Method and system for medical tracking using a plurality of camera positions

Abstract

A method for tracking trackable objects using a medical tracking device, the tracking device being a camera or an EM transmitter, during a medical workflow comprising a plurality of workflow steps, wherein each trackable object has at least one marker and the method comprises the steps of: acquiring a set of camera positions, wherein each tracking device position is associated with at least one workflow step; identifying a workflow; sequentially and automatically moving the tracking device to the camera positions associated with the workflow steps; andperforming a tracking step only when the tracking device is in a fixed position.

Claims

1. A method for tracking trackable objects using a medical tracking device, the tracking device being a tracking camera or an EM transmitter, during a medical workflow comprising a plurality of workflow steps, wherein each trackable object has at least one marker and the method comprises the steps of: identifying a workflow having a plurality of workflow steps; acquiring, prior to execution of the workflow, a set of tracking device positions for the workflow that indicate one or more positions of the tracking device, wherein each tracking device position of the set is associated with at least one workflow step of the workflow; sequentially and automatically moving the tracking device to respective tracking device positions of the set that are respectively associated with respective workflow steps during execution of the workflow, wherein moving the tracking device is responsive to acquired input indicating transitions between workflow steps; and performing tracking of the trackable objects by the tracking device only when the tracking device is in a fixed position.

2. The method according to claim 1, wherein the tracking device covers a tracking volume in each position, and a position for inclusion in the set of tracking device positions is determined automatically by: sequentially moving the tracking device to a plurality of test positions; storing a test position as a candidate position if all the markers of all the trackable objects used within a particular workflow step are within the tracking volume of the tracking device; and selecting the candidate position in which the distances from the markers to the centre of the tracking volume are minimised as a position to be included in the set of tracking device positions.

3. The method according to claim 2, wherein the highest possible candidate position is selected.

4. The method according to claim 2, wherein if the tracking device is a camera, the candidate position in which the angles between the line of sight of the camera and normal vectors which are normal to a plane in which the markers of a trackable object lie are minimised.

5. The method according to claim 2, wherein a test position is stored as a candidate position if all the markers of all the trackable objects used within a particular workflow step are within a predetermined sub-volume of the tracking volume.

6. The method according to claim 2, wherein priorities are assigned to the trackable objects used within a particular workflow step, and a test position is stored as a candidate position if all the markers of objects with a priority which is higher than a threshold value are within a predetermined sub-volume of the tracking volume.

7. The method according to claim 2, further comprising the step of providing indication information which indicates that no suitable tracking device position has been found and that the tracking device should be repositioned.

8. The method according claim 1, wherein the workflow is identified automatically.

9. The method according to claim 8, wherein the workflow is identified by identifying trackable objects used in the workflow.

10. The method according claim 1, wherein a tracking device position is corrected on the basis of the position of a marker attached to a boxy or to a part of a body to be treated.

11. The method according to claim 1, wherein a position is entered into the set of tracking device positions manually.

12. The method according to claim 1, wherein the tracking device position is corrected on the basis of the detectability of the markers.

13. The method according to claim 1, further comprising acquiring a user input indicating a transition between workflow steps.

14. The method according to claim 13, wherein the user input is a user gesture captured by the tracking device.

15. The method according to claim 1, further comprising determining a workflow step based on an arrangement of trackable objects determined by the tracking device.

16. The method according to claim 1, further comprising disabling tracking by the tracking device while the tracking device is moving between tracking device positions from the set.

17. A non-transitory computer-readable storage medium having stored thereon computer-executable instructions for a computer program which, when running on a computer or when loaded onto a computer, causes the computer to: identify a workflow having a plurality of workflow steps; acquire, prior to execution of the workflow, a set of tracking device positions for the workflow that indicate one or more positions of the tracking device, wherein each tracking device position of the set is associated with at least one workflow step of the workflow; sequentially and automatically move the tracking device to respective tracking device positions of the set that are respectively associated with respective workflow steps during execution of the workflow in response to acquired input indicating transitions between workflow steps; and performing tracking of the trackable objects by the tracking device only when the tracking device is in a fixed position.

18. A tracking system for tracking trackable objects having markers during a medical workflow, said system comprising a tracking device being a tracking camera or an EM transmitter and a computer configured to: identify a workflow having a plurality of workflow steps; acquire, prior to execution of the workflow, a set of tracking device positions for the workflow that indicate one or more positions of the tracking device, wherein each tracking device position of the set is associated with at least one workflow step of the workflow; sequentially and automatically move the tracking device to respective tracking device positions of the set that are respectively associated with respective workflow steps during execution of the workflow in response to acquired input indicating transitions between workflow steps; and perform tracking of the trackable objects by the tracking device only when the tracking device is in a fixed position corresponding to one of the tracking device positions of the set.

Description

(1) The present invention shall now be explained in more detail with reference to the accompanying figures. These figures show:

(2) FIG. 1 a schematic structure of a medical tracking system;

(3) FIG. 2 an example operating room configuration.

(4) FIG. 3 an example embodiment of a method for tracking trackable objects using a medical tracking device.

(5) FIG. 1 schematically shows the structure of a medical tracking system 1. The tracking system 1 comprises a CPU (central processing unit) 2 connected to an image pick-up unit 3, an input device 4, a display unit 5 and a memory unit 6. The image pick-up unit 3 comprises a base (not shown), a drive unit 3a and a camera 3b. The base of the image pick-up unit 3 is placed at a fixed position. The drive unit 3a is configured to drive the camera 3b relative to the base of the image pick-up unit 3, such that the camera 3b can assume a plurality of positions. The drive unit 3a could include a robotic arm.

(6) The CPU 2 is configured to support a medical workflow comprising a plurality of workflow steps by enabling trackable objects to be tracked. To this end, the memory unit 6 stores a set of camera positions, wherein each camera position is associated with at least one workflow step. More than one workflow step can be associated with a particular camera position.

(7) Depending on the workflow step, the CPU 2 determines a camera position from the set of camera positions in the memory unit 6 which corresponds to the workflow step and instructs the drive unit 3a of the image pick-up unit 3 to move the camera 3b to the determined camera position. Alternatively, the CPU 2 provides a control signal to the drive unit 3a which activates the drive unit 3a as required.

(8) The CPU 2 is also configured to interpret the output signal of the camera 3b in order to detect the positions of markers within the field of view, also referred to as the tracking volume, of the camera 3b. When a plurality of markers, preferably three or four markers, are attached to an object in a known configuration, the position of the object can be calculated from the positions of its markers. The CPU 2 can thus track objects. The positions of the tracked objects could be displayed on the display unit 5 and/or used in a medical navigation process.

(9) In order to determine the camera position to be set, the CPU 2 needs to know the workflow and the workflow step. Information regarding the workflow and the workflow step can be inputted using the input device 4, which can be a touch-sensitive surface of the display unit 5 or any other suitable input means. Alternatively, the CPU 2 can determine the objects present in the operating room by analysing the output signal of the camera 3b (or any other camera) and then determine the workflow from the set of objects present. For this purpose, the memory unit 6 can store a set of workflows and lists of objects to be used in each workflow. From the current positions of the objects, the CPU 2 can also determine the current workflow step and accordingly the associated camera position. The workflow step, in particular the transition from one workflow step to the next, can also be determined by the CPU 2 by analysing the output signal of the camera 3b (or any other camera) and detecting a gesture which is performed by a person such as a surgeon and indicates to the tracking system 1 that the next workflow step is to be performed or indicates which workflow step is to be performed next.

(10) FIG. 2 schematically shows a scenario corresponding to one step of a medical workflow. In this scenario, a patient 7 is lying on an operating room table 11. In the corresponding workflow step, an x-ray image of the patient 7, in particular of the patient's head, is to be acquired using an x-ray imaging unit 9. In order to analyse the x-ray image, it is essential to know the viewing direction from which the image was recorded. To this end, a marker device 8 comprising three markers in a known configuration is rigidly attached to the patient 7, in particular to the patient's head. A marker device 10 comprising three markers in a known configuration is attached rigidly to the x-ray imaging unit 9. If the relative position between the marker devices 8 and 10, and therefore between the patient 7 and the x-ray imaging unit 9, is known, then the viewing direction of an x-ray image of the patient 7 generated by the x-ray imaging unit 9 is also known. It is thus advantageous to track the trackable objects, i.e. the patient 7 and the x-ray imaging unit 9 using the medical tracking system 1.

(11) In order to track the patient 7 and the x-ray imaging unit 9, the marker devices 8 and 10 need to be within the tracking volume of the tracking camera 3b. The camera 3b therefore needs to be placed in a position in which this requirement is fulfilled. As explained above, the camera 3b is automatically moved to such a position, which belongs to a set of camera positions and is associated with a workflow step according to the scenario shown in FIG. 2. How this camera position is determined and stored in the set of camera positions will now be described with reference to this figure.

(12) In FIG. 2, the tracking volume of the camera 3b is indicated as a conical region. In order to determine the camera position, the camera 3b is moved into three test positions, wherein the tracking volumes for the first and third test position are indicated by a dashed boundary line and the tracking volume for the second test position is indicated by a continuous boundary line. The first test position corresponds to the upper tracking volume, while the third test position corresponds to the lower tracking volume.

(13) A set of candidate positions is determined from the set of test positions. A test position is added to the set of candidate positions if all the markers of all the objects to be tracked in the corresponding workflow step are within the tracking volume of the camera 3b when the camera 3b is in said test position. In the present example, if the camera 3b is in the first test position or in the third test position, the markers of the marker devices 8 and 10 do not all lie within the tracking volume. The first and third test positions are therefore not added to the set of candidate positions. In the second test position, the markers of the marker devices 8 and 10 all lie within the tracking volume of the camera 3b, such that the second test position is added to the set of candidate positions.

(14) In the present case, after all the test positions have been tested, the set of candidate positions only comprises one camera position, i.e. the second test position. This camera position is thus added to the set of camera positions and associated with the workflow step. If the set of candidate positions comprises more than one camera position, one or more suitable criteria are applied in order to select one candidate position as the camera position to be added to the set of camera positions.

(15) When the medical workflow is performed, one workflow step corresponds to the scenario shown in FIG. 2. When this workflow step is reached, the camera position associated with this workflow step is determined from the set of camera positions, and the camera 3b is automatically moved into this camera position. The patient 7 and the x-ray imaging unit 9 are only tracked once the camera 3b has reached the determined camera position and are not tracked while the camera is moving.

(16) FIG. 3 illustrates an example embodiment of a method 300 for tracking trackable objects using a medical tracking device, as described above.

(17) At step 310, a workflow having a plurality of workflow steps is identified.

(18) At step 320, prior to execution of the workflow, a set of tracking device positions for the workflow that indicate one or more positions of the tracking device is acquired. Each tracking device position of the set is associated with at least one workflow step of the workflow.

(19) At step 330, the tracking device is sequentially and automatically moved to respective tracking device positions of the set that are respectively associated with respective workflow steps during execution of the workflow. The moving of the tracking device is responsive to acquired input indicating transitions between workflow steps.

(20) At step 340, tracking of the trackable objects by the tracking device is performed only when the tracking device is in a fixed position.

(21) At step 350, indication information which indicates that no suitable tracking device position has been found and that the tracking device should be repositioned is provided.

(22) It should be noted that the tracking method described herein does not relate to or comprise any surgical step. In particular, attaching a marker or marker device to a (human) body is not a part of the present invention. The present invention is based on a state in which a marker or marker device has already, i.e. previously, been attached. This invention relates solely to tracking trackable objects, positioning the camera of a tracking system and determining a camera position to be associated with at least one workflow step.