Precision adjustment of navigated medical device

Abstract

It is proposed that medical devices that have not been quality-controlled do not need to be discarded, but can be reprocessed. In particular, a marked center position of a medical device is adjusted relative to a Point of Interest (POI) position of the medical device such that a difference between a calculated POI position and an actual POI position of a particular medical device is within an acceptable tolerance range.

Description

Technical Field

[0001] The present invention relates to a method for spatially adjusting the center position of a marker associated with a medical device having a point of interest, a corresponding computer program, a computer-readable storage medium storing the program, and a computer executing the program. Background Art

[0002] As is well known, navigational medical devices (such as pointers or styluses) have a point of interest (such as a tip). Such devices are provided with two or more markers and have a predefined geometry representing the spatial relationship between the markers and the point of interest. The predefined geometry is provided to a medical navigation system, which locates the markers and calculates the calculated position of the point of interest based on the marker positions and the predefined geometry. This assumes that each specifically designed device actually has a predefined geometry. The purpose of the present invention is to prove that the actual geometry of the medical device is within the acceptable range of the predefined geometry.

[0003] During the production of medical devices, deviations may occur between the predefined geometry and the actual geometry of a specific device. Therefore, quality control is often required. In this quality control, the actual geometry is measured and compared to the predefined geometry. In current processes, devices with deviations exceeding a certain threshold are discarded.

[0004] Various aspects, examples and exemplary steps of the invention and their embodiments are disclosed below.Different exemplary features of the invention may be combined according to the invention as far as this is technically feasible. Summary of the invention

[0005] The following briefly describes the specific features of the present invention, and it should not be understood that the present invention is limited to the features or feature combinations described in this section.

[0006] According to the present invention, medical devices that fail quality control need not be discarded but rather reprocessed. In particular, the position of the center of the marker of the medical device is adjusted relative to the position of the point of interest (POI) of the medical device so that the difference between the calculated position of the POI of a particular medical device and the actual position of the POI is within an acceptable tolerance range. In this context, the calculated position is calculated based on the measured position of the center of the marker of the device and the predefined geometry of the medical device. The actual position of the POI usually needs to be measured.

[0007] In this summary, general features of the invention have been described, for example, by reference to possible embodiments of the invention.

[0008] In general, a first aspect of the present invention provides a method for spatially adjusting a center position of a marker associated with a medical device having a point of interest. The method comprises performing the following exemplary steps.

[0009] In a (eg first) exemplary step, an initial position of the center relative to the point of interest is measured.

[0010] In a (eg second) exemplary step, a corrected position of the center relative to the point of interest is calculated.

[0011] In the (eg third) exemplary step, the marker is adjusted so that the center position of the marker matches the calibration position.

[0012] As used herein, the term "location" defines the position of a particular point in up to three translational dimensions. "Position" is a combination of location and rotational orientation in up to three rotational dimensions.

[0013] Measuring the initial position of the center of the marker relative to the point of interest typically uses a medical tracking system that measures the position of the center of the marker in the reference frame of the medical tracking system. For reflective markers, the medical tracking system typically includes a stereo camera, and for electromagnetic markers, the medical tracking system includes an electromagnetic transmitter or receiver.

[0014] In order to measure the initial position of the center relative to the interest point, not only the center of the marker must be measured, but also the position of the interest point must be known.

[0015] One option for measuring the location of the point of interest is to use a reference tool whose reference point is adjacent to the point of interest of the medical device when the medical device is correctly positioned on the reference tool. The reference point may be the bottom of a docking station for receiving the point of interest, such as a tip.

[0016] The reference tool may be arranged at a known position in the reference system of the medical tracking system, so that the position of the docking station in the reference system of the medical tracking system is known. This means that if the point of interest of the medical device is correctly placed at the docking station, the position of the point of interest of the medical device in the reference system of the medical tracking system is also known. Additionally or alternatively, the reference tool may include reference markers that can be detected by the medical tracking system in order to determine the position of the reference tool in the reference system of the medical tracking system.

[0017] As another option, a navigation pointer can be used to sample the location of the medical device's point of interest. The pointer has a tip and a plurality of pointer markers that can be detected by the medical tracking system. Based on the known pointer geometry and the pointer marker locations, the location of the pointer tip can be determined, and the location of the pointer tip corresponds to the location of the medical device's point of interest.

[0018] In a typical application, a medical device is positioned in a reference tool as a holder for the medical device so that the point of interest of the medical device is located at a reference point of the reference tool. For example, the tip of the medical device is positioned in a groove of the reference tool. Preferably, the groove is opposite in shape to the tip so that the tip is accommodated in a predefined orientation. The reference tool is usually positioned so that the tip falls into the groove due to gravity.

[0019] The medical tracking system is then used to determine the position of the reference marker and the position of the medical device marker. Based on the known reference tool geometry, in particular describing the position of the reference marker relative to the groove (groove bottom), the position of the groove in the reference system of the medical tracking system can be calculated. This position is used as the measured actual position of the point of interest of the medical device in the reference system of the medical tracking system. The medical tracking system can also be used to measure the initial position of the center of the marker in the reference system of the medical tracking system. From this information, the initial position of the center relative to the point of interest is known.

[0020] In this document, the term "marker" refers to a marker of a medical device. If it refers to a marker of another object, the corresponding expression is used. In addition, the term "center" generally refers to the center of a marker. In addition, the expression "point of interest" refers to a point of interest of a medical device.

[0021] For a perfect medical device, the initial position of the center (relative to the measured position of the point of interest) is equal to the predefined position of the center (relative to the predefined position of the point of interest, represented by the predefined geometric shape). From another perspective, the initial calculated position of the point of interest of the medical device can be calculated based on the measured initial position of the center and the predefined geometric shape of the medical device. If the difference between the initial calculated position of the point of interest and the measured position of the point of interest is below a predetermined threshold, the medical device is determined to be usable.

[0022] However, if the distance is higher than a predetermined threshold, the medical device is determined to be unusable. However, such a medical device is not discarded, but reprocessed to make it usable. In particular, the marked center position of the medical device is modified to a correction position, so that the POI calculated position calculated based on the center correction position and the predefined geometric shape is consistent with the actual position of the POI or differs at most by a predetermined threshold. Therefore, when calculating the position of the POI, the actual measured position of the POI is the target position of the POI.

[0023] Such reworking of the medical device involves calculating a corrected position of the center relative to the point of interest. If the marking of the medical device is at its corrected position, the calculated position of the point of interest of the medical device is calculated using the predefined geometry of the medical device, resulting in a position of the point of interest that corresponds to the target position. In this context, "correspond" means an exact match or a match within an allowed tolerance. The corrected position is defined, for example, in the reference system of the medical tracking system.

[0024] Thus, the method further involves adjusting the marker of the medical device so that the marker center position matches the correct position. After such adjustment, the predefined geometry can be used for the reworked medical device and the position of the point of interest is calculated based on the measured position of the marker center.

[0025] In one embodiment, the marker is a planar reflective marker, such as a retroreflective marker. The marker may be a patch that should be attached to a predetermined position on the medical device, but manufacturing tolerances may cause deviations from the predetermined position. In this embodiment, adjusting the marker involves making a portion of at least one marker non-reflective. The adjusted marker is smaller in size than the initial marker. The center of the marker is moved by the adjustment.

[0026] By making a portion of the planar reflective marker non-reflective, the marker center can only be displaced in the plane of the marker. Therefore, if all markers of the medical device are located in the same plane or parallel planes, the markers cannot be relatively displaced in the vertical direction of the plane. To overcome this, planar reflective markers can be arranged on the flat surface of the medical device, which are inclined relative to the plane where the marker center is located, and optionally, can also be inclined relative to each other. Based on the non-reflective portion of at least one marker, the relative position of the marker center of the medical device can be adjusted in three-dimensional space.

[0027] In one embodiment, rendering a portion of the marking non-reflective involves applying a non-reflective coating to the portion of the marking, removing the portion of the marking, or deactivating the portion of the marking. The non-reflective coating may be applied using a jetting technique commonly used with inkjet printers. Radiation (e.g., laser) may be used to cut or burn away a portion of the marking, thereby removing the portion of the marking. Deactivating a portion of the marking refers to using radiation to darken the portion of the marking.

[0028] In one embodiment, adjusting the marker involves modifying the orientation of at least one marker relative to the medical device. This embodiment is applicable to various markers, such as planar reflective markers, spherical reflective markers, electromagnetic markers, etc. In this embodiment, the size and / or shape of the marker is not modified, but only the orientation of the marker is modified.

[0029] In one embodiment, modifying the orientation of a marker relative to the medical device involves adjusting a mechanical adjustment mechanism that allows the corresponding marker to move in at least one of up to three rotational dimensions and / or up to three translational dimensions, for example by adjusting one or more adjustment members, such as adjustment screws.

[0030] In one embodiment, modifying the orientation of the marker relative to the medical device involves adjusting the orientation of the marker and hardening the connection between the marker and the medical device. There are many exemplary implementations of this embodiment.

[0031] In one embodiment, the marker is attached to a support (such as a rod), the free end of which is inserted into a soft glue or any soft material, which can harden once the marker is in its desired position. The soft medium that hardens in this process refers to the connection of this embodiment. For example, the above-mentioned mechanical adjustment mechanism or other device (such as a mechanical arm) can be used to bring the marker into the correct position. However, once the connection is hardened, the adjustment mechanism can be removed.

[0032] In another embodiment, the connection between the marker and the medical device is first softened, for example by heating, and then the orientation is modified and the connection is hardened again.

[0033] In one embodiment, calculating the corrected position of the center involves finding an optimized position of the center to minimize the distance between the calculated position of the medical device point of interest and the target position of the medical device point of interest. It should be noted that the position does not have to be absolutely optimized, but can be optimized within a certain granularity of optimization, such as a granularity of one tenth of a millimeter, one hundredth of a millimeter, or one thousandth of a millimeter.

[0034] In this embodiment, the calculated position of the point of interest is calculated based on a set of candidate positions for the center and universal calibration data representing the predefined geometry of the medical device. The set of candidate positions includes a candidate position for each mark of the medical device. The candidate positions are hypothetical positions or positions under test for which the calculated position of the point of interest is calculated using the predefined geometry of the medical device that the medical device should satisfy. In other words, this embodiment uses these candidate positions as optimized positions for the center of the mark so that the calculated position of the point of interest matches the target position of the point of interest when calculated based on the set of candidate positions for the center. Again, a small deviation may be acceptable.

[0035] In one embodiment, the predefined geometry of the medical device represents a predefined position of a center of a marker of an ideal medical device and a predefined position of a point of interest. Calculating the calculated position of the point of interest involves transforming the predefined geometry so that the predefined position of the center is aligned with the candidate position of the center, and using the position of the point of interest in the transformed predefined geometry as the calculated position of the point of interest. In other words, the predefined geometry of the medical device is transformed so that the position of the center of the marker of the predefined geometry matches the measured position of the center of the marker. For example, this involves rigid matching, where the transformation of the predefined geometry is limited to uniform scaling of the predefined geometry in three orthogonal dimensions, rotation of the predefined geometry in up to three rotational dimensions, and translation of the scaled and rotated predefined geometry in up to three orthogonal translational dimensions. When the marker in the transformed predefined geometry matches the measured marker, the position of the point of interest in the transformed predefined geometry is the calculated position of the point of interest.

[0036] In one embodiment, calculating the corrected position of the center involves calculating multiple calculated positions of the interest point, one calculated position for each of a plurality of candidate positions of the center, and selecting the candidate position that results in the smallest distance between the corresponding calculated position of the interest point and the target position of the interest point as the calculated position of the center.

[0037] Typically, this process may take the form of a brute force approach, where each of a plurality of candidate position sets is tested. However, it is preferred to use a suitable optimization method that is less computationally expensive.

[0038] In one embodiment, multiple candidate position sets are selected from a search space that is limited to the reachable positions of the center. Limiting the search space reduces computational complexity because there is no need to test impossible candidate positions.

[0039] In one embodiment, the reachable position of the center is determined by the properties of the corresponding marker. For example, for a spherical reflective marker or an electromagnetic marker, the properties describe the adjustable range of the marker position. For example, the range depends on the properties of the mechanical adjustment mechanism or the adjustable range of the connection between the marker and the medical device before the connection hardens.

[0040] If the marker is a planar reflective marker, the characteristics may be the minimum marker size and / or the possible location of the marker center. The minimum size is the size required for the medical tracking system to reliably locate the marker, which may be 1 cm, for example. 2 , 1.5cm 2 or 2cm 2If adjusting a mark involves making a portion of the mark non-reflective, this means that the area of ​​the adjusted mark or the remaining reflective portion must be within the area of ​​the mark before adjustment. For circular reflective marks, the minimum size is that the distance between the center of the mark and the boundary of the mark before adjustment cannot exceed the minimum radius required for the adjusted mark.

[0041] In one embodiment, the predefined geometry of the medical device represents a predefined position of a center of a marker and a predefined position of a point of interest, and calculating the calculated position of the point of interest involves generating a plurality of transformation matrices, including a transformation matrix for each marker. Each transformation matrix represents a transformation of the predefined position of the center of the marker into the predefined position of the point of interest. The transformation matrix describes the spatial relationship between the predefined position of the center of the marker and the predefined position of the point of interest. Therefore, the result of multiplying the transformation matrix by the position of the center of the marker is the predefined position of the point of interest.

[0042] Calculating the calculated position of the interest point also involves combining multiple transformation matrices into a total transformation matrix, and multiplying the total transformation matrix with the candidate matrix containing the candidate position set. The result of such multiplication is a vector representing the calculated position of the interest point of the candidate position set.

[0043] The advantage of this embodiment is that the total transformation matrix describes the predefined geometric shape of the medical device, so it only needs to be calculated once. Calculating the position of the interest point only requires simple matrix multiplication, thereby reducing the computational complexity.

[0044] The arrangement of multiple transformation matrices in the total transformation matrix and the arrangement of candidate positions in the candidate matrix are determined by the specific implementation method as long as they remain consistent.

[0045] A second aspect of the present invention relates to a computer program, which, when the instructions contained in the computer program are executed by at least one computer, causes the at least one computer to: obtain measurement data of a medical device having multiple markers and points of interest, the measurement data representing an initial position of a center of the marker relative to the points of interest; and calculate correction data, the correction data representing a corrected position of the center relative to the points of interest.

[0046] The computer program thus relates to computer executable parts of the method according to the first aspect. This relates to all these parts of the first aspect.

[0047] In one embodiment, the program causes the computer to further output modification data indicating how the mark must be adjusted to make the mark center position match the correction position. The output modification data can be output to an operating device, such as a laser that processes a portion of at least one mark.

[0048] For example, the output modification data define a non-reflective part of a marking, for example as a region defined in a reference system of a medical navigation system. As another example, the output modification data describe how an adjustment device of a mechanical adjustment mechanism must be operated, for example the number of turns of an adjustment screw.

[0049] Alternatively or additionally, the present invention may relate to a signal wave (e.g., a physical signal wave generated by technical means, such as an electric wave), such as a digital signal wave, such as an electromagnetic carrier wave, carrying information representing a program (e.g., the above-mentioned program), and the program, for example, includes a code mechanism suitable for executing any or all of the computer executable steps of the method according to the first aspect. In a certain example, the signal wave is a data carrier signal carrying the above-mentioned computer program. The computer program stored on the disk is a data file, and when the file is read and transmitted, the file becomes a data stream in the form of, for example, a signal (e.g., a physical signal generated by technical means, such as an electric signal). The signal may be implemented as a signal wave, such as the electromagnetic carrier wave described herein. For example, the signal (e.g., a signal wave) is constructed to be transmitted via a computer network (e.g., a LAN, a WLAN, a WAN, a mobile network, such as the Internet). For example, the signal (e.g., a signal wave) is constructed to be transmitted by optical or acoustic data transmission. Therefore, alternatively or additionally, the second aspect of the present invention may relate to a data stream representing the above-mentioned program (i.e., including the program).

[0050] The third aspect of the present invention relates to a computer-readable storage medium storing the program according to the second aspect. The program storage medium is, for example, a non-transitory program storage medium.

[0051] A fourth aspect of the present invention relates to at least one computer (e.g., a computer), comprising at least one processor (e.g., a processor) and at least one memory (e.g., a memory), wherein the program according to the second aspect is executed by the processor, or the at least one computer comprises a computer-readable storage medium according to the third aspect.

[0052] In a fifth aspect, the present invention relates to a system, comprising: a reference tool, a tracking system, and a computer according to the fourth aspect, the computer being connected to the tracking system. The computer locates a mark on the reference tool and a mark on an instrument placed on the reference tool through the tracking system, and calculates correction data to represent the corrected position of the center of the mark on the instrument relative to the point of interest.

[0053] In one embodiment, the system further comprises a laser (for removing a portion of at least one mark) or a sprayer (for spraying liquid on a portion of at least one mark), both based on the calibration data calculated by the computer.

[0054] Alternatively or additionally, a fifth aspect of the present invention relates to a computer-readable program storage medium, for example a non-transitory program, which stores computer-executable steps for causing the computer according to the fourth aspect to execute the method according to the first aspect.

[0055] definition

[0056] This section provides definitions of specific terms used in this disclosure, and also constitutes a part of this disclosure.

[0057] Marker

[0058] The function of the marker is to be detected by a marker detection device (e.g. a camera or an ultrasound receiver, or an analysis device such as a CT or MRI device) in such a way that the spatial position of the marker (i.e. its spatial position and / or alignment) can be determined. The detection device is, for example, part of a navigation system. The marker can be an active marker. An active marker can, for example, emit electromagnetic radiation and / or waves that can be in the infrared, visible and / or ultraviolet spectral range. However, the marker can also be a passive marker, i.e., it can, for example, reflect electromagnetic radiation in the infrared, visible and / or ultraviolet spectral range or can block X-ray radiation. To this end, the marker can be provided with a surface having corresponding reflective properties, or can be made of metal in order to block X-ray radiation. The marker can also reflect and / or emit electromagnetic radiation and / or waves in the radio frequency range or in an ultrasonic wavelength. The marker preferably has a spherical and / or spheroidal shape and can therefore be referred to as a marker sphere; however, the marker can also have an angular (e.g. cubic) shape.

[0059] Pointer

[0060] The pointer is a rod including one or more (advantageously, two) marks fastened thereto, which can be used to distinguish various coordinates on a part of the body, such as spatial coordinates (i.e. three-dimensional coordinates), wherein the user guides the pointer (e.g., a part of the pointer, which has a defined and advantageously fixed position relative to at least one mark attached to the pointer) to a position corresponding to the coordinate, so that the position of the pointer can be determined by using a surgical navigation system to detect the mark on the pointer. The relative position between the mark of the pointer and the part of the pointer used to measure the coordinate (e.g., the tip of the pointer) is known, for example. The surgical navigation system is then able to assign the position (of the three-dimensional coordinate system) to a predetermined body structure, wherein the assignment can be performed automatically or through user intervention.

[0061] Medical Tracking System

[0062] A tracking system (such as a medical tracking system) shall refer to a system that may include: at least one marking device; a transmitter that emits electromagnetic waves and / or radiation and / or ultrasound; a receiver that receives electromagnetic waves and / or radiation and / or ultrasound; and an electronic data processing device connected to the receiver and / or transmitter, the data processing device (such as a computer) for example including a processor (CPU) and a working memory, the electronic data processing device processes the output of the receiver to determine the position of at least one marking device, for example, the position in the reference system of the tracking system. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The present invention is described below in conjunction with the accompanying drawings, which illustrate the background of the present invention and show specific embodiments of the present invention. However, the scope of the present invention is not limited to the specific features disclosed in the context of the accompanying drawings, in which:

[0064] Figure 1 A partial exploded view of a medical device is shown;

[0065] Figure 2 The method steps according to the present invention are shown;

[0066] Figure 3 A medical device in a reference tool is shown;

[0067] Figure 4 A brute force optimization method is shown;

[0068] Figure 5 An exemplary marking adjustment is shown;

[0069] Figure 6 A three-dimensional marker adjustment is shown. DETAILED DESCRIPTION

[0070] Figure 1 A schematic diagram of a medical device 1 is shown. The medical device 1 has a body 2 made of plastic and carrying three planar reflective markings 5a, 5b, 5c. Figure 1 In the illustration of , the marker 5 c has not yet been attached to the main body 2 .

[0071] The medical device 1 also has a shaft 3, which is made of metal and is attached to the body 2. At the end of the shaft 3 facing away from the body 2, the shaft 3 has a tip 4, which is the point of interest of the medical device.

[0072] The medical device 1 in this exemplary embodiment is a disposable probe that can be manufactured in large quantities. To track the medical device 1 with a medical tracking system, this means detecting the center position of the marker 5 and calculating the position of the tip 4 based on the detected center position of the marker 5. This requires that each medical device of the design has the same geometry, i.e., a predefined geometry known to the medical tracking system. By applying the predefined geometry to the measured position of the center of the marker 5, the medical tracking system can calculate the position of the tip 4.

[0073] However, the medical device 1 may not have the predefined geometry for a number of reasons. The first reason is that one or more of the markers 5 are not in the ideal position on the body 2. Another reason is that the shaft 3 is not straight. Yet another reason is that the shaft is not properly assembled to the body 2. Any imperfections in the actual medical device 1 may cause the actual orientation of the tip 4 to deviate from the calculated orientation of the tip 4, which is calculated based on the measured positions of the markers 5 and the predefined geometry of the medical device.

[0074] Figure 2 The flowchart of shows exemplary steps of a method for spatially adjusting a center position of a marker 5 associated with a medical instrument 1 having a point of interest, ie, the tip 4 .

[0075] Step S01, placing the medical device 1 in the reference tool 6, such as Figure 3 The reference tool 6 has markings 6a, 6b, 6c, 6d and a groove 8 for receiving the tip 4 of the medical instrument 1. The bottom of the groove 8 is a reference position of the tip 4 at a predetermined position in the reference tool 6. For the medical tracking system, the geometry of the reference tool 6 is known, which defines the relative positions of the markings 6a, 6b, 6c, 6d and the groove 8.

[0076] Step S02 , using a medical tracking system to measure the initial position of the center of the marker 5 relative to the tip 4 .

[0077] The two images captured by the camera 7 of the medical tracking system show each marker from slightly different viewing directions. The medical tracking system analyses the images and determines the position of the centre of the marker in the reference system of the medical tracking system, which position is associated with the camera 7, for example.

[0078] The medical tracking system measures the initial position of the center of the marker 5 and also measures the positions of the reference markers 6a, 6b, 6c, 6d. From the positions of the reference markers 6a, 6b, 6c, 6d and the known geometry of the reference tool 6, the medical tracking system derives the reference position of the bottom of the groove 8 and thus the actual position of the tip 4. Thus, the medical tracking system measures the initial position of the center of the marker 5 relative to the tip 4. The actual position of the tip 4 is used as the target position of the tip 4 when subsequently calculating the corrected position of the center of the marker 5.

[0079] The measured initial position of the marker center is given by the vector x m,i =(t mi,x ,t mi,y ,t mi,z ) T Indicates that, where t mi,x ,t mi,y ,t mi,z are the measured coordinates of the marker i in the x, y, and z dimensions, respectively. Here, i is the index of the marker 5 representing the medical device, i=1,…,n, where n is the total number of device markers. In this example, n=3.

[0080] Figure 3 The enlarged portion of FIG. 8 shows not only the tip 4 in the groove 8, but also the initially calculated position of the tip 4 indicated by the dashed outline 3a of the shaft 3. The initially calculated position of the tip 4 is calculated based on the initial position of the center of the marker 5 and the predefined geometry of the medical device 1.

[0081] When applying the predefined geometry of the medical instrument 1 to the initial position of the center of the marking 5 , the initial calculated position of the tip 4 deviates from the actual measured position of the tip 4 .

[0082] Step S03 involves calculating the total transformation matrix This total transformation matrix describes how a predefined position of the center of the marking 5 is transformed into a predefined position of the tip 4 for a predefined geometry of the medical instrument 1 .

[0083] According to the predefined geometry, the center position of the marker is x i =[t ix t iy t iz ] T , where t ix ,t iy ,t iz are the coordinates of the center of the marker i in the x, y and z dimensions respectively. Here, i is the index of the marker 5 representing the medical device, i=1,…,n, where n is the total number of device markers. In this example, n=3.

[0084] Each marker 5 has an associated transformation matrix M i , which describes how the center position of the corresponding mark is transformed into the center position of the tip 4. The general form is

[0085]

[0086] Where R i is a 3×3 rotation matrix, t i is a 3×1 translation vector, is a 1×3 zero vector, and 1 is a scalar. Thus, M i =ΠT i , since only the position of tip 4 is relevant, where:

[0087]

[0088] So the total transformation matrix is

[0089] Step S04 involves selecting a set of candidate positions for the center of the marker 5. The set of candidate positions includes one candidate position for each marker 5a, 5b, 5c. The set of candidate positions is selected from a search space that is limited to the reachable positions of the center of the marker 5. The center of the adjusted marker 5 must be within the surface of the initial marker, because the reflective part of the marker can only become smaller. The adjusted marker must have a certain minimum size, which further restricts the position of the center.

[0090] The candidate position set is represented by the following vector:

[0091]

[0092] in,

[0093]

[0094] Here, t ci,x ,t ci,y ,t ci,z are the candidate position coordinates of the marker with index i, where i = 1, 2, ..., n, and n is the number of markers of the medical device.

[0095] Step S05 involves using the total transformation matrix to calculate the calculated position of the tip 4 for a selected set of candidate positions of the centre of the marker 5, namely The calculated position of the tip 4 is calculated in the reference frame of the medical tracking system.

[0096] Step S06 involves calculating the target position of the tip 4 and the calculated position x of the tip 4 p The distance between the calculated position and the target position is, for example, the Euclidean distance between the calculated position and the target position.

[0097] Step S07 involves storing the distance calculated in step S06 as the minimum distance if the distance calculated in step S06 is less than the currently stored minimum distance. In this case, the candidate position in the set of candidate positions selected in step S04 is stored as the corrected position of the center of the marker 5. In the first iteration of the loop, the distance calculated in step S06 is automatically set to the minimum distance.

[0098] Step S08 involves determining whether there is at least one candidate location set in the search space that has not yet been investigated. If so, the flowchart returns to step S04, in which a candidate location set that has not yet been tested is selected and steps S05 to S08 are repeated with the new candidate location set.

[0099] For example, the search space is defined around an initial position of the marker center, and in particular is centered around the initial position.

[0100] Figure 4 An example table of initial positions of the centers of markers 5a, 5b, 5c is shown. In the above process, each coordinate is varied by an offset from a to i, resulting in a nine-dimensional search space. In the brute force method, the search space is processed at a predetermined offset granularity to test multiple sets of candidate positions. Each set of candidate positions results in a calculated position of the tip 4, such as Figure 4 POI1 to POI shown in the table on the right n Among the candidate position set, those candidate positions that result in the calculated position of the tip 4 closest to the target position of the tip 4 are selected as correction positions. Figure 4 In , the target location is called the target POI.

[0101] If it is determined in step S08 that all candidate position sets in the search space have been investigated, the flowchart proceeds to step S09, in which it is determined whether the minimum distance is equal to or less than a threshold value. If not, it means that the label 5 of the medical device 1 cannot be adjusted to make the medical device 1 acceptable for use. Therefore, the flowchart proceeds to step S10, in which the medical device 1 is discarded.

[0102] However, if the minimum distance is equal to or less than the threshold value, the flowchart continues with step S11 , in which the marker 5 is adjusted so that the marker center has the correct position.

[0103] Figure 3 The dotted line 3b in FIG. 3 shows a portion of the rod body 3 and the position of the portion when the center position of the marker 5 is measured again after the marker 5 is adjusted and the predetermined geometric shape of the medical device 1 is applied.

[0104] In this example, the planar reflective mark is circular, and a portion of the mark is made non-reflective using a laser (not shown). Figure 5 shown.

[0105] Figure 5 The dashed circle in shows the initial marker with the initial center position (x1, y1, z1). Figure 5 The solid circle in the figure shows the adjusted mark, where the area between the solid circle and the dotted circle is darkened or removed by laser, and the new position of the mark center is (x1', y1', z1'). The arrow indicates the displacement of the mark center after adjustment.

[0106] Here, numerical optimization can be performed instead of a brute force approach. Figure 4 The offsets a to i shown are arranged as vectors These offsets a to i are added to the initial position of the marker center to form the candidate position. The optimization to be performed is then:

[0107]

[0108] Where β1 and β2 are scalars that weight the two variable terms. The second term represents the deviation of the candidate position from the initial position, and the smaller the deviation, the better. is a vector from the reference position of the reference tool 6 (ie, the target position of the tip 4) to the calculated position of the tip 4 (ie, the position calculated based on the central initial position of the marker 5 and the predefined geometry of the medical device 1).

[0109] exist Figure 5 In, r i is the initial radius of the marker. The new marker center must be within the initial region of the marker, which implies a constraint on the corrected position of the marker center. In addition, the adjusted marker must have a minimum radius r min , in order to keep the medical tracking system detectable, this means that the constraints on specific tags are:

[0110]

[0111] Among them, θ x ,θ y ,θ z are the x, y, and z coordinates of the center of a particular marker, respectively, between the initial and corrected positions. This limit applies to each marker, and when the limits of all markers are aggregated, the vector Creates overall restrictions.

[0112] Figure 1 In the exemplary medical instrument 1 shown, all three marks 5a, 5b, 5c are planar marks located on the same plane. Therefore, it is impossible to compensate for the position deviation of the tip 4 in the direction perpendicular to this plane by adjusting the center of the mark 5.

[0113] Figure 6An exemplary arrangement is shown in which markers are arranged on an inclined surface so that the relative positions of the marker centers can be adjusted in three orthogonal translation dimensions. In this arrangement, the search space for each candidate marker position is defined by the direction of the plane in which the corresponding marker is located, the minimum size of the corresponding marker, and the initial position of the center of the corresponding marker.

[0114] exist Figure 6 In , the y-axis and z-axis are across the paper, and the x-axis is perpendicular to the paper. The plane of marker 5 is perpendicular to the paper and tilted relative to the xy plane and the xz plane, which means that the center of marker 5 can be independently shifted along the x-axis. However, shifting along the y-axis means shifting on the z-axis, and vice versa, which means that the constraints on a particular marker are:

[0115]

[0116] where a, b, c are scalars that depend on the orientation of the marking plane. y and θ z The y and z coordinates of the marker center are the offsets between the initial and corrected positions, respectively. This restriction is applied to each marker, and when the restrictions of all markers are aggregated, it will produce a vector Overall restrictions on life.

Claims

1. A method for spatially adjusting the position of a center of a marker (5) associated with a medical device (1) having a point of interest (4), the method comprising the following steps: measuring an initial position of the center relative to the point of interest (4); calculating a corrected position of the center relative to the point of interest (4); and The mark (5) is adjusted so that the center position of the mark (5) matches the correction position.

2. The method according to claim 1, wherein: The markings (5) are planar reflective markings, and adjusting the markings (5) involves making a portion of at least one marking (5) non-reflective.

3. The method according to claim 2, wherein: Making a portion of the marking (5) non-reflective involves applying a non-reflective coating on the portion of the marking (5), removing the portion of the marking (5) or disabling the portion of the marking (5).

4. The method according to any one of claims 1 to 3, wherein: Adjusting the markings (5) involves modifying the orientation of at least one marking (5) relative to the medical device (1).

5. The method according to claim 4, wherein: Modifying the orientation of the marking (5) relative to the medical device involves adjusting the mechanical adjustment mechanism.

6. The method according to any one of claims 4 or 5, wherein: Modifying the orientation of the marker (5) relative to the medical device (1) involves adjusting the orientation of the marker (1) and hardening the connection of the marker (5) to the medical device (1).

7. The method according to any one of claims 1 to 6, wherein: Calculating the corrected position of the center involves finding an optimized position of the center so that the distance between the calculated position of the point of interest (4) of the medical device (1) and the target position of the point of interest (4) of the medical device (1) is minimized, wherein the calculated position of the point of interest (4) is calculated based on a set of candidate positions of the center and universal calibration data representing a predefined geometric shape of the medical device (1).

8. The method according to claim 7, wherein: The predefined geometric shape of the medical device (1) represents the predefined position of the center of the marker (5) and the predefined position of the point of interest (4), and calculating the calculated position of the point of interest (4) involves transforming the predefined geometric shape so that the predefined position of the center is aligned with the candidate position of the center, and using the position of the point of interest (4) in the transformed predefined geometric shape as the calculated position of the point of interest (4).

9. The method according to claim 7 or 8, wherein: Calculating the corrected position of the center involves calculating multiple calculated positions of the point of interest (4) for multiple candidate position sets of the center, and selecting the candidate position that results in the smallest distance between the corresponding calculated position of the point of interest (4) and the target position of the point of interest (4) as the calculated position of the center.

10. The method according to claim 9, wherein: The plurality of candidate location sets are selected from a search space, the search space being limited to reachable locations of the center.

11. The method according to claim 7, wherein the predefined geometry of the medical device (1) represents a predefined position of a center of a marker (5) and a predefined position of a point of interest (4), and calculating the calculated position of the point of interest (4) involves: Generate multiple transformation matrices (M i ), comprising a transformation matrix for each marker (5), the transformation matrix representing the transformation of a predefined position of the center of the marker (5) into a predefined position of the point of interest (4); The multiple transformation matrices (M i ) is combined into the total transformation matrix as well as The transformation matrix and the candidate vector (X c ) are multiplied.

12. A computer program which, when run on a computer, causes the computer to: Acquiring measurement data of a medical device (1) having a plurality of markers (5) and points of interest (4), the measurement data representing initial positions of centers of the markers (5) relative to the points of interest (4); and Correction data are calculated, the correction data representing the corrected position of the center relative to the point of interest (4).

13. A computer program according to claim 12, wherein The program causes the computer to further output modification data indicating how the mark (5) must be adjusted so that the center position of the mark (5) matches the correction position.

14. A computer storing and / or running a computer program according to claim 12 or 13.

15. A non-transitory computer readable storage medium storing the computer program according to claim 12 or 13.

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