Registration method and navigation system

Abstract

The present invention relates to a method for automatically registering an object, the method comprising the steps of providing a pre-operatively acquired model of the object, providing at least one marker carrier having a plurality of fluoroscopically detectable markers and at least one marker localization element, arranging the at least one marker carrier on an outer surface of the object, generating at least one perspective image of the at least one marker carrier arranged on the outer surface of the object and at least one segment of the object, determining the position and orientation in an electromagnetic field of the marker localization element of the marker carrier arranged on the outer surface of the object, and associating image points of the generated perspective image with model points of the pre-operatively acquired model.

Description

Technical Field

[0001] The present invention relates to a registration method for automatically registering an object. Further, the present invention relates to a navigation system configured to perform such a registration method.

Background Art

[0002] When using medical devices in surgery, in order to assist surgeons, it is known to track the position of the medical device in the patient's body and, for example, display the position of the medical device on a cross-sectional image of a patient model displayed on a monitor.

[0003] For this purpose, a navigation system generally including a data processing device, a monitor, a number of position specifying elements, and a position detection system is used. The position detection system can be, for example, an optical, ultrasonic, or electromagnetic position detection system. The position detection system is generally configured to determine the position and orientation of the position specifying elements.

[0004] As an example, an electromagnetic position detection system having an electromagnetic field generator for generating an alternating electromagnetic field is known. A medical device used with an electromagnetic position detection system generally includes a position specifying element composed of one or more coils.

[0005] When exposed to an alternating electromagnetic field, a voltage depending on the position and orientation of the coil in the alternating electromagnetic field is induced in the coil of the position specifying element. By analyzing the tap voltage signal representing the induced voltage, the position and orientation of the position specifying element can be determined. Generally, the position and orientation of the position specifying element of the medical device are also determined with respect to the position and orientation of a reference position specifying element composed of coils and fixed to the patient.

[0006] In order to display the position of a medical device on a cross-sectional image of a patient model shown on the monitor of a navigation system, it is first necessary to register the patient model. Generally, a patient model is a topographic image generated from two-dimensional, three-dimensional, or four-dimensional images of a patient acquired preoperatively by a tomographic imaging method, such as computed tomography (CT), magnetic resonance imaging (MRI), or C-arm fluoroscopy. Initially, the patient model is defined by coordinates in the coordinate system of the two-dimensional, three-dimensional, or four-dimensional image.

[0007] Registration refers to obtaining the spatial correlation between the position and orientation of a patient in real space (also called patient space) and the patient model defined by coordinates in the coordinate system of the two-dimensional, three-dimensional, or four-dimensional image used to generate the patient model. In particular, in order to obtain the spatial correlation between the patient and the patient model, a transformation function is established that defines how to associate, for example, the coordinates in patient space with each coordinate of the model points of the patient model (and vice versa).

[0008] Various approaches for establishing the transformation function within the scope of the registration method are known, such as surface-based registration and point-based registration.

[0009] In point-based registration, markers placed on the patient or anatomical landmarks used as reference points are used to establish the reference coordinate system in the patient and the reference coordinate system in the patient model generated from the two-dimensional, three-dimensional, or four-dimensional images of the patient.

[0010] Point-based registration can be performed, for example, by contacting the above-mentioned markers or landmarks with a pointer device or a sensing device that can be tracked by a position detection system. By contacting the trackable device with the marker or landmark, a point on the actual surface of the patient is identified, and the corresponding position value of the position-specifying element determined by the position detection system is associated with each model point of the patient model representing the position of the same marker or landmark. From the position of the marker or landmark, a patient model and a reference coordinate system in the patient are established, and from the reference coordinate system, the required transformation function is determined.

[0011] If the patient model is registered with respect to the patient, the position of the medical device can be displayed on a cross-sectional image of the patient model to assist the surgeon when navigating the medical device. To display the position of the medical device on the cross-sectional image of the patient model, the determined position and orientation of the position-specifying element of the medical device are converted into the respective coordinates of the model points of the patient model.

Summary of the Invention

Means for Solving the Problems

[0012] An object of the present invention is to provide an improved registration method for automatically registering an object, and an improved navigation system configured to implement the automatic registration method.

[0013] Regarding the registration method, the above object is achieved by a method for automatically registering an object of the present invention. The method includes providing a model of the object acquired preoperatively, and providing at least one marker carrier having a plurality of markers that can be detected fluoroscopically and at least one marker position-specifying element, A plurality of markers and at least one marker position specifying element are fixed to a marker carrier, at least one marker position specifying element is configured to provide a sensor signal representing the position and orientation of the marker position specifying element in an electromagnetic field, and the relative distance and direction between at least one marker position specifying element and at least one of the plurality of markers are known, in the step; placing at least one marker carrier on the outer surface of the object; generating at least one perspective image of at least one marker carrier disposed on the outer surface of the object and at least one segment of the object, the perspective image being generated such that at least two markers of at least one marker carrier and at least one segment of the object are visible, in the step; determining the position and orientation of at least one marker position specifying element of the marker carrier disposed on the outer surface of the object in the electromagnetic field; associating the image points of the generated perspective image with the model points of the model acquired preoperatively, the association of the image points of the perspective image with the model points of the model being performed using the determined position and orientation of at least one marker position specifying element, and the known overall distance and orientation between at least one marker position specifying element and at least one of the plurality of markers, and / or the known spatial relationship between a further marker of the plurality of markers and at least one marker having a known relative distance and orientation with respect to at least one marker position specifying element, in the step; including.

[0014] The above step of associating the image points of the generated perspective image with the model points of the model acquired preoperatively can be performed using the determined position and orientation of at least one marker position specifying element, and the known relative distance and orientation between at least one marker position specifying element and at least one of the plurality of markers.

[0015] In addition to, or instead of, using the known relative distances and orientations between at least one marker position specifying element and at least one of the plurality of markers, the step of associating the image points of the generated perspective image with the model points of the preoperatively acquired model can be performed using the known spatial relationships between further markers of the plurality of markers and at least one marker having known relative distances and orientations with respect to the at least one marker position specifying element.

[0016] Among the above steps, the step of "generating at least one perspective image of at least one marker carrier" can be performed before, after, or preferably, simultaneously with the step of "determining the position and orientation of at least one marker position specifying element".

[0017] According to the registration method of the present invention, an object can be automatically registered without bringing a marker or a landmark into contact with a pointer device or a sensing device.

[0018] In particular, according to the registration method of the present invention, an object including several elements displaceable relative to each other can be registered, and even when the elements of the object are displaced relative to each other during a navigation procedure, the registration accuracy can be maintained over the duration of the navigation procedure.

[0019] According to the registration method of the present invention, since the object is registered for each segment, the registration accuracy can be maintained over the duration of the navigation procedure even when the elements of the object are displaced relative to each other.

[0020] Registration for each segment means dividing an object into a plurality of segments and establishing an individual conversion function for each of the divided segments. Preferably, each segment is associated with each marker carrier arranged on each segment. A plurality of marker carriers may be arranged on each segment of the object. Also, the object may be registered by displacing the marker carrier for each segment.

[0021] The size of the segment can be defined according to various criteria. When the object includes a plurality of elements, each segment of the object can include different ones of the plurality of elements of the object, that is, one element for each segment. One segment may include two or more elements of the object. When one segment includes two or more elements, the size of the segment is preferably selected such that the relative displacement between the two or more elements included in the segment is negligible with respect to the registration accuracy. The way of segmentation may already be suggested by the shape of the object itself. For example, when the object is the spine of a patient, one or more vertebrae may be included in one segment.

[0022] In the registration method of the present invention, first, a marker carrier and a model of the object acquired before the operation are provided.

[0023] The model acquired before the operation can be generated from, for example, image data recorded by tomography. The model can be a 2D, 3D, or 4D model of the object. Preferably, the model is a 3D model generated from a 2D fluoroscopic image registered to the 3D model. First, the model is defined using the coordinates of the image data used for generating the model, for example, the coordinates of the tomographic image of the patient.

[0024] At least one marker carrier used in the registration method of the present invention has a plurality of markers that are fixedly attached to the marker carrier and are detectably transparent, and at least one marker position specifying element, and is characterized in that the relative distance and orientation between at least one marker position specifying element and at least one of the plurality of markers are known.

[0025] The known relative distance and orientation between at least one marker position specifying element and at least one of the plurality of markers mean that the relative distance and orientation between at least one marker position specifying element and at least one marker are fixed, that is, constant relative to each other and available before registering the object.

[0026] In particular, the known spatial relationship is an inherent geometric characteristic of the marker carrier and is thus available before registration. The known spatial relationship is provided as an input to the navigation system and the registration method in the form of fixed geometric data. The fixed geometric data is preferably provided by a fixed vector or matrix representing the spatial relationship between at least one marker position specifying element and at least one of the plurality of markers. For example, the geometric data can form a vector that defines the spatial relationship between at least one marker position specifying element and at least one of the plurality of markers in the coordinate system of the marker position specifying element.

[0027] When the spatial relationship between the marker position specifying element and some markers, and / or the spatial relationship between some markers is known, the known spatial relationship can be provided as an input to the navigation system and the registration method in the form of a geometric data set including the respective geometric data.

[0028] A radiologically detectable marker can be, for example, a gold plate arranged on the surface of a marker carrier. Generally, since the marker is made of a material that is more or less radiopaque compared to the marker carrier itself, it is radiologically detectable. Preferably, the radiologically detectable marker is configured to be used as a reference point in the generated fluoroscopic image. The radiologically detectable marker can have, for example, a zero-dimensional or one-dimensional geometric shape.

[0029] The marker position specifying element fixed to the marker carrier can be arranged at the position where the radiologically detectable marker is arranged, that is, at the same position as the marker. Alternatively, the marker position specifying element can also be arranged at a position different from the position where the radiologically detectable marker is arranged. However, at least one marker position specifying element needs to have a known relative distance and orientation with respect to at least one of the plurality of radiologically detectable markers. The known spatial relationship between at least one marker position specifying element and at least one of the plurality of radiologically detectable markers enables the determination of the position of the marker having a known spatial relationship in the coordinate system of the position detection system (and vice versa), and enables the determination of the position of the marker position specifying element in the coordinate system of the generated fluoroscopic image.

[0030] The marker position specifying element is configured to capture an electromagnetic field, for example, an alternating electromagnetic field, and provide a sensor signal representing the position and orientation of the marker position specifying element in the electromagnetic field. The provided sensor signal is transmitted to the position detection system via a cable or wirelessly. The position detection system is configured to determine the position and orientation of the marker position specifying element by analyzing the received sensor signal.

[0031] Preferably, the marker position specifying element is composed of one or more sensor coils. The marker position specifying element is preferably configured to capture six degrees of freedom (DOF). Such a 6DOF marker position specifying element can be composed of at least two sensor coils arranged at a certain angle to each other, for example, orthogonal to each other. When the marker position specifying element is composed of one or more coils, a voltage signal representing the position and orientation of the marker position specifying element in an alternating electromagnetic field can be tapped and transmitted to the position detection system.

[0032] The marker carrier provided with the position specifying element can be used as a reference position specifying element for navigating a medical device also provided with the position specifying element for the marker carrier within the electromagnetic field generated by the electromagnetic field generator of the position detection system. Further, the marker carrier provided with the position specifying element can be used as a reference position specifying element for tracking the position of one or more further marker position specifying elements of a further marker carrier relative to the position of the position specifying element.

[0033] In the registration method of the present invention, the marker carrier is arranged on the outer surface of the object. During the navigation procedure, it is preferable that the marker carrier remains on the outer surface of the object so that registration can be performed several times without moving the marker carrier itself. It is also possible to arrange the marker carrier on the outer surface of the object and then remove it for each registration. The conversion function can be repeatedly determined during the navigation procedure and is updated for each newly performed registration. By repeatedly updating the established conversion function, the accuracy of registration is maintained even if the elements of the object are displaced relative to each other during the navigation procedure.

[0034] The objects to be registered may include a plurality of elements that are displaceable relative to each other. For example, an object having several elements may be a patient's spine, and the elements may be the vertebrae of the spine. When the object is the spine, the marker carrier may be placed directly on the exposed spine or, for example, on the patient's skin at a distance from the patient's spine. Placing the marker carrier on the outer surface of the object may also mean that the marker carrier is placed on the patient's skin at a distance from the actual structure of interest, such as the patient's spine. Preferably, the marker carrier is placed on the outer surface of the object such that at least two of the plurality of markers of the marker carrier that are radiographically detectable are visible together with 3 to 4 vertebrae of the structure of interest, such as the patient's spine, in the image of the object displayed in the generated fluoroscopic image.

[0035] In a fluoroscopic image, a fluoroscopic image of at least one marker carrier placed on the outer surface of the object is generated such that at least two markers of the marker carrier are visible together with at least one segment of the object. The fluoroscopic image includes image points that are reconstructed from the fluoroscopic image data recorded by, for example, an X-ray device having an X-ray source and an X-ray detector to generate the fluoroscopic image.

[0036] A segment preferably refers to a limited area on the outer surface of an object. Taking the case where the object is a spine as an example, a segment refers to, for example, a vertebra of the spine. In the generated perspective image, it is preferable that 3 to 4 vertebrae including at least one vertebra on which the marker carrier is arranged are visible. The segments of the spine can also include a plurality of vertebrae such as 2, 3, or 4 vertebrae. The subdivision of the object to be registered into segments is selected, for example, such that each segment includes different elements among a plurality of elements of the object, or such that the relative displacement of two or more elements included in each segment can be ignored with respect to the registration accuracy. Advantageously, in the automatic registration method of the present invention, it is possible to detect the relative displacement between two or more segments of an object.

[0037] The area of the segment can be made larger than the portion of the outer surface covered by the marker carrier.

[0038] Since the marker carrier includes at least one marker position specifying element configured to provide a sensor signal representing the position and orientation of the marker position specifying element, the position and orientation of the at least one marker position specifying element can be determined, for example, by a position detection system configured to analyze the provided sensor signal. Generally, the position detection system is configured to determine the position and orientation of the at least one marker position specifying element in the coordinate system of the position detection system.

[0039] The position and orientation of a marker carrier disposed on the outer surface of an object can be calculated based on the determined position and orientation of at least one marker position specifying element. By disposing a marker carrier on the outer surface of the object, the position and orientation of the marker position specifying element corresponding to a point on the outer surface of the object in the real space, for example, the patient space, can be determined. Thereby, for example, the reference coordinate system in the object can be established by converting the coordinate system of the position detection system such that the origin thereof becomes a point on the surface of the object having a known spatial relationship with respect to the marker position specifying element of the marker carrier.

[0040] Since at least one marker position specifying element has a known relative distance and orientation with respect to at least one marker among a plurality of markers of the marker carrier, it is possible to calculate the coordinates of this marker having a known spatial relationship in the coordinate system of the position detection system and in the real space, that is, with respect to a point on the outer surface of the object. A marker that can be detected perspectively can be used as an artificial landmark brought into contact with a tracking pointer device or a sensing device in a conventional registration method. The determined position of the marker position specifying element corresponding to a point on the actual surface of the object can establish a reference coordinate system in the object. In order to establish a reference coordinate system in the object, furthermore, the known spatial relationship of at least one perspectively detectable marker having a known spatial relationship with respect to the marker position specifying element can be used.

[0041] In order to determine the conversion function, it is necessary to establish a reference coordinate system in the preoperatively acquired model.

[0042] In the registration method of the present invention, establishing a reference coordinate system in a model is achieved by generating a perspective image of at least one segment of an object and a marker carrier. Based on the known spatial relationship between at least one marker of the marker carrier and at least one marker position specifying element, in the generated perspective image, at least two perspectively detectable markers can be represented in terms of the coordinates in the real space of the object. For example, by associating the image points of the perspective image representing anatomical landmarks with the model points of the preoperatively acquired model, a reference coordinate system in the preoperatively acquired model is established, and a conversion function for converting the model points into the coordinates in the real space of the object can be determined (and vice versa). After registration, the tracked position of the medical device navigated with respect to the marker carrier is displayed on the cross-sectional image of the preoperatively acquired model displayed on the monitor.

[0043] The registration method of the present invention can be repeated several times during a navigation procedure so that the registration can be updated and accurately maintained.

[0044] In the registration method of the present invention, a plurality of individual segments of an object, particularly the segment on which the marker carrier is arranged, can be registered multiple times during a navigation procedure. Advantageously, in each registration performed, a conversion function is established according to the actual shape of the object at the time of registration. The frequency of performing the registration of the object can be adjusted, for example, according to the relative displacement between the elements of the object that exceeds a predetermined threshold value. When navigating a medical device from one segment of the object to another segment, the position of the medical device can be accurately displayed in the cross-sectional image of the preoperatively acquired model of the object by using the conversion function of each segment.

[0045] Hereinafter, a preferred modification of the registration method of the present invention will be described.

[0046] Preferably, the model points are points on the model surface of the model acquired before the operation, and the model surface corresponds to the outer surface of the object. The model surface can be a topographic image of the object. The model points, that is, the model acquired before the operation, can be generated from two-dimensional, three-dimensional, or four-dimensional images obtained by tomography.

[0047] In a modification of the automatic registration method of the present invention, the marker carrier disposed on the outer surface of the object is flexible, that is, the shape of the marker carrier can be adapted to the topography of the outer surface. The flexible marker carrier may be, for example, a belt or may have the shape of a belt. Preferably, the markers that can be detected transparently are fixed at fixed positions on the flexible marker carrier. The flexible marker carrier may have a hardness that cannot be stretched so that the relative positions of the markers fixed to the flexible marker carrier are maintained.

[0048] In this modification of the registration method using a flexible marker carrier, · The flexible marker carrier is disposed on the outer surface of the object, · A plurality of markers are fixed on the marker carrier such that each marker group composed of three markers forms a pattern distinguishable from the pattern formed by other marker groups in the generated perspective image, · Since different patterns formed by each marker group are assigned to each segment, at least two segments of the object are distinguishable in at least one generated perspective image.

[0049] The flexible marker carrier of the present invention is characterized in that markers that are transparently detectable are arranged such that each marker group composed of at least three markers forms a unique pattern on the flexible marker carrier. For example, when a certain marker group composed of three markers forms a triangle, the triangle can be distinguished from other patterns formed by other marker groups.

[0050] Each marker pattern can be assigned to define or identify individual segments of a plurality of segments of an object. Due to the plurality of distinguishable patterns, the flexible marker carrier can be interpreted as a plurality of individual marker carriers in which each of the individual marker carriers having an individual marker pattern is stitched to each other.

[0051] When generating a transparent image of the flexible marker carrier such that at least two segments of the object are distinguishable by the respective associated marker patterns, it is possible to reconstruct the topography of the object within at least these two segments. The reconstruction of the topography of the object can be achieved because the marker patterns respectively associated with each segment can be visually recognized in the transparent image generated together with the segment. Since the marker carrier is flexible, each pattern can be visually recognized in a deformed manner corresponding to the topography of the outer surface of the object. In the generated transparent image, since the deformation of the pattern and the spatial relationship between each pattern can be visually recognized together with the segment, the topography of the outer surface of the object can be computationally reconstructed.

[0052] The landmarks of the generated topography, particularly the image points of the transparent image representing these landmarks, can be assigned to the corresponding model points of the preoperatively acquired model in order to determine the conversion function within the scope of the automatic registration method of the present invention.

[0053] In another variant of the registration method of the present invention, several marker carriers, i.e., at least two marker carriers, are simultaneously arranged on the outer surface of the object. The marker carriers used may be configured identically to each other or may be configured differently from each other. Preferably, the marker carriers used are rigid, i.e., non-flexible.

[0054] In this variant where several marker carriers are simultaneously arranged on the outer surface of the object, · at least two marker carriers are simultaneously arranged on the outer surface of the object, · in each segment, at least one perspective image is generated from at least two segments of the object such that at least two markers of the arranged marker carriers are visible in the perspective image generated together with the respective segment, · the spatial relationship between the segments for which the perspective images are generated is determined using the positions of these markers visible in the generated perspective images.

[0055] For example, some marker carriers may be placed directly along the spine, e.g., along the exposed backbone, or may be placed on the patient's skin at a distance from the spine. Since each marker carrier includes at least one marker positioning element, the position and orientation of each marker carrier can be independently tracked by the position detection system. It is advantageous if the marker carriers are classified or labeled. For example, to independently track each marker carrier, the marker carriers placed on the outer surface of the object can be easily labeled with numbers such as 1, 2, 3, etc. The marker carriers can be arranged on the outer surface of the object in various patterns, e.g., as clusters or along a line. This is preferable when the markers are placed at a portion on the outer surface of the object where the shape of the marker is expected to change, i.e., a portion including a plurality of elements displaceable relative to each other. To register the object segment by segment using a plurality of marker carriers, a portion of the object including a plurality of elements displaceable relative to each other is divided into segments each including one or more elements so that each segment of the object can be individually registered.

[0056] Preferably, when the object is the spine, in the generated fluoroscopic image, 3 to 4 vertebrae, e.g., segments, can be seen. A respective marker carrier is placed for each vertebra so that each vertebra can be individually registered and tracked.

[0057] Also, by simultaneously placing the marker carriers on the outer surface of the object, there is an advantage that the recording of the fluoroscopic image data for generating the fluoroscopic image only needs to be done once, thus reducing the X-ray exposure of the object.

[0058] One of the position identifying elements of the marker carrier can be used as a reference position identifying element for tracking the positions of other marker carriers, and / or can be used as a reference position identifying element for tracking the position of a medical device provided with a position identifying element relative to this reference position identifying element.

[0059] Fluoroscopic images are generated such that at least two segments and at least two markers of respective marker carriers arranged for each segment are visible, so that based on the positions of the visible markers respectively assigned to one of the segments, the spatial relationship between the visible segments can be determined. Since each segment has at least two markers that are visible and have a known spatial relationship with each other, the spatial relationship between the segments can be determined using the positions of the markers visible in the fluoroscopic image. The known spatial relationship of the markers of each segment can be used to determine the spatial relationship between these markers and the markers of adjacent segments that are also visible in the generated fluoroscopic image. From the determined spatial relationship of the segments, the reconstruction of the topography of the object and / or the detection of the relative displacement of the segments can be performed.

[0060] In yet another variant of the registration method of the present invention, the marker carriers are displaced for each segment. For example, when the object is the spine, the marker carriers can be displaced for each vertebra, and a fluoroscopic image can be generated at each placement position. Each of the generated fluoroscopic images can be used to register each segment individually. It is also possible to stitch all of the generated fluoroscopic images and use the stitched fluoroscopic image for the registration of the object.

[0061] In a variant of the automatic registration of the present invention in which the marker carriers are displaced stepwise, · In successive steps, the marker carriers are placed on the outer surface of the object, · In each successive step, a fluoroscopic image is generated such that at least one segment and at least two markers of the marker carrier are visible. · Using the positions of the markers visible in each fluoroscopic image, the spatial relationship between the segments in which the fluoroscopic images are generated is determined.

[0062] In this variant, one marker carrier, for example a marker carrier arranged on the first segment of an object, remains on the outer surface of the object, and it is also possible for another marker carrier to be displaced segment by segment in order to register the object. The marker carrier remaining on the outer surface can be used as a reference position specifying element for tracking the relative position of a further marker carrier and / or as a reference position specifying element for tracking the relative position of a medical device navigated with respect to the object, which is equipped with a device position specifying element.

[0063] Also, in a variant in which the marker carrier is displaced step by step, the spatial relationship between the segments in which the fluoroscopic images are generated can be determined using the positions of the markers displayed in each fluoroscopic image. From the determined spatial relationship between the segments, the topography of the object can be reconstructed and / or the relative displacement of the segments can be detected.

[0064] Preferably, in the automatic registration method of the present disclosure, for each generated fluoroscopic image of one or more segments, each image point of these fluoroscopic images is associated, segment by segment, i.e., for each segment, with a model point of a model acquired preoperatively. Thus, an individual conversion function can be established for each segment. In order to display the position of the medical device on a cross-sectional image of the model of the object acquired preoperatively, the conversion function to be applied can be selected according to the segment in which the medical device is currently located.

[0065] Registering an object on a per-segment basis has the advantage that registration errors can be determined from the registration of individual segments. In particular, the registration error can be determined from the image points of at least two segments associated with each model point and the known spatial relationship between the at least two segments. This is possible because an individual transformation function is established for each segment. By comparing the results of coordinate transformation using each of the established transformation functions, the registration error can be detected. To correct the detected registration error, the registration accuracy of individual segments can be improved by updating or modifying the transformation function.

[0066] The automatic registration method of the present disclosure can include a step of displaying a preoperatively acquired model on an image display device, for example, a monitor of a navigation system, and registering so that the viewing direction of the model on the image display device aligns with the viewing direction in which perspective image data for generating a perspective image of at least one segment is recorded, based on the relationship between the image points and the model points on the image display device.

[0067] When the visualized model is aligned with the image displayed in the perspective image, it becomes easier for the user to compare the generated perspective image with the preoperatively acquired model displayed on the monitor during the navigation procedure. Since the spatial relationship (e.g., defined in an established reference coordinate system) of the coordinates of the image points and the model points can be analyzed and the viewing direction on the model can be adjusted accordingly, alignment of the viewing direction on the model with respect to the viewing direction of the generated perspective image can be achieved. Depending on the relationship between the image points and the model points, the model can be displayed on the image display device so that the viewing direction on the model corresponds to the viewing direction on the generated perspective image.

[0068] The automatic registration method of the present disclosure can include a step of detecting a relative displacement of elements of an object by determining a deviation of at least one model point of a preoperatively acquired model from a corresponding image point of the generated perspective image.

[0069] When an element of the object is displaced relative to other elements or relative to a reference registration element after the initial registration, the transformation function established for the segment of the object may become inaccurate, such as when an image point is associated with a model point that does not represent the same object feature as the image point. When re - performing the automatic registration of the present invention, a new transformation function is established so that, before the relative displacement of the elements of the object, the image point corresponds to a corresponding model point different from its corresponding model point. By calculating the deviation of the new corresponding model point from the previous corresponding model point, for example, a deviation vector in a reference coordinate system, the relative displacement of the elements of the object can be detected. For example, the relative displacement of the vertebrae of the spine can be detected during surgery.

[0070] As described above, the automatic registration method of the present invention including the step of "detecting the relative displacement of the elements of the object by determining the deviation between the model point and the corresponding image point" can further include a step of adapting the preoperatively acquired model of the subject for each segment using the determined deviation.

[0071] Therefore, the preoperatively acquired model generated from the two-dimensional, three-dimensional, or four-dimensional images of the patient obtained by tomography can be adapted based on the determined deviation. When the model is updated based on the determined deviation, the user can use the model representing the actual shape of the object whose shape has changed after generating the preoperatively acquired model before the navigation procedure or after adapting the model during the navigation procedure. Advantageously, individual deviations can be determined and the model can be adapted segment by segment due to the registration performed segment by segment for each segment. Adapting the preoperatively acquired model segment by segment is preferably performed during the operation by a navigation system configured to execute a properly implemented algorithm.

[0072] In particular, an automatic registration method for detecting the relative displacement of elements of an object by determining the deviation of model points from corresponding image points, optionally including the step of adapting the preoperatively acquired model segment by segment according to the determined deviation as described above. The automatic registration method comprises the step of providing a device having a device position specifying element for determining the position and orientation in an electromagnetic field; the step of determining the position and orientation of the device position specifying element in the electromagnetic field relative to the position and orientation of at least one marker position specifying element; the step of displaying the adapted model of the object on an image display device together with at least a part of the said device; and the step of adapting the position and orientation of the said device on the displayed model using the determined deviation of at least one model point from the corresponding image points of the generated perspective image.

[0073] The marker position specifying element of at least one marker carrier arranged on the outer surface of the object can likewise be used as a reference position specifying element of a device, for example a medical device, which also has a device position specifying element. If a model acquired preoperatively is registered to the object, at least a part of the position icons or digital displays of the device can be displayed on the model of the object acquired preoperatively, whereby the user can align his orientation on the displayed model when navigating the device relative to the object.

[0074] Since the model acquired preoperatively can be adapted according to the determined deviation of the model points from the corresponding image points, it is likewise preferable to adapt the position of the device on the adapted model in order to provide a representation as close as possible to the actual navigation situation. The determined deviation, for example a deviation vector, can be used to transform the position of the device to the coordinates of the corresponding model points of the adapted model. If the model and the position of the device on the model are adapted according to the determined deviation, the user can accurately navigate the device relative to the object and avoid navigation errors caused by an inaccurate display of the position of the device on the displayed model.

[0075] In an automatic registration method in which the position and orientation of the device on the displayed model are adapted using the determined deviation of at least one model point from the corresponding image points of the generated fluoroscopic image, preferably, the adaptation of the position and orientation of the device on the adapted model displayed on the monitor is carried out segment by segment for each segment of the object displayed in the generated fluoroscopic image. It is possible to adapt the position and orientation of the device on the adapted model displayed on the monitor segment by segment because within the scope of the automatic registration method of the present invention for each segment, individual registration functions that can be used for adapting the position and orientation of the device in each segment are established.

[0076] The automatic registration method described in this specification is a step of arranging at least one reference position specifying element in a fixed spatial relationship with respect to an object, wherein the at least one reference position specifying element is configured to provide a reference sensor signal representing the position and orientation of the reference position specifying element in an electromagnetic field, and the step of determining the position and orientation of at least one marker position specifying element in the electromagnetic field with respect to the position and orientation of the at least one reference position specifying element.

[0077] The reference position specifying element, which may also be referred to as a patient localizer, can be an additional element of the navigation system. Preferably, such a reference position specifying element is fixedly arranged with respect to the object. The reference position specifying element may be arranged adjacent to the object or fixedly attached to the object itself. The position and orientation of the reference position specifying element can be determined by a position detection system configured to analyze the provided reference sensor signal representing the position and orientation of the reference position specifying element in the electromagnetic field.

[0078] The position and orientation of at least one marker position specifying element of the marker carrier with respect to the position and orientation of the reference position specifying element can be determined by a position detection system having a magnetic field generator for generating an electromagnetic field, for example, an alternating electromagnetic field.

[0079] In particular, when at least one reference position specifying element is arranged adjacent to or attached to the object, when implementing the registration method of the present invention, the automatic registration method of the present invention determining the position and orientation of at least one marker position specifying element at an initial time point and subsequent time points with respect to the at least one reference position specifying element; detecting a change in the position and / or orientation of the marker position specifying element with respect to the position and orientation of the at least one reference position specifying element at a later time point relative to the relationship at the initial time point.

[0080] The position and orientation of the marker position specifying element can be tracked relative to the reference position specifying element. In addition, the position and orientation of a device equipped with a device position confirmation element can be tracked relative to the reference position confirmation element, or relative to the marker position confirmation element, or relative to both. By detecting changes in the position and / or orientation of the marker position specifying element relative to the position and orientation of the reference position specifying element at a later time point with respect to the relationship at the first time point, it is possible to detect the relative displacement of an object, particularly an element of the object, during a navigation procedure. It can be used to trigger a new auto-registration of the object in order to update information regarding at least one object or object element displaced relative to the reference position specifying element and at least one established conversion function. Since the marker carriers are associated with each segment of the object, it is possible to detect, for example, the relative displacement of a particular segment with respect to another segment or the reference position specifying element. Since the relative displacement of individual segments can be detected, it is possible to update only the conversion function associated with this particular object, while continuing to apply the conversion functions established for other segments for which no relative displacement has been detected.

[0081] When the auto-registration method of the present invention is implemented to register a patient's spine, · The object is the patient's spine, and at least one segment of the spine includes one or more vertebrae, · The model acquired preoperatively is a model of at least a part of the spine, · At least one marker carrier is arranged on the spine, · At least two of the plurality of markers that are fluoroscopically detectable on the marker carrier are made visible together with at least one vertebra, and at least one fluoroscopic image is generated from at least one segment including the vertebra on which the marker carrier is arranged, ·For each generated fluoroscopic image of one or more vertebrae, each image point of these fluoroscopic images is associated with a model point of the spinal model acquired preoperatively on a segment-by-segment basis.

[0082] Preferably, the segment includes one or two vertebrae, and the fluoroscopic image is generated such that three or four vertebrae can be seen. The marker carrier may be placed directly on one or more vertebrae of the exposed spine, or may be placed on the patient's skin, and thus, at a distance from one or more vertebrae.

[0083] In the automatic registration method of the present invention, when the object is the spine, it is particularly preferable that the image points of the fluoroscopic images representing the vertebrae are associated with the respective model points of the same vertebrae in the spinal model acquired preoperatively. The vertebrae can be used as anatomical landmarks for registering the spine.

[0084] In the automatic registration method of the present invention, when the object is the spine, the spine can be automatically registered by simultaneously placing a plurality of marker carriers along the spine. For example, an automatic registration method in which a plurality of marker carriers are simultaneously placed along the spine during spinal surgery is ·Generating at least one fluoroscopic image of at least one vertebra on which the marker carrier is placed, ·For each generated fluoroscopic image, the image points of the fluoroscopic image representing the vertebra are associated with the corresponding model points representing the same vertebra in the spinal model acquired preoperatively.

[0085] By associating the image points representing points on the vertebrae with the corresponding model points representing the same points on the vertebra model, each vertebra can be registered individually, i.e., segmentally for each vertebra, and as a result of the segmental registration for each vertebra, an individual transformation function can be established. As a result of segmentally registering the spine, the displacement of each vertebra relative to other vertebral vertebrae or to a reference position specifying element can be tracked individually. When a relative displacement of the vertebrae is detected, the corresponding transformation function can be updated by registering each vertebra again.

[0086] The relative displacement of the spine or the vertebral vertebrae can be detected during surgery, for example, by determining the deviation of at least one model point of the spine model acquired preoperatively from the corresponding image point of the generated fluoroscopic image.

[0087] Advantageously, the automatic registration method of the present disclosure can be implemented to register the patient's spine before spinal surgery for treatment planning or during spinal surgery to assist the surgeon during the treatment.

[0088] For example, spinal fixation can include registering the spine before or during surgery using at least one marker carrier disposed on the vertebrae, or using at least one marker carrier disposed only on the spine for registering the spine during surgery and then removing it. During spinal surgery, at least one marker carrier can be repeatedly placed for registration and then removed multiple times to repeatedly update one or more established transformation functions.

[0089] In a spinal fixation procedure performed on a spine registered by applying the automatic registration method of the present invention, for example, two or more vertebrae can be joined by pedicle screws, plates, or cages. Spinal fixation can treat, for example, spinal stenosis, spondylolisthesis, spondylosis, spinal fractures, spinal tumors, scoliosis, posterior branch syndrome, degenerative disc disease, intervertebral disc herniation, discogenic pain, or kyphosis.

[0090] When an object is a spine automatically registered by implementing the registration method of the present invention using at least one marker carrier disposed on a vertebra to register the spine during surgery, or at least one marker carrier disposed on the spine to register the spine only during surgery and then removed, in a spinal surgery, for example, polyaxial screws can be screwed into each spine where at least one marker carrier is disposed. Generally, in spinal surgery, polyaxial screws are used to connect vertebrae to rods, for example, to treat degenerative cervical spondylosis and curvature. Preferably, the position of the screw can be tracked using a position detection system, for example, by disposing a position specifying element on the polyaxial screw. During surgery, the position of the tracked polyaxial screw can be displayed on a spinal model to assist the surgeon in placing the polyaxial screw.

[0091] In particular, before or during a minimally invasive spinal surgery, the spine can be registered using the automatic registration method of the present disclosure. To register the spine as part of a minimally invasive spinal surgery, at least one marker carrier can be disposed on the vertebra to register the spine during surgery, or at least one marker carrier can be disposed on the spine to register the spine only during surgery and then removed.

[0092] By implementing the automatic registration method of the present invention, minimally invasive spinal surgeries in which the spine is registered include anterior cervical discectomy, artificial disc replacement or total disc replacement, epidural adhesion lysis, laminotomy, laminectomy, oblique lateral lumbar interbody fusion (OLLIF), percutaneous vertebroplasty, and endoscopic discectomy. Minimally invasive spinal surgery on the registered spine can be performed for the treatment of degenerative disc disease, disc herniation, fractures, tumors, infections, instability, and deformities.

[0093] When it is necessary to perform a bone marrow biopsy on the spine, it is advantageous to register the spine by implementing the automatic registration method of the present disclosure. Preferably, the spine undergoing the bone marrow biopsy is registered using at least one marker carrier disposed on the vertebra for registering the spine during surgery, or at least one marker carrier disposed on the spine for registering the spine only during surgery and then removed. Bone marrow biopsy can diagnose various diseases such as leukemia, multiple myeloma, lymphoma, anemia, and pancytopenia.

[0094] A Jamshidi needle can be inserted into the spine registered by implementing the automatic registration method of the present disclosure. The Jamshidi needle is a cannula needle having a tapered cutting tip capable of performing a bone marrow biopsy. The Jamshidi needle itself is provided with a device localization element and can be connected to a position detection system. The position detection system can track the position of the Jamshidi needle provided with the localization element relative to at least one position of the marker carrier disposed on the patient's body and / or relative to the position of the reference localization element. The position of the Jamshidi needle can be displayed in a preoperative model of the patient, and the surgeon can track the position of the Jamshidi needle in the patient's body, particularly the insertion of the Jamshidi needle into the vertebral body, in the cross-sectional image of the vertebral body obtained by tomography and displayed on the monitor.

[0095] Another medical device that can be used in a surgical procedure performed on a patient registered by practicing the registration method of the present invention is a hollow needle configured to be used in a fine needle aspiration biopsy (FNAB). The patient is automatically registered with at least one marker carrier placed on the patient to register the patient during the surgery, or with at least one marker carrier placed on the patient only to register the patient during the surgery and then removed, and the hollow needle is inserted into the patient's body to perform a fine needle aspiration biopsy (FNAB). Preferably, the hollow needle comprises a position specifying element used to track the position of the hollow needle relative to the patient when guiding the hollow needle to a target position that can be the patient's spine or another body part.

[0096] An automatic registration method for registering the spine using at least one marker carrier placed on the vertebra to register the spine during surgery, or at least one marker carrier placed on the spine only to register the spine during surgery and then removed, may include the step of inserting a cannula-equipped medical device, such as a catheter or a hollow needle, having at least one device position specifying element for providing position and orientation information, into the patient's body. The device position specifying element can be disposed, for example, in the lumen of the cannula-equipped medical device so that it can be removed after guiding the medical device to a target position within the patient's body. The position of the medical device having the device position specifying element can be tracked relative to the patient, or, for example, relative to a marker position specifying element and / or a reference position specifying element, using a position detection system. After the device position specifying element is removed from the lumen of the medical device, the lumen can be used, for example, for aspiration or irrigation purposes, or for delivering a drug to the patient.

[0097] In the automatic registration method for registering the spine of the present disclosure, at least one marker carrier is placed on the spine to register the spine during the operation, or at least one marker carrier is placed on the spine only for registering the spine during the operation and can then be removed, and a medical instrument with a cannula can be inserted into the patient's body to provide a working channel for additional medical devices. Preferably, the additional medical device comprises at least one device positioning element for providing position and orientation information. The position of the additional medical device guided through the working channel of the medical instrument with a cannula can be displayed on a model obtained preoperatively, which is displayed on the monitor of the navigation system.

[0098] The marker carriers that can be used in the automatic registration method described herein can be implemented in various shapes, for example, in the shapes of a cage, a plate, a stick, a cylinder, a cube, etc., and can be made of various materials or combinations of materials, preferably synthetic materials such as silicone. In particular, the marker carriers that can be used in the automatic registration method of the present disclosure can be realized in the shape of the fiducial described and explained in FIGS. 4 to 9 of WO 2014 / 184382 A1. Preferably, the marker carriers that can be used in the automatic registration method of the present disclosure have a size such that a plurality of markers that can be detected fluoroscopically can be arranged so as to be distinguishable as individual markers in the generated fluoroscopic image. Preferably, the marker carriers used in the automatic registration method of the present invention are made of a material having a lower radiopacity than the fluoroscopically detectable markers fixed thereto. Alternatively, the marker carriers used in the automatic registration method of the present invention can be made of a material that is substantially transparent to X-rays.

[0099] The marker carriers that can be used in the automatic registration method of the present disclosure have in common that they have a plurality of markers fixed thereto and that are detectably transparent, and at least one marker position specifying element fixed thereto. The at least one marker position specifying element is configured to provide a sensor signal representing the position and orientation of the marker position specifying element in an alternating electromagnetic field. In particular, the relative distances and orientations between at least one marker position specifying element and at least one of the plurality of markers of the marker carrier are known.

[0100] Regarding a navigation system, the above object is achieved by a navigation system configured to perform a registration method according to the automatic registration method of the present disclosure. The navigation system includes at least one marker carrier, a position detection system, an X-ray device, and a registration device.

[0101] The at least one marker carrier has a plurality of markers fixed thereto and that are detectably transparent, and at least one marker position specifying element. The at least one marker position specifying element is configured to provide a sensor signal representing the position and orientation of the marker position specifying element within an electromagnetic field. The at least one marker of the marker position specifying element and the plurality of markers that are detectably transparent are arranged such that the relative distances and orientations between the at least one marker position specifying element and the at least one of the plurality of markers that are detectable are known.

[0102] When the marker carrier is arranged on the outer surface of the object, the position of the marker position specifying element can correspond to or be associated with a position on the outer surface of the object in the real space, and can be determined by a position detection system. Since at least one of the plurality of markers that can be detected perspectively has a known spatial relationship with the marker position specifying element, the position of a point on the outer surface of the object in the real space can be converted into the coordinates of the model points of the preoperatively acquired model by using the conversion function established by the registration device of the navigation system.

[0103] The position detection system includes an electromagnetic field generator for generating an electromagnetic field, for example, an alternating electromagnetic field. The position detection system is configured to determine the position and orientation of at least the marker position specifying element in the electromagnetic field.

[0104] The X-ray device includes an X-ray source and an X-ray detector for recording X-ray image data capable of generating a fluoroscopic image of at least the marker carrier so that at least two markers of the marker carrier can be seen in the generated fluoroscopic image. The X-ray device can be, for example, a C-arm.

[0105] The registration device is configured to associate the image points of the generated fluoroscopic image with the model points of the preoperatively acquired model. In particular, the registration device is connected to the position detection system and can access and use the determined position and orientation of at least one marker position specifying element. The registration device is also configured to process the image information of the fluoroscopic image generated, for example, by the registration device itself or by another suitable processing device configured to reconstruct the fluoroscopic image points from the fluoroscopic image data recorded by the X-ray device to generate the fluoroscopic image.

[0106] In particular, the registration device is configured to use the determined position and orientation of at least one marker position specifying element, the known relative distances and orientations between at least one marker position specifying element and at least one of the plurality of markers, and / or the known spatial relationships between a further marker of the plurality of markers and at least one marker having known relative distances and orientations with respect to the at least one marker position specifying element.

[0107] The known spatial relationship between the marker position specifying element and at least one marker can be represented, for example, by a vector pointing from the coordinates of the marker position specifying element to the coordinates of the marker. For example, the vector can be defined in the coordinate system of the marker position specifying element. Using a position detection system, the position and orientation of the coordinate system of the marker position specifying element can be determined with respect to the coordinate system of the position detection system and can be associated, for example, with an electromagnetic field generator. The vector representing the known spatial relationship can be transformed into another coordinate system and can be used, for example, to establish a transformation function within the scope of the automatic registration method of the present invention.

[0108] The registration device is configured to establish a conversion function for converting coordinates between a reference coordinate system established in an object and a reference coordinate system established in a preoperatively acquired model by associating image points of a generated fluoroscopic image with model points of the preoperatively acquired model. The registration device may be part of a data processing device of a navigation system, or may be, for example, a separate component connected to the data processing device and / or monitor of the navigation system. When the generated fluoroscopic image shows one or more segments, the registration device is particularly preferably configured such that for each of the generated fluoroscopic images of the one or more segments, the respective image points of these fluoroscopic images can be segmentally associated with the model points of the preoperatively acquired model. The registration device can be configured to identify and / or define segments of an object according to markers of each marker carrier displayed in the generated fluoroscopic image.

[0109] Devices including device position specifying elements, such as medical devices, can be connected to a navigation system. Thereby, the position of the device with respect to an object, for example, with respect to a reference position specifying element, or with respect to a marker position specifying element used as a reference position specifying element, can be tracked. The tracked position of the device can be displayed to the user on a model of the object acquired preoperatively to assist the user when navigating the device.

Brief Description of the Drawings

[0110] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[0111]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

DETAILED DESCRIPTION OF THE INVENTION

[0112] Figure 1 is a flowchart representing a method for automatically registering an object.

[0113] The automatic registration method of the present disclosure prepares, in step S1, a model of an object acquired preoperatively. The model can be a 2D, 3D, or 4D model generated from 2D, 3D, or 4D image data recorded using a tomography method. For example, the model acquired preoperatively can be generated from 2D fluoroscopic images registered to a 3D model. The model can be generated as a topographic image of the object so as to represent the outer surface of the object or at least a part of the object.

[0114] To assist the user when navigating a device with respect to the object, the model can be displayed on a monitor of the navigation system. If the device has a device position identifying element, the position of the device can be tracked by a position detection system of the navigation system and the position of the device can be displayed on the model of the object.

[0115] In the model displayed on the monitor, in order to display the position of the device, for example, by an icon or a digital representation of the device, first, it is necessary to register the model with respect to the object.

[0116] The automatic registration method of the present disclosure performs registration using one or more marker carriers prepared in advance in step S2. At least one marker carrier has a plurality of markers that are fixedly attached thereto and are detectably transparent, and at least one marker position specifying element. In particular, one or more marker carriers used in the automatic registration method of the present disclosure may be configured in the same manner as the marker carriers described with reference to FIGS. 3 to 7.

[0117] The marker position specifying element may be composed of one or more sensor coils, for example, two sensor coils arranged orthogonally to each other and configured to capture an electromagnetic field. The electromagnetic field captured by the marker position specifying element, for example, an alternating electromagnetic field, may be an electromagnetic field generated by an electromagnetic field generator of the navigation system. The electromagnetic field captured by the marker position specifying element induces a voltage in the sensor coil that depends on the position and orientation of the marker position specifying element within the electromagnetic field. The position and orientation of the marker position specifying element can be determined from the tap sensor signal representing the voltage induced in the sensor coil by a position detection system connected to the marker position specifying element via, for example, a cable for receiving the sensor signal. In particular, by using a marker position specifying element composed of two sensor coils arranged orthogonally to each other, it is possible to determine the position and orientation in six degrees of freedom.

[0118] The detectably transparent marker of the marker carrier may be, for example, gold plating. The detectably transparent marker of the marker carrier serves as a reference point in the generated fluoroscopic image.

[0119] At least one marker carrier to which a plurality of markers detectable in perspective and at least one marker position specifying element are fixed has a known relative distance and orientation between the at least one marker position specifying element and at least one of the plurality of markers detectable in perspective.

[0120] In particular, the known spatial relationship described above is available a priori in the form of fixed geometric data, and can be provided as an input to the automatic registration method of the present disclosure, for example, by a fixed vector or matrix representing the fixed spatial relationship between the at least one marker position specifying element and at least one of the plurality of markers detectable in perspective.

[0121] For example, the geometric data can first be provided in the form of a vector representing the spatial relationship between the marker position specifying element and the marker in the coordinate system of the marker position specifying element. Within the scope of the automatic registration method of the present disclosure, the vector can be converted, for example, into a reference coordinate system for registering an object.

[0122] To implement the automatic registration method of the present disclosure, in step S3, at least one marker carrier is arranged on the outer surface of the object. In various modifications of the automatic registration method of the present disclosure, two or more marker carriers are arranged on the outer surface of the object at the same time. In other modifications of the automatic registration method of the present disclosure, one or more marker carriers are arranged on the outer surface of the object in consecutive steps.

[0123] In step S4, at least one perspective image of at least one marker carrier arranged on the outer surface of the object is generated together with at least one segment of the object. In particular, the perspective image is generated such that at least two markers of the marker carrier arranged on the outer surface of the object are visible together with at least one segment of the object in the generated perspective image.

[0124] Preferably, the area of the segment of the object is defined such that the relative displacement of the elements constituting the segment can be ignored with respect to the registration accuracy. For example, the object itself can be divided into a number of segments necessary to ensure that the potential relative displacement between two points within the area of each segment can be ignored. Within the scope of the automatic registration method of the present disclosure, the relative displacement of each segment with respect to each other can be determined. Preferably, a marker carrier is arranged on each segment and associated with each segment. In order to generate a perspective image of the object, a plurality of marker carriers can be arranged on each segment of the object. In a modification of the automatic registration method of the present disclosure, the marker carrier is displaced for each segment, and in each step of arranging the marker carrier, a perspective image of the marker carrier is generated together with each segment on which the marker carrier is arranged. The perspective image is generated from pre-recorded perspective image data.

[0125] When a plurality of marker carriers are arranged on the outer surface of an object, preferably, at least one perspective image is generated such that at least two markers of each marker carrier arranged on the outer surface of the object are visible together with each segment. In the at least one generated perspective image, in the plurality of segments and in each segment, it is preferable that at least two markers of each marker carrier arranged on this segment are visible. When the plurality of markers have a known spatial relationship with respect to each other, each of the at least two markers visible together with each segment can be used, for example, to calculate the coordinates of the markers invisible in the coordinate system of the perspective image in order to reconstruct the topography of the object. It is beneficial to assign numbers such as 1, 2, 3, etc. to the marker carriers arranged on the object at the same time. Numbering the marker carriers is advantageous for associating the visible markers with the corresponding segments. In the generated perspective image, since a plurality of segments and at least two markers are visible in each segment, it is possible to determine the spatial relationship between the segments based on the positions of these markers visible in the generated perspective image.

[0126] In the automatic registration method of the present disclosure, when the marker carriers are arranged on the outer surface of the object in continuous steps, in each of the continuous steps, a perspective image of the marker carrier and at least the segment on which the marker carrier is arranged can be generated. As a result, in each of the continuous steps, individual perspective images of the marker carrier and each segment are generated. The perspective images generated in each of the continuous steps can be generated so as to overlap with the adjacent perspective images.

[0127] Each perspective image can be used to distort the model segmentally with respect to each segment of the object. It is also possible to stitch the perspective images into a larger perspective image that displays all the segments for which the perspective images were generated. The stitched perspective image preferably has at least two perspectively detectable markers visible with each respective segment in each segment where the marker carriers are arranged in successive steps. The stitched perspective image showing a plurality of segments and at least two associated markers in each segment is similar to the perspective images generated from a plurality of marker carriers arranged simultaneously on the object. When a plurality of perspective images are stitched into one perspective image, the stitched perspective image can be used to register the preoperatively acquired model with respect to the object. It is possible to determine the spatial relationship between segments using the positions of the markers visible in each respective perspective image from a plurality of stitched or unstitched perspective images.

[0128] It is also possible to use a flexible marker carrier, such as a belt, having a plurality of perspectively detectable markers and at least one marker position specifying element to register the object. The flexible marker carrier can be arranged on the outer surface of the object and can have a topography adapted to the topography of the outer surface. The perspectively detectable markers are preferably fixed to the belt on the flexible marker carrier such that in the generated perspective image, each marker group composed of at least three markers forms a pattern distinguishable from the pattern formed by another marker group composed of at least three markers. Since each marker group composed of at least three markers can be distinguished from another group composed of at least three markers, the segments of the object can be identified in the generated perspective image by associating each segment with a separate marker group.

[0129] Using a marker group composed of at least three markers is advantageous because, for example, from the deformation of a triangle formed by a marker group composed of three markers visible in the generated perspective image, it is possible to determine the orientation of the triangle with respect to the outer surface of the object, particularly the relevant segment of the object. Since a plurality of marker groups are fixed on the marker carrier, for a plurality of segments, the orientation of each marker group with respect to the surface of each segment can be determined. This information can be used to reconstruct the topography of the outer surface of the object.

[0130] Before generating at least one perspective image, or simultaneously with generating at least one perspective image, or after generating at least one perspective image, in step S5 of the automatic registration method of the present disclosure, determine the position and orientation of at least one marker position specifying element of a marker carrier disposed on the outer surface of the object. The determination of the position and orientation of the marker position specifying element can be performed, for example, by a position detection system of a navigation system.

[0131] Since the marker carrier provided with the marker position specifying element is disposed on the outer surface of the object, the determined position and orientation of the marker position specifying element can be associated with the position of a point on the outer surface of the object in the real space. The determined position and orientation of the marker position determining element associated with a point on the outer surface of the object can be used to establish a reference coordinate system in the object.

[0132] The reference coordinate system can be established in the object using the determined position and orientation of the marker position specifying element and the position of the markers that can be detected perspectively. This is possible because the relative distance and orientation between at least one marker position specifying element and at least one of the plurality of markers are known.

[0133] To register an object, it is necessary to establish a reference coordinate system in the preoperatively acquired model in order to find a conversion function for converting coordinates between two reference coordinate systems.

[0134] To establish a reference coordinate system in the preoperatively acquired model, in step S6 of the automatic registration method of the present disclosure, the image points of the generated perspective image are associated with the model points of the preoperatively acquired model. The association of the image points of the perspective image to the model points of the model can be performed using the known spatial relationship between the marker position specifying element and at least one of the perspectively detectable markers. Instead of, or in addition to, using the known spatial relationship between the marker position specifying element and at least one perspectively detectable marker, the position and orientation of the marker position specifying element, and the known spatial relationship between another marker and at least one marker having a known spatial relationship with respect to the marker position specifying element can also be used. Further, the position of a point on the outer surface of the object in the real space, for example, a point on the real surface of the object, whose coordinates in the coordinate system of the position detection system can be determined by detecting the position and orientation of the marker position specifying element, can be used to associate it with the model points of the preoperatively acquired model.

[0135] Advantageously, in the automatic registration method of the present disclosure, in each of the generated perspective images, the image points can be associated with the model points of the model acquired preoperatively on a segment-by-segment basis. Associating the image points with the model points on a segment-by-segment basis may include associating the image points of the segment of the object with the model points of the corresponding segment of the model of the object acquired preoperatively. For example, artificial or anatomical landmarks can be identified and the image points representing the landmarks can be associated with the corresponding model points. The registration on a segment-by-segment basis includes establishing, for each segment, an individual transformation function that can be updated independently of the transformation functions established for other segments. By the registration on a segment-by-segment basis, the relative displacement of a particular segment with respect to other segments and / or with respect to the fiducial positioning elements can be detected, and the particular segment can be re-registered to update the transformation function associated with that segment, thereby making it possible to maintain a high registration accuracy.

[0136] Since individual transformation functions can be established for each segment of the object, it is possible to detect a registration error that can be corrected in order to improve the registration accuracy. The registration error may occur already in the initial registration, for example, due to fluctuations in the electromagnetic field, or may occur after the initial registration, for example, due to the relative displacement of one or more elements of the object. By analyzing some of the established transformation functions, the respective coordinate transformations can be compared, so that it is possible to detect the distortion error even during the navigation procedure or during the surgery.

[0137] By registering each segment, it is also possible to detect the relative displacement of the elements of at least one object with respect to other segments or with respect to the fiducial position identifying element. When one relative displacement of the elements of the object is detected, for example, one or more transformation functions associated with the segment displaced relative to other segments can be updated by repeating the registration of each segment. In particular, the relative displacement of the elements of the object can be detected by determining the deviation of at least one model point of the preoperatively acquired model from the corresponding image point of the fluoroscopic image. The determined deviation can represent the magnitude of the relative displacement of the elements, for example, with respect to a deviation vector defining the direction and relative distance of the relative displacement of the elements of the object.

[0138] An advantage of the automatic registration method of the present disclosure is that an object can be registered segment by segment. The automatic registration method of the present disclosure is particularly suitable for registering individual segments of an object that includes a plurality of elements that can be displaced relative to each other. For example, the object can be a patient's spine and the segments can be vertebrae. When registering the spine, for example, by arranging a plurality of marker carriers along the spine, segments can be defined that include one or more vertebrae that can be registered individually. The relative displacements between the plurality of segments can be tracked segment by segment, and the transformation function can be updated according to the detected relative displacements between the segments.

[0139] FIG. 2 shows a navigation system 200 configured to implement a registration method for automatically registering an object, for example, the registration method described with reference to FIG. 1.

[0140] The navigation system 200 includes two marker carriers 202, 204, an X-ray device including an X-ray source 206 and an X-ray detector 208, a position detection system 210 including an electromagnetic field generator 212 for generating an electromagnetic field, a registration device 214, and a monitor 216.

[0141] As an example, the marker carriers 202, 204 are arranged on the outer surface 217 of the object 218. Each of the marker carriers 202, 204 has a plurality of markers 220 that are fixedly attached to the marker carrier and are radiographically detectable, and a marker position specifying element 222. The marker carriers 202, 204 of the navigation system 200 can be configured in the same manner as the marker carriers described with reference to FIG. 1. For example, the marker carrier may be a hard or flexible marker carrier, or may be configured as described with reference to FIGS. 3 to 7. The navigation system 200 may also include only one of the marker carriers 202, 204. In order to register the object 218, the marker carrier can be displaced for each segment. Further, the navigation system 200 includes a number of marker carriers more than two marker carriers 202, 204, and in order to register the object 218, some marker carriers can be arranged simultaneously on the outer surface 217 of the object 218, for example, as a cluster or along a line. The navigation system 200 can optionally include a reference position specifying element (not shown) that is configured to capture an electromagnetic field and is fixedly arranged with respect to the object 218. If present, the reference position specifying element may be fixed to the object 218 itself, or may be fixedly arranged at a distance from the object 218. The position and orientation of the marker carriers 202, 204 can be determined using the position detection system 210, for example, with respect to the position of the reference position specifying element.

[0142] The marker position specifying element 222 is configured to capture the electromagnetic field generated by the electromagnetic field generator 212 of the position detection system 210 and provide a sensor signal representing the position and orientation of the marker position specifying element 222 in the electromagnetic field. When the marker position specifying element 222 is composed of one or more sensor coils, the provided sensor signal represents the voltage induced in the coil, which depends on the position and orientation of the marker position specifying element 222 in the electromagnetic field.

[0143] When the marker carriers 202, 204 are arranged on the outer surface 217 of the object 218, the position and orientation of the marker position specifying element 222 are determined and associated with the position of a certain point on the outer surface 217 of the object 218 in the real space 219. Based on the known spatial relationship between the marker position specifying element 222 and the position of the above point on the outer surface 217 of the object, the position of the above point can be represented by the coordinates of the coordinate system 211 of the position detection system (and vice versa).

[0144] When the marker carrier 202 is arranged on the outer surface 217 of the object 218, the marker position specifying element 222 can be designed to be directly arranged on the outer surface 217 so that the position of the marker position specifying element 222 determined by the position detection system 210 directly corresponds to the position of a certain point on the outer surface 217 of the object 218. Also, when the marker carrier 202 is arranged on the outer surface 217 of the object 218, the marker position specifying element 222 can be designed to be arranged at a distance from the outer surface 217 so that the coordinates in the coordinate system 211 of the position detection system for each point on the outer surface 217 can be calculated by considering the offset representing the relative distance between the point on the outer surface 217 and the position of the marker position specifying element 222.

[0145] Since at least one of the plurality of markers 220 that can be detected perspectively has a priori known spatial relationship (indicated by arrow 221) with respect to the marker position specifying element 222, the position of the marker 220 can be represented by coordinates in the coordinate system 211 of the position detection system 210 and also by coordinates in the object space, i.e., the real space 219. By the position and orientation of the marker position specifying element 222 and, optionally, by using at least one marker 220 having a known relative distance and orientation with respect to the marker position specifying element 222, a reference coordinate system 230 in the object 218 can be established.

[0146] Using an X-ray device, for example a C-arm, perspective image data representing at least one marker carrier 202, 204 of the object 218 and at least one segment 226, 228 can be recorded. A perspective image can be generated by reconstructing image points from the recorded perspective image data. The perspective image is preferably generated such that at least two markers 220 of each marker carrier 202, 204 are visible in the image together with at least one segment 226, 228 of the object 218. Thereby, a reference coordinate system in the preoperatively acquired model can be established, and a conversion function for converting the coordinates of the model points of the model into the coordinates of the points on the outer surface 217 of the object 218 in the real space can be obtained.

[0147] Registration of the object, i.e., establishment of the conversion function 229 for converting coordinates between the reference coordinate system 230 of the object 218 and the reference coordinate system 232 of the model, is performed by the registration device 214. The registration device 214 is configured to access the generated fluoroscopic image and associate the image points of the generated fluoroscopic image with the model points of the object 218 acquired preoperatively. The model data representing the model acquired preoperatively can be directly stored in the storage (storage medium) of the registration device. The registration device 214 is also connected to the position detection system 210 to access the determined position and orientation of the marker position specifying element 222.

[0148] The registration device 214 of the navigation system 200 is part of a data processing device (not shown) of the navigation system 200. In another embodiment, the registration device is part of the position detection system. In yet another alternative embodiment, the position detection system and the registration device are components of the same data processing device of the navigation system.

[0149] The registration device 214 is configured to establish a reference coordinate system 230 in the object 218 using the determined position and orientation of the marker position specifying element 222 and, optionally, the spatial relationship between at least one marker 220 and the marker position specifying element 222. The registration device 214 is configured to establish a reference coordinate system 232 in the model using a perspective image generated such that at least two markers 220 are visible together with at least one segment. Since the registration device 214 is configured to associate the image points of the perspective image with each model point of the model using the determined position and orientation of the marker position specifying element 222 and the known relative distances and orientations between the marker position specifying element 222 and at least one of the plurality of markers 220 that are perspectively detectable, and / or the spatial relationships between other markers having known spatial relationships with respect to the marker position specifying element 222, the establishment of the reference coordinate system in the model can be achieved by the registration device 214.

[0150] The known spatial relationship between the marker position specifying element 222 and the marker 220 is provided as geometric data as an input to the registration device 214 prior to registration. The geometric data may be provided, for example, as an input by the user, or may be stored in a storage medium of the registration device 214 such that the registration device 214 can read the geometric data from the storage medium. The geometric data may be provided, for example, in the form of a fixed vector or matrix representing a fixed spatial relationship between the marker position specifying element 222 and one of the markers 220. When the spatial relationships between the marker position specifying element 222 and two or more markers 220 are known, a geometric data set including the geometric data of each of the known spatial relationships can be provided as an input to the registration device 214.

[0151] In particular, the registration device 214 is configured to associate the image points of the generated perspective image with the model points of the preoperatively acquired model on a segment-by-segment basis.

[0152] The registration device 214 is connected to the monitor 216 of the navigation system 200. For example, when using a device (not shown) having a device position specifying element together with the navigation system 200, the position and orientation of the device can be displayed on a cross-sectional image of the preoperatively acquired model displayed on the monitor 216. The navigation system 200 can be used to assist the user when navigating the device with respect to the object 218.

[0153] FIG. 3 shows a navigation system 300 for registering a patient 302. The navigation system 300 includes a position detection system 304, a registration device 305, a C-arm 306, a reference position specifying element 308, and a marker carrier 310 having a radiologically detectable marker 312 and a marker position specifying element 314. The marker 312 and the marker position specifying element 314 are fixed to the marker carrier 310.

[0154] The marker carrier 310 is disposed on the skin of the patient 302. The marker carrier 310 is configured as a flexible belt so that the shape of the marker carrier 310 can be adapted to the topography of the outer surface of the patient 302 when disposed on an object, here the outer surface of the patient 302.

[0155] The transparently detectable marker 312 fixed on the marker carrier 310 configured as a flexible belt constitutes a marker group composed of at least three markers. Each marker group forms a pattern distinguishable from the patterns formed by other marker groups in the generated fluoroscopic image. In this example, two patterns are shown. The first pattern 320 is formed by a marker group composed of three markers, and the second pattern 322 is formed by a marker group composed of four markers. The marker position specifying element 314 is fixed on the flexible marker carrier 310 at a distance from the transparently detectable marker 312. In the marker carrier 310 configured as a flexible belt, the relative distances and orientations between all the markers 312 and the marker position specifying element 314 are fixed. Here, the relative distances and orientations between the marker 312 and the marker position specifying element 314 are defined along the surface of the marker carrier 310. The relative distance refers to the shortest distance along the outer surface of the marker carrier 310 configured as a flexible belt between each marker 312 and the marker position specifying element 314.

[0156] The C-arm 306 has an X-ray source 316 and an X-ray detector 318 and is configured to generate a fluoroscopic image of the patient 302. In particular, the fluoroscopic image of the patient 302 can be generated such that at least two segments of an object can be identified in the generated fluoroscopic image, and different patterns 320, 322 formed by a marker group composed of at least three markers 312 are assigned to each segment. Since the markers 312 are arranged at fixed positions on the marker carrier 310 and form a distinguishable pattern from other patterns, it is possible to determine the topography of the outer surface of the patient 302. Since the relative distances and orientations between the markers are known, the topography of the outer surface of the patient 302 can be determined by determining the deviation of the pattern with respect to the relative distances and orientations between the markers in the image of the pattern displayed in the generated fluoroscopic image. From this deviation, the angle of the pattern with respect to the surface displayed in the fluoroscopic image can be determined and used to reconstruct the topography of the patient's skin.

[0157] The position detection system 304 is configured to determine the position and orientation of the reference position specifying element 308 in order to determine the position and orientation of the marker position specifying element 314. In particular, the position and orientation of the marker position specifying element 314 can be determined relative to the position and orientation of the reference position specifying element 308. Preferably, the marker position specifying element 314 is composed of two sensor coils arranged orthogonally to each other, realizing a six-degree-of-freedom (DOF) sensor. In particular, when the marker carrier 310 is placed on the patient's skin, the determined position and orientation of the marker position specifying element 314 can be directly assigned to the position of a point on the skin of the patient 302. As a result of assigning the position and orientation of the marker position specifying element 314 to the position of a point on the skin of the patient 302, each point on the patient 302 can be represented by the coordinates of the coordinate system 324 of the position detection system 304 (and vice versa), and the position and orientation of the marker position specifying element 314 can be represented by the coordinates in the patient space. Therefore, the marker position specifying element 314 can be used to establish a reference coordinate system in the patient 302. For example, the reference coordinate system in the patient can be established by transforming the coordinate system 324 of the position detection system 304 so that the origin thereof is located at a point on the skin of the patient that coincides with the determined position and orientation of the marker position specifying element 314.

[0158] The position detection system 304 includes a registration device 305 configured to register a patient 302. In particular, the registration device 305 is configured to associate the image points of the fluoroscopic image generated by the C-arm 306 with the model points of the patient 302 acquired preoperatively. The registration device is configured to use the determined position and orientation of the marker position specifying element 314, and the known relative distances and orientations between each marker 312 and the marker position specifying element 314. Based on the determined position and orientation of the marker position specifying element 314, and the known relative relationships between each marker 312 and the marker position specifying element 314, it is possible to establish a reference coordinate system in the patient and a reference coordinate system in the model of the patient 302 acquired preoperatively, and obtain a conversion function for converting the coordinates between these two reference coordinate systems.

[0159] FIG. 4 shows a navigation system 400 for performing automatic two-dimensional (2D) registration of a patient's spine 402 using interpolation.

[0160] The navigation system 400 includes a position detection system 404, a reference position specifying element 406, an X-ray device having an X-ray source 408 and an X-ray detector 410, and two marker carriers 412, 414.

[0161] Each of the marker carriers 412, 414 is designed as a plate having a characteristic substantially triangular base region and a circular perforation 416. Each of the marker carriers 412, 414 has a plurality of markers 418 that are fluoroscopically detectable, and a marker position specifying element 420.

[0162] To register the spine 402, one of two marker carriers 412, 414 is disposed on each of two opposing sides of the spine 402. For example, one of the two marker carriers 412, 414 is disposed at a distance from the spine on the back side of the patient, and the other is disposed on the opposite side, e.g., the ventral side of the patient. When the spine 402 is exposed, the marker carriers 412, 414 may be disposed near the spine itself, or even attached to the vertebrae of the spine. Since the spine 402 is disposed between the two marker carriers 412, 414, for automatic two-dimensional (2D) registration of the spine 402, the position of points on the outer surface of the spine can be determined by interpolation with respect to the two marker carriers 412, 414, in particular, with respect to the determined positions and orientations of the marker position specifying elements 420 of each marker carrier 412, 414. The relative distance and orientation between the two marker carriers 412, 414 can be determined by detecting the positions and orientations of the marker position specifying elements 420 of each marker carrier 412, 414 by the position detection system 404, so that it is possible to determine the position of points on the outer surface of the spine by interpolation.

[0163] The positions and orientations of the marker position specifying elements 420 of each marker carrier 412, 414 can be determined by the position detection system 404 with respect to, for example, the position and orientation of a reference position specifying element 406 in an electromagnetic field. The reference position specifying element 406 can be attached to the patient himself, for example, attached to the skin, or directly attached to the vertebrae of the spine when the spine is exposed.

[0164] By an X-ray device, fluoroscopic images of two marker carriers 412, 414 disposed on both sides of the spine 402 can be generated such that at least two markers 418 of each of the two marker carriers 412, 414, and preferably 2 to 4 vertebrae of the spine 402 are visible.

[0165] The position detection system 404 includes a registration device 422 configured to associate the image points of the generated fluoroscopic image with the model points of the spine 402 acquired preoperatively. Associating the image points with the model points can be performed by the registration device 422 by using the determined positions and orientations of the marker position specifying elements 420 of each marker carrier 412, 414, and the known spatial relationships between one fluoroscopically detectable marker 418 of each of the two marker carriers 412, 414 and the marker position specifying element 420.

[0166] FIG. 5 shows a navigation system 500 for performing automatic two-dimensional registration of a patient's spine 502 using extrapolation.

[0167] The navigation system 500 includes a position detection system 504, a marker carrier 506, a reference position specifying element 508, and an X-ray device having an X-ray source 510 and an X-ray detector 512.

[0168] The marker carrier 506 has two plates, and the two plates are arranged parallel to their reference planes. The two plates are firmly coupled to each other via three pins. The two plates are arranged at a constant relative distance from each other by the three pins. A fluoroscopically detectable marker 514 is fixed to each of the two plates. In addition, a marker position specifying element 516 is fixed to one of the two plates. The relative distances and orientations between each marker 514 of the two plates and the marker position specifying element 516 are known.

[0169] To register the spine 502, a marker carrier 506 is placed on the spine 502. Placing the marker carrier 506 on the spine 502 includes placing the marker carrier 506 directly on the exposed spine 502 or placing the marker carrier 506 on the patient's outer skin at a distance from the spine 502. The navigation system 500 can also include additional marker carriers that are identical to the marker carrier 506 and are placed simultaneously on the patient's body, for example, along the length of the patient's spine.

[0170] When the marker carrier 506 is placed on the spine, the position and orientation of the marker localization element 516 can be determined using the position detection system 504, for example, relative to the position of the reference localization element 508. When the spine 502 is exposed, the reference localization element 508 can be rigidly attached directly to the vertebrae of the spine. Note that the reference localization element 508 can be attached to the patient's outer skin or can be fixedly placed at a distance next to the patient. From the determined position and orientation of the marker localization element 516 and the position and orientation of the reference localization element 508, the position of points on the spine 502 in the coordinate system of the position detection system 504 can be extrapolated.

[0171] An X-ray device can generate a fluoroscopic image of the marker carrier 506 such that at least two markers 514 are visible along with at least one segment of the spine 502, for example, at least one vertebra.

[0172] The position detection system 504 includes a registration device 518 configured to access the generated fluoroscopic image and the determined position and orientation of the marker localization element 516 to associate the image points of the generated fluoroscopic image with the model points of the spine 502 acquired preoperatively. The registration device 518 is configured to associate the image points with the model points using the determined position and orientation of the marker localization element 516 and the known spatial relationship between the marker 514 and the marker localization element 516.

[0173] FIG. 6 shows a navigation system 600 that can be used, for example, to register an exposed spine 602.

[0174] The navigation system 600 includes a position detection system 604, an X-ray device having an X-ray source 606 and an X-ray detector 608, a reference position specifying element 610, and a marker carrier 612.

[0175] The marker carrier 612 has a plurality of fluoroscopically detectable markers 614 fixed thereto and a marker position specifying element 616. The marker carrier 612 is configured in a cage shape so that it can be placed on the spine 602 and surround the exposed spine. This enables automatic three-dimensional (3D) registration of the spine. The marker carrier 612 is characterized in that each marker 614 has a known spatial relationship with other markers and the marker position specifying element 616.

[0176] The position and orientation of the marker position specifying element can be determined by the position detection system 604. In particular, the position and orientation of the marker position specifying element 616 can be determined by the position detection system 604 with respect to the position and orientation of the reference position specifying element 610 firmly fixed to the vertebra of the spine.

[0177] The navigation system 600 can include additional marker carriers that can be configured similarly to the marker carrier 612. If the navigation system 600 includes a cage-shaped marker carrier, several marker carriers can be arranged along the exposed spine 602 to surround the exposed spine.

[0178] The X-ray device can generate a fluoroscopic image in which the marker carrier 612 and at least one segment of the spine are visible. A segment of the spine can include one vertebra, for example, the vertebra on which the marker carrier 612 is placed, and in the generated fluoroscopic image, it is preferable that the vertebra is visible together with two to three adjacent vertebrae.

[0179] The position detection system 604 of the navigation system 600 includes a registration device 618 configured to associate the image points of the generated fluoroscopic image with the model points of the spine acquired preoperatively. The registration device 618 is configured to associate the image points with the model points using the determined position and orientation of the marker position specifying element 616, and the known relative distances and orientations between at least one of the markers 614 and the marker position specifying element 616.

[0180] FIG. 7 shows a navigation system 700 that can be used to perform automatic three-dimensional registration of the spine 702 in minimally invasive surgery.

[0181] The navigation system 700 includes two marker carriers 704, 706, a position detection system 708, a reference position specifying element 710, and an X-ray device having an X-ray source 712 and an X-ray detector 714.

[0182] Each of the two marker carriers 704, 706 is configured in a stick shape and has a plurality of fluoroscopically detectable markers 718 arranged along the length of the stick. Each marker carrier 704, 706 has a marker position specifying element 720 fixed thereto, and the relative distances and orientations between the markers 718 and the marker position specifying element 720 are known. Each marker position specifying element 720 of the marker carriers 704, 706 is connected to the position detection system 708 via a cable 722 and transmits a sensor signal representing the position and orientation of each marker position specifying element 720 in the electromagnetic field generated by a magnetic field generator (not shown) of the position detection system 708 to the position detection system 708. In particular, the position and orientation of the marker position specifying element 720 can be determined by the position detection system 708 relative to the position and orientation of the reference position specifying element 710 firmly fixed to the vertebra of the spine.

[0183] In minimally invasive surgery, two marker carriers 704, 706 can be inserted into the patient's body and navigated to the patient's spine 702 such that the marker carriers 704, 706 are disposed at positions on opposite sides of the spine. Thereby, automatic three-dimensional registration of the spine 702 can be performed.

[0184] Since the two marker carriers 704, 706 are disposed adjacent to the patient's spine 702, a fluoroscopic image can be generated by an X-ray device. The fluoroscopic image is preferably generated such that at least two markers 718 of each marker carrier 704, 706 are visible together with at least one segment of the spine 702. For example, in the generated fluoroscopic image, it is preferable that 3 to 4 vertebrae are visible.

[0185] The position detection system 708 of the navigation system includes a registration device 716 configured to associate the image points of the generated fluoroscopic image with model points of a model obtained preoperatively of the patient's spine 702. The registration device 716 is configured to associate the image points with the model points using the determined positions and orientations of the marker position specifying elements 720 of each marker carrier 704, 706, and the known spatial relationships between at least one marker 718 and the respective marker position specifying elements 720.

Claims

1. A navigation system, comprising: at least one marker carrier, having: a plurality of markers that can be detected transparently, and at least one marker position specifying element; the plurality of markers and the at least one marker position specifying element are fixed to the marker carrier; the at least one marker position specifying element is configured to provide a sensor signal representing the position and orientation of the marker position specifying element in an electromagnetic field, and the relative distance and orientation between the at least one marker position specifying element and at least one of the plurality of markers are known, the marker carrier; a position detection system having a magnetic field generator for generating an electromagnetic field, configured to determine the position and orientation of the at least marker position specifying element in the electromagnetic field; an X-ray apparatus comprising an X-ray source and an X-ray detector, configured to record fluoroscopic image data capable of generating a fluoroscopic image of the at least one marker carrier such that at least two markers are visible; a registration device configured to associate image points of the generated fluoroscopic image with model points of a model obtained preoperatively using the determined position and orientation of the at least one marker position specifying element, and the known relative distance and orientation between the at least one marker position specifying element and the at least one of the plurality of markers, and / or the known spatial relationship between a further marker of the plurality of markers and the at least one marker for which the relative distance and orientation with respect to the at least one marker position specifying element are known; The navigation system further comprises: providing a model of an object obtained preoperatively; providing the at least one marker carrier; arranging the at least one marker carrier on the outer surface of the object. Generating at least one fluoroscopic image of the at least one marker carrier disposed on the outer surface of the object and at least one segment of the object, the fluoroscopic image being generated such that at least two markers of the at least one marker carrier and the at least one segment of the object are visible; Determining the position and orientation of the at least one marker position specifying element of the marker carrier disposed on the outer surface of the object in an electromagnetic field; Associating the image points of the generated fluoroscopic image with model points of the model acquired preoperatively, the association of the image points of the fluoroscopic image with the model points of the model being performed using the determined position and orientation of the at least one marker position specifying element, and the known relative distance and orientation between the at least one marker position specifying element and the at least one marker of the plurality of markers, and / or the known spatial relationship between a further marker of the plurality of markers and the at least one marker for which the relative distance and orientation with respect to the at least one marker position specifying element are known; being configured to perform; the marker carrier is a flexible marker carrier; the flexible marker carrier is disposed on the outer surface of the object; the plurality of markers are fixed on the flexible marker carrier such that in the generated fluoroscopic image, each marker group composed of three markers forms a pattern distinguishable from the pattern formed by other marker groups; at least two segments of the object are assigned different patterns formed by the marker groups so as to be distinguishable in the generated at least one fluoroscopic image, a navigation system.

2. A method for automatically registering an object, comprising: providing a model generated from image data of the object acquired before surgery; providing at least one marker carrier having a plurality of markers detectable in a fluoroscopic manner and at least one marker position specifying element, wherein the plurality of markers and the at least one marker position specifying element are fixed to the marker carrier, wherein the at least one marker position specifying element is configured to provide a sensor signal representing the position and orientation of the marker position specifying element in an electromagnetic field, and wherein the relative distance and direction between the at least one marker position specifying element and at least one of the plurality of markers are known; placing the at least one marker carrier on the outer surface of the object; generating at least one fluoroscopic image of the at least one marker carrier disposed on the outer surface of the object and at least one segment of the object, the fluoroscopic image being generated such that at least two markers of the at least one marker carrier and the at least one segment of the object are visible; for each of the at least one generated fluoroscopic image of the at least one segment, associating each image point of the fluoroscopic image with a model point of the model acquired before surgery for each segment; determining the position and orientation of the at least one marker position specifying element of the marker carrier disposed on the outer surface of the object in an electromagnetic field; Associating the image points of the generated fluoroscopic image with model points of the model acquired preoperatively, wherein the association of the image points of the fluoroscopic image with the model points of the model is performed using the determined positions and orientations of the at least one marker position specifying element, and the known relative distances and orientations between the at least one marker position specifying element and the at least one marker of the plurality of markers, and / or the known spatial relationships between further markers of the plurality of markers and the at least one marker for which the relative distances and orientations with respect to the at least one marker position specifying element are known, and the step, including, further including the step of detecting a relative displacement of elements of the object by determining a deviation of at least one of the model points of the model acquired preoperatively from the image points of the generated fluoroscopic image corresponding to the at least one of the model points of the model acquired preoperatively, A method in which an error in registration is determined based on image points of at least two segments associated with each model point and known spatial relationships between the at least two segments.

3. The method according to claim 1 or 2, wherein the model points are points on the model surface of the model acquired preoperatively, and the model surface corresponds to the outer surface of the object.

4. The method according to claim 2 or 3, wherein the marker carrier is a flexible marker carrier, the flexible marker carrier is disposed on the outer surface of the object, the plurality of markers are fixed on the flexible marker carrier such that in the generated fluoroscopic image, each marker group composed of three markers forms a pattern distinguishable from a pattern formed by other marker groups, A method in which at least two segments of the object are each assigned a different pattern formed by the marker group so that they can be identified in at least one of the generated perspective images.

5. The method according to claim 2 or 3, wherein at least two of the marker carriers are simultaneously arranged on the outer surface of the object, and the perspective image is generated so that at least two markers of the marker carriers arranged on the outer surface of the object and at least two segments of the object are visible, A method of determining the spatial relationship between segments used to generate the perspective image using the positions of the markers visible in the perspective image.

6. The method according to claim 2 or 3, wherein in successive steps, the marker carrier is arranged on the outer surface of the object, and in each of the successive steps, the perspective image is generated so that at least two markers of the marker carriers arranged on the outer surface of the object and each segment of the object are visible, A method of determining the spatial relationship between segments used to generate the perspective image using the positions of the markers visible in each perspective image.

7. The method according to any one of claims 2 to 6, further comprising the step of displaying the model acquired preoperatively on an image display device, wherein the model on the image display device is aligned such that the viewing direction on the model on the image display device corresponds to the recording direction in which the perspective image data used to generate the perspective image of at least one segment is recorded, according to the relationship between the image points and the model points.

8. The method according to claim 2, A method further comprising the step of adapting the model obtained before the operation of the object for each segment using the detected deviation. **Claim 9** The method according to claim 2 or 8, providing a device having a device position specifying element for determining a position and an orientation with respect to an electromagnetic field; determining the position and orientation of the device position specifying element with respect to the position and orientation of the at least one marker position specifying element in the electromagnetic field; displaying the adapted model of the object on an image display device together with at least a part of the device; adapting the position and orientation of the device on the model displayed on the image display device using the determined deviation of at least one model point from the image point of the generated perspective image corresponding to at least one of the model points of the model obtained before the operation. A method further comprising: **Claim 10** The method according to claim 9, wherein the step of adapting the position and orientation of the device on the model displayed on the image display device is performed for each segment of the object displayed in the perspective image. **Claim 11** The method according to any one of claims 2 to 10, arranging at least one reference position specifying element in a fixed spatial relationship with respect to the object, the at least one reference position specifying element being configured to provide a reference sensor signal representing the position and orientation of the reference position specifying element in the electromagnetic field; the step, determining the position and orientation of the at least one marker position specifying element with respect to the position and orientation of the at least one reference position specifying element in the electromagnetic field; A method further comprising: **Claim 12** The method according to claim 11, wherein: determining the positions and orientations of the at least one marker position specifying element relative to the at least one reference position specifying element at a first time point and a later time point; detecting a change in the position and / or orientation of the marker position specifying element relative to the position and orientation of the at least one reference position specifying element at the later time point in relation to the first time point; The method further comprising.

13. A marker carrier used in the registration method according to any one of claims 2 to 12, having a plurality of markers that can be detected in a perspective manner and at least one marker position specifying element, wherein the plurality of markers and the at least one marker position specifying element are fixed to the marker carrier, the at least one marker position specifying element is configured to provide a sensor signal representing the position and orientation of the marker position specifying element in an electromagnetic field, the relative distance and orientation between the at least one marker position specifying element and at least one of the plurality of markers are known, the marker carrier is flexible.

14. A navigation system configured to perform the registration method according to any one of claims 2 to 12, a marker carrier, having a plurality of markers that can be detected in a perspective manner and at least one marker position specifying element, wherein the plurality of markers and the at least one marker position specifying element are fixed to the marker carrier, the at least one marker position specifying element is configured to provide a sensor signal representing the position and orientation of the marker position specifying element in an electromagnetic field, The marker carrier, wherein the relative distances and orientations between the at least one marker position specifying element and at least one of the plurality of markers are known, A position detection system having a magnetic field generator for generating an electromagnetic field and configured to determine the position and orientation of the at least marker position specifying element in the electromagnetic field, An X-ray apparatus including an X-ray source and an X-ray detector, and configured to record fluoroscopic image data capable of generating a fluoroscopic image of the at least one marker carrier such that at least two markers are visible in the generated fluoroscopic image, A registration device configured to associate the image points of the generated fluoroscopic image with model points of the model acquired preoperatively using the determined position and orientation of the at least one marker position specifying element, and the known overall distances and orientations between the at least one marker position specifying element and the at least one of the plurality of markers, and / or the known spatial relationship between the at least one marker, for which the relative distances and orientations to the at least one marker position specifying element are known, and a further marker of the plurality of markers, The registration device is further configured to include a step of detecting a relative displacement of elements of the object by determining a deviation of at least one model point of the model acquired preoperatively from the image points of the generated fluoroscopic image corresponding to the at least one model point of the model acquired preoperatively, a navigation system.

Images