Probe with spherical tip for intra-operative registration

Abstract

A system for registering an anatomical surface for a registration procedure includes memory storing instructions and one or more processing devices configured to execute the instructions. Executing the instructions causes the system to perform, based on a dimension of a spherical probe tip of a probe configured to perform the registration procedure, a dilation process on a first model of patient anatomy including the anatomical surface to obtain a second model of the patient anatomy, receive data indicative of a plurality of locations of the spherical probe tip relative to the patient anatomy, and register points corresponding to the plurality of locations of the spherical probe to the second model.

Description

Attorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301PROBE WITH SPHERICAL TIP FOR INTRA-OPERATIVE REGISTRATIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 702,323, filed on October 2, 2024. The entire disclosure of the application referenced above is incorporated herein by reference.FIELD

[0002] The present disclosure relates to probes for surgical systems, and more particularly to probes for registering points of an anatomical site for a surgical procedure.BACKGROUND

[0003] The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

[0004] Arthroscopic surgical procedures are minimally invasive surgical procedures in which access to the surgical site within the body is by way of small keyholes or ports through the patient’s skin. The various tissues within the surgical site are visualized by way of an arthroscope placed through a port, and the internal scene is shown on an external display device. The tissue may be repaired or replaced through the same or additional ports. In computer-assisted surgical procedures (e.g., replacement of the anterior cruciate ligament (ACL), reduction of femora-acetabular impingement), the location of various objects within the surgical site may be determined relative to theAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 bone by way of images captured by an arthroscope and a three-dimensional model of the bone.SUMMARY

[0005] A system for registering an anatomical surface for a registration procedure includes memory storing instructions and one or more processing devices configured to execute the instructions. Executing the instructions causes the system to perform, based on a dimension of a spherical probe tip of a probe configured to perform the registration procedure, a dilation process on a first model of patient anatomy including the anatomical surface to obtain a second model of the patient anatomy, receive data indicative of a plurality of locations of the spherical probe tip relative to the patient anatomy, and register points corresponding to the plurality of locations of the spherical probe to the second model.

[0006] In other features, dimension is a radius of the spherical probe tip, and performing the dilation process includes dilating the first model in accordance with the radius of the spherical probe tip. Performing the dilation process includes generating a three-dimensional (3D) triangular mesh corresponding to the first model, generating a 3D grid of points enclosing the triangular mesh, and generating a dilated mesh using the triangular mesh and the 3D grid. The triangular mesh is an open surface corresponding to the anatomical surface. A resolution of the 3D grid is at least as fine as an average side length of mesh triangles composing the triangular mesh. Generating the 3D grid includes assigning respective values to the points of the 3D grid based on respective distances from the points to the triangular mesh.

[0007] In other features, generating the dilated mesh includes generating the dilated mesh based on the assigned respective values and the radius. Generating the dilatedAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 mesh includes generating an isosurface that connects points at a same elevation from the triangular mesh, and wherein the same elevation corresponds to the radius. Executing the instructions further causes the system to modify the dilated mesh by removing portions of the dilated mesh that are not located on an external side of the triangular mesh. The data indicative of the plurality of locations corresponds to a center of the spherical probe tip.

[0008] In other features, one or more methods include steps corresponding to the functions performed by systems, processors or processing devices, controllers, circuits or circuitry, etc. as described herein.

[0009] Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0011] FIG. 1 shows a surgical system in accordance with at least some embodiments;

[0012] FIG. 2 shows a conceptual drawing of a surgical site with various objects within the surgical site tracked, in accordance with at least some embodiments;

[0013] FIG. 3 shows a method in accordance with at least some embodiments;

[0014] FIG. 4 is an example video display showing portions of a femur and a bone fiducial during a registration procedure, in accordance with at least some embodiments;Attorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301

[0015] FIG. 5 shows a method in accordance with at least some embodiments;

[0016] FIGS. 6A and 6B show example probes including a sharp probe tip;

[0017] FIG. 7 shows an example probe including a spherical probe tip in accordance with at least some embodiments;

[0018] FIGS. 8A, 8B, 8C, and 8D show other example probes including spherical probe tips in accordance with at least some embodiments;

[0019] FIG. 9A shows an example of surface dilation in accordance with at least some embodiments;

[0020] FIGS. 9B, 9C, 9D, and 9E show an example model dilation process in accordance with at least some embodiments;

[0021] FIGS. 10A, 10B, and 10C show an example calibration process for a probe having a spherical probe tip in accordance with at least some embodiments;

[0022] FIG. 11 illustrates steps of an example method for performing a touch-based registration procedure using a probe with a spherical probe tip in accordance with at least some embodiments; and

[0023] FIG. 12 shows an example computer system in accordance with at least some embodiments.

[0024] In the drawings, reference numbers may be reused to identify similar and / or identical elements.DEFINITIONS

[0025] Various terms are used to refer to particular system components. Different companies may refer to a component by different names - this document does not intend to distinguish between components that differ in name but not function. In theAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to... .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection or through an indirect connection via other devices and connections.

[0026] An endoscope having “a single optical path” through an endoscope shall mean that the endoscope is not a stereoscopic endoscope having two distinct optical paths separated by an interocular distance at the light collecting end of the endoscope. The fact that an endoscope has two or more optical members (e.g., glass rods, optical fibers) forming a single optical path shall not obviate the status as a single optical path.

[0027] Similarly, spatial and functional relationships between elements (for example, between device, modules, circuit elements, etc.) are described using various terms, including “connected,” “engaged,” “coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and “disposed.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. Nevertheless, this paragraph shall serve as antecedent basis in the claims for referencing any electrical connection as “directly coupled” for electrical connections shown in the drawing with no intervening element(s).

[0028] Terms of degree, such as “substantially” or “approximately,” are understood by those skilled in the art to refer to reasonable ranges around and including the givenAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 value and ranges outside the given value, for example, general tolerances associated with manufacturing, assembly, and use of the embodiments. The term “substantially,” when referring to a structure or characteristic, includes the characteristic that is mostly or entirely present in the characteristic or structure. As one example, numerical values that are described as “approximate” or “approximately” as used herein may refer to a value within + / - 5% of the stated value.

[0029] “A”, “an”, and “the” as used herein refers to both singular and plural referents unless the context clearly dictates otherwise. By way of example, “a processor” programmed to perform various functions refers to one processor programmed to perform each and every function, or more than one processor collectively programmed to perform each of the various functions. To be clear, an initial reference to “a [referent]”, and then a later reference for antecedent basis purposes to “the [referent]”, shall not obviate the fact the recited referent may be plural.

[0030] In general, terminology may be understood at least in part from usage in context. For example, terms, such as “and”, “or”, or “and / or,” as used herein may include a variety of meanings that may depend at least in part upon the context in which such terms are used. Typically, “or” if used to associate a list, such as A, B or C, is intended to mean A, B, and C, here used in the inclusive sense, as well as A, B or C, here used in the exclusive sense. In addition, the term “one or more” as used herein, depending at least in part upon context, may be used to describe any feature, structure, or characteristic in a singular sense or may be used to describe combinations of features, structures or characteristics in a plural sense. Similarly, terms, such as “a,” “an,” or “the,” again, may be understood to convey a singular usage or to convey a plural usage, depending at least in part upon context. In addition, the term “based on” may be understood as not necessarily intended to convey anAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 exclusive set of factors and may, instead, allow for existence of additional factors not necessarily expressly described, again, depending at least in part on context. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.”

[0031] The terms “input” and “output” when used as nouns refer to connections (e.g., electrical, software) and / or signals, and shall not be read as verbs requiring action. For example, a timer circuit may define a clock output. The example timer circuit may create or drive a clock signal on the clock output. In systems implemented directly in hardware (e.g., on a semiconductor substrate), these “inputs” and “outputs” define electrical connections and / or signals transmitted or received by those connections. In systems implemented in software, these “inputs” and “outputs” define parameters read by or written by, respectively, the instructions implementing the function. In examples where used in the context of user input, “input” may refer to actions of a user, interactions with input devices or interfaces by the user, etc.

[0032] “Controller,” “module,” or “circuitry” shall mean, alone or in combination, individual circuit components, an application specific integrated circuit (ASIC), a microcontroller with controlling software, a reduced-instruction-set computer (RISC) with controlling software, a digital signal processor (DSP), a processor with controlling software, a programmable logic device (PLD), a field programmable gate array (FPGA), or a programmable system-on-a-chip (PSOC), configured to read inputs and drive outputs responsive to the inputs.

[0033] As used to describe various surgical instruments or devices, such as a probe, the term “proximal” refers to a point or direction nearest a handle of the probe (e.g., aAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 direction opposite the probe tip). Conversely, the term “distal” refers to a point or direction nearest the probe tip (e.g., a direction opposite the handle).

[0034] For the purposes of this disclosure, a non-transitory computer readable medium (or computer-readable storage medium / media) stores computer data, which data can include computer program code (or computer-executable instructions) that is executable by a computer, in machine-readable form. By way of example, and not limitation, a computer readable medium may comprise computer readable storage media, for tangible or fixed storage of data, or communication media for transient interpretation of code-containing signals. Computer readable storage media, as used herein, refers to physical or tangible storage (as opposed to signals) and includes without limitation volatile and non-volatile, removable and non-removable media implemented in any method or technology for the tangible storage of information such as computer-readable instructions, data structures, program modules or other data. Computer readable storage media includes, but is not limited to, RAM, ROM, EPROM, EEPROM, flash memory or other solid state memory technology, optical storage, cloud storage, magnetic storage devices, or any other physical or material medium which can be used to tangibly store the desired information or data or instructions and which can be accessed by a computer or processor.

[0035] For the purposes of this disclosure, the term “server” should be understood to refer to a service point that provides processing, database, and communication facilities. By way of example, and not limitation, the term “server” can refer to a single, physical processor with associated communications and data storage and database facilities, or it can refer to a networked or clustered complex of processors and associated network and storage devices, as well as operating software and one orAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 more database systems and application software that support the services provided by the server. Cloud servers are examples.

[0036] For the purposes of this disclosure, a “network” should be understood to refer to a network that may couple devices so that communications may be exchanged, such as between a server and a client device or other types of devices, including between wireless devices coupled via a wireless network, for example. A network may also include mass storage, such as network attached storage (NAS), a storage area network (SAN), a content delivery network (CDN) or other forms of computer or machine-readable media, for example. A network may include the Internet, one or more local area networks (LANs), one or more wide area networks (WANs), wire-line type connections, wireless type connections, cellular or any combination thereof. Likewise, sub-networks, which may employ differing architectures or may be compliant or compatible with differing protocols, may interoperate within a larger network.

[0037] For purposes of this disclosure, a “wireless network” should be understood to couple client devices with a network. A wireless network may employ stand-alone ad- hoc networks, mesh networks, Wireless LAN (WLAN) networks, cellular networks, or the like. A wireless network may further employ a plurality of network access technologies, including Wi-Fi, Long Term Evolution (LTE), WLAN, Wireless Router (WR) mesh, or 2nd, 3rd, 4th or 5th generation (2G, 3G, 4G or 5G) cellular technology, mobile edge computing (MEC), Bluetooth, 802.11 b / g / n, or the like. Network access technologies may enable wide area coverage for devices, such as client devices with varying degrees of mobility, for example. In short, a wireless network may include virtually any type of wireless communication mechanism by which signals may be communicated between devices, such as a client device or a computing device, between or within a network, or the like.Attorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301

[0038] A computing device may be capable of sending or receiving signals, such as via a wired or wireless network, or may be capable of processing or storing signals, such as in memory as physical memory states, and may, therefore, operate as a server. Thus, devices capable of operating as a server may include, as examples, dedicated rack-mounted servers, desktop computers, laptop computers, set top boxes, integrated devices combining various features, such as two or more features of the foregoing devices, or the like.

[0039] For purposes of this disclosure, a client (or consumer or user) device, referred to as user equipment (UE)), may include a computing device capable of sending or receiving signals, such as via a wired or a wireless network. A client device may, for example, include a desktop computer or a portable device, such as a cellular telephone, a smart phone, a display pager, a radio frequency (RF) device, an infrared (IR) device a Near Field Communication (NFC) device, a Personal Digital Assistant (PDA), a handheld computer, a tablet computer, a phablet, a laptop computer, a set top box, a wearable computer, smart watch, an integrated or distributed device combining various features, such as features of the forgoing devices, or the like.

[0040] In some embodiments, as discussed below, the client device can also be, or can communicatively be coupled to, any type of known or to be known medical device (e.g., any type of Class I, II or III medical device), such as, but not limited to, a MRI machine, CT scanner, Electrocardiogram (ECG or EKG) device, photopletismograph (PPG), Doppler and transmit-time flow meter, laser Doppler, an endoscopic device neuromodulation device, a neurostimulation device, and the like, or some combination thereof.Attorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301DETAILED DESCRIPTION

[0041] The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, which form a part hereof, and which show, by way of non-limiting illustration, certain example embodiments. Subject matter may, however, be embodied in a variety of different forms and, therefore, covered or claimed subject matter is intended to be construed as not being limited to any example embodiments set forth herein; example embodiments are provided merely to be illustrative. Likewise, a reasonably broad scope for claimed or covered subject matter is intended. Among other things, for example, subject matter may be embodied as methods, devices, components, or systems. Accordingly, embodiments may, for example, take the form of hardware, software, firmware or any combination thereof (other than software per se). The following detailed description is, therefore, not intended to be taken in a limiting sense.

[0042] Throughout the specification and claims, terms may have nuanced meanings suggested or implied in context beyond an explicitly stated meaning. Likewise, the phrase “in one embodiment” as used herein does not necessarily refer to the same embodiment and the phrase “in another embodiment” as used herein does not necessarily refer to a different embodiment. It is intended, for example, that claimed subject matter include combinations of example embodiments in whole or in part.

[0043] The present disclosure is described below with reference to block diagrams and operational illustrations of methods and devices. It is understood that each block of the block diagrams or operational illustrations, and combinations of blocks in the block diagrams or operational illustrations, can be implemented by means of analog or digital hardware and computer program instructions. These computer program instructions can be provided to a processor of a general purpose computer to alter itsAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 function as detailed herein, a special purpose computer, ASIC, or other programmable data processing apparatus, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, implement the functions / acts specified in the block diagrams or operational block or blocks. In some alternate implementations, the functions / acts noted in the blocks can occur out of the order noted in the operational illustrations. For example, two blocks shown in succession can in fact be executed substantially concurrently or the blocks can sometimes be executed in the reverse order, depending upon the functionality / acts involved.

[0044] Various examples are directed to methods and systems of registering a three- dimensional (3D) model of a rigid structure, such as bone. More particularly, various examples are directed to methods and related systems of identifying surface features of a rigid structure visible in a video stream, and using the surface features to register a three-dimensional model for use in computer-assisted navigation of the surgical procedure (e.g., Computer-Aided Surgery, or CAS). In some examples, the surface features are determined using touchless techniques based on a known or calculated motion of the camera. In other examples, the surface features are gathered using a touch probe that is not itself directly tracked; but rather, the pose of the touch probe, and thus the locations of the distal tip of the touch probe touching the bone, may be determined by segmenting the frames of the video stream and pose estimation. In yet still further examples, the three-dimensional model may be registered by use of a patient-specific instrument that couples to the rigid structure in only one orientation; thus, a fiducial coupled to the patient-specific instrument, or in some cases the patientspecific instrument itself without a fiducial, may be used to register a three-dimensional anatomical (e.g., bone) model.Attorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301

[0045] Video-based surgical navigation (VBSN) techniques that use patient-specific instruments may include using visual fiducials or fiducial markers (also called visual markers) attached to patient anatomy to guide the surgeon throughout the medical procedure. The video-based navigation process requires the precise registration of a pre-operative anatomical model with data acquired intra-operatively. The registration process or procedure requires the surgeon to digitize the surface of interest that corresponds to the pre-operative model. The fiducial markers with known visual patterns that are attached to the anatomies define reference frames to which the preoperative model and the intra-operative acquired data are aligned. The fiducial markers may be attached both to the targeted anatomy and to the instruments and subsequently tracked such that their relative poses can be accurately estimated (e.g., by applying 3D computer vision methods on the images / video acquired by a camera). These relative poses allow the instruments to be located with respect to the anatomy at every frame time instant. For example, VBSN facilitates the tracking of instruments with respect to the targeted anatomy to which a fiducial is rigidly attached (which may be referred to as a “base marker”).

[0046] In some examples of a registration procedure, a user probes an anatomical surface using a handheld probe. Collected points (e.g., a point cloud) are processed (e.g., using a machine learning algorithm) and matched to a bone model, such as a bone model created via a scan (e.g., a CT or MRI scan) or other technique. For example, the bone model is overlaid on top of a live arthroscopic video feed to provide an augmented or mixed reality visual representation of a surgical or anatomical site.

[0047] In this manner, by using a probe with a calibrated tip (i.e., a probe that is calibrated such that the 3D position of the tip of the probe relative to the reference frame of the tip is known), 3D points can be intra-operatively reconstructed in theAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 reference frame of the fiducial marker. Once the tip is in contact with the surface of patient anatomy, the set of reconstructed 3D points is a representation of the anatomy of interest that is provided as input to the registration procedure.

[0048] However, a probe with a sharp tip can become stuck in non-rigid tissue that is present in the anatomical surface, making the reconstruction process slow and noisy due to the non-smooth motion of the probe. Furthermore, a sharp tip increases the risk of damaging structures with limited capacity of regeneration such as cartilage. Avoiding such structures may result in a very small acceptable region for reconstruction, which may in turn compromise registration accuracy.

[0049] Accordingly, a spherical probe tip according to the principles of the present disclosure overcomes issues associated with a sharp probe tip. The described spherical probe tip minimizes the likelihood of getting caught or stuck in tissue or damaging anatomical structures. However, since a spherical probe tip may have multiple points on the spherical surface in contact with patient anatomy, determining which point of the sphere is actually in contact with patient anatomy at any given instant can be difficult. As such, the present disclosure further describes techniques for determining the location of the probe tip (e.g., a center of the spherical probe tip) and contact points with patient anatomy based on the center of the spherical probe tip.

[0050] Previous example systems and methods that use a spherical probe tip require a dense reconstruction of the anatomical surface to estimate normals that provide the direction of translation along which the reconstructed points will move. Further, such dense reconstruction requires sufficient time for the surgeon to densely paint the surface and only then can points be modified to be input to the registration algorithm, which does not allow on-the-fly registration. In contrast, systems and methodsAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 according to the present disclosure are configured to operate using sparse reconstructions. Further, the spherical probe tip functions as a mechanical low pass filter and the reconstructed point cloud does not capture high frequency components of the anatomical surface (i.e., high frequency components that are present in the original model). Accordingly, an eroded reconstruction may not completely match the original model. Conversely, dilation of the original model in accordance with the principles of the present disclosure results in a filtered, dilated model that exactly matches the reconstructed points.

[0051] Various examples described herein relate to anterior-cruciate ligament (ACL) repair (e.g., for placing femoral and / or tibial tunnels during ACL reconstruction), and thus the discussion below is based on the developmental context. In this context, the rigid structure is bone and / or cartilage, and the three-dimensional model is a three- dimensional bone model. However, the techniques described herein are applicable to any suitable rigid anatomical structure, such as teeth. Moreover, the various techniques may be applicable to many types of surgical procedures, such as repairs associated with the knee, the hip, the shoulder, the wrist, or the ankle. The techniques may be applicable not only to ligament repair (e.g., medial collateral ligament repair, lateral collateral ligament repair, and posterior cruciate ligament repair), but also for planning and placing anchors to reattach soft tissue (e.g., reattaching the labrum of the hip, the rotator cuff, or the meniscal root), and surgical procedures to address femoroacetabular impingement. Thus, the description and developmental context shall not be read as a limitation of the applicability of the teachings.

[0052] FIG. 1 shows a surgical system (not to scale) 100 in accordance with at least some embodiments. In particular, the example surgical system 100 comprises a tower or device cart 102, an example mechanical resection instrument 104, an exampleAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 plasma-based ablation instrument (hereafter just ablation instrument 106), and an endoscope in the example form of an arthroscope 108 and attached camera head or camera 110. In the example systems, the arthroscope 108 is a rigid device, unlike endoscopes for other procedures, such as upper-endoscopies. The device cart 102 may comprise a display device 414, a resection controller 116, and a camera control unit (CCU) together with an endoscopic light source and video controller 118. In example cases the combined CCU and video controller 118 not only provides light to the arthroscope 108 and displays images received from the camera 110, but also implements various additional aspects, such as registering a three-dimensional bone model with the bone visible in the video images, and providing computer-assisted navigation during the surgery. Thus, the combined CCU and video controller are hereafter referred to as surgical controller 118. In other cases, however, the CCU and video controller may be a separate and distinct system from the controller that handles registration and computer-assisted navigation, yet the separate devices would nevertheless be operationally coupled.

[0053] The example device cart 102 further includes a pump controller 122 (e.g., single or dual peristaltic pump). Fluidic connections of the mechanical resection instrument 104 and ablation instrument 106 to the pump controller 122 are not shown so as not to unduly complicate the figure. Similarly, fluidic connections between the pump controller 122 and the patient are not shown so as not to unduly complicate the figure. In the example system, both the mechanical resection instrument 104 and the ablation instrument 106 are coupled to the resection controller 116 being a dualfunction controller. In other cases, however, there may be a mechanical resection controller separate and distinct from an ablation controller. The example devices and controllers associated with the device cart 102 are merely examples, and otherAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 examples include vacuum pumps, patient-positioning systems, robotic arms holding various instruments, ultrasonic cutting devices and related controllers, patientpositioning controllers, and robotic surgical systems.

[0054] FIG. 1 further shows additional instruments that may be present during an arthroscopic surgical procedure. In particular, FIG. 2 shows an example touch probe 124, a drill guide or aimer 126, and a bone fiducial 128. The touch probe 124 may be used during the surgical procedure to provide information to the surgical controller 118, such as information to register a three-dimensional bone model to an underlying bone visible in images captured by the arthroscope 108 and camera head 110. The aimer 126 may be used as a guide for placement and drilling with a drill wire to create an initial or pilot tunnel through the bone. The bone fiducial 128 may be affixed or rigidly attached to the bone and serve as an anchor location for the surgical controller 118 to know the orientation of the bone (e.g., after registration of a three- dimensional bone model). Additional tools and instruments will be present, such as the drill wire, various reamers for creating the throughbore and counterbore aspects of a tunnel through the bone, and various tools, such as for suturing and anchoring a graft. These additional tools and instruments are not shown so as not to further complicate the figure. The specification now turns to a workflow for an example anterior cruciate ligament repair.

[0055] A surgical procedure may begin with a planning phase. The example anterior cruciate ligament repair may start with imaging (e.g., X-ray imaging, computed tomography (CT), magnetic resonance imaging (MRI)) of the knee of the patient, including the relevant anatomy like the lower portion of the femur, the upper portion of the tibia, and the articular cartilage. The imaging may be preoperative imaging, hours or days before the intraoperative repair, or the imaging may take place within theAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 surgical setting just prior to the intraoperative repair. The discussion that follows assumes MRI imaging, but again many different types of imaging may be used. The image slices from the MRI imaging can be segmented such that a volumetric model or three-dimensional model of the anatomy is created. Any suitable currently available, or after developed, segmentation technology may be used to create the three-dimensional model. More specifically to the example of anterior cruciate ligament repair, a three-dimensional bone model of the lower portion of the femur, including the femoral condyles, is created.

[0056] Using the three-dimensional bone model, an operative plan is created that comprises choosing a planned-tunnel path through the femur, including locations of the apertures of the bone that define the ends of the tunnel. For an example inside- out repair, the aperture within the femoral notch is the entry location for the drilling, and the aperture on the lateral surface of the femur is the exit location. For an outsidein repair, the entry and exit locations for drilling are swapped. Still assuming an inside- out repair, the entry location may be selected to be the same as, or close to, the attachment location of the native anterior cruciate ligament to the femur within the femoral notch. In some cases, selecting the entry location within the femoral notch may involve use of a Bernard & Hertel Quadrant or grid placed on a fluoroscopic image, or by placing the Bernard & Hertel Quadrant on a simulated fluoroscopic image created from the three-dimensional bone model. Based on use of the Bernard & Hertel Quadrant, an entry location for the tunnel is selected. For an inside-out repair, selection of the exit location is less restrictive, not only because the portion of the tunnel proximate to the exit location is used for placement of the anchor for the graft, but also because the exit location is approximately centered in the femur (considered anteriorly to posteriorly), and thus issues of bone wall thickness at the exit location areAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 of less concern. In some cases, a three-dimensional bone model of the proximal end of the tibia is also created, and the surgeon may likewise choose planned-tunnel path(s) through the tibia.

[0057] The results of the planning may include: a three-dimensional bone model of the distal end of the femur; a three-dimensional bone model for a proximal end of the tibia; an entry location and exit location through the femur and thus a planned-tunnel path for the femur; and an entry location and exit location through the tibia and thus a planned-tunnel path through the tibia. Other surgical parameters may also be selected during the planning, such as tunnel throughbore diameters, tunnel counterbore diameters and depth, desired post-repair flexion, and the like, but those additional surgical parameters are omitted so as not to unduly complicate the specification.

[0058] The specification now turns to intraoperative aspects. The intraoperative aspects include steps and procedures for setting up the surgical system to perform the various repairs. It is noted, however, that some of the intraoperative aspects (e.g., optical system calibration), may take place before any ports or incisions are made through the patient’s skin, and in fact before the patient is wheeled into the surgical room. Nevertheless, such steps and procedures may be considered intraoperative as they take place in the surgical setting and with the surgical equipment and instruments used to perform the actual repair.

[0059] The example ACL repair is conducted arthroscopically and is computer- assisted in the sense the surgical controller 118 is used for arthroscopic navigation within the surgical site. More particularly, in example systems the surgical controller 118 provides computer-assisted navigation during the ligament repair by tracking location of various objects within the surgical site, such as the location of the bone within the three-dimensional coordinate space of the view of the arthroscope, andAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 location of the various instruments (e.g., a drill wire) within the three-dimensional coordinate space of the view of the arthroscope. The specification turns to brief description of such tracking techniques.

[0060] FIG. 2 shows a conceptual drawing of a surgical site with various objects within the surgical site. In particular, visible in FIG. 2 is a distal end of the arthroscope 108, a portion of a bone 200 (e.g., femur), the bone fiducial 128 within the surgical site, and the touch probe 124. Each is addressed in turn.

[0061] The arthroscope 108 illuminates the surgical site with visible light. In the example of FIG. 2, the illumination is illustrated by arrows 208. The illumination provided to the surgical site is reflected by various objects and tissues within the surgical site, and the reflected light that returns to the distal end enters the arthroscope 108, propagates along an optical channel within the arthroscope 108, and is eventually incident upon a capture array within the camera 110 (FIG. 1 ). The images detected by the capture array within the camera 110 are sent electronically to the surgical controller 118 (FIG. 1 ) and displayed on the display device 114 (FIG. 1 ). In one example, the arthroscope 108 is monocular or has a single optical path through the arthroscope for capturing images of the surgical site, notwithstanding that the single optical path may be constructed of two or more optical members (e.g., glass rods, optical fibers, etc.). That is to say, in example systems and methods the computer-assisted navigation provided by the arthroscope 108, the camera 110, and the surgical controller 118 is provided with the arthroscope 108 that is not a stereoscopic endoscope having two distinct optical paths separated by an interocular distance at the distal end endoscope.

[0062] During a surgical procedure, a surgeon selects an arthroscope with a viewing direction beneficial for the planned surgical procedure. Viewing direction refers to a line residing at the center of an angle subtended by the outside edges or peripheralAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 edges of the view of an endoscope. The viewing direction for some arthroscopes is aligned with the longitudinal central axis of the arthroscope, and such arthroscopes are referred to as “zero degree” arthroscopes (e.g., the angle between the viewing direction and the longitudinal central axis of the arthroscope is zero degrees). The viewing direction of other arthroscopes forms a non-zero angle with the longitudinal central axis of the arthroscope. For example, for a 30° arthroscope the viewing direction forms a 30° angle to the longitudinal central axis of the arthroscope, the angle measured as an obtuse angle beyond the distal end of the arthroscope. In many cases for ACL repair, the surgeon selects a 30° arthroscope or a 45° arthroscope based on location the port created through the skin of the patient. In the example of FIG. 2, the view angle 210 of the arthroscope 108 forms a non-zero angle to the longitudinal central axis 212 of the arthroscope 108.

[0063] Still referring to FIG. 2, within the view of the arthroscope 108 is a portion of the bone 200 (e.g., within the intercondylar notch), along with the example bone fiducial 128 and the example touch probe 124. The example bone fiducial 128 is a multi-faceted element, with each face or facet having a fiducial disposed or created thereon. However, the bone fiducial need not have multiple faces, and in fact may take any shape so long as that shape, a fiducial or other visual marker, etc. can be tracked within the video images. The bone fiducial, such as bone fiducial 128, may be attached to the bone 200 in any suitable form. In this example, the bone fiducial is 128 fastened by a screw portion (not visible in FIG. 2, but visible in FIG. 1 ). The patterns of the fiducials on each facet are designed to provide information regarding the position and orientation of the bone fiducial 128 in the three-dimensional coordinate space of the view of the arthroscope 108. More particularly, the pattern is selected such that the position and orientation of the bone fiducial 128 may beAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 determined from images captured by the arthroscope 108 and attached camera (FIG. 1 ).

[0064] The touch probe 124 is also shown as partially visible within the view of the arthroscope 108. The touch probe 124 may be used, as discussed more below, to identify a plurality of surface features on the bone 200 as part of the registration of the bone 200 to the three-dimensional bone model. Alternatively, though not specifically shown, the aimer 126 (FIG. 1 ) may be used as the device to assist with the registration process. In some cases, the touch probe 124 and / or the aimer 126 may carry their own, unique fiducials, such that their respective poses may be calculated from the one or more fiducials present in the video stream. However, in other cases, and as shown, the medical instrument used to help with registration of the three-dimensional bone model, be it the touch probe 124, the aimer 126, or any other suitable medical device, may omit carrying fiducials. Stated otherwise, in such examples the medical instrument has no fiducial markings. In such cases, the pose of the medical instrument may be determined by a machine learning model, discussed in more detail below.

[0065] The images captured by the arthroscope 108 and attached camera are subject to optical distortion in many forms. For example, the visual field between a distal end of the arthroscope 108 and the bone 200 within the surgical site is filled with fluid, such as bodily fluids and saline used to distend the joint. Many arthroscopes have one or more lenses at the distal end that widen the field of view, and the wider field of view causes a “fish eye” effect in the captured images. Further, the optical elements within the arthroscope (e.g., rod lenses) may have optical aberrations inherent to the manufacturing and / or assembly process. Further still, the camera may have various optical elements for focusing the images received onto the capture array, and the various optical elements may have aberrations inherent to the manufacturing and / orAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 assembly process. In example systems, prior to use within each surgical procedure, the endoscopic optical system is calibrated to account for the various optical distortions. The calibration creates a characterization function that characterizes the optical distortion, and further analysis of the frames of the video stream may be, prior to further analysis, compensated using the characterization function.

[0066] The next example step in the intraoperative procedure is the registration of the bone model created during the planning stage. During the intraoperative repair, the three-dimensional bone model is obtained by or provided to the surgical controller 118. Again using the example of anterior cruciate ligament repair, and specifically computer-assisted navigation for tunnel paths through the femur, the three- dimensional bone model of the lower portion of the femur is obtained by or provided to the surgical controller 118. Thus, the surgical controller 118 receives the three- dimensional bone model, and assuming the arthroscope 108 is inserted into the knee by way of a port through the patient’s skin, the surgical controller 118 also receives video images of a portion of the lower end of the femur. In order to relate the three- dimensional bone model to the images received by way of the arthroscope 108 and camera 110, the surgical controller 118 registers the three-dimensional bone model to the images of the femur received by way of the arthroscope 108 and camera 110.

[0067] In order to perform the registration, and in accordance with example methods, the bone fiducial 128 is attached to the femur. The bone fiducial placement is such that the bone fiducial is within the field of view of the arthroscope 108, but in a location spaced apart from the expected tunnel entry / exit point through the lateral condyle. More particularly, in example cases the bone fiducial 128 is placed within the intercondylar notch superior to the expected location of the tunnel through lateral condyle. To relate or register bone visible in the video images to the three-dimensionalAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 bone model, the surgical controller 118 (FIG. 1 ) is provided or determines a plurality of surface features of an outer surface of the bone. Identifying the surface features may take several forms, including a touch-based registration using the touch probe 124 without a carried fiducial, a touchless registration technique in which the surface features are identified after resolving the motion of the arthroscope 108 and camera relative to the bone fiducial 128, and a third technique in which uses a patient-specific instrument.

[0068] In the example touch-based registration, the surgeon may touch a plurality of locations using the touch probe 124 (FIG. 1 ). In some cases, particularly when portions of the outer surface of the bone are exposed to view, receiving the plurality of surface features of the outer surface of the bone may involve the surgeon “painting” the outer surface of the bone. “Painting” is a term of art that does not involve application of color or pigment, but instead implies motion of the touch probe 124 when the distal end of the touch probe 124 is touching bone. In this example, the touch probe 124 does not carry or have a fiducial visible to the arthroscope 108 and the camera 110. It follows that the pose of the touch probe 124 and the location of the distal tip of the touch probe 124 needs to be determined in order to gather the surface features for purposes of registering the three-dimensional bone model.

[0069] FIG. 3 shows a method 300 in accordance with at least some embodiments. The example method 300 may be implemented in software within a computer system, such as the surgical controller 118. In particular, the example method 300 comprises obtaining a three-dimensional bone model (block 302). That is to say, in the example method 300, what is obtained is the three-dimensional bone model that may be created by segmenting a plurality of non-invasive images (e.g., CT, MRI) taken preoperatively or intraoperatively. With the bone segmented from or within theAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 images, the three-dimensional bone model may be created. The three-dimensional bone may take any suitable form, such as a computer-aided design (CAD) model, a point cloud of data points with respect to an arbitrary origin, or a parametric representation of a surface expressed using analytical mathematical equations. Thus, the three-dimensional bone model is defined with respect to the origin and in any suitable an orthogonal basis.

[0070] The next step in the example method 300 is capturing video images of the bone fiducial attached to the bone (block 304). The capturing is performed intraoperatively. In the example case of an arthroscopic anterior cruciate ligament repair, the capturing of video images is by way of the arthroscope 108 and camera 110. Other endoscopes may be used, such as endoscopes in which the capture array resides at the distal end of the device (e.g. , chip-on-the-tip devices). However, in open procedures where the skin is cut and pulled away, exposing the bone to the open air, the capturing may be by any suitable camera device, such as one or both cameras of a stereoscopic camera system, or a portable computing device, such as a tablet or smart-phone device. The video images may be provided to the surgical controller 118 in any suitable form.

[0071] The next step in the example method 300 is determining locations of a distal tip of the medical instrument visible within the video images (block 306), where the distal tip is touching the bone in at least some of the frames of the video images, and the medical instrument does not have a fiducial. Determining the locations of the distal tip of the medical instrument may take any suitable form. In one example, determining the locations may include segmenting the medical instrument in the frames of the video images (block 308). The segmenting may take any suitable form, such as applying the video images to a segmentation machine learning algorithm. TheAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 segmentation machine learning algorithm may take any suitable form, such as neural network or convolution neural network trained with a training data set showing the medical instrument in a plurality of known orientations. The segmentation machine learning algorithm may produce segmented video images where the medical instrument is identified or highlighted in some way (e.g., box, brightness increased, a highlighted outline, other objects removed, etc.).

[0072] With the segmented video images, the example method 300 may estimate a plurality of poses of the medical instrument within a respective plurality of frames of the video images (block 310). The estimating the poses may take any suitable form, such as applying the video images to a pose machine learning algorithm. The pose machine learning algorithm may take any suitable form, such as neural network or convolution neural network trained to perform six-dimensional pose estimation. The resultant of the pose machine learning algorithm may be, for at least some of the frames of the video image, an estimated pose of the medical instrument in the reference frame of the video images and / or in the reference frame provided by the bone fiducial. That is, the result of the pose machine learning algorithm may be a plurality of poses, one pose each for at least some of the frames of the segmented video images. While in many cases a pose may be determined for each frame, in other cases it may not be possible to make a pose estimation for at least some frame because of video quality issues, such as motion blur caused by electronic shutter operation.

[0073] The next step in the example method 300 is determining the locations based on the plurality of poses (block 312). In particular, for each frame for which a pose can be estimated, based on a model of the medical device the location of the distal tip can be determined in the reference frame of the video images and / or the bone fiducial.Attorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301Thus, the resultant is a set of locations that, at least some of which, represent locations of the outer surface of the bone.

[0074] FIG. 3 shows an example three-step process for determining the locations of the distal tip of the medical instrument. However, the method 300 is merely an example, and many variations are possible. For example, a single machine learning model, such as a convolution neural network, may be set up and trained to perform all three steps as a single overall process, though there may be many hidden layers of the convolution neural network. That is, the convolution neural network may segment the medical instrument, perform the six-dimensional pose estimation, and determine the location of the distal tip in each frame. The training data set in such a situation would include a data set in which each frame has the medical device segmented, the six-dimensional pose identified, and the location of the distal tip identified. The output of the determining step 306 may be a segmented video stream distinct from the video images captured at step 304. In such cases, the later method steps may use both segmented video stream and the video images to perform the further tasks. In other cases, the location information may be combined with the video images, such as being embedded in the video images, or added as metadata to each frame of the video images.

[0075] FIG. 4 is an example video display showing portions of a femur and a bone fiducial during a registration procedure. The display may be shown, for example, on the display device 114 associated with the device cart 102, or any other suitable location. In particular, visible in the main part of the display of FIG. 4 is an intercondylar notch 400, a portion of the lateral condyle 402, a portion the medial condyle 404, and the example bone fiducial 128. Shown in the upper right corner of the example display is a depiction of the bone, which may be a rendering 406 of the bone created from theAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 three-dimensional bone model. Shown on the rendering 406 is a recommended area 408, the recommended area 408 being portions of the surface of the bone to be “painted” as part of the registration process. Shown in the lower right corner of the example display is a depiction of the bone, which again may be a rendering 412 of the bone created from the three-dimensional bone model. Shown on the rendering 412 are a plurality of surface features 416 on the bone model that have been identified as part of the registration process. Further shown in the lower right corner of the example display is progress indicator 418, showing the progress of providing and receiving of locations on the bone. The example progress indicator 418 is a horizontal bar having a length that is proportional to a level of confidence that the registration is accurate, but any suitable graphic or numerical display showing progress may be used (e.g., 0% to 100%).

[0076] Referring to both the main display and the lower right rendering, as the surgeon touches the outer surface of the bone within the images captured by the arthroscope 108 and camera 110, the surgical controller 118 receives the surface features on the bone, and may display each location both within the main display as dots or locations 416, and within the rendering shown in the lower right corner. More specifically, the example surgical controller 118 overlays indications of identified surface features 416 on the display of the images captured by the arthroscope 108 and camera 110, and in the example case shown, also overlays indications of identified surface features 416 on the rendering 412 of the bone model. Moreover, as the number of identified locations 416 increases, the surgical controller 118 also updates the progress indicator 418.

[0077] Returning to FIG. 3, the plurality of surface features 416 may be, or the example surgical controller 118 may generate, a registration model relative to the boneAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 fiducial 128 (block 314). The registration model may take any suitable form, such as a computer-aided design (CAD) model or point cloud of data points in any suitable orthogonal basis. The registration model, regardless of the form, may have fewer overall data points or less “structure” than the bone model created by the non-invasive computer imaging (e.g., MRI). However, the goal of the registration model is to provide the basis for the coordinate transforms and scaling used to correlate the bone model to the registration model and relative to the bone fiducial 128. Thus, the next step in the example method 300 is registering the bone model relative to the location of the bone fiducial based on the registration model (block 316). Registration may conceptually involve testing a plurality of coordinate transformations and scaling values to find a correlation that has a sufficiently high correlation or confidence factor. Once a correlation is found with the sufficiently high confidence factor, the bone model is said to be registered to the location of the bone fiducial. Thereafter, the example registration method 300 may end; however, the surgical controller 118 may then use the registered bone model to provide computer-assisted navigation regarding a procedure involving the bone.

[0078] In the examples discussed to this point, registration of the bone model involves a touch-based registration technique using the touch probe 124 without a carried fiducial. However, other registration techniques are possible, such as a touchless registration technique. The example touchless registration technique again relies on placement of the bone fiducial 128. As before, when the viewing direction of the arthroscope 108 is relatively constant, the bone fiducial may have fewer faces with respective fiducials. Once placed, the bone fiducial 128 represents a fixed location on the outer surface of the bone in the view of the arthroscope 108, even as the position of the arthroscope 108 is moved and changed relative to the bone fiducial 128. Again,Attorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 in order to relate or register the bone visible in the video images to the three- dimensional bone model, the surgical controller 118 (FIG. 1 ) determines a plurality of surface features of an outer surface of the bone, and in this example determining the plurality of surface features is based on a touchless registration technique in which the surface features are identified based on motion of the arthroscope 108 and camera 110 relative to the bone fiducial 128.

[0079] Another technique for registering the bone model to the bone uses a patientspecific instrument. In both touch-based and touchless registration techniques, a registration model is created, and the registration model is used to register the bone model to the bone visible in the video images. Conceptually, the registration model is used to determine a coordinate transformation and scaling to align the bone model to the actual bone. However, if the orientation of the bone in the video images is known or can be determined, use of the registration model may be omitted, and instead the coordinate transformations and scaling may be calculated directly.

[0080] FIG. 5 shows a method 500 in accordance with at least some embodiments. The example method may be implemented in software within one or more computer systems, such as, in part, the surgical controller 118. In particular, the example method 500 starts and comprises obtaining a three-dimensional bone model (block 502). Much like the prior techniques, in the patient-specific instrument registration technique what is obtained is the three-dimensional bone model that may be created by segmenting a plurality of non-invasive images (e.g., MRI) taken preoperatively or intraoperatively.

[0081] The next step in the example method 500 is generating a patient-specific instrument that has a feature designed to couple to the bone represented in the bone model in only one orientation (block 504). Generating the patient-specific instrumentAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 may first involve selecting a location at which the patient-specific instrument will attach. For example, a device or computer system may analyze the bone model and select the attachment location. In various examples, the attachment location may be a unique location in the sense that, if a patient-specific instrument is made to couple to the unique location, the patient-specific instrument will not couple to the bone at any other location. In the example case of an anterior cruciate ligament repair, the location selected may be at or near the upper or superior portion on the intercondylar notch. If the bone model shows another location with a unique feature, such as a bone spur or other raised or sunken surface anomaly, such a unique location may be selected as the attachment location for the patient-specific instrument.

[0082] Moreover, forming the patient-specific instrument may take any suitable form. In one example, a device or computer system may directly print, such as using a 3D printer, the patient-specific instrument. In other cases, the device or computer system may print a model of the attachment location, and the model may then become the mold for creating the patient-specific instrument. For example, the model may be the mold for an injection-molded plastic or casting technique. In some examples, the patient-specific instrument carries one or more fiducials, but as mentioned above, in other cases the patient-specific instrument may itself be tracked and thus carry no fiducials.

[0083] The next step in the example method 500 is coupling the patient-specific instrument to the bone, in some cases the patient-specific instrument having the fiducial coupled to an exterior surface (block 506). As previously mentioned, the attachment location for the patient-specific instrument is selected to be unique such that the patient-specific instrument couples to the bone in only one location and in only one orientation. In the example case of an arthroscopic ACL repair, the patient-specificAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 instrument may be inserted arthroscopically. That is, the attachment location may be selected such that a physical size of the patient-specific instrument enables insertion through the ports in the patient’s skin. In other case, the patient-specific instrument may be made or constructed of a flexible material that enables the patient-specific instrument to deform for insertion in the surgical site, yet return to the predetermined shape for coupling to the attachment location. However, in open procedures where the skin is cut and pulled away, exposing the bone to the open air, the patient-specific instrument may be a rigid device with fewer size restrictions.

[0084] The next step in the example method 500 is capturing video images of the patient-specific instrument (block 508). Here again, the capturing may be performed intraoperatively. In the example case of an arthroscopic anterior cruciate ligament repair, the capturing of video images is by the surgical controller 118 by way of arthroscope 108 and camera 110. However, in open procedures where the skin is cut and pulled away, exposing the bone to the open air, the capturing may be by any suitable camera device, such as one or both cameras of a stereoscopic camera systems, or a portable computing device, such as a tablet or smart-phone device. In such cases, the video images may be provided to the surgical controller 118 in any suitable form.

[0085] The next step in the example method 500 is registering the bone model based on the location of the patient-specific instrument (block 510). That is, given that the patient-specific instrument couples to the bone at only one location and in only one orientation, the location and orientation of the patient-specific instrument is directly related to the location and origination of the bone, and thus the coordinate transformations and scaling for the registration may be calculated directly. Thereafter, the example method 500 may end; however, the surgical controller 118 may then useAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 the registered bone model to provide computer-assisted navigation regarding a surgical task or surgical procedure involving the bone.

[0086] For example, with the registered bone model the surgical controller 118 may provide guidance regarding a surgical task of a surgical procedure. The specific guidance is dependent upon the surgical procedure being performed and the stage of the surgical procedure. A non-exhaustive list of guidance comprises: changing a drill path entry point; changing a drill path exit point; aligning an aimer along a planned drill path; showing location at which to cut and / or resect the bone; reaming the bone by a certain depth along a certain direction; placing a device (suture, anchor or other) at a certain location; placing a suture at a certain location; placing an anchor at a certain location; showing regions of the bone to touch and / or avoid; and identifying regions and / or landmarks of the anatomy. In yet still other cases, the guidance may include highlighting within a version of the video images displayed on a display device, which can be the arthroscopic display or a see-through display, or by communicating to a virtual reality device or a robotic tool.

[0087] In these and other examples of a registration procedure, a user probes an anatomical surface using a handheld probe. FIGS. 6A and 6B show example probes 600 and 602, respectively. In these examples, the probes 600, 602 include one or more fiducials or fiducial markers 604. Tips 608 of the probes 600, 602 can be calibrated such that locations of the tips 608 relative to the fiducials 604 are known. For example, the probes 600, 602 are calibrated, in a pre-operative calibration procedure, to obtain geometrical and dimensional data such that position or location, orientation, etc. of various features of the probes 600, 602, such as the tips 608, relative to the fiducials 604 are known. In this manner, 3D points can be intra- operatively reconstructed in the reference frame of the fiducial marker. For example,Attorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 points can be obtained when the tip is in contact with the surface of patient anatomy (by determining the location of the tip based on the detected fiducials 604). Accordingly, the set of reconstructed 3D points is a representation of the anatomy of interest that is provided as input to the registration procedure.

[0088] As shown in FIGS. 6A and 6B, the tips 608 of probes 600, 602 are “sharp” or tapered. Such tips can become stuck in non-rigid tissue that is present in the anatomical surface, complicating the reconstruction process and overall registration procedure. Accordingly, a spherical probe tip according to the principles of the present disclosure overcomes issues associated with a sharp probe tip. The described spherical probe tip minimizes the likelihood of getting caught or stuck in tissue or damaging anatomical structures, facilitates entry into portals, etc. Accordingly, the usability of surgical navigation systems is improved by making the registration process faster and easier to perform.

[0089] A challenge associated with spherical probe tips is determining which point on the spherical probe tip (e.g., a sphere) is in contact with the anatomy at a given time. However, when the sphere is in contact with a surface of patient anatomy, a center of the sphere is at a distance r (where r is a radius of the sphere) from the surface at all times. Thus, by calibrating the probe such that the coordinates of the center of the sphere are known with respect to at least one fiducial marker located on the probe, points that are a distance of r (e.g., r mm) away from the surface can be reconstructed. These points are then registered with a model that is dilated by r mm with respect to an original pre-operative 3D model (e.g., a pre-operative model that is obtained via MRI, CT, or other scan or imaging process as described above). The dilation process is performed before the surgical procedure as a pre-operative step. AlthoughAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 described with respect to the radius, other suitable dimensions of a spherical probe tip (e.g., a diameter) can be used in a similar manner.

[0090] As used herein, the terms “dilate” or “dilation” refer to a morphological process or operation in which boundaries of features, objects, surfaces, etc. within the 3D model are expanded, resulting in a dilated 3D model having an increased scale (e.g., relative to the original, non-dilated 3D model). Accordingly, anatomical surfaces within the dilated 3D model are dilated (i.e. , not simply offset or shifted) relative to the same surfaces in the original pre-operative model.

[0091] Accordingly, the systems and methods according to the present disclosure as described below are configured to implement a probe having a spherical probe tip. Although described herein as being “spherical,” the principles of the present disclosure can be implemented for probes having probe tips that are not completely spherical but include partially or substantially spherical tips (e.g., semispherical or rounded tips with a known radius of curvature).

[0092] FIG. 7 shows an example probe 700 that includes a spherical probe tip 704 according to the principles of the present disclosure. In various examples, the probe tip 704 has a radius in a range of approximately 1 .0 to 4.5 mm. In one example, the probe tip has a radius of approximately 1 .5 mm. In other examples, the probe tip 704 may have a radius within other ranges. For example, an optimum or desired radius may vary in accordance with the surgical procedure (and corresponding anatomy) being performed.

[0093] The probe tip 704 is located at a proximal end of the probe 700. As shown, the probe tip 704 is attached (e.g., fixedly or removably) to an end of a probe tip shaft 708. The probe tip 704 can be comprised of a same or different material as the probeAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 tip shaft 708. For example, the probe tip 704 may be comprised of plastic or polymer, rubber, metal, etc. In some examples, the probe tip 704 is fixedly (i.e. , non-removably) attached to the probe tip shaft 708. In other examples, the probe tip 704 may be removably attached (e.g., via threaded or friction-based attachment mechanisms) to the probe tip shaft 708. In some examples, the probe tip shaft 708 may be configured to attach to a plurality of different probe tips (e.g., probe tips having different radiuses, geometries, materials, etc.). As shown, the probe tip shaft 708 is shown as having a central axis that is inclined (i.e., not parallel) relative to a central axis of the probe 700 (e.g., a body or handle 712 of the probe 700). In other words, the probe tip shaft 708 is angled / inclined or forms an “L” shape relative to the handle 712.

[0094] The probe 700 includes one or more fiducial markers 716. As shown, the fiducial markers 716 are located at or adjacent to a distal end of the probe 700 (i.e., at an end of the probe 700 nearer to the probe tip 704 than to a proximal end of the handle 712). For example, the probe 700 may include a substantially flat or planar surface proximate the distal end of the probe 700 and the fiducial markers 716 are disposed on the planar surface. The probe 700 can be calibrated such that coordinates of a center 720 of the probe tip 704 are known with respect to locations of the fiducial markers 716. In other words, during the registration procedure, one or more of the fiducial markers 716 and their respective coordinates can be identified (i.e., by detecting the fiducial markers 716 in one or more images obtained of the probe 700 within the surgical environment). Since the location of the center 720 of the probe tip 704 relative to the fiducial markers 716 is known, the coordinates of the center 720 can be obtained using the coordinates of the one or more fiducial markers 716. Accordingly, when the probe tip 704 is in contact with a surface corresponding to patient anatomy (e.g., a bone surface), the location of the center 720 is obtained, andAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 points that are a distance of r mm away from the contacted surface can be reconstructed as described below in more detail.

[0095] Similar to the example intra-operative registration procedures described above with respect to FIGS. 1-5, registration can be performed with the probe 700 according to the present disclosure by moving the probe 700 within a field-of-view of an arthroscopic camera while maintaining contact between the spherical probe tip 704 and the surface of the anatomy. In contrast to registration performed with a probe having a sharp probe tip, since the probe tip 704 is spherical, the exact point on the probe tip 704 that is in contact with the anatomical surface is initially unknown. However, a distance between the center of the sphere and the anatomical surface is constant and equal to the radius of the sphere r. Accordingly, to reconstruct points that correspond to the center of the spherical probe tip 704, the probe 700 is calibrated before the surgical procedure to determine the coordinates of the center of the probe tip 704 with respect to the one or more fiducial markers 716 as described below in more detail.

[0096] FIGS. 8A, 8B, 8C, and 8D show other example probes 800, 802, 804, and 806, respectively, having spherical probe tips 808. Various example probes may have probe tips 808 having different radiuses, probe shafts 812 having different lengths or angles / inclinations, and so on. For example, the probes 800, 802, 804, and 806 have respective probe tips 808 with radiuses ranging from 4.5 mm to 1 .5 mm.

[0097] FIG. 9A shows an example of surface dilation in accordance with at least some embodiments of the present disclosure. Example positions of a spherical probe tip according to the present disclosure are shown at 900. The probe tip 900 is shown in contact with various points on an anatomical surface 902. A center 904 of the probe tip 900 (i.e., a center of a sphere defined by the probe tip 900) is maintained at aAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 constant distance (e.g., a distance r corresponding to a radius of the sphere) from the surface 902. A path 906 of the center 904 of the probe tip 900 represents the possible locations of the center 904 as the probe tip 900 is moved along the surface 902, and points acquired during the registration procedure correspond to the path 906.

[0098] Accordingly, the points on the path 906 are reconstructed a distance of r mm from the actual surface 902 and do not align with the corresponding surface in an original, pre-operative model being used for registration (which may be referred to herein as a first or original model). To compensate for this misalignment, systems and methods according to the present disclosure dilate the original model by a distance equal to the radius r of the sphere. In this manner, the dilated model (which may be referred to herein as a second or dilated model) is aligned with the points acquired using the spherical probe tip 900 during registration.

[0099] The spherical probe tip 900 is further configured to function as a mechanical low pass filter that eliminates high frequency components from the original model. For example, the anatomical surface 902 may include various high-frequency surface features 908 (e.g., small surface irregularities) that may catch / trap or otherwise obstruct a sharp probe tip. In contrast, the spherical probe tip 900 passes / slides over the surface feature 908. Accordingly, the feature 908 is “filtered” from the path 906, and the reconstruction / dilation of the original model does not include the feature 908. In this manner, the spherical probe tip 900 of the present disclosure provides a smoother representation of reconstructed points and decreases noise levels in the acquired points / data (the reconstructed point cloud) that are provided to the registration procedure.

[0100] In some examples, the size / radius of the probe tip 900 can be selected (i.e. , pre-operatively based on a desired amount of filtering). For example, as the radius isAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 increased, the amount of filtering also increases. In this manner, probe tips of various sizes can be selected based on the surgical procedure to be performed, patient specific anatomy, etc.

[0101] FIGS. 9B, 9C, 9D, and 9E show an example model dilation process according to at least some embodiments of the present disclosure. Steps / functions of the model dilation process as described herein can be performed by one or more processors or processing devices executing instructions stored in memory, computing devices, controllers, etc. As described herein, the original model is dilated in an outward direction (i.e., scaled outward relative to the anatomical surface) by an amount that equals the radius of the spherical probe tip 900.

[0102] As shown in FIG. 9B, the original model 920 may correspond to an open surface represented by a 3D triangular mesh 922. The original model 920 may be a model of an anatomical surface obtained pre-operatively as described in various examples herein.

[0103] As shown in FIG. 9C, a 3D grid 926 (e.g., a 3D grid of points, as shown) containing / enclosing the entire original model 920 (i.e., the triangular mesh 922) is generated / constructed. The grid 926 is larger than the model 920 by a margin larger than the radius of the probe tip 900. In other words, the grid 926 is constructed to at least enclose the model 920 when dilated by the radius of the probe tip 900. In an example, a resolution of the grid 926 is set to be similar or finer than an average side length of the mesh triangles composing the triangular mesh 922. Each point on the grid 926 is then assigned a value (a grid point value) corresponding to a shortest distance from the point to the mesh 922 of the original model 920. The respective shortest distances can be obtained using various shortest distance search algorithmsAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 or techniques, and in some examples may be obtained using an acceleration data structure.

[0104] As shown in FIG. 9D, a meshing algorithm is used to generate a dilated mesh 928 representing an isosurface on a field generated using the grid point values. For example, the isosurface is a 3D surface that connects points (e.g., the grid points) at a same elevation or distance from the mesh 922. Here, the elevation corresponds to the radius of the spherical probe tip 900. As shown, the dilated mesh 928 encloses / surrounds the mesh 922 (i.e., includes points / areas both inward of (below) and outward of (above) the mesh 922). Example meshing algorithms or techniques used to generate the dilated mesh 928 include, but are not limited to, Naive Surface Nets techniques.

[0105] As shown in FIG. 9E, the dilated mesh 928 is modified to obtain a final dilated mesh 930. The final dilated mesh 930, like the original mesh 922, is an open-surface mesh. In other words, the final dilated mesh 930 represents a dilated open-surface and does not enclose / surround the mesh 922. For example, to obtain the final dilated mesh 930, triangles that are not on an external (outward) side of the mesh 922 are removed from the dilated mesh 928. Accordingly, only triangles / portions of the dilated mesh 928 on the external side of the mesh 922 remain in the final dilated mesh 930.

[0106] The registration procedure can then be performed with a probe having the spherical probe tip 900 using the final dilated mesh 930. For example, registration points that are obtained using the spherical probe tip 900 are attributed to locations on the final dilated mesh 930.

[0107] In some examples, instead of or in addition to using model dilation process described above in FIGS. 9A, 9B, 9C, and 9D, a deep learning or other machineAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 learning technique can be used to infer or generate a dilated model. In some examples, surface information (e.g., a normal at each point on the surface) can be used to determine a set of possible locations for the center of the sphere. In some examples, a segmentation label in an image obtained from a CT scan, MRI, or other technique can be modified to represent a dilated model.

[0108] FIGS. 10A, 10B, and 10C show an example calibration process for a probe 1000 having a spherical probe tip 1004 according to the principles of the present disclosure. Calibrating the probe 1000 includes determining 3D coordinates of a center 1008 of the spherical probe tip 1004 in a reference frame of the probe 1000 (e.g., a reference frame of one or more fiducial markers 1012 located on the probe 1000).

[0109] In this example, calibration is performed using a calibration plate 1016 that includes a calibration marker 1020 with one or more calibration or plate fiducial markers 1024 and dimples or recesses 1026. The recesses 1026 are sized / configured to receive respective spherical probe tips having different radiuses. For example, the recesses 1026 are hemispherical (e.g., the recesses 1026 are a “half-sphere”).

[0110] With the probe tip 1004 inserted within the appropriate one of the recesses 1026, a center of the half-sphere (e.g., a point P as shown in FIG. 10A, which is known in coordinates of the calibration plate 1016) is aligned with the center 1008 of the spherical probe tip 1004. Accordingly, the coordinates of the center 1008 in a reference frame / coordinates of the probe 1000 can be obtained by measuring a relative pose T between the calibration plate 1016 and the fiducial markers 1012.

[0111] Alternatively, in cases where the point P is not known, the probe 1000 can be calibrated by placing the probe tip 1004 on the recess 1026 and rotating the probeAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-253011000 while recording, for each frame i, poses of the plate fiducial markers 1024 (Rwi, twi) and probe fiducial markers 1012 (Rti, tti) in a reference frame or coordinates of a camera. Then, a linear system of equations Ax=b is constructed, with A being obtained by stacking matrices [Rwi -Rti] row-wise and b being obtained by stacking vectors - twi+tti row-wise, for all images i. A solution x is a 6-dimensional (6D) vector, with the first three elements of the 6D vector corresponding to a rotation point in the coordinates of the calibration plate 1016 and the final three elements of the 6D vector corresponding to a rotation point in the coordinates of the probe fiducial markers 1012. In this manner, by obtaining the final three elements of x, the calibration of the probe 1000 can be achieved.

[0112] FIG. 11 illustrates steps of an example method for performing a touch-based registration procedure using a probe with a spherical probe tip (e.g., a touch-based registration procedure performed using any of the probes with spherical probe tips as described herein, such as the probes described in FIGS. 7-8 and 10). The method 1100 can be performed in conjunction with any of the other methods described herein.

[0113] The registration procedure begins at 1104. For example, the registration procedure may begin in response to a command from a user (e.g., at the surgical system 100 or an associated computer system or computing device, application, etc.).

[0114] At 1108, the method 1100 includes dilating an original model. For example, dilating the original model may include dilating the original model by an amount based on a dimension (e.g., a radius) of a spherical probe tip as described above with respect to FIGS. 9A-9E to obtain a dilated registration model.

[0115] At 1112, the method 1100 includes determining locations of a center of the spherical probe tip (e.g., as a surgeon “paints” or otherwise contacts various locationsAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 on an anatomical surface, such as a bone surface, with the spherical probe tip) and registering, to the dilated registration model, points corresponding to the locations of the center. Determining the locations may include obtaining, using an arthroscopic or other camera or imaging device, images of a surgical environment including the probe, fiducial markers on the probe, a fixed fiducial marker (e.g., a bone fiducial), etc., and determining the locations of the center in a coordinate system of the fixed fiducial marker based on a known relationship between the fiducial markers on the probe and the center of the spherical probe tip. Accordingly, determining the locations of the center of the spherical probe tip includes receiving or obtaining data indicative of a plurality of locations of the spherical probe tip relative to the patient anatomy (e.g., the anatomical surface). Registering the points includes, for example, registering the points to a 3D anatomical (e.g., bone) model corresponding to the dilated registration model in accordance with any of the techniques described herein.

[0116] FIG. 12 shows an example computer system 1200. In one example, the computer system 1200 may correspond to the surgical controller 118, a tablet device within the surgical room, or any other system that implements any or all the various methods discussed in this specification. The computer system 1200 may be connected (e.g., networked) to other computer systems in a local-area network (LAN), an intranet, and / or an extranet (e.g., device cart 102 network), or at certain times the Internet (e.g., when not in use in a surgical procedure). The computer system 1200 may be a server, a personal computer (PC), a tablet computer or any device capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that device. Further, while only a single computer system is illustrated, the term “computer” shall also be taken to include any collection of computers thatAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methods discussed herein.

[0117] The computer system 1200 includes a processing device 1202, a main memory 1204 (e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM)), a static memory 1206 (e.g., flash memory, static random access memory (SRAM)), and a data storage device 1208, which communicate with each other via a bus 1210.

[0118] Processing device 1202 represents one or more general-purpose processing devices such as a microprocessor, central processing unit, or the like. More particularly, the processing device 1202 may be a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VLIW) microprocessor, or a processor implementing other instruction sets or processors implementing a combination of instruction sets. The processing device 1202 may also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. The processing device 1202 is configured to execute instructions for performing any of the operations and steps discussed herein. Once programmed with specific instructions, the processing device 1202, and thus the entire computer system 1200, becomes a special-purpose device, such as the surgical controller 118.

[0119] The computer system 1200 may further include a network interface device 1212 for communicating with any suitable network (e.g., the device cart 102 network). The computer system 1200 also may include a video display 1214 (e.g., display device 414), one or more input devices 1216 (e.g., a microphone, a keyboard, and / or a mouse), and one or more speakers 1218. In one illustrative example, the video displayAttorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-253011214 and the input device(s) 1216 may be combined into a single component or device (e.g., an LCD touch screen).

[0120] The data storage device 1208 may include a computer-readable storage medium 1220 on which the instructions 1222 (e.g., implementing any methods and any functions performed by any device and / or component depicted described herein) embodying any one or more of the methodologies or functions described herein is stored. The instructions 1222 may also reside, completely or at least partially, within the main memory 1204 and / or within the processing device 1202 during execution thereof by the computer system 1200. As such, the main memory 1204 and the processing device 1202 also constitute computer-readable media. In certain cases, the instructions 1222 may further be transmitted or received over a network via the network interface device 1212.

[0121] While the computer-readable storage medium 1220 is shown in the illustrative examples to be a single medium, the term “computer-readable storage medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and / or associated caches and servers) that store the one or more sets of instructions. The term “computer-readable storage medium” shall also be taken to include any medium that is capable of storing, encoding or carrying a set of instructions for execution by the machine and that cause the machine to perform any one or more of the methodologies of the present disclosure. The term “computer- readable storage medium” shall accordingly be taken to include, but not be limited to, solid-state memories, optical media, and magnetic media.

[0122] The computer system 1200 or one or more computing or processing devices may be configured to perform functions of the registration procedure described herein, including functions related to communication and / or control of any of the probes,Attorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301 functions, steps, etc. described in FIGS. 7-11 , and / or functions of the methods described herein.

[0123] The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and / or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure.

Claims

Attorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-25301CLAIMSWhat is claimed is:1 . A system for registering an anatomical surface for a registration procedure, the system comprising: memory storing instructions; and one or more processing devices configured to execute the instructions, wherein executing the instructions causes the system to perform, based on a dimension of a spherical probe tip of a probe configured to perform the registration procedure, a dilation process on a first model of patient anatomy including the anatomical surface to obtain a second model of the patient anatomy, receive data indicative of a plurality of locations of the spherical probe tip relative to the patient anatomy, and register points corresponding to the plurality of locations of the spherical probe to the second model.

2. The system of claim 1 , wherein the dimension is a radius of the spherical probe tip, and wherein performing the dilation process includes dilating the first model in accordance with the radius of the spherical probe tip.

3. The system of claim 2, wherein performing the dilation process includes: generating a three-dimensional (3D) triangular mesh corresponding to the first model; generating a 3D grid of points enclosing the triangular mesh; and generating a dilated mesh using the triangular mesh and the 3D grid.Attorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-253014. The system of claim 3, wherein the triangular mesh is an open surface corresponding to the anatomical surface.

5. The system of claim 3, wherein a resolution of the 3D grid is at least as fine as an average side length of mesh triangles composing the triangular mesh.

6. The system of claim 3, wherein generating the 3D grid includes assigning respective values to the points of the 3D grid based on respective distances from the points to the triangular mesh.

7. The system of claim 6, wherein generating the dilated mesh includes generating the dilated mesh based on the assigned respective values and the radius.

8. The system of claim 7, wherein generating the dilated mesh includes generating an isosurface that connects points at a same elevation from the triangular mesh, and wherein the same elevation corresponds to the radius.

9. The system of claim 3, wherein executing the instructions further causes the system to modify the dilated mesh by removing portions of the dilated mesh that are not located on an external side of the triangular mesh.

10. The system of claim 1 , wherein the data indicative of the plurality of locations corresponds to a center of the spherical probe tip.Attorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-2530111. A method for registering an anatomical surface for a registration procedure, the method comprising: performing, based on a dimension of a spherical probe tip of a probe configured to perform the registration procedure, a dilation process on a first model of patient anatomy including the anatomical surface to obtain a second model of the patient anatomy; receiving data indicative of a plurality of locations of the spherical probe tip relative to the patient anatomy; and registering points corresponding to the plurality of locations of the spherical probe to the second model.

12. The method of claim 11 , wherein the dimension is a radius of the spherical probe tip, and wherein performing the dilation process includes dilating the first model in accordance with the radius of the spherical probe tip.

13. The method of claim 12, wherein performing the dilation process includes: generating a three-dimensional (3D) triangular mesh corresponding to the first model; generating a 3D grid of points enclosing the triangular mesh; and generating a dilated mesh using the triangular mesh and the 3D grid.

14. The method of claim 13, wherein the triangular mesh is an open surface corresponding to the anatomical surface.Attorney Docket No. PT-6188-WO-PCTDW Ref. No. 73888-2530115. The method of claim 13, wherein a resolution of the 3D grid is at least as fine as an average side length of mesh triangles composing the triangular mesh.

16. The method of claim 13, wherein generating the 3D grid includes assigning respective values to the points of the 3D grid based on respective distances from the points to the triangular mesh.

17. The method of claim 16, further comprising generating the dilated mesh based on the assigned respective values and the radius.

18. The method of claim 17, wherein generating the dilated mesh includes generating an isosurface that connects points at a same elevation from the triangular mesh, and wherein the same elevation corresponds to the radius.

19. The method of claim 13, further comprising modifying the dilated mesh by removing portions of the dilated mesh that are not located on an external side of the triangular mesh.

20. The method of claim 11 , wherein the data indicative of the plurality of locations corresponds to a center of the spherical probe tip.

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