Transformation Selection Method Based on Tracker Movement

Abstract

To provide 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 apparatus.SOLUTION: A method is executed by a processor and includes: acquiring tracking information showing a plurality of different poses of a tracker that is fixedly arranged to a movable part of a medical imaging apparatus; determining movement of the tracker on the basis of the acquired tracking information; and 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 apparatus on the basis of the determined movement of the tracker. A corresponding system and non-transitory computer-readable storage medium are also provided.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure generally relates to 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, and also provides a system, a computer program, and a carrier such as a non-transitory computer storage medium. [Background technology]

[0002] In surgical navigation procedures, it may be necessary to align image data acquired by a medical imaging device, such as an X-ray device with a C-arm, with a tracker tracked by a tracking system. Such alignment may be based on a transformation between the pose of the tracker and a coordinate system associated with the image data.

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

[0004] In some surgical scenarios, the tracking system may have limited visibility of a tracker placed on a medical imaging device. This may be due, for example, to a medical instrument being placed between the tracking system's camera and the medical imaging device. For this and other reasons, it may be desirable to place the tracker in a pose that is different from the single predetermined pose described above. In such placements, the transformation between the different poses of the tracker and the coordinate system of the image data may be different. As a result, it may not be possible to always use the same single predetermined transformation to register the image data to the tracker. Summary of the Invention

[0005] There is a need in the art for techniques that address one or more of the above and other problems.

[0006] In 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 executed by at least one processor and includes acquiring tracking information indicative of a plurality of different poses of a tracker positioned at a fixed position relative to a movable part of the medical imaging device. The method includes determining a movement of the tracker based on the acquired tracking information. The method further includes selecting one of a plurality of transformations between the pose of the tracker and the coordinate system associated with image data acquired by the medical imaging device based on the determined movement of the tracker.

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

[0008] A transformation can be selected from among multiple transformations based on the determined spatial relationship.

[0009] The spatial relationship can include the side of the moving part on which the tracker is positioned.

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

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

[0012] The side of the movable part can be selected 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 can include the position of the moving part on which the tracker is positioned.

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

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

[0016] The movable part may be configured to move along a circle or a spiral.

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

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

[0019] The spatial relationship can include the orientation of the tracker relative to the moving part.

[0020] The method may further include obtaining gravity information indicative of a direction of gravity.

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

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

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

[0024] The method further includes obtaining at least one setup of the medical imaging device selected from a start pose and an end pose of the movable part of the medical imaging device relative to a stationary part of the medical imaging device or a component that is in a fixed spatial relationship to the stationary part of the medical imaging device.

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

[0026] The method can further include determining and obtaining at least one setup of the medical imaging device based on the tracking information, the gravity information, and the determined movement of the tracker.

[0027] The side of the moving part can be determined based on the direction of movement of the tracker and at least one acquired setup of the medical imaging device.

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

[0029] At least two or all of the different poses of the tracker can be associated with different points in time during an image acquisition process performed by the medical imaging device to acquire image data, during which a movable part of the medical imaging device is moving.

[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] A second aspect provides a system comprising at least one processor configured to perform the method of the first aspect. The at least one processor can be 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 includes acquiring tracking information indicative of a plurality of different poses of a tracker positioned at a fixed position relative to a movable part of the medical imaging device, determining a movement of the tracker based on the acquired tracking information, and selecting, based on the determined movement of the tracker, one of a plurality of transformations between the pose of the tracker and the coordinate system associated with image data acquired by the medical imaging device.

[0033] The system may further comprise at least one of the following entities: (i) a medical imaging device having a moving 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, optionally affixed to the tracking system and / or camera; (iv) Tracker

[0034] In a third aspect, a non-transitory computer-readable storage medium is provided, the storage medium storing a computer program including instructions that, when executed on at least one processor, cause the at least one processor to perform the method of the first aspect. The storage medium can store the computer program including instructions that, when executed on at least one processor, cause the at least one processor to perform a method for selecting one of transformations between a pose of a tracker and a coordinate system associated with image data acquired by a medical imaging device, the method including acquiring tracking information indicative of multiple different poses of a tracker positioned fixedly relative to a movable part of a medical imaging device, determining a movement of the tracker based on the acquired tracking information, and selecting one of multiple transformations between the 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.

[0035] In a fourth aspect, there is provided a computer program comprising instructions which, when executed by at least one processor, cause the at least one processor to perform the method of the first aspect. The computer program can be transmitted by a data stream or stored on a (e.g., non-transitory, computer-readable) storage medium.

[0036] In a fifth aspect, there is provided a carrier carrying the computer program of the fourth aspect. The carrier may be a data stream or a (for example non-transitory computer-readable) storage medium. [Brief explanation of the drawings]

[0037] Further details, advantages, and aspects of the present disclosure will become apparent from the embodiments referenced in conjunction with the drawings. [Figure 1] 1 illustrates a system according to the present disclosure. [Figure 2]1 illustrates a method according to the present disclosure. [Figure 3] 1 shows different mounting arrangements of the tracker on the C-arm. [Figure 4a] 4 shows a side view of the different mounting arrangement of FIG. 3. [Figure 4b] 4 shows a side view of the different mounting arrangement of FIG. 3. [Figure 5a] 1 shows a medical imaging device with a tracker. [Figure 5b] 1 shows a medical imaging device with a tracker. [Figure 5c] 1 shows a medical imaging device with a tracker. DETAILED DESCRIPTION OF THE INVENTION

[0038] Exemplary embodiments of the present technology will now be described with reference to the drawings, in which, unless otherwise specified, the same reference numerals refer to the same or similar structural features.

[0039] 1 illustrates a system 100 according to the present disclosure. System 100 may be a surgical navigation system.

[0040] The system 100 includes a processing device 2 including at least one processor 4. The at least one processor 4 is communicatively connected to a memory 6, which is an example of a non-transitory computer-readable storage medium. The at least one processor 4 may be further communicatively coupled to an interface 8 of the device 2. The device 2 may also be implemented as a spatially distributed processing device 2, for example, by implementing the at least one processor 4, the memory 6, and / or the interface (e.g., virtual processor, virtual memory, or memory) on different servers. In other words, at least a portion of the device 2 may be realized by a cloud computing platform. Alternatively, the device 2 may be implemented as a local processing device 2 located, for example, in a hospital scanning room or operating room.

[0041] The system 100 further includes a tracking system 10. In the illustrated example, the tracking system 10 is an optical tracking system including a stereo camera 12. A gravity sensor 14 (e.g., a three-axis accelerometer) may be positioned fixedly relative to the stereo camera 12 to acquire a gravity direction 16. The tracking system 10 may be communicatively coupled to at least one processor 4 via an interface 8 and configured to provide tracking data indicative of a pose of the tracked tracker to the at least one processor 4. As used herein, the term "pose" should be understood to mean "at least one of position and orientation."

[0042] The system 100 further 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 a stationary (e.g., fixed) part 22 and a movable part 24. When image data is acquired by the medical imaging device 18, the movable part 24 is configured to move relative to the stationary part 22. The stationary part 22 is configured to remain stationary (e.g., in an operating room) when the image data is acquired. The medical imaging device 18 is communicatively connected to at least one processor 4 via an interface 8 and may be configured to provide the acquired image data to the at least one processor 4. In the illustrated example, the medical imaging device 18 is configured to acquire computed tomography, or CT, images of the patient's body 20 as image data, and includes a C-arm having an X-ray source 26 and an X-ray detector 28 as the movable part 24 and a cart as the stationary part 22. The C-arm is configured to rotate about a central point 29, also called an isocenter, when acquiring a CT image, also called a CT scan.

[0043] System 100 further includes one or more trackers 30-34. Tracker 30 is fixedly positioned relative to moving part 24 of medical imaging device 18 and, in the illustrated example, is attached directly to X-ray detector 28, and thus may be referred to as a medical imaging device tracker. Tracker 32 is spatially fixed relative to patient body 20, e.g., glued to the patient's skin, and thus may be referred to as a patient tracker. Tracker 34 is attached to a medical device 36 manipulated by a surgeon or surgical robot, and thus may be referred to as a medical device tracker. Each of trackers 30-34 can be tracked by tracking system 10, which means that tracking system 10 can determine the pose of each of trackers 30-34 in a (e.g., real-world) tracking coordinate system. The tracking coordinate system (e.g., the origin and orientation of the coordinate system) can be defined by one of the trackers, e.g., patient tracker 32. Tracking system 10 can be configured to provide at least one processor 4 with information indicative of the tracked poses of trackers 30-34, e.g., information in a tracking coordinate system. In the illustrated example, each of trackers 30-34 includes a plurality of optical tracking markers detectable by stereo camera 12, although the disclosure is not limited thereto.

[0044] The system 100 further 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 in which the tracked pose of the medical device 36 is shown relative to a representation of the patient's body 20. For example, the trajectory 40 is shown superimposed on a medical image 42 of the patient's body 20 contained in the image data acquired by the imaging device 18.

[0045] To this end, a transformation may be required between the tracker coordinate system and a coordinate system associated with the image data (e.g., associated with or defined by one or more images contained in the image data, such as medical image 42). The coordinate system associated with the image data may be defined by an isocenter 29 that is in a fixed spatial relationship with respect to the x-ray detector 28. More generally, the coordinate system associated with the image data may have a (e.g., pre-defined) spatial relationship relative to the movable part 24 of the medical imaging device 18.

[0046] In the present disclosure, tracker 30 can be attached to movable part 24 in two or more predetermined poses. This means that the relative pose of tracker 30 and movable part 24 can vary with each image acquisition process, and therefore, different instances of acquired image data will have different transformations between the pose of tracker 30 and the coordinate system associated with each image data. The techniques disclosed herein enable automatic selection of an appropriate transformation from among multiple transformations. This approach is described in detail below. While reference numerals used in FIG. 1 are used below, this should not be understood as necessarily limiting the features described below to the respective features shown and described in FIG. 1.

[0047] 2 illustrates a method according to the present disclosure, which may be performed by at least one processor 4. A memory 6 may store a computer program including instructions that, when executed by the at least one processor 4, cause the at least one processor 4 to perform the method of FIG.

[0048] In optional step 202, the medical imaging device 18 is initiated to acquire image data.

[0049] Step 202 may include acquiring image data by starting the medical imaging device 18 and performing an image acquisition process in which the movable part 24 moves.

[0050] At least steps 202-214 of the methods disclosed herein may be performed prior to scanning the patient's body 20. However, in some scenarios, it may be desirable for the image data acquired by the medical imaging device 18 initiated in step 202 to include a depiction of at least a portion of the patient's body 20.

[0051] The image data may include or 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 image data is acquired by the medical imaging device 18 while the movable part 24 moves relative to the stationary part 22. The image data may include computed tomography (CT) images, also known as CT scans. The image data may include cone-beam CT (CBCT) scans. The image data may include spiral CT scans or multi-slice CT scans. The image data may include one or more single-spectrum or multi-spectral 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 while the movable part 24 moves relative to the stationary part 22.

[0052] In step 204, tracking information is obtained.

[0053] The tracking information indicates a plurality of different poses of a tracker 30 that is fixedly positioned relative to a movable part 24 of the medical imaging device 18. The tracker 30 may be attached directly to the movable part 24 or may be attached to the movable part 24 via a mounting assembly disposed on the movable part 24. In at least one of the movable parts 24, the mounting assembly and tracker 30 may be configured such that the tracker 30 is fixedly positioned relative to the movable part 24 in two or more (e.g., predetermined) poses. The movable part 24 may have a plurality of (e.g., opposing) sides (e.g., two or more of a left side, a right side, a front side, and a back side) on which the tracker 30 can be positioned.

[0054] The tracking information may further indicate one or more tracked 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 the tracking coordinate system.

[0055] At least two or all of the different poses of tracker 30 can be associated with different points on a time axis (e.g., one time point per pose). The different time points can be part of an image acquisition process performed by medical imaging device 18 to acquire image data. The different poses of tracker 30 can be acquired by tracking system 10 during the image acquisition process. During that image acquisition process, movable part 24 of medical imaging device 18 can move relative to stationary part 22. As a result, tracker 30 can also move in space as it acquires image data, resulting in different tracked poses of tracker 30.

[0056] In optional step 206, gravity information is obtained.

[0057] Gravity information can be obtained from gravity sensor 14. The gravity information can indicate, for example, a gravity direction 16 for one or more of the tracked poses of trackers 30-34 (e.g., for one or more of a plurality of different poses of tracker 30). A tracking coordinate system (e.g., its orientation) can be defined based on gravity direction 16. One or more, for example, all, of the tracked poses of trackers 30-34 can be defined relative to the gravity direction.

[0058] In step 208, the movement of tracker 30 is determined.

[0059] The movement of tracker 30 is determined based at least on the obtained tracking information.

[0060] The movement of the tracker 30 can be determined relative to the direction of gravity 16 indicated by the gravity information.

[0061] The determined movement of tracker 30 may indicate a direction of movement of tracker 30, for example, a clockwise or counterclockwise direction of movement (e.g., as observed by tracking system 10). Movable part 24 and tracker 30 may move in that direction of movement during an image acquisition process (e.g., initiated in step 202) to acquire image data.

[0062] The determined movement of tracker 30 may indicate a movement path of tracker 30. Movable part 24 and tracker 30 may move along the movement path during an image acquisition process (e.g., initiated in step 202) to acquire image data. For example, movable part 24 may be configured to move along (e.g., at least a portion of) a circle or a spiral. In this case, the movement path of tracker 30 may include at least one segment of the circle, ellipse, or spiral.

[0063] The determined movement of tracker 30 can indicate a rotation of tracker 30, for example, a clockwise or counterclockwise rotation (e.g., as observed by tracking system 10). Movable part 24 can move during the image acquisition process (e.g., initiated in step 202) to acquire image data. For example, tracker 30 rotates and, optionally, moves in space (e.g., along a movement path).

[0064] Determining the movement of tracker 30 may include virtually connecting multiple different poses of tracker 30 indicated by the tracking information. The direction of movement may be determined based on different time points associated with the multiple different poses of tracker 30. The movement of tracker 30 may be determined by a machine vision algorithm based at least on the tracking information. The machine vision algorithm may be configured to separate the pose of tracker 30 from the poses of other tracked trackers 32, 34, remove outlier poses of tracker 30 (e.g., due to tracking error), and / or interpolate, average, and / or extrapolate between two or more of the multiple different poses of tracker 30.

[0065] In optional step 210, at least one setup of the medical imaging device 18 is obtained.

[0066] At least one setup includes a start pose and / or an end pose of the movable portion 24 of the medical imaging device 18. The start pose and / or end pose may be defined relative to the operating room, the stationary portion 22 of the medical imaging device 18, and / or a component having a fixed spatial relationship to the stationary portion 22 of the medical imaging device 18. The start pose may correspond to the pose of the movable portion 24 at the beginning of the image acquisition process, and the end pose may correspond to the pose of the movable portion 24 at the end of the image acquisition process. Examples of start and end poses include a pose with the detector 28 of the medical imaging device 18 at its top-most (“12 o'clock”) position, a pose with the detector 28 of the medical imaging device 18 at its left-most (“9 o'clock”) position, a pose with the detector 28 of the medical imaging device 18 at its bottom-most (“6 o'clock”) position, and a pose with the detector 28 of the medical imaging device 18 at its right-most (“3 o'clock”) position.

[0067] At least one setup can be obtained by determining the at least one setup based on tracking information, and optionally, gravity information and / or determined movement of tracker 30. For example, a start pose can be determined by comparing an earliest tracked pose of tracker 30 with one or more later poses of a plurality of different poses of tracker 30. As another example, an end pose can be determined by comparing a most recent tracked pose of tracker 30 with one or more earlier poses of a plurality of different poses of tracker 30. Gravity information can be used to avoid ambiguity (e.g., distinguishing a top position from a bottom position). This is particularly useful when tracking system 10 (e.g., camera 12) can be positioned at different orientations relative to gravity direction 16. The start pose and / or end pose may be derived from the determined movement.

[0068] In optional step 212, the spatial relationship between tracker 30 and movable part 24 is determined.

[0069] A spatial relationship between tracker 30 and movable part 24 is determined based at least on the determined movement of the tracker.

[0070] The spatial relationship between tracker 30 and movable part 24 may include the side (e.g., one of multiple sides) of movable part 24 on which tracker 30 was and / or is positioned (e.g., while tracker 30 is moving through multiple different poses and / or during an image acquisition process to acquire image data).

[0071] As described above, the determined movement of the tracker can indicate the direction of movement of the tracker. In this case, the side of the movable part 24 can be determined based on the direction of movement of the tracker 30. In one variation, the side of the movable part 24 is determined by selecting from among a first side (e.g., the right side) of the movable part 24 along which the direction of movement of the tracker 30 is clockwise, and a second (e.g., opposite) side (e.g., the left side) of the movable part 24 along which the direction of movement of the tracker 30 is counterclockwise. The association between each side and the direction of movement of the tracker 30 can be predefined, obtained from the medical imaging device 18, and / or input by a user. These associations can be specific to the medical imaging device 18.

[0072] The side of the movable part 24 can be determined based on the direction of movement of the tracker 30 and at least one acquired setup of the medical imaging device 18. The side of the movable part 24 can be determined by selecting a side of the movable part 24 from a first side (e.g., the right side) and a second side (e.g., the left side) based on the determined direction of movement of the tracker 30 and at least one acquired setup of the medical imaging device 18. The first side of the movable part 24 can be associated with (i) a clockwise direction of movement of the tracker 30 and a first setup of the medical imaging device 18, and / or (ii) a counterclockwise direction of movement of the tracker 30 and a second setup of the medical imaging device 18. The second side of the movable part 24 can be associated with (i) a clockwise direction of movement of the tracker 30 and a second setup of the medical imaging device 18, and / or (ii) a counterclockwise direction of movement of the tracker 30 and a first setup of the medical imaging device 18. The associations between each side, the direction of movement and the setup of the tracker 30 may be predefined, obtained from the medical imaging device 18, and / or input by the user. These associations may be specific to the medical imaging device 18.

[0073] The spatial relationship may include a location of movable part 24 where tracker 30 was and / or is located (e.g., while tracker 30 moves through multiple different poses and / or during an image acquisition process to acquire image data). As mentioned above, the determined movement of tracker 30 may indicate a path of movement of tracker 30. In this case, the position of movable part 24 may be determined based on the path of movement of tracker 30.

[0074] For example, the path of movement of the tracker 30 can be compared with multiple predetermined paths of movement associated with different positions of the movable part 24 where the tracker 30 can be located to determine the position of the movable part 24 where the tracker 30 was and / or is located. If the path of movement of the tracker 30 includes at least one segment of a circle, ellipse, or spiral, the position of the movable part 24 can be determined based on at least one segment of the path of movement of the tracker 30 (e.g., by comparing the at least one segment with multiple predetermined paths of movement). The path of movement or at least one segment can be compared with the multiple predetermined paths of movement using a curve matching algorithm such as the Affine Curve Matching Algorithm (ACMA) and / or the Fast Marching Method (FMM). It is also possible to determine the position without comparing with a predetermined path of movement, for example, by matching the path of movement or at least one segment to a predefined geometric model of the movable part 24 or the entire medical imaging device 18.

[0075] The spatial relationship may include an orientation of the tracker 30 relative to the movable part 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 part 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 setup of the medical imaging device 18.

[0076] In step 214, one (e.g., only one) of multiple transformations between the pose of tracker 30 and the coordinate system associated with the image data acquired by medical imaging device 18 is selected.

[0077] One of the plurality of transformations is selected based at least on the determined movement of tracker 30.

[0078] 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 memory 6.

[0079] Each of the multiple transformations can be associated with a different predetermined (e.g., possible) movement of the tracker 30. One of the multiple transformations can be associated with a predetermined movement of the tracker 30 that matches (e.g., by at least a predetermined amount) the determined movement of the tracker 30.

[0080] One of the plurality of transformations can be further selected based on one or more inputs selected from (i) a determined spatial relationship between the tracker 30 and the movable part 24, (ii) gravity information, (iii) a determined movement of the tracker 30 relative to the gravity direction 16, and (iv) at least one setup of the medical imaging device 18. Each of the plurality of transformations can be associated with one or more different (e.g., possible) predetermined criteria selected from (i) a predetermined spatial relationship between the tracker 30 and the movable part 24, (ii) predetermined gravity information, (iii) a predetermined movement of the tracker 30 relative to the predetermined gravity direction, and (iv) at least one predetermined setup of the medical imaging device 18. The selected one of the plurality of transformations can be associated with one or more predetermined criteria that match (e.g., at least to a predetermined degree) one or more inputs. Such a selection can be referred to as a “direct” selection based on one or more inputs. Alternatively, one of the plurality of transformations can be “indirectly” selected based on information derivable from one or more inputs. For example, the selection can be based on the direction of movement of the tracker 30 and, optionally, the side of the moving part 24, which is determined based on at least one setup. A combination of direct and indirect inputs is also possible to select a single transformation.

[0081] The method can further include determining a relative pose between the coordinate system of the image data and the tracking coordinate system based on the selected one transformation and, optionally, the pose of the tracker in the tracking coordinate system. Alignment between the image data and a real-world coordinate system, such as the tracking coordinate system, can be determined based on the selected one transformation. Step 214 can include determining the alignment based on the selected one transformation.

[0082] In optional step 216, the display of the navigation view is initiated.

[0083] A navigation view can be initiated for display on the display unit 38. The navigation view is generated based on the one transformation selected in step 214. The navigation view can show the tracked pose of the medical device 36 relative to the medical image 42. For example, the navigation view can be generated by overlaying the trajectory 40 of the medical device 36 on the medical image 42. The details of how such a navigation view is generated when a transformation between the pose of the tracker 30 and the coordinate system associated with the image data acquired by the medical imaging device 18 is selected will be apparent to those skilled in the art.

[0084] Exemplary details and implementation options of the techniques disclosed herein, including the method of FIG. 2, are described below with reference to FIGS. 3-5c.

[0085] Figure 3 shows different mounting arrangements of the tracker on the C-arm.

[0086] The tracker 30 can be positioned on the left side of the detector 28, as indicated by the reference numeral 30a. Alternatively, the tracker 30 can be positioned on the right side of the detector 28, as indicated by the reference numeral 30b. As can be seen, different predetermined transformations 44a, 44b are required to describe the spatial relationship between each tracker position 30a, 30b and the isocenter 29 between the detector 28 and the x-ray source 26. If only a single pose of the tracker 30 is available, it may not be possible to clearly determine which of the transformations 44a, 44b to use. The present technique relies on determining the movement of the tracker 30 based on tracking information to select the appropriate transformation.

[0087] 4a-4b show side views of different mounting arrangements of FIG. 3. In the illustrated example, detector 28 is in the top 12 o'clock position at the start of the image acquisition process, and the C-arm has a predetermined direction of movement along which movable part 24 moves during CT scan acquisition, as indicated by the large arrow. In this case, if tracker 30 is determined to be moving in a clockwise direction, it can be deduced that the tracker is located on the left side of the C-arm according to arrangement 30a, and therefore, the correct transformation 44a can be selected. On the other hand, if tracker 30 is determined to be moving in a counterclockwise direction, it can be deduced that the tracker is located on the right side of the C-arm according to arrangement 30b, and therefore, the correct transformation 44b can be selected.

[0088] The same approach is possible if one considers the direction of rotation of tracker 30 rather than the direction of translation of tracker 30, such that clockwise translation of movable part 24 also results in clockwise rotation (and optionally clockwise translation) of tracker 30.

[0089] Furthermore, the position on detector 28 at which tracker 30 is to be located can be determined according to the radius of the path of movement of tracker 30 about isocenter 29. Then, an appropriate transformation can be selected from among a plurality of predetermined transformations associated with various positions at which tracker 30 can be located on detector 28.

[0090] Some C-arms are manually reconfigured, and the predetermined movement direction shown in Figures 4a and 4b may be reversed. In these cases, the predetermined movement direction may still be specific to various combinations of the side of moving part 24 on which tracker 30 is located and the start and / or end pose of moving part 24. Thus, even when the C-arm is manually reconfigured, the techniques disclosed herein allow for unambiguous selection of the correct transformation by further considering the start and / or end pose in addition to the movement of tracker 30.

[0091] 5a, the coordinate system of the image data need not be defined by isocenter 29, but may instead be defined by a spatial location 46 (e.g., arbitrarily selected) that is outside the volume imaged by medical imaging device 18 when acquiring the image data. This spatial location may also have a predetermined spatial relationship with respect to movable part 24. It is also shown that tracker 30 may be located at x-ray source 26 rather than at x-ray detector 28.

[0092] As shown in FIG. 5b, the present disclosure is not limited to medical imaging device 18 in which movable part 24 moves along a circular movement path. Instead, movable part 24 can move along a linear movement path 48 while medical imaging device 18 performs the image acquisition process. Furthermore, tracker 30 can be located on emitter 50 used in the image acquisition process instead of X-ray detector 28. Detector 52 used in the image acquisition process can be part of stationary part 22 of medical imaging device 18. It is also possible for movable part 24 and stationary part 22 to be configured with a detector and each to be used in the image acquisition process.

[0093] As shown in FIG. 5c, the movable part 24 can be configured to move along a path of any shape (e.g., two-dimensional and / or three-dimensional) that is neither linear nor circular, and the shape may or may not be predefined. Also, as illustrated in FIG. 5c, a transformation can be selected not only based on the determined movement of a single tracker 30, but also based on the determined movements of multiple trackers 30, each attached to a different portion of the movable part 24. This approach not only improves reliability through redundancy, but can also be useful when the shape of the movable part 24 changes during the image acquisition process.

[0094] The techniques disclosed herein may be modified in various ways. For example, the variations illustrated in FIGS. 5a through 5c may be combined with each other and / or with the configuration illustrated in FIG. 1. The techniques disclosed herein are not limited to optical tracking systems. Instead, other tracking modalities may be used. For example, tracking system 10 may be an electromagnetic tracking system that includes an electromagnetic field generator and uses one or more electromagnetic field sensors as trackers. The techniques disclosed herein are not limited to medical imaging devices configured to acquire X-ray images. For example, medical imaging device 18 may be configured to acquire magnetic resonance (MR) image data, ultrasound image data, microscopy image data, microwave image data, or positron emission tomography (PET) image data. The moving parts of the medical imaging device may not be part of a C-arm, and may include one or both of the emitters and detectors of the medical imaging device, although the emitters and detectors need not be configured for X-rays. Furthermore, the order of steps 202 through 216 of one or more methods may differ from that shown in FIG. 2. For example, gravity information may be used only to determine at least one setup of step 210, and step 206 may be performed between steps 206 and 208. Multiple steps may be performed simultaneously, such as data acquisition steps 204 and 206. It should be understood that optional steps 202, 206, 210, 212, and 216 are not required, but one or more, or all, of these steps may be performed.

[0095] Details of the techniques disclosed herein, including the method of FIG. 2, are restated and described below with reference to the numerals used in the figures, which should not be understood as limiting the following disclosure to the features described with respect to each figure.

[0096] Registration of volumetric image data acquired by a 3D C-arm scanner as medical imaging device 18 may require the following prerequisites to be met: 1. The C-arm may need to be trackable, and therefore a tracker 30, also called a C-arm tracker, may need to be attached to the C-arm. 2. The spatial relationship between the tracker 30 and the tracking coordinate system defined by, for example, the patient tracker 32 may need to be determined based on the tracking data. 3. A pre-calculated calibration matrix, also referred to herein as a predetermined transformation, containing the spatial relationship between tracker 30 and the volumetric image data may need to be known.

[0097] If these three conditions are met, automatic image registration is calculated when the acquired volumetric image data is sent to at least one processor 4. A calibration matrix can define the transformation between the pose of the tracker 30 and the isocenter 29 of the C-arm. The isocenter 29 is the point about which the C-arm rotates and can be the center of the resulting image volume (see, for example, Figure 1).

[0098] Some C-arm models provide multiple interface points for attaching tracker 30 to the C-arm. These different attachment points result in different calibration matrices (see FIG. 3). In order to select the correct calibration matrix 44a or 44b, it may be desirable to determine which side of the C-arm tracking system 10 is currently tracking.

[0099] Because navigational tracking technology is relative in nature and the orientation of each tracker may not be known in advance, information provided in a static scenario where neither the patient tracker 32 nor the C-arm tracker 30 is moving cannot be relied upon. Instead, it is proposed to use tracking data acquired during the image data acquisition process. When acquiring 3D volumetric image data, the 3D C-arm rotates around the isocenter 29 from a start pose to an end pose. The direction in which the C-arm tracker 30 rotates in the tracking coordinate system during the image acquisition process determines the side of the C-arm currently presented toward the camera 12. This allows for the use of a single tracker 30 that can be positioned in various locations on the moving part 24 (e.g., attached to multiple adapter points on the C-arm) and for selecting the correct calibration matrices 44a, 44b for the alignment calculation. This allows customers to remount the same tracker 30 on multiple mounting points depending on the surgeon's current needs and / or the spatial layout of the operating room.

[0100] To determine the direction of C-arm movement, the continuous movement of the C-arm tracker 30 can be tracked over a specific period of time, or a starting point and one or more points during the rotation of the C-arm can be captured. These tracked points can form a segment of a circle or ellipse.

[0101] The direction of movement (e.g., clockwise or counterclockwise) can be determined from the circular or elliptical spatial path formed by the tracking points of the tracker 30. If the C-arm tracker 30 is fixed to one side of the C-arm, the determined direction of movement of the tracker 30 directly translates into an observed 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 for each side is known in advance. When moving and rotating the camera 12, clockwise and counterclockwise always maintain the same relationship to the C-arm side (see, e.g., Figure 4).

[0102] Camera 12 does not need to be positioned so that its field of view is aligned with (e.g., parallel to or centered on) the C-arm's axis of rotation. If camera 12 is positioned in front of or behind the C-arm, C-arm tracker 30 moves toward or away from the C-arm. As long as the angular difference between camera 12 and C-arm tracker 30 is other than 0 or 90 degrees, the circular or linear back-and-forth movement is converted into an ellipse. Tracking this ellipse not only identifies the C-arm mounting side, but also makes it possible to distinguish between different mounting points on the same side.

[0103] Some C-arms are reconfigured (e.g., manually) by rotating the "C" along the rotation axis. This may result in the clockwise / counterclockwise rotation of the C-arm relative to each side of the C-arm being reversed. In this case, the gravity direction 16 can be taken into consideration. Based on the gravity direction, it is clear whether the detector 28 starts its rotation from the top position or the bottom position, allowing the starting pose (e.g., the starting position of the detector 28) of the imager 18 to be determined at the beginning of the image acquisition process. Without a clear gravity direction as an external reference, the camera 12 does not know how it is rotating in space, and it may be impossible to calculate absolute maximum and minimum positions unless the camera 12 is assumed to always face the same direction relative to the gravity direction 16. Combining the gravity direction with the determined movement direction of the tracker 30 allows for the determination of various starting and ending poses for the setup of the imager 18.

[0104] The relationship between the rotation directions and the side of the C-arm to be tracked can be predefined, for example based on a calibration in which the user saves the relationship. The user can be asked to rotate the C-arm in each direction or to skip one of the rotations if it is not applicable (e.g., if the C-arm does not support rotation along the roll axis). Once the association between the rotation directions and the side of the C-arm to be tracked (and optionally one or more setups of the C-arm) is defined, the association is stored in memory 6 and can potentially be used for subsequent image acquisition processes.

[0105] There may be some error component in the rotational information acquired, as there may be jitter in both rotation and tracking, however, the recorded curve is detectable despite the jitter, and this jitter in the recorded position can be the same across all C-arm models, as only the clockwise / counterclockwise information (and optionally the C-arm setup) may be relevant to determining the side on the C-arm where the tracker 30 is mounted.

[0106] By implementing side detection, it may be possible to acquire registered, navigable medical images using a single C-arm tracker 30, with cameras 12 being mountable on either side of the C-arm, where the tracker 30 can be switched between different mounting points, each with its own calibration based on a selected single transformation 44 a, 44 b.

[0107] In summary, the techniques disclosed herein may enable automatic selection of a transformation between the pose of a medical imaging device tracker and a coordinate system associated with image data acquired by a medical imaging device. The transformation can be selected based on different poses of the medical imaging device tracker tracked during an image acquisition process that acquires one or more medical images of a patient's body. The selected transformation enables registration of the medical images to a real-world coordinate system without requiring imaging of the patient or a registration phantom. This technique is particularly useful when a surgeon wants to attach the medical imaging device tracker to the device at different mounting poses. Because no user input regarding the mounting pose is required, errors in the selection of the transformation can be reduced. Further advantages of this technique will be apparent to those skilled in the art. [Example]

[0108] The present disclosure also provides the following non-limiting examples.

[0109] [Example 1] A method for selecting a transformation between a pose 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), comprising: acquiring (204) tracking information indicative of a plurality of different poses of a tracker (30) fixedly positioned relative to a movable part (24) of a medical imaging device (18); determining (208) movement of the tracker (30) based on the acquired tracking information; selecting (214) one of a plurality of transformations between a pose 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); and A method comprising:

[0110] [Example 2] further comprising determining (212) a spatial relationship between the tracker (30) and the movable part (24) based on the determined movement of the tracker; 2. The method of claim 1, wherein the one transformation is selected from the plurality of transformations based on the determined spatial relationship.

[0111] [Example 3] 3. The method of claim 1 or 2, wherein the spatial relationship includes a side of the movable part (24) on which the tracker (30) is located.

[0112] [Example 4] 4. The method of claim 3, wherein the determined tracker movement indicates a direction of movement of the tracker (30), and the side of the movable part (24) is determined based on the direction of movement of the tracker (30).

[0113] [Example 5] 5. The method of 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 direction of movement of the tracker (30) and a second side of the movable part (24) associated with a counterclockwise direction of movement of the tracker (30).

[0114] [Example 6] 6. The method according to any one of claims 2 to 5, wherein the spatial relationship comprises a position of the movable part (24) where the tracker (30) is located.

[0115] [Example 7] 7. The method of claim 6, wherein the determined movement of the tracker (30) indicates a path of movement of the tracker (30), and the position of the movable part (24) is determined based on the path of movement of the tracker (30).

[0116] [Example 8] The method of Example 7, wherein the movable part (24) is configured to move along a circle or a spiral, the movement path of the tracker (30) includes at least one section of a circle, an ellipse, or a spiral, and the position of the movable part (24) is determined based on the at least one section of the movement path of the tracker (30).

[0117] [Example 9] 9. The method according to any one of claims 2 to 8, wherein the spatial relationship comprises an orientation of the tracker (30) relative to the movable part (24).

[0118] [Example 10] Further, the method includes obtaining gravity information indicating a direction of gravity; 10. The method according to any one of claims 1 to 9, wherein the transformation is selected based on the gravity information.

[0119] [Example 11] 11. The method of claim 10, wherein the movement of the tracker is determined relative to the direction of gravity indicated by the gravity information, and the transformation is selected based on the movement of the tracker determined relative to the direction of gravity.

[0120] [Example 12] further comprising obtaining at least one setup of the medical imaging device selected from a start pose and an end pose of the movable portion of the medical imaging device relative to a stationary portion of the medical imaging device or a component in a fixed spatial relationship with respect to the stationary portion of the medical imaging device; 12. The method according to any one of claims 1 to 11, wherein the transformation is selected based on at least one setup of the medical imaging device (18).

[0121] [Example 13] The method of any one of Examples 12 and 10 or 11, further comprising determining the at least one setup of the medical imaging device (18) based on the tracking information, the gravity information, and the determined movement of the tracker (30), and obtaining the at least one setup of the medical imaging device (18).

[0122] [Example 14] A method according to any one of claims 12 to 13, dependent on claim 4, wherein the side of the movable part (24) is determined based on the movement direction of the tracker (30) and the acquired at least one setup of the medical imaging device (18).

[0123] [Example 15] adjusting the side of the movable part based on the determined direction of movement of the tracker (30) and the acquired at least one setup of the medical imaging device (18); (i) a first side of the movable part associated with a clockwise direction of movement of the tracker and a first setup of the medical imaging device, and (ii) a counterclockwise direction of movement of the tracker and a second setup of the medical imaging device; and (i) a clockwise direction of movement of the tracker and the second setup of the medical imaging device, and (ii) a second side of the movable part associated with a counterclockwise direction of movement of the tracker and the first setup of the medical imaging device. 15. The method of claim 14, wherein the side of the movable part (24) is determined by selecting from the following:

[0124] [Example 16] 16. The method according to any one of claims 1 to 15, wherein at least two or all of the plurality of different poses of the tracker (30) are associated with different points in time of an image acquisition process performed by the medical imaging device (18) to acquire the image data, during which the movable part of the medical imaging device (18) moves.

[0125] [Example 17] 17. The method according to any one of claims 1 to 16, wherein the medical imaging device (18) is configured to acquire image data of a computed tomography (CT) method, and the movable part (24) of the medical imaging device (18) is part of a C-arm.

[0126] [Example 18] A system comprising at least one processor (4) configured to perform the method according to any one of Examples 1 to 17.

[0127] [Example 19] The system of Example 18 further comprises at least one of the following entities: i) the medical imaging device (18) comprising the movable part (24) and configured to acquire the image data; ii) a tracking system (10), such as an optical tracking system comprising a camera, configured to provide said tracking information; iii) a gravity sensor configured to provide said gravity information, optionally fixed to said tracking system (10) and / or said camera (12); iv) the tracker

[0128] [Example 20] A computer program comprising instructions that, when executed by at least one processor (4), cause the at least one processor (4) to perform the method described in any one of Examples 1 to 17, the computer program optionally being transmitted in a data stream or stored on a (e.g., non-transitory, computer-readable) storage medium (6).

Claims

1. 1. A method of operating a medical device 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 performed by at least one processor and comprising: acquiring tracking information indicative of a plurality of different poses of a tracker positioned fixedly relative to a moving part of a medical imaging device; determining a direction or path of movement of the tracker based on the acquired tracking information; selecting one of a plurality of transformations between the 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; A method comprising:

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

3. The method of claim 2 , wherein the spatial relationship includes a side of the movable part on which the tracker is located.

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

5. 5. The method of 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 of claim 2 , wherein the spatial relationship includes a position of the moving part at which the tracker is located.

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

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

9. The method of claim 2 , wherein the spatial relationship includes an orientation of the tracker relative to the moving part.

10. Further, the method includes obtaining gravity information indicating a direction of gravity; The method of claim 1 , wherein the transformation is selected based on the gravity information.

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

12. further comprising obtaining at least one setup of the medical imaging device selected from a start pose and an end pose of the movable part of the medical imaging device relative to a stationary part of the medical imaging device or a component in a fixed spatial relationship with respect to the stationary part of the medical imaging device; The method of claim 1 , wherein the transformation is selected based on at least one setup of the medical imaging device.

13. further obtaining gravity information indicative of a direction of gravity for one or more of a plurality of different poses of the tracker; determining the at least one setup of the medical imaging device based on the tracking information, the gravity information, and the determined movement of the tracker, and obtaining the at least one setup of the medical imaging device; 13. The method of claim 12, comprising:

14. the spatial relationship includes a side of the movable part on which the tracker is disposed, the determined movement of the tracker indicates the direction of movement of the tracker; the side of the movable part is adjusted based on the direction of movement of the tracker and the acquired at least one setup of the medical imaging device; The method of claim 12 wherein the

15. adjusting the side of the movable part based on the determined direction of movement of the tracker and the acquired at least one setup of the medical imaging device; (i) a first side of the movable part associated with a clockwise direction of movement of the tracker and a first setup of the medical imaging device, and (ii) a counterclockwise direction of movement of the tracker and a second setup of the medical imaging device; (i) a clockwise direction of movement of the tracker and the second setup of the medical imaging device, and (ii) a second side of the movable part associated with a counterclockwise direction of movement of the tracker and the first setup of the medical imaging device. The method of claim 14, wherein the side of the movable part is determined by selecting the side of the movable part from

16. 2. The method of claim 1 , wherein at least two or all of the plurality of different poses of the tracker are associated with different points in an image acquisition process performed by the medical imaging device to acquire the image data, during which the movable part of the medical imaging device moves.

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

18. 1. A system comprising at least one processor configured to execute 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: acquiring tracking information indicative of a plurality of different poses of a tracker positioned at a fixed position relative to a movable part of a medical imaging device; determining a movement of the tracker based on the acquired tracking information; 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; A system including:

19. 20. 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) an optical tracking system configured to provide said tracking information and comprising a camera; iii) a gravity sensor configured to provide gravity information, optionally fixed to the tracking system and / or the camera; iv) the tracker

20. 1. A non-transitory computer-readable storage medium storing a computer program comprising instructions that, when executed on 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: The method acquiring tracking information indicative of a plurality of different poses of a tracker disposed at a fixed position relative to a movable part of a medical imaging device; determining a movement of the tracker based on the acquired tracking information; 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; 1. A non-transitory computer-readable storage medium comprising:

Images