Tracker movement-based transition selection techniques

Abstract

A method for selecting a transformation between a posture of a tracker and a coordinate system associated with image data acquired by a medical imaging device is provided. The method is performed by a processor and includes: obtaining tracking information indicative of a plurality of different poses of a tracker fixedly positioned relative to a movable portion of a medical imaging device; determining a movement of the tracker based on the obtained tracking information; and selecting one of a plurality of transformations between a posture of the tracker and a coordinate system associated with image data acquired by the medical imaging device based on the determined movement of the tracker. A corresponding system and a non-transitory computer readable storage medium are also provided.

Description

Technical Field

[0001] The present disclosure generally relates to a method for selecting a pose of a tracker and a transformation between a coordinate system associated with image data acquired by a medical imaging device. A system, a computer program, and a carrier such as a non-transitory computer storage medium are also provided. Background Art

[0002] During surgical navigation, it may be necessary to register image data acquired by a medical imaging device (e.g., an X-ray device including a C-arm) to a tracker tracked by a tracking system. This registration can be based on a transformation between the tracker's pose and a coordinate system associated with the image data.

[0003] In current technical solutions, the tracker can be fixedly positioned relative to the medical imaging device, which means that the transformation can be the same as long as the tracker is in the same pose relative to the medical imaging device. In other words, the tracker can only be arranged in a single predefined pose relative to the medical imaging device, and the image data can be registered to the tracker using a single predefined transformation between the single predefined pose of the tracker and the coordinate system of the image data acquired by the medical imaging device.

[0004] Depending on the surgical scenario, the visibility of the tracker of the tracking system arranged on the medical imaging device may be limited, for example due to the arrangement of the medical machine between the camera of the tracking system and the medical imaging device. For this and other reasons, it may be desirable to arrange the tracker in a posture different from the aforementioned single predefined posture. Such an arrangement may result in different transformations between the different postures of the tracker and the coordinate system of the image data. Therefore, it may not always be possible to register the image data to the tracker using the same single predefined transformation. Summary of the invention

[0005] What is needed is a technique that addresses one or more of the above problems or other problems.

[0006] According to a first aspect, a method for selecting a transformation between a pose of a tracker and a coordinate system associated with image data acquired by a medical imaging device is provided. The method is performed by at least one processor and comprises obtaining tracking information indicating a plurality of different poses of a tracker fixedly positioned relative to a movable portion of the medical imaging device. The method comprises determining a movement of the tracker based on the obtained tracking information. The method further comprises selecting one of a plurality of transformations between a pose of the tracker and a coordinate system associated with image data acquired by the medical imaging device based on the determined movement of the tracker.

[0007] The method may also include determining a spatial relationship between the tracker and the movable part based on the determined movement of the tracker.

[0008] A transformation may be selected from the plurality of transformations based on the determined spatial relationship.

[0009] The spatial relationship may include a side of the movable portion on which the tracker is disposed.

[0010] The determined movement of the tracker may indicate a direction of movement of the tracker,

[0011] The side of the movable part may be determined based on the moving direction of the tracker.

[0012] The side of the movable part may be determined by selecting the side of the movable part from a first side of the movable part associated with a clockwise direction of movement of the tracker and a second side of the movable part associated with a counterclockwise direction of movement of the tracker.

[0013] The spatial relationship may include the location of the movable portion at which the tracker is arranged.

[0014] The determined movement of the tracker may indicate a movement path of the tracker.

[0015] The position of the movable part may be determined based on the movement path of the tracker.

[0016] The movable portion may be configured to move in a circle or a spiral.

[0017] The movement path of the tracker may include at least a portion of a circle, an ellipse, or a spiral.

[0018] The position of the movable part may be determined based on at least a portion of the movement path of the tracker.

[0019] The spatial relationship may include the orientation of the tracker relative to the movable portion.

[0020] The method may further include acquiring gravity information indicating a direction of gravity.

[0021] The transformation may be selected based on gravity information.

[0022] The movement of the tracker may be determined relative to the gravity direction indicated by the gravity information.

[0023] The transformation may be selected based on the movement of the tracker determined relative to the direction of gravity.

[0024] The method may also include obtaining at least one setting of the medical imaging device, the at least one setting being selected from a start posture and an end posture of a movable part of the medical imaging device relative to an immovable part of the medical imaging device, or a component having a fixed spatial relationship with the immovable part of the medical imaging device.

[0025] The conversion may be selected based on at least one setting of the medical imaging device.

[0026] The method may further include determining at least one setting of the medical imaging device based on the tracking information, the gravity information and the determined movement of the tracker to obtain at least one setting of the medical imaging device.

[0027] The one side of the movable part may be determined based on a movement direction of the tracker and at least one obtained setting of the medical imaging device.

[0028] The side of the movable part can be determined by selecting the side of the movable part from the following items based on the determined movement direction of the tracker and at least one setting of the obtained medical imaging device: a first side of the movable part, which is associated with (i) the clockwise movement direction of the tracker and the first setting of the medical imaging device and (ii) the counterclockwise movement direction of the tracker and the second setting of the medical imaging device; and a second side of the movable part, which is associated with (i) the clockwise movement direction of the tracker and the second setting of the medical imaging device and (ii) the counterclockwise movement direction of the tracker and the first setting of the medical imaging device.

[0029] At least two or all of the plurality of different poses of the tracker may be associated with different points in time of an image acquisition procedure performed by the medical imaging device to acquire image data, wherein a movable part of the medical imaging device moves during the image acquisition procedure.

[0030] The medical imaging device may be configured to acquire computed tomography (CT) image data.

[0031] The movable part of the medical imaging device may be part of a C-arm.

[0032] According to a second aspect, a system is provided. The system comprises at least one processor configured to perform a method according to the first aspect. The at least one processor may be configured to perform a method for selecting a transformation between a posture of a tracker and a coordinate system associated with image data acquired by a medical imaging device, the method comprising: obtaining tracking information indicating a plurality of different postures of a tracker fixedly positioned relative to a movable portion of the medical imaging device; determining a movement of the tracker based on the obtained tracking information; and selecting one of a plurality of transformations between a posture of the tracker and a coordinate system associated with image data acquired by the medical imaging device based on the determined movement of the tracker.

[0033] The system may also include at least one of the following entities: i) a medical imaging device comprising a movable part and configured to acquire image data; ii) a tracking system, such as an optical tracking system comprising a camera, configured to provide tracking information; iii) a gravity sensor configured to provide gravity information and optionally fixed to the tracking system and / or the camera; (iv) a tracker.

[0034] According to a third aspect, a non-transitory computer-readable storage medium is provided. The storage medium stores a computer program including instructions, which, when executed by at least one processor, causes the at least one processor to perform a method according to the first aspect. The storage medium may store a computer program including instructions, which, when executed by at least one processor, causes the at least one processor to perform a method for selecting a transformation between a posture of a tracker and a coordinate system associated with image data acquired by a medical imaging device, the method comprising: obtaining tracking information indicating a plurality of different postures of a tracker fixedly positioned relative to a movable portion of the medical imaging device; determining a movement of the tracker based on the obtained tracking information; and selecting one of a plurality of transformations between a posture of the tracker and a coordinate system associated with image data acquired by the medical imaging device based on the determined movement of the tracker.

[0035] According to a fourth aspect, a computer program is provided. The computer program comprises instructions which, when executed by at least one processor, cause the at least one processor to perform the method according to the first aspect. The computer program may be carried by a data stream or stored on a (eg, non-transitory computer-readable) storage medium.

[0036] According to a fifth aspect, there is provided a carrier carrying a computer program according to the fourth aspect. The carrier may be a data stream or a (eg non-transitory computer-readable) storage medium. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Other details, advantages and aspects of the present disclosure will become apparent from the following embodiments in conjunction with the accompanying drawings, in which:

[0038] Figure 1 A system according to the present disclosure is shown;

[0039] Figure 2 A method according to the present disclosure is shown;

[0040] Figure 3 Different mounting arrangements of the tracker on the C-arm are shown;

[0041] Figure 4a to Figure 4b Shows Figure 3 side views of different mounting arrangements;

[0042] Figure 5a to Figure 5c Different medical imaging devices with trackers are shown. DETAILED DESCRIPTION

[0043] Hereinafter, exemplary embodiments of the present application will be explained with reference to the accompanying drawings. Unless otherwise specified, the same reference numerals denote the same or similar structural features.

[0044] Figure 1 A system 100 is shown in accordance with the present disclosure. The system 100 may be a surgical navigation system.

[0045] The system 100 includes a processing device 2, which includes at least one processor 4. The at least one processor 4 is communicatively coupled to a memory 6, which is an example of a non-transitory computer-readable storage medium. The at least one processor 4 can also be communicatively coupled to an interface 8 of the device 2. For example, by implementing at least one processor 4, memory 6 and / or interface (for example, as a virtual processor, one or more virtual memories) on different servers, the device 2 can be implemented as a spatially distributed processing device 2. In other words, at least a portion of the device 2 can be implemented by a cloud computing platform. Alternatively, the device 2 can be implemented as a local processing device 2, for example, arranged in a scanning room or an operating room of a hospital.

[0046] The system 100 also includes a tracking system 10. In the example shown, the tracking system 10 is an optical tracking system including a stereo camera 12. A gravity sensor 14 (e.g., a 3-axis accelerometer) can be fixedly arranged relative to the stereo camera 12 to obtain a gravity direction 16. The tracking system 10 can be communicatively coupled to at least one processor 4 via an interface 8 and can be configured to provide tracking data indicating a tracking pose of the tracker to the at least one processor 4. The term "pose" as used herein should be understood as "at least one of a position and an orientation".

[0047] The system 100 also includes a medical imaging device 18 configured to acquire image data. The image data may include one or more medical images of a patient's body 20. The medical imaging device 18 includes an immovable (e.g., fixed) portion 22 and a movable portion 24. The movable portion 24 is configured to move relative to the immovable portion 22 when the medical imaging device 18 acquires image data. The immovable portion 22 is configured to remain stationary (e.g., remain stationary in an operating room) when acquiring image data. The medical imaging device 18 can be communicatively coupled to at least one processor 4 via an interface 8 and can be configured to provide the acquired image data to the at least one processor 4. In the example shown, the medical imaging device 18 is configured to acquire a computed tomography (CT) image of the patient's body 20 as image data, and includes a C-arm as the movable portion 24 and a cart as the fixed portion 22, the C-arm having an X-ray source 26 and an X-ray detector 28. The C-arm is configured to rotate around a center point 30 (also referred to as an isocenter) when acquiring a CT image (also referred to as a CT scan).

[0048] The system 100 also includes one or more trackers 30 to 34. The tracker 30 is fixedly positioned relative to the movable part 24 of the medical imaging device 18, and in the example shown is directly attached to the X-ray detector 28, and can therefore be referred to as a medical imaging device tracker. The tracker 32 is fixed in space relative to the patient's body 20, for example adhered to the patient's skin, and can therefore be referred to as a patient tracker. The tracker 34 is attached to a medical instrument 36 handled by a surgeon or a surgical robot, and can therefore be referred to as a medical instrument tracker. Each of the trackers 30 to 34 can be tracked by the tracking system 10, which means that the tracking system 10 can determine the pose of each of the trackers 30 to 34 in a (e.g., real-world) tracking coordinate system. The tracking coordinate system (e.g., the origin and orientation of the tracking coordinate system) can be defined by one of the trackers (e.g., by the patient tracker 32). The tracking system 10 can be configured to provide information indicating the tracking pose of the trackers 30 to 34, for example, in the tracking coordinate system to at least one processor 4. In the example shown, each of trackers 30 - 34 includes a plurality of optical tracking markers detectable by stereo camera 12 , but the present disclosure is not limited in this regard.

[0049] The system 100 also includes a display unit 38. The display unit 38 may be communicatively coupled to the at least one processor 4 via the interface 8. The display unit 38 may display a navigation view indicating a tracked pose of the medical instrument 36 relative to a representation of the patient's body 20, for example by superimposing a trajectory 40 onto a medical image 42 of the patient's body 20, wherein the medical image is included in the image data acquired by the image acquisition device 18.

[0050] To this end, it may be necessary to track transformations between a coordinate system and a coordinate system associated with the image data (e.g., associated with or defined by one or more images (e.g., medical image 42) included in the image data). The isocenter 30 having a fixed spatial relationship with the x-ray detector 28 can define the coordinate system associated with the image data. More generally, the coordinate system associated with the image data can have a (e.g., predefined) spatial relationship relative to the movable portion 24 of the medical imaging device 18.

[0051] According to the present disclosure, the tracker 30 can be mounted on the movable part 24 in two or more predefined postures. This means that the relative posture between the tracker 30 and the movable part 24 can be different due to different image acquisition processes, so the corresponding transformation between the posture of the tracker 30 and the coordinate system associated with the corresponding image data is also different between different instances of the acquired image data. The technology disclosed herein can realize the automatic selection of a suitable transformation from multiple transformations. The method will now be described in detail. Although it will be used below Figure 1 The reference numerals used in the drawings should not be construed as necessarily limiting the features described below to those for Figure 1 Corresponding features shown and described.

[0052] Figure 2 The method according to the present disclosure is shown. The method can be executed by at least one processor 4. The memory 6 can store a computer program including instructions, which, when executed by at least one processor 4, causes at least one processor 4 to execute Figure 2 method.

[0053] In optional step 202 , the medical imaging device 18 is triggered to acquire image data.

[0054] Step 202 may include triggering the medical imaging device 18 to acquire image data by performing an image acquisition process, during which the movable portion 24 moves.

[0055] At least steps 202 to 214 of the method disclosed herein may be performed prior to scanning the patient body 20. However, in some scenarios, it may be desirable that image data acquired by the medical imaging device 18 when triggered accordingly in step 202 include a representation of at least a portion of the patient body 20.

[0056] The image data may include or may be medical image data. The image data may include one or more medical images (e.g., images acquired using medical imaging techniques). The image data may include three-dimensional image data. The medical imaging device 18 may acquire image data when the movable portion 24 moves relative to the immovable portion 26. The image data may include a computed tomography (CT) image, also known as a CT scan. The image data may include a cone beam CT (CBCT) scan. The image data may include a spiral CT scan or a multi-column CT scan. The image data may include one or more single-spectrum or multi-spectrum images. The image data may include one or more three-dimensional images. The image data may include one or more images acquired by the medical imaging device 18 when the movable portion 24 moves relative to the immovable portion 26.

[0057] In step 204, tracking information is obtained.

[0058] The tracking information indicates a plurality of different postures of the tracker 30 fixedly positioned relative to the movable portion 24 of the medical imaging device 18. The tracker 30 may be attached to the movable portion 24 directly or via a mounting assembly disposed on the movable portion 24. At least one of the movable portion 24, the mounting assembly, and the tracker 30 may be configured such that the tracker 30 may be fixedly positioned relative to the movable portion 24 in two or more (e.g., predefined) postures. The movable portion 24 may include a plurality of (e.g., opposing) sides (e.g., two or more of a left side, a right side, a front side, and a rear side) on which the tracker 30 may be disposed.

[0059] The tracking information may also indicate one or more tracking poses of trackers 32 and / or 34. The one or more poses indicated by the tracking information may be indicated relative to a similar coordinate system, such as a tracking coordinate system.

[0060] At least two or all of the plurality of different postures of the tracker 30 may be associated with different points in time (e.g., one point in time for each posture). The different points in time may be part of an image acquisition process performed by the medical imaging device 18 to acquire image data. The tracking system 10 may obtain a plurality of different postures of the tracker 30 during the image acquisition process. During the image acquisition process, the movable portion 24 of the medical imaging device 18 may move relative to the immovable portion 26. Thus, the tracker 30 may also move in space while acquiring image data, resulting in different tracking postures of the tracker 30.

[0061] In optional step 206, gravity information is obtained.

[0062] Gravity information may be obtained from gravity sensor 14. Gravity information indicates, for example, gravity direction 16 relative to one or more tracking poses of trackers 30 to 34 (e.g., relative to one or more of a plurality of different poses of tracker 30). A tracking coordinate system (e.g., an orientation of the tracking coordinate system) may be defined based on gravity direction 16. One or more (e.g., all) tracking poses of trackers 30 to 34 may be defined relative to the gravity direction.

[0063] In step 208 , the movement of the tracker 30 is determined.

[0064] Movement of the tracker 30 is determined based at least on the obtained tracking information.

[0065] Movement of tracker 30 may be determined relative to gravity direction 16 indicated by the gravity information.

[0066] The determined movement of the tracker 30 may indicate a direction of movement of the tracker 30, such as a clockwise or counterclockwise direction of movement (e.g., as observed by the tracking system 10). The movable portion 24 and the tracker 30 may move along the direction of movement during an image acquisition process (e.g., triggered in step 202) for acquiring image data.

[0067] The determined movement of the tracker 30 may indicate a movement path of the tracker 30. The movable portion 24 and the tracker 30 may move along the movement path during an image acquisition process (e.g., triggered in step 202) for acquiring image data. For example, the movable portion 24 may be configured to move along a circle or a spiral (e.g., at least a portion of a circle or a spiral). In this case, the movement path of the tracker 30 may include at least a portion of a circle, an ellipse, or a spiral.

[0068] The determined movement of the tracker 30 may indicate a rotation of the tracker 30, such as a clockwise or counterclockwise rotation (e.g., as observed by the tracking system 10). The movable portion 24 may be moved during an image acquisition process (e.g., triggered in step 202) for acquiring image data, such that the tracker 30 rotates and optionally translates in space (e.g., along a movement path).

[0069] Determining the movement of the tracker 30 may include virtually connecting a plurality of different postures of the tracker 30 indicated by the tracking information. The direction of movement may be determined based on different time points associated with the plurality of different postures of the tracker 30. The machine vision algorithm may determine the movement of the tracker 30 based at least on the tracking information. The machine vision algorithm may be configured to separate the posture of the tracker 30 from postures of other tracked trackers 32, 34, may be configured to filter out abnormal postures of the tracker 30 (e.g., due to tracking errors), and / or may be configured to interpolate, average, and / or extrapolate between two or more postures of the plurality of different postures of the tracker 30.

[0070] In optional step 210 , at least one setting of the medical imaging device 18 is obtained.

[0071] The at least one setting may include a starting pose and / or an ending pose of the movable portion 24 of the medical imaging device 18. The starting pose and / or the ending pose may be defined relative to an operating room, relative to an immovable portion 26 of the medical imaging device 18, and / or relative to a component having a fixed spatial relationship with the immovable portion 26 of the medical imaging device 18. The starting pose may correspond to a pose of the movable portion 24 at the beginning of an image acquisition process, and the ending pose may correspond to a pose of the movable portion 24 at the end of an image acquisition process. Examples of the starting pose and the ending pose include a pose of the detector 28 of the medical image acquisition device 18 at an uppermost ("12 o'clock") position, a pose of the detector 28 of the medical image acquisition device 18 at a leftmost ("9 o'clock") position, a pose of the detector 28 of the medical image acquisition device 18 at a lowermost ("6 o'clock") position, and a pose of the detector 28 of the medical image acquisition device 18 at a rightmost ("3 o'clock") position.

[0072] The at least one setting may be obtained by determining at least one setting based on the tracking information and optionally based on the gravity information and / or the determined movement of the tracker 30. For example, the start pose may be determined by comparing the earliest tracking pose of the tracker 30 to one or more later poses of the plurality of different poses of the tracker 30. For another example, the end pose may be determined by comparing the latest tracking pose of the tracker 30 to one or more earlier poses of the plurality of different poses of the tracker 30. Gravity information may be used to avoid ambiguity (e.g., distinguishing a highest position from a lowest position), which may be particularly advantageous in situations where the tracking system 10 (e.g., the camera 12) may be arranged at different orientations relative to the gravity direction 16. The start pose and / or the end pose may also be derived from the determined movement.

[0073] In optional step 212 , a spatial relationship between the tracker 30 and the movable portion 24 is determined.

[0074] A spatial relationship between the tracker 30 and the movable portion 24 is determined based at least on the determined movement of the tracker.

[0075] The spatial relationship between the tracker 30 and the movable portion 24 may include a side (e.g., one of multiple sides) of the movable portion 24 on which the tracker 30 was and / or is being positioned (e.g., during movement of the tracker 30 through multiple different postures and / or during an image acquisition process for acquiring image data).

[0076] As described above, the determined movement of the tracker may indicate a direction of movement of the tracker. In this case, the side of the movable portion 24 may be determined based on the direction of movement of the tracker 30. In one variation, the side of the movable portion 24 is determined by selecting the side of the movable portion 24 from a first side (e.g., right side) of the movable portion 24 associated with a clockwise direction of movement of the tracker 30 and a (e.g., opposite) second side (e.g., left side) of the movable portion 24 associated with a counterclockwise direction of movement of the tracker 30. The associations between the respective sides of the tracker 30 and the direction of movement may be predefined, obtained from the medical imaging device 18, and / or input by a user. These associations may be specific to the medical imaging device 18.

[0077] The side of the movable part 24 may be determined based on the movement direction of the tracker 30 and at least one setting of the obtained medical imaging device 18. The side of the movable part 24 may be determined by selecting the side of the movable part 24 from a first side (e.g., right side) and a second side (e.g., left side) based on the determined movement direction of the tracker 30 and at least one setting of the obtained medical imaging device 18. The first side of the movable part 24 may be associated with (i) the clockwise movement direction of the tracker 30 and the first setting of the medical imaging device 18 and / or (ii) the counterclockwise movement direction of the tracker 30 and the second setting of the medical imaging device 18. The second side of the movable part 24 may be associated with (i) the clockwise movement direction of the tracker 30 and the second setting of the medical imaging device 18 and / or (ii) the counterclockwise movement direction of the tracker 30 and the first setting of the medical imaging device 18. The association between the respective sides of the tracker 30, the movement direction, and the setting may be predefined, obtained from the medical imaging device 18, and / or input by a user. These associations may be specific to the medical imaging device 18 .

[0078] The spatial relationship may include the position of the movable portion 24 where the tracker 30 was and / or is being positioned (e.g., during movement of the tracker 30 through a plurality of different postures and / or during an image acquisition process for acquiring image data). As described above, the determined movement of the tracker 30 may indicate a movement path of the tracker 30. In this case, the position of the movable portion 24 may be determined based on the movement path of the tracker 30.

[0079] For example, the movement path of the tracker 30 may be compared to a plurality of predefined movement paths associated with different predefined positions at which the tracker 30 of the movable part 24 may be arranged to determine the position where the tracker 30 of the movable part 24 was and / or is being arranged. In the case where the movement path of the tracker 30 includes at least a portion of a circle, an ellipse, or a spiral, the position of the movable part 24 may be determined based on at least a portion of the movement path of the tracker 30 (e.g., by comparing the at least a portion to a plurality of predefined movement paths). The movement path or at least a portion may be compared to a plurality of predefined movement paths by a curve matching algorithm such as an affine curve matching algorithm (ACMA) and / or using a fast marching method (FMM). The position may also be determined without comparing to a predefined movement path, for example, by mapping the movement path or at least a portion to a predefined geometric model of the movable part 24 or the entire medical imaging device 18.

[0080] The spatial relationship may include an orientation of the tracker 30 relative to the movable portion 24. As described above, the determined movement of the tracker 30 may indicate a rotation of the tracker 30. In this case, the orientation of the tracker 30 relative to the movable portion 24 may be determined based on the rotation. It may be desirable to further determine the orientation of the tracker 30 based on at least one setting of the medical imaging device 18.

[0081] In step 214 , (eg, only or exactly) one of a plurality of transformations between the pose of the tracker 30 and a coordinate system associated with the image data acquired by the medical imaging device 18 is selected.

[0082] One of the plurality of transitions is selected based at least on the determined movement of the tracker 30 .

[0083] One or more (e.g., each) of the plurality of transformations may be predefined. One or more (e.g., each) of the plurality of transformations may be specific to one or more of the medical imaging device 18, the tracker 30, the mounting assembly, and combinations thereof. One or more (e.g., each) of the plurality of transformations may be stored in the memory 6.

[0084] Each of the plurality of transformations may be associated with a different (e.g., possibly) predefined movement of tracker 30. One of the plurality of transformations may be associated with a predefined movement of tracker 30 that matches the determined movement of tracker 30 (e.g., matches at least to a predefined amount).

[0085] One of the plurality of transformations may be further selected based on one or more inputs selected from: (i) a determined spatial relationship between the tracker 30 and the movable portion 24; (ii) gravity information; (iii) a movement of the tracker 30 determined relative to the gravity direction 16; (iv) at least one setting of the medical imaging device 18. Each of the plurality of transformations may be associated with one or more different (e.g., possible) predefined criteria selected from: (i) a predefined spatial relationship between the tracker 30 and the movable portion 24; (ii) predefined gravity information; (iii) a predefined movement of the tracker 30 relative to a predefined gravity direction; (iv) at least one predefined setting of the medical imaging device 18. The selected one of the plurality of transformations may be associated with one or more predefined criteria that matches (e.g., matches at least to a predefined degree) the one or more inputs. Such selection may be referred to as a "direct" selection based on the one or more inputs. Alternatively, one of the plurality of transformations may be selected "indirectly" based on information derived from one or more inputs (e.g., based on the side of the movable portion 24 that may be determined based on the direction of movement of the tracker 30, and optionally at least one setting). A combination of using an input directly and another input indirectly to select a transformation is also possible.

[0086] The method may also include determining a relative pose between a coordinate system of the image data and a tracking coordinate system based on the selected one of the transformations and optionally further based on a pose of the tracker in the tracking coordinate system. A registration between the image data and a real-world coordinate system such as the tracking coordinate system may be determined based on the selected one of the transformations. Step 214 may include determining the registration based on the selected one of the transformations.

[0087] In optional step 216, display of the navigation view is triggered.

[0088] Display of a navigation view on the display unit 38 may be triggered. The navigation view may be generated based on a transformation selected in step 214. The navigation view may indicate a tracking pose of the medical instrument 36 relative to the medical image 42. For example, a trajectory 40 of the instrument 36 may be superimposed on the medical image 42 to generate the navigation view. Details of how such a navigation view may be generated will be apparent to those skilled in the art once a transformation between the pose of the tracker 30 and a coordinate system associated with image data acquired by the medical imaging device 18 is selected.

[0089] Now refer to Figure 3 to Figure 5c Describes exemplary details and implementation options for the technology disclosed herein, including Figure 2 method.

[0090] Figure 3 Different mounting arrangements of the tracker on the C-arm are shown.

[0091] The tracker 30 may be arranged at the left side of the detector 28, resulting in the arrangement indicated by reference numeral 30a. The tracker 30 may alternatively be arranged at the right side of the detector 28, resulting in the arrangement indicated by reference numeral 30b. It can be seen that different predefined transformations 44a, 44b are required to describe the spatial relationship between the respective tracker arrangements 30a, 30b and the isocenter 30 located between the detector 28 and the X-ray source 26. In the case where only a single pose of the tracker 30 is obtained, it may not be possible to unambiguously determine which of the transformations 44a, 44b to use. The present technology relies on determining the movement of the tracker 30 based on the tracking information to select the appropriate transformation.

[0092] Figure 4a to Figure 4b Shows Figure 3 4. Side views of different mounting arrangements of the C-arm. In the example shown, the detector 28 is at the uppermost 12 o'clock position at the start of the image acquisition process, and the C-arm has a predefined movement direction indicated by a large arrow, along which the movable part 24 moves during the acquisition of the CT scan. In this case, if it is determined that the tracker 30 moves in a clockwise direction, it can be deduced from the arrangement 30a that the tracker is arranged at the left side of the C-arm, so that the correct transformation 44a can be selected. On the other hand, if it is determined that the tracker 30 moves in a counterclockwise direction, it can be deduced from the arrangement 30b that the tracker is arranged at the right side of the C-arm, so that the correct transformation 44b can be selected.

[0093] Since a clockwise movement of the movable part 24 will also result in a clockwise rotation (and possibly a clockwise translation) of the tracker 30 , the same approach is possible when considering the rotation direction of the tracker 30 rather than its movement direction.

[0094] In yet another aspect, the position at which the tracker 30 is arranged on the detector 28 may be determined depending on the radius of the movement path of the tracker 30 around the isocenter 30. Then, a suitable transformation may be selected from a plurality of predefined transformations associated with different positions at which the tracker 30 may be arranged on the detector 28.

[0095] Some C-arms can be manually reconfigured, resulting in Figure 4a and Figure 4b In these cases, the predefined movement direction may still be specific to the side of the movable part 24 on which the tracker 30 is arranged and a different combination of the starting and / or ending posture of the movable part 24. Therefore, even in the case of manual reconfiguration of the C-arm, the technology disclosed herein can achieve unambiguous selection of the correct transformation by further considering the starting and / or ending posture in addition to the movement of the tracker 30.

[0096] like Figure 5a As shown, when acquiring image data, the coordinate system of the image data need not be defined by the isocenter 30, but may be defined by a (e.g., arbitrarily selected) spatial position 46, which may even be located outside the space captured by the medical imaging device 18. The spatial position may have a predefined spatial relationship relative to the movable part 24. It is also shown that the tracker 30 may be arranged at the X-ray source 26 instead of the X-ray detector 28.

[0097] like Figure 5b As shown, the present disclosure is not limited to a medical imaging device 18 in which the movable part 24 moves along a circular movement path. Instead, the movable part 24 may move along a linear movement path 48 when the medical imaging device 18 performs an image acquisition process. In addition, the tracker 30 may be arranged on the emitter 50 used in the image acquisition process instead of the X-ray detector 28. The detector 52 used in the image acquisition process may be part of the immovable part 26 of the medical imaging device 18. It is also possible that the movable part 24 includes a detector and the immovable part 26 includes a detector, each of which is configured to be used in the image acquisition process.

[0098] like Figure 5c As shown, the movable portion 24 can be configured to move along a movement path that is neither linear nor circular but has an arbitrary (e.g., two-dimensional and / or three-dimensional) shape that may or may not be predefined. A transition can also be selected based not only on the determined movement of a single tracker 30 but also on the determined movement of multiple trackers 30, each of which can be attached to a different portion of the movable portion 24, such as Figure 5cThis method may not only improve reliability due to redundancy, but is also advantageous in the case where the movable part 24 changes its shape during the image acquisition process.

[0099] Various other modifications of the technology disclosed herein are also possible. Figure 5a to Figure 5c The variants discussed can be combined with each other and / or Figure 1 The configuration combination shown. The technology disclosed herein is not limited to optical tracking systems. Other tracking methods may be used instead. For example, the tracking system 10 may be an electromagnetic tracking system that includes a field generator and uses one or more electromagnetic field sensors as a tracker. The technology disclosed herein is not limited to medical imaging devices configured to acquire X-ray images. For example, the medical imaging device 18 may be configured to acquire magnetic resonance (MR) image data, ultrasound image data, microscopic image data, microwave image data, or positron emission tomography (PET) image data. The movable portion of the medical imaging device may not be part of the C-arm, but may include one or both of the emitter and detector of the medical imaging device, which emitter and detector do not need to be configured for X-rays. In addition, the order of one or more method steps 202 to 216 may be the same as Figure 2 For example, gravity information may only be used to determine at least one setting in step 210, so step 206 may be performed between steps 206 and 208. Multiple steps may be performed simultaneously, such as data acquisition steps 204, 206. It should be understood that one or more of the optional steps 202, 206, 210, 212, 216, or even all of these steps may be performed, although this is not required.

[0100] The details of the technology disclosed herein will now be described with reference to the reference numerals used in the accompanying drawings (including Figure 2 ), although these reference numerals should not be understood as limiting the following disclosure to the features described above with respect to the corresponding figures.

[0101] In order to register volumetric image data acquired by a 3D C-arm scanner as the medical imaging device 18, the following prerequisites may need to be met:

[0102] 1. The C-arm needs to be trackable, so a tracker 30 needs to be attached to the C-arm, and the tracker 30 is also called a C-arm tracker;

[0103] 2. The spatial relationship between the tracker 30 and a tracking coordinate system defined, for example, by the patient tracker 32 needs to be determined based on the tracking data; and

[0104] 3. One needs to know a pre-computed calibration matrix (also referred to herein as a pre-defined transformation) which contains the spatial relationship between the tracker 30 and the volumetric image data.

[0105] In case these three conditions are met, once the resulting volumetric image data is sent to at least one processor 4, an automatic image registration can be calculated. The calibration matrix can define the transformation between the pose of the tracker 30 and the isocenter 30 of the C-arm, which is the point about which the C-arm rotates and can be located at the center of the resulting image volume (see, e.g. Figure 1 ).

[0106] Some C-arm models provide multiple interface points to mount the tracker 30 to the C-arm. These different mounting points may result in different calibration matrices (see e.g. Figure 3 ). It is desirable to determine which side of the C-arm the tracking system 10 is currently tracking in order to select the correct calibration matrix 44a or 44b.

[0107] Due to the relative nature of navigation tracking techniques, one may not rely on information given in a static scenario where neither the patient tracker 32 nor the C-arm tracker 30 moves, since the orientation of each tracker may not be known in advance. Instead, it is proposed to use tracking data acquired during the image data acquisition process. While acquiring 3D volumetric image data, the 3D C-arm rotates from its starting pose to its ending pose around the ISO center 30. Depending on the direction of rotation of the C-arm tracker 30 in the tracking coordinate system while performing the image acquisition process, the side of the C-arm currently facing the camera 12 display can be determined. This enables the use of one tracker 30 that can be arranged at various locations on the movable part 24 (e.g., attached to multiple adapter points on the C-arm), and the selection of the correct calibration matrix 44a, 44b for registration calculations. This can enable the customer to re-mount the same tracker 30 at multiple mounting points depending on the current needs of the surgeon and / or the spatial operating room layout.

[0108] To determine the moving direction of the C-arm, the continuous movement of the C-arm tracker 30 may be tracked for a certain duration, or the starting point and one or more points during the rotation of the C-arm may be captured. These tracking points may form a part of a circle or an ellipse.

[0109] Based on the circular or elliptical spatial path formed by the tracking points of the tracker 30, the direction of movement (e.g., clockwise or counterclockwise) can be determined. If the C-arm tracker 30 is fixed to one side of the C-arm, the determined direction of movement of the tracker 30 can be directly related to the clockwise or counterclockwise rotation of the C-arm. In this case, it can be assumed that the C-arm always rotates in the same way and the direction of rotation of each side is known in advance. When moving and rotating the camera 12, clockwise and counterclockwise can always maintain the same relationship to the side of the C-arm (see, e.g., Figure 4a and 4b ).

[0110] The camera 12 need not be arranged so that its field of view is aligned with the rotation axis of the C-arm (e.g., parallel to or centered on the rotation axis of the C-arm). When the camera 12 is placed in front of or behind the C-arm, the C-arm tracker 30 will move toward or away from it. As long as there is an angle different from 0 or 90 degrees between the camera 12 and the C-arm tracker 30, the circular or linear backward / forward movement will be converted into an ellipse. By tracking this ellipse, not only can the mounting side of the C-arm be determined, but even different mounting points on the same side can be distinguished.

[0111] Some C-arms can be reconfigured (e.g., manually) by turning "C" along the roll axis. This can result in an exchange of the relationship between the clockwise / counterclockwise rotation of the C-arm and the corresponding C-arm side. In this case, the gravity direction 16 can be taken into account. Based on the gravity direction, since it is clear whether the detector 28 is rotated from the top position or the lowest position, the starting pose of the imaging device 18 at the beginning of the image acquisition process (e.g., the starting position of the detector 28) can be determined. In the absence of an explicit gravity direction pointing to an external reference, unless it is assumed that the camera 12 is always oriented in the same way relative to the gravity direction 16, the camera 12 may not know how it is rotated in space, and therefore an absolute top position and low position may not be calculated. When combined with the gravity direction and the determined movement direction of the tracker 30, different starting poses and ending poses can be determined as settings for the image acquisition device 18.

[0112] The association between the rotation direction and the tracked C-arm side may be predefined, for example, based on a calibration in which the user has stored the association. The user may be asked to rotate the C-arm in each direction, or if one of these rotations is not applicable (e.g., if the C-arm does not support rotation along the roll axis), the user may be asked to skip that rotation. Once the association between the rotation direction and the tracked C-arm side (and optionally one or more settings of the C-arm) is defined, these associations may be stored in the memory 6 and may also be used in subsequent image acquisition processes.

[0113] Since both rotation and tracking may be subject to jitter, the acquired knowledge of the rotation may require a certain error factor. However, since the recorded curves may be detected with any jitter, such jitter of the recorded positions may be equal between all C-arm models, and only the clockwise / counterclockwise information (and optionally the setting of the C-arm) may be relevant for determining the attachment side of the tracker 30 on the C-arm.

[0114] By implementing side detection, a single C-arm tracker 30 can be used to acquire registered and navigable medical images, where the camera 12 can be located on either side of the C-arm. The tracker 30 can then be switched between different mounting points, and the corresponding calibration based on the selected one of the transformations 44a, 44b can be used.

[0115] In summary, the technology disclosed herein can allow for automatic selection of a transformation between a pose of a medical imaging device tracker and a coordinate system associated with image data acquired by the medical imaging device. The transformation can be selected based on different poses of the medical imaging device tracker tracked during an image acquisition process of acquiring one or more medical images of a patient's body. The selected transformation can be able to align the medical image to a real-world coordinate system without imaging the patient or a registration model. The technology can be particularly advantageous in situations where a surgeon wishes to attach a medical imaging device tracker to the device in different mounting poses. Since no user input regarding the mounting pose is required, errors in selecting a transformation can be reduced. Further advantages of the technology are apparent to those skilled in the art.

[0116] The present disclosure also provides the following non-limiting examples:

[0117] Example 1: A method for selecting a transformation between a posture of a tracker (30) and a coordinate system associated with image data acquired by a medical imaging device (18), the method being performed by at least one processor (4) and comprising: obtaining (204) tracking information indicating a plurality of different postures of a tracker (30) fixedly positioned relative to a movable portion (24) of the medical imaging device (18); determining (208) movement of the tracker (30) based on the obtained tracking information; and selecting (214) one of a plurality of transformations between a posture of the tracker (30) and a coordinate system associated with image data acquired by the medical imaging device (18) based on the determined movement of the tracker (30).

[0118] Example 2: The method according to Example 1 also includes: determining (212) a spatial relationship between the tracker (30) and the movable part (24) based on the determined movement of the tracker, wherein a transformation is selected from a plurality of transformations based on the determined spatial relationship.

[0119] Example 3: The method of example 1 or 2, wherein the spatial relationship includes a side of the movable portion (24) on which the tracker (30) is disposed.

[0120] Example 4: The method of Example 3, wherein the determined movement of the tracker indicates a direction of movement of the tracker (30), wherein the side of the movable part (24) is determined based on the direction of movement of the tracker (30).

[0121] Example 5: A method according to Example 4, wherein the side of the movable part (24) is determined by selecting the side of the movable part (24) from a first side of the movable part (24) associated with a clockwise movement direction of the tracker (30) and a second side of the movable part (24) associated with a counterclockwise movement direction of the tracker (30).

[0122] Example 6: The method of any one of Examples 2 to 5, wherein the spatial relationship includes a position of the movable part (24) at which the tracker (30) is arranged.

[0123] Example 7: The method of Example 6, wherein the determined movement of the tracker (30) indicates a movement path of the tracker (30), wherein the position of the movable part (24) is determined based on the movement path of the tracker (30).

[0124] Example 8: A method according to Example 7, wherein the movable part (24) is configured to move in a circle or a spiral, wherein the movement path of the tracker (30) includes at least a portion of the circle, ellipse or spiral, and the position of the movable part (24) is determined based on at least a portion of the movement path of the tracker (30).

[0125] Example 9: The method of any of Examples 2 to 8, wherein the spatial relationship includes an orientation of the tracker (30) relative to the movable portion (24).

[0126] Example 10: The method according to any one of Examples 1 to 9 further includes: obtaining gravity information indicating a direction of gravity, wherein the conversion is selected based on the gravity information.

[0127] Example 11: The method of Example 10, wherein the movement of the tracker (30) is determined relative to a gravity direction indicated by the gravity information, and wherein the transition is selected based on the movement of the tracker (30) determined relative to the gravity direction.

[0128] Example 12: The method according to any one of Examples 1 to 11 further includes: obtaining (210) at least one setting of the medical imaging device (18), the at least one setting being selected from a start posture and an end posture of a movable part (24) of the medical imaging device (18) relative to an immovable part (26) of the medical imaging device (18), or a component having a fixed spatial relationship with the immovable part (26) of the medical imaging device (18), wherein the transformation is selected based on at least one setting of the medical imaging device (18).

[0129] Example 13: The method according to Example 12 and Example 10 or 11 also includes: determining at least one setting of the medical imaging device (18) based on the tracking information, gravity information and the determined movement of the tracker (30) to obtain at least one setting of the medical imaging device (18).

[0130] Example 14: A method according to Example 12 or 13 dependent on Example 4, wherein the side of the movable part (24) is determined based on a moving direction of the tracker (30) and at least one obtained setting of the medical imaging device (18).

[0131] Example 15: The method according to Example 14, wherein the side of the movable part (24) is determined by selecting the side of the movable part (24) from the following items based on the determined movement direction of the tracker (30) and at least one setting of the obtained medical imaging device (18): a first side of the movable part (24), the first side being associated with (i) the clockwise movement direction of the tracker (30) and the first setting of the medical imaging device (18) and (ii) the counterclockwise movement direction of the tracker (30) and the second setting of the medical imaging device (18); and a second side of the movable part (24), the second side being associated with (i) the clockwise movement direction of the tracker (30) and the second setting of the medical imaging device (18) and (ii) the counterclockwise movement direction of the tracker (30) and the first setting of the medical imaging device (18).

[0132] Example 16: A method according to any one of Examples 1 to 15, wherein at least two or all of the multiple different postures of the tracker (30) are associated with different time points of an image acquisition process performed by a medical imaging device (18) to acquire image data, wherein a movable part of the medical imaging device (18) moves during the image acquisition process.

[0133] Example 17: A method according to any one of Examples 1 to 16, wherein the medical imaging device (18) is configured to acquire computed tomography (CT) image data, and the movable part (24) of the medical imaging device (18) is part of a C-arm.

[0134] Example 18: A system (100) comprising at least one processor (4), the at least one processor (4) being configured to perform the method according to any one of Examples 1 to 17.

[0135] Example 19: The system of Example 18, further comprising at least one of the following entities:

[0136] i) A medical imaging device (18) comprising a movable portion (24) and configured to

[0137] Get image data;

[0138] ii) A tracking system (10), such as an optical tracking system including a camera, is configured

[0139] To provide tracking information;

[0140] iii) a gravity sensor (14) configured to provide gravity information and optionally fixed

[0141] to a tracking system (10) and / or a camera (12);

[0142] iv) Tracker (30).

[0143] Example 20: A computer program comprising instructions which, when executed by at least one processor (4), cause the at least one processor (4) to perform a method according to any one of Examples 1 to 17, the computer program optionally being carried by a data stream or stored on a (e.g., non-temporary computer-readable) storage medium (6).

Claims

1. A method for selecting a transformation between a pose of a tracker and a coordinate system associated with image data acquired by a medical imaging device, the method being executed by at least one processor and comprising: obtaining tracking information indicative of a plurality of different poses of a tracker fixedly positioned relative to a movable portion of a medical imaging device; determining movement of the tracker based on the obtained tracking information; as well as Based on the determined movement of the tracker, one of a plurality of transformations between a pose of the tracker and a coordinate system associated with image data acquired by the medical imaging device is selected.

2. The method according to claim 1, further comprising: determining a spatial relationship between the tracker and the movable part based on the determined movement of the tracker, Wherein, the one transformation is selected from the plurality of transformations based on the determined spatial relationship.

3. The method according to claim 1, wherein: The spatial relationship includes a side of the movable portion on which the tracker is disposed.

4. The method according to claim 3, wherein: The determined movement of the tracker indicates a movement direction of the tracker, wherein the side of the movable part is determined based on the movement direction of the tracker.

5. The method according to claim 4, wherein: The side of the movable part is determined by selecting the side of the movable part from a first side of the movable part associated with a clockwise direction of movement of the tracker and a second side of the movable part associated with a counterclockwise direction of movement of the tracker.

6. The method according to claim 2, wherein: The spatial relationship includes the position of the movable portion at which the tracker is arranged.

7. The method according to claim 6, wherein: The determined movement of the tracker indicates a movement path of the tracker, wherein the position of the movable part is determined based on the movement path of the tracker.

8. The method according to claim 7, wherein: The movable part is configured to move in a circle or a spiral, wherein the movement path of the tracker includes at least a portion of the circle, ellipse or spiral, and the position of the movable part is determined based on the at least a portion of the movement path of the tracker.

9. The method according to claim 2, wherein: The spatial relationship includes an orientation of the tracker relative to the movable portion.

10. The method according to claim 1, further comprising: Get gravity information indicating the direction of gravity, Wherein, the transformation is selected based on the gravity information.

11. The method according to claim 10, wherein: Movement of the tracker is determined relative to the gravity direction indicated by the gravity information, wherein the transition is selected based on the movement of the tracker determined relative to the gravity direction.

12. The method according to claim 1, further comprising: obtaining at least one setting of the medical imaging device, the at least one setting being selected from a starting pose and an ending pose of the movable portion of the medical imaging device relative to an immovable portion of the medical imaging device or a component having a fixed spatial relationship with the immovable portion of the medical imaging device, Wherein the transformation is selected based on the at least one setting of the medical imaging device.

13. The method according to claim 12, further comprising: obtaining gravity information indicating a direction of gravity relative to one or more of the plurality of different postures of the tracker; as well as The at least one setting of the medical imaging device is determined based on the tracking information, the gravity information and the determined movement of the tracker to obtain the at least one setting of the medical imaging device.

14. The method according to claim 12, wherein: The spatial relationship includes a side of the movable portion on which the tracker is disposed, wherein the determined movement of the tracker indicates a moving direction of the tracker, Wherein, the one side of the movable part is determined based on the movement direction of the tracker and the at least one obtained setting of the medical imaging device.

15. The method according to claim 14, wherein: The side of the movable part is determined by selecting the side of the movable part from: a first side of the movable portion, the first side being associated with (i) a clockwise direction of movement of the tracker and a first setting of the medical imaging device and (ii) a counterclockwise direction of movement of the tracker and a second setting of the medical imaging device; as well as A second side of the movable portion is associated with (i) a clockwise direction of movement of the tracker and a second setting of the medical imaging device and (ii) a counterclockwise direction of movement of the tracker and a first setting of the medical imaging device.

16. The method according to claim 1, wherein: At least two or all of the plurality of different postures of the tracker are associated with different points in time of an image acquisition procedure performed by the medical imaging device to acquire the image data, wherein the movable part of the medical imaging device moves during the image acquisition procedure.

17. The method according to claim 1, wherein: The medical imaging device is configured to acquire computed tomography (CT) image data, and the movable portion of the medical imaging device is a part of a C-arm.

18. A system comprising at least one processor configured to perform a method for selecting a transformation between a pose of a tracker and a coordinate system associated with image data acquired by a medical imaging device, the method comprising: obtaining tracking information indicative of a plurality of different poses of a tracker fixedly positioned relative to a movable portion of a medical imaging device; determining movement of the tracker based on the obtained tracking information; as well as Based on the determined movement of the tracker, one of a plurality of transformations between a pose of the tracker and a coordinate system associated with image data acquired by the medical imaging device is selected.

19. The system of claim 18, further comprising at least one of the following entities: i) the medical imaging device comprising the movable part and configured to acquire the image data; ii) a tracking system, such as an optical tracking system including a camera, configured to provide said tracking information; iii) a gravity sensor configured to provide gravity information and optionally fixed to the tracking system and / or the camera; iv) Tracker.

20. A non-transitory computer-readable storage medium storing a computer program, the computer program comprising instructions that, when executed by at least one processor, cause the at least one processor to perform a method for selecting a transformation between a pose of a tracker and a coordinate system associated with image data acquired by a medical imaging device, the method comprising: obtaining tracking information indicative of a plurality of different poses of a tracker fixedly positioned relative to a movable portion of a medical imaging device; determining movement of the tracker based on the obtained tracking information; as well as Based on the determined movement of the tracker, one of a plurality of transformations between a pose of the tracker and a coordinate system associated with image data acquired by the medical imaging device is selected.

Images