Field generator assembly and method for surgical navigation

Abstract

A field generator assembly for surgical navigation is provided. The field generator assembly includes: a field generator configured to generate an electromagnetic field; an attachment member configured to attach the field generator to the body of the patient; at least one first arm including a first portion configured to contact a surface of the body when the field generator is attached to the body of the patient and a second portion movably attached relative to the field generator; and at least one sensor configured to measure a spatial relationship between the at least one arm and the field generator. A method of obtaining a relative pose between a surface of a body and a field generator is also provided.

Description

[0001] This application is a divisional application of the Chinese invention patent application with application number 202110477752.7 (application date: April 29, 2021; invention name: field generator assembly and method for surgical navigation). Technical Field

[0002] The present disclosure generally relates to surgical navigation. A field generator assembly for surgical navigation is provided. A method for obtaining a relative posture between a surface of a patient's body and a field generator of the field generator assembly is also provided. A computer program and a carrier containing the computer program are also provided. Background Art

[0003] In surgical navigation, it is often necessary to display the pose (i.e., at least one of the position and orientation) of a surgical instrument or other medical component (e.g., a bone plate of an implant) relative to patient image data. The patient image data may be computed tomography (CT) image data, magnetic resonance (MR) image data, or the like.

[0004] Surgical navigation relies on a tracking system comprising a tracking unit for positioning a movable tracker relative to the tracking unit. The tracker can be attached to different components in the operating room to be tracked by the tracking unit. Different types of trackers are known in the prior art, such as active or passive optical markers or electromagnetic sensors. In the case of optical markers, the tracking unit is a (e.g., stereo) camera of an optical tracking system. In the case of an electromagnetic sensor, the tracking unit can be a localizer of an electromagnetic tracking system, which is communicatively coupled to the electromagnetic sensor.

[0005] One or more trackers can, for example, be attached to a surgical instrument, and the tracking system can provide the pose of the attached electromagnetic sensor relative to a camera, or in the case of an electromagnetic tracking system, relative to an electromagnetic field generator. Based on the pose provided by the tracking system, the pose of the surgical instrument relative to the camera or relative to the field generator can be determined. In order to obtain the pose of the surgical instrument relative to the patient image data, it is necessary to know or determine the alignment between the camera or field generator and the patient image data. In particular, the alignment can be used to convert the pose of the surgical instrument relative to the camera or field generator into the pose of the surgical instrument relative to the patient image data.

[0006] In order to obtain the registration between the field generator and the patient image data, the posture of the patient's body relative to the field generator can be determined. Subsequently, the determined posture of the body can be matched with the patient image data to obtain the registration.

[0007] There are several possibilities how to determine the pose of the patient's body relative to the field generators. Some methods rely on manually defining different registration points on the surface of the patient's body with a pointer tracked by a (e.g., electromagnetic) tracking system. Other methods rely on manually attaching a tracker to different registration points on the surface of the patient's body. The tracked positions of the registration points relative to the field generators can then be matched to a model surface of the patient's body defined by the patient image data to obtain a registration.

[0008] Depending on the number and placement of the registration points, these and other methods may result in registrations with varying degrees of accuracy. For example, the registration points may be located at different parts of the body, depending on the surgeon's preferences and patience, resulting in registrations with varying and often lower accuracy. Furthermore, it may not be possible to track the registration points on parts of the body that are outside the electromagnetic field detection range of the electromagnetic sensor, reducing the flexibility of the registration point placement and the accuracy of the registration obtained.

[0009] Corresponding prior art is known from US 5,829,444 A1 and US 8,473,026 B2 as well as US 2014 / 0135746 A1. Summary of the invention

[0010] What is needed is a technique that addresses one or more of the foregoing or other problems in the context of electromagnetic surgical navigation that relies on a field generator configured to generate an electromagnetic field.

[0011] According to a first aspect, a field generator assembly for surgical navigation is provided. The field generator assembly includes a field generator configured to generate an electromagnetic field and an attachment member configured to attach the field generator to a patient's body. The field generator assembly also includes at least one first arm. The at least one first arm includes a first portion configured to contact a surface of the body when the field generator is attached to the patient's body and a second portion movably attached relative to the field generator. The field generator assembly also includes at least one sensor configured to measure a spatial relationship between at least one arm and the field generator.

[0012] The spatial relationship between at least one arm and the field generator may include or consist of a posture (i.e., at least one of a position and an orientation) of at least one arm (e.g., a portion or part thereof) relative to the field generator. Measurements by at least one sensor may represent or be used to determine a posture of the first portion relative to the field generator. The first portion in contact with the surface of the body may be used as a registration point or area for matching the posture of the surface of the patient's body with patient image data. The posture of the first portion relative to the field generator may be defined by physical characteristics of the at least one arm (e.g., size, material, etc.). Alternatively or in addition, the posture of the first portion relative to the field generator may be defined by at least one of a shape and a posture of the surface of the patient's body.

[0013] At least one arm may be formed as an elongated member. The first portion may be a first end of at least one first arm. The first end may be formed as a tip of at least one first arm. When the field generator is attached to the body, at least one arm or the first portion may be arranged on a first side of the body. When the field generator is attached to the body, the field generator may be arranged on a second side of the body. The first side may be opposite to the second side. The first side may be a front side. The second side may be a rear side. The field generator assembly may be configured such that when the field generator is attached to the body, the patient's body is at least partially located between the field generator and the at least one arm, or at least partially located between the field generator and the first portion.

[0014] The second part may be a second end of at least one first arm. The second part may be formed as a connecting element of at least one first arm. This may enable a large distance between the first part and the second part, for example greater than 5 cm or greater than 10 cm, thereby ensuring a large distance between the first end and the field generator, for example greater than 10 cm or greater than 15 cm.

[0015] The attachment member may include or consist of an adjustable strap such as a headband (also known as a head strap) or a chest strap. The attachment member may include or consist of at least one first arm (eg, two or more arms).

[0016] The first portion may be configured to be tensioned (e.g., spring biased) on the surface of the patient's body when the field generator is attached to the body. The first portion may be configured to be advanced (e.g., pressed or pushed) in the direction of the field generator at least when the field generator is attached to the body. When the field generator is attached to the body, e.g., on the second side of the body, the first portion may be configured to be tensioned on the surface of the body on a first side of the body, e.g., on the front surface. The field generator assembly, e.g., the first arm, may include one or more elastic members that tension the first portion on the surface of the body. The first arm may be made of an elastic material and configured to tension the first portion on the surface of the body. The contact force between the first portion and the surface of the body may be equal to or less than a first predetermined force, wherein the first predetermined force may be selected to avoid injury to the patient. The contact force between the first portion and the surface of the body may be equal to or higher than a second predetermined force, wherein the second predetermined force may be selected to ensure stable (e.g., fixed for a certain period of time) contact between the first portion and the surface of the body.

[0017] The first portion may be configured to contact the surface of a predetermined landmark on the surface of the patient's body when the field generator is attached to the body. The predetermined landmark may be a point, region, or shape of a part of the body that can be extracted or identified, for example, automatically in the patient image data. The surface of the predetermined landmark may be a point or region of the body's surface that is determined to be advantageous or optimal for matching the posture of the patient's body with the patient image data. The predetermined landmark may be an anatomical body part or organ, such as a nose, an ear, an eye, etc.

[0018] At least one first arm may include the first part multiple times, for example twice or three times. In other words, at least one first arm may include multiple first parts. Each of the multiple first parts is configured to contact the surface of the patient's body when the field generator is attached to the body. For example, at least one first arm includes a hand with three fingers, each finger including one of the three first parts included in at least one arm. At least one first arm may additionally or alternatively include multiple protrusions on the hand, each protrusion including one of the multiple first parts. In the following, when referred to as a "first part", this should include the meaning of "each, all or at least one of the multiple first parts".

[0019] The field generator assembly may further comprise a second arm connected to the first arm so as to be movable together with the first arm. Thus, the two arms together with the field generator may form a kind of loop.

[0020] The field generator assembly may also include a third arm, wherein at least one first arm and the third arm are located on opposite sides relative to the field generator. The field generator assembly may include a plurality of third arms corresponding to the plurality of first arms. The third arm may be connected to the first arm so as to be movable with the first arm. The field generator assembly may include at least one sensor configured to measure the posture of the third arm relative to at least one of the at least one arm and the field generator. The third arm may include a first portion configured to contact the surface of the body when the field generator is attached to the patient's body and a second portion movably attached relative to the field generator. The third arm may include the first portion multiple times, as described above with respect to the first arm.

[0021] The attachment member can be configured to attach the field generator to the back side of the patient's head. The field generator can be configured to generate an electromagnetic field that surrounds at least the sensor of the field generator assembly when the field generator is attached to the patient's body. The electromagnetic field can also surround at least the patient's head.

[0022] At least one of the at least one first arm, the second arm, and the third arm may be attached to the field generator or its housing (i.e., container) via a joint so as to be movable relative to the field generator. At least one of the at least one first arm, the second arm, and the third arm may be configured to rotate (e.g., only) about an axis extending substantially in a lateral medial direction or substantially in an up-down direction.

[0023] In certain variations, the field generator assembly may be formed as a substantially symmetrical component.The field generator assembly may be formed as a mirror-symmetrical component relative to a sagittal plane (eg, of a patient's body).

[0024] As a first variant, at least one sensor may be fixedly attached relative to (or directly attached to) a third portion of at least one first arm. The third portion may be fixedly connected relative to the first portion or equivalent to the first portion. The at least one sensor may be an electromagnetic sensor configured to measure an electromagnetic field generated by a field generator. The at least one sensor may be configured to measure the posture of the at least one sensor relative to the field generator. The at least one sensor may be configured to measure the posture of the at least one arm relative to the at least one sensor. The third portion may be configured to position the at least one sensor in a first predetermined spatial relationship relative to the first portion when the first portion is in contact with the surface of the body. The first predetermined spatial relationship may include or consist of the relative posture between the at least one sensor and the first portion. The at least one sensor may be directly attached to or embedded in the at least one arm.

[0025] As a second variation, at least one sensor may be fixedly attached in a second predetermined relationship relative to the field generator. The at least one sensor may be an optical or mechanical sensor. The at least one sensor may be configured to measure a posture of the at least one first arm relative to the at least one sensor. The at least one sensor may alternatively or additionally be configured to measure a posture of the field generator relative to the at least one sensor. The at least one sensor may be configured to measure a posture (e.g., orientation or rotational position) of a second portion of the at least one arm relative to the field generator. The at least one sensor may be directly attached to or embedded in the housing.

[0026] As a third variation, at least one sensor may be movably attached relative to the field generator and the at least one arm. The at least one sensor may be an optical sensor, such as a camera. The at least one sensor may be configured to measure a posture of the at least one first arm relative to the at least one sensor. The at least one sensor may alternatively or additionally be configured to measure a posture of the field generator relative to the at least one sensor.

[0027] Note that in the first to third modifications, the term "at least one arm" may replace one or both of the "second arm" and "third arm" described above. In other words, one or both of the second arm and the third arm may be configured similarly to or included in at least one first arm.

[0028] According to a second aspect, a method for obtaining a relative posture between a surface of a patient's body and a field generator is provided. The field generator is configured to generate an electromagnetic field and is included in a field generator assembly, such as the field generator assembly of the first aspect. The method includes obtaining measurement data. The measurement data describes a measurement result of a spatial relationship between at least one first arm of the field generator assembly and the field generator, and the at least one first arm is movably attached relative to the field generator. The measurement is obtained by at least one sensor of the field generator assembly when the field generator is attached to the patient's body and a first portion of the at least one first arm is in contact with the surface of the patient's body. The method also includes determining the relative posture between the surface of the patient's body and the field generator based on the spatial relationship and at least one predetermined geometric characteristic of the at least one first arm.

[0029] The spatial relationship between at least one first arm and the field generator may include or consist of a relative posture between at least one first arm and the field generator. The spatial relationship between at least one first arm and the field generator may include or consist of a relative posture between the field generator and a reference portion, the reference portion being selected from at least one sensor fixedly attached relative to at least one arm, a second portion of at least one first arm, and an optical marker fixedly attached relative to at least one first arm. The relative posture between the surface of the body and the field generator may include or consist of a posture of at least one point or area on the surface of the patient's body relative to the field generator. One or more first portions may be in contact with at least one point or area on the surface of the body.

[0030] At least one predetermined geometric property may include or consist of a relative posture between at least one sensor and the first part (e.g., when the first part is in contact with a surface of the patient's body). At least one predetermined geometric property may include or consist of a relative posture between the first part and the second part (e.g., when the first part is in contact with a surface of the patient's body). At least one predetermined geometric property may include or consist of a relative posture between the first part and at least one arm (e.g., when the first part is in contact with a surface of the patient's body). At least one predetermined geometric property may include a physical property of at least one arm, such as material, elasticity, deformability of at least one arm, a predetermined deformation when the first part is in contact with a surface, etc.

[0031] The method may also include obtaining patient image data describing (e.g., including) an image of the patient's body. The method may also include matching the patient image data (e.g., a model surface described by or extracted from the patient image data) with the determined relative pose between the surface of the patient's body and the field generator. As a result of the matching, a registration between the patient image data and the field generator may be determined or obtained.

[0032] Note that in the description of the method of the second aspect, the term "at least one first arm" may be replaced by the "second arm" or "third arm" described above with reference to the first aspect. In the description of the first and second aspects, in one example, the attachment of component X relative to component Y means that component X is attached to component Y (e.g., directly).

[0033] According to a third aspect, a computer program is provided. The computer program comprises instructions which, when executed on at least one processor, cause the at least one processor to perform the method according to the second aspect.

[0034] According to a fourth aspect, a carrier is provided. The carrier comprises the computer program of the third aspect and is one of an electric signal, an optical signal, a radio signal or a computer-readable storage medium. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Further details, advantages and aspects of the present disclosure will become apparent from the following embodiments considered in conjunction with the accompanying drawings, in which:

[0036] Figure 1 shows an exemplary embodiment of a field generator assembly according to the present disclosure attached to a patient's head;

[0037] Figure 2 An exemplary embodiment of a field generator assembly according to the present disclosure is shown;

[0038] Figure 3 shows an exemplary embodiment of an arm included in an exemplary embodiment of a field generator assembly according to the present disclosure;

[0039] Figure 4 An exemplary embodiment of the method according to the present invention is shown; and

[0040] Figure 5 An exemplary embodiment of an apparatus according to the present disclosure is shown. DETAILED DESCRIPTION

[0041] In the following description, exemplary embodiments of a surgical navigation system and a surgical navigation method will be explained with reference to the accompanying drawings. The same reference numerals will be used to represent the same or similar structural features.

[0042] Figure 1 An exemplary embodiment of a field generator assembly 100 is shown attached to a patient's body 200, in particular the patient's head. The field generator assembly 100 is configured for surgical navigation. The field generator assembly 100 includes a field generator 2 configured to generate an electromagnetic field (not shown) for electromagnetic navigation. Such an electromagnetic field may be advantageous for cranial surgery (e.g., placing a shunt with a stylus having an electromagnetic sensor). The field generator 2 may be at least one of attached to and surrounded by a housing 4 of the field generator assembly. Alternatively, the field generator 2 may form the housing 4.

[0043] The field generator assembly 100 in the illustrated example includes a plurality of first arms 6, 8, and 10. Each of the arms 6, 8, and 10 includes a first portion 12, 14, and 16 that contacts a surface of a patient's body 200. This may mean that when the field generator 2 is attached to the patient's body 200 by the attachment member, the first portions 12, 14, and 16 are in contact with the surface (e.g., at least one of constant and stable), for example, for at least an extended period of time. The first portions 12, 14, and 16 of the respective arms 6, 8, and 10 being in contact with the surface may mean that the first portions 12, 14, and 16 are in a fixed posture relative to the surface for at least an extended period of time.

[0044] The first portions 12, 14 and 16 may generally be first ends, such as protrusions or tips of respective arms 6, 8 and 10. The first portions 12, 14 and 16 may be tensioned or biased against the surface of the patient's body 200. Each arm 6, 8 or 10 may include an elastic member that tensions or biases the first portions 12, 14 and 16 against the surface of the patient's body 200. For example, the arms 6, 8 or 10 may be at least partially constructed of a flexible material such as rubber or plastic. For example, the elastic member includes a spring that tensions or biases each arm against the surface. Alternatively or in addition, the field generator 2 or the housing 4 may include an elastic member. This approach may allow the first portion to be stably placed relative to the surface of the patient's body, thereby enabling accurate and reliable determination of the relative posture between the surface of the patient's body 200 and the field generator 2.

[0045] The first portions 12, 14 and 16 may be in contact with the surface of a predetermined landmark of the patient's body 200. The predetermined landmark is preferably a feature of the patient. The predetermined landmark may be automatically extractable from the patient image data using image analysis. In the example shown, the first portion 12 of the arm 6 is in contact with the surface of (the bridge of) the nose as a predetermined landmark, the first portion 14 of the arm 8 is in contact with the surface of (the inside of) the ear hole as a predetermined landmark, and the first portion 16 of the arm 10 is in contact with the surface of the corner of the eye as a predetermined landmark.

[0046] Note that the field generator assembly 100 can be formed as a symmetrical component and at least one first arm can be connected to Figure 1 The arms 6, 8 and 10 are shown to be arranged laterally opposite (e.g., mirror-symmetrically about the sagittal plane). In this case, at least one laterally opposite first arm may include a first portion that is aligned with a predetermined landmark (the ear hole of the right ear) and is aligned with the first portion of the ear. Figure 1 The surface of the ear hole (the inner side) shown is in contact with the ear hole laterally opposite to the ear hole, or the predetermined landmark (right eye) Figure 1 The surfaces of the laterally opposite corners of the eyes are shown in contact. Such landmarks can make it possible to determine the relative pose between the surface of the body 200 and the field generator 2 with high accuracy, even in different patient cases.

[0047] The arms 6, 8 and 10 each further comprise a second portion 18, 20 and 22 movably attached relative to the field generator 2. The second portions 18, 20 and 22 may be second ends, attachment elements or coupling elements of the respective arms 6, 8 and 10. In the example shown, the second portion 18 of the arm 6 is attached to a substantially tubular component 24 having a longitudinal axis extending substantially in the lateral-medial direction. The component 24 may be stably (e.g., immovably or fixedly) attached relative to the field generator 2 and arranged on the upper side relative to the field generator 2. The component 24 may be stably attached to the housing 4 or may be a part of the housing 4. The arm 6 may be configured to be rotatable only about an axis extending substantially in the lateral-medial direction. Likewise, in the example shown, the second portion 20 of the arm 8 is movably connected relative to the field generator in a slot 26 of the housing 4. The arm 8 may be configured to be rotatable only about an axis extending substantially in the up-down direction. Further, in the example shown, the second portion 22 of the arm 10 is movably connected in the hole 28 of the housing 4 relative to the field generator. The arm 8 can be configured to rotate about both an axis extending substantially in the up-down direction and an axis extending substantially in the lateral-medial direction. The up-down direction and an axis extending substantially in the lateral medial direction. In another variation, each of the arms 6, 8 and 10 can rotate in all directions relative to the field generator 2. This configuration can achieve a compact configuration of the field generator assembly 100, easy placement of the field generator assembly 100 on the patient's body 200, and stable contact between the first portions 12, 14, 16 and the surface of the body 200.

[0048] The field generator 2 in the example shown is attached to (e.g., relative to) the back side of the head of the patient's body 200 by an attachment member. The attachment member includes a headband 30. The headband 30 is preferably adjustable in size or flexible to fit the heads of different patients. The headband 30 is attached to the belt connection portion 29 of the housing 4. In one variation, the attachment member includes or is composed of one or more arms (e.g., arms 6, 8, and 10) included in the field generator assembly 100. That is, one or more arms, such as all arms, included in the field generator assembly 100 can attach the field generator 2 to the patient's body 200. It can be said that when the field generator 2 is attached to the body 200, the body 200 is positioned, clamped, or stuck between the housing 4 and the arms included in the field generator assembly 100. This can achieve a secure attachment of the field generator relative to the patient's body 200 and optionally avoid the need for additional attachment devices such as headband 30.

[0049] The field generator assembly 100 also includes at least one sensor 40, 41, 44, 46 configured to measure a spatial relationship between at least one first arm (e.g., one or more of arms 6, 8, and 10) and the field generator. The spatial relationship may include or consist of a posture (i.e., at least one of a position and an orientation) of at least one first arm (e.g., a portion thereof) relative to the field generator 2.

[0050] Thus, at least one sensor 40, 41, 44, 46 provides a measurement based on which the relative attitude of a point or area of ​​the surface of the patient's body 200 (e.g., a predetermined landmark thereof) with respect to the field generator 2 can be determined. Thus, the field generator assembly 100 can enable a rapid determination of the attitude of the surface of the patient's body 200 with respect to the field generator 2 with high accuracy.

[0051] As a first variation of at least one sensor, the sensor 40 is fixedly (i.e., immovably or stably) attached relative to the third portion 42 of the arm 6 and is configured to measure the attitude of the sensor 40 relative to the field generator 2. The sensor 40 is, for example, an electromagnetic sensor configured to detect the electromagnetic field generated by the field generator 2 to measure its attitude relative to the field generator 2. In this case, the sensor 40 includes one or more coils configured to measure the electromagnetic field. Each coil may be electrically connected to a locator of an electromagnetic tracking or navigation system (also not shown) via dedicated wiring (not shown).

[0052] The sensor 40 may be embedded in the arm 6. In this variation, the third portion 42 may be configured to position the sensor 40 in a first predetermined spatial relationship with the first portion 12 when the first portion 12 is in contact with the surface of the body 200. In other words, the arm 6 may be configured such that the sensor 40 is in a first predetermined spatial relationship with the first portion 12 when the first portion 12 is in contact with the surface of the body 200. The first predetermined spatial relationship may include or consist of a first predetermined posture of the sensor 40 relative to the first portion 12.

[0053] In a first variant example, the third portion 42 may be fixedly connected relative to the first portion 12. The fixed connection may then define a first predetermined spatial relationship.

[0054] In another example of the first variation, the third portion 42 can be movably connected relative to the first portion 12. For example, the arm 6 can include an elastic or flexible material, or can include one or more joints. The arm 6 can be configured so that when the first portion 12 contacts the surface, the arm deforms in a predetermined manner (e.g., reversibly) and by a predetermined amount, for example, by moving one or more joints or by bending the elastic or flexible material. That is, the predetermined deformation of the arm 6 that describes the deformation of the arm 6 when the first portion 12 contacts the surface can define (e.g., together with a predetermined geometric property of the arm 6) a first predetermined spatial relationship of the sensor 40 relative to the first portion 12.

[0055] As a second variant of at least one sensor, the sensor 41 is fixedly attached relative to the first portion 16 of the arm 10 and is configured to measure the attitude of the sensor 41 relative to the field generator 2. The sensor 41 is, for example, an electromagnetic sensor configured to detect the electromagnetic field generated by the field generator 2 to measure its attitude relative to the field generator 2. The sensor 41 can be directly attached to the first portion 16 of the arm 10. In these cases, the attitude of the sensor 41 relative to the field generator 2 can correspond to the attitude of the first portion 16 relative to the field generator 2. As in the case of the sensor 40, the sensor 41 can be, for example, an electromagnetic sensor embedded in the arm 10.

[0056] One or more of the at least one arm 6, 8, 10 may include more than one sensor 40, 41, each sensor being stably attached relative to a specific portion of the at least one arm 6, 8, 10, which specific portion is optionally configured to contact the surface of the patient's body 200 when the field generator 2 is attached to the patient's body 200. The specific portions may be movably connected relative to each other. That is, the posture of the at least one arm 6, 8, 10 may be described by more than one sensor measurement, and / or the at least one arm 6, 8, 10 may define more than one point or area on the surface of the patient's body 200, which may then be used to determine the posture of the surface relative to the field generator 2.

[0057] In one example, the headband 30 includes an electromagnetic sensor (not shown) configured to detect the electromagnetic field generated by the field generator 2. The headband 30 may then include a first portion, such as a protrusion, a contact pad, or a section of the headband 30 configured to contact the surface of the patient's body 200 when the field generator 2 is attached to the body 200. The sensor included in the headband 30 may be arranged similar to the sensor 40 (e.g., arranged at the first portion) or the sensor 41 (e.g., arranged in a fixed spatial relationship relative to the first portion) described herein to determine the relative posture between the first portion included in the headband 30 and the field generator 2.

[0058] As a third variation of at least one sensor, the sensor 44 is fixedly attached in a second predetermined relationship relative to the field generator 2. The second predetermined spatial relationship may include or consist of a second predetermined posture of the sensor 44 relative to the field generator 2. For example, the sensor 44 is fixedly attached to the housing 4. The sensor 44 may be embedded in the housing 4. The sensor 44 may be configured to measure the posture of the arm 44 (e.g., the second portion 20 thereof) relative to the field generator 2. The sensor 44 may be an optical or mechanical sensor configured to measure the (e.g., rotational) position of the second portion 20 relative to the field generator 2. The sensor 44 may be configured to measure the posture of the arm 8 relative to the housing 4, wherein the housing 4 is in a known spatial relationship with the field generator 2.

[0059] As a fourth variation of at least one sensor, the sensor 46 is movably attached relative to the field generator 2 and at least one arm 6, 8, 10. The sensor 46 can be attached to the housing 4 via a coupling element 48. The sensor 46 can be an optical sensor such as a camera. The sensor 46 can be configured to measure the posture of one or more of the arms 6, 8 and 10 relative to the sensor 46. The sensor 46 can also be configured to measure the posture of the field generator 2 relative to the sensor 46. Alternatively or in addition, the sensor 46 can be configured to measure the posture of the housing 4 relative to the sensor 46, and determine the posture of the field generator 2 relative to the sensor 46 based on the known relative posture between the housing 4 and the field generator 2. One or more of the arms 6, 8 and 10, the housing 4 or the field generator 2 can be fixedly attached to a corresponding passive or active optical tracker that can be detected by the sensor 46. Alternatively or in addition, the sensor 46 can extract the posture of the arm from the acquired image based on image analysis and / or feature recognition.

[0060] The field generator assembly 100 further comprises a cable 35 and a plug 37 connected to the cable 35. The cable 35 connects the field generator 2 to an external power source. Additionally or alternatively, the cable 35 transmits the measurement signals of at least one sensor 40, 41, 44, 46 to a processor of a tracking system or device as described herein.

[0061] Figure 2 An exemplary embodiment of a field generator assembly 100 according to the present disclosure is shown, which is not attached to the patient's body. In this example of the field generator assembly 100, the first arm 6 is directly attached to the housing 4. In this example, the housing 4 includes a front side to be oriented toward the patient's body 200, a rear side opposite the front side, and two opposite lateral sides, wherein all arms included in the field generator assembly 100 are coupled to the housing 4 on their lateral sides. Other attachment positions of the arms are also possible.

[0062] The field generator assembly 100 includes a second arm 32 connected to the first arm 6 so as to be movable together with the first arm 6. Figure 2 As shown, the second arm 32 can be movably attached relative to the field generator 2. The second arm 6 and the second arm 32 can each include a first portion configured to contact the surface of the patient when the field generator 2 is attached to the patient, and the respective first portions can be directly connected to each other via a connecting portion that attaches the second arm 32 to the first arm 6. The first arm 6 can be connected to the second arm 32 via the first portion 12. The connected first arm 6 and second arm 32 can form a substantially arcuate portion. The second arm 32 can increase rigidity and ensure stable placement of the first portion 12 of the first arm 6 on the surface of the body 200.

[0063] Figure 2 Two third arms 34 and 36 are shown. The third arms 34 and 36 and the second arm 32 are located on a first (e.g., lateral) side relative to the field generator 2, while the first arms 6, 8 and 10 are located on a second (e.g., lateral) side relative to the field generator 2. The first side is opposite to the second side relative to the field generator 2. Figure 1 and Figure 2 It can be seen that the field generator assembly 100 can be formed as a substantially symmetrical component. In particular, the field generator assembly 100 can be formed as a mirror-symmetrical component with respect to the sagittal plane. Such a configuration may be advantageous because the human body is also substantially mirror-symmetrical. In particular, as described above, landmarks of the same type (e.g., ear holes or canthi) can be mirror-symmetrical with respect to the sagittal plane. Moreover, such a configuration may increase the symmetry of the electromagnetic field generated by the field generator 2.

[0064] One or more of the arms 6, 8, 10, 32, 34, 36 may be removably attached to the housing 4. One or more of the arms 6, 8, and 10 may be formed as a sterilizable component or a disposable, disposable component. Note that the second arm 32 and one or more of the third arms 34, 36 may be configured similarly to the first arms 6, 8, 10, and in particular, may include a first portion configured to contact a surface of the patient's body 200 and a second portion to which the corresponding second arm or third arm is movably attached relative to the field generator 2. One or more of the second arm 32 and the third arm 34, 36 may correspond to at least one first arm described herein.

[0065] Figure 3An exemplary embodiment of an arm 6 of a field generator assembly 100 is shown. In this case, the arm 6 is not connected to another arm. The arm 6 shown includes the first portion 12 multiple times, in particular exactly three times. The arm 6 includes a hand 50 with three fingers, each finger having a fingertip configured to contact a surface of a body 200 when the field generator 2 is attached to the body 200. That is, each of the three fingers of the hand 50 includes a first portion 12 (e.g., an example thereof).

[0066] The hand 50 can be movably connected to an element 52 of the arm 6 that includes the second portion 18. In the example shown, the hand 50 is connected to a ball 54 via a connecting member 56. The ball 50 forms part of a ball joint 58 that movably connects the hand 50 to the element 52 of the arm 6. The ball 50 is rotatably held in position by a socket 60 of the ball joint 58. The socket 58 is formed at the end of the element 52 opposite to the end at which the second portion 22 is located. Other ways of movably connecting the hand 50 to the element 52 are also possible. The sensor 40 ( Figure 3 The sensor 40 may be rigidly attached relative to the hand 50 (not shown). For example, the sensor 40 is embedded in or rigidly attached to the connecting member 56. In this case, the third portion 42 described herein may be formed by at least a portion of the connecting member 56 and a finger of the hand 50. Based on a first predetermined spatial relationship between the sensor 40 and each of the first portions 12 (e.g., instances thereof) of the hand 50, a posture of each of the first portions 12 (e.g., instances thereof) relative to the field generator 2 may be determined based on measurements of the sensor 40, wherein the measurements of the sensor indicate a relative posture between the sensor 40 and the field generator 2.

[0067] The first part 12 may be included not only in the finger of the hand 50 but also in an additional protrusion or contact tip formed on the element 52 of the arm 6. In this case, a plurality of sensors 40, 41, 42, 46 may be provided to determine the relative posture between the plurality of first parts 12 of the arm 6 and the field generator. For example, the first sensor 40 may be embedded in the element 52 of the arm 6 so as to enable the determination of the posture of the first part 12 included in the protrusion formed on the element 52 relative to the field generator, and the additional second sensor 40 may be embedded in the connecting element 56 so as to enable the determination of the relative posture between the first part 12 included in the finger of the hand 50 and the field generator 2. In other words, the arm 6 may include a plurality of first parts 12, and one or more sensors may be provided for determining the relative posture between all the first parts 12 and the field generator 2 based on sensor measurements and, for example, a first predetermined spatial relationship.

[0068] Alternatively, the hand 50 may be fixed relative to the element 52, for example by rigidly attaching the connecting member 54 to the element 52 of the arm 6. The sensors 40 may be arranged and configured as described above with reference to the sensors 41, 44 or 46. Such a sensor arrangement and configuration also enables the attitude between each of the first parts 12 of the arm 6 and the field generator 2 to be determined.

[0069] exist Figure 3 In the embodiment, arm 6 is taken as an example, although it is noted that one or more of arms 6, 8, 10, 32, 34, and 36 included in field generator assembly 100 may have a similar structure. In other words, one or more of arms 6, 8, 10, 32, 34, and 36 may include a plurality of first portions configured to contact the surface of body 200 when field generator 2 is attached to the body. Where referred to herein as a "first portion" of an arm (e.g., first portion 12, 14, or 16), it should be understood that each, all, or at least one of the plurality of first portions included in the arm may be meant.

[0070] Figure 4 An exemplary embodiment of a method of obtaining a relative posture between a surface of a patient's body and a field generator configured to generate an electromagnetic field and included in a field generator assembly is shown. Figures 1 to 3 An embodiment of a field generator assembly 100 is described to illustrate the method embodiments.

[0071] The method comprises a step 402 of obtaining measurement data describing measurements of a spatial relationship between at least one first arm 6, 8, 10 of the field generator assembly and the field generator 2, the at least one first arm 6, 8, 10 being movably attached relative to the field generator 2. The measurements are acquired by at least one sensor 40, 41, 44, 46 of the field generator assembly 100 when the field generator 2 is attached to the patient's body 200 and the first portion 12, 14, 16 (e.g., each of them) of the at least one first arm 6, 8, 10 is in contact with a surface of the patient's body 200. The measurement data may also describe measurements of a spatial relationship between a sensor included in the headband 30 and the field generator 2. The method further comprises a step 404 of determining a relative pose between the surface of the patient's body 200 and the field generator 2 based on the spatial relationship and at least one predetermined geometric characteristic of the at least one first arm 6, 8, 10.

[0072] Step 404 may also include determining a relative posture between the first portion included in the headband 30 and the field generator 2 based on a predetermined relative posture of the sensor included in the headband 30 and the first portion included in the headband 30. The relative posture determined in step 404 may be determined by determining the posture of one or more points or regions on the surface of the body 200 relative to the field generator 2, which corresponds to the posture of the respective first portions of one or more of the arms 6, 8, 10, 32 and optionally the headband 30 relative to the field generator 2. In other words, the posture of the first portion 12, 14, 16 relative to the field generator 2 may be assumed to be equivalent to the posture of one or more points or regions on the surface of the body 200 relative to the field generator, with which the first portion 12, 14, 16 is in contact. Therefore, the relative posture between the first portion 12, 14, 16 and the field generator 2 may be determined as the relative posture between the surface of the body 200 and the field generator 2. For example, only one point may be determined as the relative pose in step 404, where the point is located on the surface of the bridge of the patient's nose and corresponds to the position of the first portion 12 of the arm 6 relative to the field generator 2. In other words, the relative pose determined in step 404 may define the position of the point on the surface of the bridge of the patient's nose relative to the field generator 2. The relative pose determined in step 404 may be determined based on a plurality of (e.g., exactly three or more) points or areas on the surface of the patient's body 200 corresponding to the first portion of one or more of the arms 6, 8, 10, 32, 34, 36.

[0073] The measured spatial relationship preferably comprises or consists of the attitude of at least one arm 6 , 8 , 10 relative to the field generator 2 .

[0074] In a first variation, the measured spatial relationship may include or consist of the pose of the sensor 40 relative to the field generator 2. In this case, the geometric property may include or consist of the first predetermined spatial relationship described above. For example, as described above, the sensor 40 may be embedded in the connecting member 56 of the hand 50, and the first predetermined spatial relationship includes the relative pose between the sensor 40 and each first portion 12 of the hand 50. The geometric relationship may include the predetermined deformation described above.

[0075] In a second variant, the measured spatial relationship may comprise or consist of the attitude of the sensor 41 relative to the field generator 2. In this case, the geometrical properties may indicate that the sensor 41 is arranged at the first portion 16 of the arm 10, and therefore the attitude of the sensor corresponds to the attitude of the first portion 16.

[0076] In a third variation, the measured spatial relationship may comprise or consist of a posture of the second portion 20 of the arm 14 relative to the field generator 2 as measured by the sensor 44. The geometric relationship may comprise at least one of a spatial relationship between the second portion 20 and the first portion 14 and the predetermined deformation described above.

[0077] In a fourth variant, the measured spatial relationship may include or consist of the above-mentioned attitude of at least one arm 6, 8, 10 relative to the sensor 46 and the attitude of the field generator 2 relative to the sensor 46. As described above, the attitude of the field generator 2 relative to the sensor 46 can be determined based on the measured attitude of the housing 4 relative to the sensor 46 and the known attitude of the field generator 2 relative to the housing 4. Alternatively or in addition, in the case where the sensor 46 is a camera, the attitude of the field generator 2 relative to the sensor 46 can be measured directly by the sensor 46, for example using image analysis of images acquired by the sensor 46. The geometric relationship may include the spatial relationship of the first part 12, 14, 16 of at least one arm 6, 8, 10 relative to at least one arm 6, 8, 10, and optionally the above-mentioned predetermined deformation.

[0078] The method may further comprise a step 406 of acquiring patient image data, the patient image data comprising or describing an image of the patient's body 200. The patient image data may be CT or MR image data of the patient. The method may further comprise a step 408 of matching the determined relative pose between the surface of the patient's body 200 and the field generator 2 (or the determined pose of a point or region of or on the surface of the body 200 relative to the field generator 2) with the patient image data to obtain a registration between the patient image data and the patient's body 200. In particular, the surface of the model body extracted from the patient image data may be matched with the determined pose of a point or region of the surface of the body 200 when acquiring the sensor measurements, the pose of the point or region being associated with or corresponding to the pose of the first part 12, 14, 16 of at least one of the arms 6, 8, 10, 32, 34, 36. As a result of step 408, a registration between the patient image data and the field generator 2 may be obtained.

[0079] The method may enable a reliable and accurate determination of the relative pose between the surface of the patient's body 200 and the field generator 2 and, optionally, a reliable and accurate determination of the registration between the patient's image data and the field generator 2 .

[0080] Figure 5An exemplary embodiment of an apparatus 500 according to the present disclosure is shown. The apparatus comprises a processor 502, a memory 504, and may also comprise an interface 506. The memory 504 is a computer-readable storage medium and contains a computer program comprising instructions that, when executed on the processor 502, cause the processor 502 to perform the methods described herein. The interface may be configured to obtain, receive, retrievably provide or send information such as measurement data and / or a relative posture between a surface of a patient's body and a field generator.

[0081] The invention is defined by the accompanying claims.As will be apparent to a person skilled in the art, variations and combinations of the examples and exemplary embodiments described herein are possible.

Claims

1. A field generator assembly for surgical navigation, comprising: a field generator configured to generate an electromagnetic field; an attachment member configured to attach the field generator to a patient's body; at least one first arm comprising a first portion configured to contact a surface of the patient's body when the field generator is attached to the patient's body; as well as a second portion movably attached relative to said field generator; as well as at least one sensor configured to measure a spatial relationship between the at least one arm and the field generator Wherein, the at least one sensor is fixedly attached relative to the third portion of the at least one arm and is configured to measure a posture of the at least one sensor relative to the field generator.

2. The field generator assembly according to claim 1, wherein: The third portion is configured to position the at least one sensor in a first predetermined spatial relationship relative to the first portion when the first portion is in contact with the surface of the body.

3. The field generator assembly of claim 1, wherein: The third portion is fixedly connected relative to the first portion.

4. A field generator assembly for surgical navigation, comprising: a field generator configured to generate an electromagnetic field; an attachment member configured to attach the field generator to a patient's body; at least one first arm comprising a first portion configured to contact a surface of the patient's body when the field generator is attached to the patient's body; as well as a second portion movably attached relative to said field generator; as well as at least one sensor configured to measure a spatial relationship between the at least one arm and the field generator wherein the at least one sensor is fixedly attached in a second predetermined relationship relative to the field generator.

5. The field generator assembly of claim 4, wherein: The at least one sensor is configured to measure a posture of the second portion of the at least one first arm relative to the field generator.

6. A field generator assembly according to claim 1 or claim 4, wherein: At least one of the following conditions is met: (i) The first portion is a first end of the at least one first arm, and optionally, the second portion is a second end of the at least one first arm. (ii) The first portion is configured to be tensioned on the surface of the patient's body when the field generator is attached to the body. (iii) the first portion is configured to contact a surface of a predetermined landmark of the patient's body when the field generator is attached to the patient's body.

7. A field generator assembly according to claim 1 or claim 4, wherein: At least one of the following conditions is met: (i) the attachment member comprises or consists of the at least one first arm; (ii) The attachment member is configured to attach the field generator to the back of the patient's head.

8. A field generator assembly according to claim 1 or claim 4, wherein: At least one of the following conditions is met: (i) said at least one first arm comprises said first portion a plurality of times; (ii) The at least one first arm is configured to be rotatable about an axis extending substantially in the lateral-medial direction or substantially in the up-down direction.

9. The field generator assembly of claim 1 or claim 4, further comprising at least one of the following: (i) A second arm connected to the first arm so as to be movable together with the first arm. (ii) A third arm, wherein: The at least one first arm and the third arm are located on opposite sides relative to the field generator.

10. A field generator assembly according to claim 1 or claim 4, wherein The field generator assembly is formed as a substantially mirror-symmetrical component with respect to the sagittal plane.

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