Patent Description:
In a procedure, an instrument can be tracked relative to a portion on which a procedure is performed. According to various systems, the portion having the procedure performed thereon may be a human subject. The procedure may include various surgical procedures, such as a cardiac procedure, neurologic procedure, or spinal procedure, or the like. In specific procedures, an intervertebral body may be replaced. The intervertebral body may include a complete or partial replacement of the intervertebral body (also referred to as a spinal disc) in a spinal column of a patient. To assist in performing the procedure, a location of an instrument may be illustrated with a display device. Image data acquired of a patient, however, may lack detail regarding various anatomical structures, such as soft tissue. Accordingly, the image displayed for viewing by a user may lack details or any information regarding various anatomical structures, such as soft tissues. Imaging and tracking systems are known from <CIT>, <CIT> and <CIT>.

The invention provides a system as defined by claim <NUM>.

In a selected procedure, an instrument may be tracked. The procedure may include surgical procedures performed on a subject. The subject may include a living subject, such as a human subject. It is understood, however, that non-human subjects or non-living subjects may also be subject to a procedure. Nevertheless, the location of the instrument may be displayed on a display for viewing by a user to assist in performing the procedure. In various embodiments, the display may illustrate both imaged and non-imaged portions.

A display may display a region of an anatomy that is not within the field of view or directly manipulated or contacted by the surgical instrument. For example, according to various embodiments, an intervertebral implant (also referred to as a disc) trial or implant may be moved relative to a subject. The image data of the subject may include x-ray image data, such as x-ray image slice data, such as computed tomography (CT) slice image data. When illustrating on a display device the image data acquired of a subject, the display may display image data not specifically within the range of the tracked instrument. In various embodiments, therefore, the tracked location of the instruments can be determined and the adjacent anatomical structures may be displayed even though they are not specifically affected by the instrument being tracked. Accordingly, although an intervertebral body instrument or trial is positioned relative to an anatomy, the end plates of vertebral bodies may be displayed when the location of the tracked instrument is determined to be within a predetermined distance range of and adjacent to the vertebral body. Accordingly, a user may better or more efficiently understand and visualize the location of a vertebral body relative to an instrument, which may include an intervertebral body implant or trial for performing a procedure.

An exemplary electromagnetic (EM) navigation system <NUM> is shown in <FIG>. Although the EM navigation system <NUM> is primarily described with respect to performing a procedure on a human patient <NUM>, the EM navigation system <NUM> may be used to perform a procedure on other animate and/or inanimate subjects. Also, the implementations disclosed herein may be applied to other EM systems and for purposes other than for position tracking of devices. For example, the implementations may be used to generate EM fields in a transcranial magnetic stimulation system. Also, procedures disclosed herein can be performed relative to a volume, a mechanical device, and/or an enclosed structure. The volume may be of an animate or inanimate object. The subject can be an object that includes an enclosed mechanical device. It is further understood, that any appropriate tracking or navigation system may be used such as an optical tracking system having cameras to track/view viewable portions. Further acoustic/ultrasound tracking systems may be used to track an instrument. Thus, although the disclosure herein relates to an EM navigation system, it is understood that any appropriate navigation system may be used unless specifically indicated otherwise.

With reference to <FIG>, an instrument assembly <NUM> may include an appropriate tool or instrument, such as one including a handle or motor and a toolbit or implant portion <NUM>. According to various embodiments, the implant portion <NUM> may be a trial member for use in trialing an implant placement. The implant may be a trial for an intervertebral or disk replacement. In various procedures, the trial implant <NUM> may be used to determine or select an appropriate implant size for a specific patient by moving the trial into the implant space.

The instrument <NUM> may include a portion that is positioned relative to, such as within, a spine <NUM> of the subject <NUM>. The tool assembly <NUM> may include a tracking device <NUM> and may be a navigated instrument. The instrument <NUM> is merely exemplary, and other navigated instruments may include catheters, leads, stimulators, etc. Also, the tracking device <NUM> may be incorporated into a separate element, such as a removable stylet. The stylet may be placed within a lumen of a catheter.

The tracking device <NUM> may be interconnected with the navigation system <NUM>. The navigation system <NUM>, as discussed further herein, may include a tracking system <NUM> that can track the tracking device <NUM> in six degrees of freedom, including three-dimensional space including a X, Y, Z location and various orientations to determine a position of the tracking device <NUM> in space. As illustrated above, the instrument <NUM> may include the tracking device <NUM> that allows for directly tracking the tool <NUM> during an implantation and positioning of tool <NUM>. Appropriate tracking devices can include tracking devices as disclosed in <CIT>. Additionally, the navigation system can include the navigation system disclosed in <CIT>.

With continuing reference to <FIG>, the tool <NUM> may be inserted into an opening, such through a surgical opening in a dermal layer of the subject <NUM> and into an intervertebral space <NUM> in the spine <NUM> of the subject <NUM>. The tool <NUM> may be tracked either directly via the tracking device <NUM> or via the tracking device on a stylet or other portion associated with the tool <NUM>. Further, as noted above, the tracking device <NUM> may be associated directly with the trial member <NUM>. Thus, any one or more of these may be used to track the selected portion of the tool assembly <NUM>. Further, the tool <NUM> may be a catheter that is placed in a vasculature of the subject <NUM>, a nasal cavity, or other portion of the subject <NUM>.

The navigation of the tool assembly <NUM> relative to the subject <NUM> may proceed according to various navigation procedures and techniques, such as those generally known in the art and discussed below, to ensure or assist in positioning the trial <NUM> in a selected, including a predetermined or preselected location, within the subject <NUM>. Further, although the following description is related generally to positioning the tool assembly <NUM> relative to the spine <NUM> of the subject <NUM>, other navigated procedures may be performed.

The navigation system <NUM>, which may include an electromagnetic navigation system, is primarily described with respect to performing a procedure on a human patient, the navigation system <NUM> may be used to perform a procedure on other animate and/or inanimate subjects, including those navigation systems as disclosed in <CIT>. Also, procedures disclosed herein can be performed relative to a volume, a mechanical device, and/or an enclosed structure. The volume may be of an animate or inanimate object. The subject can be an object that includes an enclosed mechanical device.

The navigation system <NUM> assists in performing a navigated or guided procedure. The guided procedure can be, for example, a surgical procedure, a vasculature procedure, a cardiac procedure, a neural procedure, a spinal procedure, and an orthopedic procedure. The navigation system <NUM> allows a user, such as a surgeon <NUM>, to view on a display <NUM> a position of the tool assembly <NUM> in a coordinate system. The coordinate system can be related to an image, such as in an image guided procedure, or can be related to an imageless procedure.

The navigation system <NUM> can operate as an image-based system or as an imageless system. While operating as an imageless system, the navigation system <NUM> can register a subject space (generally defined within and near the subject <NUM>) to a graphical display representing an area of the subject <NUM>, rather than to both the subject space and an image space. Image data of the subject <NUM> need not be acquired at any time, although image data can be acquired to confirm various locations of instruments or anatomical portions of the subject <NUM>. Positions of the subject <NUM> can be tracked and positions of the tool assembly <NUM> relative to the subject <NUM> can be tracked.

While operating as an imageless system, a position of an anatomical structure can be determined relative to the instrument and the positions of the anatomical structure and the instrument can be tracked. For example, a plane of an acetabulum can be determined by touching several points with the tool assembly <NUM>, or selected tracked tool with at least one of the tracking devices <NUM>. As another example, a position of a one or more vertebrae may be determined in a similar manner or by attached one or more dynamic reference frames (DRF) <NUM> to selected vertebrae. The position of the tool assembly <NUM> and the anatomical structure can be shown on a display with icons or graphics. The display, however, may not show actual image data captured of the subject <NUM>. Other data can be provided, such as atlas data or morphed atlas data. The atlas data can be image data that is generated or generalized from the subject <NUM>. For example, a brain atlas can be generated based on detail analysis of image data of a brain of a patient. Operation of the navigation system <NUM> as an image based system is further described below.

Although the navigation system <NUM> is described herein as acquiring image data using an imaging device <NUM>, other data may be acquired and/or used, such as patient and non-patient specific data. The imaging device <NUM> acquires pre-, intra-, or post-operative image data and/or real-time image data of a subject <NUM>. The imaging device <NUM> can be, for example, a fluoroscopic x-ray imaging device that may be configured as a C-arm having an x-ray source <NUM> and an x-ray receiving device <NUM>. Other imaging devices may be included and mounted on the imaging device <NUM>. Calibration and tracking targets and radiation sensors may be included with the imaging system <NUM>.

The navigation system <NUM> may further include an imaging device controller <NUM>. The imaging device controller <NUM> controls the imaging device <NUM> to (i) capture x-ray images received at the x-ray receiving section <NUM>, and (ii) store the x-ray images. The imaging device controller <NUM> may be separate from the imaging device <NUM> and/or control the rotation of the imaging device <NUM>. For example, the imaging device <NUM> can move in selected directions around the patient <NUM>. Also, the imaging device may include an O-arm ® imaging device as sold by Medtronic, Inc. , having a place of business in Minnesota.

Further, an imager tracking device <NUM> may be included to track a position of selected portions of the imaging device <NUM> to identify the position of the imaging device <NUM> relative to the subject <NUM> while acquiring the image data to assist in registration. The image data can then be forwarded from the imaging device controller <NUM> to a processing module of a navigation computer <NUM> wirelessly or via a link <NUM>. The navigation computer <NUM> can include a processing module that is configured to execute instructions to perform a procedure.

A work station <NUM> can include the navigation computer <NUM>, a navigation display <NUM>, a user interface <NUM>, and an accessible memory system <NUM>. The image data may be transmitted from the controller <NUM> to the work station <NUM> or to a tracking system <NUM>. The workstation <NUM> may be a portable computer, such as a laptop computer or a tablet computer. The navigation computer <NUM> including the computer module may include a general purpose processor that executes instructions for navigating the tool assembly <NUM> and/or may include an application specific circuit. The tracking system <NUM>, as discussed further herein, may include a coil array controller (CAC) <NUM> having a navigation device interface (NDI) <NUM>.

While the imaging device <NUM> is shown in <FIG>, any other alternative 2D, 3D or 3D imaging acquired over time to include four dimensions, imaging modality may also be used. Examples include those discussed above, and further any imaging device, such as isocentric fluoroscopy, bi-plane fluoroscopy, ultrasound, computed tomography (CT), multi-slice computed tomography (MSCT), T1 weighted magnetic resonance imaging (MRI), T2 weighted MRI, high frequency ultrasound (HIFU), positron emission tomography (PET), optical coherence tomography (OCT), intra-vascular ultrasound (IVUS), ultrasound, intraoperative, computed tomography (CT), single photo emission computed tomography (SPECT), and/or planar gamma scintigraphy (PGS) imaging devices may be used. Any of these imaging devices may be used to acquire pre- or post-operative and/or real-time images or image data of the subject <NUM>. The images may also be obtained and displayed, generally, in two or three dimensions. In more advanced forms, 3D surface rendering regions are achieved of the subject, which may be rendered or changed in time (fourth dimension). The 3D surface rendering regions may be achieved by incorporating subject data or other data from an atlas or anatomical model map or from pre-operative image data captured by MRI, CT, or echocardiography modalities. Image data sets from hybrid modalities, such as positron emission tomography (PET) combined with CT, or single photon emission computer tomography (SPECT) combined with CT, can also provide functional image data superimposed onto anatomical data to be used to reach target sites within the subject <NUM>.

The navigation system <NUM> further includes the tracking system <NUM>. The tracking system <NUM> includes a localizer <NUM>, which may also be referred to as a transmit coil array (TCA), a tracking array, or a transmit coil assembly. As noted above, the tracking system may include a non-EM tracking system, thus the localizer may be a camera array, an acoustic array, etc. as generally known in the art. The TCA <NUM> includes one or more coil groups or sets <NUM>, as discussed further herein, that can transmit or receive a signal and/or generate a field. The tracking system <NUM> may include the CAC <NUM>, the localizer <NUM>, and the instrument tracking device <NUM>, <NUM>, <NUM> of the tool assembly <NUM>. It is understood that the tracked portion may be generally referred to as an instrument and that the tracking device may be generally referred to as an instrument tracking device. The tracking system may also track a dynamic reference frame (DRF) <NUM>. All tracked portions are connected to the CAC <NUM> via the NDI <NUM>. The CAC <NUM> and the NDI <NUM> can be provided in a CAC/NDI container <NUM>. The NDI <NUM> may have communication ports that communicate with the localizer <NUM>, the instrument tracking device <NUM>, <NUM>, <NUM> and/or the DRF <NUM> wirelessly or via wires.

The coil arrays localizer <NUM> can transmit signals that are received by the DRF <NUM> and at least one tracking device <NUM> (e.g., the instrument tracking device <NUM>). The tracking device <NUM> can be associated with the tool assembly <NUM> at a location that is generally positioned within the subject <NUM> during a procedure. The DRF <NUM> can then transmit and/or provide signals, from the DRF tracking device <NUM>, based upon the received/sensed signals of the generated fields from the localizer <NUM> and/or other localizers. It is understood that the tracking system may also be operated in reverse, where the tracking devices <NUM><NUM> transmit a field that is sensed by the TCA <NUM>.

The DRF <NUM> can be connected to the NDI <NUM> to forward the information to the CAC <NUM> and/or the navigation computer <NUM>. The DRF <NUM> may be fixed to the subject <NUM> and adjacent to the region where navigation is occurring such that any movement of the subject <NUM> is detected as relative motion between the localizer <NUM> and the DRF <NUM>. The DRF <NUM> can be interconnected with the subject <NUM>. Any relative motion is indicated to the CAC <NUM>, which updates registration correlation and maintains accurate navigation.

In operation, the navigation system <NUM> creates a map between points in image data or an image space, such as one defined by an image <NUM> shown on the display <NUM>, and corresponding points in a subject space (e.g., points in an anatomy of a patient or in a patient space). After the map is created, the image space and subject space are registered to each other. This includes correlating position (location and orientations) in an image space with corresponding positions in a subject space (or real space). Based on the registration, the navigation system <NUM> may illustrate an icon <NUM> (which may include a three-dimensional rendering of the instrument, including the tool assembly <NUM>) at a navigated position of the tool assembly <NUM> relative to an image of the subject <NUM> in a super-imposed image. For example, the icon <NUM> can be illustrated relative to a proposed trajectory and/or a determined anatomical target. The work station <NUM> alone and/or in combination with the CAC <NUM> and/or the C-arm controller (or control module) <NUM> can identify the corresponding point on the pre-acquired image or atlas model relative to the tracked tool assembly <NUM>; and display the position on display <NUM> and relative to the image <NUM>. This identification is known as navigation or localization. The work station <NUM>, the CAC <NUM>, and the C-arm controller <NUM> and/or selected portions thereof can be incorporated into a single system or implemented as a single processor or control module.

To register the subject <NUM> to the image <NUM>, the user <NUM> may use point registration by selecting and storing particular points from the pre-acquired images and then touching the corresponding points on the subject <NUM> with a pointer probe or any appropriate tracked device. The navigation system <NUM> analyzes the relationship between the two sets of points that are selected and computes a match, which allows for a correlation of every point in the image data or image space with its corresponding point on the subject <NUM> or the subject space.

The points that are selected to perform registration or form a map are the fiducial markers, such as anatomical or artificial landmarks. Again, the fiducial markers are identifiable on the images and identifiable and accessible on the subject <NUM>. The fiducial markers can be artificial landmarks that are positioned on the subject <NUM> or anatomical landmarks that can be easily identified in the image data.

The navigation system <NUM> may also perform registration using anatomic surface information or path information (referred to as auto-registration). The navigation system <NUM> may also perform 2D to 3D registration by utilizing the acquired 2D images to register 3D volume images by use of contour algorithms, point algorithms or density comparison algorithms.

In order to maintain registration accuracy, the navigation system <NUM> tracks the position of the subject <NUM> during registration and navigation with the DRF <NUM>. This is because the subject <NUM>, DRF <NUM>, and localizer <NUM> may all move during the procedure. Alternatively the subject <NUM> may be held immobile once the registration has occurred, such as with a head holder. Therefore, if the navigation system <NUM> does not track the position of the subject <NUM> or an area of an anatomy of the subject <NUM>, any subject movement after registration would result in inaccurate navigation within the corresponding image. The DRF <NUM> allows the tracking system <NUM> to track the anatomy and can be used during registration. Because the DRF <NUM> is rigidly fixed to the subject <NUM>, any movement of the anatomy or the localizer <NUM> is detected as the relative motion between the localizer <NUM> and the DRF <NUM>. This relative motion is communicated to the CAC <NUM> and/or the processor <NUM>, via the NDI <NUM>, which updates the registration correlation to thereby maintain accurate navigation.

The tracking system <NUM> can position the localizer <NUM> adjacent to the patient space to generate an EM field (referred to as a navigation field). Because points in the navigation field or patient space is associated with a unique field strength and direction, the tracking system <NUM> can determine the position (which can include location and orientation) of the tool assembly <NUM> by measuring the field strength and direction or components of the EM field at the tracking device <NUM>. The DRF <NUM> is fixed to the subject <NUM> to identify the location of the subject <NUM> in the navigation field. The tracking system <NUM> continuously determines the relative position of the DRF <NUM> and the tool assembly <NUM> during localization and relates this spatial information to subject registration data. This enables image guidance of the tool assembly <NUM> within and/or relative to the subject <NUM>.

To obtain a maximum accuracy it can be selected to fix the DRF <NUM> in each of at least six degrees of freedom. Thus, the DRF <NUM> or any tracking device, such as the tracking device <NUM>, can be fixed relative to axial motion X, translational motion Y, rotational motion Z, yaw, pitch, and roll relative to a portion of the subject <NUM> to which the DRF <NUM> is attached. Any appropriate coordinate system can be used to describe the various degrees of freedom. Fixing the DRF <NUM> relative to the subject <NUM> in this manner can assist in maintaining maximum accuracy of the navigation system <NUM>.

The tool assembly <NUM> can include the stylet, drill, etc., as discussed above. Thus, reference to the tool assembly <NUM> is not intended to limit the instrument that may be tracked and navigated. With reference to any appropriate navigated instrument, it may include the tracking device <NUM> that may include a power source and/or be connected directly to the CAC <NUM>.

In the navigation system <NUM>, illustrated in <FIG>, the spine <NUM> may be the object of a procedure. During the procedure, the image data acquired of the spine <NUM> may be displayed on the display device <NUM>. In displaying the image of the spine, however, generally, the portion of the spine being directly affected by the instrument <NUM> is displayed on the display device <NUM>. Accordingly, certain parts of an anatomy may not be viewable with a limited display.

With continued reference to <FIG> and additional reference to <FIG>, image data can be acquired of the spine <NUM> prior to a procedure. The image data may be acquired with the imaging system <NUM>, or any appropriate imaging system. Further examples include the O-arm ® imaging device or a CT imaging system.

Image data regarding the spine <NUM> can be displayed on the display device <NUM> relative to the icon <NUM> of the instrument <NUM>, including the trial <NUM> as trial icon <NUM>'. This can allow the surgeon <NUM> to visualize on the display <NUM> the determined location of the trial <NUM> relative to the spine <NUM>. As is understood in the art, however, image data acquired of the subject <NUM>, including the spine <NUM>, can be acquired in various manners, including those discussed above. In various examples, slice image data can be acquired of the spine <NUM>, such as with a CT imaging device. Such image data generally includes slices that are taken axially along the length of the spine <NUM>. As illustrated in <FIG>, the spine <NUM> can include adjacent vertebrae <NUM> and <NUM>. The vertebrae <NUM>, <NUM> can include various anatomical portions including vertebral bodies <NUM> and <NUM>. Each of the vertebral bodies can include end plates. For example, the vertebral body <NUM> may include an superior end plate <NUM> and the vertebral body <NUM> may include an inferior end plate <NUM>. Further, the vertebrae may each include a spinous process, such as spinous process <NUM>.

It is understood that each of the vertebral bodies <NUM>, <NUM> may both include inferior and superior endplates, but generally, the inferior endplate <NUM> and the superior endplate <NUM> are adjacent to or contact a disc or define a disc or intervertebral body space <NUM>. In various embodiments, the intervertebral implant <NUM> can be positioned in the intervertebral space <NUM> when the natural intervertebral body is damaged or degenerated. Various implants and trials can include the implants and system portions included with the Prestige® Cervical Disc or the Bryan® Cervical Disc System, both sold by Medtronic, Inc. , having a place of business in Minnesota. Further, it is understood that discs may be replaced in other portions of the anatomy, including lumbar and thoracic regions of the spine <NUM>.

During imaging of the spine <NUM>, the disc space <NUM> can be imaged along with portions of the adjacent vertebrae <NUM>, <NUM>. As is understood in the art, however, CT image slices may generally be substantially thin, such as on the order of one or a few millimeters thick. Additionally, CT or other x-ray imaging techniques may not image soft tissue with high contrast. Further, certain imaging techniques may allow for imaging portions of the anatomy, such as the intervertebral space <NUM>, while not imaging the adjacent vertebral bodies <NUM>, <NUM>. Alternatively, or in addition thereto, as discussed further herein, during navigation of the trial or the implant <NUM>, the display <NUM> may display generally the intervertebral space <NUM> as this is where the implant portion <NUM> is positioned. Thus, if the imaging technique does not acquire image data of the soft tissue, the display may be substantially free to anatomical portions, as illustrated in <FIG>.

Accordingly, with additional reference to <FIG>, in various embodiments, the display <NUM> may generally include substantially only the icons <NUM>, <NUM>' representing the instrument <NUM> and/or the implant member <NUM>. It is understood that although the following discussion may refer to the implant or trial <NUM>, that the portion <NUM> may refer to either or both an implant and a trial, or other appropriate portion, being navigated relative to the patient <NUM>. Nevertheless, the icon <NUM> may generally be the only displayed portion on the display device <NUM> as the imaging technique acquiring image data of the spine <NUM> may not substantially image soft tissue, such as a disc or portion of a disc in the disc space <NUM>.

As the display <NUM> is displaying the anatomy adjacent to or at the dimensions of the tracked implant <NUM>, adjacent portions of the vertebrae <NUM>, <NUM> may not be illustrated, such as the endplates <NUM>, <NUM>. As illustrated in <FIG>, the implant portion <NUM> may include a surface that is illustrated in the icon <NUM>' and only image portions that are in the same plane are shown. Thus, the disk space <NUM> includes no high contrast tissue (e.g. bone). However, portions of the bone, such as the spinous process <NUM> may extend into the plane (although not within the disk space <NUM>) and may be seen in the view as spinous process portion <NUM>'. In various embodiments, therefore, a precise relative position of the implant <NUM> to the endplates <NUM>, <NUM> may not be known as visual clues may be missing regarding the endplates <NUM>, <NUM>. For example, the surgeon <NUM> may not have direct visualization on the display device <NUM> of the spacing of the implant <NUM> relative to the endplates <NUM>, <NUM>.

With reference to <FIG>, the display <NUM> may be altered based upon instructions from the user <NUM>, direction from the user <NUM>, or substantially automatically by the navigation system <NUM>. As discussed above, the tracking device <NUM> is tracked relative to the subject <NUM>, including the spine <NUM>. Due to the registration of the subject space to the image space, the navigation system <NUM> can determine, by tracking the tracking device <NUM>, the position of the implant <NUM> relative to the spine <NUM>, including the intervertebral space <NUM>. Accordingly, once the navigation system <NUM> has determined that the implant <NUM> is in or near the intervertebral space <NUM>, the navigation system can alter the display <NUM> to include further images based upon image data of the subject <NUM>. As illustrated in <FIG>, limiting the display <NUM> to display only the icon <NUM> may limit the amount of visual cues for the user <NUM> regarding the position of the implant <NUM> relative to the endplates <NUM>, <NUM>.

With reference to <FIG>, however, a first screen portion <NUM> may illustrate the inferior endplate <NUM> as an image portion <NUM>' and a second screen portion <NUM> may illustrate the superior endplate <NUM> as an image portion <NUM>'. Additionally, a third screen portion <NUM> may illustrate the intervertebral space <NUM> substantially alone with the icon <NUM> of the instrument including an intervertebral implant portion <NUM>'. As discussed further herein, therefore, the display <NUM> may display an icon representing the implant <NUM> and portions of the vertebrae <NUM>, <NUM>.

With continued reference to <FIG>, the display <NUM> may automatically or manually, or combinations thereof, display the three screen portions <NUM>-<NUM> to provide visual guidance and cues to the user <NUM>. For example, the user may view the screen portions <NUM>-<NUM> to view differing perspectives of the implant <NUM> relative to the anatomy. All of the view portions <NUM>-<NUM> may be shown on a single display device or screen <NUM>, as illustrated in <FIG> and <FIG>. For example, the first screen portion illustrates the icon <NUM>' superimposed on the superior endplate of the vertebral body <NUM>. Thus, the screen portion <NUM> may provide an inferior-to-superior viewing perspective. The second screen portion <NUM> illustrates the icon <NUM>' superimposed on the inferior endplate of the vertebral body <NUM>. Thus, the screen portion <NUM> may provide a superior-to-inferior viewing perspective. The perspectives may be labeled on the screen portions <NUM> and <NUM> for identification by the user <NUM>.

Further, the user <NUM> may view the display screen portions <NUM>-<NUM> to understand dimensions of the implant <NUM>, represented by the icon <NUM>' relative to the endplate images <NUM>', <NUM>'. For example, as illustrated in the screen portion <NUM>, the user <NUM> can view the implant icon <NUM>' relative to the medial-to-lateral and posterior-to-interior dimensions of the vertebrae endplate <NUM> based upon the image portion <NUM>'. Further, a height dimension may be illustrated or written on the display, such as in a text box <NUM> to illustrate the dimension of distance from a surface of the implant <NUM> to the endplate <NUM>. Therefore, the user <NUM> may view the screen portion <NUM> to determine the dimension of the implant <NUM> relative to the endplate <NUM>. Similarly, the user <NUM> can view the image portion <NUM> to determine the distance of a surface of the implant <NUM> relative to the endplate <NUM>. Further, a text box <NUM> can illustrate the distance from the endplate <NUM>.

The endplate images <NUM>', <NUM>' may be a single slice image or may include an average of several slices. As is known in the art, image data, such as in a CT image data, may be collected as a plurality of slices. The slices may each be a selected thickness, such as about <NUM>. To provide a general view of the boney portion which may include more than a small thickness (e.g. <NUM>) into the boney portion, several slices may be averaged together. For example, as illustrated in <FIG>, a distance <NUM> may extend between planes that define or form the intervertebral area <NUM>. A distance <NUM> into the vertebral body <NUM> may include about <NUM> to about <NUM>, and further include about <NUM> to about <NUM>. In various examples, the distance <NUM> may be about <NUM>. Thus, all slices within the distance <NUM> may be averaged together. The averaged image may then be displayed at the endplate <NUM>'. Similarly, a distance <NUM> into the vertebral body <NUM> may include about <NUM> to about <NUM>, and further include about <NUM> to about <NUM>. In various examples, the distance <NUM> may be about <NUM>. Thus, all slices within the distance <NUM> may be averaged together. The averaged image may then be displayed at the endplate <NUM>'.

The averaging of the slices to form the images <NUM>', <NUM>' may be formed with pixel averaging. For example, CT image slices are generally acquired along an axis, such as an axis of a spine including the vertebral bodies <NUM>, <NUM>. Thus, pixels from one slice to another may be aligned along the axis. The aligned pixels from several slices may be averaged together. In this way, one image may be generated that is based on averaging of several slices. It is understood that other appropriate averaging techniques may also be used.

The averaging allows the surgeon <NUM> to view portions, such as anatomical portions, that are not immediately adjacent the intervertebral space <NUM>. For example, an anatomical feature (e.g. an osteophyte) may be <NUM> from the space <NUM>. Thus, an image slice that is <NUM> or <NUM> thick would not image the osteophyte. However, in averaging a distance, such as about <NUM>, the osteophyte would be viewable in the averaged image that is displayed for the user <NUM>. This may assist the user in selecting an appropriate implant and placing the selected implant.

The screen portion <NUM> may show image data that is substantially bounded by the implant dimensions. Thus, the screen portion <NUM> may not show any of the high contrast image data that is beyond the disc space <NUM>. The screen portion <NUM> may show the endplate <NUM> that is away from the implant <NUM> in a superior direction. The screen portion <NUM> may show the endplate that is a distance away from the implant <NUM> in an inferior direction. Thus, the screen portions <NUM>-<NUM>, together, may show image data that is limited to the planes or extent of the implant <NUM> (e.g. screen portion <NUM>) along with image data that is spaced away from the implant <NUM> (i.e. screen portions <NUM> and <NUM>). All of the screen portions, however, may be understood to be viewed along an axis of the spine <NUM> of the patient <NUM>, but in the specific direction for the specific anatomical portion being viewed. Such direction information may also be provided on the screen portions regarding direction of view.

Claim 1:
A system for displaying information regarding a common axis in a subject, comprising:
a navigation system (<NUM>) having a tracking system (<NUM>) configured to determine a location of an instrument relative to at least a first portion of a subject and a second portion of the subject different from the first portion along the common axis;
a navigation processor (<NUM>) configured to execute instructions to determine the location of the instrument for illustrating with a display device (<NUM>) a representation of the instrument in both of a first direction along the common axis extending through the first portion of the subject and a second direction along the common axis extending through the second portion of the subject;
imaging means for providing a first image of the first portion of the subject and a second image of the second portion of the subject which are operable to be displayed along the common axis extending through the first portion and the second portion of the subject; and
wherein the first image of the first portion of the subject and the second image of the second portion of the subject are of the respective first portion and second portion at a respective selected distance along the single common axis away from the instrument;
wherein the first image is of the first portion of the subject and the second image is of the second portion of the subject along the single common axis;
the system further comprising:
a display device (<NUM>) configured to display simultaneously both (i) the first image and the representation of the instrument in the first direction and (ii) the second image and the representation of the instrument in the second direction along the common axis, wherein the first direction is opposite the second direction along the common axis.