Method for generating a manufacturing model for a medical implant

A method is disclosed for generating a manufacturing model for a medical implant. In the method, image data of a body region is provided, and regions corresponding to structures of different tissue are segmented; a shape of the implant is defined on the basis of the regions corresponding to the structures and an interaction with the implant is determined for at least one structure in a patient-specific manner on the basis of the image data; for a number of structures, the respective interaction with the implant is checked for an exceedance of a critical stress; and the shape of the implant is defined as a manufacturing model. The manufacturing model is then stored on a non-transitory data carrier and/or output via an interface if the critical stress is not exceeded for any checked interaction of the implant with the respective structure.

PRIORITY STATEMENT

The present application hereby claims priority under 35 U.S.C. § 119 to German patent application number DE 102015202286.2 filed Feb. 10, 2015, the entire contents of which are hereby incorporated herein by reference.

FIELD

At least one embodiment of the invention generally relates to a method for generating a manufacturing model for a medical implant, wherein image data of a body region is provided, regions are segmented in the image data, the regions corresponding in each case to structures of different tissue, and wherein a shape of the implant is defined on the basis of the regions which correspond to the structures.

BACKGROUND

It is desirable for the production of a medical implant, with as high a level of automation as possible for high efficiency, nevertheless to achieve the best possible adjustment to the individual conditions of the anatomy of the relevant patient, which a priori challenges complete automation of the manufacturing process. The desire for a patient-specific anatomical adaptation thus applies here to different implants such as bone implants, an intervertebral disk replacement or cartilage structures for plastic or reconstructive surgery.

Particularly with an implant which, on account of an interaction, for instance as a result of movements, with one or a number of adjacent tissue structures is exposed to a constant stress, a detailed patient-specific adjustment of the implant to the surrounding tissue can prevent wear of the implant due to the stress. Similarly, unwanted reactions by the implant to the tissue structures involved in the interaction can also be reduced here, which helps with preventing inflammations, degeneration, sclerosis and physical wear responses of the tissue structures as a result of the implant.

WO 2004/110309 discloses a method, which, for the manufacture of an implant, first records three-dimensional tomographic image data of the body region for which the implant is provided, and on the basis of this image data of the body region creates a manufacturing model of the implant. The implant is then produced on the basis of the manufacturing model created based on the tomographic image data. WO 2014/036551 discloses a method for the patient-specific embodiment of an implant, which uses three-dimensional tomographic image data in particular to determine two-dimensional contact surfaces of a bone implant with the bone for which the implant is intended.

However, with the cited methods the image data is generally only recorded with one modality, in other words for instance using computed tomography (CT) or magnetic resonance tomography (MRT), and a manufacturing model of the implant is then generated directly by way of this image data generated by one modality. In the generation of the manufacturing model, this then results in substantially only the anatomical structures of the relevant body region which are particularly effectively resolved by the modality used, in other words bone structures in CT or soft tissue structures in MRT, being taken into account.

Information relating to any damage to the structures which are less effectively resolved by the modality used in each case is therefore not actually available for the generation of the manufacturing model. Moreover, as a result of the static nature of the image data, possible anatomical changes to the relevant body region (for instance as a result of movements), which could affect the implant, are not taken into account during the adjustment of the implant, and nor is the stress on the implant that may be produced by such anatomical changes.

SUMMARY

At least one embodiment of the invention specifies a method for generating a manufacturing model for a medical implant, which enables as effective an adjustment of the implant to the patient-specific anatomical conditions of the tissue structures surrounding the implant as possible and in the process takes into account the long-term effects of the interactions of the implant and the surrounding tissue.

At least one embodiment of the invention is directed to a method for generating a manufacturing model for a medical implant, wherein image data of a body region is provided, regions which correspond in each case to structures of different tissue are segmented in the image data, a shape of the implant is defined on the basis of the regions which correspond to the structures, an interaction with the implant is determined in a patient-specific manner for at least one structure on the basis of the image data, the respective interaction with the implant checks for an exceedance of a predefined critical stress for a number of structures and the shape of the implant is defined as a manufacturing model, and the manufacturing model is stored on a non-transitory data carrier and/or output by way of an interface if the predefined critical stress is not exceeded for any checked interaction of the implant with the respective structure.

Advantageous and in part separately considered inventive embodiments of the inventions are presented in the claims and in the description which follows.

At least one embodiment of the invention further specifies an apparatus which is set up to perform the method described above for generating a manufacturing model. This comprises in particular a processor or computer, which can be configured in particular with at least one ASIC designed especially for this purpose. The advantages specified for the method and its developments can be analogously transferred to the apparatus.

At least one embodiment of the invention moreover specifies a computer program with program code for performing the method described above for generating a manufacturing model, when the computer program is run on a computer.

At least one embodiment of the invention moreover specifies a non-transitory computer readable medium including program code, for performing an embodiment of the method when the program code is executed on a computer.

At least one embodiment of the invention also specifies a method for producing a medical implant, which has method steps firstly comprising the generation of a manufacturing model via a method as described above, secondly the generation of a construction program which can be read by a producing apparatus on the basis of the manufacturing model and thirdly the generation of the implant in the producing apparatus on the basis of the construction program. One particular advantage here is that the manufacturing model can be output by the method for generation in a data format, which has a matrix-like three-dimensional volume representation of the implant, such as e.g. a CAD file.

Such a representation can be translated directly for a plurality of producing apparatuses, thus for instance for a 3D printer or a milling machine, into a construction program which can be read by the apparatus, which can comprise the instructions for the apparatus which are necessary for manufacture such as, in the case of the 3D printer, a file in the .stl format. A high probability of the manufacturing model output and a practical usability are thus ensured. Particularly with an output in an advantageous file format, the generation of the manufacturing model can be separated from the material production of the implant, which can contribute to simplifying the manufacture

Parts and variables which correspond to one another are provided with the same reference numerals in all the figures.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

At least one embodiment of the invention is directed to a method for generating a manufacturing model for a medical implant, wherein image data of a body region is provided, regions which correspond in each case to structures of different tissue are segmented in the image data, a shape of the implant is defined on the basis of the regions which correspond to the structures, an interaction with the implant is determined in a patient-specific manner for at least one structure on the basis of the image data, the respective interaction with the implant checks for an exceedance of a predefined critical stress for a number of structures and the shape of the implant is defined as a manufacturing model, and the manufacturing model is stored on a non-transitory data carrier and/or output by way of an interface if the predefined critical stress is not exceeded for any checked interaction of the implant with the respective structure.

Advantageous and in part separately considered inventive embodiments of the inventions are presented in the claims and in the description which follows.

An embodiment of the method is preferably to be performed here by a computer, which has a data connection with a non-transitory data carrier and/or an interface. Image data of the body region, for which the implant is intended, is preferably to be provided here. In particular, the image data can also represent the body region in a time-resolved manner, for instance a dynamic representation of a cardiac movement, if for example the implant is intended as a supporting structure in a coronary vessel or as a cardiac valve.

Field markers which can in particular also be positioned manually can also be used for the segmentation. The segmentation is also preferably assisted by learning algorithms, so that e.g. for the segmentation a classification of the image data into regions of a known pattern takes place first and regions which at first do not correspond to any known pattern are classified manually, wherein the pattern recognition “learns” the corresponding classification.

An implant here may also comprise any implantation aids used for the implantation that are directly connected to the implant prior to implantation. The definition of the shape of the implant can take place in particular by the surface of a structure which corresponds to a segmented region being calculated. The implant can then at least partially have a negative mold with respect to the surface of the structure identified by segmentation. In particular, a shape of the implant can be predetermined by a calculation, which can still be manually adjusted prior to determining the or each interaction with the respective structure.

The interaction of the at least one structure with the implant comprises in particular a stress on the implant caused by the structure and a stress on the structure caused by the implant.

At least one embodiment of the invention is first based here on the consideration that a patient-specific adjustment of an implant to the individual anatomical conditions is most likely to be effected by the use of image data of the relevant body region of the patient. It is apparent here that the spatial resolution of the body region, which is available from the image data, can be used directly to define a shape of the implant, if regions which correspond in each case to structures of a different tissue can be segmented in the image data in each case. The segmentation of the individual regions allows a model of the body region to be created, which enables a definition of the shape of the implant by assigning individual pixels in a region, for which the implant is intended, to their position information. This type of definition of the geometry of the implant by way of the position information of pixels from image data allows a final shape as a manufacturing model also to be easily translated into a data format which can be read directly by a manufacturing machine so that it can manufacture the implant directly.

In a further step, it is now apparent that, for a structure which was already identified previously on the basis of the segmentation of its corresponding image regions in order to define the shape of the implant, an interaction with the implant can be determined in a patient-specific manner on the basis of the image data. During the construction of medical implants the possible stresses on the implant due to the surrounding tissue structures are at present calculated on the basis of standardized models. This at least allows possible stresses on the implant to be taken into account that could in the long term potentially result in signs of wear and tear. However, patient-specific changes to the relevant body region are not considered at all during the determination of the stresses.

However, precisely those body regions in which an implant is to be used for medical reasons often exhibit noticeable individual anatomical deviations from the standard given by a patient who is completely healthy in this body region. For instance vertebrae, between which an intervertebral disk is to be inserted, can be worn on one side due to a prolonged incorrect posture and resulting inappropriate stress, which would also be considered to be a cause of the damage to the intervertebral disk. If the extent of the wear is now not taken into account in the design of an intervertebral disk implant, the permanent inappropriate stress on the spinal column at this point cannot be corrected. An implant which only uses the degeneration of the vertebrae to be inferred from the image data statically for the definition of the shape, but not dynamically for the determination of the interaction of the vertebrae with the implant, is not optimally adjusted to the course of motions on account of the diverse movement pattern of the spinal column and the associated inadequate consideration of the effects of the patient-specific anatomical conditions produced here due to degeneration.

The result is on the one hand the risk of increased wear of the implant, which may make an early replacement of the implant necessary. This is undesirable on account of the operative intervention required. On the other hand an implant which is not optimally adjusted to the interactions can also place stress on the surrounding tissue structures. A body region into which an implant is inserted on account of a medical indication may as a result of the implant experience a temporary improvement in the condition that caused the indication. However, after some time the long-term stresses which the implant exerts on the surrounding tissue structures can on the one hand cause the medical indication to recur.

On the other hand, other indications such as tissue sclerosis or inflammations can also occur if the implant adversely subjects the tissue to long-term stress. With movable implants such as e.g. cardiac valves, a longer-term loss of optimal mobility also cannot be ruled out. In the worst case, an implant, in which the anatomical conditions of the patient are only taken into account statically to define the shape but not dynamically to determine possible stresses, could temporarily alleviate the symptoms of the medical indication requiring the implant, without however effectively eliminating their causes in the long term.

In contrast, it is now proposed to determine an interaction with the implant in a patient-specific manner for at least one structure on the basis of the segmented image data already present for the definition of the shape of the implant, and to check whether a predefined stress on the implant and/or on the structure is exceeded as a result of the interaction. If this is not the case, in other words if a predetermined stress limit is not exceeded for any of the checked structures during interaction with the implant, then the shape of the implant is accepted as a permissible manufacturing model and can be stored on a non-transitory data carrier or output by way of an interface for further processing, in particular for translation into a constructional language which can be read by a manufacturing machine.

It has proven advantageous for a model of the body region shown to be created from the segmented regions of the image data. The segmented regions correspond here to the structures of different tissue. The model here is in particular a data model of the body region shown, which is used to determine the interaction of the at least one structure with the implant. In order to determine the said interaction, a model of the body region shown in the image data has proven to be particularly advantageous, since the interaction can thus be determined in a patient-specific manner. In this way, it is possible to avoid disadvantages which result due to standardized stress models for the implant, e.g. due to force vectors which are not optimally adjusted in the implant, which would result in a reaction in the surrounding tissue and thus permanent stresses with associated consequences such as irritations or inflammations.

Image data generated by at least one medical imaging method is preferably provided. In particular, the image data here represents a three-dimensional resolution of the relevant body region. The image data which can be provided by a conventional medical imaging method in most cases has a resolution which is good enough to perform the method, in particular to define the shape of the implant on the basis of the position data of the individual pixels.

In an advantageous embodiment of the invention, image data generated by at least two medical imaging methods in each case with a different modality is provided, wherein a set of first image data and a set of second image data are generated by a first modality and a second modality in each case. In particular, the at least two medical imaging methods here in each case have a different resolution capability in respect of different structures of different body tissue so that the first image data in particular particularly effectively resolves at least a number of first structures and the second image data particularly effectively resolves at least a number of second structures. The quality of the resolution can be provided here for instance by the signal-to-noise ratio or the image contrast. In particular, the at least two medical imaging methods here comprise an MRT and a CT, with the structures effectively resolved by the MRT comprising soft tissue and the structures effectively resolved by the CT comprising bone tissue. This is advantageous in order to be able to determine interactions of the implant with a number of structures of different tissue.

In the first image data a number of regions which correspond to structures and in the second image data a number of regions which correspond to structures are expediently segmented here respectively, wherein a model of the body region shown is created from the regions of the first image data and the regions of the second image data. By using image data with different modalities, the model of the body region can represent the different structures of different tissue, which are effectively resolved in each case by different modalities, in particularly exact detail. The quality of the determination of the stress can be improved here by the or each interaction.

A shape of the implant is favorably defined by a predefined template being selected and the shape of the template being modified in a patient-specific manner on the basis of the image data. The template can in particular be superimposed here with a patient-specific data model of the relevant body region and adjusted on the basis of the segmented regions. An at least partially manual adjustment, which uses the graphical representation on a monitor, is also included here. The use of a predetermined template, which is individually adjusted to the anatomy of the patient, allows for the fact that implants of the same type often only deviate by a few percent (with respect to the overall volume of the implant) from a basic shape determined by the average anatomy. These deviations are however often essential to the correct medical function of the implant in the body region of the patient.

The use of such a basic shape as a template and its adjustment now allows the definition of the shape to be configured in a less compute-intensive manner, since only the patient-specific deviations from the basic shape have still to be calculated, and no longer the entire implant. Since the selection of the template can take place by way of simple pattern recognition for instance, this allows the compute-intensive part of the definition of the shape to be restricted to a few percent of the volume of the implant.

In a further advantageous embodiment of the invention, the interaction with the implant is determined for the at least one structure by a numerical simulation. A data model of the body region, for which the implant is intended, is preferably used for the simulation. In particular, the simulation can dynamically determine the stresses produced by the interaction of the implant with the relevant structures, i.e. that the stresses occurring during different movements of the body region are simulated here as part of a stress model forming the basis of the simulation.

A blood flow is additionally preferably simulated here in the simulation. This is particularly advantageous in the case of an implant intended for a blood vessel or as a cardiac valve.

Parameters for a critical stress are favorably predetermined for the definition of the manufacturing model for a number of areas of the implant and/or a number of areas of the at least one structure in each case and are compared in areas to a stress determined by the simulated interaction. In particular, position-dependent parameter functions can be predetermined here for the or each area in each case and as a function of its position coordinates the respective parameter function can be compared to the stresses determined for this by the simulation. A procedure of this type makes it possible in particular to determine, for an existing shape of the implant, the value by which at a certain point on the implant a permissible stress is exceeded. This information can then be used for the adjustment. In particular, the values determined by the simulation for the respective position-dependent stress on the implant and on the surrounding structures can be used to determine the locally occurring forces.

In a further advantageous embodiment of the invention, provision is made for the shape of the implant to be changed if the predefined critical stress is exceeded due to at least one interaction of the implant with a structure, wherein the interaction of the implant with the structure is determined again on the basis of the changed shape of the implant. This process can in particular be iterated. If the predefined critical stress is now no longer exceeded for the relevant structure, in particular for at least one, preferably for all adjacent structures, the current shape of the implant can be defined as a manufacturing model and the manufacturing model can be stored on a non-transitory data carrier and/or output by way of an interface.

Deviations, in areas, of a stress determined by a simulated interaction from a predefined critical stress are preferably used here to change the shape of the implant in each case. The change in the shape can be performed here particularly at areas where the predetermined values for the critical stress are exceeded significantly. The calculations for a redefinition of the shape can be implemented here in a more computationally-efficient manner.

A local density and/or a local material selection of the implant is preferably changed if the predefined critical stress is exceeded by at least one interaction of the implant with a structure, wherein the interaction of the implant with the structure is determined again on the basis of the changed local density and/or local material selection of the implant. This process can in particular be iterated. If the predefined critical stress is now no longer exceeded for the relevant structure, in particular for all adjacent structures, the current local density and/or local material selection of the implant can be defined as properties of the manufacturing model and the manufacturing model can be stored on a non-transitory data carrier and/or output by way of an interface.

At least one embodiment of the invention further specifies an apparatus which is set up to perform the method described above for generating a manufacturing model. This comprises in particular a processor or computer, which can be configured in particular with at least one ASIC designed especially for this purpose. The advantages specified for the method and its developments can be analogously transferred to the apparatus.

At least one embodiment of the invention moreover specifies a computer program with program code for performing the method described above for generating a manufacturing model, when the computer program is run on a computer.

At least one embodiment of the invention also specifies a method for producing a medical implant, which has method steps firstly comprising the generation of a manufacturing model via a method as described above, secondly the generation of a construction program which can be read by a producing apparatus on the basis of the manufacturing model and thirdly the generation of the implant in the producing apparatus on the basis of the construction program. One particular advantage here is that the manufacturing model can be output by the method for generation in a data format, which has a matrix-like three-dimensional volume representation of the implant, such as e.g. a CAD file.

Such a representation can be translated directly for a plurality of producing apparatuses, thus for instance for a 3D printer or a milling machine, into a construction program which can be read by the apparatus, which can comprise the instructions for the apparatus which are necessary for manufacture such as, in the case of the 3D printer, a file in the .stl format. A high probability of the manufacturing model output and a practical usability are thus ensured. Particularly with an output in an advantageous file format, the generation of the manufacturing model can be separated from the material production of the implant, which can contribute to simplifying the manufacture.

FIG. 1shows in a block diagram a schematic representation of a method1for generating a manufacturing model2for a medical implant. In the present case, a set of first image data6and a set of second image data8are provided by two medical imaging methods CT, MRT, which are provided here by a computed tomography system CT and a magnetic resonance tomography system MRT. Another embodiment variant of the method1(not shown here), in which image data is provided by just one medical imaging method, has a comparable process flow. The first image data6and the second image data8are segmented separately from one another in each case. This means that in the individual image data associated regions10,12are determined on the basis of certain homogeneity criteria, which in each case map structures11,13with the same tissue. The regions10which are segmented in the first image data6provided by the CT correspond in the present case to structures11made of bone tissue, since this is particularly effectively resolved by the CT. The regions12which are segmented in the second image data8provided by the MRT accordingly map structures13of soft tissues of the relevant body region14.

A virtual model16of the mapped body region14is now created from the regions10segmented in the first image data6and the regions12segmented in the second image data8. A shape18for the implant to be manufactured is now defined on the basis of this model16. The template which is as similar as possible to the implant to be manufactured in terms of its shape is first selected here from a number of predefined templates by way of pattern recognition in the model16. The selected template20is then directly or indirectly modified in a patient-specific manner on the basis of the image data6,8, i.e. on the basis of the model16generated from the regions10,12segmented therefrom. Within the scope of the model16or the image data6,8from which it is generated, possible interactions22with the structures11,13surrounding the implant are now determined in a numerical simulation24for the defined shape18of the implant. Here the simulation24calculates in a spatially-resolved manner on the basis of mechanical stress models the effects which an interaction22has on the implant with the shape18and on the surrounding structures11,13during movements of the body region14, and also determines respective local stress parameters25.

If a predefined critical stress26is exceeded by the respective local stress parameter25, then the shape18is modified on the basis of the local stress parameters25determined, in particular on the basis of the respective level of exceedance of the critical stress26by the local stress parameter25, and the simulation24for the interactions22is performed again. This is now iterated until the critical stress26for the entire body region14and the implant remains unexceeded. The shape18of the implant thus determined as permissible is defined as a manufacturing model2for the implant and can now be stored on a non-transitory data carrier30or output by way of an interface32.

FIG. 2shows a schematic representation in a block diagram of the process flow of a method40for manufacturing a medical implant42designed according toFIG. 1. According to the above-described method1shown inFIG. 1, a manufacturing model2for the implant42is generated on a computer43configured especially for this purpose and is output by way of an interface32. The manufacturing model2is now translated into a construction program44, which can be read directly by a producing apparatus, which is provided here by a 3D printer46, in other words into a file in the. Stl format. The 3D printer46now generates the implant42on the basis of the construction program44, which represents a direct implementation of the manufacturing model2.

FIG. 3andFIG. 4each show schematic representations of the same longitudinal section plane of a cut-out of a spinal column in first image data6and in second image data8, which map two vertebrae50,52and an intermediate intervertebral disk54. In the first image data6shown inFIG. 3, the two vertebrae50,52are particularly easily identified by the high contrast, in the second image data8shown inFIG. 4, the intervertebral disk54and the underlying spinal cord56are better resolved. A slight protrusion58on the lower vertebra52can be seen in the first image data, said protrusion representing a deviation from a shape60of the same vertebra which is usually to be expected in an average person. For the sake of clarity, this usually expected shape60is shown with a dashed line and does not represent an integral part of the image data. Here the protrusion58may be congenital, or may have developed due to a long-standing incorrect posture or stress on account of degeneration. It is apparent in the second image data8that the spinal cord56passes the vertebrae50,52in the vicinity of the protrusion58.

FIG. 5shows a schematic representation of a simulation24of an interaction22of an implant42with the structures11that surround it. A model16of the corresponding body region, which comprises the vertebrae50,52, the intervertebral disk54and the spinal cord58, has been produced here on the basis of the image data6,8according toFIG. 3andFIG. 4. The intervertebral disk54is now replaced in the model16for a numerical simulation24of the interaction22by the implant42with a predefined shape.

The interaction22consists here of a curvature of the spinal column. The stress on the implant42during the interaction22is now calculated in each case by the simulation24of the interaction22. With a movement of the patient which results in the corresponding curvature of the spinal column, this determines that stronger forces in the direction of the spinal cord56act on the implant42on account of the protrusion58which represents an individual anatomical anomaly and a critical stress26in the area64of the implant is exceeded. In the long term, this can result either in a protrusion of the implant42or in its excessive wear and tear as a result of friction with the vertebrae50,52. In the present case, the shape of the implant42was adjusted on the basis of the knowledge obtained by the simulation24, and the interaction22(and if necessary others) was again checked for critical stresses on the implant42. If these are now no longer exceeded as a result of the changed shape of the implant42, the thus defined shape of the implant42can be defined as a manufacturing model and output.

FIG. 6shows a cross-sectional representation of a simulation24of an interaction22of a cardiac valve implant42with the surrounding tissue66. The interaction22consists here essentially of the effects on the surrounding tissue66of opening and closing the cardiac valve implant42. A blood flow68is taken into account here for the simulation24. If the aorta70, into which the implant42is to be inserted, has a constriction72for instance, then an excessively strong blood flow68in this region could increase the blood pressure for instance, which in the long term could cause sequelae in the patient. In the present case, the shape of the implant42can be adjusted to the requirements of the blood flow68, which result from the individual anatomy of the patient, in particular his/her aorta70.

Although the invention has been illustrated and described in more detail by the preferred example embodiment, the invention is not restricted by this example embodiment. Other variations can be derived herefrom by the person skilled in the art without departing from the scope of protection of the invention.

The example embodiment or each example embodiment should not be understood as a restriction of the invention. Rather, numerous variations and modifications are possible in the context of the present disclosure, in particular those variants and combinations which can be inferred by the person skilled in the art with regard to achieving the object for example by combination or modification of individual features or elements or method steps that are described in connection with the general or specific part of the description and are contained in the claims and/or the drawings, and, by way of combinable features, lead to a new subject matter or to new method steps or sequences of method steps, including insofar as they concern production, testing and operating methods. Further, elements and/or features of different example embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims.

Further, at least one embodiment of the invention relates to a non-transitory computer-readable storage medium comprising electronically readable control information stored thereon, configured in such that when the storage medium is used in a controller of a magnetic resonance device, at least one embodiment of the method is carried out.