Pulsed-light emitting marker device

An active marker device (100) is introducible into a human tissue and for tracking a region of interest of a human body. The active marker device includes a light source (101) for emitting light such that the emitted light can be detected by an optical sensor. In this way, the active marker device and/or the region of interest can be tracked by a tracking system including the optical sensor. The active marker device (100) also includes a switch (102) for turning the light source on and off and for operating the light source in a pulsed mode.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2015/079513, filed on Dec. 14, 2015, which claims the benefit of European Patent Application No. 14198296.7, filed on Dec. 16, 2014. These applications are hereby incorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to marking and/or tracking a region of interest of a human body. In particular, the invention relates to an active marker device, a tracking system, and an examination apparatus.

BACKGROUND OF THE INVENTION

In surgery, there may be a need to provide intra-operative imaging. This is because the anatomy that has been imaged pre-operatively may change significantly during surgery. For example, deformations may be caused by tissue cutting or by the movement of an organ, e.g. the liver, in the human body. Thus, there may be a significant non-linear deformation of the tissue and a simple registration of intra-operative imaging with pre-operative imaging may be difficult.

For this purpose, it is known to use tissue markers in order to find back the relevant tissue identified in pre-operative imaging during a subsequent procedure. Such markers are introduced into the tissue during the pre-operative phase. For example, X-ray absorbing markers may be used that are visible in an X-ray image acquired intra-operatively.

However, the usage of X-rays during surgery should be limited, not only to limit a dose of harmful radiation received by a patient, but also for example due to the fact that the surgery environment has to be sterile. This is more difficult when applying X-ray imaging, as intraoperative X-ray imaging requires the surgeon to wear for example lead shielding cloths, which may be inconvenient.

SUMMARY OF THE INVENTION

There may be a need to provide a marking device adapted for a precise and reliable marking of an object of interest of a human body.

A first aspect of the invention relates to a marker device being introducable into a tissue for marking a region of interest of a subject, such as a body of a patient. The marker device comprises a light source adapted for emitting light such that the marker device is visible to an optical sensor. Furthermore, the marker device comprises a switch adapted for operating the light source in a pulsed mode.

Hereinafter, a marker device according to the invention is also referred to as an “active marker device”, i.e. a marker device comprising an active emitter, in particular a light source. This is contrary to “passive” marker devices, such as an X-ray absorbing marker.

A gist of the invention may be seen in providing an optical marker for tracking and/or registering an object or region of interest of a human body. For this purpose, the active marker device described in the context of the invention is provided. It may be understood that the light source of the active marker device is in particular configured for emitting pulsed light.

The active marker can be implanted into the body during a pre-operative phase. During a subsequent procedure, the active marker device can be tracked using a suitable tracking device, which preferably comprises an optical sensor and more preferably at least one time-of-flight camera. Thus, the marked tissue structures can directly be linked to the coordinate system in the surgery room, and for example also to the coordinate system of a medical imaging system, such as an X-ray system.

By emitting pulsed light, the active marker device consumes less electrical power. Moreover, the active marker device emitting pulsed light can be detected more reliably by a time-of-flight camera. Further, the pulsed light emitted from the active marker device is better distinguishable from surrounding light, e.g. light emitted by a surgical task light or by lighting fixtures in the ceiling of the operating room, than a static light source.

In addition, the active marker device may be identifiable through a property of the pulsed light, e.g., the frequency or a specific pulse pattern. A further advantage of pulsing a LED may be the ability to over-drive the LED, i.e. the peak power may be larger than the maximum average power. In this way, the average LED temperature may be lower such that efficiency is improved and brighter light flashes may be emitted from the LED.

Although the active marker device is described for being introducible into a human tissue, the active marker device may be adapted for being introduced into animal tissue, e.g., for veterinary purposes. Moreover, the active marker device may be adapted for being introduced into dead tissue, e.g., for pathology.

The active marker device thus relates to a temporarily implantable light emitting marker, which is adapted for being detected outside the body, for example during a medical procedure. Preferably, the active marker device is adapted for emitting light pulses that can be detected with a time-of-flight camera. The active marker device may comprise an epoxy resin (e.g. EPO-TEK 301) into which the electronic components of the active marker device (e.g. the light source and the switch) are encapsulated. In other words, the active marker device may comprise a capsule into which the light source and the switch and other components may be encapsulated. The capsule of the active marker device may comprise an elongated shape and may fit into a cannula of an insertion needle.

The light source may be a light emitting diode (LED), e.g., a low power LED or a semiconductor laser diode. The light source may also be another kind of light source having a low power consumption and a small size.

The light source may be configured to emit light with a luminous intensity greater than 150 mcd, preferably greater than 500 mcd, even more preferred, greater than 1000 mcd. Furthermore, the light source may be configured to emit light with a luminous flux greater than 1 lm, preferably greater than 5 lm, even more preferred greater than 10 lm.

The switch may relate to an electronic circuit for switching on and off the light source and for operating the light source in the pulsed mode. There may be different possibilities how the switch can be structured. For example, the switch may be a mechanical switch such that the active marker device may be manually activated by operating the switch, e.g., just prior to the implantation of the active marker device. The switch may for example be operated by pressing a miniature button.

Furthermore, the switch may be adapted for being operated in a contactless manner such that the light source of the active marker device can be remotely activated, i.e. activated from outside a patient's body, in a contactless manner, for example after the active marker device has been temporarily implanted into body tissue. For example, the light source may be activated by means of a magnetic field. For being activated with a magnetic field, the switch may for example comprise a miniature bi-stable reed switch. Furthermore, the switch may comprise an electronic fuse which may be activated via RF pulses. The switch may also comprise phase change materials. The phase change of the phase change material can for example be induced by an external heating or by the body heat when the active marker is introduced into the body. In this case, the switch may be operated by an expansion or contraction of the phase change material which causes a mechanical force (e.g. a pressure) onto a mechanical switch such that an electrical circuit is closed. The switch may alternatively comprise a material which changes its electrical conductivity upon a phase change of the material for operating the switch.

The switch may comprise an electrical circuit for operating the light source in the pulsed mode. For example, the switch may comprise a timer for operating the light source in the pulsed mode. Furthermore, the switch may comprise a receiving unit for being triggered remotely. In other words, the light source may be operated to emit separated pulses of light. The pulsed mode of the light source may for example be characterized by a frequency of the pulses. The frequency may for example be between 0.1 Hz and 100 MHz. In other words, a pulsed mode may relate to a frequency with which the pulsed light is emitted by the light source. The pulse duration may be, e.g., 50% of the duty cycle of the pulsed mode of the light source. However, the pulse duration may also be more or less than 50% of the duty cycle. Alternatively or additionally, the pulsed mode may be characterized by one or more specific pulse patterns.

Furthermore, it is possible to provide a plurality of active marker devices, wherein each marker device emits light with a different pulsed mode, e.g. with a different frequency of pulses or a different pulse pattern. Moreover, each active marker device of the plurality of active marker devices may be uniquely identifiable via the pulsed mode.

According to an exemplary embodiment of the invention the switch is configured for operating the light source in a plurality of different pulsed modes. Furthermore, the switch is configurable for operating the light source in one specific pulsed mode of the plurality of different pulsed modes.

In this way, a plurality of active marker devices can be used for tracking an object of interest, wherein each active marker device has its own pulsed mode and is uniquely identifiable via its pulsed mode.

For example, the switch can be adapted for operating the light source with different frequencies. The switch may be programmable to emit light with a specific pulsed mode, e.g. a specific frequency, or a specific pulse pattern. The switch may also comprise a mechanic switch for mechanically switching between different pulsed modes. Furthermore, the switch may comprise a receiving unit for receiving an information about the pulsed mode with which the light source shall emit light.

According to a further exemplary embodiment of the invention, the active marker device further comprises a receiving unit adapted for receiving an activation signal for the light source. Moreover, the switch is configured to switch the light source on when the receiving unit receives the activation signal. The receiving unit may be encapsulated in a capsule of the active marker device.

The receiving unit may be a wireless receiving unit, e.g. an RF (radio frequency) antenna. The switch may be adapted for operating the light source in the pulsed mode, only when the receiving unit receives the activation signal, e.g. only when the RF antenna receives a radio signal.

In this way, the active marker device can be activated remotely, when the object of interest is to be tracked optically. Thus, it may be ensured that the active marker device only consumes electrical power while it is being used for tracking the object of interest.

According to a further exemplary embodiment of the invention, the receiving unit is configured for receiving a signal comprising information about a property of the pulsed mode. Furthermore, the switch is configured for operating the light source in the pulsed mode having said property.

The property of the pulsed mode may for example be a frequency of the pulses emitted by the light source.

In this way, a signal can be sent to the active marker device such that the active marker device emits light in a specific pulsed mode. Thus, the active marker device can be operated to emit light in a specific pulsed mode such that the light can be processed by an optical sensor and a processing unit coupled to said optical sensor, e.g., for identifying the marker device.

According to a further exemplary embodiment of the invention, the receiving unit is configured for receiving a triggering signal triggering the generation of a pulse by the light source. Furthermore, the switch is configured for turning the light source on, only when the triggering signal is received by the receiving unit.

In other words, the pulses generated by the light source can be triggered by an external triggering signal, e.g. a RF triggering signal. In this way, the pulsed mode can be defined by an external source emitting the signal triggering the pulses of the light source. Thus, the specific pulsed mode can be determined during the operation of the active marker device and does not need to be determined before implanting the active marker device.

According to a further exemplary embodiment of the invention, the active marker device further comprises an energy source adapted for supplying the light source with electrical energy.

The energy source may be encapsulated in a capsule of the active marker device.

According to a further exemplary embodiment of the invention, the energy source comprises a battery.

To provide power for the light source, the energy source may comprise a Lithium-ion battery. Moreover, the battery can be configured to provide energy to the light source only for less than 24 hours, preferably less than 10 hours, even more preferable less than 5 hours, since the active marker only needs to emit light during surgery. Thus, the battery can be made small enough such that it is prevented that the active marker device becomes bulky.

According to a further exemplary embodiment of the invention, the energy source comprises an LC circuit for a wireless power supply of the energy source.

According to a further exemplary embodiment of the invention, the active marker device is configured for being introduced into a cannula of an insertion needle.

For example, the active marker device can have an outer diameter which is smaller than 2.4 mm. Moreover, the active marker device may have dimensions such that it fits into the channel of 16 gauge, preferably 14 gauge, even more preferred 11 gauge, of an insertion needle.

According to a further exemplary embodiment of the invention, the light source is configured for emitting light with a wavelength in the range between 600 nm and 1300 nm, preferably between 700 nm and 1000 nm.

For said range of wavelength the human tissue may have a low absorption which allows the active marker device to be tracked even deep inside the tissue.

The light source may alternatively be configured to emit light with a wavelength, which is absorbed by the tissue to a greater extent. In this way, not only the active marker can be found but it can also enhance the visibility of the tissue structure to the physician.

Furthermore, the active marker device can also be configured to be used in conjunction with a contrast agent that has been injected into the patient. Since the light source may be inserted into the tissue, a good illumination of the contrast agent (which may be a fluorescent contrast agent) can be achieved.

A second aspect of the invention relates to a tracking system for tracking an object of interest of a human tissue. The tracking system comprises an active marker described in the context of the invention and an optical sensor adapted for detecting the light emitted by the light source of the active marker device. Furthermore, the tracking system comprises a processing unit adapted for determining a position of the active marker device on the basis of the light detected by the optical sensor.

In other words, the tracking system can be configured for determining a position of the active marker device on an optical basis. The optical sensor of the tracking system may have imaging capabilities. For example, the optical sensor may be an optical camera. The optical sensor may also be configured to detect infrared light emitted by the light source of the active marker device.

According to a further exemplary embodiment, the optical sensor comprises at least two optical cameras. Furthermore, the processing unit is configured for performing a triangulation on the basis of images recorded by the at least two optical cameras for determining the position of the active marker device.

According to an exemplary embodiment of the invention, the optical sensor comprises at least one time-of-flight camera for receiving the light emitted by the active marker device. The processing unit is configured for determining the position of the active marker device by triangulation.

As is understood in the art, a time-of-flight (TOF) camera is a camera that produces a depth image; each pixel of such camera encodes the distance to a corresponding point in the field of view of the camera. TOF cameras are typically configured to measure phase delays of incoming light, in accordance to the invention in particular light pulses emitted by an active marker device.

According to an exemplary embodiment, the processing unit is configured for determining three spherical surfaces, on which the active marker device is located. Furthermore, the processing unit is configured for determining the position of the marker device by determining an intersection of the three spherical surfaces. In other words, the position of the active marker device in 3D space can be determined. Information associated with the receipt of a light pulse emitted by the active marker device by at least one pixel of a TOF camera, such as the estimated time of flight of the light pulse, can be used for determining the path length between the active marker device and a surface point, for example a point on an exterior surface of a patient associated with the at least one pixel of the TOF camera. Thus, a spherical surface can be determined in 3D space on which the active marker device is located. By determining the intersection point of three such spherical surfaces, the marker location in 3D space can be identified with high accuracy.

For example, the optical sensor comprises a single time-of-flight camera, which comprises at least three image points or pixels. The time-of-flight camera may comprise at least three pixels for receiving the light emitted by the marker device, wherein the processing unit may be configured for determining a spherical surface for each one of the at least three pixels. Furthermore, the processing unit may be configured for determining the position of the marker device by determining an intersection of the three spherical surfaces.

The tracking system can be configured to determine the position of the active marker device in that different pixels of a single time-of-flight camera receive a light pulse of the active marker device emitted from a plurality of corresponding points (e.g. 3 points) on the surface of the body. Moreover, the tracking system can be configured to determine the position of said points on the surface of the body, e.g. during the registration procedure and/or by a standard reflective time-of-flight measurement. As the positions of the points on the surface of the body are known, the tracking system may be configured to determine the distance between each of said points on the surface and the active marker device from a phase delay in signals of the TOF camera signals representing a receipt of the emitted light pulse at the different pixels. Thus, the tracking system can be configured for triangulating the position of the active marker device, i.e. determining spherical surfaces for each of said points and for determining the intersection of the spherical surfaces yielding the position of the active marker device.

The tracking system may be configured for triggering a pulse of the light source of the active marker device, e.g. by emitting a RF signal. Furthermore, the tracking system may be configured for determining the time period between transmitting the RF signal for triggering the pulse of the light source and between detecting the pulse by the time-of-flight camera. In this way, the tracking device can determine the distance between the active marker device and each time-of-flight camera.

Moreover, the tracking system may also comprise more than one time-of-flight camera for improving the robustness of the system. In this way, the position in 3D space can also be determined if one camera cannot capture the light of the active marker device. Furthermore, the tracking system may be configured for taking into account light propagation time between tissue and air in order to determine the distance between the active marker device and the time-of-flight camera more accurately. For example, the distance between the each time-of-flight camera and the active marker device can be estimated using a patient surface model which may be registered in the surgical setup.

According to a further exemplary embodiment of the invention, the processing unit is configured for identifying the active marker device on the basis of the pulsed mode of the light received by the camera.

For example, the processing unit can identify the active marker device on the basis of the frequency of the pulses emitted by the light source.

According to a further exemplary embodiment of the invention, the tracking system further comprises a transmitting unit for transmitting an activation signal to the marker device.

A third aspect of the invention relates to a medical examination apparatus, comprising a medical imaging apparatus and a tracking system described in the context of the invention.

The medical imaging apparatus may be an X-ray device, a MRI, a US, a PET-CT or another imaging device. For example, the medical imaging apparatus may comprise a C-arm, on which the optical sensor or sensors of the tracking system is or are attached.

Furthermore, the exact position of the active marker device may be determined first by the imaging device, e.g. the X-ray system or other modality (MRI, X-ray, CT, US). Once the exact position of the active marker device is known, small movements of the active marker device can be tracked with the cameras with high precision.

The figures are schematic and not true to scale. If in the following description elements of different figures are labeled with the same reference signs, they refer to the same or similar elements. The same or similar elements may, however, also be labeled with different reference signs.

DETAILED DESCRIPTION OF EMBODIMENTS

InFIG. 1, an active marker device100according to an exemplary embodiment of the invention is shown. The active marker device is adapted for being introduced into human tissue for marking and for tracking an object of interest, e.g. a tumor, of a human body. The active marker device comprises100a light source101adapted for emitting light104such that the active marker device100is visible to an optical sensor. In an embodiment, the light source101may be a low power LED, for example. Furthermore, the active marker device100comprises a switch102adapted for turning the light source101on and off and for operating the light source101in a pulsed mode. Furthermore, the active marker device100comprises an energy source103, e.g. a battery or a LC circuit for wireless power transfer to the active marker device100. The light source101, the switch102, and the energy source103are encapsulated in a capsule105of the active marker device100.

For example, the active marker device100comprises a low power LED101such as a Nichia NESL 157AT-H3 LED. This LED typically has a luminous flux of 11.5 lm and a luminous intensity of 4.0 cd. The LED101may, e.g., be connected to a small battery103and the switch102may be switchable from the distance. The LED can also be an HSMW white ChipLED having a size of 1.5×0.8×0.6 mm. Furthermore, the LED can be a PICOLED of ROHM having a size of 1.0×0.52×0.2 mm. The LED and the electronics of the active marker100may be capsulated in a capsule105of epoxy resin (e.g. EPO-TEK 301) that is biocompatible and optically transparent. The capsule105is made in an elongated shape such that it fits inside a cannula of an insertion needle.

InFIGS. 2A to 2Cthe introduction of an active marker device100according to an exemplary embodiment of the invention into a body201(e.g., a human body) is shown. The active marker device100is located in a cannula of an insertion needle200. The body201comprises a region of interest203, e.g. a tumor. Furthermore, the human body has a body surface202.

InFIG. 2B, the introduction or insertion of the active marker device100into the body201at or near the region of interest203is shown. For that purpose, the insertion needle200is pierced into the body201through the body surface202and the active marker device100is implanted in or near the region of interest203.

InFIG. 2C, it is shown that the active marker device100implanted in or near the region of interest203emits light104in a pulsed mode for tracking the active marker device100and the region of interest203, respectively. The light source of the active marker device100can be activated before implanting the active marker device into the body201, e.g. by manually operating a switch. Alternatively, the light source can be activated in a contactless manner when the active marker device is already implanted in the body201, e.g. by sending an RF activation signal.

FIG. 3Ashows an insertion needle301and a stylet302, the insertion needle301comprising a cannula303for introducing an active marker device according to an exemplary embodiment of the invention. InFIG. 3B, an enlarged section of the cannula303is shown. It can be gathered that an active marker device is located inside the cannula303of the insertion needle.

FIG. 4Ashows an example electrical circuit400for operating the light source401of the active marker device according to an exemplary embodiment of the invention. The light source is embodied as a light emitting diode (LED)401. Furthermore, the electrical circuit comprises an energy source402, e.g. a battery. Moreover, the light source401is coupled to a switching circuit408comprising a field-effective transistor404, an RF antenna403, a diode405, a resistor406, and a capacitor407. The RF antenna403, the diode405, the resistor406, and the capacitor407are part of an AM receiver of the switching circuit408.FIG. 4Bshows a simple circuit410for operating the light source411of the active marker device according to an exemplary embodiment of the invention. Again, the light source411is embodied as a light emitting diode (LED). In this case, the AM receiver comprises the RF antenna413, the diode415, and the transistor414and uses the input capacitance of the transistor414.

InFIG. 5, an electrical circuit501and an energy supplying device502for wirelessly providing an active marker device500with electrical energy are shown.

The electrical circuit501comprises an LC circuit503having a coil504and a capacitor505. Furthermore, the electrical circuit501comprises a load circuit506including a coil508and a LED driving electronics507.

The electrical energy is wirelessly provided to the electrical circuit501by the energy supplying device502. The energy supplying device502comprises an LC circuit509including a coil510and a capacitor511. The energy supplying device502further comprises a source circuit including an alternating energy source and a coil514.

The source circuit512is configured to couple the energy into the resonant LC circuit509via the coils514and510. The LC circuit503of the active marker device receives a part of the electromagnetic flux generated by the LC circuit509and couples the energy into the load circuit506which supplies the LED driver electronics with electrical energy.

InFIG. 6, a medical examination system600comprising a medical imaging apparatus601according to an exemplary embodiment of the invention is shown. In this exemplary embodiment, the medical imaging apparatus601comprises a C-arm having an X-ray source603and an X-ray detector602. The medical imaging apparatus601(e.g., a C-arm) further comprises a tracking system having optical sensors604and605as well as a processing unit610.

Furthermore, a human body606is located between the X-ray source603and the X-ray detector602of the C-arm. The human body606comprises a region of interest, e.g. a tumor. Moreover, an active marker device608is implanted into the human body at or near the region of interest607. In this way, the active marker device608and/or the region of interest can be tracked without having to activate the X-ray source, e.g., when the human body is moved during surgery. The processing unit610is adapted for determining a position, e.g. a 3D position, of the active marker device608on the basis of the light detected by the optical sensors604,605. The processing unit610is adapted to determine the position of the active marker device608by applying triangulation.

InFIG. 7a tracking system700according to an exemplary embodiment of the invention is shown. The tracking system comprises a support structure701for the time-of-flight cameras702,703,704,705. The support structure701is, e.g., a C-arm of a medical examination apparatus.

A body of a patient706having a tumor (region of interest)707is schematically shown. Furthermore, three implanted active marker devices708,709and710circumscribing the tumor are shown. The tracking system700is configured for determining the position of the implanted active marker devices708,709and710by determining an intersection of the three spherical surfaces determined by at least three time-of-flight cameras of the four time-of-flight cameras702,703,704and705. In other words, the position of the active marker device in 3D space is determined using path information of the pulsed light emitted by the implanted active marker devices708,709,710, as detected by the time-of-flight cameras. The estimated time of flight of the light pulse, which represents a path length for the emitted light from the active marker device to the camera, is used for determining the spherical surface on which the active marker device is located.

In order to explain the working principle of the time-of-flight camera, exemplary embodiments in a simplified 2D representation are shown inFIGS. 8A and 8B.

InFIG. 8Aa tracking system according to an embodiment of the invention is shown. Furthermore, a body having a surface801is depicted, in which an active marker device802is implanted. The active marker device802is configured to emit light in a pulsed mode. A signal curve803of the switch of the active marker device causing a light pulse of the active marker device802is further shown. The tracking system comprises a first time-of-flight camera804and a second time-of-flight camera806. It is further shown that the first time-of-flight camera804generates a pulse-shaped signal805caused by the light pulse of the active marker device802. The second time-of-flight camera806generates a pulse-shaped signal807caused by the light pulse of the active marker device802. Furthermore, the tracking system comprises a device808for determining a phase delay between the pulse-shaped signals805and807of the first and second time-of-flight cameras804and806. The phase delay between the pulse-shaped signals805and807correlates to the average path delay from the active marker device802to the surface801plus the distance from the surface801to the first and second time-of-flight cameras804,806. In other words, the phase delay corresponds to the difference in path length between the sum of the distances of the paths810and811and the sum of distances of the paths814and815. The path810corresponds to the path between the active marker device802and the point809on the surface801and the path811corresponds to the path between the point809on the surface and the first time-of-flight camera804. Equally, the path814corresponds to the path between the active marker device802and the point813on the surface801and the path815corresponds to the path between the point813on the surface and the second time-of-flight camera806. In this way, the tracking system can triangulate the position of the active marker device802by determining the intersection of spherical surfaces812and816.

Preferably, an additional third time-of-flight camera (not shown) may be used so that a 3D position of the active marker device802corresponds to a single intersection point of three spherical surfaces, one for each camera device.

InFIG. 8B, the determination of the position of the active marker device802with a single time-of-flight camera817is shown. A plurality of pixels of the time-of-flight camera receives the light pulse from the active marker. A first pixel receives the light being emitted from point809of the surface801of the body and a second pixel receives the light emitted from point813of the surface801of the body. For each of these of pixels, the distance between the camera and the corresponding points809,813on the patient surface is known, e.g. from registering the camera position with an existing patient outline scan, from standard reflective time-of-flight measurement or from any other suitable distance measurement.

At the first pixel that receives light from the point809on the surface801, the measured value is composed of sum of the distances of paths810and818. Equally, at the second pixel that receives light from the point813on the surface801, the measured value is composed of sum of the distances of paths814and819. Similar to the previous embodiment, the phase delay measured at the first and second pixel of the time-of-flight camera corresponds to the difference in path length between the sum of the paths810and818and the sum of the paths814and819.

As the length of the paths818and819are known from the 3D position of points809and813and the 3D position of the single time-of-flight camera817, the tracking system can determine the distances of paths810and814and subsequently triangulate the position of the active marker device by determining the intersection of spherical surfaces820and821.

In 3D, preferably the position of the active marker device is determined using signals from at least three separate pixels of the time-of-flight camera. That is, based on a phase delay between these signals, the distances from the active marker device to at least three surface points observed by the corresponding pixels of the single time-of-flight camera may be determined. Again, the position of the active marker device is subsequently triangulated by determining the single intersection point of the three spherical surfaces corresponding to these distances.

A typical image may have many more surface points visible to different pixels of the TOF camera. Thus, preferably, signals from additional pixels receiving the light pulse from the marker at different time instances may be relied upon in order to further improve the accuracy of the marker position determination.

Optionally, a collimator may be used to restrict the image information received by the different pixels to a limited area of the total surface. That is, for example, the first pixel may receive light from the point809on the surface801, but the collimator prevents light from surface point813from reaching the first pixel. Similarly, the collimator prevents light from the point809on the surface801from reaching the second pixel of the time-of-flight camera.

LIST OF REFERENCE SIGNS

100active marker device101light source102switch103energy source104light105capsule200insertion needle201human body202body surface203object of interest (e.g. tumor)301insertion needle302insertion needle303cannula304active marker device400electrical circuit401light source (LED)402energy source (battery)403receiving unit (RF antenna)404field effective transistor405diode406resistor407capacitor410electrical circuit411light source (LED)412energy source (battery)413receiving unit (RF antenna)414transistor415diode500active marker device501electrical circuit502energy supplying device503LC circuit504coil505capacitor506load circuit507LED driver electronics508coil509LC circuit510coil511capacitor512source circuit513alternating current source514coil600medical examination apparatus601C-arm602X-ray detector603X-ray source604optical sensor605optical sensor606body607region of interest (tumor)608active marker device609tracking system610processing unit700tracking system701camera support702time-of-flight camera703time-of-flight camera704time-of-flight camera705time-of-flight camera706body707region of interest (tumor)708active marker device709active marker device710active marker device801surface of the body802active marker device803signal of a light pulse804first time-of-flight camera805signal generated by the first time-of-flight camera806second time-of-flight camera807signal generated by the second time-of-flight camera808device for determining a phase delay809first point on the surface of the body810path between active marker and the first point811path between the first point and the first time-of-flight camera812first spherical surface813second point on the surface of the body814path between the active marker and the second point815path between the second point and the second time-of-flight camera816second spherical surface817single time-of-flight camera818distance between the first point and the single time-of-flight camera819distance between the second point and the single time-of-flight camera820first spherical surface821second spherical surface