METHOD AND APPARATUS FOR DETERMINING OR PREDICTING THE POSITION OF A TARGET

Abstract

A data processing method for determining the position of a target, comprising the steps performed by a computer: a) acquiring a target movement model specifying a movement cycle of the target; b) acquiring a target position signal representing a view of the target from a single direction and/or provided by a single imager; c) determining, based on the acquired target position signal and the target movement model, the position of the target.

Claims

1.-15. (canceled)

16. A data processing method performed by a computer for determining the position of a target, comprising: a) acquiring a target movement model specifying a movement cycle of the target; b) acquiring a target position signal representing a view of the target from a single direction and/or provided by a single imager; c) determining, based on the acquired target position signal and the target movement model, the position of the target, the determining including the determination of the position of the target based on an epipolar line corresponding to the target position detected by a first imager providing a target position signal, the epipolar line being a projection of the target's line of sight of the first imager onto the imaging plane of a second imager, and determining the intersection(s) between the epipolar line and a projected target trajectory being a target movement model and specifying the target movement when projected onto the imaging plane of the second imager.

17. The data processing method of claim 16 for updating a correlation model correlating a surrogate signal with a positional information of the target, the update being based on an update signal being the target position signal and including the determined position information of the target and the target movement model, further comprising: d) acquiring the surrogate signal; and e) correlating the surrogate signal with the determined position of the target to obtain the updated correlation model.

18. A data processing method performed by a computer for determining the position of a target, comprising: a) acquiring a target movement model specifying a movement cycle of the target; b) acquiring a target position signal representing a view of the target from a single direction and/or provided by a single imager, wherein the acquired target position signal is a signal of a single imager of a stereoscopic X-ray imaging apparatus; c) determining, based on the acquired target position signal and the target movement model, the position of the target, the determining including the determination of the position of the target based on a prior determined area or plane within which the position of the target can be and the target back projection from the imaging plane of the imager acquiring the target position signal.

19. The data processing method of claim 18 for updating a correlation model correlating a surrogate signal with a positional information of the target, the update being based on an update signal being the target position signal and including the determined position information of the target and the target movement model, further comprising: d) acquiring the surrogate signal; and e) correlating the surrogate signal with the determined position of the target to obtain the updated correlation model.

20. The data processing method of claim 16, wherein the acquired target position signal is a signal of a single imager of a stereoscopic imaging apparatus.

21. The data processing method of claim 16, wherein the target movement model acquired in step a) is acquired based on at least one of: latest target detection on obstructed or not used imager; latest stereoscopic target detection; latest prediction of the target position, the prediction being based on the latest correlation model and surrogate signal; latest prediction of the target position being projected onto obstructed or not used imager.

22. The data processing method of claim 16, wherein the target movement model specifies at least two sections that are associated with different or specific movement phases or an inhale phase and an exhale phase.

23. The data processing method of claim as 22, wherein the specific movement phases are associated with a surrogate signal or relative marker positions.

24. The data processing method of claim 22, wherein information on the specific movement phases is used when determining the target position.

25. The data processing method of claim 17, wherein the updated correlation model is based on a number of update points distributed over a movement cycle or breathing cycle or respiratory cycle of the target.

26. The data processing method of claim 17, further comprising updating a prediction model predicting the position of a target in a body using the updated correlation model.

27. The data processing method of claim 17, further comprising updating a prediction model predicting the position of a target in a body, wherein the prediction model is updated based on the updated correlation model, wherein a prediction of the position of the target in the body is made by: predicting a future value of a surrogate signal and/or a future position of a surrogate element using a surrogate movement model; and determining the predicted position of the target in the body, based on the predicted future value of the surrogate signal and/or the predicted future position of the surrogate element, using the correlation model.

28. The data processing method of claim 16, wherein the target movement model is stored in a memory and can be read from the memory.

29. A system for determining the position of a target comprising: a target movement model generator configured to acquire a target movement model specifying the movement behavior or a movement cycle of the target; a target position acquiring element configured to acquire a target position signal; and a determination section connected to the target movement model generator and the target position acquiring element and receiving information or signals therefrom to determine, based on the acquired target position signal and the target movement model, the position of the target, wherein the determination includes the determination of the position of the target based on an epipolar line corresponding to the target position detected by a first imager providing a target position signal, the epipolar line being a projection of the target's line of sight of the first imager onto the imaging plane of a second imager, and determining the intersection(s) between the epipolar line and a projected target trajectory being a target movement model and specifying the target movement when projected onto the imaging plane of the second imager.

30. A system for determining the position of a target comprising: a target movement model generator configured to acquire a target movement model specifying the movement behavior or a movement cycle of the target; a target position acquiring element being a stereoscopic imaging apparatus configured to acquire a target position signal; and a determination section being connected to the target movement model generator and the target position acquiring element and receiving information or signals therefrom to determine, based on the acquired target position signal and the target movement model, the position of the target, wherein the determination includes the determination of the position of the target based on a prior determined area or plane within which the position of the target can be and the target back projection from the imaging plane of the imager acquiring the target position signal.

31. The system of claim 29 for updating a correlation model correlating a surrogate signal with a positional information of the target, the update being based on an update signal being the target position signal and including the determined position information of the target and the target movement model, the system being further configured to: d) acquire the surrogate signal; and e) correlate the surrogate signal with the determined position of the target to obtain the updated correlation model.

32. The system of claim 30 for updating a correlation model correlating a surrogate signal with a positional information of the target, the update being based on an update signal being the target position signal and including the determined position information of the target and the target movement model, the system being further configured to: d) acquire the surrogate signal; and e) correlate the surrogate signal with the determined position of the target to obtain the updated correlation model.

33. The system of claim 29, wherein the target position acquiring element is a stereoscopic imaging apparatus, and the acquired target position signal is a signal of a single imager of the stereoscopic imaging apparatus.

34. The system of claim 30, wherein the acquired target position signal is a signal of a single imager of the stereoscopic imaging apparatus.

35. The system of claim 31, wherein the updated correlation model is based on a number of update points distributed over a movement cycle or breathing cycle or respiratory cycle of the target.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0099] In the following, the invention as described with reference to the enclosed figures which represent preferred embodiments of the invention. The scope of the invention is however not limited to the specific features disclosed in the figures, which show:

[0100] FIG. 1 a depiction of the base line shift;

[0101] FIG. 2 the relationship between the 3D target position and its 2D projection onto an imager plane;

[0102] FIG. 3 a target detection based on a target movement model and a non-stereoscopic image;

[0103] FIG. 4 a system for determining the position of a target according to a first aspect; and

[0104] FIG. 5 a system for determining the position of a target according to a second aspect.

DETAILED DESCRIPTION

[0105] FIG. 1 shows in an abstract form a positional change of a surrogate signal being an upper sinusoidal wave. The surrogate signal might be the detected positions of one or more markers being located on the body surface of a patient, the body surface moving, for example due to a breathing motion. As can be seen on the left side of FIG. 1, the surrogate signal is a periodic signal having repeated cycles 1, 2, . . . .

[0106] Below the surrogate signal there is shown as another sinusoidal signal the position of a target also moving due to a vital motion, such as a breathing motion. Same as the above surrogate signal, the below target position performs a periodic movement.

[0107] If the target's position at a specific time is correlated with the marker position or surrogate signal, then a target-marker-model TMM or in an abstract manner a correlation model can be defined specifying the relation between the detected surrogate signal (e.g. movement of the body surface) with the movement of the target. Thus, it is possible to determine a target's position based on only the surrogate signal alone, e.g. based on only the detected marker position(s). As can be seen, the relationship or distance between the surrogate signal and the target position may vary over a cycle, which variation can be included into the target-marker-model. The target-marker-model can e.g. be this stored relationship over one cycle.

[0108] However, this relation may change due to for example sagging movement of the patient lying on a couch for a longer time. If for example the body surface to which the markers are attached sags down, then the target-marker-model TMM or correlation model changes. As can be seen on the right side of FIG. 1, even after the change in relationship, it is still possible to use a surrogate signal to determine the position of the target. However, the target-marker-model or correlation model has to be adapted to the change of the relation.

[0109] FIG. 2 shows a target T moving in a simplified manner along a predefined path being a circle. The movement cycle of the target T defines a trajectory drawn in a solid line.

[0110] An imager viewing the target's movement from a single specified direction has an imaging plane P. The trajectory of the target T is projected onto the imaging plane P of the imager when the target's movement is seen from the imager. The target's movement cycle being in the shown example a circle may be projected onto the imaging plane P being there an oval. The projected trajectory can itself be acquired and can for example be used as an embodiment of a target movement model. Advantageously, parts of the trajectory can be associated with specific movement cycles, such as “inhale” and “exhale”. The trajectory can have a specific direction (in the shown example: clockwise) as indicated by arrows.

[0111] When the target T moving along the trajectory is imaged by a stereoscopic camera, i.e. by two cameras viewing the target from different viewing angles, the target's trajectory is projected onto each of the respective imaging planes and for every imager there can be made a target movement model as described above. If both imagers see the target, the target's position can be determined by back projection.

[0112] According to an aspect, the target movement model (for example the target trajectory line projected onto the image plane) of the obstructed imager is used in combination with the image of the imager seeing the target for determining the target's position.

[0113] A target movement model can thus for example be built by the projected trajectory of one or of both imagers.

[0114] A target movement model can for example be built during an initial stereoscopically taken movement sequence, such as an X-ray fluoro sequence, and can be updated whenever images from both imagers or both X-ray panels are simultaneously available. The update of the target movement model can be a full update e.g. establishing a new target movement model in total, or can be a partial update, e.g. updating or modifying only a section of a prior known target movement model.

[0115] For example, a series of shots can be taken at a predetermined phase, such as e.g. “fully exhale”, and depending on the determined position of the target the target movement model can be modified. If for example an offset is detected in a specific phase, the whole target movement model can be updated or shifted by the detected offset.

Exemplary Solution

[0116] If coordinates of target's projection are given with x.sub.i and y.sub.i, and predicted 3D target position with x′, y′ and z′ then this model has the form:

f.sub.x(x.sub.i,y.sub.i).fwdarw.x′  (1)

f.sub.y(x.sub.i,y.sub.i).fwdarw.y′  (2)

f.sub.z(x.sub.i,y.sub.i).fwdarw.z′  (3)

[0117] Dependency between 3D position and projection is modeled with linear functions whose parameters are calculated using linear regression and have the form:

x′=a.sub.xx.sub.i+b.sub.xy.sub.i+c.sub.x  (4)

y′=a.sub.yx.sub.i+b.sub.yy.sub.i+c.sub.y  (5)

z′=a.sub.zx.sub.i+b.sub.zy.sub.i+c.sub.z  (6)

[0118] These equations can be written as:

{right arrow over (t.sub.3D′)}=M.sub.3D{right arrow over (t.sub.2D)}  (7)

where {right arrow over (t.sub.3D′)}=(x′,y′,z′).sup.T represents predicted target position, {right arrow over (t.sub.2D)}=(x.sub.i,y.sub.i,z.sub.i).sup.T represents projection's position and the actual 3D model is:

[00001]$\begin{array}{cc}{M}_{3.Math.D}=\left(\begin{array}{ccc}{a}_x& b_x& c_x\\ a_y& b_y& c_y\\ a_z& b_z& c_z\end{array}\right)& \left(8\right)\end{array}$

[0119] According to an alternative solution, the 3D position of the target can be predicted or determined out of an image taken from a single imager (2D detection), for example being based on the principles of epipolar geometry.

[0120] This is illustrated in FIG. 3 which shows the imaging planes of two imagers, imager 1 and imager 2, which were able to both image the target when setting up the target movement model. Imager 2 is obstructed in the shown example, but from a prior measurement the estimated target's trajectory as being projected onto the imaging plane of imager 2 is shown in the dotted oval line. Imager 1 can detect a point corresponding to the position of the target T. The back projection of the detected position of target T onto the target T (i.e. the line of sight of imager 1) is projected as the epipolar line shown as a broken line onto the imaging plane of imager 2. The epipolar line can be interpreted as specifying all possible locations of target T as detected by imager 1 when projected onto the image plane of imager 2. Since from the prior measurement the target's projected trajectory is known, the epipolar line can be intersected with the target's trajectory, thus obtaining two possible solutions shown as two crosses within the imaging plane of imager 2 defining two possible locations of the target in space (which can be determined when back projecting the detected position of imager 1 and the estimated position being one of the possible solutions of imager 2, the intersection of both back projections being the position of the target). The absolute or relative position and/or orientation of the imagers being known.

[0121] In case the specific movement cycles or specific phases of the target's movement are as well known (being for example part of the target movement model), then it can be determined which one of the two possible solutions of FIG. 3 is the correct solution, thus ruling out one of the intersection points. The current breathing phase is for example known from the surrogate signal, such as from an acquired infrared marker signal.

[0122] By computing the movement phases, such as breathing phases, a plausibility check can additionally be performed to determine how “valid” the model for the obstructed imager still is.

[0123] In order to predict the 3D position of the target at any given moment the target's projection onto the X-ray panel (2D position) at the same moment can be predicted as well. For this a correlation model between a surrogate signal position and the velocity and 2D position is determined. This model can be built using a given number of most recent 2D position detections and can be updated whenever there is a new 2D detection. Furthermore, newer 2D detections can be weighted more. There can be one such model for every X-ray panel.

[0124] The couch on which a patient is located can be moved whenever a beam has to be shot from a plane other than the one in which the gantry is rotating (if the couch is in the starting position this is the axial plane). This way the angle between patient and X-ray panels changes and with it the projection, as well as the patient position in machine coordinate system, which makes existing models invalid. A straightforward solution for this problem would be to discard all previous data and make a new stereoscopic X-ray fluoro sequence, but that would extend treatment time, expose the patient to unnecessary radiation (skin dose) and could even lead to overheating.

[0125] In order to solve the couch rotation problem, a transformation matrix is used to rebuild the models, which projects 3D target positions onto X-ray panels at a new angle. This way new models can be built without a need to make new stereoscopic X-ray fluoro sequences.

[0126] FIG. 4 shows an embodiment where a movement cycle or in a more simplified manner a plane is determined as a movement model. The orientation of the plane being known when determining the target movement model. FIG. 4 shows two imagers 1 and 2 being able to provide a stereoscopic X-ray view of the target T moving along movement cycle C within plane P.

[0127] In case imager 2 is blocked, the position of the target T can be determined based on only an image signal from imager 1 having a view on the target T, since the back projected image of target T being intersected with plane P and/or correlated or intersected with movement cycle C delivers the position of target T.

[0128] A stereoscopic camera IR being able to detect a surrogate signal, such as an infrared marker signal (marker is not being shown in FIG. 4) also viewing the operation scene or couch can be connected to a computer also receiving the imager signals to perform the described method.

[0129] FIG. 5 shows a further embodiment, wherein again imager 2 does not provide a positional signal of target T due to for example being blocked by a gantry.

[0130] The target movement model is the estimated projection of the target movement cycle C onto the imaging plane of imager 2 being shown as projected trajectory C′.

[0131] The projected trajectory C′ is intersected with the epipolar line of the line of sight of imager 1 and the target's position is determined as described with reference to FIG. 3.