Mobile imaging of an object using penetrating radiation

A system for imaging a target object comprises a first unmanned vehicle including a source of penetrating radiation. The first vehicle positions the source such as to direct the radiation toward the target object. A second unmanned vehicle comprises an image detector for registering a spatial distribution of the radiation as an image, in which the second vehicle positions the detector to register the distribution of radiation when transmitted through the target object. These unmanned vehicles are autonomous vehicles adapted for independent propelled motion, and comprise a positioning unit for detecting a position of the vehicle. A processing unit controls the motion of the unmanned vehicles to acquire at least two images corresponding to at least two different projection directions of the radiation through the target object. The processing unit is adapted for generating data representative of an internal structure of the target object from the at least two images.

FIELD OF THE INVENTION

The invention relates to the field of mobile radiation imaging. More specifically it relates to a system and method for imaging a target object, and a related computer program product.

BACKGROUND OF THE INVENTION

The U.S. Pat. No. 8,194,822 describes systems and methods for inspecting an object with a scanned beam of penetrating radiation. Scattered radiation from the beam is detected, in either a backward or forward direction. Characteristic values of the scattered radiation are compared to expected reference values to characterize the object.

However, a need exists in the art for flexible, unmanned systems for inspecting objects. An autonomous system for imaging objects could be particularly advantageous in hazardous environments, confined spaces and difficult to reach spaces. It may furthermore be advantageous to provide an imaging solution that can autonomously detect and image objects in a volume of space without substantial intervention of an operator.

SUMMARY OF THE INVENTION

It is an object of embodiments of the present invention to provide good and efficient means and methods for imaging target objects.

Embodiments of the present invention relate, in a first aspect, to a system for imaging a target object. The system comprises a first unmanned vehicle that comprises a source of penetrating radiation, e.g. an X-ray tube or a gamma radiation source. The first unmanned vehicle is adapted for positioning the source such as to direct the penetrating radiation toward the target object. The system further comprises a second unmanned vehicle that comprises an image detector for registering a spatial distribution of this penetrating radiation as an image.

The first unmanned vehicle and the second unmanned vehicle are autonomous vehicles adapted for independent propelled motion. Each of the first and the second unmanned vehicle comprises a positioning unit for detecting a position of the corresponding vehicle, e.g. of the unmanned vehicle in which the positioning unit is comprised.

The system further comprises a processing unit for controlling the propelled motion of the first unmanned vehicle and the second unmanned vehicle such as to acquire at least two images using the image detector corresponding to at least two different projection directions of the penetrating radiation through the target object. For example, the processing unit may be adapted for controlling the propelled motion of the first unmanned vehicle to position the source such as to direct the penetrating radiation toward the target object, and for controlling the propelled motion of the second unmanned vehicle to position the image detector such as to register the spatial distribution of the penetrating radiation when transmitted through the target object.

The processing unit is furthermore adapted for generating data representative of an internal structure of the target object from these at least two images.

It is an advantage of embodiments of the present invention that a target object in a difficult to reach location may be imaged efficiently.

It is an advantage of embodiments of the present invention that objects to be imaged may be detected and imaged automatically without requiring prior knowledge of their exact position.

It is an advantage of embodiments of the present invention that objects may be easily and safely imaged in a hazardous environment.

In a system in accordance with embodiments of the present invention, the first unmanned vehicle and/or the second unmanned vehicle may comprise a propulsion system for providing the propelled motion and a power source for sustaining the propelled motion.

In a system in accordance with embodiments of the present invention, the first unmanned vehicle and/or the second unmanned vehicle may be a ground vehicle, e.g. a wheeled vehicle, a aerial vehicle, a space craft, a watercraft and/or a submersible vehicle.

In a system in accordance with embodiments of the present invention, the positioning unit may comprise an indoor positioning system and/or an outdoor positioning system.

In a system in accordance with embodiments of the present invention, the positioning unit may use laser positioning and/or echo positioning to measure a distance with respect to objects in its vicinity.

In a system in accordance with embodiments of the present invention, the positioning unit may be adapted for determining a relative position of the unmanned vehicle in which it is comprised with respect to the target object and/or the other unmanned vehicle.

In a system in accordance with embodiments of the present invention, the source of penetrating radiation may comprise an X-ray tube and/or a gamma radiation source.

In a system in accordance with embodiments of the present invention, the first unmanned vehicle may comprise a pivotable support for allowing a rotation of the source and/or the second unmanned vehicle may comprise a pivotable support for allowing a rotation of the image detector.

In a system in accordance with embodiments of the present invention, the processing unit may be, fully or in part, integrated in the first unmanned vehicle, in the second unmanned vehicle and/or in a separate base station, e.g. in a base station.

In a system in accordance with embodiments of the present invention, the processing unit may be adapted for receiving position information from the first unmanned vehicle and/or from the second unmanned vehicle.

In a system in accordance with embodiments of the present invention, the positioning unit may be adapted for determining the position of the target object when present, in which the first unmanned vehicle and/or the second unmanned vehicle may be adapted for transmitting an indicative position of the target object to the processing unit when the presence of the target object is detected by the positioning unit.

In a system in accordance with embodiments of the present invention, the processing unit may be adapted for controlling the independent propelled motion of the first unmanned vehicle and the second unmanned vehicle such as to acquire the at least two images, using the image detector, corresponding to the at least two different projection directions of the penetrating radiation through the target object, in which the at least two different projection directions are determined by the processing unit as a uniform angular sampling around the target object.

In a system in accordance with embodiments of the present invention, the processing unit may be adapted for generating the data representative of the internal structure of the target object by performing a tomographic reconstruction.

In a system in accordance with embodiments of the present invention, this tomographic reconstruction may comprise a partial reconstruction taking a first plurality of images into account. The processing unit may furthermore be adapted for determining a further projection direction for acquiring a further image of the target object by taking this partial reconstruction into account.

In a system in accordance with embodiments of the present invention, the tomographic reconstruction may be performed by the processing unit using a discrete algebraic reconstruction method.

In a system in accordance with embodiments of the present invention, the tomographic reconstruction may comprise a compensation method for taking unpredictable variations in positioning of the first unmanned vehicle, of the second unmanned vehicle and/or of the target object into account.

In a second aspect, embodiments of the present invention relate to a method for imaging a target object. This method comprises providing a first unmanned vehicle that comprises a source of penetrating radiation, and providing a second unmanned vehicle that comprises an image detector for registering a spatial distribution of this penetrating radiation as an image. The first unmanned vehicle and the second unmanned vehicle are autonomous vehicles adapted for independent propelled motion. Each of the first and the second unmanned vehicle comprises a positioning unit for detecting a position of the corresponding vehicle.

The method further comprises controlling, using a processing unit, the propelled motion of the first unmanned vehicle to position the source such as to direct the penetrating radiation toward the target object, and controlling, using the processing unit, the propelled motion of the second unmanned vehicle to position the image detector such as to register the spatial distribution of the penetrating radiation when transmitted through the target object.

The method also comprises acquiring at least two images using the image detector, wherein the propelled motion of the first unmanned vehicle and of the second unmanned vehicle are controlled such that the at least two images correspond to at least two different projection directions of the penetrating radiation through the target object.

The method further comprises generating data representative of an internal structure of the target object from the at least two images, using the processing unit.

In a method in accordance with embodiments of the present invention, the controlling of the propelled motion of the first and second unmanned vehicle may take positioning information provided by the positioning unit into account.

A method in accordance with embodiments of the present invention, may further comprise determining the position of the target object by the positioning unit, and this controlling of the propelled motion of the first unmanned vehicle and of the second unmanned vehicle may take the position of the target object into account, e.g. as determined by the positioning unit.

In a method in accordance with embodiments of the present invention, the propelled motion of the first unmanned vehicle and the second unmanned vehicle may be controlled such as to acquire the at least two images corresponding to the at least two different projection directions, in which the at least two different projection directions are determined by the processing unit as a uniform angular sampling around the target object.

In a method in accordance with embodiments of the present invention, the generating of the data representative of the internal structure of the target object may comprise a tomographic reconstruction.

In a method in accordance with embodiments of the present invention, this tomographic reconstruction may comprise a partial reconstruction taking a first plurality of images into account, in which the method may further comprise determining a further projection direction for acquiring a further image of the target object by taking this partial reconstruction into account.

In a method in accordance with embodiments of the present invention, the tomographic reconstruction may be performed by the processing unit using a discrete algebraic reconstruction method.

In a method in accordance with embodiments of the present invention, the tomographic reconstruction may comprise a compensation method for taking unpredictable variations in positioning of the first unmanned vehicle, the second unmanned vehicle and/or the target object into account.

In a further aspect, embodiments of the present invention relate to a computer program product for, if executed by a processing unit, performing steps of a method in accordance with embodiments of the second aspect of the present invention. These performed steps comprise at least the controlling of a propelled motion of a first unmanned vehicle, the controlling of the propelled motion of a second unmanned vehicle and the generating of data representative of an internal structure of a target object from at least two acquired images.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Where in the present description is referred to an unmanned vehicle, reference is made to an uncrewed vehicle or unmanned vehicle that can operate without a human operator on board. Particularly, in the present disclosure, such unmanned vehicle refers to a vehicle capable of sensing its environment and navigating in response to control instructions from a processing unit in accordance with embodiments of the present invention. These control instructions may be determined by the processing unit without human intervention, e.g. hence the reference to ‘autonomous’, which should be interpreted in the context of the system as a whole and not necessarily to the vehicle as an independent unit as such. The vehicle may be ground vehicle, water vehicle, air vehicle or space vehicle, but may explicitly exclude mobile machines adapted for moving along a fixed track, e.g. having only a single degree of freedom of translation, which are thus not considered as unmanned vehicles in the context of present disclosure.

In a first aspect, the present invention relates to a system for imaging a target object. This system comprises a first unmanned vehicle and a second unmanned vehicle. The first and second unmanned vehicle are each an autonomous vehicle, adapted for independent propelled motion. Furthermore, each of the first and the second unmanned vehicle comprises a positioning unit for detecting a position of the corresponding vehicle, e.g. a navigation unit for controlling the motion of the unmanned vehicle in response to a detected position of the vehicle.

The first unmanned vehicle comprises a source of penetrating radiation, and this first unmanned vehicle is adapted for positioning the source such as to direct the penetrating radiation toward the target object. The second unmanned vehicle comprises an image detector for registering a spatial distribution of the penetrating radiation as an image. This second unmanned vehicle is adapted for positioning the image detector such as to register the spatial distribution of the penetrating radiation when transmitted through the target object.

The system also comprises a processing unit, e.g. a processor, for controlling the propelled motion of respectively the first and the second unmanned vehicle such as to acquire at least two images using the image detector. These at least two images correspond to at least two different projection directions of the penetrating radiation through the target object. The processing unit is further adapted for generating data representative of an internal structure of the target object from the at least two images.

Referring toFIG. 1andFIG. 2, exemplary systems10in accordance with embodiments of the present invention are shown schematically. Such system10is adapted for imaging a target object15. For example, the target object may be difficult to reach by conventional imaging systems, e.g. a blade of a wind turbine, a submerged object, a conduit or device in a crawl space, a monumental piece of art, an object in a hazardous environment, such as a vacuum, toxic or irradiated environment, and/or an archaeological artifact in an unstable and/or delicate excavated building.

This system10comprises a first unmanned vehicle11and a second unmanned vehicle12. The first unmanned vehicle11, respectively the second unmanned vehicle12, is an autonomous vehicle adapted for independent propelled motion. Particularly, the first and/or second unmanned vehicle may be adapted for autonomous movement in at least two dimensions, e.g. allowing substantially unconstrained translation in at least two dimensions, for example for autonomous movement three dimensions, e.g. allowing substantially unconstrained translation in three dimensions. The first and/or second unmanned vehicle may allow, in addition to an autonomous translation movement, a rotation movement of at least a part thereof, e.g. a rotation of a radiation source of the first unmanned vehicle and/or a rotation of a detector of the second unmanned vehicle. This rotation movement may be a rotation around a single axis of rotation, around a pair of orthogonal axes or three orthogonal axes. For example, the unmanned vehicle may allow a substantially unconstrained positioning and orienting of a component, e.g. the source, respectively the detector, providing six degrees of freedom, e.g. three degrees of freedom of translation and three degrees of freedom of rotation.

For example the vehicle11,12may comprise a propulsion system, such as at least one propulsion engine, wheels, rotors, fluid jet outlets or a combination thereof. For example, each vehicle11,12may be a ground vehicle, aerial vehicle, space craft, watercraft, e.g. a boat, ship or hovercraft, and/or submersible vehicle. The vehicle11,12may be a drone. Each vehicle11,12may comprise a power source for sustaining the propelled motion, e.g. a combustion fuel tank, fuel cell, battery and/or solar power module.

Furthermore, each of the first and the second unmanned vehicle11,12comprises a positioning unit13for detecting a position of the corresponding vehicle11,12. The vehicle11,12may comprise a navigation unit for controlling the motion of the unmanned vehicle in response to a detected position of the vehicle, e.g. as supplied by the positioning unit13. The positioning unit13may comprise an indoor positioning system for locating the vehicle inside a building, and/or an outdoor positioning system for locating the vehicle, e.g. with respect to global coordinate system. The positioning unit may use radio waves, magnetic fields, acoustic signals, optical imaging, or other sensory information to determine a position of the vehicle with respect to a reference coordinate system. The positioning unit may comprise laser positioning and/or echo positioning to measure a distance with respect to objects in its vicinity. The reference coordinate system may be provided by anchor nodes with known position, such as global positioning system (GPS) satellites, cellular telephone network stations, WiFi access points or markers. The positioning system may furthermore be adapted for determining a relative position with respect to the target object15and/or the other vehicle. The positioning system may perform a trilateration operation to determine the position of the corresponding vehicle, the object and/or the other vehicle.

The first unmanned vehicle11comprises a source14of penetrating radiation, for example a Röntgen tube, e.g. an X-ray tube, or a gamma radiation source. For example, the source14may be a compact source of penetrating radiation, such as the XRS-3 lightweight X-ray tube, commercially available from Golden Engineering, Centerville, USA. The first unmanned vehicle11is adapted for positioning the source14such as to direct the penetrating radiation toward the target object15. For example, the unmanned vehicle11may position itself at a position such as to direct the radiation emissions, e.g. a cone of radiation, toward the object15to be imaged. Furthermore, the first unmanned vehicle11may comprise a pivotable support, e.g. at least one gimbal, that allows rotation of the source14about at least one axis of rotation. For example, two or three gimbals, mounted on to the other with orthogonal pivot axes, may be provided to improve stability of the source14under movement of the vehicle11, and/or to provide an accurate control of the emission direction of the penetrating radiation.

The second unmanned12vehicle comprises an image detector16for registering a spatial distribution of the penetrating radiation as an image. This second unmanned vehicle12is adapted for positioning the image detector16such as to register the spatial distribution of the penetrating radiation17when transmitted through the target object15.

For example, the image detector16may be a light-weight, small X-ray digital image sensor, e.g. comprising a photodiode array. Such photodiode array may have a detector surface area of less than or equal to 1 m2, e.g. less than or equal to 30 cm×30 cm, e.g. less than or equal to 20 cm×20 cm, such as, for example 120 mm by 120 mm, or even less, e.g. less than or equal to 10 cm×10 cm. This image detector16may comprise an array of pixels, e.g. at least 100 by 100 pixels, e.g. at least 500 by 500 pixels, or at least 1000 by 1000 pixels, e.g. 2400 by 2400 pixels, or even a larger number of pixels, e.g. 10000 by 10000 pixels. Each pixel may be adapted for quantifying the amount of radiation incident thereon, e.g. using a digital output value, such as a 4 bit value, an 8 bit value, a 12 bit value, a 16 bit value, a 24 bit value, a 32 bit value, or even a higher analog-to-digital conversion resolution. Particularly, the detector may have a suitably high dynamic range, e.g. in combination with low noise characteristics. For example, the C7942CA-22 may be a suitable, commercially available image detector, available from Hamamatsu Photonics, Shizuoka Pref., Japan.

Furthermore, the second unmanned vehicle12may comprise a pivotable support, e.g. at least one gimbal, that allows rotation of the image detector16about at least one axis of rotation. For example, two or three gimbals, mounted on to the other with orthogonal pivot axes, may be provided to improve stability of the image detector16under movement of the vehicle12, and/or to provide an accurate control of the image plane orientation with respect to the incident penetrating radiation.

The system also comprises a processing unit18, e.g. a processor, for controlling the propelled motion of respectively the first and the second unmanned vehicle11,12such as to acquire at least two images using the image detector16. For example, the processor may comprise a computer, an application specific integrated circuit, a field programmable gate array and/or a microprocessor, programmed and/or configured for controlling the motion of the unmanned vehicles. For example, the processing unit may comprise a digital storage memory, input and/or output means, and/or a communication module. The processing unit may be integrated in the first unmanned vehicle11, in the second unmanned vehicle12, or in a separate base station. Furthermore, the processing unit may comprise different components, e.g. a first component integrated in the first unmanned vehicle11and a second component integrated in the second unmanned vehicle12, which are adapted for exchanging data, e.g. over a wireless communication link.

The processing unit may be adapted for receiving position information from the first and/or second unmanned vehicle11,12, identifying a position of the vehicle with respect to a common position reference. The processing unit may be adapted for sending control instructions to the first and/or second unmanned vehicle11,12to adjust the position of the vehicle to a target location.

For example, the processing unit18may be adapted for receiving, e.g. as user input or via an external control interface, an indicative position of the target object15, or an indicative position of the target object may be predetermined, e.g. stored as a configuration parameter in a memory accessible to the processing unit. Likewise, a spatial extent of the object may be received, or known as a predetermined parameter. In response to this information, the processing unit may determine a first position for the first unmanned vehicle11and a second position for the second unmanned vehicle12, such that radiation emitted by the source mounted on the first unmanned vehicle target impinges on the detector mounted on the second unmanned vehicle, and the target object15may be assumed to be positioned in between the first and the second unmanned vehicle, such that the penetrating radiation impinging on the detector16varies as function of position on the imaging detector due to an interaction between the penetrating radiation and the structure of the target object.

Alternatively, the first and/or second unmanned vehicle11,12may comprise a position detector for determining the position of the target object when present. For example, an laser range finder, a camera with image recognition system, an echo-locator or a radio detector may be provided on one or each of the vehicles11,12to detect the presence of the target object, and for transmitting an indicative position of the object to the processing unit when the presence of this object is detected. Thus, the system may be adapted for finding the target object, e.g. as identified by recognition of its appearance in a camera image, the presence of a marker, or other suitable detection mechanism known in the art. The processing unit may then respond to such indicative position by controlling the movement of the first and second unmanned vehicle, e.g. similarly as described hereinabove where such information was predetermined or received as input from a user.

When the first and second unmanned vehicle have reached the target position, as controlled by the processing unit, an image may be acquired by the detector. For example, the processing unit may control the source to emit radiation and, simultaneously, the detector to acquire an image. This image may be transmitted by the detector to the processing unit.

As described hereinabove, the processing unit18is adapted for controlling the propelled motion of respectively the first and the second unmanned vehicle11,12such as to acquire at least two images using the image detector16. For example, after acquiring the first image, as described hereinabove. These at least two images correspond to at least two different projection directions of the penetrating radiation through the target object.

The processing unit may thus be adapted for sending control instructions to the first and/or second unmanned vehicle11,12, after acquiring the first image, to adjust the position of the vehicles to second target locations. As mentioned hereinabove, the processing unit18may have access to an indicative position of the target object15, as predetermined, received from a user or inferred from sensor data received from the first and/or second unmanned vehicle11,12. Taking this information and the first locations that the first, respectively the second, unmanned vehicle where positioned in to acquire the first image into account, the processing unit may determine a second position for the first unmanned vehicle11and a second position for the second unmanned vehicle12, such that radiation emitted by the source mounted on the first unmanned vehicle target impinges on the detector mounted on the second unmanned vehicle, and the target object15may be assumed to be positioned in between the first and the second unmanned vehicle, such that the penetrating radiation impinging on the detector16varies as function of position on the imaging detector due to an interaction between the penetrating radiation and the structure of the target object. When the first and second unmanned vehicle have reached the second positions, as controlled by the processing unit, a second image may be acquired by the detector. For example, the processing unit may control the source to emit radiation and, simultaneously, the detector to acquire the second image, which may be transmitted by the detector to the processing unit. These second positions may be determined by the processing unit such as to differ sufficiently from the first positions, such that the first and second image, and optionally in further iterations any further image, correspond to at least two different projection directions of the penetrating radiation through the target object.

The processing unit18is further adapted for generating data representative of an internal structure of the target object from the at least two images. For example, the processing unit may perform a three-dimensional reconstruction, e.g. a tomographic reconstruction, of the target object15. For example, the plurality of images may correspond to projection directions around the object that constitute a uniform angular sampling over an angle of at least 180°, e.g. an angle of 180° plus the fan-angle of the spatial configuration. However, embodiments of the present invention are not limited to such conventional computed tomography acquisitions. For example, the control unit may perform a partial reconstruction when a first plurality of images has been obtained, and determine a next projection angle in order to maximize the expected information content of a next image to be acquired.

The processing unit may perform an algebraic reconstruction method for reconstructing the internal structure of the object from a plurality of images, for example a discrete algebraic reconstruction method. A dynamic angle selection method may be applied to determine a sequence of projection angles for acquiring the at least two images. Furthermore, a variable distance approach may be applied. The determining of the positions of the first and second unmanned vehicle to define a projection for acquiring any of the images may also be subject to additional constraints. For example, physical constraints of the movement of the unmanned vehicles may be taken into account, e.g. constraints representative of obstructions, such as walls or other confinements of the range of motion. Such physical constraints may be received from at least one sensor integrated in the first and/or second unmanned vehicle, e.g. an echo-location sensor, camera system with a suitable image recognition system and/or a laser rangefinder. Alternatively or additionally, the processing unit may have access to a model of the physical space in which the unmanned vehicles operate, e.g. as received from a user input or pre-stored in an integrated memory or on removable data carrier. In embodiments of the present invention, the processing unit may implement a method as disclosed in “Towards in loco X-ray computed tomography,” a doctoral thesis by Andrei Dabravolski, publicly available online via http://anet.uantwerpen.be/docman/irua/c3935c/11225.pdf, and from the Universiteit Antwerpen Library, Antwerp, Belgium (see library reference http://hdl.handle.net/10067/1305000151162165141).

The contents of this prior disclosure by Dabravolski is hereby incorporated by reference. Particular features of this disclosure that may be incorporated can be found in sections 2.2, 3.2 and 4.2, which may be implemented in isolation or in combination in embodiments of the present invention, embodiments of the present invention not necessarily being limited by the disclosure in these explicitly referenced sections alone.

The processing unit may also be adapted for taking small variations in positioning of the unmanned vehicles11,12into account. For example, while the processing unit may control the movement of the unmanned vehicles11,12to determined locations, the final position reached by the unmanned vehicles11,12may be inaccurate, due to, for example, measurement errors of positioning sensors. The processing unit may therefore apply an alignment method when generating the data representative of the internal structure of the target object, e.g. a tomographic reconstruction. Such alignment methods are known in the art, e.g. as disclosed by Folkert Bleichrodt et al. in “An alignment method for fan beam tomography,” proceedings of the 1stInternational Conference on Tomography of Materials and Structures (ICTMS) 2013, p. 103-106. The contents of this disclosure by Bleichrodt et al. is hereby incorporated by reference. Particularly, a method as disclosed in section 2 of this paper may be implemented by the processing unit in accordance with embodiments of the present invention, embodiments of the present invention not necessarily being limited to features disclosed in this section alone. Furthermore, where the prior art disclosure assumes fixed and known positions of the detector and radiation source, while the object may be subject to small and unpredictable motion in between projection image acquisitions, the skilled person will understand that the disclosed approach is not necessarily limited thereto, and may, for example, equally apply to unpredictable variations in position of the source, the detector or the object, or any combination thereof.

However, the processing unit18may, additionally or alternatively, be adapted for generating the data representative of the internal structure of the target object from the at least two images using a model of the internal structure of the target object. For example, the at least two projection images may be compared to a simulated radiograph determined from such model to identify internal features of the target object, e.g. to identify a corresponding feature in each of the plurality of projection images.

In a second aspect, the present invention also relates to a method for imaging a target object. This method comprises providing a first unmanned vehicle comprising a source of penetrating radiation, and providing a second unmanned vehicle comprising an image detector for registering a spatial distribution of the penetrating radiation as an image. This first and second unmanned vehicle are autonomous vehicles adapted for independent propelled motion, and the first and the second unmanned vehicle comprise a positioning unit for detecting a position of the corresponding vehicle. The method further comprises controlling, using a processing unit, the propelled motion of the first unmanned vehicle to position the source such as to direct the penetrating radiation toward the target object. The method also comprises controlling, using the processing unit, the propelled motion of the second unmanned vehicle to position the image detector such as to register the spatial distribution of the penetrating radiation when transmitted through the target object.

The method further comprises acquiring at least two images using the image detector, wherein the propelled motion of the first unmanned vehicle and of the second unmanned vehicle is controlled such that the at least two images correspond to at least two different projection directions of the penetrating radiation through the target object. The method also comprises generating data representative of an internal structure of the target object from the at least two images, using the processing unit.

A method in accordance with embodiments of the present invention may relate to the operation of a system in accordance with embodiments of the present invention. Details of a method in accordance with embodiments of the second aspect of the present invention may therefore be clear from the description provided hereinabove relating to embodiments of the first aspect of the present invention.

Referring toFIG. 3, an exemplary method100for imaging a target object in accordance with embodiments of the present invention is illustrated. The method100comprises providing101a first unmanned vehicle11that comprises a source14of penetrating radiation, and providing102a second unmanned vehicle12that comprises an image detector16for registering a spatial distribution of the penetrating radiation as an image. The first and the second unmanned vehicle are autonomous vehicles adapted for independent propelled motion, and each of the first and the second unmanned vehicle comprises a positioning unit13for detecting a position of the corresponding vehicle.

The method100further comprises controlling103, using a processing unit18, the propelled motion of the first unmanned vehicle11to position the source14such as to direct the penetrating radiation17toward the target object15, and controlling104, using this processing unit18, the propelled motion of the second unmanned vehicle12to position the image detector such as to register the spatial distribution of the penetrating radiation when transmitted through the target object15.

The steps of controlling103the first unmanned vehicle motion and controlling104the second unmanned vehicle motion may advantageously take positioning information provided by the positioning unit13into account, e.g. positioning information provided by the positioning unit of the first unmanned vehicle and/or provided by the positioning unit of the second unmanned vehicle.

The method100may for example comprise a step of determining107the position of the target object15by the positioning unit, e.g. by processing information provided by the positioning unit in the processing unit18. This position of the target object may be determined relative to the first unmanned vehicle and/or the second unmanned vehicle, or may be determined in an absolute coordinate reference frame. However, in a method in accordance with embodiments of the present invention, the position of the target object may alternatively be known a-priori, or provided as an input, e.g. by a user.

Controlling103,104the propelled motion of the first unmanned vehicle and of the second unmanned vehicle may take the position of the target object15into account, e.g. regardless of whether this position information is determined from sensor data provided by the positioning unit13, is predetermined or is provided as input to the method by other means.

The method also comprises a step of acquiring105at least two images using the image detector16, wherein the propelled motion of the first unmanned vehicle11and of the second unmanned vehicle12is controlled103,104such that the at least two images correspond to at least two different projection directions of the penetrating radiation through the target object15.

For example, the propelled motion of the first unmanned vehicle and/or of the second unmanned vehicle may be controlled103,104such as to acquire the at least two images corresponding to the at least two different projection directions, in which the at least two different projection directions are determined by the processing unit18as a uniform angular sampling around the target object15.

The method further comprises generating106data representative of an internal structure of the target object from the at least two images, using the processing unit18. For example, generating106the data representative of the internal structure of the target object15may comprise performing a tomographic reconstruction. Such tomographic reconstruction may comprise a partial reconstruction that takes a first plurality of images of the at least two images into account. Furthermore, the method may comprise determining a further projection direction for acquiring a further image of the target object by taking the partial reconstruction into account.

The tomographic reconstruction may be performed by using a discrete algebraic reconstruction method.

The tomographic reconstruction may comprise applying a compensation method for taking unpredictable variations in positioning of the first unmanned vehicle11, the second unmanned vehicle12and/or the target object15into account.

In a third aspect, the present invention also relates to a computer program product for, if executed by a processing unit, e.g. a processing unit in a system in accordance with embodiments of the first aspect of the present invention, performing steps of a method in accordance with embodiments of the second aspect of the present invention. These performed steps comprise at least the steps of controlling103a propelled motion of a first unmanned vehicle11, controlling104a propelled motion of a second unmanned vehicle12and generating106data representative of an internal structure of a target object from at least two acquired images.