NL2026875B1

NL2026875B1 - Device, method and system for aiding a surgeon while operating

Info

Publication number: NL2026875B1
Application number: NL2026875A
Authority: NL
Inventors: Karel Vos Wouter; Voormolen Eduard; Jan Noordmans Herke; Jozef Herman Diederen Sander
Original assignee: Elitac B V; Umc Utrecht Holding Bv
Priority date: 2020-11-11
Filing date: 2020-11-11
Publication date: 2022-06-30
Also published as: WO2022103254A1

Abstract

The invention relates to a device, method and system for aiding a surgeon in guiding an invasive tool into the body of a patient while operating. Claimed is a haptic feedback device arranged for being part of a guidance system for aiding a surgeon during an invasive procedure on a body, wherein the haptic feedback device comprises: haptic actuators arranged for having a spatial arrangement defining a haptic interaction surface, and for being in haptic communication with the surgeon; and a controller arranged for: retrieving information on locations of critical structures in an area of the body; retrieving information on the spatial arrangement of the haptic actuators; receiving a tool tip location indicative of a location of a tool tip of an invasive tool used for invading a body area of the body during the invasive procedure in an invading direction, wherein the tool tip is arranged for being thrusted fon/vard in and/or sideward from the invading direction; selecting a nearest critical structure of the critical structures relative to the tool tip location; projecting a direction of the nearest critical structure onto the haptic interaction surface; and actuating one or more of the haptic actuators based on the projection.

Description

DEVICE, METHOD AND SYSTEM FOR AIDING A SURGEON WHILE OPERATING

FIELD OF THE INVENTION The invention relates to a device, method and system for aiding a surgeon while operating. More specific, the invention relates to a device, method and system for aiding a surgeon in guiding an invasive tool into the body of a patient.

BACKGROUND OF THE INVENTION Operations on the brain typically require diligence of the surgeon. To obtain access to the brain, the surgeon has to drill through the skull of the patient. The skull as well as the surrounding of the skull of the patient has many vital structures that should be kept intact while drilling. To guide the surgeon around the vital structures preceding the operation the vital structures will be identified in a 3D scan. This scan is typically shown during the operation. Furthermore, the tool or tools of the surgeon are inserted real-time virtually in the 3D scan of the vital structures and shown on a screen during the operation to the surgeon. A disadvantage is that the surgeon has to switch his field of view between the area operated on and the screen showing his tools and the vital structures.

SUMMARY OF THE INVENTION An object of the invention is to overcome one or more of the disadvantages mentioned above. According to a first aspect of the invention, a haptic feedback device arranged for being part of a guidance system for aiding a surgeon during an invasive procedure on a body, wherein the haptic feedback device comprises: - haptic actuators arranged for having a spatial arrangement defining a haptic interaction surface, and for being in haptic communication with the surgeon; and - a controller arranged for: - retrieving information on locations of critical structures in an area of the body; - retrieving information on the spatial arrangement of the haptic actuators; - receiving a tool tip location indicative of a location of a tool tip of an invasive tool used for invading a body area of the body during the invasive procedure in an invading direction, wherein the tool tip is arranged for being thrusted forward in and/or sideward from the invading direction;

- selecting a nearest critical structure of the critical structures relative to the tool tip location; - projecting a direction of the nearest critical structure onto the haptic interaction surface; and - actuating one or more of the haptic actuators based on the projection. A surgeon operating on the body of a patient may have to invade the body with a tool. This tool, such as a drill, may be used to get to a specific location and/or may be used at a specific location. The surgeon may be a neurosurgeon. A neurosurgeon may be operating on the brain typically has to go through the skull. A neurosurgeon may also be operating on the skull itself. The skull comprises critical structures, such as veins and nerves. These critical structures are typically soft and easily damaged. When operating on the skull and/or going through the skull, bone matter may need to be removed from the skull by a drill.

The body is typically a patient, more specific a human patient. The surgeon is typically a neurosurgeon. The typical invading procedure is an operation on the brain where there is a need for drilling through the skull, and/or an operation on the skull itself.

The guidance system typically comprises a microscope wherethrough the surgeon may view the area of the body operated on, or at least the entrance in the body wherethrough the area of the body operated on is accessible. Typically, in the latter case, the viewing direction of the microscope is such that the area operated on is visible through the microscope.

The guidance system may further comprise a tool addon sensing the orientation and location of the tool attached to it. Typically, during operation the body is fixated to make sure the body is not moving. The addon and/or the tool attached whereto the addon is attached is calibrated, such that the guidance system detects and/or calculates the location and/or orientation of the tool, especially a specific point or volume of the tool, relative to the body.

Typically, prior to the operation the body is scanned and critical and/or vital structures and/or the area operated upon are identified. In an alternative embodiment, identification may be done real-time or almost real-time. In an alternative embodiment, identification may be done alternating with the actual invasive procedure.

The guidance system may further comprise a screen visualizing the scan of the body and the tool, specifically the tool tip. The screen provides the surgeon with a

2D view of the body and its structures, such as critical and/or vital structures, and the tool, specifically the tool tip.

The haptic feedback device comprises haptic actuators. The haptic actuators are arranged for having a spatial arrangement defining a haptic interaction surface. The haptic interaction surface is typically substantially flat. The haptic interaction surface typically follows the curvature of the body of the surgeon to be in haptic communication with the surgeon.

The haptic feedback device comprises a controller. The controller is typically loaded with software. The controller may be centralized or distributed. The controller may be arranged or loaded with software for executing several steps. The steps may be executed in any order. The steps may be repeated over the course of the operation. One step may be repeated more than the other step.

The controller is arranged for the step of retrieving information on locations of critical structures in an area of the body. This information is typically provided by another part of the guidance system. This other part of the guidance system may be a database. Alternatively, this information may be provided by an external source, such as an external database e.g. from a hospital database system. The locations of the critical structures in the body are represented by 3D information. The critical structures are typically represented as a volume in this 3D space. The critical structures are typically specified relative to stable reference points in the body. Stable reference points in the body may be a bone structure, such as notches in or protrusions from a bone. When operating on the skull, typically notches in and protrusions from the skull are selected as stable reference point. The same reference points are typically used during scan as well as during the invasive procedure, such as an operation.

The controller is arranged for the step of retrieving information on the spatial arrangement of the haptic actuators. This information may be predefined or prestored in memory associated with the controller. The information is typically the relative position of the haptic actuators to each other. Typically, the relative positions are within the haptic interaction surface. As reference for the relative positions one haptic actuator may be selected. Alternatively, as reference for the relative positions an arbitrary point is selected. This arbitrary point is typically a logical point in relation to the pattern that the haptic actuators form. For example, if at least a selection of the haptic actuators is arranged in the shape of a circle, the arbitrary reference point may be selected on a side or corner of a square enveloping or even touching the circle. For example, if at least a selection of the haptic actuators is arranged in the shape of a circle, the arbitrary reference point may be selected as the centre of this circle.

The controller is arranged for the step of receiving a tool tip location indicative of a location of a tool tip of an invasive tool used for invading a body area of the body during the invasive procedure in an invading direction. The tool tip is arranged for being thrusted forward in and/or sideward from the invading direction. The tool tip location is typically provided by other parts of the guidance system.

The controller is arranged for the step of selecting a nearest critical structure of the critical structures relative to the tool tip location. The controller may do the selection based on the 3D coordinate of the tool tip and the 3D coordinates of the critical structures relative to reference points. In an alternative embodiment, as meant within the scope of the invention, the steps of retrieving information on locations of critical structures in an area of the body, and selecting a nearest critical structure of the critical structures relative to the tool tip location are replaced with the step of receiving a nearest critical structure of the critical structures relative to the tool tip location. The step of receiving a nearest critical structure may be serviced by another part of the guidance system, which is executing the replaced steps.

The controller is arranged for the step of projecting a direction of the nearest critical structure onto the haptic interaction surface. A direction is a 3D vector, typically the normalized 3D vector. This 3D vector may be projected on a 2D haptic interface surface. Several projections may be suitable to convey the information via vibrations in the haptic interface surface to the surgeon.

The controller is arranged for the step of actuating one or more of the haptic actuators based on the projection. This step effectively conveys the information to the surgeon. The actual vibration thus represents the direction starting out from the tool tip towards the nearest structure information.

The haptic feedback device provides an alternative means for perceiving the nearest critical structure for the surgeon. The surgeon typically uses the screen of the guidance system for visually perceiving the location of the tool tip relative to critical structures. The surgeon while guiding and/or manoeuvring the tool, especially the tool tip, typically has to swap between the screen and viewing the operating area typically via a microscope. The haptic feedback device allows the surgeon to swap less or even not swap anymore between screen and operating area. Less swapping or even not swapping may have the effect of decreasing unintended movement by the surgeon of the tool tip due to this swapping, thus decreasing the likelihood of unintended damaging of critical structures. Less swapping or even not swapping may have the effect of lessening the stress, physically and/or mentally, for the surgeon. Less swapping or even not swapping may have the effect of increasing the handling speed of the surgeon invading the body with a tool, specifically a tool tip. The screen 5 visualizing the tool, specifically the tool tip, and the surrounding critical structures, is a 2D visualization of 3D space. The screen typically provides a limited insight in the distance between the tool tip and the surrounding critical structures. One critical structure may be shown more distant relative to another critical structure in relation to the tool tip on the screen, but in reality, this one critical structure may actually be closer to the tool tip. This confusion and/or loss of sense of distance between the critical structures and the tool, specifically the tool tip, is advantageously mitigated by the haptic feedback device.

In an embodiment of the invention, the spatial arrangement of the haptic actuators is a 2D spatial arrangement. The 2D spatial arrangement is advantageously curved to fit to the body of the surgeon. The spatial arrangement is typically held together or placed upon a resilient material, such as a resilient plastic or fabric e.g. of some clothing. The spatial arrangement, more specific the 2D spatial arrangement, advantageously covers a 2D area.

In an embodiment of the invention, the guidance system comprises a microscope for displaying to the surgeon at least partly a body surface of the body area invaded, having a viewing direction; and the controller is arranged for receiving a viewing direction; and the projecting is based on the viewing direction. If the guidance system comprises a microscope, the viewing direction of the surgeon may advantageously be derived from the settings, such as the orientation, of the microscope relative to the body operated on or invaded by a tool. The microscope may advantageously be linked or calibrated relative to the operating table carrying the body or to a frame holding the body. As the viewing direction is known to the guidance system as well as the location of the tool tip, the guidance system may relate these two values relative to each other. Furthermore, the guidance system may insert the tool tip location and the viewing direction into the frame of reference of the critical structures for advantageously using the viewing direction for projecting.

In an embodiment of the invention, projecting comprises: - defining an equator plane at the tool tip location and perpendicular to the viewing direction; - defining a semisphere having its centre at the tool tip location and below the equator plane with regard to the viewing direction; - calculate a semisphere location on the semisphere based on a vector from the tool tip location towards the nearest critical structure; and - mapping the semisphere location onto a haptic location of the haptic interaction surface. The semisphere is typically a unity sphere. The semisphere location is the crossing of a line segment starting at the tool tip and extending along the vector and the semisphere up to the nearest critical structure. The semisphere advantageously allows to map the semisphere location having a uniform distance from the tool tip, such as unity distance, onto the haptic location of the haptic interaction surface. An alternative definition of the location of the semisphere may be that the semisphere is located on the opposite or other side of the equator plane relative to the viewing direction.

In a further embodiment of the preceding embodiment, if the nearest critical structure is above the equator plane, the vector may be mirrored in the equator plane as part of calculation step for obtaining a semisphere location.

In an embodiment of the invention, the mapping is advantageously based on: - an orthographic infinity projection; - a near-side general perspective, such as a GEO, a MEO or a LEO near- side general perspective, preferably based on a focal point in the range of 0.01 to infinity, more preferably in the range of 0.02 to10, most preferably around 0.05, 1 or

5.62; - a Gnomonic projection; - a Stereographic projection; - a far-side general perspective, such as a Twilight, a Clarke, a James or La Hire far-side general perspective; - an azimuthal projection, more specific an azimuthal equidistant projection; or - a projection based on a focal point in the range of -6 to 0.3, more preferably in the range of -4 to 0.5, most preferably around -2.7, -2.5, -2.4, -2, -1.7 or -

1.

In an embodiment of the invention, the mapping advantageously is one of the group of a stereographic projection, an orthographic projection, an azimuthal projection, and a Lambert azimuthal equal-area projection. The azimuthal equidistant projection has shown to be specifically beneficial during tests.

In an embodiment of the invention, the haptic interaction surface has a circumference, which is substantially a circular surface. A circle on the semisphere can be defined by the set of crossings of the semisphere and line segments extending from the tool tip location and in directions having an equal angle relative to the viewing direction. This circle is parallel to the equator plane. Typically, the direction of the viewing direction is advantageously mapped onto the centre of the substantially circular surface. The substantially circular surface of the haptic interaction surface provides the advantage that the mapping step will cause the points on the circle to be mapped at equal distance from the centre point of the substantially circular surface. This in turn provides the advantage that the haptic sensation of the surgeon is independent of where the direction crosses this circle on the semisphere pointing to the nearest critical structure to perceive the same deviation from the centre of the haptic interaction surface.

In an embodiment of the invention, the haptic actuators are arranged to predefined locations in the haptic interaction surface. The haptic location on the haptic interaction surface is typically not at one of the predefined locations of the actuators. The haptic location may be mapped to the closest actuator, whereafter the closest actuator is activated. Although simple in its solution, this also provides a relatively low haptic accuracy. Alternatively, in case the haptic location is not at one of the predefined locations of the actuators, two, three or more actuators may be activated for interpolating between the activated actuators. The interpolation between the activated actuators advantageously allows to provide a haptic sensation at the haptic location while none of the activated actuators is arranged to this haptic location. As the activated haptic actuators are arranged to predefined locations, the interpolation calculation is advantageously simplified.

In an embodiment of the invention, when the haptic location is unequal to a location of any of the haptic actuators, actuating comprises actuating two or more haptic actuators for perceiving a haptic actuation signal by the surgeon at the haptic location. The step of actuating typically comprises interpolating between different haptic actuators, preferably between three haptic actuators positioned in a triangle, for simulating a haptic location between the position of the haptic actuators. The haptic actuators are typically arranged such close together that the haptic actuators may be used for interpolation. If the haptic actuators are arranged too far away from each other, the haptic actuators will be perceived as individual haptic actuators.

Further, the haptic actuators are typically arranged far enough apart such that the arrangement of haptic actuators cover a substantial area.

The larger the covered area the higher the accuracy of the direction the surgeon may distinguish.

Further, the less haptic granularity and/or actuators are used, the simpler the control of these different actuators and/or the complexity of the haptic feedback device in general.

Thus, the distance between the haptic actuators is a balance between the aforementioned effects and advantages.

In a further embodiment, the haptic interaction surface is advantageously divided up in triangles forming the substantially circular haptic surface.

Haptic actuators are arranged to the corners of the triangles.

The triangles are advantageously arranged such that the corners of the different triangles are adjacent, such as in a Delaunay triangulation.

In an embodiment of the invention, calculating comprises if the nearest critical structure is located above the equator plane with regard to the viewing direction, placing the semisphere location on the rim of the semisphere.

Typically, from the tool tip location the intention is to drill sideways of or in the viewing direction.

If the nearest critical structure is above the equator plane, more specific above the tool tip location, it should be indicated that e.g. the tool tip is not lifted upwards against the viewing direction.

To prevent this lifting upwards, the semisphere location is advantageously placed on the rim of the semisphere.

The rim of the semisphere may coincide with the rim of the haptic interaction surface in this embodiment.

A typical reaction is to move the tool tip in a direction in the equator plane away from the semisphere location, which is located on the rim of the semisphere.

The semisphere location may be the same as the haptic location, which is located on the edge of the haptic interaction surface rim in this case.

The tool tip is advantageously moved away from below the nearest critical structure.

Furthermore, another possible reaction is to retract the tool tip backwards along the elongated axis of the tool.

After the retraction, the equator plane, as it is relative to the retracted tool tip location, may place the nearest critical structure below the equator plane allowing to get a better sense of the location of the nearest critical structure.

Furthermore, another possible reaction is to not retract, but continue to move the tool tip down along the viewing direction or sideways from the viewing direction, except for the sideway direction indicated by the semisphere location on the rim.

This allows to continue operating, such as drilling with the tool tip, and being confident that no critical structure is damaged.

And when done,

retracting along the elongated axis of the typically elongated tool should not damage any critical structures as described above.

In an embodiment of the invention, the haptic actuators are advantageously arranged for being in haptic communication with the back of the surgeon. The back of the surgeon is a relatively large and substantially flat or lightly curved surface. The surgeon typically bends over during the invasive procedure, leaving the front with too many wrinkles and curves or even insensitive to haptic communication. During the invasive procedure, typically while bending over, the back of the surgeon is typically stretched and/or flattened, advantageously allowing haptic communication.

In an embodiment of the invention, the haptic actuators are advantageously arranged for being on both sides of the spine in haptic communication with the surgeon. The spine is relatively insensitive to haptic communication, such as vibrations. The spine is an indentation relative to other parts of the back, requiring additional measures to have haptic actuators at this position in haptic communication with the back of the surgeon. These additional measures are prevented, thus simplifying the haptic feedback device.

In an embodiment of the invention, the haptic actuators are advantageously arranged for being symmetrical around the spine in haptic communication with the surgeon. This symmetry simplifies the actuation of the haptic actuators. This symmetry prevents different interpolation perceptions for left and right from the spine. As the haptic feedback device is typically worn, symmetry typically allows and/or is perceived as a more comfortable fitting to the body.

In an embodiment of the invention, the arrangement of haptic actuators advantageously comprises 10, 12, 14, or 16 haptic actuators. These arrangements typically allow for the haptic actuators to be arranged in triangles, such as: near equilateral triangles and/or more or less equally sized triangles; symmetry around the spine; a balance between a large haptic interaction surface and interpolation between the haptic actuators, advantageously arranging such that the arrangement complies to the Delaunay triangulation requirements; haptic actuators to be arranged to substantially cover a circular area and/or low complexity of the haptic feedback device due to the low amount of haptic actuators, specifically less than or equal to 16, which may be coded in a nibble in software, or in case of one hot in two bytes.

In an embodiment of the invention, projecting comprises: - calculate a distance between the tool tip location and the nearest critical structure; and

- mapping the distance to an activation pattern for the one or more of the haptic actuators. The distance may advantageously be incorporated in the activation pattern. This advantageously allows the surgeon to decide if it is still possible to move the tool tip in the direction of the nearest critical structure or not. This may especially be advantageous if the surgeon is e.g. making a hole or an opening in a skull for providing a large access area to the area to be further operated on.

In a further embodiment of the invention, the activation pattern comprises one or more of the group of a vibration frequency, a vibration amplitude, a vibration activation duration and a vibration activation interval. As the semisphere location and/or the haptic location is used as indication for the direction of the nearest critical structure, other options at this semisphere location and/or this haptic location should be advantageously used to convey the distance information. These other options are advantageously summarized as activation pattern.

According to another aspect of the invention, a guidance system for aiding a surgeon during an invasive procedure on a body comprising critical structures, wherein the system comprises: - an invasive tool for invading a body area of the body during the invasive procedure in an invading direction, wherein the invasive tool is having a tool tip arranged for being thrusted forward in and/or sideward from the invading direction, which tool tip has a tool tip location; - a microscope for displaying to the surgeon at least partly a body surface of the body area invaded, having a viewing direction; and - a haptic feedback device comprising haptic actuators arranged for being in haptic communication with the surgeon wherein actuation of the haptic actuators is indicative of a direction based on, and preferably a distance between, the tool tip and a nearest critical structure of the critical structures. This aspect of the invention provides the advantages as specified for the other aspects of the invention.

According to another aspect of the invention, a method for a haptic feedback for a guidance system for aiding a surgeon during an invasive procedure on a body, wherein the haptic feedback method comprises: - retrieving information on locations of critical structures in an area of the body; - retrieving information on the spatial arrangement of haptic actuators defining a haptic interaction surface, and arranged for being in haptic communication with the surgeon;

- receiving a tool tip location indicative of a location of a tool tip of an invasive tool used for invading a body area of the body during the invasive procedure in an invading direction, wherein the tool tip is arranged for being thrusted forward in and/or sideward from the invading direction; - selecting a nearest critical structure of the critical structures relative to the tool tip location; - projecting a direction of the nearest critical structure onto the haptic interaction surface; and - actuating one or more of the haptic actuators based on the projection.

This aspect of the invention provides the advantages as specified for the other aspects of the invention.

In an embodiment of the invention, the preceding method advantageously combined with any of the features of the haptic feedback device according to the invention.

According to another aspect of the invention, a system comprising a microprocessor arranged and loaded with software for carrying out any of the methods according to the invention. This aspect of the invention provides the advantages as specified for the other aspects of the invention.

According to another aspect of the invention, a computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method specified in an embodiment according to the invention. This aspect of the invention provides the advantages as specified for the other aspects of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be apparent from and elucidated further with reference to the embodiments described by way of example in the following description and with reference to the accompanying drawings, in which: Figure 1 schematically shows an operating theatre; Figure 2 schematically shows a haptic feedback method; Figure 3 schematically shows the step of projecting; Figure 4 schematically shows an embodiment of the step of mapping; Figure 5 schematically shows an embodiment of the step of mapping; Figure 6 schematically shows an embodiment of the step of mapping;

Figure 7 schematically shows an embodiment of an arrangement of haptic actuators; Figure 8 schematically shows an embodiment of an arrangement of haptic actuators; Figure 9 schematically shows an embodiment of an arrangement of haptic actuators; Figure 10 schematically shows an embodiment of an arrangement of haptic actuators; Figure 11 schematically shows an embodiment of an arrangement of haptic actuators; Figure 12 schematically shows an embodiment of a computer program product, computer readable medium and/or non-transitory computer readable storage medium according to the invention.

The figures are purely diagrammatic and not drawn to scale. In the figures, elements which correspond to elements already described may have the same reference numerals.

LIST OF REFERENCE NUMERALS

315 retrieving information on spatial arrangement of haptic RE == 600, 601, 602, 603, | arrangement of haptic actuators wm

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS The following figures may detail different embodiments. Embodiments can be combined to reach an enhanced or improved technical effect. These combined embodiments may be mentioned explicitly throughout the text, may be hint upon in the text or may be implicit.

Figure 1 schematically shows an operating theatre 10. The operating theatre may comprise a patient 20 and a surgeon 30 operating on the patient. The surgeon may use a guidance system 200 for guiding him during the operation. An example of such a guidance system is the Stealth system of Medtronic, Cranial Navigation Application of Brainlab, Navigation of Stryker, or Cranial or Spine Navigation of 7D Surgical. The guidance system may comprise an invasive tool 210 and a haptic feedback device 100. Typically, the surgeon will view 250 the part of the body of the patient operated on through a microscope 240. The surgeon is therefore looking 245 into the microscope. To operate on the patient, the surgeon will manipulate 215 the invasive tool. The invasive tool will in response to this manipulation move 220 typically in the body of the patient. The translation of manipulation to movement may be direct or indirect. Indirect may be that the manipulations are fed through control software and/or mechanical controllers for e.g. stabilizing, translating, rotating and/or scaling the manipulations. The haptic feedback device is typically in haptic communication 115 with the surgeon for providing haptic feedback to the surgeon during the operation. The haptic feedback device takes as input the viewing direction 105 of the surgeon typically from the microscope. The haptic feedback device takes further as input the tool tip location 110 provided by the invasive tool or derived from the invasive tool by the guidance system.

The guidance system may optionally comprise a screen typically showing the invasive tool, especially the invasive tool tip, and/or the critical structures in the operating area. The critical structures may be selected as only showing the nearest or few of the nearest critical structures. The surgeon may look on the screen to prevent damaging the critical structures with the invasive tool, especially the invasive tool tip.

When the surgeon is swapping from the screen to the microscope and vice versa, the surgeon may unwillingly waver with the invasive tool. Especially as the head of the surgeon may be turning and moving, the hand should be kept stable at all times to prevent damaging critical structures. The haptic feedback device has the effect to provide the surgeon with a feedback allowing the surgeon to not take his eyes of or take his eyes less from the operating area. This effect is due to that the haptic feedback uses a different sense organ than the eyes. The haptic feedback allows the surgeon to less swap or not swap at all with his eyes and therefore reduces the change on damaging a critical structure of the patient. Thus, the effect of the haptic feedback device is to reduce the change of damaging critical structures in the patient by the surgeon.

Furthermore, the screen provides a 2D view of a 3D situation. This requires the surgeon to frequently change perspective on the 2D screen to be able to estimate the distance between the tool tip location and the nearest critical structure. This changing of perspective increases the issue of or chance on unwillingly wavering of the invasive tool of the surgeon. Hence, the effect of the reduction of the change from the haptic feedback device is increased.

Furthermore, as this 2D view limits to estimate the distance between the tool tip location and the nearest critical structure, this cause inaccuracies in the distance estimation by the surgeon. The estimation of this distance is improved by providing the surgeon with the haptic feedback. The effect of this improved estimation is that the change that the surgeon damages a critical structure of the patient is reduced.

Figure 2 schematically shows a haptic feedback method 300. The method may be implemented in a controller of a haptic feedback device. The method starts with retrieving 310 information on locations of critical structures in an area of the body. The retrieving of this information may come from a database. This database may be part of a guidance system or part of a hospital information system. This information is typically coming from a scan, such as an MRI, done prior to the operation. In an alternative embodiment, this scanning may be done during the operation in real-time or almost real-time. By doing it real-time or almost real-time, the haptic feedback device or method according to the invention may be used also in the softer tissue where the critical structures have some mobility.

The method may continue with the step of retrieving 315 information on the spatial arrangement of haptic actuators. This information is typically predefined. In an alternative embodiment the haptic arrangement may calibrate the distances between the haptic actuators based on the transmission of vibrations during a calibration procedure at start-up. The haptic actuators define a haptic interaction surface. The haptic surface is typically resilient to follow the curvature of the body of the surgeon. The haptic actuators are arranged for being in haptic communication with the surgeon.

The method may continue with the step of receiving 320 a tool tip location. The tool tip location is indicative of a location of a tool tip of an invasive tool used for invading a body area of the body during the invasive procedure, such as a surgery, in an invading direction. The tool tip is arranged for being thrusted forward in and/or sideward from the invading direction.

The tool tip may be a drill for e.g. drilling away bone of the skull for gaining access to the brain and/or parts of the skull.

A drill for this type of drilling is typically most effective drilling sideways and has limited drilling effectiveness drilling straight forward from the elongated axis of the drill.

The tool tip is typically a volume, such as the point of a drill.

The tool tip location is therefore typically a volume representing the tool tip.

The distance between the nearest critical structure and the tool tip therefore becomes the smallest distance between a volume representing the nearest critical structure and the volume of the tool tip.

The method may continue with the step of selecting 325 a nearest critical structure of the critical structures relative to the tool tip location.

The critical structures are typically represented by different volumes.

Depending on the granularity of the information on the critical structures, these critical structures are represented in memory by more data requiring more calculations.

The method may continue with the step of projecting 330 a direction of the nearest critical structure onto the haptic interaction surface.

The projecting step may be done in multiple ways as specified throughout this description.

Depending on the way of projecting the accuracy for different directions is kept stable or may vary with several advantages.

The method may continue with the step of actuating 335 one or more of the haptic actuators based on the projection.

The actuation may comprise interpolating between haptic actuators for providing a higher granularity of the haptic feedback communication.

The steps in the method may be done in parallel.

The order of the steps is randomly chosen unless the order is determined by the flow of information.

Steps may be performed multiple times in comparison to other steps of the method.

Figure 3 schematically shows the step of projecting 330. The projecting may be done with the use of a sphere having a top half 445 and a bottom half 440. Figure 3 is therefore a cross section of the sphere.

The surgeon 30 looks with his eye 35 typically through a microscope 240. The surgeon may further manipulate an invasive tool 210 having a tool tip having a tool tip location 110. The line segment from the eye of the surgeon to the tool tip location and beyond is the viewing direction 105. Perpendicular to the viewing direction an equator plane 415 is shown.

The equator plane is shown at the level of the tool tip location 110. The half of the sphere closest to the eye of the surgeon is the top half of sphere 445, the half of the sphere furthest away from the eye of the surgeon is the bottom half of the sphere 440.

The eye of the surgeon may have a field of view having boundaries forming a viewing cone 37, 37’ having a focal point 36 at the eye of the surgeon. The radius of the sphere may be determined by or derived from the viewing cone or predefined as 1. If the radius is predefined and/or set to one, the size of the haptic surface might have to be scaled to fit onto the area covered by the haptic actuator arrangement.

The figure further shows a nearest critical structure 420. The line segment between the tool tip location 110 and the nearest critical structure 420 has a direction 425, which may be normalized to a unit vector 430 relative to the sphere. The semisphere location 450 on the sphere pointed at by the unit vector is the projection of the nearest critical structure on the bottom half of the sphere. The last step of projection may be mapping of the semisphere location onto the haptic interaction surface. The haptic interaction surface may be represented by the equator plane, but may also be represented by surfaces positioned elsewhere, but typically perpendicular to the viewing direction.

It should further be noted that the haptic interaction surface is advantageously oriented such that it is prevented that the surgeon does have to mentally rotate the haptic surface to match his field of view. Thus, e.g. a direction above the tip location with regard to the field of view of the surgeon is shown on the haptic surface above the centre point of the haptic surface, such as higher up on the back of the surgeon. The orientation of the field of view of the surgeon, specifically the orientation of the microscope, may be provided by the guidance system.

Figure 4 schematically shows an embodiment of the step of mapping 500. The radius 505 of the sphere equals the sides of the mapping 510, 510’. Figure 4 is therefore a cross section of the sphere. The sides of the mapping define the edge of the haptic interaction surface 520, and form a cylinder. The mapping has a focal point at infinity. The vectors 525, 525’, 525” indicate arbitrary mappings shown as examples. Each of the vectors ends at a specific point 526, 526’, 526” on the bottom half of the semisphere 440. This specific point indicates a specific direction. Further, each of the vectors has a specific intersection 527, 527°, 527” with the haptic interaction surface.

Each of these intersections specifies a specific mapping from a specific direction to a specific intersection, which is a one-to-one mapping or unambiguous mapping. This mapping may be labelled as orthographic mapping.

Figure 5 schematically shows an embodiment of the step of mapping 550. Figure 5 is therefore a cross section of the sphere. The sides of the mapping 510, 510’ define the edge of the haptic interaction surface 520, and form a cone. The mapping has a focal point 530 at a radius distance from the sphere. Thus, the distance between the focal point and the centre of the sphere is two times the radius of the sphere. Alternative distances between the focal point and the centre of the sphere are possible. The vectors 525, 525’, 525” indicate arbitrary mappings shown as examples. Each of the vectors ends at a specific point on the bottom half of the semisphere 440, similar to Figure 4. This specific point indicates a specific direction. Further, each of the vectors has a specific intersection with the haptic interaction surface, similar to Figure

4. Each of these intersections specifies a specific mapping from a specific direction to a specific intersection, which is a one-to-one mapping or unambiguous mapping. This mapping may be labelled as MEO near-side general perspective mapping. A disadvantage of this mapping may be that the bottom part of the semisphere cannot unambiguously mapped. The bottom part of the semisphere is used to indicate directions which are close to parallel to or at a shallow angle with the equator plane. Figure 6 schematically shows an embodiment of the step of mapping 560. The sides of the mapping 510, 510’ define the edge of the haptic interaction surface 520, and form a cone. The mapping has a focal point 530 at minus two and a half times the radius of the sphere. Thus, the distance between the focal point and the centre of the sphere is minus one and a half times the radius of the sphere. Alternative distances between the focal point and the centre of the sphere are possible. The vectors 525, 525’, 525" indicate arbitrary mappings shown as examples. Each of the vectors ends at a specific point of the haptic surface 520, in contrast to Figure 4. This specific point indicates a specific direction. Further, each of the vectors has a specific intersection with the haptic interaction surface, similar to Figure 4. Each of these intersections specifies a specific mapping from a specific direction to a specific intersection, which is a one-to-one mapping or unambiguous mapping for the larger and/or important part of the directions. This mapping may be labelled as James far- side general perspective mapping. Note that specifically around the edge of the semisphere and/or the edge of the haptic surface the mapping may become ambiguous depending on the selected mapping. Other mappings are foreseen by the inventor and are within the scope of the invention. Figure 7 schematically shows an embodiment of an arrangement of haptic actuators 600. This arrangement has 12 vertices forming 13 triangles. The number of vertices equals the number of haptic actuators located at the vertices. The triangles identify the areas of interpolation for the three haptic actuators located at the corners or respective vertices of the triangle.

Figure 8 schematically shows an embodiment of an arrangement of haptic actuators 601. This arrangement has 10 vertices forming 10 triangles. Rotating this arrangement slightly left or right allows to place this arrangement substantially symmetrically around the spine.

Figure 9 schematically shows an embodiment of an arrangement of haptic actuators 602. This arrangement has 14 vertices forming 16 triangles. Rotating this arrangement left or right allows to place this arrangement substantially symmetrically around the spine. It is further noted that the triangles of this arrangement are substantially the same shape and/or size providing the advantage of similar perception of the interpolation.

Figure 10 schematically shows an embodiment of an arrangement of haptic actuators 603. This arrangement has 16 vertices forming 20 triangles.

Figure 11 schematically shows an embodiment of an arrangement of haptic actuators 604. This arrangement has 12 vertices forming 14 triangles. Without rotating this arrangement may be placed substantially symmetrically around the spine. It is further noted that the triangles of this arrangement are substantially of the same shape and/or size providing the advantage of similar perception of the interpolation.

Figure 12 schematically shows an embodiment of a computer program product 1000, computer readable medium 1010 and/or non-transitory computer readable storage medium comprising computer readable code 1020 according to the invention.

Examples, embodiments or optional features, whether indicated as non- limiting or not, are not to be understood as limiting the invention as claimed.

It should be noted that the figures are purely diagrammatic and not drawn to scale. In the figures, elements which correspond to elements already described may have the same reference numerals.

It will be appreciated that the invention also applies to computer programs, particularly computer programs on or in a carrier, adapted to put the invention into practice. The program may be in the form of a source code, a code intermediate source and an object code such as in a partially compiled form, or in any other form suitable for use in the implementation of the method according to the invention. It will also be appreciated that such a program may have many different architectural designs. For example, a program code implementing the functionality of the method or system according to the invention may be sub-divided into one or more sub-routines.

Many different ways of distributing the functionality among these sub-routines will be apparent to the skilled person.

The sub-routines may be stored together in one executable file to form a self-contained program.

Such an executable file may comprise computer-executable instructions, for example, processor instructions and/or interpreter instructions (e.g.

Java interpreter instructions). Alternatively, one or more or all of the sub-routines may be stored in at least one external library file and linked with a main program either statically or dynamically, e.g. at run-time.

The main program contains at least one call to at least one of the sub-routines.

The sub-routines may also comprise function calls to each other.

An embodiment relating to a computer program product comprises computer-executable instructions corresponding to each processing stage of at least one of the methods set forth herein.

These instructions may be sub- divided into sub-routines and/or stored in one or more files that may be linked statically or dynamically.

Another embodiment relating to a computer program product comprises computer-executable instructions corresponding to each means of at least one of the systems and/or products set forth herein.

The carrier of a computer program may be any entity or device capable of carrying the program.

For example, the carrier may include a data storage, such as a ROM, for example, a CD ROM or a semiconductor ROM, or a magnetic recording medium, for example, a hard disk.

Furthermore, the carrier may be a transmissible carrier such as an electric or optical signal, which may be conveyed via electric or optical cable or by radio or other means.

When the program is embodied in such a signal, the carrier may be constituted by such a cable or other device or means.

Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted to perform, or used in the performance of, the relevant method.

The term “substantially” herein, such as in “substantially all emission” or in “substantially consists”, will be understood by the person skilled in the art.

The term “substantially” may also include embodiments with “entirely”, “completely”, “all”, etc.

Hence, in embodiments the adjective substantially may also be removed.

Where applicable, the term “substantially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including

100%. The term “comprise” includes also embodiments wherein the term “comprises” means “consists of”.

The term "functionally" will be understood by, and be clear to, a person skilled in the art. The term “substantially” as well as “functionally” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective functionally may also be removed. When used, for instance in “functionally parallel”, a skilled person will understand that the adjective “functionally” includes the term substantially as explained above. Functionally in particular is to be understood to include a configuration of features that allows these features to function as if the adjective “functionally” was not present. The term “functionally” is intended to cover variations in the feature to which it refers, and which variations are such that in the functional use of the feature, possibly in combination with other features it relates to in the invention, that combination of features is able to operate or function. For instance, if an antenna is functionally coupled or functionally connected to a communication device, received electromagnetic signals that are receives by the antenna can be used by the communication device. The word “functionally” as for instance used in “functionally parallel” is used to cover exactly parallel, but also the embodiments that are covered by the word “substantially” explained above. For instance, “functionally parallel’ relates to embodiments that in operation function as if the parts are for instance parallel. This covers embodiments for which it is clear to a skilled person that it operates within its intended field of use as if it were parallel.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The devices or apparatus herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim.

The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer.

In the device or apparatus claims enumerating several means, several of these means may be embodied by one and the same item of hardware.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The invention further applies to an apparatus or device comprising one or more of the characterising features described in the description and/or shown in the attached drawings.

The invention further pertains to a method or process comprising one or more of the characterising features described in the description and/or shown in the attached drawings.

The various aspects discussed in this patent can be combined in order to provide additional advantages.

Furthermore, some of the features can form the basis for one or more divisional applications.

EMBODIMENTS

1. Haptic feedback device (100) arranged for being part of a guidance system (200) for aiding a surgeon (30) during an invasive procedure on a body (20), wherein the haptic feedback device comprises: - haptic actuators arranged for having a spatial arrangement defining a haptic interaction surface (520), and for being in haptic communication (115) with the surgeon; and - a controller arranged for: - retrieving (310) information on locations of critical structures in an area of the body; - retrieving (315) information on the spatial arrangement of the haptic actuators; - receiving (320) a tool tip location (110) indicative of a location of a tool tip of an invasive tool (210) used for invading a body area of the body during the invasive procedure in an invading direction, wherein the tool tip is arranged for being thrusted forward in and/or sideward from the invading direction; - selecting (325) a nearest critical structure (420) of the critical structures relative to the tool tip location; - projecting (330) a direction of the nearest critical structure onto the haptic interaction surface; and - actuating (335) one or more of the haptic actuators based on the projection.

2. Haptic feedback device according to the preceding embodiment, wherein the spatial arrangement of the haptic actuators is a 2D spatial arrangement.

3. Haptic feedback device according to any of the preceding embodiments, wherein the guidance system comprises a microscope (240) for displaying to the surgeon at least partly a body surface of the body area invaded, having a viewing direction (105); and wherein the controller is arranged for receiving a viewing direction; and wherein the projecting is based on the viewing direction.

4. Haptic feedback device according to the preceding embodiment, wherein projecting comprises: - defining an equator plane (415) at the tool tip location and perpendicular to the viewing direction; - defining a semisphere (440) having its centre at the tool tip location and below the equator plane with regard to the viewing direction; - calculate a semisphere location (450) on the semisphere based on a vector (430) from the tool tip location towards the nearest critical structure; and - mapping (500, 550, 560) the semisphere location onto a haptic location (527, 527, 527”) of the haptic interaction surface.

5. Haptic feedback device according to the preceding embodiment, wherein the mapping is based on: - an orthographic infinity projection; - a near-side general perspective, such as a GEO, a MEO or a LEO near-side general perspective, preferably based on a focal point in the range of 0.01 to infinity, more preferably in the range of 0.02 to10, most preferably around 0.05, 1 or 5.62; - a Gnomonic projection; - a Stereographic projection; - a far-side general perspective, such as a Twilight, a Clarke, a James or La Hire far-side general perspective; - an azimuthal projection, more specific an azimuthal equidistant projection; or - a projection based on a focal point in the range of -6 to 0.3, more preferably in the range of -4 to 0.5, most preferably around -2.7, -2.5, -2.4, -2, -1.7 or -1.

6. Haptic feedback device according to any of the preceding embodiments 4-5, wherein the haptic interaction surface has a circumference, which is substantially a circular surface.

7. Haptic feedback device according to any of the preceding embodiments 4-6, wherein the haptic actuators are arranged to predefined locations in the haptic interaction surface.

8. Haptic feedback device according to any of the preceding embodiment 4-7, wherein, when the haptic location is unequal to a location of any of the haptic actuators, actuating comprises actuating two or more haptic actuators for perceiving a haptic actuation signal by the surgeon at the haptic location.

9. Haptic feedback device according to any of the preceding embodiments 4-8, wherein calculating comprises if the nearest critical structure is located above the equator plane with regard to the viewing direction, placing the semisphere location on the rim of the semisphere.

10. Haptic feedback device according to any of the preceding embodiments, wherein the haptic actuators are arranged for being in haptic communication with the back of the surgeon.

11. Haptic feedback device according to the preceding embodiment, wherein the haptic actuators are arranged for being on both sides of the spine in haptic communication with the surgeon.

12. Haptic feedback device according to any of the preceding embodiments 10-11, wherein the haptic actuators are arranged for being symmetrical around the spine in haptic communication with the surgeon.

13. Haptic feedback device according to any of the preceding embodiments 10-12, wherein the arrangement of haptic actuators comprises 10, 12, 14, or 16 haptic actuators.

14. Haptic feedback device according to any of the preceding embodiments, wherein projecting comprises: - calculate a distance between the tool tip location and the nearest critical structure; and - mapping the distance to an activation pattern for the one or more of the haptic actuators.

15. Haptic feedback device according to the preceding embodiment, wherein the activation pattern comprises one or more of the group of a vibration frequency, a vibration amplitude, a vibration activation duration and a vibration activation interval.

16. Guidance system (200) for aiding a surgeon (30) during an invasive procedure on a body (20) comprising critical structures, wherein the system comprises: - an invasive tool (210) for invading a body area of the body during the invasive procedure in an invading direction, wherein the invasive tool is having a tool tip arranged for being thrusted forward in and/or sideward from the invading direction, which tool tip has a tool tip location (110); - a microscope (240) for displaying to the surgeon at least partly a body surface of the body area invaded, having a viewing direction; and - a haptic feedback device (100) comprising haptic actuators arranged for being in haptic communication (115) with the surgeon wherein actuation (335) of the haptic actuators is indicative of a direction based on, and preferably a distance between, the tool tip and a nearest critical structure (420) of the critical structures.

17. Method (300) for a haptic feedback for a guidance system (200) for aiding a surgeon (30) during an invasive procedure on a body (20), wherein the haptic feedback method comprises: - retrieving (310) information on locations of critical structures in an area of the body; - retrieving (315) information on the spatial arrangement of haptic actuators defining a haptic interaction surface (520), and arranged for being in haptic communication (115) with the surgeon; - receiving (320) a tool tip location (110) indicative of a location of a tool tip of an invasive tool (210) used for invading a body area of the body during the invasive procedure in an invading direction, wherein the tool tip is arranged for being thrusted forward in and/or sideward from the invading direction; - selecting (325) a nearest critical structure (420) of the critical structures relative to the tool tip location; - projecting (330) a direction of the nearest critical structure onto the haptic interaction surface; and - actuating (335) one or more of the haptic actuators based on the projection.

18. System comprising a microprocessor arranged and loaded with software for carrying out the preceding method.

19. Computer program product (1000) comprising a computer readable medium (1010) having computer readable code (1020) embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the steps of the controller of embodiments 1-15, or method 17.

Claims

CONCLUSIONS

A haptic feedback device (100) arranged to form part of a guidance system (200) for supporting a surgeon (30) during an invasive procedure on a body {20}, the haptic feedback device comprising: - haptic actuators which are arranged to have a spatial arrangement defining a haptic interaction surface (520), and to be in haptic communication (115) with the surgeon; and - a controller for: - retrieving (310) information about locations of critical structures in an area of the body; - retrieving (315) information about the spatial arrangement of the haptic actuators; - receiving (320) a tool tip location (110) indicative of a tool tip location of an invasive tool (210) used to penetrate a body region of the body during the invasive procedure in an invasive direction, wherein the tool tip is adapted to be pushed forward and/or sideways from the penetrating direction; - selecting (325) a closest critical structure (420) of the critical structures relative to the tool tip location; - projecting {330} a direction of the nearest critical structure onto the haptic interaction surface; and - controlling (335) one or more of the haptic actuators based on the projection.

A haptic feedback device according to the preceding claim, wherein the spatial arrangement of the haptic actuators is a 2D spatial arrangement.

The haptic feedback device of any preceding claim, wherein the guidance system comprises a microscope (240) for displaying to the surgeon at least partially a body surface of the invaded body region, with a viewing direction (105); and wherein the control unit is adapted to receive a viewing direction; and wherein the projection is based on the viewing direction.

A haptic feedback device according to the preceding claim, wherein the projecting comprises: - defining an equator plane (415) at the tool tip position and perpendicular to the viewing direction; - defining a hemisphere (440) with its center at the tool tip position and below the equator plane with respect to the viewing direction; - calculating a hemisphere location (450) on the hemisphere based on a vector (430) from the tool tip location to the nearest critical structure; and - mapping (500, 550, 560) the hemisphere location to a haptic location (527, 527°, 527'') of the haptic interaction surface.

A haptic feedback device according to the preceding claim, wherein the mapping is based on: - an orthographic infinity projection; - a close general perspective, such as a GEO, a MEO or a LEO close general perspective, preferably based on a focal point in the range from 0.01 to infinity, more preferably in the range from 0.02 to 10, with the most preferably around 0.05, 1, or 5.62; - a gnomonic projection; - a stereographic projection; - a far general perspective, such as a Twilight, a Clarke, a James or La Hire far general perspective, - an azimuthal projection, more specifically an azimuthal equidistant projection; or - a projection based on a focal point in the range of -6 to 0.3, more preferably in the range of -4 to 0.5, most preferably around -2.7, -2.5, - 2 ,4, -2,-1.7 or 1.

A haptic feedback device according to any one of the preceding claims 4-5, wherein the haptic interaction surface has a periphery which is substantially a circular surface.

A haptic feedback device according to any one of the preceding claims 4-6, wherein the haptic actuators are arranged at predetermined locations in the haptic interaction surface.

A haptic feedback device according to any one of the preceding claims 4-7, wherein, when the haptic location is different from a location of one of the haptic actuators, the driving controls two or more haptic actuators to sense a haptic activation signal by the surgeon at the haptic location.

A haptic feedback device according to any one of the preceding claims 4-8, wherein the calculating comprises locating the hemisphere location on the edge of the hemisphere if the closest critical structure is above the equatorial plane with respect to the viewing direction.

A haptic feedback device according to any one of the preceding claims, wherein the haptic actuators are adapted to be in haptic communication with the surgeon's back.

A haptic feedback device according to the preceding claim, wherein the haptic actuators are adapted to be in haptic communication with the surgeon on both sides of the spinal column.

A haptic feedback device according to any one of the preceding claims 10-11, wherein the haptic actuators are arranged to be in haptic communication with the surgeon symmetrically about the spinal column.

A haptic feedback device according to any one of the preceding claims 10-12, wherein the arrangement of haptic actuators comprises 10, 12, 14 or 16 haptic actuators.

A haptic feedback device according to any one of the preceding claims, wherein the projecting comprises: - calculating a distance between the tool tip location and the nearest critical structure; and - mapping the distance to an activation pattern for one or more of the haptic actuators.

The haptic feedback device of the preceding claim, wherein the activation pattern comprises one or more of the group of a vibration frequency, a vibration amplitude, a vibration activation duration and a vibration activation interval.

A guide system (200) for assisting a surgeon (30) during an invasive procedure on a body (20) comprising critical structures, the system comprising: - an invasive tool (210) for penetrating a body region of the body in an invasive direction during the invasive procedure, the invasive tool having a tool tip adapted to be pushed forward and/or sideways from the entering direction, the tool tip having a tool tip position (110); - a microscope (240) for displaying to the surgeon at least partially a body surface of the entered body region, with a viewing direction; and - a haptic feedback device (100) comprising haptic actuators arranged to be in haptic communication (115) with the surgeon, the actuation (335) of the haptic actuators being indicative of a direction, and preferably a distance between, the tool tip and a closest critical structure (420) of the critical structures.

A haptic feedback method (300) for a guidance system (200) for supporting a surgeon (30) during an invasive procedure on a body (20), the haptic feedback method comprising: - retrieving (310) information about locations of critical structures in an area of the body; - retrieving (315) information about the spatial arrangement of haptic actuators defining a haptic interaction surface (520), and arranged to be in haptic communication (115) with the surgeon; - receiving (320) a tool tip location (110) indicative of a tool tip location of an invasive tool (210) used to enter a body region of the body during the invasive procedure in an entering direction, wherein the tool tip is adapted to be pushed forward and/or sideways from the entering direction; - selecting (325) a closest critical structure (420) of the critical structures relative to the tool tip location; - projecting (330) a direction of the nearest critical structure onto the haptic interaction surface; and - controlling (335) one or more of the haptic actuators based on the projection.

18. System comprising a microprocessor configured and loaded with software for performing the foregoing method.

A computer program product (1000) comprising a computer readable medium (1010) with computer readable code (1020) embodied therein, the computer readable code being configured such that, when executed by a suitable computer or processor, the computer or processor is caused to perform the steps of perform the controller of claims 1-15 or method 17.