process is analogous to the process described for ultrasound extracted contours below.

In certain situations, markers may be used on the skin surface as reference pointe to allow the transformation of the pre-procedural image data set into the displaced image data set. Reciprocally, skin surface fiducials applied at the time of imaging can be used to re-position the body to match the geometry during imaging and is described below.

Localization of body elements 10, 20, 30 may be desired without intra-procedural exposure of the reference points A, B, C on those body elements.

Examples wherein the spine is minimally exposed include percutaneous biopsy of the spine or discectomy, spinal fixation, endoscopy, percutaneous spinal implant insertion, percutaneous fusion, insertion of drug delivery systems, and radiation delivery, in thie situation, localization of reference pointe on the body elements must be determined by some form of imaging which can localize through overlying soft tissue and/or discriminate surrounding tissue and structures. There are currently two imaging techniques which are available to a surgeon in the operating room or a doctor in a procedure room which satisfy the needs of being low cost and portable. Both imaging techniques, ultrasonography and radiography, can produce two-or three-dimensional images which can be employed in the fashion described herein to register a three-dimensional form such as a skeletal element.

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The coupling of a three-dimensional digitizer to a probe of an ultrasound device affords benefits in that a contour can be obtained which can be related directly to a reference system that defines three-dimensional coordinates in the procedural work space, i.e., the surgical space. In the context of the present invention, a patient is imaged prior to a procedure to generate a pre-procedural image data set which is stored in memory 106. In the procedure room, the patient's body is immobilized to stabilize the spatial relationship between the body elements 10, 20,

30. A procedural reference system, surgical space, for the body is established by attaching a reference frame 116 to one of the body elements or by otherwise attaching emitters to the patient or body elements as noted above, or by attaching emitters to a device capable of tracking one of the body elements thereby forming a known relationship with the body element. For example, this could be performed by using the percutaneous placement of a reference frame similar to the one described above, radiopaque markers screwed into the elements or by placing emitters 130 directly on the skins, as illustrated in Fig. 6, based on the assumption that the skin does not move appreciably during the procedure or in respect to the body elements.

An ultrasound probe 128 equipped with at least three emitters 130 is then placed over the body element of interest. The contour (which can be either two- or three-dimensional) of the body element is then obtained using the ultrasound probe 128. This contour can be expressed directly or indirectly in the procedural coordinates defined by the reference system (surgical space). Emitters 130 communicate with sensors 112 of reference array 110 to indicate the position of the ultrasound probe 128. An ultrasound scanner 131 which energizes probe 128 determines the contour of the body

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PCTZÜS95/12894 element of interest and being scanned. This contour information is provided to processor 104 for storage in intra-procedural geometry data memory 121.

The intra-procedural contour stored in memory 121 is then compared by a contour matching algorithm to a corresponding contour extracted from the pre-operative image data set stored in memory 106. Alternatively, a pre-procedural contour data set may be stored in memory 134 based on a pre-procedural ultrasound scan which is input into memory 134 via scanner interface 102 prior to the procedure. This comparison process continues until a match is found for each one of the elements. Through this contour matching process, a registration is obtained between the images of each body element and the corresponding position of each element in the procedural space, thereby allowing the formation of the displaced image data set 122 used for localization and display.

Note that the contours used in the matching process only have to be sufficiently identical to accomplish a precise match - the contours do not have to be the same extent of the body element.

In certain instances, the ultrasound registration noted above may not be applicable. For example, ultrasound does not penetrate bone, and the presence of overlying bone would preclude the registration of an underlying skeletal element- Further, the resolution of ultrasound declines as the depth of the tissue being imaged increases and may not be useful when the skeletal element is so deep as to preclude obtaining an accurate ultrasonically generated contour. In these circumstances, a radiological method is indicated, which utilizes the greater penetrating power of x-rays.

Pre-operative imaging occurs as usual and the skeletal elements may be discriminated from the soft tissue in the image data set as above. In particular, a CT scan of the skeletal elements 10, 20, 30 could be

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PCT/US95/12894 taken prior to the procedure. Processor 104 may then discriminate the skeletal elements and store the preprocedural image data set in memory 106. Next, the patient is immobilized for the procedure. A radiograph of the skeletal anatomy of interest is taken by a radiographic device equipped with emitters detectible by the digitizer. For example, a fluoroscopic localizer 136 is illustrated in Fig. 7. Localizer 136 includes a device which emits x-rays such as tube 13 8 and a screen 140 which is sensitive to x-rays, producing an image when x-rays pass through it. This screen is referred to as a fluoroscopic plate. Emitters 142 may be positioned on the tube 138, or on the fluoroscopic plate 140 or on both. For devices in which the tube 138 is rigidly attached to the plate 140, emitters need only be provided on either the tube or the plate. Alternatively, the reference array 110 may be attached to the tube or the plate, obviating the need for emitters on this element.

By passing x- rays through the skeletal element 141 of interest, a two-dimensional image based on bone density is produced and recorded by the plate. The image produced by the fluoroscopic localizer 136 is determined by the angle of the tube 138 with respect to the plate 140 and the position of the skeletal elements therebetween and can be defined with respect to procedure coordinates (surgical space). Fluoroscopic localizer 136 includes a processor which digitizes the image on the plate 140 and provides the digitized image to processor 104 for possible processing and subsequent storage in intra-procedural geometry data memory 121. Processor 104 may simulate the generation of this two-dimensional x-ray image by creating a series of two-dimensional projection of the three-dimensional skeletal elements that have been discriminated in the image data set stored in memory 106. Each two dimensional projection would represent the passage of an X-ray beam through the body at a specific

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PCT/US95/12894 {φ angle and distance. In order to form the displaced data set and thus achieve registration, an iterative process is used which selects that a two-dimensional projection through the displaced data set that most closely matches the actual radiographic image(s) stored in memory 121.

The described process can utilize more than one radiographic image. Since the processor 104 is also aware of the position of the fluoroscopic localizers because of the emitters 142 thereon, which are in communication with localizer 108, the exact position of the skeletal elements during the procedure is determined.

As noted above, the procedural reference system or surgical space for the body can be established by attaching emitters to a device capable of detecting and tracking, i.e. identifying, one of the body elements thereby forming a known relationship with the body element. For example, the emitters 130 on the ultrasound probe 128 together and without the three emitters on the patient's body form a type of reference frame 116 as depicted in Figure 6 which can be virtually attached to body element 10 by continuously or periodically updating the ultrasound contour of body element 10 stored in intra-procedural geometry data memory 121 which the processor 104 then uses to match to the contour of body element 10 stored in pre-procedural memory 106 thereby continuously or periodically updating the displaced image data set in memory 122 so that registration with the procedural position of the body elements is maintained.

It is contemplated that a virtual reference frame can be accomplished using any number of devices that are capable of detecting and tracking a body element such as radiographic devices (fluoroscope), endoscopes, or contour scanners.

The above solutions achieve registration by the formation of a displaced image data set stored in memory 122 which matches the displacement of the skeletal

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PCT/ÜS9S/12894 elements at the time of the procedure. An alternative technique to achieve registration is to ensure that the positions of the skeletal elements during the procedure are identical to that found at the time of imaging. This can be achieved by using a frame that adjusts and immobilizes the patient's position. In this technique, at least three markers are placed on the skin prior to imaging. These markers have to be detectible by the imaging technique employed and are called fiducials. A multiplicity of fiducials is desirable for improving accuracy.

During the procedure, the patient's body is placed on a frame that allows precise positioning. Such frames are commonly used for spinal surgery and could be modified to allow their use during imaging and could be used for repositioning the patient during the procedure. These frames could be equipped with drive mechanisms that allow the body to be moved slowly through a variety of positions. The fiducials placed at the time of imaging are replaced by emitters. By activating the drive mechanism on the frame, the exact position of the emitters can be determined during the procedure and compared to the position of the fiducials on the preprocedural image data set stored in memory 106. Once the emitters assume a geometry identical to the geometry of the fiducials of the image data set, it is considered that the skeletal elements will have resumed a geometric relationship identical to the position during the preprocedural scan, and the procedure can be performed using the unaltered image data set stored in memory 106.

In general, instrumentation employed during procedures on the skeleton is somewhat different than that used for cranial applications. Rather than being concerned with the current location, surgery on the skeleton usually consists of placing hardware through bones, taking a biopsy through the bone, or removing

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PCT/US95/12894 fragments. Therefore, the instrumentation has to be specialized for this application.

One instrument that is used commonly is a drill. By placing emitters , on a surgical drill, and by having a fixed relationship between the drill body and its tip (usually a drill bit), the direction and position of the drill bit can be determined. At least three emitters would be needed on the drill, as most drills have a complex three-dimensional shape. Alternatively, emitters could be placed on a drill guide tube 800 having emitters 802, and the direction 804 of the screw being placed or hole being made could be determined by the digitizer and indicated on the image data set (see Fig.

.8) . The skeletal element 806 would also have emitters thereon to indicate its position.

Besides modification of existing instrumentation, new instrumentation is required to provide a reference system for surgery as discussed above. These reference frames, each equipped with at least 3 emitters, require fixation to the bone which prevents movement or rotation.

For open surgery, a clamp like arrangement, as depicted in Fig. 9, can be used. A clamp 900 is equipped with at least two points 902, 904, 906, 908 which provide fixation to a projection 910 of a skeletal element. By using at least two point fixation the clamp 900, which functions as a reference frame, will not rotate with respect to the skeletal element. The clamp includes emitters 912, 914, 916 which communicate with the array to indicate the position of the skeletal element as it is moved during the procedure.

Many procedures deal with bone fragments 940 which are not exposed during surgery, but simply fixated with either wires or screws 950, 952 introduced through the skin 954. Fig. 10 depicts a reference platform 956 attached to such wires or screws 950, 952 projecting

<img file="CA2201877C_D0001.tif" />

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PCTZÜS95/12894 through the skin 954. The platform 956 includes a plurality of emitters 958, 960, 962, 964 which communicate with the array to indicate the position of the bone fragment 940 as it is moved during the procedure.

The reference frame can be slipped over or attached to the projecting screws or wires to establish a reference system. Alternatively, the frame can be attached to only one wire, as long as the method of attachment of the frame to the screw or wire prevents rotation, and that the wire or screw cannot rotate within the attached skeletal element.

REFERENCE AND LOCALIZATION FRAMES

Fig- 11 is a schematic diagram of one preferred embodiment of a cranial surgical navigation system according to the invention. Portable system cabinet 102 includes a surgical work station 104 which is supported for viewing by the surgeon or technician using the system. Work station 104 includes a screen 106 for illustrating the various scans and is connected to a personal computer 108 for controlling the monitor 106.

The system also includes an optical digitizer including a camera array 110, a camera mounting stand 112 for supporting the array remote from and in line of sight with the patient, a digitizer control unit 114 on the portable system cabinet 102 and connected to the computer 108, a foot switch 116 for controlling operation of the system and a breakout box 118 for interconnecting the foot switch 116 and the digitizer control unit 114.

Also connected via the break out box 118 is a reference frame assembly 120 including a reference frame 122 with cable connected to the break out box 118, a vertical support assembly 124, a head clamp attachment

126 and a horizontal support assembly 128. Optical probe

130 (which is a localization frame) is also connected via

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64725-841 cable to the digitizer control unit 114 via the break out box 118.

In operation, a patient's head (or other rigid body element) is affixed to the head clamp attachment 126. To determine the position of optical probe 130 with respect to the head within the head clamp attachment 126, a surgeon would step on pedal 116 to energize the emitters of reference frame 122. The emitters would generate a light signal which would be picked up by camera array 110 and triangulated to determine the position of the head. The emitters of the optical probe 164 Would also be energized to emit light signals which are picked up by the camera array to determine the position of the optical probe 164. Based on the relative position of the head and the probe is4, control box 114 would illustrate a preoperative scan on the screen of monitor 106 which would indicate the position of the probe relative to and/or within the head.

Fig. 11A is a top plan view of one preferred embodiment of a cranial reference arc frame 122 according to the invention. Reference frame 122 is for use with a surgical navigation system such as illustrated in Fig. 11 having a sensor array such as camera array 110 which is in communication with the reference frame 122 to identify its position. The reference frame 122 includes a base member 132 having an upper base 134 and a base plate 136 which each have a semi-circular configuration and are joined together by screws 138 to form a cavity 140 therebetween. The base and plate may be made of anodized aluminum or other autoclavable material. The top of the upper base may be provided with one or more spring clamps 142 for engaging a Leyla retractor arm. As shown in Fig. 11A, the upper base is provided with five spring clamps 142.

Either or both ends of the reference frame 122 may be provided with a bayonet fitting 144 for engaging a

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64725-841 clamp which would also engage a Leyla retractor. One or both ends of the reference frame 122 is also formed into a radial projection 146 for supporting a screw 149 and crank handle 150 used to lock the reference frame to a head clamp such as head clamp 126 shown in Fig. ll or a

Mayfield Triad™ surgical clamp. This allows the reference frame 122 to be placed in a fixed position relative to the head so that any movement of the head would also include corresponding movement of the reference frame 122.

Radial projection 146, screw 148 and handle 150 constitute a coupling on the base member 132 for engaging a structure attached to a body part (the head) thereby providing a fixed reference relative to the head in order to maintain the base member 132 in fixed relation to the head.

Equally spaced about the reference frame 122 are a plurality of LEDs 152 for communicating with the camera array 110. The LEDs 152 are mounted in holes 154 in the upper base 134, which holes 154 are in communication with the cavity 140. Wires 156 are connected to each of the terminals of the LEDs 152 are positioned within the cavity 140. The other ends of the wires are connected to a connector 158 for engaging a cable connected to the digitizer 114 of the surgical navigation system. The cable provides signals for activating the LEDs 152. Connector 158 is mounted on a support projection 160 which projects from the base plate 136. This support projection 160 has a channel therein for permitting the wires to be connected to the connector 128. Fig. 11A is a wiring diagram of one preferred embodiment of the reference frame 122 according to the invention. As is illustrated in Fig. 11C, each LED terminal is connected to a separate pin of the connector 158. Although the invention is illustrated as having a connector for engaging a cable, it is contemplated that

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PCT/ÜS95/12894 the reference frame 122 may be battery operated so that no cable is necessary.

The reference frame 122 is essentially a semicircular arc so that it fits around the head of the patient to allow communication of multiple LEDs 152 on the reference frame 122 with the camera array 110. The multiple LEDs 152 on the reference frame 122 are positioned in a precisely known geometric arrangement so that the calibration of the camera array 110 can be checked continuously by comparing the LEDs geometric positions as calculated by the digitizer 114 with those precisely known geometric positions. Inconsistencies in this information indicates the need to recalibrate the system or to reposition the reference frame 122 so that it can more accurately communicate with the camera array

110. Frame 122 also includes a calibration divot 162.

In particular, divot 162 is an exactly located depression within the upper base 134 and is used to calibrate or check the calibration during the medical or surgical procedure the position of the tip of the probe. The precise location of each of the LEDs 152 relative to the calibration divot 162 is known. Therefore, locating a tip of a localization frame probe in the calibration divot 162 allows the calibration or the calibration check of the probes in the following manner. The tip of the probe is located within the calibration divot 162 and the LEDs on the probe are energized to provide light signals to the camera array 110. The LEDs on the reference frame 122 are also energized to communicate with the camera array 110. Using the known position of the divot 162 with respect to the position of each of the LEDs 152 as calculated by the digitizer 114, the location of the calibration divot 162 is compared to the location of the tip of the probe as calculated by the digitizer using the

LEDs on the probe in order to confirm that there is no distortion in the probe tip relative to the divot 162.

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Distortion in the probe tip indicates the need to recalibrate the probe so that it can more accurately communicate with the camera array 110 or to retire the probe 5 Figs. 12A, 12B, and 12C illustrate another preferred embodiment of the reference frame in the form of a spine reference arc frame 200. As with reference frame 122, spine reference arc frame 200 has an upper base 202 which engages a base plate 204 to form a cavity

206 therebetween. As shown in Fig. 12A, the spine reference arc frame 200 has a generally U-shape configuration with LEDs 208 located at the ends of the legs 209 of the ϋ-shaped member and at the intersection of the legs and base 211 of the U-shaped member.

Projecting laterally from the base 211 is a coupling 210 for engaging a thoraco-lumbar mount 212 as illustrated in Figs. 12D, 12E, and 12F. Also positioned on the base 211 is a calibration divot 214 which is a depression having the same purpose as the calibration divot 162 of the reference frame 122. Coupling 210 has twenty-four evenly spaced teeth 216 arranged in a circular pattern for engaging the twenty-four equally spaced teeth 218 of the thoraco-lumbar mount. This allows the spine reference arc frame 200 to be positioned to form various angles relative to the mount 212., It is contemplated that any other variable position connector may be used to join the spine reference arc frame 200 and the mount 212. Base plate 204 has an opening therein for engaging a connector 220 for receiving a cable to the digitizer control unit

114. The LEDs 208 are connected to the connector 220 by wires 222 as illustrated in wiring diagram Fig. 12G.

Referring to Figs. 12D, 12E, and 12F, thoracolumbar mount 212 comprises a clamp shaft 224 having an axial bore therein within which is positioned an actuating shaft 226 which is connected to an actuating knob 228 extending beyond the end of clamp shaft 224.

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The end of the actuating shaft 226 opposite the actuating knob 228 has an internal threaded bore 230 which engages external threads of an actuation screw 232. A U-shaped head 234 of screw 232 supports a pivot pin 236 between its legs. The pivot pin passes through the jaws 238 so that the jaws 23 8 rotate about the pivot pin 23 6 and move relative to each other defining a receiving area 240 within which a spinal bone or other body part may be clamped. The jaws 238 have teeth 239 for engaging a spinal bone or other body part and are spring loaded and held in their open position by spring plungers 242. As the actuating knob 228 is turned to engage the threads of actuation screw 232, the screw 232 is drawn into the bore 230 also drawing the jaws into a housing 246. This results in the camming surfaces 244 of housing 246 engaging the follower surfaces 248 of the jaws 238 closing the jaws and closing the receiving area 240 as the jaws are pulled into the housing.

The other end of clamp shaft 224 has a perpendicular projection 250 for supporting the teeth 218 which engage the teeth 216 of the coupling 210 of the spine reference arc frame 200. A spine reference arc clamp screw 252 passes through the array of teeth 218 and engages a threaded opening 254 in the coupling 210 of frame 200. Screw 252 engages opening 254 and locks teeth 216 and teeth 218 together to fix the angle between the spine reference arc frame 200 and the thoraco-lumbar mount 212. As a result, when the mount 212 is connected to a bone by placing the bone in the receiving area 240 and turning the actuating knob 228 to close the jaws 238 and the receiving area, the frame 200 is in a fixed position relative to the bone which is engaged by the jaws. Any movement of the bone results in movement of the frame 200 which can be detected by the camera array 110.

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Referring to Figs. 13A, 13B and 13C, one preferred embodiment of a localization biopsy guide frame 300 is illustrated. In general, the frame 300 includes a localization frame 302 which supports a biopsy guide 304 5 and which also supports a support pin 306. The localization frame 302 is comprised of an upper base 308. and a base plate 310 which join to form a cavity 312 within which the wires 314 connecting to the LEDs 316 are located. As shown in the figure 13A, the localization 10 frame has an elongated portion 318 and a generally Vshaped portion 320 having legs 322 and 324. An LED 316 is located at the end of each of the legs 322 and an LED 316 is also located at the ends of the elongated portion 318. As a result the four LEDs 316 form a rectangular 15 array. However, the underlying localization frame 302 does not have a rectangular configuration which allows it to be adapted for other uses, such as a drill guide assembly as illustrated and described below with regard to Figs. 13D and 13E. In general, the V-shaped portion 20 320 extends laterally from the elongated portion 318 in order to accomplish the rectangular configuration of the LEDs 316. Note that a rectangular configuration for the LEDs 316 is not required and that in fact, a trapezoidal configuration for the LEDs 316 may be preferred in order 25 to uniquely distinguish the orientation of the localization frame 302. Support pin 306 passes through the upper base 308 and is essentially parallel to a linear axis defined by the elongated portion 318. The purpose of support pin 306 is to allow clamps to engage 30 it so that the localization biopsy guide frame 300 can be placed in a particular position relative to a body part in order to guide a biopsy needle.

In order to guide a biopsy needle, the localization frame 302 is fitted with a biopsy guide 304 which is mounted to the top of the upper base 308 and held in place by a clamp 328 which engages

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64725-841 the upper base 3 08 via four screws 33 0. The upper base 308 is also provided with a semicircular channel 332 which forms a seat for receiving the biopsy guide 326. The guide 304 comprises a hollow tube 334 having a collar 336 at one end thereof, which has a threaded radial opening for receiving set screw 338.

The base plate 310 is fitted with a connector 340 for engaging a cable which is connected to the digitizer 114 for providing signals for energizing the LEDs 316. Figure 12G illustrates one preferred embodiment of a wiring diagram which interconnects the connector 340 and four LEDs.

The localization frame 302 is made of the same

TM material as the reference frame 122, i.e., ULTEM 1000 black which is autoclavable. The biopsy guide 304 may be stainless steel or any other autoclavable metal or plastic material. As with the reference frame, the localization frame may be battery operated thereby avoiding the need for a cable or a connector for engaging the cable.

Figs. 13D and 13E illustrate another localization device in the form of a localization drill guide assembly 350. The assembly 350 includes a localization frame 302 which is the same as the frame used for the localization biopsy guide frame 300, except that it does not have a support pin 306. It does have a semicircular channel 332 in the upper base 308 which receives a handle and drill guide assembly 354 instead of the biopsy guide tube assembly 304. Assembly 354 includes a handle 356 which is used by the surgeon, doctor, technician or nurse conducting the procedure. Handle 356 has a bore 358 therein for receiving a shaft 360 which is seated within the semicircular channel 332. The shaft terminates into an integral collar 362 which supports a drill guide tube 364. The axis of the drill

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64725-841 guide tube 364 is at an angle relative to the axis of the shaft 360 to assist in aligning the drill guide tube 364 relative to the point at which the drill bit will be entering the patient's body. In one preferred embodiment, handle and drill guide assembly 354 is a standard off-the-shelf instrument which is mounted to the channel 332 of the localization frame 302. The handle and drill guide assembly 354 may be a Sofamor Danek Part 870-705. Screws 366 (having heads insulated with high temperature RTV compound) attach the shaft 360 to the upper base 308 of the localization frame 302 and hold the shaft 360 in place within the channel 332. As noted above, the V-shaped portion 320 of the localization frame 302 forms an opening 368 between its legs 322 and 324 so that the drill guide tube 364 may be located therebetween and project downwardly from the plane generally defined by the localization frame 302. This allows the surgeon to sight in the position of the drill guide tube 364 by looking through the tube. Connector 370 is similar to connector 340, except that it provides an angular engagement with the cable which allows for more freedom of movement of the localization drill guide assembly 350. As with the localization frame noted above, the frame itself is made of ULTEM 1000 which is autoclavable. The handle may be wood, plastic, or any other autoclavable material and the shaft, collar and drill guide may be metal, plastic or other autoclavable material, such as stainless steel. Figure 13J illustrates a preferred embodiment of the wiring diagram for the localization drill guide assembly 350.

Figs. 13F and 13G illustrate another localization device in the form of a drill yoke localization frame 400. This frame 400 includes a localization frame 302 of the same configuration as the localization frames for the localization biopsy guide frame 300 and the localization drill guide assembly 350.

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64725-841

Projecting from the underside of the base plate 310 is a support member 402 which also supports a drill yoke 404 in a plane which is essentially perpendicular to the plane defined by the localization frame 302. Yoke 404 is essentially a collar which fits over the housing of a Midas Rex™ drill and is fixedly attached thereto by a set screw 406.

The drill yoke localization frame 400 allows the drill housing to be precisely positioned for use during surgery.

Support member 402 also supports a connector 408 for receiving a cable which is connected to the digitizer control unit 114. Support member 402 has a hollow channel therein so that the connector 408 may be connected to the wires 410 which connect to the LEDs 316.

Figure 13J illustrates one preferred embodiment of a wiring connection between the LEDs 316 and the connector 408.

Figs. 13H and 131 illustrate another localization device in the form of a ventriculostomy probe 500. Probe 500 includes a handle 502 having a bore 504 therein for receiving a support shaft 506 which in turn supports a catheter guide tube 508 along an axis which is parallel to the axis of the handle 502. The handle includes three LEDs 510 mounted along its top surface for communication with the camera array 110. The handle 502 has a hollow channel terminating in a bore 512 for receiving a connector 514. The connector 514 is connected to wires 516 which are also connected to the terminals of the LEDs 510. Figure 13J illustrates one preferred embodiment of a wiring diagram for interconnecting the connector 514 and the LEDs 510. In operation, the tube 508 is positioned within the body, the brain for example, so that a catheter may be inserted within the body. Tube 508 includes a top slot 518 which allows a catheter to be inserted therein. Preferably, the tube tip at its center is collinear with the chip

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PCT/ÜS95/12894 height of all three LEDs 510 so that a linear axis is defined therebetween. Based on this linear axis and the predetermined knowledge of the distance between the tip and the LEDs 510, the camera array 110 and digitizer 114 can determine the position of the tip at any instant during a surgical or medical procedure.

The system of the invention may be used in the following manner. A reference frame is attached to a body part. For example, cranial reference arc frame 122 may be attached directly to a head via a head clamp such as a Mayfield clamp or spine reference arc frame 200 may be attached directly to a spinous bone via thoraco-lumbar mount 212. Thereafter, movement of the body part will result in corresponding movement of the attached reference frame. The position of the body part may be tracked by energizing the LEDs of the reference frame to provide a signal to the camera array 110 so that the array can determine and track the position of the reference frame and, consequently, the position of the body part.

A localization frame is used to precisely position an instrument relative to the body part. For example, a localization biopsy guide frame 300 may be used to position a biopsy needle relative to the body part. Alternatively, a localization drill guide assembly 350 may be used to position a drill bit relative to the body part. Alternatively, a drill yoke localization frame 400 may be used to position a drill relative to the body part. Alternatively, a ventriculostomy probe 500 may be used to position a catheter relative to a body part. The position of the instrument may be tracked by energizing the LEDs of the localization frame to provide a signal to the camera array 110 so that the array can determine and track the position of the localization frame and, consequently, the position of the instrument96/11624

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During calibration of the system, the position of the reference frame relative to the body part is determined. Markers used during the preoperative scan are located and identified in coordinates of the surgical space as defined by the reference frame. Note that anatomic landmarks may be used as markers. This provides a relationship between the preoperative scan space and the surgical space. Once this relationship is established, the system knows the position of the preoperative scans relative to the reference frame and thus can generate scans which illustrate the position of the localization frame and the instrument relative to the body part. In other words, the system accomplishes image guided surgery. The system is ideally suited for locating small, deep-seated vascular lesions and tumors and for reducing the extent of the microsurgical dissection. It is also useful in identifying boundaries. For example, suppose a surgeon is trying to identify a boundary between normal brain and large supratentorial gliomas, which may be clearly shown on the preoperative scans but which may be difficult to visually locate in the operating room during a procedure. The surgeon would take a localization probe and position it a point near the boundary. The LEDs of the reference frame and localization probe are fired by use of the foot switch 116. As a result, the monitor 106 would provide a screen showing the position of the probe relative to a preoperative scan. By referring to the monitor, the surgeon can now determine the direction in which the probe should be more to more precisely locate the boundary. One the boundary is located, microcottonoid markers can be placed at the boundary of the tumor as displayed on the monitor before resection is started.

The placement of ventricular catheters for shunts, ventriculostomy, or reservoirs is also facilitated by the use of the system, especially in patients who have small

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64725-841 ventricles or who have underlying coagulopathy (e.g., liver failure, acquired immunodeficiency syndrome) that makes a single pass desirable. The system can also be useful for performing stereotactic biopsies. For further information regarding the system, see the following articles:

Germano, Isabelle M., The NeuroStation System for ImageGuided, Frameless Stereotaxy, Neurosurgery, Vol. 37, No.

2, August 1995.

Smith et al., The Neurostation™-A Highly accurate, Minimally Invasive Solution to Frameless Stereotactic Neurosurgery, Computerized Medical Imaging and Graphics, Vol. 1Θ, No. 4, pp. 247-256, 1994.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions, products, and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.