Head mount for fixating trackable optical marker

Abstract

A head mount for fixating a visual marker to a head of a person is provided, the head mount comprising a base provided with a nose arm, a forehead arm, and a mounting plate support, the nose arm and the forehead arm extending from the base and defining an arm plane The mounting plate support is provided at its distal end with a mounting plate configured to carry the visual marker. The nose arm is provided at its distal end with a V-shaped nose rest configured to rest on a nose of the person. The forehead arm is provided at its distal end with a hinge defining an axis of rotation extending transversally to the arm plane and two mutually fixed forehead rests each originating from the hinge and arranged to be pivotable around said axis of rotation, each forehead rest being configured to rest on a forehead of the person. The V-shaped nose rest and the two mutually fixed forehead rests form a tripod-like structure. A use of the head mount for fixating a visual marker to a head of a person is further provided.

Description

[0001] P36798PC00 / SMI

[0002] Head mount for fixating trackable optical marker

[0003] BACKGROUND

[0004] Augmented Reality (AR)-based systems increase the accuracy and efficiency of certain surgical procedures. Traditionally, surgical procedures that require the surgeons to insert tools into the body of the patient are planned beforehand and executed based on a freehand approach where anatomical landmarks are used to mentally visualize the insertion trajectory. AR-based systems are used to assist a surgeon during such surgical procedures by providing real-time interaction with virtual stereoscopic 3D models that are overlaid onto the surgeon’s real-world view through transparent Augmented Reality Head-Mounted Displays (AR-HMDs). These devices display, for example, a direct macroscopic overlay of anatomical structures onto the real patient. For example, AR-HMDs are used to assist the surgeon during head and brain surgical procedures. These surgical procedures are performed on the head / brain of the patient and typically requires the surgeon to create an opening in the skull of the patient, to subsequently access the anatomical structures within the skull. An example of such a surgical procedure is External Ventricular Drain (EVD) placement, in which an EVD catheter is inserted into the brain to drain fluid from the ventricles and monitor intracranial pressure.

[0005] The virtual stereoscopic 3D models are constructed based on scans of the anatomical structures of interest, for example scans of the skin, skull, and ventricles. The surgeon can then plot a desired trajectory, e.g., an EVD trajectory, within the hologram by indicating an entry point and target point inside the hologram. Subsequently, the 3D model is projected onto the real- world view by overlaying the 3D model onto the real-world anatomical structure of the patient. This projection is based on a mapping of coordinates of the 3D model onto coordinates in the real world. Such mapping, also called image-to-patient registration, is for example performed by using point-based and / or contour-based matching techniques. In point-based matching techniques, the surgeon indicates the position of points on the real patient that correspond to virtual points of the 3D model, e.g., by tapping the anatomical structure of interest with a pointer device. In contour-based registration, the surgeon indicates contours on the real patient that correspond to contours of the 3D model, e.g., tracing a contour over the head with a pointer device that is tracked during said tracing. Registration is then performed, e.g., using an iterative closest point (ICP) algorithm.

[0006] To track any head movement during and after image-to-patient registration, a visual pattern, in particular a geometric pattern (e.g., a QR-code) is commonly attached at a fixed location to the anatomical structure of interest. This geometric pattern is detected using a camera, e.g., which is mounted on the AR-HMD that is worn by the surgeon. The geometric pattern is tracked during image-to-patient registration and during the surgical procedure. Since the geometric pattern is at a fixed location relative to the anatomical structure, it functions as a reference point for the projection of the 3D model onto the real-world view. If the head of the patient is moved, then the geometric pattern is moved correspondingly, thereby enabling the AR- based system to project the 3D model onto the newly detected location of the anatomical structure.

[0007] Existing devices for fixating the geometric pattern to the anatomical structure may comprise sharp tips that are driven into the anatomical structure. Such devices are not suitable to be placed on certain anatomical structures, such as the head of the patient. Existing devices that are suitable for attaching the geometric pattern onto the head of the patient often require complex frames that surround the head, thereby preventing certain orientations / placements of the head of the patient during surgery and blocking certain areas that are to be accessed during the surgical procedure by the surgeon. Further, existing devices do not allow for a surgical cover to be passed over the location where the geometric pattern is located, unless a large opening is made in the surgical cover through which the geometric pattern and the frame holding the geometric pattern is passed. Such a large opening in the surgical cover, however, leaves a major part of the anatomical structure uncovered, which has a negative impact on sterility of the surgical procedure. Further, the orientation of the geometric pattern in certain prior art devices is not fully configurable, which means the surgeon must be positioned within a predefined area with respect to the anatomical structure of interest in order for the geometric pattern to be within the field of view of the surgeon and / or the camera of the AR-HMD. Therefore, these prior art devices are unsuitable for use in surgical procedures that require the surgeon to be positioned at different locations with respect to the anatomical structure of interest.

[0008] An object of the invention is to overcome some or all of the identified disadvantages of existing head mounts for fixating a visual marker to a head of a person or at least to provide an alternative to these existing head mounts.

[0009] SUMMARY

[0010] In a first aspect of the invention, the object of the invention is achieved by a head mount for fixating a visual marker to a head of a person, the head mount comprising a base provided with a nose arm, a forehead arm, and a mounting plate support, the nose arm and the forehead arm extending from the base and defining an arm plane. The mounting plate support is provided at its distal end with a mounting plate configured to carry the visual marker. The nose arm is provided at its distal end with a V-shaped nose rest configured to rest on a nose of the person. The forehead arm is provided at its distal end with a hinge defining an axis of rotation extending transversally to the arm plane and two forehead rests each originating from the hinge and arranged to be pivotable around said axis of rotation, each forehead rest being configured to rest on a forehead of the person. The V-shaped nose rest and the two forehead rests form a tripod-like structure.

[0011] Optionally, the mounting plate support also extends from the base within the arm plane. The forehead rests are for example mutually adjustable over the axis of rotation.

[0012] Optionally the forehead rests are mutually fixed.

[0013] The device, i.e. , the head mount, according to the invention is compact and is easily placed on the head of the person, i.e., the patient, while having minimal impact on the accessibility of the areas of interest of the head of the patient. Only access to part of the forehead (in particular, the middle of the forehead extending upwards from the nose) of the patient is limited using the device according to the invention. Thus, the remainder of the head of the patient is accessible to the surgeon. In particular, the top part and side parts of the head of the patient are fully accessible.

[0014] The tripod-like structure of the device offers a stable construction that enables a stable mounting of the visual marker onto the head of the patient. In use, the V-shaped nose rest is placed on the nose of the patient, wherein each leg of the V-shaped nose rest contacts a respective side of the nose. In other words, the legs of the V-shaped nose rest are configured to be arranged on opposite side faces of the nose of the patient. The nose rest is optionally taped to the nose of the patient to ensure that the nose rest cannot be moved with respect to the nose of the patient. In use, the (optionally, mutually fixed) forehead rests are placed on the forehead, i.e., in the area of the front of the head of the patient extending from the base of the nose to around the hairline. The (optionally, mutually fixed) forehead rests are, in other words, placed in an area of the head of the person corresponding to the frontal bone extending upwards from the nose of the person. These forehead rests are like branches originating from the hinge provided at the distal end of the forehead arm. For example, these branches extend substantially transversally to, preferably orthogonally to, the arm plane in which the nose arm, the forehead arm, and (optionally) the mounting plate support extend from the base. In use, the forehead rests are placed on the forehead of the patient and, to keep these forehead rests in a fixed position, are fixed to the forehead of the patient using an adhesive, for example using tape. As a result, the device, is supported on the head of the patient at three points: the V-shaped nose rest and the two forehead rests. In use, the device is fixed to the head of the patient, i.e., it remains in a fixed location with respect to the head of the patient. Therewith, the device is configured to support a visual marker, which is to be placed onto the mounting plate. The shape of the device is configurable to the shape of the head of the person because the forehead rests are pivotable around an axis of rotation that extends transversally (preferably orthogonally) to the arm plane. In use, the forehead rests are pivoted such that the forehead rests are aligned with the forehead of the patient. Thereby, the forehead rests optimally conform to the shape of the forehead. Therewith, it is ensured that the forehead rests are stably mounted on the forehead of the patient.

[0015] In an embodiment according to the first aspect of the invention, the nose arm, the forehead arm, and the mounting plate support are arranged at an angle of less than 150°, preferably 120°, with respect to each other in the arm plane.

[0016] Therewith, the nose arm, the forehead arm, and the mounting plate support form a stable three-legged configuration in the arm plane having the base as its origin. In this embodiment, each of the nose arm, the forehead arm, and the mounting plate support are arranged at an angle of less than 150°, preferably 120°, with respect to each of the other ones of the nose arm, the forehead arm, and the mounting plate support in the arm plane. Thus, the nose arm is arranged at an angle of less than 150°, preferably 120°, with respect to the forehead arm and the mounting plate support in the arm plane. The forehead arm is arranged at an angle of less than 150°, preferably 120°, with respect to the nose arm and the mounting plate support in the arm plane. The mounting plate support is arranged at an angle of less than 150°, preferably 120°, with respect to the nose arm and the forehead arm in the arm plane. Preferably, the nose arm, the forehead arm, and the mounting plate support are each arranged at an angle of 120° with respect to each other in the arm plane.

[0017] In an embodiment according to the first aspect of the invention, the two forehead rests are formed as a plate.

[0018] In other words, each forehead rest may comprise a plate or the forehead rests may be formed by a single plate. Such a plate is for example substantially rectangular or substantially square. The plate is optionally curved to conform to the curvature of the forehead of the person. The forehead rests originate from the hinge: for example, the plates extend laterally from the hinge within a plane that is parallel to the axis of rotation. Alternatively, the plates are fixed to the hinge with a connection member which each extend from the hinge transversally to the arm plane. For example, the connection members each are arranged at an angle of 25°-45° with respect to the arm plane. Optionally, in this embodiment, the two forehead rests are integrally formed, forming a forehead plate.

[0019] Thus, the two (optionally, mutually fixed) forehead rests are integrally formed as a single part, which part is formed as a plate extending substantially parallel to the axis of rotation, i.e. , extending transversally, preferably orthogonally, to the arm plane. The plate thereby extends laterally from the hinge within a plane that is parallel to the axis of rotation. The lateral end portions of the plate each form one of the forehead rests. These lateral end portions optionally extend outwards in a plane that is orthogonal to the axis of rotation, i.e., in the arm plane. Therewith, a forehead rest is formed that are configured to provide support to the head mount on a larger surface area of the forehead of the person. The forehead plate optionally is curved to conform to the curvature of the forehead of the person. The forehead plate is for example substantially rectangular.

[0020] In an embodiment according to the first aspect of the invention, the two forehead rests are configured to be mounted with an adhesive to the forehead.

[0021] For example, an adhesive layer is provided on the underside of the forehead rests such that the forehead rests, when placed on the forehead of the patient, are attached to the forehead by the adhesive strength of the adhesive layer. In such examples, the adhesive layer is configured to release from the forehead of the patient if sufficient force is applied once the head mount is to be dismounted from the head of the patient. In an alternative example, an adhesive tape is placed over the forehead rests when the head mount is placed on the head of the person. Therewith, the forehead rests are mounted in a fixed location on the forehead of the patient. The forehead rests provide two of the support points of the tripod-like structure. Together with the V-shaped nose rest, which rests fixedly on the nose of the person, the tripod-like structure is, in use, fixedly mounted to the head of the person. Therewith, it is ensured that the mounting plate remains in a fixed position with respect to the head of the patient, which mounting plate is configured to carry the visual marker. As a result, in use, the visual marker carried by the mounting plate also remains in a fixed position with respect to the head of the patient.

[0022] In an embodiment according to the first aspect of the invention, the mounting plate comprises a plurality of recesses configured to receive a plurality of protrusions arranged on a first surface of the visual marker. In this embodiment, when the mounting plate carries the visual marker, the protrusions arranged on the surface of the visual marker are arranged within the recesses of the mounting plate. Thereby, the orientation of the visual marker with respect to the plane defined by the mounting plate is fixed. In other words, rotation of the visual marker with respect to the mounting plate is prevented. Therewith, it is ensured that the orientation of the visual marker remains constant, allowing for the visual marked to be reliably detected.

[0023] In an embodiment according to the first aspect of the invention, the head mount further comprises the visual marker which is removably coupled to the mounting plate. A visual pattern is provided on a second surface of the visual marker.

[0024] In use, the visual marker is to be identified and tracked by using, for example, a camera mounted on a headset such as an Augmented Reality Head-Mounted Display (AR-HMD) worn by the surgeon performing a procedure on the person to which the head mount is fixed. The visual marker is for example a plate made of a suitable material such as metal or plastic. The visual pattern is for example a QR-code. By coupling the visual marker to the mounting plate, the visual marker is positioned parallel to the mounting plate. The visual pattern is provided on the surface of the visual marker facing away from the mounting plate. Therewith, the visual pattern is oriented in such a way that it is visible to the surgeon performing the procedure, and thereby can be detected by the camera mounted on the headset worn by the surgeon.

[0025] In case that a plurality of protrusions are arranged on a first surface of the visual marker, in this embodiment, the second surface on which the visual pattern is provided is opposite the first surface on which the plurality of protrusions is arranged.

[0026] Therewith, in use, the first surface is facing the mounting plate since it comprises the plurality of protrusions that are arranged to engage into the plurality of recesses on the mounting plate. The first surface is therefore not visible in use. The visual pattern is provided on the surface opposite the first surface, i.e. , on the second surface and is therefore visible in use.

[0027] In an embodiment according to the first aspect of the invention, the head mount further comprises a screw with external screw thread extending transversally, preferably orthogonally, from the mounting plate, the screw being configured to be passed through a hole of the visual marker. The head mount in this embodiment further comprises a nut member with internal screw thread configured to receive the external screw thread to removably couple the visual marker to the mounting plate. In this embodiment, a structure for removable coupling the visual marker to the mounting plate is provided comprising a screw with external screw thread and a nut member with internal screw thread. The male treaded screw is, in use, passed through a hole in the visual marker. By subsequently passing the nut member with internal screw thread over the screw with external screw thread, a mechanical connection between the visual marker and the mounting plate is formed as the nut member with internal screw thread is tightened against the visual marker. Therewith, it is ensured that the visual marker cannot accidentally be removed from the mounting plate.

[0028] In case the mounting plate comprises a plurality of recesses configured to receive a plurality of protrusions arranged on a first surface of the visual marker, these protrusions are placed into the recesses in use of the device before the nut member with internal screw thread is tightened over the screw with external screw thread.

[0029] Alternative means for removably coupling the visual marker to the mounting plate are possible. For example, the mounting plate and the visual marker may be magnetic. In this example, the visual marker is removably coupled to the mounting plate by placing the visual marker onto the mounting plate in the desired position and orientation. The visual marker is thereby attached to the mounting plate due to the magnetic force between the visual marker and the mounting plate. In case the mounting plate comprises a plurality of recesses configured to receive a plurality of protrusions arranged on a first surface of the visual marker, these protrusions are placed into the recesses in use of the device so that, in this example, the magnetic mounting plate and the magnetic visual marker are positioned and oriented fixedly with respect to each other. To remove the magnetic visual marker from the magnetic mounting plate, a sufficient force facing away from the mounting plate is applied on the visual marker to dislodge the magnetic visual marker from the magnetic mounting plate. In this example, the screw with external screw thread, the hole in the visual marker, and the nut member with internal screw thread may be omitted.

[0030] In an embodiment according to the first aspect of the invention, the mounting plate support comprises a ball joint which rotatably supports the mounting plate on the base.

[0031] In this embodiment, a ball joint is provided. The ball joint rotatably couples the mounting plate to the base. Therewith, the mounting plate is rotatable in 3D-space. In case that a visual marker is carried by the mounting plate, the rotation of the mounting plate enables rotating the visual marker carried by the mounting plate to an orientation that is optimal for the field of view of the surgeon. Optionally, in this embodiment, the mounting plate support further comprises a ball joint locking mechanism configured to lock the ball joint, thereby preventing rotation of the mounting plate.

[0032] For example, the ball joint locking mechanism comprises a screw that, when tightened, contacts the ball joint and locks it into place. Optionally, a number of protrusions are provided on the ball joint such that the ball joint may only be locked into a discrete set of positions.

[0033] In an embodiment according to the first aspect of the invention, the forehead arm is provided with a forehead arm locking mechanism configured to prevent rotation of the two forehead rests over the axis of rotation.

[0034] For example, the forehead arm locking mechanism comprises a screw that engages into the forehead arm and, when tightened, presses the two forehead rests, or a part thereof, in between a part of the screw and the forehead arm. Therewith, pivoting of the two forehead rests around the axis of rotation is prevented.

[0035] In a second aspect of the invention, the object of the invention is achieved by a use of the head mount according to the device of the first aspect of the invention for fixating a visual marker to a head of a person, comprising the steps of:

[0036] - placing the nose rest onto the nose of the person;

[0037] - pivoting the forehead rests around the axis of rotation to align the forehead rests with the forehead of the person;

[0038] - fixing the forehead rests on the forehead of the person using adhesive;

[0039] - mounting the visual marker onto the mounting plate.

[0040] In the method according to the second aspect of the invention, the visual marker is placed in a position where it is in the field of view of the surgeon performing the procedure.

[0041] Optionally, the steps of the method according to the second aspect of the invention are performed in order.

[0042] In an embodiment according to the second aspect of the invention, the head mount used is a head mount wherein the mounting plate comprises a plurality of recesses configured to receive a plurality of protrusions arranged on a first surface of the visual marker, the step of mounting the visual marker onto the mounting plate further comprises the step of inserting the plurality of protrusions on the surface of the visual marker into the plurality of recesses of the mounting plate.

[0043] In this embodiment, the visual marker is mounted to the mounting plate in such a way that rotation of the visual marker with respect to the mounting plate is prevented.

[0044] In an embodiment according to the second aspect of the invention, the step of mounting the visual marker onto the mounting plate further comprises the steps of:

[0045] - passing the screw through a hole in a surgical cover which is to be placed over the person;

[0046] - passing the visual marker over the screw by passing the screw through the hole of the visual marker;

[0047] - passing the nut member over the screw, thereby removably fixing the visual marker onto the mounting plate which is at least partially covered by the surgical cover.

[0048] The person on which the procedure is performed is generally covered by a surgical cover for reasons of sterility. In this embodiment, a small hole is made in the surgical cover through which the screw with external screw thread is passed. The visual marker is then placed on the surgical cover which covers the mounting plate. Thereby, the visual marker is mounted on the mounting plate with the surgical cover in between the visual marker and the mounting plate. Therewith, only a small hole is required to be made in the surgical cover, ensuring continued sterility.

[0049] In case the mounting plate comprises a plurality of recesses configured to receive a plurality of protrusions arranged on a first surface of the visual marker, these protrusions fit into the recesses wherein the surgical cover is arranged in-between the protrusions and the recesses. The protrusions engage, but do not pass through, the surgical cover.

[0050] By passing the nut member with internal screw thread over the screw with external screw thread, the nut member with internal screw thread is tightened against the visual marker, which visual marker is in turn tightened against the mounting plate.

[0051] In an example where the visual marker and the mounting plate are magnetic and wherein the screw with external screw thread and the nut member with internal screw thread are omitted from the construction, the surgical cover does not comprise a hole through which the screw with external screw thread is passed. Instead, the surgical drape is placed over the mounting plate, and the visual marker is placed directly onto the surgical drape at a position beneath which the mounting plate is located. Therewith, the visual marker is removably fixed to the mounting plate.

[0052] BRIEF DESCRIPTION OF THE DRAWINGS The invention is described below with reference to the figures. These figures serve as examples to illustrate the invention and will not be construed as limiting the scope of the claims. In the different figures, like features are indicated by the like reference numerals.

[0053] In the figures:

[0054] Fig. 1 schematically shows a side view of the head mount according to an embodiment of the first aspect of the invention in use.

[0055] Fig. 2 schematically shows a perspective view of the head mount according to an embodiment of the first aspect of the invention.

[0056] Fig. 3a and Fig. 3b each schematically show a perspective view of the head mount according to an embodiment of the first aspect of the invention.

[0057] Fig. 4 schematically shows an exploded side view of the head mount according to an embodiment of the first aspect of the invention.

[0058] Fig. 5 schematically shows an exploded view of a part of the head mount according to an embodiment of the first aspect of the invention.

[0059] Fig. 6a and Fig. 6b schematically show the head mount according to an embodiment of the first aspect of the invention in use.

[0060] Fig. 7 schematically shows, according to the second aspect of the invention, the steps of the use of the head mount according to the first aspect of the invention.

[0061] Fig. 8 schematically shows, according to an embodiment of the second aspect of the invention, further steps of the use of the head mount according to the first aspect of the invention.

[0062] DETAILED DESCRIPTION

[0063] Fig. 1 schematically shows a side view of the head mount 100 according to the first aspect of the invention in use. Fig. 2 schematically shows a perspective view of the head mount according to an embodiment of the first aspect of the invention. To more clearly depict the different elements of the head mount 100, Fig. 2 shows the head mount 100 not in use.

[0064] The head mount 100 is configured to fixate a visual marker 101 to a head of a person.

[0065] The head mount 101 comprises a base 102. The base 102 joins three arms which originate from the base 102: a first arm, also called a nose arm 103, a second arm, also called a forehead arm 104, and a third arm, also called a mounting plate support 105. These three arms are arranged at an angle with respect to each other in the plane in which they extend from the base. In Fig. 1 , as shown, this plane, i.e., the arm plane, is parallel to the sides of the three arms 103, 104, 105 that are visible in the figure. Thus, the legs of the V-shape are arranged on opposite side faces of the nose. The nose arm 103 extends from the base 102. Thus, at is proximal end, the nose arm

[0066] 103 is attached to the base 102. At its distal end, the nose arm 103 is provided with a V-shaped nose rest 107. The V-shaped nose rest 107 comprises two prongs, each of the prongs being arranged to rest on a respective side of the nose of the person. Therewith, the V-shaped nose rest 107 provides for a point of support for supporting the head mount 100 on the head of the person.

[0067] The forehead arm 104 extends from the base 102. Thus, at is proximal end, the forehead arm 104 is attached to the base 102. At its distal end, the forehead arm 104 is provided with two mutually fixed forehead rests 109a and 109b (forehead rest 109b is not visible in Fig. 1). The forehead arm 104 is further provided with a hinge 108, from which the forehead rests 109a, 109b originate. The forehead rests 109a and 109b are therewith rotatably attached to the forehead arm 104 via the hinge 108. This hinge 108 defines an axis of rotation which extends transversally to the arm plane. The forehead rests are therewith pivotable around the axis of rotation defined by the hinge 108. In the embodiment shown in Fig. 1, the axis of rotation extends perpendicular to the arm plane. The forehead rests 109a and 109b are mutually fixed and are thereby rotatable in unison, i.e., mutually rotatable, over the axis of rotation defined by the hinge 108. As shown, the forehead rests 109a and 109b are therefore rotatable, i.e., pivotable, to a position in which the forehead rests 109a and 109b are aligned with (i.e., are substantially flush to) the forehead of the person to which the visual marker 101 is to be mounted. The forehead rests 109a, 109b are thus placed on the forehead of the person by arranging the forehead rests 109a, 109b at an angle with respect to the forehead arm 104 in the arm plane. The angle at which the forehead rests 109a, 109b are arranged with respect to the forehead arm 104 depends on the position of the forehead and its location with respect to the nose of the patient. Said angle is typically larger than 90° and smaller than 180°, preferably smaller than 160°, typically in the range of 100°-140°. For reasons of clarity, a neutral position of the forehead rests 109a, 109b with respect to the forehead arm 104 is also shown in Fig. 1 in dotted lines. In this neutral position, the forehead rests 109a, 109b are arranged as an extension of, i.e., in line with, i.e., at an angle of 180° with, the forehead arm 104. In Figs. 2-4, the forehead rests 109a, 109b are shown in this neutral position, i.e., Figs. 2-4 show the device while not in use.

[0068] The forehead rests 109a and 109b extend outwards from the hinge 108 in a plane perpendicular to the arm plane. Thus, the forehead rests 109a and 109b are attached to the hinge 108 perpendicular to the distal end of the forehead arm 104. The right angle with which the forehead rests 109a and 109b are arranged with respect to the distal end of the forehead arm

[0069] 104 is denoted with E in Fig. 1.

[0070] The forehead arm is further provided with a forehead arm locking mechanism configured to prevent the pivoting of the two mutually fixed forehead rests 109a, 109b around the axis of rotation. The forehead arm locking mechanism is in the form of or comprises a threaded bolt 110 which engages in the forehead arm 104 and therewith can be tightened to prevent pivoting of the two mutually fixed forehead rests 109a, 109b around the axis of rotation. Thus, once the forehead rests 109a, 109b are aligned to the forehead of the person to which the visual marker 101 is to be mounted, the threaded bolt 110 is tightened to prevent said pivoting.

[0071] The forehead rests 109a and 109b are arranged at a distance from the forehead arm 104. Thus, when viewing the head mount from an orientation as shown in Fig. 2, the forehead rests 109a and 109b are arranged to the left and the right of the forehead arm 104 and therewith also to the left and the right of the V-shaped nose rest 107. Therewith, the forehead rests 109a and 109b each provide for a respective point of support for supporting the head mount on the head of the person. Together with the V-shaped nose rest 107, three points of support are provided. Due to the positioning of these three points of support, the V-shaped nose rest 107 and the two mutually fixed forehead rests 109a, 109b form a tripod-like structure that is configured to stably support the head mount onto the head of the person, and thereby stably support the visual pattern onto the head of the person.

[0072] In the embodiment shown in Figs. 1 and 2, the two mutually fixed forehead rests are integrally formed, forming a forehead plate 201. The forehead plate 201 is slightly curved to conform to the shape of the forehead of the person on which the head mount is to be placed.

[0073] The mounting plate support 105 extends from the base 102. Thus, at is proximal end, the mounting plate support 105 is attached to the base 102. At its distal end, the mounting plate support 105 is provided with a mounting plate 106. The mounting plate 106 is arranged in a plane that is substantially perpendicular to the arm plane. So, the mounting plate 106 is attached to the distal end of the mounting plate support 105 such that the surfaces of the mounting plate 106 (not visible in Fig. 1 , but the “back” surface of the mounting plate 106 is visible in Fig. 2) are arranged at a right angle with respect to the mounting plate support. This right angle between the surfaces of the mounting plate 106 and the mounting plate support 105 is indicated with 5 in Fig. 1. Fig. 1, the visual marker 101 is shown removably attached to the mounting plate 106. The mounting plate 106 thus carries, in use, the visual marker 101. As a result, the orientation of the visual marker 101 is identical to the orientation of the mounting plate 106, i.e., the visual marker 101 is arranged substantially parallel to the mounting plate 106.

[0074] A dotted line is drawn parallel to each of the three arms which meet at an intersection point to illustrate the angles with which the arms are arranged with respect to each other. The nose arm 103 is arranged at an angle a with respect to the mounting plate support 105. The nose arm 103 is arranged at an angle y with respect to the forehead arm 104. The forehead arm 104 is arranged at an angle p with respect to the mounting plate support 105. In the embodiment shown in Fig. 1 , these angles a, p, and y are identical and equal to 120°. Alternatively, the angles a, p, and y are non-identical and less than 150°. Typically, the angles a, p, and y are each greater than 90°. For example, the angles a and p may be identical but smaller than 120°, for example 110° or 100°. In such examples, the angle y is greater than 120° but smaller than 150°. In other examples, the angle y is less than 120°, for example 110° or 100°. In yet other examples, all of the angles a, p, and y are different.

[0075] It was found that a value of less than 150°, preferably 120°, for each of the angles a, p, and Y provides for a stable tripod-like structure which is configured to support the visual pattern at three points: the V-shaped nose rest and the two forehead rests.

[0076] In the embodiment shown in Figs. 1 and 2, the mounting plate support comprises a ball joint 111 which rotatably supports the mounting plate 106 on the base. The functioning of the ball joint 111 is further explained below in reference to Figs. 3a, 3b, and 5.

[0077] Fig. 3a and Fig. 3b each schematically show a perspective view of the head mount according to an embodiment of the first aspect of the invention. To more clearly depict the different elements of the head mount 100, Figs. 3a and 3b show the head mount 100 not in use. Figs. 3a and 3b illustrate the rotational freedom of movement of the mounting plate 106 which is rotatably supported by the ball joint 111 on the base 102. The ball joint 111 defines a point of rotation of the mounting plate 106 with respect to the base 102. The ball joint 111 allows the mounting plate 106 to be rotated over, i.e. , pivoted around, this point of rotation in two planes, as explained further below.

[0078] The arrow shown in Fig. 3a illustrates that the mounting plate 106 (and the visual marker 101 which is carried by the mounting plate 106) is rotatable, i.e., pivotable, within a plane that is perpendicular to the mounting plate support 105. The mounting plate 106 is arranged within said plane. In other words, the mounting plate 106 is rotatable within a plane parallel to its surfaces. Said rotation within said plane allows to orient the visual marker optimally so that it is accurately detectable by, for example, a camera that is mounted to the head of the surgeon viewing the visual marker 101.

[0079] The arrow shown in Fig. 3b illustrates that the mounting plate 106 (and the visual marker 101 which is carried by the mounting plate 106) is rotatable within the arm plane, i.e., the plane that is parallel the sides of the three arms 103, 104, 105 that are visible in the figure. Said rotation allows the mounting plate 106 to be tilted towards the nose rest 107 and towards the forehead rests 109a, 109b. The tilt of the mounting plate 106 shown in Fig. 3b towards the nose rest 107 is suitable for surgical procedures in which the surgeon is positioned facing towards the underside of the head of the patient. For example, if the patient is laying down on their back, the surgeon is positioned beside the patient in the area around the neck of the patient and facing towards the face of the patient. In such an orientation of the mounting plate 106, the mounting plate 106 is arranged at a shallow angle (preferably less than 30°) with respect to the nose arm 103. In some examples, the mounting plate 106 is arranged substantially parallel to the nose arm 103. Such an orientation of the mounting plate 106 results in the mounting plate 106 being arranged at a shallow angle (preferably less than 30°) with respect to the face of the person, in certain cases substantially parallel to the face of the person. A tilt of the mounting plate 106 in the other direction, i.e. , towards the forehead rests 109a, 109b, is suitable for surgical procedures in which the surgeon is positioned facing towards the top of the head of the patient. For example, if the patient is laying down on their back, the surgeon is positioned behind the head of the patient, facing towards the top of the skull of the patient. In such an orientation of the plate 106, the mounting plate 106 is arranged at a shallow angle (preferably less than 30°) with respect to the forehead arm 104. In some examples, the mounting plate 106 is arranged substantially parallel to the nose arm 104. Such an orientation of the mounting plate 106 results in the mounting plate 106 being arranged at a shallow angle (preferably less than 30°) with respect to the top of the skull of the patient, in certain cases substantially parallel to the top of the skull of the person.

[0080] The mounting plate support 105 comprises a recess 205. The recess 205 is arranged within an encasing 113 which encases a ball of the ball joint 111. The recess 205 is configured to accommodate a connection member, i.e., a pin 114 which supports the mounting plate 106 on the ball joint 111. Therewith, a large angle of rotation of the mounting plate 106 within the arm plane towards the recess 205 is facilitated. As shown in Fig. 3a, the recess 205 is located on the side of the encasing 113 facing the forehead rests 109a, 109b. Thus, as shown in Fig. 3b, when the mounting plate 106 is rotated, i.e., pivoted, towards the forehead rests 109b, at some point during rotation, the pin 214 will engage within the recess 205. Therewith, rotation over an angle which allows to rotate the mounting plate 106 to be substantially parallel to the forehead arm 104 is facilitated. Optionally, a second recess is provided in the encasing 113 opposite the recess 205 so that a larger angle of rotation is facilitated when rotating the mounting plate 106 towards the nose rest 107.

[0081] The mounting plate 106 being rotatably supported by the ball joint 111 thus allows to orient the mounting plate 106 optimally so that the visual marker 101 carried by the mounting plate 106 is detectable by, for example, a camera mounted on the head of the surgeon performing the procedure on the person to which the head mount 100 is attached. The head mount 100 thus allows multiple positions of the surgeon with respect to the patient (i.e., positions where the surgeon is facing towards the top of the skull of the patient or, alternatively, towards the underside of the head of the patient). Further, the head mount allows the visual marker 101 carried by the mounting plate 106 to be rotated to an orientation in which it is optimally detectable by, for example, a camera mounted on the head of the surgeon. Fig. 4 schematically shows an exploded side view of the head mount 100 according to an embodiment of the first aspect of the invention. To more clearly depict the different elements of the head mount 100, Fig. 4 shows the head mount 100 not in use. Fig. 4 shows the side of the head mount 100 opposite the side of the head mount shown in Fig. 1. Fig. 4 shows the head mount 100 in an unassembled state, i.e. , in a state in which the visual marker 101 is not carried by the mounting plate 106.

[0082] Two protrusions 401a, 401b are arranged on a first surface 203 of the visual marker 101. These protrusions have a suitable shape, such as pyramidical or conical. Other shapes of the protrusions are possible, such as dome-shaped. These protrusions 401a, 401b fit into recesses 202a, 202b of the mounting plate 106 (not shown in Fig. 4, but visible in Fig. 2). These recesses 202a, 202b have a reciprocal shape to the shape of the protrusions 401a, 401b so that, when the protrusions 401a, 401b are placed into the recesses 202a, 202b, a connection between the visual marker 101 and the mounting plate 106 is made such that the visual marker 101 cannot be moved or rotated with respect to the mounting plate 106 within a plane defined by the mounting plate 106.

[0083] A screw 402 with external screw thread, hereafter also called male threaded screw, is arranged on the mounting plate 106 perpendicular to a plane defined by mounting plate 106. This male threaded screw 402 is arranged to be passed through a hole 403 in the visual marker 101. This hole has suitable dimensions to accommodate the male threaded screw 402. Typically, the inner sides of the hole 403 are not threaded, but optionally the inner sides of the hole 403 are female threaded to engage the male threaded screw 402. A nut member 112 with internal screw thread is configured to engage, i.e., receive, the male threaded screw 402. In use, once the male threaded screw is passed through the hole 403, the visual marker 101 is moved along the male threaded screw 402 towards the mounting plate 106 until the visual marker 101 engages the mounting plate 106. Then, the visual marker 101 is rotated until the protrusions 401a, 401b engage the recesses 202a, 202b. Then, as shown in Fig. 4, the nut member 112 is passed over the male threaded screw 402. The female thread bolt 112 thereby engages the male threaded screw 402. The nut member 112 is tightened until it engages the second surface 404 of the mounting plate 106 which is opposite the first surface 203 of the mounting plate 106. Therewith, the visual marker 101 is fixedly mounted to the mounting plate 106, which means that the mounting plate 106 carries the visual marker 101 , resulting in an assembled state of the head mount 100 as shown, e.g., in Figs. 1 and 2. The visual marker 101 is removably coupled to the mounting plate 106: the visual marker 101 is removable from the mounting plate 106 by unscrewing the nut member 112 from the male threaded bolt 402 and subsequently moving the visual marker 101 away from the mounting plate 106 such that the protrusions 401a, 401b disengage from the recesses 202a, 202b. The protrusions 401a, 401b, the recesses 202a, 202b, the hole 403 and the screw 402 are preferably positioned in such a way that the visual marker 101 can only be mounted on the mounting plate 106 in a single orientation with respect to the mounting plate 106. The recesses 202a, 202b and the screw 402 form a triangle on the mounting plate 106. The protrusions 401a, 401b and the hole 403 form a reciprocal triangle on the visual marker 101. Only a single orientation of the visual marker 101 with respect to the mounting plate 106 is possible in which the male threaded screw 402 is arranged within the hole 403, and the protrusions 401a, 401b are arranged within the recesses 202a, 202b.

[0084] Fig. 5 schematically shows an exploded view of a part of the head mount according to an embodiment of the first aspect of the invention. The part shown in Fig. 5 shows the ball joint 111 which rotatably supports the mounting 106 on the base 102. The ball joint 111 comprises a ball 501 , a socket 502 which rotatably holds the ball 501 and an encasing 113 which encases the ball 501. This ball-and-socket assembly forms the ball joint 111. A pin 114 extends from the ball 501. This pin 114 connects the ball 501 to the mounting plate 106 as shown, e.g., in Figs. 1-2. The encasing 113 comprises a recess 205 which appropriately limits the movement of the ball joint 111. When, in use, the ball 501 is rotated within the socket 502, the pin 114 will, at certain angles of the pin 114 with respect to the encasing 113, engage the encasing 113, thereby preventing further rotation of the ball 501 within the socket 502. The recess 205 is wide enough to accommodate the pin 114. Thereby, the ball joint is pivotable around an angle in the direction of the recess 205 which is greater than directions in which no recess is provided in the encasing 113. This greater angle allows to orient the mounting plate 106 so that the visual marker 101 which is, in use, mounted on the mounting plate 106 to be visible in certain positions of the surgeon with respect to the person to which the head mount 100 is fixated, as explained above with respect to Fig. 3a and 3b.

[0085] A ball joint locking mechanism, in the form of a male threaded screw 204, is provided. The threaded screw 204 is passed through a hole of the encasing 113 and the socket 502. When, in use, the threaded screw 204 is tightened, the threaded screw 204 engages the ball 501 , thereby preventing rotation of the ball 501 within the socket 502. As a result, the orientation of the mounting plate 106 is fixed. By loosening the threaded screw 204, the threaded screw 204 disengages the ball 501. Therewith, the ball 501 is again rotatable within the socket 502.

[0086] Fig. 6a and Fig. 6b schematically show the head mount 100 according to an embodiment of the first aspect of the invention in use. The head mount 100 fixates visual marker 101 to a head of a person.

[0087] The nose rest 107 is placed on the nose of the person. As shown in Fig. 6a, the two sides of the V-shaped nose rest 107 each engage a single side of the nose of the person, or in other words, the legs of the V-shape are arranged on opposite side faces of the nose. Therewith, the V-shaped nose rest prevents the head mount 100 to be moved laterally with respect to the face of the person. The forehead rests 109a, 109b are placed on the forehead of the person. The forehead rests 109a, 109b are each formed as a plate and are mounted to the forehead with an adhesive. In the example shown in Fig. 6a, adhesive tape 603a, 603b is placed over the forehead rests 109a and 109b.

[0088] The orientation of the visual marker 101 shown in Fig. 6a is in a neutral position. By rotating the visual marker 101 towards the forehead rests 109a, 109b, the visual marker 101 is in an orientation which is used in case that the procedure requires the surgeon to stand behind the head of the person, facing towards the skull of the person. In that case, the visual marker 101 is within the field of view of the surgeon (and, also, within the field of view of any camera mounted to the head of the surgeon). By rotating the visual marker 101 towards the nose rest 108 (and therewith towards the nose of the person), the visual marker 101 is in an orientation which is used in case that the procedure requires the surgeon to stand at approximately the height of the neck of the person, facing towards the underside of the head of the patient.

[0089] The visual marker 101 is provided with a visual pattern 604 on its second surface 404. The visual pattern 604 shown in Fig. 6a is a QR-code, but other visual patterns are possible. The visual pattern 604 is detectable by, for example, a camera mounted on the head of the surgeon performing the procedure on the person to which the head mount 100 is fixated.

[0090] Fig. 6b shows a cross section of the head mount 100 in use. In use, during a surgical procedure, the person is covered in a surgical cloth 601 for sterility of the procedure. The head mount is configured to minimize the impact on sterility. In use, most parts of the head mount 100 are placed under the surgical cloth 601 , i.e., on the side of the surgical cloth 601 facing towards the person. Only the male threaded screw 402 passes through a hole 602 in the surgical cloth 601. The hole 602 in the surgical cloth 601 is either made before passing the male threaded screw 402 through the surgical cloth 601, or, alternatively, the male threaded screw 402 is provided with a sharp tip which is able to pierce the hole 602 in the surgical cloth 602 when the male threaded screw 402 is passed through the surgical cloth 601. In either case, only a small hole 602 is made in the surgical cloth 601 , while the rest of the surgical cloth 601 that is covering the person remains intact. The visual marker 101 may then be passed over the male threaded screw 402 until it engages the surgical cloth 601 . Then, the protrusions 401a, 401 b engage, through the surgical cloth 601 (but, without passing through the surgical cloth 601), the recesses 202a, 202b. After that, the visual marker 101 is fixated to the mounting plate 106 by tightening nut member 112 as explained above. As a result, at least the second surface 404 of the visual marker 101 is visible to the surgeon: the visual marker 101 is arranged above the surgical cloth 601 , i.e., on the side of the surgical cloth 601 facing away from the person and towards the surgeon. Therewith, sterility provided by the surgical cloth 601 is minimally impacted by the head mount 100.

[0091] Fig. 7 schematically shows, according to the second aspect of the invention, the steps of the use of the head mount 101 according to the first aspect of the invention.

[0092] The use according to the second aspect of the invention is a method of fixating a visual marker 101 to a head of a person.

[0093] The method starts with the step S701 of placing the nose rest 107 onto the nose of the person. In doing so, with reference to Fig. 6a, the V-shaped nose rest 107 contacts either side of the nose of the person to which the visual marker 101 is to be fixated. Therewith, the V-shaped nose rest 107 creates a point of contact between the head mount 101 and the head of the person (at the location of the nose of the person).

[0094] In a next step S702, the (optionally, mutually fixed) forehead rests 109a, 109b are pivoted over the axis of rotation to align the forehead rests with the forehead of the person. The hinge 108 defines the axis of rotation over which the forehead rests 109a, 109b are pivotable. Said pivoting, in some examples, is preventable by tightening the forehead arm locking mechanism, i.e., the threaded bolt 110. In such examples, the threaded bolt 110 is first loosened in order to allow for the pivoting of the forehead rests 109a, 109b over the axis of rotation. The forehead rests 109a, 109b are pivoted over the axis of rotation such that the forehead rests 109a, 109b are positioned substantially flush with the forehead of the person. As a result, when the forehead rests 109a, 109b are placed on the forehead of the person, the forehead rests 109a, 109b each provide for a stable point of contact between the head mount 101 and the forehead of the person.

[0095] In a next step S703, the forehead rests 109a, 109b are fixed on the forehead of the person using adhesive. In doing so, the forehead rests 109a, 109b are unmovably attached to the head of the person. The two points of contact provided by the forehead rests 109a, 109b and the point of contact provided by the V-shaped nose rest 107 form a tripod-like structure which is configured to stably support the visual marker 101 on the head of the person.

[0096] In a last step S704, the visual marker 101 is mounted onto the mounting plate 106. Optionally, the step S704 comprises the step of inserting the plurality of protrusions 401a, 401 b on the first surface 203 of the visual marker 101 into the plurality of recesses 202a, 202b of the mounting plate 106. The mounting of the visual marker 101 onto the mounting plate 106 is completed by creating a connection between the visual marker 101 and the mounting plate 106. Said connection is for example realized by a nut member 112 which is passed over the male threaded screw 402 and tightened against the visual marker 101. Doing so removably couples the visual marker 101 to the mounting plate 106: by unscrewing the nut member 112 from the male threaded screw 402, the connection between the visual marker 101 and the mounting plate 106 is undone.

[0097] Fig. 8 schematically shows, according to an embodiment of the second aspect of the invention, further steps of the use of the head mount according to the first aspect of the invention.

[0098] In this embodiment, the step of mounting the visual marker 101 onto the mounting plate 106 further comprises the steps S801 , S802, and S803.

[0099] In the step S801 , the male threaded screw 402 is passed through a hole 602 in a surgical cover 601 which is to be placed over the person. In the step S802, the visual marker 101 is passed over the male threaded screw 402 by passing the male threaded screw 402 through the hole 303 of the visual marker 101. In the step S803, the nut member 112 is passed over the male threaded screw 402, thereby removably coupling the visual marker 101 onto the mounting plate 106 which is at least partially covered by the surgical cover 601.

[0100] The result of performing these additional steps is illustrated in Figs. 6a and 6b. By performing these steps, sterility provided by the surgical cloth 601 is minimally impacted by the head mount 100.

[0101] Embodiments and further embodiments of the present invention - which (further) embodiments may be broader than claimed in the claims - may be expressed in words as set out in the following clauses:

[0102] Clause 1] A head mount for fixating a visual marker to a head of a person, the head mount comprising a base provided with a nose arm, a forehead arm, and a mounting plate support, the nose arm and the forehead arm extending from the base and defining an arm plane; wherein the mounting plate support is provided at its distal end with a mounting plate configured to carry the visual marker; wherein the nose arm is provided at its distal end with a V-shaped nose rest configured to rest on a nose of the person; wherein the forehead arm is provided at its distal end with: a hinge defining an axis of rotation extending transversally to the arm plane; and two forehead rests each originating from the hinge and arranged to be pivotable around said axis of rotation, each forehead rest being configured to rest on a forehead of the person; wherein the V-shaped nose rest and the two forehead rests form a tripod-like structure. Clause 2] The head mount according to clause 1, wherein the arm plane is orthogonal to the forehead of the person and extends in the length direction of the person.

[0103] Clause 3] The head mount according to any one of clauses 1-2, wherein the nose arm, the forehead arm, and the mounting plate support extend from the base in the arm plane. Clause 4] The head mount according to any one of the preceding clauses, wherein the nose arm, the forehead arm, and the mounting plate support are arranged at an angle of less than 150°, preferably 120°, with respect to each other in the arm plane.

[0104] Clause 5] The head mount according to any one of the preceding clauses, wherein the two forehead rests are formed as a plate.

[0105] Clause 6] The head mount according to clause 5, wherein the two forehead rests are integrally formed, forming a forehead plate.

[0106] Clause 7] The head mount according to any one of the preceding clauses, wherein the two forehead rests are configured to be mounted with an adhesive to the forehead.

[0107] Clause 8] The head mount according to any one of the preceding clauses, wherein the mounting plate comprises a plurality of recesses configured to receive a plurality of protrusions arranged on a first surface of the visual marker.

[0108] Clause 9] The head mount according to any one of the preceding clauses, further comprising the visual marker which is removably coupled to the mounting plate; wherein a visual pattern is provided on a second surface of the visual marker.

[0109] Clause 10] The head mount according to clauses 8 and 9, wherein the second surface on which the visual pattern is provided is opposite the first surface on which the plurality of protrusions is arranged.

[0110] Clause 11] The head mount according to any one of the preceding clauses, further comprising: a screw with external screw thread extending transversally, preferably orthogonally, from the mounting plate, the screw being configured to be passed through a hole (403) of the visual marker; and a nut member with internal screw thread configured to receive the external screw thread to removably couple the visual marker to the mounting plate.

[0111] Clause 12] The head mount according to any one of the preceding clauses, wherein the mounting plate support comprises a ball joint which rotatably supports the mounting plate on the base.

[0112] Clause 13] The head mount according to clause 12, wherein the mounting plate support further comprises a ball joint locking mechanism configured to lock the ball joint, thereby preventing rotation of the mounting plate. Clause 14] The head mount according to any one of the preceding clauses, wherein the forehead arm is provided with a forehead arm locking mechanism configured to prevent rotation of the two forehead rests over the axis of rotation.

[0113] Clause 15] Use of the head mount according to any one of clauses 1-14 for fixating a visual marker to a head of a person, comprising the steps of:

[0114] - placing the nose rest onto the nose of the person;

[0115] - pivoting the forehead rests around the axis of rotation to align the forehead rests with the forehead of the person;

[0116] - fixing the forehead rests on the forehead of the person using adhesive;

[0117] - mounting the visual marker onto the mounting plate.

[0118] Clause 16] Use according to clause 15 of the head mount according to any one of clauses 8-14, wherein the step of mounting the visual marker onto the mounting plate further comprises the step of inserting the plurality of protrusions on the surface of the visual marker into the plurality of recesses of the mounting plate.

[0119] Clause 17] Use according to any one of clauses 15-16 of the head mount according to any one of clauses 11-14, wherein the step of mounting the visual marker onto the mounting plate further comprises the steps of:

[0120] - passing the screw through a hole in a surgical cover which is to be placed over the person;

[0121] - passing the visual marker over the screw by passing the screw through the hole of the visual marker;

[0122] - passing the nut member over the screw, thereby removably fixing the visual marker onto the mounting plate which is at least partially covered by the surgical cover.

[0123] As required, this document describes detailed embodiments of the present invention. However, it must be understood that the disclosed embodiments serve exclusively as examples, and that the invention may also be implemented in other forms. Therefore, specific constructional aspects which are disclosed herein should not be regarded as restrictive for the invention, but merely as a basis for the claims and as a basis for rendering the invention implementable by the average skilled person. Furthermore, the various terms used in the description should not be interpreted as restrictive but rather as a comprehensive explanation of the invention. The word "a" used herein means one or more than one, unless specified otherwise. The phrase "a plurality of' means two or more than two. The words "comprising" and "having" do not exclude the presence of more elements. Reference figures in the claims should not be interpreted as restrictive of the invention. Particular embodiments need not achieve all objects described. The mere fact that certain technical measures are specified in different dependent claims still allows the possibility that a combination of these technical measures may advantageously be applied.

Claims

- 23 -CLAIMS1] A head mount (100) for fixating a visual marker (101) to a head of a person, the head mount comprising a base (102) provided with a nose arm (103), a forehead arm (104), and a mounting plate support (105), the nose arm and the forehead arm extending from the base and defining an arm plane; wherein the mounting plate support is provided at its distal end with a mounting plate (106) configured to carry the visual marker; wherein the nose arm is provided at its distal end with a V-shaped nose rest (107) configured to rest on a nose of the person; wherein the forehead arm is provided at its distal end with: a hinge (108) defining an axis of rotation extending transversally to the arm plane; and two forehead rests (109a, 109b) each originating from the hinge and arranged to be pivotable around said axis of rotation, each forehead rest being configured to rest on a forehead of the person; wherein the V-shaped nose rest and the two forehead rests form a tripod-like structure.2] The head mount according to claim 1, wherein the nose arm, the forehead arm, and the mounting plate support are arranged at an angle (a, p, y) of less than 150°, preferably 120°, with respect to each other in the arm plane.3] The head mount according to any one of the preceding claims, wherein the two forehead rests are formed as a plate.4] The head mount according to claim 3, wherein the two forehead rests are integrally formed, forming a forehead plate (201).5] The head mount according to any one of the preceding claims, wherein the two forehead rests are configured to be mounted with an adhesive to the forehead.6] The head mount according to any one of the preceding claims,wherein the mounting plate comprises a plurality of recesses (202a, 202b) configured to receive a plurality of protrusions (401a, 401b) arranged on a first surface (203) of the visual marker.7] The head mount according to any one of the preceding claims, further comprising the visual marker which is removably coupled to the mounting plate; wherein a visual pattern (604) is provided on a second surface (404) of the visual marker.8] The head mount according to claims 6 and 7, wherein the second surface on which the visual pattern is provided is opposite the first surface on which the plurality of protrusions is arranged.9] The head mount according to any one of the preceding claims, further comprising: a screw (402) with external screw thread extending transversally, preferably orthogonally, from the mounting plate, the screw being configured to be passed through a hole (403) of the visual marker; and a nut member (112) with internal screw thread configured to receive the external screw thread to removably couple the visual marker to the mounting plate.10] The head mount according to any one of the preceding claims, wherein the mounting plate support comprises a ball joint (111) which rotatably supports the mounting plate on the base.11] The head mount according to claim 10, wherein the mounting plate support further comprises a ball joint locking mechanism(204) configured to lock the ball joint, thereby preventing rotation of the mounting plate.12] The head mount according to any one of the preceding claims, wherein the forehead arm is provided with a forehead arm locking mechanism (110) configured to prevent rotation of the two forehead rests over the axis of rotation.13] Use of the head mount according to any one of claims 1-12 for fixating a visual marker to a head of a person, comprising the steps of:- placing the nose rest onto the nose of the person (S701);- pivoting the forehead rests around the axis of rotation to align the forehead rests with the forehead of the person (S702);- fixing the forehead rests on the forehead of the person using adhesive (S703);- mounting the visual marker onto the mounting plate (S704).14] Use according to claim 13 of the head mount according to any one of claims 6-12, wherein the step of mounting the visual marker onto the mounting plate further comprises the step of inserting the plurality of protrusions on the surface of the visual marker into the plurality of recesses of the mounting plate.15] Use according to any one of claims 13-14 of the head mount according to any one of claims 9-12, wherein the step of mounting the visual marker onto the mounting plate further comprises the steps of:- passing the screw through a hole (602) in a surgical cover (601) which is to be placed over the person (S801);- passing the visual marker over the screw by passing the screw through the hole of the visual marker (S802);- passing the nut member over the screw, thereby removably fixing the visual marker onto the mounting plate which is at least partially covered by the surgical cover (S803).

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