Patent Description:
A surgical procedure may be performed on a subject, such as a human subject. The surgical procedure may require an incision into a subject to obtain access to tissue or organs covered by a dermal layer of a subject. Visual access or visual acuity in these areas may be limited due to covering by opaque tissues. Accordingly, determining a pose of an instrument within a subject may be selected.

In <CIT>, a system for calibrating an electromagnetic navigation system is provided. The system includes an antenna assembly having a substrate, multiple pairs of transmit coils, multiple receive coils, multiple input terminals, and multiple output terminals. The substrate includes multiple layers, and each of the transmit coils is deposited on a respective one of the layers and each of the receive coils is deposited on another respective one of the layers. Each of the pairs of transmit coils corresponds to a respective one of the receive coils. Each of the transmit coils is coupled to a respective one of the input terminals, and each of the receive coils is coupled to a respective one of the output terminals.

<CIT> discloses a method to remove distortion from a navigation system. The navigation system may be used to perform a procedure on a subject. The procedure may be any appropriate procedure. The navigation system may be used to account for the distortive effects of various conductive objects positioned near the subject on which the procedure is performed.

<CIT> discloses a system and a method for determining absolute position using a multiple wavelength signal.

The invention provides a method of operating a navigation system according to claim <NUM> and a method of operating a navigation system according to claim <NUM>.

A navigation system may be used to track and determine a pose, which can include at least some coordinates of position and/or orientation, of an instrument over time. In various embodiments, pose of the instrument is understood to include at least some tracked or navigated position coordinates (e.g. x, y, z) and/or orientation coordinates (e.g. roll, pitch, yaw). The navigation system may track a position and/or orientation, including six degree of freedom of motion (e.g. a three-dimensional position and a plurality, e.g. pitch, roll, and yaw orientation). The pose or position and/or orientation of the tracked instrument, therefore, may be determined over time. In various embodiments a visual representation of the instrument may be illustrated with a display device relative to a portion of the subject.

The navigation system, therefore, may be used to determine a position and/or orientation and/or a combination as a pose, including a plurality of positions and/or orientations and/or poses, of the instrument over time. In various embodiments, the pose of the tracked instrument may be determined relative to a subject. The subject may be any appropriate subject such as a living or non-living subject. In various embodiments, a non-living subject may include a hollow or enclosed casing, or other appropriate inanimate object. The inanimate object may have an outer covering that is opaque. Accordingly, a navigation or tracking system may be used to track an instrument during use relative to the inanimate object.

In various embodiments, the subject may include a living subject, such as a human subject. A procedure may include a surgical procedure where an instrument is posed within a subject for a selected period of time to perform a procedure, such as a stent placement, deep brain stimulation probe placement, or placing or implanting other implantable member. Further, selected procedures may include a bone resection, bore formation, or the like relative to the subject. Regardless, the pose of the instrument may be determined with the navigation system.

The navigation system may operate by transmitting data between various elements or portions of the tracking system. For example, in various embodiments, the navigation system may include a tracking device connected with an instrument (e.g. fixed or incorporated into the instrument) that wirelessly transmits a signal to an array. The array may include an antenna array, as discussed further herein. Similarly, or alternatively, the array may transmit a signal wirelessly to be received by the tracking device.

A spread spectrum, which may include various techniques as discussed herein, may be used to transmit a signal, determine a distorted signal and to either disregard and/or correct for the distorted signal. A spread spectrum system, such as frequency hopping, may include modulation and demodulation of a selected signal, and selected transforms of a signal to confirm or eliminate distortion or distorted signals within a system. Thus, the navigation system may incorporate a spread spectrum system to confirm or determine a signal for the tracking device.

Disclosed herein are exemplary embodiments, as discussed further herein. Generally, various embodiments may be disclosed relative to a human subject. It is understood, however, that various disclosed systems, such as navigation or tracking systems, may be used relative to any subject or system that may have an outer hull or shell that may encompass internal components or operations. For example, an air frame or automobile frame may obscure internal components, which may be selected to be operated on in a selected procedure. The selected procedure may include removal, replacement, or the like of various components of any non-animate or inanimate system. Accordingly, it is understood that a discussion herein relative to a subject, such as a human subject, is merely exemplary.

Further, as discussed herein, a navigation system may include tracking various components, such as an instrument, relative to a reference frame within a coordinate system or space. In various embodiments, the coordinate space may include a subject coordinate space or a real space defined by real space relative to the subject. Additional coordinate spaces may include image space that has an image coordinate space defined an image of the subject. A pose of an instrument, as discussed above that may include a position and orientation of the instrument, may be illustrated relative to, for example superimposed on, the image with a graphical representation for viewing by a user. Such illustrations may require or use registration between a subject space or subject coordinate space and an image coordinate space or image space.

A method to register a subject space defined by a subject to an image space may include those disclosed in U. <CIT>; <CIT>; <CIT>; and <CIT>.

<FIG>, according to various embodiments, is a diagrammatic view illustrating an overview of a procedure room or arena. In various embodiments, the procedure room may include a surgical suite. The surgical suite may include a navigation system <NUM> that can be used for various procedures, such as those relative to a subject <NUM>.

The navigation system <NUM> can be used to track the pose of one or more tracking devices, and the tracking devices may include a subject tracking device or dynamic reference frame (DRF) <NUM>, an imaging system tracking device <NUM>, and/or a tool tracking device <NUM>. It is understood that other tracking devices may also be included, such as a user or clinician tracking device alone or in combination with other systems (e.g. augmented reality systems). A tool <NUM> may be any appropriate tool such as a drill, forceps, or other tool operated by a user <NUM>. The tool <NUM> may also include an implant, such as a spinal implant or orthopedic implant. It should further be noted that the navigation system <NUM> may be used to navigate any type of instrument, implant, or delivery system, including: guide wires, arthroscopic systems, orthopedic implants, spinal implants, deep brain stimulation (DBS) probes, etc. Moreover, the instruments may be used to navigate or map any region of the body. The navigation system <NUM> and the various instruments may be used in any appropriate procedure, such as one that is generally minimally invasive or an open procedure.

An imaging device <NUM> may be used to acquire pre-, intra-, or post-operative or real-time image data of a subject, such as the subject <NUM>. It will be understood, however, that any appropriate subject can be imaged and any appropriate procedure may be performed relative to the subject. In the example shown, the imaging device <NUM> comprises an O-arm® imaging device sold by Medtronic Navigation, Inc. having a place of business in Louisville, Colorado, USA. The imaging device <NUM> may have a generally annular gantry housing <NUM> in which an image capturing portion is moveably placed. The image capturing portion may include an x-ray source or emission portion and an x-ray receiving or image receiving portion located generally or as practically possible <NUM> degrees from each other and mounted on a rotor relative to a track or rail. The image capturing portion can be operable to rotate <NUM> degrees during image acquisition. The image capturing portion may rotate around a central point or axis, allowing image data of the subject <NUM> to be acquired from multiple directions or in multiple planes. The imaging device <NUM> can include those disclosed in <CIT>; <CIT>; <CIT>; <CIT>; and <CIT>. In one example, the imaging device <NUM> can utilize flat plate technology having a <NUM>,<NUM> by <NUM>,<NUM> pixel viewing area.

The position of the imaging device <NUM>, and/or portions therein such as the image capturing portion, can be precisely known relative to any other portion of the imaging device <NUM>. The imaging device <NUM>, according to various embodiments, can know and recall precise coordinates relative to a fixed or selected coordinate system. This can allow the imaging system <NUM> to know its position relative to the patient <NUM> or other references. In addition, as discussed herein, the precise knowledge of the position of the image capturing portion can be used in conjunction with a tracking system to determine the position of the image capturing portion and the image data relative to the tracked subject, such as the patient <NUM>.

The imaging device <NUM> can also be tracked with the image tracking device <NUM>. The image data defining an image space acquired of the patient <NUM> can, according to various embodiments, be inherently or automatically registered relative to an object space. The object space can be the space defined by a patient <NUM> in the navigation system <NUM>. The automatic registration can be achieved by including the tracking device <NUM> on the imaging device <NUM> and/or the determinable precise pose of the image capturing portion. According to various embodiments, as discussed herein, imageable portions, virtual fiducial points and other features can also be used to allow for registration, automatic or otherwise. It will be understood, however, that image data can be acquired of any subject which will define subject space. Patient space is an exemplary subject space. Registration allows for a map between patient space and image space.

The patient <NUM> can also be tracked as the patient moves with the patient tracking device, DRF, or tracker <NUM>. Alternatively, or in addition thereto, the patient <NUM> may be fixed within navigation space defined by the navigation system <NUM> to allow for registration. As discussed further herein, registration of the image space to the patient space or subject space allows for navigation of the instrument <NUM> with the image data. When navigating the instrument <NUM>, a pose of the instrument <NUM> can be illustrated relative to image data acquired of the patient <NUM> on a display device <NUM>. Various tracking systems, including at least one of an optical localizer <NUM> or an electromagnetic (EM) localizer <NUM>, can be used to track the instrument <NUM>. As discussed herein, in various embodiments, the localizer <NUM> may transmit a signal that is received by the tracking device <NUM>, or other appropriate tracking device. In addition, an appropriate antenna, e.g. a coil, may also be provided as a received. For example, a calibration receiver <NUM> (e.g. a coil) may be provided to receive a signal form the localizer <NUM>. The calibration receiver <NUM> may be included in any appropriate portion of the navigation system <NUM>, such as a controller <NUM>, as discussed further herein. It is understood by one skilled in the art that the calibration receiver <NUM> need not be incorporated into the navigation system <NUM> during a use, but may be provided or used during an initial (e.g. factory) production or calibration of the navigation system <NUM>. In various embodiments, the calibration receiver <NUM> may receive the signal from the localizer <NUM> in a manner similar to the tracking device <NUM> and be used for various purposes, as discussed herein.

More than one tracking system can be used to track the instrument <NUM> in the navigation system <NUM>. According to various embodiments, tracking systems can include an electromagnetic tracking (EM) system having the EM localizer <NUM> and/or an optical tracking system having the optical localizer <NUM>. Either or both of the tracking systems can be used to tracked selected tracking devices, as discussed herein. It will be understood, unless discussed otherwise, that a tracking device can be a portion trackable with a selected tracking system. A tracking device need not refer to the entire member or structure to which the tracking device is affixed or associated.

It is further appreciated that the imaging device <NUM> may be an imaging device other than the O-arm® imaging device and may include in addition or alternatively a fluoroscopic C-arm. Other exemplary imaging devices may include fluoroscopes such as bi-plane fluoroscopic systems, ceiling mounted fluoroscopic systems, cath-lab fluoroscopic systems, fixed C-arm fluoroscopic systems, isocentric C-arm fluoroscopic systems, 3D fluoroscopic systems, etc. Other appropriate imaging devices can also include MRI, CT, ultrasound, etc..

In various embodiments, an imaging device controller <NUM> may control the imaging device <NUM> and can receive the image data generated at the image capturing portion and store the images for later use. The controller <NUM> can also control the rotation of the image capturing portion of the imaging device <NUM>. It will be understood that the controller <NUM> need not be integral with the gantry housing <NUM>, but may be separate therefrom. For example, the controller may be a portion of the navigation system <NUM> that may include a processing and/or control system <NUM> including a processing unit or processing portion <NUM>. The controller <NUM>, however, may be integral with the gantry <NUM> and may include a second and separate processor, such as that in a portable computer.

The patient <NUM> can be positioned, including fixed, on an operating table <NUM>. According to one example, the table <NUM> can be an Axis Jackson ® operating table sold by OSI, a subsidiary of Mizuho Ikakogyo Co. , having a place of business in Tokyo, Japan or Mizuho Orthopedic Systems, Inc. having a place of business in California, USA. Patient positioning devices can be used with the table, and include a Mayfield ® clamp or those set forth in <CIT> (<CIT>) entitled "An Integrated Electromagnetic Navigation And Patient Positioning Device".

The position of the patient <NUM> relative to the imaging device <NUM> can be determined by the navigation system <NUM>. The tracking device <NUM> can be used to track and determine a pose of at least a portion of the imaging device <NUM>, for example the gantry or housing <NUM>. The patient <NUM> can be tracked with the dynamic reference frame <NUM>, as discussed further herein. Accordingly, the position of the patient <NUM> relative to the imaging device <NUM> can be determined. Further, the pose of the imaging portion can be determined relative to the housing <NUM> due to its precise position on the rail within the housing <NUM>, substantially inflexible rotor, etc. The imaging device <NUM> can include an accuracy of within <NUM> microns, for example, if the imaging device <NUM> is an O-Arm® imaging device sold by Medtronic Navigation, Inc. having a place of business in Louisville, Colorado. Precise positioning of the imaging portion is further described in <CIT>; <CIT>; <CIT>; <CIT>; and <CIT>.

According to various embodiments, the imaging device <NUM> can generate and/or emit x-rays from the x-ray source that propagate through the patient <NUM> and are received by the x-ray imaging receiving portion. The image capturing portion generates image data representing the intensities of the received x-rays. Typically, the image capturing portion can include an image intensifier that first converts the x-rays to visible light and a camera (e.g. a charge-coupled device) that converts the visible light into digital image data. The image capturing portion may also be a digital device that converts x-rays directly to digital image data for forming images, thus potentially avoiding distortion introduced by first converting to visible light.

Two dimensional and/or three dimensional fluoroscopic image data that may be taken by the imaging device <NUM> can be captured and stored in the imaging device controller <NUM>. Multiple image data taken by the imaging device <NUM> may also be captured and assembled to provide a larger view or image of a whole region of a patient <NUM>, as opposed to being directed to only a portion of a region of the patient <NUM>. For example, multiple image data of the patient's <NUM> spine may be appended together to provide a full view or complete set of image data of the spine.

The image data can then be forwarded from the image device controller <NUM> to the navigation computer and/or processor system <NUM> that can be a part of a controller or work station <NUM> having the display <NUM> and a user interface <NUM>. It will also be understood that the image data is not necessarily first retained in the controller <NUM>, but may also be directly transmitted to the work station <NUM>. The work station <NUM> can provide facilities for displaying the image data as an image <NUM> on the display <NUM>, saving, digitally manipulating, or printing a hard copy image of the received image data. The user interface <NUM>, which may be a keyboard, mouse, touch pen, touch screen or other suitable device, allows the user <NUM> to provide inputs to control the imaging device <NUM>, via the image device controller <NUM>, or adjust the display settings of the display <NUM>. The work station <NUM> may also direct the image device controller <NUM> to adjust the image capturing portion of the imaging device <NUM> to obtain various two-dimensional images along different planes in order to generate representative two-dimensional and three-dimensional image data.

With continuing reference to <FIG>, the navigation system <NUM> can further include the tracking system including either or both of the electromagnetic (EM) localizer <NUM> and/or the optical localizer <NUM>. The tracking systems may include the controller and interface portion <NUM>. The controller <NUM> can be connected to the processor portion <NUM>, which can include a processor included within a computer. The EM tracking system may include the STEALTHSTATION® AXIEM™ Navigation System, sold by Medtronic Navigation, Inc. having a place of business in Louisville, Colorado; or can be the EM tracking system described in <CIT>, and entitled "METHOD AND APPARATUS FOR SURGICAL NAVIGATION"; <CIT>; and <CIT>. It will be understood that the navigation system <NUM> may also be or include any appropriate tracking system, including a STEALTHSTATION® TREON ® or S7™ tracking systems having an optical localizer, that may be used as the optical localizer <NUM>, and sold by Medtronic Navigation, Inc. of Louisville, Colorado. Other tracking systems include an acoustic, radiation, radar, etc. The tracking systems can be used according to generally known or described techniques in the above references. Details will not be included herein except when to clarify selected operation of the subject disclosure.

Wired or physical connections can interconnect the tracking systems, imaging device <NUM>, etc. Alternatively, various portions, such as the instrument <NUM> may employ a wireless communications channel, such as that disclosed in <CIT>, as opposed to being coupled directly to the controller <NUM>. Also, the tracking devices <NUM>, <NUM>, can generate a field and/or signal that is sensed by the localizer(s) <NUM>, <NUM>. In various embodiments, the instrument tracking device <NUM>, and/or other appropriate tracking devices, may communicate with a wireless signal <NUM>, as discussed herein, with the controller <NUM> and/or the array <NUM>. In various embodiments, the array <NUM> may operate with a spread spectrum signal to communicate with the tracking device <NUM>.

Various portions of the navigation system <NUM>, such as the instrument <NUM>, and others as will be described in detail below, can be equipped with at least one, and generally multiple, of the tracking devices <NUM>. The instrument can also include more than one type or modality of tracking device <NUM>, such as an EM tracking device and/or an optical tracking device. The instrument <NUM> can include a graspable or manipulable portion at a proximal end and the tracking devices may be fixed near the manipulable portion of the instrument <NUM>. It is understood, however, that the tracking device may also be placed at a distal or intervention end of the instrument <NUM>.

Additional representative or alternative localization and tracking system is set forth in <CIT>. The navigation system <NUM> may be a hybrid system that includes components from various tracking systems.

According to various embodiments, the navigation system <NUM> can be used to track the instrument <NUM> relative to the patient <NUM>. The instrument <NUM> can be tracked with the tracking system, as discussed herein, such as by tracking and determining a pose of the tracking device <NUM>. Image data of the patient <NUM>, or an appropriate subject, can be used to assist the user <NUM> in guiding the instrument <NUM>. The image data, however, is registered to the patient <NUM>. The image data defines an image space that is registered to the patient space defined by the patient <NUM>. The registration can be performed as discussed herein, automatically, manually, or combinations thereof.

Generally, registration allows a map, also referred to as a registration map, to be generated of the physical pose of the instrument <NUM> relative to the image space of the image data. The map allows the tracked pose of the instrument <NUM> to be displayed on the display device <NUM> relative to the image data <NUM>. It is understood that the display device <NUM> may be any appropriate display device, or include more than a single display device, such as including augmented reality viewers, head mounted displays, etc. A graphical representation 68i, also referred to as an icon, can be used to illustrate the pose (e.g. three-dimensional coordinate location and one or more degree of freedom orientation) of the instrument <NUM> relative to the image <NUM>.

With continuing reference to <FIG> and additional reference to <FIG>, a subject registration system or method can use the subject tracking device <NUM>. The tracking device <NUM> may include portions or members <NUM> that may be trackable, but may also act as or be operable as a fiducial assembly. The fiducial assembly <NUM> can include a clamp or other fixation portion <NUM> and the imageable fiducial body <NUM>. It is understood, however, that the members <NUM> may be separate from the tracking device <NUM>. The fixation portion <NUM> can be provided to fix any appropriate portion, such as a portion of the anatomy. As illustrated in <FIG>, the fiducial assembly <NUM> can be interconnected with a portion of a spine such as a spinous process of the subject <NUM>.

The fixation portion <NUM> can be interconnected with the spinous process in any appropriate manner. For example, a pin or a screw can be driven into the spinous process. Alternatively, or in addition thereto, a clamp portion <NUM> can be provided to interconnect the spinous process. The fiducial portions <NUM> may be imaged with the imaging device <NUM>. It is understood, however, that various portions of the subject (such as a spinous process) may also be used as a fiducial portion.

In various embodiments, when the fiducial portions <NUM> are imaged with the imaging device <NUM>, image data is generated that includes or identifies the fiducial portions <NUM>. The fiducial portions <NUM> can be identified in image data automatically (e.g. with a processor executing a program), manually (e.g. by selection an identification by the user <NUM>), or combinations thereof (e.g. by selection an identification by the user <NUM> of a seed point and segmentation by a processor executing a program). Methods of automatic imageable portion identification include those disclosed in <CIT>. Manual identification can include selecting an element (e.g. pixel) or region in the image data wherein the imageable portion has been imaged. Regardless, the fiducial portions <NUM> identified in the image data can be used as fiducial points or positions that can be used to register the image data or the image space of the image data with patient space.

In various embodiments, to register an image space or coordinate system to another space or coordinate system, such as a navigation space, the fiducial portions <NUM> that are identified in the image <NUM> may then be identified in the subject space defined by the subject <NUM>, in an appropriate manner. For example, the user <NUM> may move the instrument <NUM> relative to the subject <NUM> to touch the fiducial portions <NUM>, if the fiducial portions are attached to the subject <NUM> in the same position during the acquisition of the image data to generate the image <NUM>. It is understood that the fiducial portions <NUM>, as discussed above in various embodiments, may be attached to the subject <NUM> and/or may include anatomical portions of the subject <NUM>. Additionally, a tracking device may be incorporated into the fiducial portions <NUM> and they may be maintained with the subject <NUM> after the image is acquired. In this case, the registration or the identification of the fiducial portions <NUM> in a subject space may be made. Nevertheless, according to various embodiments, the user <NUM> may move the instrument <NUM> to touch the fiducial portions <NUM>.

The tracking system, according to various embodiments, may track the pose of the instrument <NUM> due to the tracking device <NUM> attached thereto. This allows the user <NUM> to identify in the navigation space (which may include or be a portion of the subject space) the poses (including, for example, six degree of freedom information including locating and orientation) of the fiducial portions <NUM> that are identified in the image <NUM>. After identifying the positions of the fiducial portions <NUM> in the navigation space, the map may be made between the subject space defined by the subject <NUM> in a navigation space and the image space defined by the image <NUM>. Accordingly, identical or known locations allow for registration as discussed further herein.

During registration, the map is determined between the image data coordinate system of the image data such as the image <NUM> and the patient space defined by the patient <NUM>. Once the registration occurs, the instrument <NUM> can be tracked with the tracking system that is registered to the image data to allow an identification and illustration of a pose of the tracked instrument <NUM> as an icon superimposed on the image data. Registration of the image <NUM> (or any selected image data) to the subject <NUM> may occur at any appropriate time.

In various embodiments, the image space <NUM> and the subject space defined by the subject <NUM> may be registered according to a method <NUM>. As discussed above, the image to patient registration may include acquiring and/or accessing (e.g. from a memory system having the image data stored thereon) image data of a subject, such as the subject <NUM>, with fiducials in block <NUM>. The image data of the subject <NUM> may be any appropriate image data, such as image data acquired with the imaging system <NUM>. Further, the fiducials may include the fiducial portions <NUM>, as discussed above, and/or appropriate anatomical portions of the subject <NUM>. For example the fiducial portions may include portions of the anatomy such as the spinous process of the subject <NUM>. Nevertheless, the acquired image data may include the fiducials therein. Once the image data is acquired of the subject with the fiducials, identification of the fiducials in the image space may occur in block <NUM>.

The identification of the fiducials in the image space in block <NUM> may occur, as also discussed above. For example, an automatic identification of the fiducials may be made in the image data that defines the image space, such as through automatic segmentation of the fiducial portions within the image. Also manual identification and/or combination manual-and-automatic identification may be used to determine the fiducials in the image space. The combination may include the user <NUM> identifying one or more pixels as seed pixels and a processor executing a segmentation program based on the seed pixels.

The identification of the fiducials in a subject space and/or navigation space occurs in block <NUM>. The subject space may be coextensive with the navigation space and/or may overlap. Generally, the navigation space is the volume that may be tracked with the tracking system, such as the localizer <NUM> and may encompass all or a portion of the subject or patient <NUM>. The identification of the fiducials in the navigation space may occur in various manners such as moving a trackable instrument, such as the instrument <NUM>, relative to the fiducial portions <NUM> (which may also be a tracking device) and/or the spinous process. The tracking system of the navigation system <NUM> may track the instrument <NUM> and the navigation system <NUM> may include an input to input the portions that are the fiducial portions <NUM> in the navigation space. The determination or identification of the pose (e.g. including at selected degree of freedom information including three dimensional location and orientation) of the fiducials in the navigation space may then be used to form the map, between two or more coordinate systems, in block <NUM>.

Determination of the map determined in block <NUM> may be a correlation or registration of the coordinate system of the image space to the coordinate system of the navigation space relative to and/or including the subject <NUM>. The map allows for a determined pose of a tracked portion in the navigation space to be mapped to an equivalent or identical pose in the image. Once the mapped pose is determined, the pose may be illustrated or displayed with the display relative to the image <NUM>, such as by the superimposing of the icon 68i on or relative to the image <NUM>.

The image to patient registration allows for the illustration of tracked instruments or items relative to the image <NUM>. Without the registration, however, any element not trackable or registered to the image <NUM> may not be appropriately or precisely illustrated at a real world pose relative to the image <NUM>. Thus, registration may allow for illustration, such as with the icon 68i, of a determined pose of the instrument <NUM> relative to the subject <NUM>.

After the registration of the image space to the patient space, the instrument <NUM> can be tracked relative to the image <NUM>. As illustrated in <FIG>, the icon 68i representing a pose (which may include a <NUM> degree of freedom pose (including <NUM> dimensional location and <NUM> degree of freedom orientation)) of the instrument <NUM> can be displayed relative to the image <NUM> on the display <NUM>. Due to the registration of the image space to the patient space, the pose of the icon 68i relative to the image <NUM> can substantially identify or mimic the pose of the instrument <NUM> relative to the patient <NUM> in the patient space. As discussed above, this can allow a navigated procedure to occur.

With additional reference to <FIG>, and continuing reference to <FIG>, the localizer <NUM>, which may also be referred to as an array or an antenna array, may be provided in any physical configuration for use of a selected or appropriate procedure. For example, as illustrated in <FIG>, the localizer <NUM> is provided or formed to include a selected geometry, such as lobes. In various embodiments the localizer <NUM>, as illustrated in <FIG>, may be planar or more elongated in shape. The localizer <NUM> may include a plurality of coils, such as any appropriate number, to generate the navigation field or domain. The navigation field or domain may include a volume <NUM>. The navigation volume <NUM> is generally sized or moved or placed relative to the subject <NUM> to allow for navigation of one or more instruments, such as the instrument <NUM> relative to the subject <NUM>. The instrument <NUM> may include one or more tracking devices, such as the tool tracking device <NUM>. The array <NUM> may transmit a signal, as discussed further herein, which may be received by the tracking device <NUM> or other appropriate tracking devices, such as the subject tracker <NUM> and/or the imaging device tracker <NUM>.

In various embodiments, the array <NUM> may be incorporated into the bed or support <NUM>. Alternatively, or in addition thereto, the array <NUM> may be configured into a shape or size such that the array may be placed below the subject <NUM> and the subject <NUM> is placed atop at least a portion of the array <NUM>. In various embodiments, for example, the array <NUM> may be placed (e.g. fixed) near a lumbar spine of the subject <NUM> and/or a head of the subject <NUM> to allow for the navigation field <NUM> to be centered and/or encompass the selected area of the subject <NUM> for navigation.

The navigation system <NUM> may be operated in selected environments, such as in an operating room that includes various other components in addition to the instrument <NUM>. For example, the navigation system <NUM> may operate in an operating room including the imaging system <NUM>, the operating table <NUM>, and/or other components. Further, a plurality of instruments may be provided for a selected procedure such as the instrument <NUM> and additional or alternative instruments such as a drill motor <NUM> that may be placed in a storage or holding area <NUM>. The holding area <NUM> may include a conductive and/or magnetic material, such as a metal tray or a conductive polymer tray. The tray <NUM> may be formed of various or selected metal or metal alloys, such as aluminum or stainless steel. In various embodiments, the signal transmitted by the array <NUM> may be interfered with due to interactions or distortions from various metallic substances, such as the tray <NUM>, the drill <NUM>, the imaging system <NUM>, or other metal portions in the operating room in which the navigation system <NUM> is placed. Objects or items that may distort the field or signal may be referred to as distorting or distortion objects.

The array <NUM> may be operated, as discussed further herein, to emit a signal or field. The field emitted by the localizer <NUM> may be sensed by one or more of the tracking devices, such as the instrument tracking device <NUM>. The field emitted by the array <NUM>, therefore, may be distorted due to the metallic objects in or near the navigation volume <NUM>. Accordingly, the signal received by the tracking device <NUM>, or other tracking devices in the navigation system <NUM>, may include both the emitted signal and distortion. Distortion may be generated by eddy currents in conductive items or magnetizations in magnetic items, which may be referred to herein as "distorting items". The signal received by the tracking device <NUM> may be transmitted to an appropriate processing system such as one or more processors in the controller <NUM> and/or the processing unit <NUM>. The signal received may include distortion, if objects are near the navigation volume <NUM> that cause distortion. Accordingly, a distortion detection and correction (DDC) module <NUM> (which may include an equalization) may be incorporated or executed by the processing unit <NUM>. The DDC module <NUM>, as discussed further herein, may be used to assist in removing distortion from the signal received by the tracking device <NUM>. Once the distortion is removed in the DDC module <NUM>, a navigation module <NUM> may also be incorporated into the processing unit <NUM> and/or executed by the processing unit <NUM>. The navigate module <NUM> navigates with the corrected signal to determine a pose of the tracking device <NUM> in the navigation volume <NUM>. Thus, a tracking signal may be emitted by the localizer and received by the tracking device <NUM>. The received tracking signal may include distortion. As discussed above, the navigation of the instrument <NUM> including in the tracking device <NUM> may allow for an illustration of a graphical representation 68i of the instrument <NUM> relative to the image <NUM> of the subject <NUM>.

Due to the navigation registration, therefore, the user <NUM> may view a pose of the instrument <NUM> relative to the subject <NUM> with the monitor <NUM>. It is understood, by one skilled in the art, that the tracking device <NUM> may also transmit a signal that is received by the localizer <NUM>. The transmitted signal may be received by the localizer <NUM> and a similar equalizer and navigation module may be used to determine a pose of the tracking device <NUM> relative to the subject <NUM> in a similar manner but where the signal is received by the localizer <NUM>, rather than transmitted by the localizer <NUM>. Further, one skilled in the art will understand that the plurality of instruments may be navigated substantially simultaneously to allow for illustration of a plurality of instruments relative to the image <NUM> simultaneously when a plurality of instruments are tracked relative to the subject <NUM> in the navigation volume <NUM> substantially simultaneously.

The localizer <NUM>, regardless of its configuration or external geometry may include one or more coils <NUM>. The localizer may include an appropriate number of coils <NUM>, such as enough to transmit a signal to resolved at the tracking device <NUM> to navigate the tracking device <NUM>. The localizer <NUM>, therefore, may include one or more coils <NUM>, including nine or more coils, <NUM> or more coils <NUM>, or up to <NUM> coils, or an appropriate number of the coils <NUM> The coils <NUM> may be provided in any appropriate number and the number discussed herein is merely exemplary. For example, the localizer <NUM> may include three coils that are substantially orthogonally oriented and placed relative to one another around a single center or origin. Alternatively, or in addition thereto, one or more coils may be placed and oriented at a selected angle relative to one another within the localizer <NUM>. Regardless of the configuration, the one or more coils generate a navigation field with an electromagnetic (EM) signal that may be sensed by the respective tracking devices, including the tracking device <NUM>, to allow for determination of a pose of the tracking device <NUM> in space.

With continuing reference to <FIG> and additional reference to <FIG>, the localizer <NUM> may be configured in any appropriate manner, including those discussed herein. Exemplary illustrated in <FIG> is a rectangular localizer assembly. The localizer assembly <NUM> may include one or more coils <NUM>, such as a first coil 200a. The coil 200a may be included in the localizer <NUM> along with one or more other coils, such as a second coil 200b. It is understood that any appropriate number of coils may be provided and two coils 200a, 200b is merely exemplary. Further, the localizer <NUM> may be controlled by the controller <NUM> and/or have an onboard controller such as a controller or control module <NUM>'. Further, in various embodiments a local power source or converter may be provided at the localizer <NUM>. For example, a power converter or battery may be provided to provide power to the controller <NUM>' and/or the coils <NUM> to transmit the tracking signal. In various embodiments, an external power source, as an alternative to and/or in addition to the local power source, may transmit power to the controller <NUM>,<NUM>' and/or the coils <NUM> from a location away from the localizer <NUM>.

Regardless of the number or configuration, the respective coils, including the coils <NUM>, may be driven to transmit a signal that may be received by the tracking device <NUM>. In various embodiments, for example, the respective coils 200a, 200b may be placed or incorporated into an "H" bridge configuration or switch system. With reference to the coil 200a, and understanding of the second coil 200b may be incorporated into a similar configuration, the coil 200a may be interconnected between a drive source and a ground with a plurality of switches. In various embodiments, for example, the coil 200a may be integrated into an "H" bridge assembly <NUM>. The "H" bridge assembly <NUM> may include a plurality of switches including a first switch <NUM>, a second switch <NUM>, a third switch <NUM> and a fourth switch <NUM>. The switches <NUM>-<NUM> may selectively allow a current to be driven through the coil 200a from a source or voltage source <NUM> to a ground or outlet <NUM>.

For example, the first switch <NUM> and the second switch <NUM> may be closed to allow a voltage to form across the coil 220a and a current to flow through the coil 200a in a first direction. Similarly the third switch <NUM> and the fourth switch <NUM> may be closed, with the respective first and second switches <NUM>, <NUM> being open, to allow current to be driven through the coil 200a in a second direction. As discussed above, the controller <NUM> may be used to control selected switches to pass a current through the coil 200a. The currents pass through the coil 200a to cause signals to be emitted by the coil 200a and to be received by the tracking device <NUM>.

Similarly an "H" bridge 220b may be connected to the coil 200b and operate in a similar manner. The controller <NUM> and/or control <NUM>' may operate both of the "H" bridge assemblies 220a, 220b to power or transmit a signal through the respective coils 200a, 200b. It is understood that the "H" bridge assemblies may be provided in any appropriate manner such as with manual or physical switches, transistors switches, or any appropriate switches relative to the respective coils. Moreover, as discussed above, any appropriate number of coils may be provided with the localizer <NUM> to generate navigation field as selected to generate or provide the navigation volume <NUM>. The schematic or illustration of <FIG> is merely exemplary for the current discussion.

The coils, such as the coil 200a, may be powered via the "H" bridge assembly 220a to provide a signal for navigation of the instrument <NUM>. The "H" bridge assembly 220a may be provided in the localizer <NUM> to allow the coil 200a to be driven while maintaining a selected energy or field emission and heat generation of the coil 200a and localizer <NUM>. The localizer <NUM>, therefore, may include an appropriate number of coils such as between <NUM> and <NUM> coils, including three coils to <NUM> coils, while still maintaining a selected field emission and heat generation. The plurality of coils may be driven with the controller <NUM>, <NUM>' in an appropriate manner, as discussed herein, to generate the navigation domain <NUM>.

The tracking system may include the localizer <NUM>, as discussed above. The localizer <NUM> may be controlled by a controller <NUM>. The localizer <NUM> may transmit a field or emit a field <NUM> that may be sensed by the tracking device <NUM> of the instrument <NUM>. It is understood that other appropriate tracking devices or receiving devices (e.g. the calibration receiver <NUM>) may also sense the field <NUM> of the localizer <NUM>. The field <NUM> may be generated in an appropriate manner, such as including or having a spread spectrum. The field <NUM> may also have, in addition or alternatively, a modulation that may be sensed by the tracking device <NUM>. The field <NUM> may assist in reducing or eliminating distortion or interference of the filed sensed by the tracking device <NUM>, as discussed further herein, due to an interfering, also referred to as a distorting or distortion, object.

As discussed above the localizer <NUM> may be controlled by the controller <NUM>, <NUM>' (discussion herein related to the controller <NUM> is intended to encompass all appropriate controllers, including those discussed above, and reference to only controller <NUM> is merely for ease of the current discussion), according to an appropriate transmission system. As discussed above, the coil, such as the coil 200a (also discussion herein to the single coil 200a is merely exemplary and for ease of the current discussion), may be powered or connected with the "H" bridge configuration 220a. The "H" bridge configuration <NUM> may be provided in any appropriate manner including switches (e.g. physical or manual) and/or transistors that may be operated with the controller <NUM>. Regardless, the coil or plurality of coils of the localizer <NUM> may be operated to transmit with a binary transmission system or scheme including a binary near orthogonal (BNO) transmission system or scheme. The coil or plurality of coils of the localizer <NUM> may be operated to transmit signals as sets of binary near orthogonal (BNO) sequences for efficient recovery of both the transmitted signals and the impulse responses of the system and the impulse responses of distorters (also referred to as distortion items) in the navigation field.

Under the BNO scheme, a pseudorandom binary (PRB) sequence, also referred to as a pseudo-noise (PN) sequence with one such type being a maximum length (ML) sequence, may be generated with the controller <NUM> to be transmitted by the localizer <NUM> as the tracking signal <NUM>. The tracking signal <NUM> transmission may be also be a spread spectrum transmission such that it is spread across a large or broad frequency spectrum or over a large or broad frequency spectrum which may also be segmented due to time.

The PN sequence may be provided in a generally orthogonal or near orthogonal manner to provide an appropriate transmission for receiving by the tracking device <NUM>, or other appropriate tracking device. The tracking signal <NUM> may be used for navigation of the tracking device <NUM>. Further, discussion of the single tracking device <NUM>, or any appropriate or single portion of the navigation system <NUM> herein, is merely exemplary and intended for the ease of the current discussion unless specifically indicated otherwise.

In various embodiments, therefore, cyclic shifts or offsets of the same repeating PN sequence are transmitted, one on each transmit coil. Statistically, an autocorrelation function of the PN sequence is equal to <NUM> at an offset zero and <MAT> at all other offsets, where the sequence length equals <NUM>n - <NUM> and the number of sequence generator bits equals n with n = <NUM> useable in various embodiments. Cyclic shifts or offsets of the PN sequence may be understood to be nearly orthogonal to one another in the sense that any pair of distinct shifts of the sequence are poorly correlated for any sufficiently-large value "n". Systems which demodulate all cyclic shift amplitudes in the repeating PN frame may recover the associated coil signal amplitudes by multiplying by the inverse of the PN leakage matrix, which has <NUM> on the diagonals and <MAT> elsewhere. In addition, when the PN offsets of the transmit coils have spacings greater than distorter response durations (i.e. a time of receiving a distortion from a distorting object), this method may recover the distorter impulse response to each generator coil. In various embodiments, an offset may be <NUM> sequence generator bits. Select methods may be used to perform the calculations, discussed above, including the Walsh-Hadamard transform via the fast-Walsh-transform based method as described "Impulse response measurements using MLS", by Jens Hee, http://www. dk/signalprocessing/mls. pdf (<NUM>). The method may be used to directly perform both the demodulation (multiplication by the PN sequence at all offsets) and the leakage inversion.

As discussed above, the controller <NUM> may power the coil 200a to transmit a signal that may be received by the tracking device <NUM>. It is understood, as discussed above, that the tracking device <NUM> may also transmit a signal in a similar manner, as discussed herein, that is received by the one or more coils of the localizer <NUM>. The tracking device <NUM> may also include a plurality of coils, such as coils that are oriented substantially orthogonally to one another around a central point and/or separated from one another. In various examples, the tracking device <NUM> may include a plurality of coils, such as three coils 66a, 66b, and 66c. The tracking device <NUM>, or any appropriate receiving coil device (e.g. the calibration receiver <NUM>), however, may include a selected number of coils For example, one coil, more than one coil, at least three coils, or more than three coils, such as six coils. The number of receiving coils may be appropriate to navigate the tracking device <NUM>. Each of the coils may be formed of a selected conductive material to have a current induced therein by the signal from the localizer. In various embodiments the coils may include wire wrapped around a center and/or traces formed on a printed circuit board (PCB). Nevertheless, the tracking device <NUM>, as discussed herein, may receive a signal from the localizer <NUM> although it is understood by one skilled in the art that the localizer may receive a signal from the tracking device and vice versa.

In various embodiments, as discussed above, the controller <NUM> may cause or signal the one or more coils, such as the coil 200a, of the localizer <NUM> to transmit a signal which may also be referred to as a tracking signal, as discussed herein. The coils <NUM> may be formed of a selected conductive material, such as a coil of metal or metal alloy wire. An impulse response(s) is(are) calculated from the received, continuously-transmitted BNO signal set from the transmit coils. The tracking signals are a set of BNO signals that include the same binary PN signal that is delayed by a different amount for each coil of the localizer. An inter-coil offset may include a selected time delay spacing is greater than the length of the metallic distorter impulse response length. The signal delay or spacing may include a selected duration, such as about <NUM> to <NUM> milliseconds, including <NUM> to <NUM> milliseconds, with an equivalent or greater spacing between signals from each coil.

The tracking signal transmitted may be in any appropriate frequency range such as in a frequency range of about <NUM> hertz (Hz) to about <NUM> megahertz (MHz), further including about <NUM> to about <NUM>, and further including about <NUM> to about <NUM> kilohertz (kHz). The signal may be transmitted at a selected frequency or over a range of frequencies in a spread spectrum fashion in the selected range. For example, a spread spectrum signal may transmit a signal across a spectrum of about <NUM> to <NUM>, including about <NUM> to about <NUM> that is transmitted at a sample rate at or about <NUM>. In various embodiments, the control over the signal is the sample rate and waveform, which may include a binary drive waveform. The spectrum may be flat from the direct current (D. ) to the sample rate. In various embodiments, therefore, the spectrum is flat when navigating the instrument, as discussed above. The controller via the H-bridge configuration may drive the coils, such as the coil 200a, at the selected frequency or across a spread spectrum of frequency near the selected frequency.

As discussed above, the localizer <NUM> may transmit a signal from the controller <NUM> through one or more of the coils, such as the coil 200a. As further discussed above the H-bridge configuration 220a may be provide in any appropriate configuration such as including transistors at the switches <NUM>-<NUM>. Accordingly, the controller <NUM> may cause the coil 200a to transmit a signal (e.g. an electromagnetic signal) to be received by the tracking device <NUM>. The navigation system <NUM>, however, may transmit a magnetic signal using any appropriate manner, including but not limited to, H-bridge circuits and closed loop analog circuits.

With reference to <FIG>, a transmit to receive calibration and/or equalization (C/E) procedure <NUM> and related schematic thereof is illustrated. As discussed herein, with reference to <FIG> and <FIG>, various additional and/or alternative C/E methods and systems may be used. I various embodiments, the C/E may include or be performed as a full system C/E and/or as various sub-channels or components.

With initiate reference to <FIG>, the C/E procedure <NUM> may be a full system C/E also referred to as an end-to-end C/E include various procedural steps such as starting in start block <NUM>. After starting in the start block <NUM>, a calibration or equalization signal is generated from the controller <NUM> and sent to the localizer <NUM> (which may also be referred to as a transmitter) in block <NUM>, illustrated schematically as <NUM>'. The calibration signal is then transmitted from the localizer <NUM> in block <NUM>, illustrated schematically as <NUM>', to be received, such as at the calibration receiving coil <NUM> and/or other appropriate receiver, such as the tracking device <NUM>. Transmission of the calibration signal in block <NUM> may include transmitting a calibration signal according to the spread spectrum scheme, as discussed above. Further, the transmission may include the PN signal from the coil 200a and the other coils <NUM> of the localizer <NUM>.

As discussed above the signal sent by the coils may be generated as a PN sequence. The PN sequence may include selected lengths, such as a length of <NUM> to <NUM> in a sequence. The various coils may be off-set relative to one another by an appropriate number such as about <NUM> length to achieve a distinction between the several coils <NUM> of the localizer <NUM>. The PN sequence may be generated and transmitted with the controller <NUM>. The transmitted signal at the selected frequency or spread spectrum, as discussed above, is to be respectively received by the tracking device <NUM> and/or other appropriate receiver, such as the calibration receiver <NUM> (even with reference to only one receiver coil herein). The coils <NUM>, therefore, may generate or transmit the signal in an appropriate time, such as in sequence or substantially simultaneously to be received by the tracking device <NUM>. The PN sequence may be generated according to any appropriate technique. In various embodiments, for example, a PN sequence may be generated with an irreducible polynomial.

The tracking device <NUM> receives the transmitted calibration signal and transmits the received signal to the controller <NUM> in block <NUM>, illustrated schematically as <NUM>'. The received calibration signal in block <NUM> may then be sampled and various calculations may be performed by the controller <NUM> (or any appropriate processor system) to perform a calibration in block <NUM>. The calibration in block <NUM> includes calibration based upon various parameters such as transmission distance, field strength at a known pose, or other appropriate calibration parameters.

Calibration in block <NUM> can be performed according to appropriate techniques, as discussed below. In various embodiments, calibration in block <NUM> could include impulse response normalization via placing the tracking device <NUM> (e.g. including coils) at a fixed pose with respect to the localizer <NUM> including one or more of the coils <NUM>. Transmission calibration could include transmitted magnetic field measurements via an external or separate magnetometer and/or as previously characterized at the tracking device <NUM> (e.g. sensing coil). Receiver coil calibration could include received voltage measurement via external multimeter at or near the tracking device and/or as previously characterized with the tracking device <NUM> (e.g. sensing coil).

The calibration in block <NUM> may include ensuring a known or clean room field strengths at selected poses. The calibration may include placing the localizer <NUM> at a selected location, which may also be referred to as an origin, and moving the tracking device <NUM> or an appropriate receiving tracking device at a plurality of known poses (i.e. locations and orientations) relative to the origin. The signal received by the tracking device <NUM> may then be used in the calibration <NUM>. For example, the calibration may include or account for possible distortion or noise in the signal as the signal starts and travels through transmitter (e.g. localizer <NUM>) circuitry and filters, transmitter coils, air, tracking device <NUM> coils, circuitry and filters related to or included with the tracking device <NUM>, and then as the signal is received back at the controller.

The calibration, regardless how determined including as discussed above, is then equalized in an equalization step in block <NUM>. In the equalization in block <NUM> an equalization is determined between each of the coils <NUM> of the localizer <NUM> and the tracking device <NUM>. Each transmit coil <NUM> and the tracking device <NUM> may be equalized for impulse response recovery and normalization of the signal. It is understood that discussion of the tracking device <NUM> may include discussion of a plurality of coils in the tracking device <NUM>, such as three coils, as discussed above. Accordingly, equalization may be between each of the coils <NUM> of the localizer <NUM> and each of the coils of the tracking device <NUM>. For example, between the coil 200a and each of the coils 66a, 66b, and 66c.

Equalization includes removing distortion and/or accounting for noise of the system, including from the controller <NUM> and the various circuits of the localizer <NUM> and receiver <NUM> to allow recovery of a discreet time binary signal from an interference free system. Generally, the equalization is performed by removing distortions of the drive and reception hardware and is to leave only the signal and noise from any external distortion responses. In particular, a binary unitary magnitude pseudo-noise signal measured as a voltage at the receive coil of the tracking device <NUM> may be measured and an inverse thereof is computed. The equalization then convolves the determined inverse with the signal received at the tracking device <NUM> (i.e. coils in the tracking device <NUM>) to remove the effects of the localizer <NUM> and the tracking device <NUM> and the hardware associated therewith to leave the drive signal from the controller <NUM> and noise or external distortions in the field.

The equalization is performed by determining coefficients. In particular, an algorithm may be used to determine the coefficients in a test or calibration equalization determination. Equalization may be performed in any appropriate manner, including those generally understood by one skilled in the art. For example, optimize and combine finite impulse response (FIR) and bidirectional infinite impulse response (IIR) filters may be used to equalize channels. The determined coefficients may be used to remove hardware distortion in the equalization between the localizer coil <NUM> and any coil of the tracking device <NUM>.

Therefore, equalization block <NUM> may be used to generate or determine a signal that is without distortion due to the hardware of the localizer <NUM> transmitting via the coils <NUM> and being received at the tracking device <NUM> and the coils included therein. Thus, the equalized signal may be used to determine a pose of the tracking device in a field generated by the localizer <NUM>. As discussed above, the localizer <NUM> may transmit a signal according to BNO scheme where each coil <NUM> is offset from another coil by about <NUM> bits in the PN sequence.

In various embodiments, as briefly noted above, a selected sub-channel or sub-portion of the navigation system <NUM> may be calibrated and equalized. For example, with reference to <FIG>, the respective sub-channels of/to each the transmitter or localizer <NUM> and/or the receiver or tracking device <NUM> may be individually calibrated and equalized. This may be in addition to and/or alternatively to calibrating and equalizing the entire system, and end, as discussed above and illustrated in <FIG>.

With initial reference to <FIG>, a method 300a for calibration and equalization is illustrated. The method 300a may include portions similar to those discussed above in the method <NUM>, and like reference numerals will be used augmented with a lowercase "a". Accordingly, the method 300a begins at block 310a. The process 300a then moves to block 311a to generate a signal with the controller, such as the controller <NUM>. The signal that is generated may include the PN sequence, as discussed above. Therefore, generating the signal at the controller in block 311a is similar to the generation of the signal in block <NUM> as discussed above. The generation of the signal and the controller 311a may then be sent through and/or to various components of the navigation system <NUM>, including those as discussed above.

The calibration signal is sent to the localizer in block <NUM>, illustrated schematically as line <NUM>'. The signal may be sent to the various components from the controller <NUM> to the localizer <NUM>, including various circuitry and filters, the transmitter coils (e.g. coils <NUM>), and other components between the controller <NUM> and the localizer <NUM> and/or including the localizer <NUM>. The signal sent to the localizer <NUM> is then transmitted back to the controller <NUM>, after having passed through all of the components of the localizer portion of the navigation system <NUM>. Therefore, the controller <NUM> receives a signal returned from the localizer components, such as transmitted from the coils and/or return through a return line to the controller <NUM>, after having passed through all of the components of the localizer <NUM> portion.

The controller <NUM> also transmits a signal to the receiving coils, such as the tracking device <NUM> and/or the calibration receiver <NUM>(also referred to herein as the receiver). The signal transmitted to the receiver <NUM> may be substantially identical to the signal transmitted to the localizer <NUM>. Moreover, the signals may be transmitted substantially simultaneously and/or sequentially. Thus, the signal generated from the controller <NUM> is also transmitted to the receiver <NUM> such as through all of the components thereof, including the receiver circuitry and/or filters, the sensor receive coils (e.g. of the tracking device <NUM>) including all of the selected or appropriate components thereof. The signal is then returned to the controller <NUM> after having passed through all of the components such as the controller <NUM> receives the return signal from the receiver <NUM>.

Accordingly, both of the blocks <NUM> and <NUM> may include two components including a transmission and return signal from the respective components including the localizer and the receiver. In other words, the signal is sent from the controller <NUM> and return to the controller <NUM> for calibration and equalization. Accordingly, rather than only or requiring a signal to be transmitted to the localizer <NUM> which is then transmitted and received by the receiver <NUM>, and then transmitted back to the controller <NUM>, the signal is sent and returned from each of the separate components as a separate sub-channel calibration and equalization.

The return signals is further processed by the controller <NUM> or appropriate processor system, as discussed above. Calibration may occur in block 322a in a manner similar to that discussed above. The calibration may include various calibration techniques or measurements, similar to those discussed above. For example, the calibration can include measurements of fields such as with a selected magnetometer and/or as previously characterized by the respective coils in the localizer <NUM> and/or the receiver <NUM>. The calibration signal and/or information may then be used for equalization in block 324a. Again the equalization in block 324a may include that as discussed above for equalization of the signal in the navigation system <NUM>.

Accordingly, calibration and equalization of the navigation system <NUM> may include separate or sub-channel calibration and equalization portions and/or steps as discussed above and as exemplary illustrated in <FIG>.

A further and/or alterative sub-channel calibration and equalization may include the method as illustrated in <FIG>. Initially, a method 300b may include steps or portions that are similar to the method <NUM> and the method 300a, as discussed above. Like portions will be referenced with like numerals augmented with a "b". Accordingly the method 300b may begin in start block 310b and include generation of a signal at a controller in block 311b. Generation of the signal at the controller may be similar or identical to the generation of the signal at the controller <NUM> as discussed above.

The signal may be a PN sequence and may then be transmitted or sent to various components of the navigation system <NUM>. For example, the signal may be sent to the localizer <NUM> through the various components of the localizer system including the circuits, filters, transmitter coils, and the like. The sending of the signal to the localizer <NUM> in block 326b and the return of the signal to the controller may be similar to that as discussed above in block <NUM>. The signal sent to the localizer <NUM> may be sent through the various circuitry of the localizer from the controller <NUM> to the localizer <NUM>. The return signal, that is returned to the controller <NUM> for various calibration and equalization, as discussed above and further herein, may be returned in various selected manners. As discussed above the signal may be sent or returned to the controller through a various return path from the localizer <NUM> to the controller <NUM>. In addition or alternatively, various external components may receive the transmitted signal from the localizer <NUM>, such as a magnetometer or the like and the signal from the external components may be returned to the controller. The signal, however, need not be wirelessly transmitted. The signal after having been passed through the various components, such as the circuitry, filter, and coils of the localizer <NUM>, may have a signal that is then returned to the controller <NUM>.

Further, the generated signal may be transmitted to various circuitry and components of the receive <NUM> channel, as illustrated in <FIG>. For example, receive coil circuitry <NUM>'/<NUM>' may include various circuitry, cables, filters, and the like that are associated with the tracking device <NUM> and/or the calibration coil <NUM>. The receive coil circuitry <NUM>'/<NUM>' may include various hardware or components that are generally understood to be fixed with the navigation system <NUM>. For example, as discussed above, the controller <NUM> may be connected to various tracking devices and/or receive tracking device information from various selected tracking devices, such as the tracking device <NUM>. In addition and/or alternatively thereto, the various other tracking devices, such as the tracking device <NUM> may also be connected to the controller <NUM>.

During a selected procedure, for example, the tracking device coils or components <NUM>, <NUM> may be interchangeably with the receiver electronics <NUM>'/<NUM>' and, therefore, connected to the controller <NUM>. Further, as is understood by one skilled in the art, during a selected procedure or a plurality of procedures, more than one instruments may be individually and separately tracked. Therefore, a plurality of the tracking device <NUM> may be individually and separately tracked. At a selected time, therefore, the identity of the selected and attached tracking device <NUM> may be input. The system, such as the controller <NUM>, therefore, may recall from a storage system the characterization of the selected and input tracking device <NUM>. Accordingly the subcomponent calibration and equalization of the receiving circuitry <NUM>'/<NUM>', may allow for calibration of the navigation system <NUM> separate from the individual components that are tracked therein, such as with the tracking device <NUM>.

In light of the above, the generated signal from block 311b may be transmitted to the receive circuitry in block <NUM>. The signal received from the receive circuitry <NUM>'/<NUM>' may be received in any appropriate manner, such as in a return signal and/or received from external components including a voltage measurement from an external multimeter, or other appropriate sensors.

The calibration and equalization of the navigation system <NUM>, therefore, may also include, therefore, recalling a characterization of a selected receiver, also referred to as a receiver coil or component. For example, as discussed above, various components may be interconnected with the navigation system <NUM> for navigation of the selected components. Accordingly, the navigation system <NUM> may be calibrated and equalized without the specific and selected tracking device <NUM>. During a selected time, such as during a procedure, when the specific tracking device is selected, the identity of the selected tracking device may be input (e.g. manually by the user <NUM>, automatically by sensing or receiving a signal from the tracking device, or other appropriate mechanism). The navigation system <NUM> may recall the previously made and predetermined characterization (including equalization) of the selected tracking device. The characterization of the tracking device, therefore, may have been completed at any prior time. The characterization may include calibration and equalization information may that is previously determined and stored in a selected memory, such as in a database and/or in the memory of the navigation system <NUM> including the workstation <NUM> or processor system <NUM>.

The prior determined characterization may be recalled, such as manually and/or automatically and/or combinations thereof, for completing a calibration and an equalization of the entire navigation system <NUM> including the selected specific receive coil <NUM>/<NUM>. Accordingly, when the selected receiver is selected the recalled characterization may be incorporated and/or used with the received signal from the received circuitry in block <NUM> and the received signal from the localizer in block 326b to allow for calibration and equalization. Thus, with the recalled characterization from block <NUM>, calibration may proceed in block 322b. After calibration in block 322b equalization may occur in block 324b. Calibration and equalization may include such a procedure, as discussed above.

Accordingly, calibration and equalization of the navigation system <NUM> may occur in an appropriate manner, including those discussed above such as described and illustrated in the <FIG>. It is understood that a calibration and equalization of the navigation system <NUM> may occur in any appropriate manner and may include any one of the above described systems or methods and/or combinations thereof. For example, an end to end complete calibration and equalization may occur according to the method <NUM>. Further, during a selected procedure, the calibration method 300b may be used to augment and/or update a calibration equalization of the navigation system <NUM> when the tracking device is added and/or changed during a selected procedure and/or between procedures. Accordingly, it is understood that the calibration and equalization may occur in any appropriate manner and need not be limited to only a single one of the methods as discussed above, but may include a plurality and/or combination thereof, such as an end to end calibration and equalization according to the method <NUM> that may be supplemented and/or redone according to the sub-channel procedures according to either and/or both of the method 300a and 300b.

According to various embodiments, including those discussed above, the signal received at the tracking device <NUM> may be equalized with the equalizer <NUM> in step <NUM> according to the equalization process discussed above. With reference to <FIG>, a non-equalized impulse response may include a causal portion <NUM> and anti-causal portion <NUM>. The anti-causal portion may be used to compensate for various components of the navigation system <NUM> and may vary in light thereof. Accordingly, various different components may be used in the navigation system <NUM> and allow or cause the causal portion <NUM> to vary. The causal portion <NUM> may be used to compensate for variation and phase in the system's pass band and also in various components of the circuitry of the localizer <NUM>. The equalized signal in block <NUM>, therefore, may use the pre-equalization impulse response as illustrated in <FIG> to calibrate and equalize the signal.

The localizer <NUM> may transmit a signal to generate an electromagnetic field. The signal may be a spread spectrum signal that is transmitted with a BNO scheme. The signal, including the BNO scheme, may be referred to as a tracking signal that includes an binary signal. The binary signal may be measured at the tracking device <NUM> that relates to the transmitted signal. The received signal may include various components, as discussed further herein, due to various distortions as discussed above and also herein. The equalization may assist in ensuring the recovery of the impulse response transmitted by the localizer <NUM>.

Turning reference to <FIG> and <FIG>, a pre-equalized signal is illustrated in <FIG> as received by the tracking device <NUM>. The pre-equalized signal in <FIG> illustrates different received signals due to system distortions and including distortion causing materials in the field or near the path of the tracking device <NUM>. For example, graph line <NUM> relates to a value over time of the pre-equalized signal received by the tracking device <NUM> with no distorting item. A second graph line <NUM> illustrates the received signal over time when a portion of aluminum is placed or located near or causes distortion in the received signal. A third graph line <NUM> illustrates the received signal when a selected steel material is located near the tracking device <NUM>. As illustrated in <FIG>, by the graph lines <NUM>-<NUM>, the signal received by the tracking device <NUM> may vary depending upon material located near the tracking device <NUM> and/or that would distort the signal transmitted by the localizer <NUM>. As discussed further herein, the distortion caused by selected materials may be removed by analyzing the received signal to determine whether distortion is present and, if present remove the same. As discussed herein, distortion, whether present or not, may be determined. If distortion is determined to be present, it may be removed to allow recovery of an undistorted tracking signal including the impulse response.

With reference to <FIG>, a method or process of navigation <NUM> is illustrated. The navigation process can begin at start block <NUM> and include transmitting a signal or signals in block <NUM>. As discussed above the signal as transmitted may include the spread spectrum signal according to the BNO scheme, discussed above. The signal transmitted by the localizer <NUM> may be transmitted into the navigation volume <NUM>. As discussed above, the transmitted signal may generate near field magnetic fields with wavelengths greater than or equal to <NUM> meters. The navigation volume <NUM> may be dependent upon various factors such as the size of the coil <NUM>, the overall size of the localizer <NUM>, power transmission, and other factors. Nevertheless the navigation volume <NUM> may be a volume of about <NUM><NUM> to about <NUM><NUM>, including about <NUM><NUM> to about <NUM><NUM>.

The transmitted signal or signals may be received by the tracking device <NUM> in block <NUM>. The received signal in block <NUM> may be received by the tracking device <NUM> and/or transmitted to the navigation processor <NUM>. It is understood that the method or process <NUM> may be executed by the processor <NUM> with a transmit signal <NUM> may be a signal to the localizer <NUM> to transmit a signal and may receive signal in block <NUM> may be the signal received and transmitted to the navigation processor <NUM> from the tracking device <NUM>. The method <NUM> may include a transmission of the signal by the localizer <NUM> and receiving the signal by the tracking device <NUM>, or vice versa, and the navigation processor <NUM> may execute instructions to make a determination of the navigation in the method <NUM>.

After the signal or signals is received in block <NUM>, a signal may be processed, such as demultiplexed and equalized, in block <NUM>. As discussed above, the received signal is received with the BNO scheme and therefore each cyclically shifted or offset code, corresponding to each transmit coil, may be demultiplexed from the received signal for further analysis. Equalization in block <NUM> may be similar to the equalization block <NUM>, as discussed above. Generally, as discussed above, the localizer <NUM> may include the coil 200a and the tracking device <NUM> may include the coil 66a. It is understood that discussion herein to the coil 66a may include or be similar to the discussion of a plurality of coils at the tracking device <NUM> and discussion of the single coils 66a herein is merely exemplary. The equalization between the coil 66a and the coil 200a may allow for the impulse response recovery of the transmitted signal.

After equalizing the signal in block <NUM>, as discussed above such as with the equalizer <NUM>, the equalized signal may be evaluated to allow for a determination in block <NUM> of whether distortion is present. The determination of whether distortion is present may be made based upon the received signal, for example as illustrated in <FIG>. The received signal, as illustrated in <FIG>, may include a determination or evaluation of an initial impulse as illustrated by a black dot <NUM> in the graph of <FIG>. The impulse response may be the equalized impulse response from the received signal as equalized in block <NUM>. The impulse response may further include a residual or tail that is a non-impulse or distortion portion that may include one or more tail signals or points <NUM>. The tail points <NUM> may include a plurality of tail points in a tail portion <NUM>. The tail portion <NUM>, or a presence of a tail portion, may be used to determine whether distortion is present. Accordingly, if the signal, that includes an impulse response as illustrated in <FIG>, as graphed over time, includes substantially no tail, a determination that no distortion is made, and a no-distortion path <NUM> is followed. Calibration and equalization, as discussed above according to one or more of the various methods, may include a characterization of the system including a noise floor and a distortion limit. No presence of tails, i.e. distortion, may be defined as within these previously determined limits.

If no distortion is found in the received signal after the equalization, such as determining that the tail <NUM> is not present in the signal, and the No distortion path <NUM> is followed, then a navigation of the tracking device <NUM> may be performed without correcting for a distortion. As discussed above, distortion may be present or found in the received signal due to various distorting items in the signal path, such as effecting the signal transmitted by the localizer <NUM>. Distortion may be caused by various items such as items in or near the navigation system <NUM>, as discussed above including the imaging device <NUM>, the instrument <NUM>, the operating or patient support table <NUM>, or other items. Further, distortion may occur due to other items actively transmitting a field, such as an electrical field from an electrically powered drill, other coils in the localizer <NUM> other than the pair being resolved or evaluated at a time, or other items. The equalization may be made on a pairwise (e.g. single coil 200a of the localizer <NUM> and single coil 66a and the tracking device <NUM>) basis. Accordingly, a determined pose of the tracking device <NUM> may be made by determining a pose of each of the coils 66a-66c and the tracking device <NUM> for each of the coils 200a-200n of the localizer <NUM>. It is understood, however, that tracking of the instrument <NUM> with the tracking device <NUM> may include navigation between a selecting number of coils of the localizer and the tracking device <NUM>. Thus, for example, navigation may occur with one tracking device and using nine or twelve transmit coils in the localizer <NUM>. Other examples may include combinations of one receive coil using five transmit coils to three receive coils using three transmit coils to twelve receive coils using one transmit coil.

After determining there is no distortion, an evaluation of whether certain metrics are accepted may be made in block <NUM>. Metrics may include signal metrics, or any other appropriate metrics. Further predetermined acceptable ranges or thresholds for the metrics may be made and saved to be accessed by the navigation processor <NUM>. In various examples, predetermined signal strength values that are above or below a threshold may be determined. Thus, if a signal received is above a threshold it may be determined that a tracking device is too near the localizer and if a signal received is below a threshold the tracking device may be too far from the localizer. The threshold, however, may relate to localizer size and/or power, tracking device configuration, etc. Accordingly the metrics may be analyzed and determined in block <NUM>.

If it is determined that the metrics are not acceptable in block <NUM>, a return or loop path <NUM> may be followed to transmit the signal in block <NUM> and/or to the receive signal again in block <NUM>. In various embodiments, the transmission may repeat automatically, thus looping to transmission may not be necessary or desirable and looping to receiving in block <NUM> may be appropriate. By receiving the signal again at the tracking device <NUM>, the signal may be reanalyzed. The transmitted signal may be transmitted over a selected span of time such as milliseconds, including a sequence of <NUM> to <NUM> milliseconds including about <NUM> milliseconds that may or may not be followed by a break or pause in a transmission. Therefore, the determination of whether the metrics are acceptable in block <NUM>, if not found to be acceptable, may allow for receiving a signal again in block <NUM> but not distributing navigation of the navigation system <NUM> in a time acceptable by the user <NUM>. However, if the metrics are not found to be acceptable over a reasonable period of time, such as about <NUM> to <NUM> milliseconds, the navigation system <NUM> may provide an output, such as with the display device <NUM> that may identify to the user <NUM> that an error has occurred and must be resolved.

If the metrics are acceptable in block <NUM> a YES or solve path <NUM> may be followed. The solve path <NUM> may lead to a navigation solve or pose determination in block <NUM>. The navigation solve in block <NUM> may allow for illustration of the representation 68i on the display device relative to the image data <NUM> on the display device <NUM>. The navigation solve allows for illustration and/or determination of a pose of the tracking device <NUM> relative to the subject <NUM>. Thus, navigation may occur of the instrument <NUM> relative to the subject <NUM>.

With continuing reference to <FIG>, the navigation method <NUM> may also follow a distortion determined or distortion found path <NUM>, if distortion is found to be present in block <NUM>. The Yes distortion path <NUM> may lead to or enter a distortion correction, also referred to as remove, subroutine <NUM>. The subroutine <NUM> may include various procedures or processes to identify and correct for selected distortion, as discussed herein. In the subroutine, it is understood by one skilled in the art, that the herein described processes may be carried out sequentially and/or simultaneously, as discussed herein. Accordingly, while <FIG> illustrates that the subroutine in a selected order, the processes in the subroutine <NUM> may occur substantially simultaneously.

The cause of distortion may be any cause of distortion, including those discussed above. For example, a metal object that is conductive may be in the path of the field generated by the localizer <NUM>. For example, as illustrated in <FIG>, an aluminum object, such as the tray <NUM> that may be formed therefrom, may be in the path of the signal from the localizer <NUM> to the tracking device <NUM>. The aluminum tray <NUM> may cause the tail <NUM>, as illustrated in <FIG>. The tail <NUM> may include a plurality of response data points separated by time as illustrated along the x-axis in <FIG>. As exemplary illustrated in <FIG> the time may be separated by increments of microseconds but may also be any appropriate time segmentation. Nevertheless, the determination and identification of the tail <NUM> may be used to ensure or determine an appropriate magnitude of the initial impulse <NUM>.

Generally, the initial impulse <NUM> occurs at a time "zero" when receiving the signal in block <NUM>. In particular, the signal is transmitted in block <NUM> and received in block <NUM> and the receiving of the signal in block <NUM> would be time zero which is also understood to be the start of the PN code or signal or shifts of the PN code. Any trailing or residual signal received signal thereafter may be caused due to distortion or a distorting object within the field along the signal path, such as the tray <NUM>. Thus, the initial impulse <NUM> may be distorted, such as in magnitude, and this distortion noted by the distortion tail <NUM>.

With continuing reference to <FIG> the initial impulse <NUM>, may be illustrated on a graph for ease of discussion and calculation, as discussed herein. The initial impulse <NUM> is illustrated at zero time response to exemplary illustrate the initial impulse at time zero on the X-axis. Further, the initial impulse is shown at zero magnitude to better illustrate the value of the residual or tail response received in block <NUM> if distortion is present. The corrected or non-distorted dimension of the initial impulse <NUM> may be determined by calculating the tail <NUM> into the initial impulse <NUM>. The initial impulse and the tail may generally be a causal response where the tail <NUM> may be used to determine the expected or un-distorted impulse magnitude.

The distortion present path <NUM> may first go to a residual or tail separation in block <NUM>. The residual separation may include a determination of all of the tail portion. As discussed above, the initial impulse at time zero may be determined such as based upon a determined or selected amount of time between the transmit signal and the received signal in block <NUM>, <NUM> respectively. For example, it may be determined that the time between the transmitting of the signal from the localizer <NUM> and the receiving of the signal at the tracking device <NUM> may be much less than microseconds. Accordingly, the navigation system <NUM> may determine that a received signal at the selected amount of time after transmission of the signal in block <NUM>, may be a zero time and the initial impulse. Any recovered impulse response thereafter may be determined to be the tail <NUM>. The determination of the tail <NUM>, however, may be in any appropriate manner, such as any recovered signal after the identified initial impulse. Regardless, the tail <NUM>, that may be determined or detected in block <NUM> when determining whether a distortion is present, may be separated from the initial impulse or first impulse <NUM>. The separation of the residuals provides separation of the tail dimensions or magnitude for further reconstruction.

After separation of the tail in block <NUM>, a reconstruction may be performed in block <NUM>. The reconstruction block <NUM> may include reconstruction the distortion impulse response. As discussed above, the initial or zero time impulse <NUM> may be distorted and this distortion may be determined by the tail <NUM>, if present. Accordingly, once the tail is separated in block <NUM> the separated tail may be reconstructed into the distortion initial impulse to determine an actual or corrected impulse. The reconstruction may be in any appropriate type of reconstruction.

For example a direct reconstruction may include an addition or additive reconstruction by adding the values of the tail <NUM> for a selected amount of time, such as about <NUM> to <NUM> milliseconds including <NUM> milliseconds, to the value of the distortion initial or zero time impulse. The direct reconstruction may allow for a fast reconstruction of the distortion impulse and may be appropriate for selected materials, such as conductive materials such as certain plastics or polymers, metal alloys or the like.

Reconstruction may also include a modeled reconstruction of the impulse response that may be based upon weighting certain portions of the tail, adding or eliminating certain portions of the tail <NUM>, or other appropriate modeling techniques. In various embodiments, the reconstruction may not include first removing the tail in block <NUM>, but may include simultaneous separation and modeling. IN various embodiments, the tail may be summed and added to the impulse, particularly for conductive distortion materials. In other words, as a function of the residuals in a direct calculation summing the residuals to determine the distortion initial impulse. In a modeled or indirect calculation, the tail may be decomposed into separate functions and then fit for determining the distortion effect. For example, the decomposed functions may be fit to pre-determined or measured distorting materials or items. In other words, residuals may be modeled with a combination of parameterized impulse responses having conductive and conductive and magnetic contributions and/or with a combination of measured impulse responses including expected conductive and conductive and magnetic contributions.

The reconstruction may be made in block <NUM> to determine the corrected or undistorted impulse response in block <NUM>. Following the reconstruction of the distortion impulse response in block <NUM>, a removal or deconvolution of the impulse response is made in block <NUM>. The removal or deconvolution of the impulse response in block <NUM> may include separating the distortion impulse response from the full impulse response via removal or deconvolution to determine the corrected or undistorted impulse response and impulse.

Following the removal or deconvolution in block <NUM>, the navigation method <NUM> may then enter the determination of whether selected metrics are acceptable in block <NUM>. Similar to that discussed above, the determination of whether the metrics are acceptable in block <NUM> may allow for receiving an additional signal in the loop path <NUM> and/or navigation solving in block <NUM>.

Accordingly, the method <NUM> may follow a no distortion path <NUM> and/or a distortion path <NUM> to solve a navigation and determine the pose of the tracking device <NUM> in space relative to the subject <NUM>. The method <NUM> may include the no-distortion path <NUM> and the distortion path <NUM>, the distortion path may include the distortion correction subroutine <NUM>. The distortion correction subroutine <NUM> may be executed by the controller <NUM> or navigation processor <NUM> to allow for removal or correction of the distortion from a distorting object to determine a true or correct pose of the tracking device <NUM>. The distortion may be detected in block <NUM> and removed in the distortion correction subroutine <NUM> as discussed above.

As briefly discussed above, the subroutine <NUM> may be substantially sequential as discussed above. Thus, the various calculations may be processed, such as with a processor executed instructions, in the order as discussed above and illustrated directly in <FIG>. In various embodiments, however, all of the processes in the subroutine <NUM> may occur simultaneously or selected plurality of the processes may occur simultaneously. In other words, the subroutine <NUM> may occur via concurrent separation <NUM>, reconstruction <NUM>, and removal or deconvolution <NUM>. The subroutine <NUM> may, however, still follow the decision of wherein the recovered impulse response includes a distortion tail in block <NUM>. Then, the subroutine <NUM> may include simultaneous separation and deconvolution of reconstructed distortion impulse responses from the recovered impulse response to find a corrected impulse response and impulse. The corrected impulse response and impulse may be determined with a fit of the residuals to a combination of measured or modeled impulse responses including expected conductive and conductive and magnetic contributions.

Accordingly, the navigation system <NUM>, as discussed above, may be used to determine a pose of the tracking device <NUM> that is associated, such as connected to, the instrument <NUM>. The navigation system <NUM> may therefore track the tracking device <NUM> and navigate the instrument <NUM> such as by illustrating the instrument <NUM> as the representation 68i on the display device <NUM>. The use of the spread spectrum transmission may allow for a low power and high fidelity signal transmission with select electronics, such as the "H" bridge configuration discussed above. Further a selected scheme, such as the BNO scheme, may allow for transmission of a signal based substantially free of distortion or confusion with extraneous signals relative to the tracking device <NUM>. Further the received signal may be analyzed or reconstructed to determine is distortion is present or has been caused by distorting object and, if present, may be removed. Thus the pose of the tracking device <NUM> may be determined with a selected preciseness and correctness due to the received signal at the tracking device <NUM>.

It is not intended to be exhaustive or to limit the invention.

Claim 1:
A method of operating a navigation system (<NUM>), the method comprising:
generating (<NUM>) a signal with a controller (<NUM>);
sending the signal to a transmitter system (<NUM>);
transmitting (<NUM>) the signal with the transmitter system (<NUM>);
receiving the transmitted signal at a receiver (<NUM>);
sending a receiver signal to the controller (<NUM>) based on the received transmitted signal at a receiver (<NUM>); and
evaluating the receiver signal to characterize the navigation system (<NUM>),
wherein evaluating the receiver signal to characterize the navigation system (<NUM>) includes calibrating (<NUM>) and equalizing (<NUM>) the receiver signal to the signal.