Method and apparatus for operating a dental diagnostic imaging system

Abstract

Method for operating a dental diagnostic imaging system for temporomandibular joint (TMJ) diagnostics and / or TMJ therapy, providing at least two modalities for generating (205, 210) three-dimensional image data, wherein a first image and at least a second image depicting the surface of the object (120) to be imaged are tomographically generated for a dental object (120) comprising at least one TMJ (105, 110), wherein the at least two three-dimensional image data generated (205, 210) in the at least two images are combined by means of a multimodal registration (225, 230) (225), wherein the generation (205, 210) of the at least two three-dimensional image data on the object (120) to be imaged is carried out with markings (125, 310 - 325) captured in the at least two images of different modalities (200).and wherein the at least two three-dimensional image data are spatially assigned to the temporomandibular joint (105, 110) by means of multimodal registration (225, 230) on the basis of the markers (125, 310-325) captured in the three-dimensional image data of both modalities (225), wherein the markers (125, 310-325) are arranged in a spatially restricted recording area for the at least two recordings of different modalities, wherein the markers (125, 310-325) are visible in the at least two recordings of different modalities, and wherein the image data generation is carried out at least by means of the first tomographic recording with the spatially restricted recording area corresponding to the markers (125, 310-325) (205, 210), wherein the spatially restricted recording area is arranged within the oral region of a patient for temporomandibular joint diagnostics and / or for temporomandibular joint therapy, characterized in thatthat the markings (125, 310 - 325) are arranged on a template (115) that can be precisely positioned within the patient's oral cavity, wherein the template (115) is placed in the restricted recording area (200) before the generation (205, 210) of the three-dimensional image data.

Description

Technical field

[0001] The invention relates to image generation and display systems suitable for use in dental medicine and dental diagnostics for temporomandibular joint (TMJ) diagnostics and therapy, in which at least two three-dimensional image data sets are multimodally combined or merged, wherein at least one of the at least two three-dimensional image data sets is tomographically generated, and in particular a method for operating such an image generation system used in TMJ diagnostics and therapy. Furthermore, the invention relates to a computer program, a machine-readable data carrier for storing the computer program, and a device and image generation and display system by means of which the method according to the invention can be carried out. State of the art

[0002] Modern imaging systems, used particularly in dentistry, produce image data or volumetric data that represent the object being imaged in its three-dimensional (3D) state and must be processed and displayed for the user or viewer. It is now possible to access 3D image data of the object to be treated, such as a human jaw or tooth, acquired preoperatively or intraoperatively, in order to make a diagnosis or to plan for a medical procedure.

[0003] In dentistry, the well-established method of three-dimensional or spatial dental or digital volume tomography (DVT) is already used. This technique employs a cone-shaped beam of X-rays and is a three-dimensional imaging tomography procedure that generates cross-sectional images. Similar to digital X-rays, in DVT an X-ray tube and an opposing digital image sensor or detector, which may have a radiopaque scintillator layer, rotate around a patient who is lying down, sitting, or standing. The X-ray tube, which typically rotates 180 to 360 degrees at a fan angle, emits a cone-shaped, usually pulsed, X-ray beam.

[0004] Furthermore, optical scanning methods, such as those using so-called "CEREC" devices or systems, are increasingly being used in dentistry and dental diagnostics. These systems employ CAD / CAM processes for the reconstruction of dental restorations. This allows dentists to design, manufacture, and potentially insert patient-specific ceramic restorations themselves in a single appointment, saving time and efficiency, directly at the treatment unit. An intraoral camera creates an optical impression of the anatomical object to be treated, such as a tooth stump intended for an inlay or crown. A three-dimensional model is then calculated from the resulting optical image data using computer software.

[0005] When generating the optical image data, a corresponding opposing bite can also be included in the calculations. Using a combined copying / grinding process, the calculated restoration (e.g., an inlay) is milled from a ceramic block using a three-axis milling machine with suitable grinding media.

[0006] Alternatively, a video camera as described in DE 42 26 990 A1 can be used to record or generate optical 3D image data, with which objects in the oral cavity of a patient can be viewed and recorded, and from the image data thus recorded, corresponding optical 3D image data can be calculated by a computer.

[0007] After generating the aforementioned 3D X-ray images and optical 3D images, it is necessary to spatially align this image data for subsequent diagnostics or other dental treatment procedures; that is, to perform a so-called "multimodal registration" or "3D-3D registration." Such a procedure for combining or merging 3D image data acquired through the aforementioned optical scanning with other generated 3D image datasets is described in WO 2009 / 140582 A2. This involves linking or stitching (i.e., connecting or joining) several polygons to create an electronic model of the object to be examined or imaged, based on a polygon mesh.

[0008] German patent DE 10 2007 001 684 A1 discloses a method for image registration of volume and surface data, enabling precise and automated registration of an optical image with a patient's X-ray image. This method allows for the spatial superimposition of the optical and tomographic images without the use of any external reference objects, physical models (such as plaster casts), or mechanical devices. The registration process is largely automated and can be completed in a relatively short time of approximately 15-30 seconds.In particular, a transformation function is used to align a distinctive volume structure extracted from the volume data, for example, formed by the object's edges, with the corresponding structure of the surface data, hereinafter referred to as the surface structure, as closely as possible. A measure for the quality of this alignment is defined, and the extracted structure is iteratively adapted to the surface structure visible in the surface data, optimizing this measure of accuracy. As a result, the coordinates of the optical image are aligned with the coordinates of the X-ray image through iteration.

[0009] From the publication "Fusion of computer tomography data and optical 3D images of the dentition for stretch artefact correction in the simulation of orthognathic surgery" (Nkenke E., Zachow, S. et al., published in Dentomaxillofacial Radiology (2004), 33, 226-232), a prototype for registering a radiographic dataset of the jaw and the surface dataset of a corresponding plaster model is also known. In this process, the visible surface, i.e., the surface of the teeth and mucosa, is first extracted from the radiographic image of the plaster model before being registered with the surface from the optical image using an ICP algorithm ("Iterative Closest Point"). However, this method is hardly applicable in practice because the extraction of the surface from the radiographic dataset of a real patient is inaccurate, so the requirements for precise surface registration are not met.

[0010] Furthermore, the use of reference bodies (markers) for the registration process discussed here is known. However, due to the associated problems of attachment and the discomfort for the patient, markers are only used when no simpler alternative exists. For example, US 5,842,858 A discloses a method in which the patient wears a template with markers during the X-ray examination. This template is then placed on a model to which a sensor for 3D position detection is attached. After determining the positional relationship between the sensor and the markers, the template can be removed and an optical image acquired. The 3D sensor then enables registration relative to the patient's image.

[0011] The imaging systems affected here now also feature a so-called "SICAT" function, which allows, for example, the movement of a lower jaw in a 3D volume to be displayed anatomically true to the original, whereby the movement traces of the temporomandibular joint can be visualized and reproduced for any point using an anatomically correct trajectory.

[0012] A device and a method for measuring jaw movement are disclosed in DE 103 39 241 A1. The device comprises a pair of fixed markers arranged on both sides of a patient's face, as well as a pair of movable markers positioned at a distance from the fixed markers and moving in unison with the movement of the mandible. Furthermore, four cameras are arranged to record the three-dimensional movement of the movable markers relative to the fixed markers during mandibular movement. The device enables precise measurement of the center of rotation of a mandibular movement and the corresponding spatial trajectory of the mandible.

[0013] US Patent 2007 / 0190481 A1 discloses a dental diagnostic imaging system in which two three-dimensional image datasets of different modalities are generated: a radiographic image and a non-radiographic image. These datasets are merged using markers on a template that are clearly positioned outside the patient's oral cavity.

[0014] US Patent 2012 / 0214121A1 discloses a dental diagnostic imaging system in which a computed tomography (CT) dataset and optical scanning data are generated and these image data are then merged. The merging of the two image data sets from different modalities is achieved using an optical marker, with two separate registrations being performed: a first registration of radiographic markers and a second registration of optical markers. Each marker is positioned on a template such that it is always located outside the oral cavity of the patient during image generation.

[0015] A disadvantage of the known methods is that, in order to enable the aforementioned multimodal registration of the 3D image data concerned here, it is necessary to also image the anatomical area surrounding the respective object to be imaged on a large scale or in large volume using radiographic or tomographic techniques, i.e., radiation therapy. Description of the invention

[0016] The invention is based on the idea of ​​providing, in an image generation system and a method for its operation, in which a first three-dimensional image data set of volume data representing, in particular, an area of ​​the jaw of a patient encompassing at least one temporomandibular joint and which are acquired using a transilluminating tomographic imaging method of a first modality, and in which at least a second three-dimensional image data set of surface data representing, at least partially, the same area of ​​the jaw of the patient and which are acquired using a method of a second modality for acquiring visible surfaces, is provided, that the image data generation of the at least two three-dimensional image data sets is carried out on the object to be imaged with markings captured in the at least two acquisitions of different modalities.wherein the image data generation is carried out at least by means of the tomographic first acquisition with an acquisition area restricted according to the markings, and that the at least two three-dimensional image data are spatially assigned with respect to the temporomandibular joint by means of multimodal registration on the basis of the markings recorded in the three-dimensional image data of both modalities.

[0017] The first image data set is preferably generated radiographically or tomographically, in particular by so-called volume tomography (DVT), wherein, according to the invention, the radiographic or tomographic (acquisition) volume is spatially limited in such a way that it represents, as far as possible, only the anatomical or medical situation of the dental object to be imaged, which includes at least one temporomandibular joint, e.g., a temporomandibular joint. This limitation of the volume serves in particular to limit or minimize the radiation dose or radiation exposure for the patient or the operating personnel during image generation, as well as to limit the irradiation time, which is also cost-effective.

[0018] It should be emphasized that the imaging system in question can also be a distributed system, in which the aforementioned image data are generated by different imaging devices and / or at different times, and information relevant for treatment only emerges from the superimposition of these image datasets. For example, to plan a dental procedure, such as a dental implant, computed tomography (CT) or cone-beam (CB) X-ray images of a patient's jaw can be taken, providing detailed anatomical information. On the other hand, for the planning and fabrication of dental prosthetic restorations, three-dimensional surface images are generated directly from the jaw or from an impression of the jaw using an optical imaging unit, such as a CEREC device or system from the applicant.

[0019] Unlike tomographic images, these surface data contain information about the course of the visible surface of the respective jaw, especially the surface of the teeth and the mucous membrane.

[0020] The method according to the invention, particularly suitable for temporomandibular joint (TMJ) diagnostics and therapy, can provide that relative movements (or corresponding "condylography data") of the two jaws are recorded using a signal transmitter and signal receiver rigidly connected to the upper and lower jaws, and that the movement path of an imaginary hinge axis of the two TMJs during the chewing process is determined, for example, by a treating physician, using the condylography data thus obtained. The aforementioned signal transmitter and corresponding signal receiver can be ultrasound devices. Based on the movement path thus determined, which corresponds to an imaginary hinge axis, the treating physician can, for example, diagnose pathologies of the TMJs by means of the axial trace of the movement path.

[0021] The method according to the invention relates in particular to the image generation of first 3D image data, generated, for example, by means of a DVT or MRI method or system, and of at least second 3D image data, optically scanned or acquired, for example, by means of a CEREC device or system, wherein the generated image data are precisely spatially assigned to one another or these data are brought into spatial alignment (so-called "multimodal registration"). Through multimodal registration, the two 3D image datasets can be combined accordingly for the purpose of an integrated display (so-called "data fusion").

[0022] In order to enable the multimodal registration of the already generated image data, according to the invention, natural or anatomical markings are defined during the generation of the first and second 3D image data on the patient, preferably in the oral region of the patient, or a special marking device, e.g. a template, is applied, which, due to its shape or a suitable arrangement of markings or structures that are preferably both optically and radiographically measurable or visible, enables the aforementioned subsequent assignment or merging of the first and second 3D image data.

[0023] Such a template can be produced at low cost and is easy to use in the image generation process relevant here. The template can have a shape or arrangement of markings or structures visible in at least two modalities, by means of which the multimodal registration of the generated three-dimensional image data can be easily carried out subsequently.

[0024] To enable precise multimodal or 3D-3D registration of the marking device or template, it must be positioned as accurately as possible in the patient's oral cavity relevant for image acquisition, i.e., with a force-fit and / or form-fit connection, so that it does not change its position or shift during the two image acquisition processes. Therefore, the template is preferably temporarily fixed between individual teeth or rows of teeth, similar to orthodontic braces or similar devices, or temporarily placed over entire rows of teeth, similar to a treatment splint.

[0025] The aforementioned optical generation of the first image data and the aforementioned radiographic generation of the second image data must therefore both cover or capture at least one part of the template relevant to the aforementioned marking or structuring. The shape, structuring, or markings of the template must be recognizable or visible in the respective 3D image data generated during both optical and radiographic acquisition, so that partial information or information from the template overlapping the two image data sets is visible in both sets. This enables a significantly improved multimodal registration of the aforementioned different modalities (e.g., optical and radiographic acquisition) compared to the use of optically acquired tooth surfaces.

[0026] Multimodal registration can be achieved, for example, by mapping radiographic markers from the CBCT scan to artificial optical markers acquired via optical scanning. Alternatively or additionally, natural or anatomically determined markers, such as the surfaces of optically scanned teeth, can also be used.

[0027] The aforementioned template structure can consist of at least three hole-like or dot-like perforations arranged at intervals to enable the multimodal registration described below using the ICP algorithm. A similar procedure for registering initial 3D image data of an anatomical model (dental model) with secondary 3D image data obtained through 3D image generation, using the aforementioned ICP algorithm, is described in US 2009 / 0316966 A1. This allows overlapping areas or corresponding image data to be eliminated from one of the image datasets. However, this relates to a different application scenario.

[0028] Using a template according to the invention, it is particularly possible to significantly limit the X-ray area, e.g., the captured CBCT volume, compared to the prior art, and thus reduce the required radiation dose, since the merging of the 3D image data advantageously no longer needs to be based on further anatomical structures arranged around the object to be captured. This minimizes the radiation exposure for the patient and the operating personnel of the imaging system and significantly reduces the costs for the X-ray generation of the second 3D image data.

[0029] When using the aforementioned template, there is therefore no longer a need for large-volume radiographically generated initial image data or volume information, such as that produced in the prior art, for example, by a large-volume CBCT scan, e.g., using a known "Galileos" imaging system. Thus, with the method according to the invention, for treatment or diagnosis in the anterior region of a patient, or for diagnostics where only the position of the teeth in relation to a temporomandibular joint situation is concerned, it is no longer necessary to radiographically or tomographically capture the entire jaw or dental arch.

[0030] Based on the 3D image data generated according to the invention, which are associated or combined with each other, a multimodal functional analysis of, for example, the patient's temporomandibular joints can be performed. In such functional therapy or diagnosis, the position or spatial location of the temporomandibular joint sockets and joint bones during movement or dynamics, as well as the corresponding orientation or positioning of the teeth in the upper and lower jaws relative to each other, are of considerable importance in order to design or manufacture a suitable therapeutic splint.

[0031] To manufacture such a therapeutic splint, the relatively high image resolution, for example when using a CEREC device or system, is utilized for generating the initial 3D image data. Secondly, the second set of 3D image data, acquired radiographically, for example using the aforementioned CBCT (Cone Beam Computed Tomography) procedure or system, serves to capture the coupling of dynamics and movement in the mandible. This is because the area of ​​the glenoid cavity and the articular bones cannot be imaged both internally and externally (with respect to the patient's oral cavity) using an optical imaging technique such as a CEREC device or system. This area can only be imaged tomographically, for example, using a CT or MRI scan.

[0032] In the inventive method for operating an image generation system, it is therefore particularly provided that the image data generation of the at least two three-dimensional image data of an object to be imaged is carried out with markings captured during the at least two images or irradiations of different modalities, that the image data generation is carried out in at least one modality with a capture area or recording area restricted according to the markings, and that the at least two three-dimensional image data are spatially assigned by means of multimodal registration based on the markings captured in the three-dimensional image data. The markings provided, so to speak, as reference data for carrying out the multimodal registration. The tomographic images can be acquired by means of magnetic resonance imaging (MRI) or by means of X-ray irradiation.

[0033] The two modalities are preferably provided by a DVT procedure and a Cerec procedure.

[0034] As an alternative to using a template, multimodal registration can be achieved by assigning natural or anatomically determined markers. While this eliminates the need for a template, it can be more difficult to find suitable anatomical markers that are detectable or visible in image data generated in at least two modalities.

[0035] The method according to the invention is particularly applicable to a dental or dental diagnostic imaging system equipped with a SICAT function as described herein, and enables functional analysis of movable anatomical objects even when generating the 3D image data described herein in a relatively small field of view (FoV). Thus, a functional analysis of temporomandibular joints can be performed by operating a multimodal imaging system according to the invention, whereby the generation of the underlying X-ray images is achieved with a relatively low radiation dose compared to the prior art.

[0036] When using a so-called “Cerec Omnicam” as described below, the result of a 3D-3D registration according to the invention can be further improved or stabilized by additional color information, since precise optical 3D recordings including color information provide additional usable material information for the 3D-3D registration.

[0037] The computer program according to the invention is configured to perform each step of the method, particularly when running on a computer or a control unit. It enables the implementation of the method according to the invention on an electronic control unit without requiring any structural modifications to the unit. For this purpose, a machine-readable data carrier is provided on which the computer program according to the invention is stored. By uploading the computer program according to the invention to an electronic control unit, the electronic control unit according to the invention is obtained, which is configured to control an image generation system as described herein by means of the method according to the invention.

[0038] The invention further relates to a dental imaging system which is designed to be controlled by means of a method according to the invention, whereby the aforementioned advantages result.

[0039] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0040] It is understood that the features mentioned above and those to be explained below can be used not only in the respective combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention. Brief description of the drawings Fig. Figure 1 shows a schematic representation of a mandibular layer in the axial direction with a template according to the invention inserted. Fig. Figure 2 shows an embodiment of the method according to the invention using a flowchart. Fig. Figures 3a - 3d show a schematic calculation example of a multimodal registration according to the invention. Fig. Figure 4 shows an exemplary embodiment of a possible image merging or image data fusion using optical and X-ray markers. Fig. Figure 5 shows an embodiment of a template for possible use in image merging or image data fusion according to Fig. 4. Examples of implementation

[0041] Fig. Figure 1 shows a schematic representation of an axial mandibular layer 100 with the two temporomandibular joints 105, 110 of a patient to illustrate an image data fusion made possible by the invention through the combination or superimposition of three different modalities, namely optical CEREC acquisition / generation, radiographic CBCT acquisition / generation, and the template. During optical and radiographic image data acquisition, the mandible 100 can additionally be moved around the axis of rotation formed by the temporomandibular joints 105, 110 in order to also perform the aforementioned functional analysis of the temporomandibular joints 105, 110.

[0042] One in Fig. The template 115, preferably equipped with a handle 117, shown in Figure 1, is clamped precisely between the dental arches 120 of the mandible 100, e.g., in the two areas 122, 123, during the entire image data acquisition of the various modalities, i.e., in a form-fit and / or force-fit manner. In the present embodiment, the template 115 has eight perforating bores or holes 125, which serve as the aforementioned markings for the subsequent multimodal or 3D-3D registration.

[0043] The described stencil 115 can be made of a ceramic material or of metal, e.g., stainless steel. The optical markings mentioned can be, for example, spheres, cylinders, or pins, or be based on specific textures. The markings can also be color-coded and, for example, be blue spheres or spheres that emit light in the UV range. Another embodiment of the stencil is shown in Fig. 5 is shown and is described below.

[0044] The template 115 is positioned in the patient's oral cavity such that the CEREC scan area 130 of the optical CEREC scan and the radiographic CBCT volume 135, during image data acquisition, cover both the three teeth 120 to be imaged and at least a relevant part of the template 115, i.e., scan or illuminate them. The relevant part consists of at least three holes 125 of the template 115 required for spatial 3D-3D registration, wherein the relevant part preferably represents the intersection of the CEREC scan area 130 and the CBCT volume 135. In the present embodiment, the lower four of the eight holes 125 are even covered by the data-acquiring optical beams and the X-rays.

[0045] If there is no overlap between the optical CEREC image and the tomographically or radiographically acquired CBCT image, the spatial relationship between these two images must be determined using a transformation based on known marker data. For the tomographic area, radiographic markers, such as ceramic spheres, can be used in a manner known per se, and for the optical area, optically effective markers, such as spheres or cylinders with a specific color or surface texture, can be used. The spatial relationship between these markers is determined using a transformation matrix described below, for example, based on transformation data specified for the respective template at the factory.

[0046] Since both the optical Cerec image and, in particular, the radiographic DVT image only need to be generated in the relevant area of ​​the template 115 mentioned above, the radiation exposure of the patient and the operating personnel is significantly reduced compared to the state of the art.

[0047] At the in Fig. In the flowchart shown in Figure 2 for carrying out an image acquisition according to the invention and subsequent 3D-3D registration, a template 115 according to the invention is first fixed at the aforementioned suitable location in the oral cavity of the patient to be examined 200. However, it should be emphasized that the method according to the invention can also be carried out without such a template 115, in which case suitable anatomical features, such as the surfaces of the three teeth shown, are used as the basis for registration instead of the template 115.

[0048] After the template 115 is fixed in place, optical 3D image data are generated in the scan area shown using the Cerec method in the present embodiment. Simultaneously, or before or after, radiographic 3D image data are generated using the CBCT method, wherein the underlying CBCT volume corresponds to the Cerec scan area at least in the area of ​​the anatomical objects to be examined, i.e., in this case, the three in Fig. The teeth shown in point 120, as well as the relevant marking area of ​​the template 115, overlap. In the aforementioned 3D image data acquisition using Cerec and CBCT, the image data are captured together with 3D coordinates.

[0049] In the optical and radiographic 3D image data generated, the aforementioned markings (e.g., at least three specified holes) of the template 115 are identified 215, 220, and based on the identified markings, a 3D-3D registration of the optical and radiographic image data is performed using the ICP algorithm described below 225. As a result of the 3D-3D registration 230, optical and radiographic 3D image data are available which fit together anatomically correctly and can therefore be displayed or superimposed simultaneously, e.g., on a monitor.

[0050] For 3D-3D registration of the first and second 3D image data, the [device] in the Fig. 3a - 3d The schematically represented, well-known "Iterative Closest Point" (ICP) algorithm is used, by means of which the point clouds 310, 315 contained in the 3D image data, shown schematically here, can be aligned or brought into spatial correspondence with each other. As in Fig. 3a and Fig. As can be seen in 3b, the CBCT scan taken in volume 135 is relatively tilted compared to the optical scan taken in Cerec scan area 130. This is evident, for example, from the three teeth 120 captured by the scans, which are in Fig. 3a were essentially recorded axially from above, whereas these teeth 120 according to Fig. 3b during the DVT scan, more of the side was captured and therefore in Fig. 3b are depicted in a slightly more spatial way.

[0051] Such point clouds are defined as markings or anatomical structures according to the invention, in particular in Fig. The markings or structures shown in the first image, based on a template 115, are used as a basis. This allows a complete image or model to be created from the first and second image data.

[0052] For point clouds 320 and 325, a coordinate transformation is determined such that the distances between them (310 and 315) are minimized. As is known, for each point in one point cloud, the nearest point in the other is determined. The sum of the squares of these distances is minimized by adjusting the transformation parameters iteratively until an optimal match between point clouds 320 and 325 is achieved.

[0053] The aforementioned initial 3D image data will be in Fig. 3c through a three-dimensional Cerec data space 300 and the second 3D image data in Fig. The 3D representation is schematically represented by a similarly three-dimensional CBCT data space 305. In order to bring the two point clouds 320 and 325 into spatial alignment, the CBCT data space 305 is rotated in this embodiment about a first axis of rotation 330 with an angle φ and about a second axis of rotation 335 with an angle ϑ until alignment is achieved with an empirically predetermined accuracy. The two rotational transformations shown, with the two angles φ and ϑ, bring the point clouds of the two data spaces 300 and 305 into overall alignment according to the dashed arrow lines 340, 345, 350, and 355.

[0054] To achieve the aforementioned agreement, the following optimization problem is solved according to a preferred embodiment of the method according to the invention. In this optimization, a quadratic distance minimization is particularly sought according to the following relationship:

[0055] Min(dist(D1i, ~D2i)) for all i, where: ~D2=R*D2+T.

[0056] In the equation, R represents a rotation matrix and T a translation vector. The two quantities D1i and D2i correspond to the i data points contained in data space 1 and data space 2, respectively. The free parameters available for the optimization are R and T. Since there are generally more data points than unknowns in this case, an iterative approach with a least-squares solution is preferred for the optimization. The solution of such an approach then corresponds to the best-fitting transformation R|T, which describes a rigid transformation with six degrees of freedom.

[0057] If, instead of a template such as 115, natural markers arranged on the teeth are used, the number of data points i considered during optimization varies. This allows, for example, outliers to be filtered out.

[0058] Alternatively, the following system of equations can be solved, using, for example, a pseudo-inverse and a least-mean-squares approach, where: R=(R11R12R13R21R22R23R31R32R33) and T=(TxTyTz)

[0059] Using R as a linearized form of an Euler angle representation, the following results: R=Rz(θz)⋅Ry(θy)⋅Rx(θx)=[cz−sz0szcz0001][1000cy−sy0sycy][cx0sx010−sx0cx]=[ (cxcz−sxsysz)−cysz(sxcz+cxsysz)(cxsz+sxsycz)cycz(sxsz−cxsycz)−sxcysycxcy] sx=sin(θx),cx=cos(θx),sy=sin(θy),cy=cos(θy),sz=sin(θz),cz=cos(θz)

[0060] Therefore, for a correspondence point i (e.g., a named marker or a natural, three-dimensional point distribution) Mi=(MxiMyiMzi), that its transformed version satisfies the following linear transformation equation: Mι^=R⋅Mi+T

[0061] For one axis, e.g. X, a simple conversion yields an overdetermined system of equations of the form: (Mx1˜Mxt˜ ⋮MxN˜)=(Mx1My1My21R11R12R131R11R12R131R11R12R131)⋅(R11R12R13 Tx)

[0062] This system of equations can be solved independently of each other by linearization. The resulting linear system of equations has the form b = Ax

[0063] This results in a possible solution using a pseudo-inverse and a least-mean-squares approach, where: ‖Ax−b‖22→min! or ATax=ATb

[0064] The result is therefore the following compensatory solution: ‖ATAx−ATb‖22→min!

[0065] In Fig. Figure 4 is an exemplary top view of a "mandibular" slice, i.e., a slice relating to the mandible 400 of a patient, schematically depicted, illustrating a possible image fusion using optical markers 405 and radiographic markers 410. It should be noted that these markers 405, 410 can also be arranged at several heights, as described below. Fig. Figure 5 shows the field of view (FOV) for optical data acquisition using the aforementioned optical surface scan (OSS). The second line (435) represents the field of view for radiographic data acquisition using cone beam computed tomography (CBCT). It should be emphasized that the field of view (435) for CBCT corresponds to a relatively small X-ray volume, resulting in relatively low radiation exposure for both the patient and the operator. In this example, optical data acquisition (445) is performed according to the first field of view (430) on a number of teeth (445) located in the patient's oral cavity (440), while radiographic data acquisition (425) is performed according to the second field of view (435) on one or both temporomandibular joints (415, 420) of the patient.

[0066] As from the Fig. 4 As can be further seen from the drawn soft tissue-air boundary 450 and from the example of the radiographic markers 410, the markers 405, 410 can also be arranged outside the patient's head, e.g. in the vicinity of the temporomandibular joints 415, 420, on a correspondingly modified template 425.

[0067] The markers 405 and 410 can be assigned to each other using a previously described spatial transformation rule, which is known per se for the respective template 425. The markers 405 and 410 arranged on the template 425 serve to ensure stability when finding a solution to the above-described system of equations for the transformation, particularly in situations where there is little or no overlap between the optically and X-ray-recorded data.

[0068] Fig. Figure 5 shows an embodiment 500 of a Fig.The previously shown template 425 enables the described transformation. Using this bite template 500, the aforementioned spherical 510, 515 or cylindrical 505 optical or radiographic markers can be implemented. As described above, these markers 505, 510, 515 are preferably positioned outside the patient's oral cavity, but with a fixed spatial relationship to a respective bite block 520. Advantageously, with such a template 500, the arrangement of the spheres or cylinders, such as the spherical markers 515 in this case, can be further varied in the vertical direction to provide the spatial information required for the transformation even more precisely.

[0069] The described method can be implemented in the form of a control program for an image generation or display system affected here, or in the form of one or more corresponding electronic control units (ECUs). REFERENCE MARK LIST 100 mandibular layer 105, 110 Temporomandibular joints 115 Template 117 Handle 120 rows of teeth 122, 123 Lower jaw areas 125 holes, bores 130 Cerec scan areas 135 DVT volume 200 Fixing Template 205 Generation of 3D image data (Cerec) 210 Generation of 3D image data (DVT) 215, 220 Identification Marks 225, 230 3D-3D registration 300 Cerec data room 305 DVT data room 310, 315 point clouds 320, 325 point clouds 330, 335 axes of rotation 340 - 355 arrow lines 400 lower jaw 405 optical markers 410 radiographic markers 425, 500 template 430, 435 fields of view (FOV) 440 Oral cavity 445 teeth 450 Soft tissue-air boundary 505 - 515 Marker 520 Bissblock

Claims

[1] Method for operating a dental diagnostic imaging system for temporomandibular joint (TMJ) diagnostics and / or TMJ therapy, which provides at least two modalities for generating (205, 210) three-dimensional image data, wherein a first image and at least a second image depicting the surface of the object (120) to be imaged are tomographically generated for a dental object (120) comprising at least one TMJ (105, 110), wherein the at least two three-dimensional image data generated (205, 210) in the at least two images are combined by means of a multimodal registration (225, 230) (225), wherein the generation (205, 210) of the at least two three-dimensional image data on the object (120) to be imaged is carried out with markings (125, 310 - 325) captured in the at least two images of different modalities (200),and wherein the at least two three-dimensional image data are spatially assigned to the temporomandibular joint (105, 110) by means of multimodal registration (225, 230) on the basis of the markers (125, 310-325) captured in the three-dimensional image data of both modalities (225), wherein the markers (125, 310-325) are arranged in a spatially restricted recording area for the at least two recordings of different modalities, wherein the markers (125, 310-325) are visible in the at least two recordings of different modalities, and wherein the image data generation is carried out at least by means of the first tomographic recording with the spatially restricted recording area corresponding to the markers (125, 310-325) (205, 210), wherein the spatially restricted recording area is arranged within the oral region of a patient for temporomandibular joint diagnostics and / or for temporomandibular joint therapy, , characterized by, that the markings (125, 310 - 325) are arranged on a template (115) that can be precisely positioned within the patient's mouth area, wherein the template (115) is placed in the restricted recording area (200) before the generation (205, 210) of the three-dimensional image data. [2] Method according to claim 1, characterized by , that the number of markings (125, 310 - 325) is at least three. [3] Method Claim 1 or 2, characterized by , that the template (115) has a shape or arrangement of markings (125, 310 - 325) or structures visible in at least two modalities. [4] Method according to any one of the preceding claims, characterized by , that the multimodal registration (225, 230) is carried out by matching X-ray markers (410) to artificial optical markers (405). [5] Method according to any one of the preceding claims, characterized by, that the multimodal registration (225, 230) is carried out by assigning natural and / or anatomically determined points. [6] Method according to any one of the preceding claims, characterized by , that the multimodal registration (225, 230) is carried out using an ICP algorithm that combines the recorded markings (125, 310 - 325). [7] Method according to any one of the preceding claims, characterized by , that image data generation is carried out using a radiographic DVT procedure (210) or MRI procedure as well as an optical scanning procedure (205). [8] Computer program which is configured to perform each step of a method according to any one of claims 1 to 7. [9] Machine-readable data carrier on which a computer program according to claim 8 is stored. [10] Marking device for a dental diagnostic imaging system operated according to a method according to one of claims 1 to 7, characterized by , that the marking device is formed by a template (115) that can be inserted precisely (122, 123) into the oral cavity (440) of a patient. [11] Marking device according to claim 10, characterized by , that the template (115) has a shape or arrangement of markings (125, 310 - 325) or structures visible in at least two modalities. [12] Dental imaging system which is configured to be controlled by a method according to any one of claims 1 to 7.

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