LIGHT POINT IDENTIFICATION METHOD

Abstract

A data processing method performed by a computer for detecting reflections of light pulses, comprising the steps: acquiring a camera signal representing a series of camera images of a camera viewing field; detecting whether the camera signal includes one or more light mark portions within the camera viewing field possibly representing a light pulse reflection; relating the detected light mark portions in the series of camera images to a pre-defined emission pattern of the light pulses; and determining that a light mark portion is a reflected light pulse, if the light mark portion in the series of camera images matches to the pre-defined emission pattern of the light pulses.

Claims

1. A method for detecting reflections of light pulses, comprising the steps: acquiring, from a camera system, a series of camera images of a camera viewing field; detecting whether the series of camera images include one or more light mark portions within the camera viewing field, wherein the one or more light mark portions detected represent possible light pulse reflections; comparing the one or more light mark portions detected in the series of camera images to a pre-defined emission pattern of the light pulses; and determining that a light mark portion is a reflected light pulse, when the light mark portion detected in the series of camera images matches the pre-defined emission pattern of the light pulses.

2. The method of claim 1, wherein the series of camera images of the camera viewing field is at least one of a series of subsequent camera images taken with a pre-defined time interval between two camera images or a series of stereoscopic camera images, or includes 3D data.

3. The method of claim 1, wherein the pre-defined emission pattern of the light pulses includes a light pulse during every n-th camera image, wherein n is greater than or equal to 2.

4. The method of claim 1, further comprising determining a match of the light mark portion in the series of camera images to the pre-defined emission pattern of the light pulses when the light mark portion is only detected in camera images corresponding to emissions in the pre-defined emission pattern of the light pulses and is not detected in camera images corresponding to periods of no emission in the pre-defined emission pattern of the light pulses.

5. The method of claim 1, further comprising determining a light mark portion in the series of camera images to be a reflected light pulse when the light mark portion is detected m times in n consecutive camera images, wherein n is greater than or equal to 3 and m is less than n.

6. The method of claim 1, further comprising determining a light mark portion in the series of camera images to be a reflected light pulse when two subsequently detected light mark portions are determined to not exceed a pre-defined maximum distance.

7. The method of claim 1, further comprising determining a light mark portion in the series of camera images to be a reflected light pulse when a single reflected light pulse is identified in a camera image.

8. A method for determining or registering to a shape of a surface using a medical navigation system comprising the following steps: generating light marks (3) on the surface by means of a light beam (2); acquiring, from a camera system, a series of camera images of a camera viewing field; detecting whether the series of camera images include one or more light mark portions within the camera viewing field, wherein the one or more light mark portions detected represent possible light pulse reflections; comparing the one or more light mark portions detected in the series of camera images to a pre-defined emission pattern of the light pulses; determining that a light mark portion is a reflected light pulse, when the light mark portion detected in the series of camera images matches the pre-defined emission pattern of the light pulses; determining three-dimensional, spatial positions of the light pulse reflections using the navigation system; and determining or registering to the shape of the surface by means of the positional data of the light pulse reflections.

9. A computer-readable storage medium having stored thereon a computer-executable instruction for a program which, when running on a computer, causes the computer to perform the method of claim 1.

10. A system comprising a computer having the computer-readable storage medium of claim 9 and which executes the computer-executable instruction of the program stored thereon.

11-15. (canceled)

16. A method, comprising: acquiring, from a camera system, a series of camera images of a camera viewing field; detecting whether the series of camera images include a light mark within the camera viewing field, wherein the light mark detected represents a possible light pulse reflection; comparing a time pattern of the light mark detected in the series of camera images to a pre-defined emission pattern of light pulses; and determining that the light mark detected is a reflected light pulse when the time pattern the light mark detected in the series of camera images matches the pre-defined emission pattern.

17. The method of claim 16, wherein the series of camera images of the camera viewing field is a series of subsequent camera images taken with a pre-defined time interval between two camera images a series of stereoscopic camera images, or includes 3D data.

18. The method of claim 16, wherein the pre-defined emission pattern of light pulses includes a light pulse during every n-th camera image, wherein n is greater than or equal to 2.

19. The method of claim 16, further comprising determining a match of the time pattern of the light mark detected in the series of camera images to the pre-defined emission pattern of light pulses when the light mark is only detected in camera images that align with emissions in the pre-defined emission pattern of light pulses and the light mark is not detected in camera images corresponding to periods of no emission in the pre-defined emission pattern of light pulses.

20. The method of claim 16, further comprising determining the light mark detected in the series of camera images to be a reflected light pulse when the time pattern of the light mark detected indicates m detections in n consecutive camera images, wherein n is greater than or equal to 3 and m is less than n.

21. The method of claim 16, further comprising determining the light mark detected in the series of camera images to be a reflected light pulse when the time pattern of the light mark includes two subsequent detection within a pre-defined maximum distance.

22. The method of claim 16, determining the light mark detected in the series of camera images to be a reflected light pulse when a single reflected light pulse is identified in a camera image.

23. The method of claim 16, further comprising generating a light mark on a surface via a light beam.

24. The method of claim 23, further comprising determining three-dimensional spatial positions of the reflected light pulse corresponding to the light mark generated on the surface.

25. The method of claim 24, further comprising registering a shape of the surface based on positional data of the reflected light pulse.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The components and the Figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. The Figures show:

[0059] FIG. 1 an embodiment of a laser pointer system;

[0060] FIG. 2 a flow chart of a data processing method for detecting reflections;

[0061] FIG. 3 an embodiment illustrating the principle of detecting reflections considering pre-defined motion constraints.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0062] FIG. 1 illustrates schematically the computer and display of the camera-assisted navigation system, identified as a whole by the reference numeral 9. This computer can also perform the function of the camera control unit and is connected to the camera mount 4 via the cable connection 8. Two infrared cameras 5 and 6 for monitoring the target area being attached to the camera mount 4 spaced apart from each other. Transmission elements 11, such as lighting elements issuing a light or infrared illuminating and control signal to the detection element 1a of the laser pointer element 1 are provided adjacent the cameras 5 and 6.

[0063] In this embodiment, it is the position of the human head shown that is to be referenced or registered. For this purpose, use is made of the light beamer 1 being a laser pointer, which projects an infrared laser light beam 2 on the facial surface of the patient. The light beamer 1 is indicated as 1′ by the broken line in a second position to indicate its movement during referencing. The light beamer 1 or laser pointer element comprises the mentioned detection element 1a receiving signals from at least one transmission element 11 of the camera system, a laser controller 1b which controls, depending on the control signal received by the detection element 1a and a predefined emission pattern stored within laser pointer element 1 and being known to the camera control unit 9, operation of laser 1c to emit a sequence of laser light pulses 2 onto the object corresponding to the acquisition frames of the cameras 5, 6 and complying with the pre-defined emission pattern.

[0064] The facial surface is then scanned by the referencing light beam 2, resulting in light reflections or light spots 3 being produced in sequence on the surface. In the drawing, only a few such light marks are represented by way of example, i.e. by a line of such light spots. However, these spots or reflections may also in general be produced individually at suitable locations by appropriately moving pointer 1, 1′.

[0065] Before a later treatment, the person conducting the treatment can simply takes hold of the light beamer 1 and scans the facial surface with the light beam 2 for some time. Due to the fast recording in sequence of single images, the camera system acquires and detects respective light reflections 3 each arranged in sequence, the light path of which for a single light spot is indicated in the drawing by the dot-dash line 7. The two cameras 5, 6 are able to three-dimensionally map the spatial location of the light reflection and the computer system 9 can determine from the data of the detected light marks the position of light spots assigned to the facial surface.

[0066] Stored in the computer are the data from a scan of the patient's head, and thus also the data for the facial surface. The computer then continually determines with the aid of a matching routine whether the number of the imaging spots obtained from referencing by means of the light beam is sufficient for it to assign or make congruent the detected surface points of the surface, as known to it from the scan data set. Once sufficient agreement exists, an acoustic and/or visual signal is output to indicate to the person conducting treatment that referencing has been successfully concluded.

[0067] The imaging spots 3 generated thus eliminate the need for attached markers or markers otherwise applied, as used hitherto separately. The plurality of light spots 3 obtained makes it possible to perform high accuracy referencing.

[0068] Also schematically shown in the figure is that a reference adapter 10 is fixedly positioned to the head of the patient. This adapter comprises three reflectors or markers, the positions of which can be likewise tracked by the cameras 5, 6. Should it now be necessary to turn the head of the patient during referencing or to move the cameras 5, 6, to eliminate camera shades, for instance by the nostril, the relative movement is tracked with the aid of the adapter 10 and taken into account in referencing so that detecting errors are avoided.

[0069] The light beamer 1 may project in addition to the invisible (e.g. infrared) light beam 2 also a visible light beam in the same direction and with the same focus to enable the person conducting treatment to keep visual track of the light spots generated and to prevent beaming into the eyes.

[0070] The referencing system in accordance with the invention may be employed with all methods of treatment involving an image-assisted operation. This applies to both surgical operations and radiation treatments. Referencing can also be employed for tracking systems with passive marker arrays as well as for those with active emitter markers, as used for instance in tracking medical instruments. Although hitherto it has mainly been indicated that the light marks are generated by means of the light beam on the skin surface of the patient, it is also conceivable within the scope of the invention to reference bone structures already exposed in this way for treatment, for instance, exposed bone portions of the skull or spine.

[0071] FIG. 2 shows an embodiment of a flowchart for detecting reflections of light pulses.

[0072] In a first step S1, all light mark portions within the viewing field of cameras 5 and 6 are collected including the point history for every light mark portion. In the shown example, three light mark portions (candidates C1, C2 and C3) were identified as being possible reflections of pulses emitted by laser 1c. The history collected in step S1 considers according to the embodiment only light mark portions relating to light marks moving on the surface with a speed being below a predefined maximum speed (see FIG. 3).

[0073] The bars b shown at the timely adjacent “odd” and “even” frame locations represent a detected light mark or light spot for each possible candidate to be evaluated for being a light pulse reflection of laser 1c or not. The top candidate C1 shown in the point history collection includes three subsequent light spot detections in three subsequent camera frames followed by three missing frames followed by eight subsequent detections. The second candidate C2 includes only two light spot detections separated by a single frame. The third candidate C3 includes light spot detections only in odd frames and has no light spot detection in any even frame.

[0074] Step S2 defines whether or not there is a sufficient visibility of light spots. Since the second candidate C2 including only two light spot detections is no reliable basis, this candidate is sorted out as being not a light spot.

[0075] Sufficient visibility in step S2 can for example be defined by considering a predefined number of frames, such as in the described example 15 frames, showing at least another pre-defined number of detection signals, such as for example at least four signals within the predefined number of e.g. 15 frames.

[0076] Thus, only candidates C1 and C3 remain.

[0077] In step S3, it is determined whether or not the remaining candidates C1 and C3 match to the predefined emission pattern being in the present case that the rule that the light beam is issued only in odd frames by laser 1c, whereas laser 1c does not emit a signal in even frames.

[0078] Comparing the remaining candidates C1 and C3 with the predefined emission pattern, candidate C1 is sorted out as not being a light spot, since light signals are also present in even frames which might be an indication that these light signals were acquired based on other light sources than the pointer 1.

[0079] It follows that there is only a single remaining candidate C3 matching the pre-defined emission pattern. In an optional step S4, it is decided whether the number of remaining candidates matches the number of employed laser pointer elements. Since in the described embodiment a single laser pointer element 1 is used and only a single candidate C3 remains in the point history collection after step S3, candidate C3 is identified as being or corresponding to the reflected light pulse.

[0080] Although candidate C3 does not indicate a light reflection in every odd frame, it is nevertheless determined to be or corresponding to the reflected light spots and the missing of a signal is not detrimental to the detection, since a missing signal can result from any kind of distortion, such as for example blocking the line of sight between the laser 1 and the object or between the object and the cameras 5, 6. The criterion leading to the exclusion of a candidate is the presence of light signals in frames which are not allowed to contain light signals according to the pre-defined emission pattern, not the missing of a signal in a “allowed” frame.

[0081] FIG. 3 shows a surface on which light spots 3a, 3b and 3c were seen by cameras 5, 6 with earlier light spot signals A for light spot 3a, and later light spot signals B and C for light spots 3b and 3c, respectively. All light spot signals 3A, 3B and 3C are considered to meet the pre-defined emission pattern. In the shown example, light spots 3b and 3c show the same later signals B and C and light spot 3b has a smaller distance to light spot 3a than 3c to 3a. If the criterion of the maximum allowable velocity of the light spot 3 on the surface is set appropriately low, it can be decided in the illustrated embodiment that light spot 3b is the light spot originating from laser 1c, since the larger distance of light spot 3c from light spot 3a implies a too large velocity of light spot 3c on the surface leading to the ruling out of this light spot 3c.