Calibration structures

Abstract

A calibration structure 100 comprising a shaft 101 configured for engagement at a first end 105 in a chuck of a surgical tool, the shaft having an axis of rotation (A). An arm 103 depending from the s

Description

Technical Field The present disclosure relates, in general, to calibration structures. Aspects relate to calibration structures for use with surgical tools. Background Surgical procedures can be carried out using surgical tools that may require alignment in order to enable a user to operate on the correct part of a patient’s body, thereby ensuring that the procedure is effective and efficient. Some procedures, such as free hand procedures, can use alignment jigs in order to ensure that any surgical tool is correctly positioned before use, and sometimes as the tool in question is in use. For example, a total knee replacement procedure requires a prosthesis to be accurately implanted to ensure that joint surfaces are properly aligned. Inaccurate alignment can lead to failure of the joint. Jigs used to ensure alignment are complex devices and require a significant amount of time to install during a surgical procedure. Furthermore, as a procedure is carried out, misalignment can occur as a result of movement of any one or more of a surgical tool, the patient, and a jig. It can also be the case that a jig is used only at the start of a procedure in order to provide an initial alignment. Accordingly, subsequent removal of the jig during the procedure can lead to the introduction of alignment errors. Such errors and movement may be difficult to detect or rectify during a procedure, leading to mistakes or failures in a procedure. In some cases, a computerised system can be used to guide a surgeon during a procedure. However, the complexity and expense of such systems can be a barrier to their implementation, particularly in respect of some procedures where performance by free hand can be advantageous. Furthermore, calibration of the surgical tool being used is required to ensure that a user has confidence that the surgical tool and / or an accessory connected thereto is being positioned where intended to ensure that any procedure being carried out is performed accurately. Summary An objective of the present disclosure is to provide a calibration structure that enables quick and easy calibration of a surgical tool and / or accessories to be used in combination with a surgical tool. The foregoing and other objectives are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description, and the Figures. A first aspect of the present disclosure provides a calibration structure for a surgical tool, the calibration structure comprising a shaft configured for releasable engagement at a first end of the shaft with a chuck device of a tool, wherein the shaft comprises an axis of rotation, and an arm, depending from the shaft, the arm provided perpendicular to the axis of rotation at a second end of the shaft, wherein the arm comprises an optical reference portion provided in spaced relation on the arm relative to the axis of rotation. In an implementation of the first aspect, the arm can comprise one or more additional optical reference portions provided in spaced relation on the arm relative to the axis of rotation. The second end of the shaft can comprise a probe registration structure provided in line with the axis of rotation of the shaft, wherein the probe registration structure is configured to receive the tip of a probe. The probe registration structure can comprise a female portion configured to receive the tip of the probe. In an example, the probe registration structure can comprise an opening in the second end of the shaft, wherein the opening converges in a direction towards the first end of the shaft to a point. The point of the probe registration structure can comprise a profile and / or size selected to prevent lateral movement of the tip of a probe. The first end of the shaft can comprise a shank portion configured to releasably engage with a chuck of a tool, whereby to secure the calibration structure to the tool. The optical reference portion can comprise a planar surface with a surface normal parallel to the axis of rotation. A second aspect of the present disclosure provides a method for calibration, the method comprising mounting a calibration structure as provided according to the first aspect to a tool, rotating the calibration structure in order to bring the optical reference portion within a first preselected portion of a field of view of an imaging apparatus mounted on the tool, whereby to calibrate an axis of rotation of the tool, mounting a probe on the calibration structure, the probe comprising a probe optical reference portion, and rotating the probe optical reference portion in order to bring the probe optical reference portion within a second preselected portion of the field of view of the imaging apparatus mounted on the tool, whereby to register the position of a tip of the probe relative to a preselected reference point of the tool. In an implementation of the second aspect, mounting the probe on the calibration structure can comprise bringing the tip of the probe into contact with a probe registration structure provided in line with the axis of rotation of the shaft of the calibration structure. The method can further comprise determining a first set of positions of the optical reference portion within a first set of preselected portions of a field of view of an imaging apparatus mounted on the tool. The method can further comprise determining a set of rotational positions of the shaft of the calibration structure corresponding to the first set of positions of the optical reference portion, and calculating the axis of rotation of the shaft using the set of rotational positions of the shaft of the calibration structure. The method can further comprise determining a second set of positions of the probe optical reference portion within a second set of preselected portions of a field of view of an imaging apparatus mounted on the tool. The method can further comprise determining a set of rotational positions of the probe corresponding to the second set of positions of the probe optical reference portion, and calculating the position of the tip of the probe using the set of rotational positions of the probe. The method can further comprise, for at least some of the second set of positions of the probe optical reference portion, adjusting a position of the probe optical reference portion in a direction parallel to the axis of rotation, whereby to modify a distance of the probe optical reference portion from the preselected reference point of the tool. These and other aspects of the invention will be apparent from the embodiment(s) described below. Brief Description of the Drawings In order that the present disclosure may be more readily understood, embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of a calibration structure for an on-tool imaging system according to an example; Figure 2 is a schematic representation of a calibration structure for an on-tool imaging system according to an example; Figure 3 depicts an exploded portion from a cross sectional view of the second end of the shaft of the calibration structure, according to an example; Figure 4 is a schematic representation of a probe, according to an example; Figure 5 is a schematic representation of a probe, according to an example; and Figure 6 is a schematic representation of a probe, according to an example. Detailed Description Example embodiments are described below in sufficient detail to enable those of ordinary skill in the art to embody and implement the systems and processes herein described. It is important to understand that embodiments can be provided in many alternate forms and should not be construed as limited to the examples set forth herein. Accordingly, while embodiments can be modified in various ways and take on various alternative forms, specific embodiments thereof are shown in the drawings and described in detail below as examples. There is no intent to limit to the particular forms disclosed. On the contrary, all modifications, equivalents, and alternatives falling within the scope of the appended claims should be included. Elements of the example embodiments are consistently denoted by the same reference numerals throughout the drawings and detailed description where appropriate. The terminology used herein to describe embodiments is not intended to limit the scope. The articles “a,” “an,” and “the” are singular in that they have a single referent, however the use of the singular form in the present document should not preclude the presence of more than one referent. In other words, elements referred to in the singular can number one or more, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and / or “including,” when used herein, specify the presence of stated features, items, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, items, steps, operations, elements, components, and / or groups thereof. The term “and / or” is only an association relationship for describing associated objects and represents that three relationships may exist such that A and / or B may indicate that A exists alone, A and B exist at the same time, or B exists alone. The character “ / ” generally represents that the associated objects are in an “or” relationship. Unless otherwise defined, all terms (including technical and scientific terms) used herein are to be interpreted as is customary in the art. It will be further understood that terms in common usage should also be interpreted as is customary in the relevant art and not in an idealized or overly formal sense unless expressly so defined herein. The following contains specific information related to implementations of the present disclosure. The drawings and their accompanying detailed disclosure are merely directed to implementations. However, the present disclosure is not limited to these implementations. Other variations and implementations of the present disclosure will be obvious to those skilled in the art. The phrases “in one implementation,” or “in some implementations,” may each refer to one or more of the same or different implementations. The term “coupled” is defined as connected whether directly or indirectly through intervening components and is not necessarily limited to physical connections. The expression “at least one of A, B and C” or “at least one of the following: A, B and C” means “only A, or only B, or only C, or any combination of A, B and C ” The terms “system” and “network” may be used interchangeably. For the purposes of explanation and non-limitation, specific details such as functional entities, techniques, protocols, and standards are set forth for providing an understanding of the present disclosure. In other examples, detailed disclosure of well-known methods, technologies, systems, and architectures are omitted so as not to obscure the present disclosure with unnecessary details. Persons skilled in the art will immediately recognize that any network function(s) or algorithm(s) disclosed may be implemented by hardware, software or a combination of software and hardware. Disclosed functions may correspond to modules which may be software, hardware, firmware, or any combination thereof. A software implementation may include machine- and / or computer- readable and / or executable instructions stored on a machine- and / or computer-readable medium such as memory or other types of storage devices. One or more microprocessors or general-purpose computers with communication processing capability may be programmed with corresponding executable instructions and perform the disclosed network function(s) or algori thm(s). The microprocessors or general-purpose computers may include Applications Specific Integrated Circuitry (ASIC), programmable logic arrays, and / or using one or more Digital Signal Processor (DSPs). Although some of the disclosed implementations are oriented to software installed and executing on computer hardware, alternative implementations implemented as firmware or as hardware or as a combination of hardware and software are well within the scope of the present disclosure. The computer readable medium includes but is not limited to Random Access Memory (RAM), Read Only Memory (ROM), Erasable Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), flash memory, Compact Disc Read Only Memory (CD-ROM), magnetic cassettes, magnetic tape, magnetic disk storage, or any other equivalent medium capable of storing computer-readable instructions. Figure 1 is a schematic representation of a calibration structure for an on-tool imaging system according to an example. In the example of figure 1, shown in perspective view, the calibration structure 100 comprises a shaft 101, and an arm 103 depending from the shaft. The shaft 101 is configured to releasably engage, at a first end 105 thereof, with a chuck device of a tool. The shaft 101 comprises an axis of rotation, A. The first end 105 of the shaft 10 comprises a shank portion 113 configured to releasably engage with a chuck of a tool, whereby to secure the calibration structure 100 to the tool. In an example, the arm 103 is provided perpendicular to the axis of rotation, A, of the shaft 101 at a second end 107 of the shaft 101. The arm 103 comprises an optical reference portion 109 provided in spaced relation on the arm relative to the axis of rotation, A. In the example of figure 1, the arm comprises an additional optical reference portion 111 provided in spaced relation on the arm relative to the axis of rotation, A. The optical reference portion 109 / 111 comprises a planar surface with a surface normal 115 parallel to the axis of rotation, A. Figure 2 is a schematic representation of a calibration structure for an on-tool imaging system according to an example. In the example of figure 2, shown in perspective view, the second end 107 of the shaft 101 comprises a probe registration structure 201 provided in line with the axis of rotation of the shaft. In an example, the probe registration structure 201 is configured to receive the tip of a probe, which will be described in more detail below. According to an example, the probe registration structure 201 comprises a female portion configured to receive the tip of a probe. For example, the probe registration structure 201 can comprise an opening in the second end 107 of the shaft 101. The opening can converge in a direction towards the first end 105 of the shaft to a point. The probe registration structure 201 comprises a profile and / or size selected to prevent lateral movement of the tip of a probe. Figure 3 depicts an exploded portion from a cross sectional view of the second end of the shaft of the calibration structure, according to an example. In the example of figure 3, the probe registration structure 201 comprises an opening 301 in the second end 107 of the shaft 101. The opening 201 converges in a direction towards the first end 105 of the shaft to a point 303. The point 303 is aligned with the centre of the axis of rotation, A of the shaft 101. As such, the tip of a probe introduced into the mouth of the opening 301 and directed towards the first end 105 of the shaft 101 will be forced to follow a path that leads it to the terminus of the opening 301, i.e., the point 303, at which the tip of the probe cannot move any farther towards the first end 105 of the shaft 101 and will thus come to rest. Although the opening 301 as depicted in figure 3 comprises a cross-sectional profile that curves to the point 303 from the mouth of the opening, it will be appreciated that any suitable profile that defines the convergence of the opening to the point 303 can be used. For example, opening 301 may be triangular in cross-section (i.e., conical). Figure 4 is a schematic representation of a probe, according to an example. In the example of figure 4, shown in perspective view, the probe 400 comprises a probe tip 403 and a probe optical reference portion 401 (and / or probe optical reference portion 402) provided in spaced relation from the probe tip 403. Both probe optical reference portions comprise a planar surface with a surface normal 405. Figure 5 is a schematic representation of a probe, according to an example. In the example of figure 5, in which the probe 400 is shown in side view, it can be seen that the probe tip 403 comprises a hook-shaped portion that extends parallel to the surface normal 403. In an example, the probe tip 403 terminates at a plane 407 that is parallel to and aligned with the planar surface of the probe optical reference portions. The probe tip 403 points in a direction, B, that is generally perpendicular to the plane 407 (i.e., parallel to the surface normal 405). Figure 6 is a schematic representation of a probe, according to an example. In the example of figure 6, in which the probe 400 is shown from the front, it can be seen that the probe tip 403 is directly in line with the centre of the probe optical reference portions. According to an example, the calibration structure as described above can be used to calibrate a tool, which tool may be used for a surgical procedure. For example, the calibration structure 100 can be mounted to a tool. That is, shank portion 113 can be fixed into or otherwise engaged with a chuck of the tool, whereby to secure the calibration structure 100 to the tool. The calibration structure can be rotated in order to bring the optical reference portion 109 within a first preselected portion of a field of view of an imaging apparatus mounted on the tool, whereby to calibrate an axis of rotation of the tool. The probe 400 can be mounted on the calibration structure 100. Mounting the probe 400 on the calibration structure 100 can comprise bringing the tip 403 of the probe 400 into contact with the probe registration structure 201; 301. For example, the tip 403 can be provided in the opening 301 so that it engages or otherwise rests in or at point 303. The probe optical reference portion 401 can be rotated in order to bring the probe optical reference portion 401 within a second preselected portion of the field of view of the imaging apparatus mounted on the tool, whereby to register the position of the tip 403 of the probe 400 relative to a preselected reference point of the tool. The present disclosure relates to the physical structure of the calibration structure and / or the probe. Accordingly, precisely how calibration may be performed will not be described further in detail save to highlight that for tool (e.g., drill) calibration, four preselected portions of the field of view of the imaging apparatus mounted on the tool can be provided, also referred to as calibration sections. A user of the tool can mount the calibration structure to the tool and move the calibration structure so that an optical reference portion moves though each calibration section. For example, in the case of a drill, with the calibration structure mounted in the chuck of the drill and the imaging apparatus mounted to the drill such that its field of view is directed towards the front of the drill (i.e., towards the direction of the calibration structure mounted in the chuck of the drill) the user can move the calibration structure (e.g., by rotating it around the axis, A). In doing so, an optical reference portion will pass through the calibration sections, which define regions within the field of view of the imaging apparatus within which data representing the position of an optical reference portion can be collected. For example, as an optical reference portion passes through a calibration section as the user rotates the arm of the calibration structure, multiple optical points can be generated per calibration section, each optical point representing the position of the optical reference portion within a calibration section. If the distance between optical points for a calibration section falls within a preselected threshold, the calibration section question can be considered calibrated. When all calibration sections are calibrated, the tool can be considered calibrated. Probe calibration can proceed in a similar manner. Multiple probe calibration sections (e.g., five) can be used. With the probe tip 403 at the point 303 of the opening 301, the user can hold the probe in each probe calibration section for multiple (e.g., three) optical measurements to be taken. If the measurements are, e.g., close to each other, and close to the drill line (both according to some preselected threshold values), then the probe tip is calculated for each section and if the five probe tips are close to the nominal a calibrated probe tip is calculated. According to an example, a calibrated probe and surgical tool can be used in concert with one another. For example, the tip of the probe can be positioned on one side of a part of a patient on which a procedure is to be carried out. The tip of the probe can be used as part of a computerised system to guide a surgeon during the procedure. That is, the tip of the probe can represent the point at which, e.g., a drill is pointing during a procedure, since both the drill and the probe are calibrated with respect to one another using the calibration structure described above. Accordingly, during a procedure, a user of a calibrated surgical tool can have confidence that the position of the tool and / or an accessory (such as a drill bit) is accurate. The preceding description has been provided to enable others skilled in the art to best utilize various aspects of the exemplary embodiments disclosed herein. This exemplary description is not intended to be exhaustive or to be limited to any precise form disclosed. Many modifications and variations are possible without departing from the spirit and scope of the instant disclosure. The embodiments disclosed herein should be considered in all respects illustrative and not restrictive. Reference should be made to the appended claims and their equivalents in determining the scope of the instant disclosure.

Claims

1. A calibration structure for a surgical tool, the calibration structure comprising:a shaft configured for releasable engagement at a first end of the shaft with a chuck device of the surgical tool, wherein the shaft comprises an axis of rotation; andan arm, depending from the shaft, the arm provided perpendicular to the axis of rotation at a second end of the shaft, wherein the arm comprises an optical reference portion provided in spaced relation on the arm relative to the axis of rotation.

2. The calibration structure as claimed in claim 1, wherein the arm comprises one or more additional optical reference portions provided in spaced relation on the arm relative to the axis of rotation.

3. The calibration structure as claimed in claim 1 or 2, wherein the second end of the shaft comprises a probe registration structure provided in line with the axis of rotation of the shaft, wherein the probe registration structure is configured to receive the tip of a probe.

4. The calibration structure as claimed in claim 3, wherein the probe registration structure comprises a female portion configured to receive the tip of the probe.

5. The calibration structure as claimed in claim 3 or 4, wherein the probe registration structure comprises an opening in the second end of the shaft, wherein the opening converges in a direction towards the first end of the shaft to a point.

6. The calibration structure as claimed in claim 5, wherein the point of the probe registration structure comprises a profile and / or size selected to prevent lateral movement of the tip of a probe.

7. The calibration structure as claimed in any preceding claim, wherein the first end of the shaft comprises a shank portion configured to releasably engage with a chuck of a tool, whereby to secure the calibration structure to the tool.

8. The calibration structure as claimed in any preceding claim, wherein the optical reference portion comprises a planar surface with a surface normal parallel to the axis of rotation.

9. A method for calibration, the method comprising:mounting a calibration structure as claimed in any preceding claim to a tool;rotating the calibration structure in order to bring the optical reference portion within a first preselected portion of a field of view of an imaging apparatus mounted on the tool, whereby to calibrate an axis of rotation of the tool;mounting a probe on the calibration structure, the probe comprising a probe optical reference portion; androtating the probe optical reference portion in order to bring the probe optical reference portion within a second preselected portion of the field of view of the imaging apparatus mounted on the tool, whereby to register the position of a tip of the probe relative to a preselected reference point of the tool.

10. The method as claimed in claim 9, wherein mounting the probe on the calibration structure comprises bringing the tip of the probe into contact with a probe registration structure provided in line with the axis of rotation of the shaft of the calibration structure.

11. The method as claimed in claim 9 or 10, further comprising:determining a first set of positions of the optical reference portion within a first set of preselected portions of a field of view of an imaging apparatus mounted on the tool.

12. The method as claimed in claim 11, further comprising:determining a set of rotational positions of the shaft of the calibration structure corresponding to the first set of positions of the optical reference portion; andcalculating the axis of rotation of the shaft using the set of rotational positions of the shaft of the calibration structure.

13. The method as claimed in any of claims 9 to 12, further comprising:determining a second set of positions of the probe optical reference portion within a second set of preselected portions of a field of view of an imaging apparatus mounted on the tool.

14. The method as claimed in claim 13, further comprising:determining a set of rotational positions of the probe corresponding to the second set of positions of the probe optical reference portion; andcalculating the position of the tip of the probe using the set of rotational positions of the probe.

15. The method as claimed in claim 13 or 14, further comprising, for at least some of the second set of positions of the probe optical reference portion, adjusting a position of the probe optical reference portion in a direction parallel to the axis of rotation, whereby to modify a distance of the probe optical reference portion from the preselected reference point of the tool.14

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