Computer-implemented method for tomosynthesis

Abstract

The invention provides a computer-implemented method for tomosynthesis, the method comprising the steps of X-ray image data acquisition by means of a 2D X-ray scanner and tomosynthesis image reconstruction from the X-ray image data. An X-ray viewing axis of the 2D X-ray scanner is moved relative to a patient table during the X-ray image data acquisition in a movement comprising at least two movement directions, and the 2D X-ray scanner is configured and arranged in such a manner that the movement is independent of guide-elements.

Description

[0001] Brainlab AG

[0002] Attorney’s File: B17950WO2

[0003] COMPUTER-IMPLEMENTED METHOD FOR TOMOSYNTHESIS

[0004] FIELD OF THE INVENTION

[0005] The present invention relates to a computer-implemented method for tomosynthesis, a corresponding computer program product and computer-readable medium, and a system for tomosynthesis.

[0006] TECHNICAL BACKGROUND

[0007] Tomosynthesis image reconstruction allows for reconstructing depth information from X-ray image data, e.g., image data acquired by a 2D X-ray scanner.

[0008] Tomosynthesis techniques involve X-ray image data acquisition by means of a 2D X-ray scanner and tomosynthesis image reconstruction from the X-ray image data. The reconstructed data usually yields a focused image for only for a limited depth range, e.g., in specific slices, whereas for other depths the images will be blurry.

[0009] Tomosynthesis (or Digital Tomosynthesis) is an X-ray imaging modality that acquires a series of projection radiographs over a limited angular range. It allows for the reconstruction of an arbitrary number of 2D image slices through the corresponding 3D volume. Usually, a tomosynthesis acquisition comprises a lower number of discrete exposures than a helical CT or traditional Cone-Beam CT acquisition. For example, tomosynthesis may entail methods using only a limited rotation angle as compared to a 180 degree or more rotation of a helical CT and accordingly may be seen as a limited-angle tomography method.

[0010] Thus, the set of projections may be considered as incomplete. The set of projections is digitally processed to yield images similar to conventional tomography with a limited depth of field. A series of slices at different depths, optionally with different thicknesses, can be reconstructed from the same acquisition. The data, i.e. set of projections, may be considered as being purposefully / systematically incomplete, e.g. rather than accidentally or due to errors.

[0011] The present invention, has the object of providing a method for tomosynthesis that improves the result of image reconstruction, particularly providing an increased depth range where the reconstructed image is in focus, rather than blurry.

[0012] The present invention can be used for medical imaging, particularly allowing for periodic or non-periodic motion of the imaged subject and / or the imaging device, e.g. in connection with a Loop-X imaging system, or navigation in medical procedures and / or together with systems for image-guided radiotherapy such as VERO® and ExacTrac®, both products of Brainlab AG.

[0013] Aspects of the present invention, examples and exemplary steps and their embodiments are disclosed in the following. Different exemplary features of the invention can be combined in accordance with the invention wherever technically expedient and feasible.

[0014] EXEMPLARY SHORT DESCRIPTION OF THE INVENTION

[0015] In the following, a short description of the specific features of the present invention is given which shall not be understood to limit the invention only to the features or a combination of the features described in this section.

[0016] The invention provides a computer-implemented method for tomosynthesis, the method comprising the steps of X-ray image data acquisition by means of a 2D X-ray scanner and tomosynthesis image reconstruction from the X-ray image data. A viewing axis of the 2D X-ray scanner is moved relative to a patient table during the X- ray image data acquisition in a movement comprising at least two movement directions, and the 2D X-ray scanner is configured and arranged in such a manner that the movement is independent of guide elements, in particular fixed-position guide-elements.

[0017] GENERAL DESCRIPTION OF THE INVENTION In this section, a description of the general features of the present invention is given for example by referring to possible embodiments of the invention.

[0018] The invention provides a computer-implemented method for tomosynthesis, a corresponding computer program product and computer-readable medium, and a system for tomosynthesis according to the independent claims. Preferred embodiments are laid down in the dependent claims.

[0019] The invention provides a computer-implemented method for tomosynthesis, the method comprising the steps of X-ray image data acquisition by means of a 2D X-ray scanner and tomosynthesis image reconstruction from the X-ray image data. A viewing axis of the 2D X-ray scanner is moved relative to a patient table during the X- ray image data acquisition in a movement comprising at least two movement directions, and the 2D X-ray scanner is configured and arranged in such a manner that the movement is independent of guide elements, in particular fixed-position guide-elements.

[0020] By providing the two movement directions, additional image data is obtained as compared to known methods, which only include scans along an axis. Said data, when used for tomosynthesis image reconstruction, allows for improved depth information and / or correction of parallax errors.

[0021] When the scanner only carries out a translational movement along the scanning direction, limited depth information in tomosynthesis images will be obtained. The angular coverage range of incident X-rays, in this case, is equivalent to the effective X-ray opening angle that can be captured by the detector. This coverage range of X-rays is important for 3D reconstruction. An entirely correctly reconstructed 3D image can only be reconstructed if the coverage range of incident X-rays is 180°.

[0022] The present application envisions increasing accuracy by combining the translational movement, e.g. along the scanning direction, with a rotational movement. Said additional movement will yield image data allowing to increase the effective coverage range and, when incorporated in the reconstruction, improves depth information.

[0023] As will be seen below in more detail, coverage range can be increased by a gantry tilt in and / or against the translational direction. Such gantry tilt is supported, for example by some imaging rings like the Loop-X. Accordingly, depth reconstruction is improved.

[0024] Alternatively, coverage range can be increased by a rotation in a plane that is essentially perpendicular to the translational movement direction. For example, source and / or detector may rotate around an axis that is parallel to the translational movement direction. In such a scenario, a relative position between source and detector may remain the same, i.e., they may be rotated together, or their relative position may change, e.g., by independent rotation of source and detector. For example, source arm and detector may be independently movable.

[0025] Image reconstruction may be based on an inverse Radon transform, for example. Image reconstruction may entail filtered back projection combined with methods allowing to compensate for the incomplete data set of tomosynthesis imaging, for example by means of iterative algorithms or machine learning methods such as deep-learning.

[0026] The viewing axis of the 2D X-ray scanner may, for example, correspond to the effective central axis of a central beam, for example, in case of a cone beam CT, a cone axis. It is noted that, particularly, the viewing axis may be the viewing axis from the perspective of the detector of the X-ray scanner, for example, the effective central axis of a central beam as received at the detector. In some cases this may coincide with the viewing axis as perceived by the X-ray source, but in some scanner configurations, this may not be the case.

[0027] The scanner being configured and arranged in such a manner that the movement is independent of a, in particular fixed-position, guide-element may, in other words, be referred to as a freely movable scanner or as an independently movable scanner. Particularly, the scanner may be independently or freely movable on a floor.

[0028] Particularly, the scanner may be configured and arranged in such a manner that the movement is independent of guide elements, in particular fixed-position guide-elements like rails or tracks or railings.

[0029] The 2D X-ray scanner being moved in a movement comprising at least two movement directions may comprise a first movement along a main scanning direction, for example along the length of the patient table, superimposed with a second movement in another direction, for example perpendicular to the main scanning direction.

[0030] As an example, in case of a ring-shaped X-ray imaging system, the source and detector arranged on a ring, the ring may be moved in a translational movement along a first axis, e.g. parallel to the main scanning direction. The second movement may be a rotation around an axis parallel to said first axis or around an axis that is perpendicular to said first axis.

[0031] The movement may be a continuous movement. In particular, the movement may be a continuous movement in at least one of the at least two movement directions, in particular in the at least two movement directions. As an example, at least the movement along a / the main scanning direction, for example along the length of the patient table, may be a continuous movement. A movement superimposed with the movement along the main scanning direction may be continuous or may be continuous, optionally except for at a reversal point in case of alternating movement directions, e.g. when wobbling.

[0032] The 2D X-ray scanner is also referred to as “scanner” throughout the present disclosure for the sake of readability.

[0033] The X-ray imaging system may comprise a CT (computed tomography) imaging system. In particular, the medical imaging system may comprise a CBCT (cone beam CT).

[0034] The X-ray imaging system may be an autonomously movable system. The X- ray imaging system may have a tiltable gantry, which may be ring-shaped, or C-arm.

[0035] As an example, the X-ray imaging system may be configured such that several degrees of freedom are possible, including one or more of C-arm tilt, gantry-tilt, C- arm-yaw, gantry-yaw, longitudinal translational movements of the gantry or C-arm. A trajectory of the gantry or C-arm combining two or more of these motions of the gantry or C-arm may be referred to as saddle trajectories.

[0036] According to the present disclosure, the X-ray imaging system may comprise a tiltable gantry or a tiltable C-arm, particularly a gantry configured such that its rotation plane is tiltable or a C-arm configured such that its rotation plane is tiltable. An example for such an X-ray imaging system is the Loop-X. In general, medical imaging systems allow for rotation of the source and detector in a plane. In addition, some imaging systems allow for a translational movement, e.g., in a direction perpendicular to the plane. According to the present disclosure, the gantry or C-arm may be configured and mounted such that the plane itself may be tilted. For example, the gantry may rotate around an axis that is parallel to the longitudinal axis of a patient bed. The gantry, in addition, may describe a translational movement in a direction parallel to the longitudinal axis. The gantry may also tilt around a horizontal axis that is perpendicular to the longitudinal axis, e.g., towards and against the translational movement direction.

[0037] For example, a tilt rotation of the C-arm or gantry may be a rotation around hinges used for mounting the C-arm or gantry, e.g., mounted to a fixed or movable support structure like one or more feet, particularly a support structure movable on wheels.

[0038] According to the present disclosure, the X-ray imaging system may comprise a gantry or a C-arm, particularly a tiltable gantry or a tiltable C-arm as described above, and the X-ray imaging system may be configured such that the gantry or the C-arm are movable to describe a yaw rotation. For example, a yaw rotation may be achieved by a wheeled support structure to which the C-arm or gantry is mounted, wherein particularly the wheeled support structure may be driven via traction, e.g., using back wheels. As an example, all wheels might be set to a 45 ° so as to form a circle yaw rotation.

[0039] The method may comprise using a tracking device for providing positional awareness of the medical imaging system. As an example, a tracking device may be a camera, for example, infrared (IR) or in the visible spectrum, configured for tracking markers. Hereinbelow, the terms “tracking device” and “tracking system” are used interchangeably.

[0040] A patient table, according to the present disclosure, is where the subject of the X-ray imaging, e.g. a patient, is located during the X-ray image acquisition and any suitable known patient table may be used. As briefly mentioned above, according to the present disclosure, the movement may comprise a translational movement along a first axis and a superimposed rotational movement around a second axis.

[0041] The first axis may be parallel to the main scanning direction mentioned above, e.g. along the length of the patient bed. The rotational movement may comprise tilting backwards and / or forwards. Alternatively or in addition, the rotational movement may comprise a sideways rotation, particularly around the first axis, as compared to the translational movement.

[0042] As an example, in case of a ring-shaped X-ray imaging system, the source and detector arranged on a ring, the ring may be moved in a translational movement along the first axis.

[0043] The tilting backwards and / or forwards may be carried out in an angular range selected to avoid collisions with other components of the X-ray imaging system, the patient bed, and the patient.

[0044] The sideways rotation may be selectable more freely, for example as collisions are less likely and the movement may not necessarily entail the entire C-arm or gantry, but may entail moving only part thereof, e.g. a part that holds the X-ray source and / or a part that holds the detector.

[0045] According to the present disclosure, the second axis may be perpendicular to the first axis. This may result in a tilting movement backwards and / or forwards with respect to the translational movement, i.e., in or against the direction of the translational movement. Additional angles provide additional information that can be used for improving depth resolution.

[0046] According to the present disclosure, the second axis may be parallel with, in particular coincide with, the first axis. This may result in a rotational movement sideways with respect to the translational movement. Also in this case, additional angles provide additional information that can be used for improving depth resolution.

[0047] According to the present disclosure, the first axis may be parallel to or coincide with a patient table’s longitudinal axis. That is, the translational movement may be along the longitudinal axis of the patient table. Accordingly, the translational movement may be along the patient lengthwise. This allows for scanning a region of interest extending beyond the field of view of the scanner in a single position.

[0048] According to the present disclosure, the rotational movement may comprise repeated alternating rotations in opposite directions.

[0049] Particularly, the frequency of changing the rotation direction may depend on the speed of the translational movement. As an example, for a given speed of translational movement, a predetermined frequency value or an interval of frequency values may be retrieved and set as the frequency of changing the rotation direction. For example, said frequency may be selected so as to allow for multiple angles to be covered while an area of interest is in a field of view of the scanner.

[0050] Alternating movements provide many additional views and may cover two sides of a patient, for example, which allows for improving depth information to a higher degree.

[0051] According to the present disclosure, the rotational movement may be a wobbling movement. A wobbling movement is a rotational movement comprising repeated alternating rotations in opposite directions, particularly the directions alternating at a customizable frequency.

[0052] According to the present disclosure, the rotational movement may comprise a rotational movement of an X-ray source during X-ray image data acquisition. Alternatively or in addition, the rotational movement may comprise a rotational movement of an X-ray detector during X-ray image data acquisition.

[0053] In other words, the rotational movement of the viewing direction may be implemented by a corresponding rotational movement of the X-ray source and / or X- ray detector. The X-ray detector may be a flat panel detector.

[0054] X-ray source and X-ray detector may be arranged in a common plane. The rotational movement may comprise tilting said plane. Alternatively or in addition, the rotational movement may comprise a rotational movement of X-ray source and / or X- ray detector in said plane, for example by rotating a source arm and / or a detector arm. Such movement is well defined and supported by many systems. In particular, the rotational movement may comprise a coordinated, particularly synchronous, rotational movement of the X-ray source and the X-ray detector. This may particularly be the case for the rotation in said common plane.

[0055] According to the present disclosure, the rotational movement may comprise a rotational movement of a C-arm or ring gantry on which the X-ray source and X-ray detector are mounted. In particular, according to the present disclosure, the rotational movement may comprise a tilting movement of a gantry during X-ray image data acquisition. The tilting movement may, in particular, be a tilting movement in or against the translational movement direction.

[0056] According to the present disclosure, the translational movement may comprise a translational movement of the 2D X-ray scanner. In other words, the translational movement of the viewing direction may be achieved via a translational movement of the scanner. The scanner may, for example, move along a longitudinal direction of a patient bed, e.g. for performing a lengthwise scan of a patient.

[0057] According to the present disclosure, the 2D X-ray scanner may be mounted on a wheeled device configured to allow for moving the 2D X-ray scanner. In particular, the wheeled device may be a non-rail-borne wheeled device. The wheeled device may drive on any floor, thereby allowing for universal applicability of the method, irrespective of the environment where the method is carried out.

[0058] According to the present disclosure, the movement, in particular the translational movement, may comprise moving the wheeled device relative to the patient table. Thus, for example, the wheeled device may drive along a patient table to accomplish an X-ray scan along the driving direction. In view of the freely movable device on wheels, the scanning direction can be chosen freely and the device can be used in any environment.

[0059] According to the present disclosure, the wheeled device may comprise four independently steerable wheels, in particular with rear wheels having an active drive. This allows for particularly flexible use of the device.

[0060] According to the present disclosure, the wheeled device may, for example, be an automated guided vehicle, AGV. This is advantageous, since this type of vehicle may be suitable for autonomously positioning itself, particularly by means of an integrated and / or an external tracking system.

[0061] The method of the present disclosure may further comprise optical tracking, wherein the optical tracking may comprise tracking a position of the 2D X-ray scanner and / or an orientation of the 2D X-ray scanner.

[0062] Optical tracking may be carried out using a tracking device.

[0063] As described above, according to the present disclosure, the X-ray imaging system may be a wheeled system, particularly that is autonomously movable, and the method may comprise using a / the tracking device for providing positional awareness of the medical imaging system. Hereinbelow, the terms “tracking device” and “tracking system” are used interchangeably. As an example, the tracking device may be a camera, for example, infrared (IR) or in the visible spectrum, configured for tracking markers.

[0064] The method may comprise tracking the X-ray imaging system, specifically its spatial arrangement relative to a room, a patient bed, and / or a patient. The tracking may entail a marker-based tracking.

[0065] The X-ray imaging system may comprise the tracking device and / or an external tracking device may be used. The tracking may be a marker-based tracking and markers may be provided in the room, particularly on the floor, on a patient bed, on the patient, and / or on the X-ray imaging system. The external tracking device may be part of a surgical navigation system.

[0066] Information obtained by the tracking may be used to take into account the actual arrangement of the X-ray imaging device at the time of image acquisition so as to provide improved image reconstruction. Moreover, the information may be used for controlling movement of the X-ray imaging device, e.g., according to a predetermined trajectory.

[0067] According to the present disclosure, the X-ray image data acquisition may be carried out in a manner allowing for non-isocentricity of the 2D X-ray scanner.

[0068] When carrying out the imaging, particularly with the movement having the movement direction as described above, it may not be the case that the region of interest, e.g., the patient is in the physical isocenter of the 2D X-ray scanner. As an example, independent rotation of the source and / or detector and / or a superposition of translation and rotation / tilt may be applied such that the imaging center is not in the physical isocenter.

[0069] For example, a source and a detector may rotate around an axis parallel to the movement direction of the translational movement. The source may be rotated faster and / or with larger range than the detector, e.g. a range of + / - 20° for the source and a range of + / - 10° of the detector. When the source oscillates around 0° and the detector oscillates around 180° relative to a given reference point, such a rotation would cause an imaging center to shift away from the physical isocenter, e.g., downwards. The method may entail adjusting the collimation accordingly, e.g., to ensure that the radiation is properly received by the detector.

[0070] As another example, the plane in which source and detector are arranged may carry out a tiling movement around a rotation axis being perpendicular to the movement direction of the translational movement, e.g., the gantry or arm may tilt forwards and / or backwards. The rotation axis may not be through the mechanical isocenter, particularly, be located lower than the mechanical isocenter, e.g. due to where the bearings are located.

[0071] To achieve a tilt movement around an effective tilt axis at a desired height, the tilt motion can be combined with a translational movement at a suitable speed. The selection of the tilt height may support improved sampling of X-rays at specific heights of the imaged object (i.e. at a specific tomosynthesis slice).

[0072] According to the present disclosure, the tomosynthesis image reconstruction may comprise a reconstruction based on filtered backprojection, FBP, particularly with adequate, trajectory-specific weighting.

[0073] Alternatively or in addition, the tomosynthesis image reconstruction may comprise iterative reconstruction, which optionally incorporates for initialization the FBP and / or a, particularly 3D, deconvolution (of the projections) using a set of known point spread functions, PSF, that is derived from the geometries of the tomosynthesis data acquisition. According to the present disclosure, the 2D X-ray scanner may be a cone beam computed tomography, CBCT, scanner. In a CBCT, the X-rays are divergent, forming a cone. The viewing axis for a CBCT may, for example, be the cone axis.

[0074] In some examples of the present disclosure, the projection direction during thomosynthesis may vary dependent on the imaged anatomy during image acquisition. This may be referred to as adaptive image acquisition. For example, such varying of the projection direction dependent on the imaged anatomy may comprise image-based and / or tracking-based (e.g. using marker-based techniques) detection of an anatomy or part thereof. For example, this may allow for better acquisition and reconstruction of images.

[0075] In some examples, the adaptive imaging is carried out in the context of angiography.

[0076] In particular, in some examples, the adaptive imaging is carried out in the context of projecting vessels, particularly a 3D vessel segmentation, into a sequence of (e.g. live / real-time) fluoroscopic images. This can be done at any angle and position due to the nature of the tomosynthesis according to the present disclosure.

[0077] 3D vessel segmentation obtained from tomosynthesis according to the present disclosure, particularly combined with adaptive imaging, may allow, among others, for overlaying a projection of the vessel (which may be referred to as a 2D projected vessel mask) with fluoroscopic image sequences (also be referred to as roadmapping) from any angle and, consequently, allows for lower radiation and contrast agent doses. This is not possible with conventional 2D DSA (digital subtraction angiography) approaches, since the 2D fluoroscopy and 2D vessels mask (i.e. roadmap) must have been generated using exactly the same projection I imaging geometry.

[0078] As mentioned above, the present disclosure also provides a system, computer program product, and computer readable medium according to the independent claims.

[0079] The present disclosure provides a system for tomosynthesis, the system comprising an X-ray imaging system comprising a 2D X-ray scanner, configured to carry out X-ray image data acquisition, and a processing system configured to carry out tomosynthesis image reconstruction from the X-ray image data. The system is configured to move a viewing axis of the 2D X-ray scanner relative to a patient table during the X-ray image data acquisition in a movement comprising at least two movement directions. The 2D X-ray scanner is configured and arranged in such a manner that the movement is independent of guide elements, in particular fixed- position guide-elements.

[0080] The X-ray imaging system may comprise a CT (computed tomography) imaging system. In particular, the medical imaging system may comprise a CBCT (cone beam CT). Specifically, the 2D X-ray scanner may be a cone beam computed tomography, CBCT, scanner.

[0081] The system may comprise a wheeled device, the wheeled device particularly being a non-rail-borne wheeled device. The 2D X-ray scanner may be mounted on the wheeled device and the wheeled device may be configured to move the 2D X-ray scanner. The movement, in particular a translational movement, of the viewing axis of the 2D X-ray scanner may comprise moving the wheeled device relative to the patient table.

[0082] The wheeled device may comprise four independently steerable wheels, in particular with rear wheels having active drive, also referred to as traction.

[0083] The wheeled device may, for example, be an automated guided vehicle, AGV.

[0084] According to the present disclosure, the system may be configured to carry out the method according to the present disclosure, particularly of the method claims, in particular, wherein the method steps are controlled and / or carried out by the processing system.

[0085] The X-ray imaging system may be an autonomously movable system. The X- ray imaging system may have a tiltable gantry or C-arm.

[0086] As an example, the X-ray imaging system may be configured such that several degrees of freedom are possible, including one or more of C-arm tilt, gantry-tilt, C- arm-yaw, gantry-yaw, longitudinal translational movements of the gantry or C-arm. A trajectory of the gantry or C-arm combining two or more of these motions of the gantry or C-arm may be referred to as saddle trajectories. According to the present disclosure, the X-ray imaging system may comprise a tiltable gantry or a tiltable C-arm, particularly a gantry configured such that its rotation plane is tiltable or a C-arm configured such that its rotation plane is tiltable.

[0087] An example for such an X-ray imaging system is the Loop-X. In general, medical imaging systems allow for rotation of the source and detector in a plane. In addition, some imaging systems allow for a translational movement, e.g., in a direction perpendicular to the plane. According to the present disclosure, the gantry or C-arm may be configured and mounted such that the plane itself may be tilted. For example, the gantry may rotate around an axis that is parallel to the longitudinal axis of a patient bed. The gantry, in addition, may describe a translational movement in a direction parallel to the longitudinal axis. The gantry may also tilt around a horizontal axis that is perpendicular to the longitudinal axis, e.g., towards and against the translational movement direction.

[0088] For example, a tilt rotation of the C-arm or gantry may be a rotation around hinges used for mounting the C-arm or gantry, e.g., mounted to a fixed or movable support structure like one or more feet, particularly a support structure movable on wheels.

[0089] According to the present disclosure, the X-ray imaging system may comprise a gantry or a C-arm, particularly a tiltable gantry or a tiltable C-arm as described above, and the X-ray imaging system may be configured such that the gantry or the C-arm are movable to describe a yaw rotation. For example, a yaw rotation may be achieved by a wheeled support structure to which the C-arm or gantry is mounted, wherein particularly the wheeled support structure may be driven via traction, e.g., using back wheels. As an example, all wheels might be set to a 45 ° so as to form a circle yaw rotation.

[0090] The present disclosure also provides a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to control and / or carry out any of the steps of the method according to the present disclosure, particularly of the method claims.

[0091] The present disclosure also provides a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to control and / or carry out any of the steps of the method according to the present disclosure, particularly of the method claims.

[0092] The present disclosure also relates to the use of the method and / or system of the present disclosure for medical imaging.

[0093] For the sake of completeness, it is noted that for example the invention does not involve or in particular comprise or encompass an invasive step which would represent a substantial physical interference with the body requiring professional medical expertise to be carried out and entailing a substantial health risk even when carried out with the required professional care and expertise. For example, the invention does not comprise a step of positioning a medical implant in order to fasten it to an anatomical structure or a step of fastening the medical implant to the anatomical structure or a step of preparing the anatomical structure for having the medical implant fastened to it. More particularly, the invention does not involve or in particular comprise or encompass any surgical or therapeutic activity. The invention is instead directed as applicable to medical imaging, navigation, positioning and / or alignment. For this reason alone, no surgical or therapeutic activity and in particular no surgical or therapeutic step is necessitated or implied by carrying out the invention.

[0094] The features and advantages outlined above in the context of the method similarly apply to the system, use, computer program product and computer readable medium of the present disclosure.

[0095] DEFINITIONS

[0096] In this section, definitions for specific terminology used in this disclosure are offered which also form part of the present disclosure.

[0097] Computer implemented method

[0098] The method in accordance with the invention is for example a computer implemented method. For example, all the steps or merely some of the steps (i.e. less than the total number of steps) of the method in accordance with the invention can be executed by a computer (for example, at least one computer). An embodiment of the computer implemented method is a use of the computer for performing a data processing method. An embodiment of the computer implemented method is a method concerning the operation of the computer such that the computer is operated to perform one, more or all steps of the method.

[0099] The computer for example comprises at least one processor and for example at least one memory in order to (technically) process the data, for example electronically and / or optically. The processor being for example made of a substance or composition which is a semiconductor, for example at least partly n- and / or p-doped semiconductor, for example at least one of II-, III-, IV-, V-, Vl-semiconductor material, for example (doped) silicon and / or gallium arsenide. The calculating or determining steps described are for example performed by a computer. Determining steps or calculating steps are for example steps of determining data within the framework of the technical method, for example within the framework of a program. A computer is for example any kind of data processing device, for example electronic data processing device. A computer can be a device which is generally thought of as such, for example desktop PCs, notebooks, netbooks, etc., but can also be any programmable apparatus, such as for example a mobile phone or an embedded processor. A computer can for example comprise a system (network) of "subcomputers", wherein each sub-computer represents a computer in its own right. The term "computer" includes a cloud computer, for example a cloud server. The term "cloud computer" includes a cloud computer system which for example comprises a system of at least one cloud computer and for example a plurality of operatively interconnected cloud computers such as a server farm. Such a cloud computer is preferably connected to a wide area network such as the world wide web (WWW) and located in a so-called cloud of computers which are all connected to the world wide web. Such an infrastructure is used for "cloud computing", which describes computation, software, data access and storage services which do not require the end user to know the physical location and / or configuration of the computer delivering a specific service. For example, the term "cloud" is used in this respect as a metaphor for the Internet (world wide web). For example, the cloud provides computing infrastructure as a service (laaS). The cloud computer can function as a virtual host for an operating system and / or data processing application which is used to execute the method of the invention. The cloud computer is for example an elastic compute cloud (EC2) as provided by Amazon Web Services™. A computer for example comprises interfaces in order to receive or output data and / or perform an analogue-to-digital conversion. The data are for example data which represent physical properties and / or which are generated from technical signals. The technical signals are for example generated by means of (technical) detection devices (such as for example devices for detecting marker devices) and / or (technical) analytical devices (such as for example devices for performing (medical) imaging methods), wherein the technical signals are for example electrical or optical signals. The technical signals for example represent the data received or outputted by the computer. The computer is preferably operatively coupled to a display device which allows information outputted by the computer to be displayed, for example to a user. One example of a display device is a virtual reality device or an augmented reality device (also referred to as virtual reality glasses or augmented reality glasses) which can be used as "goggles" for navigating. A specific example of such augmented reality glasses is Google Glass (a trademark of Google, Inc.). An augmented reality device or a virtual reality device can be used both to input information into the computer by user interaction and to display information outputted by the computer. Another example of a display device would be a standard computer monitor comprising for example a liquid crystal display operatively coupled to the computer for receiving display control data from the computer for generating signals used to display image information content on the display device. A specific embodiment of such a computer monitor is a digital lightbox. An example of such a digital lightbox is Buzz®, a product of Brainlab AG. The monitor may also be the monitor of a portable, for example handheld, device such as a smart phone or personal digital assistant or digital media player.

[0100] The invention also relates to a program which, when running on a computer, causes the computer to perform one or more or all of the method steps described herein and / or to a program storage medium on which the program is stored (in particular in a non-transitory form) and / or to a computer comprising said program storage medium and / or to a (physical, for example electrical, for example technically generated) signal wave, for example a digital signal wave, carrying information which represents the program, for example the aforementioned program, which for example comprises code means which are adapted to perform any or all of the method steps described herein.

[0101] Within the framework of the invention, computer program elements can be embodied by hardware and / or software (this includes firmware, resident software, micro-code, etc.). Within the framework of the invention, computer program elements can take the form of a computer program product which can be embodied by a computer-usable, for example computer-readable data storage medium comprising computer-usable, for example computer-readable program instructions, "code" or a "computer program" embodied in said data storage medium for use on or in connection with the instruction-executing system. Such a system can be a computer; a computer can be a data processing device comprising means for executing the computer program elements and / or the program in accordance with the invention, for example a data processing device comprising a digital processor (central processing unit or CPU) which executes the computer program elements, and optionally a volatile memory (for example a random access memory or RAM) for storing data used for and / or produced by executing the computer program elements. Within the framework of the present invention, a computer-usable, for example computer-readable data storage medium can be any data storage medium which can include, store, communicate, propagate or transport the program for use on or in connection with the instructionexecuting system, apparatus or device. The computer-usable, for example computer- readable data storage medium can for example be, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared or semiconductor system, apparatus or device or a medium of propagation such as for example the Internet. The computer- usable or computer-readable data storage medium could even for example be paper or another suitable medium onto which the program is printed, since the program could be electronically captured, for example by optically scanning the paper or other suitable medium, and then compiled, interpreted or otherwise processed in a suitable manner. The data storage medium is preferably a non-volatile data storage medium. The computer program product and any software and / or hardware described here form the various means for performing the functions of the invention in the example embodiments. The computer and / or data processing device can for example include a guidance information device which includes means for outputting guidance information. The guidance information can be outputted, for example to a user, visually by a visual indicating means (for example, a monitor and / or a lamp) and / or acoustically by an acoustic indicating means (for example, a loudspeaker and / or a digital speech output device) and / or tactilely by a tactile indicating means (for example, a vibrating element or a vibration element incorporated into an instrument). For the purpose of this document, a computer is a technical computer which for example comprises technical, for example tangible components, for example mechanical and / or electronic components. Any device mentioned as such in this document is a technical and for example tangible device.

[0102] Acquiring data

[0103] The expression "acquiring data" for example encompasses (within the framework of a computer implemented method) the scenario in which the data are determined by the computer implemented method or program. Determining data for example encompasses measuring physical quantities and transforming the measured values into data, for example digital data, and / or computing (and e.g. outputting) the data by means of a computer and for example within the framework of the method in accordance with the invention. The meaning of "acquiring data" also for example encompasses the scenario in which the data are received or retrieved by (e.g. input to) the computer implemented method or program, for example from another program, a previous method step or a data storage medium, for example for further processing by the computer implemented method or program. Generation of the data to be acquired may but need not be part of the method in accordance with the invention. The expression "acquiring data" can therefore also for example mean waiting to receive data and / or receiving the data. The received data can for example be inputted via an interface. The expression "acquiring data" can also mean that the computer implemented method or program performs steps in order to (actively) receive or retrieve the data from a data source, for instance a data storage medium (such as for example a ROM, RAM, database, hard drive, etc.), or via the interface (for instance, from another computer or a network). The data acquired by the disclosed method or device, respectively, may be acquired from a database located in a data storage device which is operably to a computer for data transfer between the database and the computer, for example from the database to the computer. The computer acquires the data for use as an input for steps of determining data. The determined data can be output again to the same or another database to be stored for later use. The database or database used for implementing the disclosed method can be located on network data storage device or a network server (for example, a cloud data storage device or a cloud server) or a local data storage device (such as a mass storage device operably connected to at least one computer executing the disclosed method). The data can be made "ready for use" by performing an additional step before the acquiring step. In accordance with this additional step, the data are generated in order to be acquired. The data are for example detected or captured (for example by an analytical device). Alternatively or additionally, the data are inputted in accordance with the additional step, for instance via interfaces. The data generated can for example be inputted (for instance into the computer). In accordance with the additional step (which precedes the acquiring step), the data can also be provided by performing the additional step of storing the data in a data storage medium (such as for example a ROM, RAM, CD and / or hard drive), such that they are ready for use within the framework of the method or program in accordance with the invention. The step of "acquiring data" can therefore also involve commanding a device to obtain and / or provide the data to be acquired. In particular, the acquiring step does not involve an invasive step which would represent a substantial physical interference with the body, requiring professional medical expertise to be carried out and entailing a substantial health risk even when carried out with the required professional care and expertise. In particular, the step of acquiring data, for example determining data, does not involve a surgical step and in particular does not involve a step of treating a human or animal body using surgery or therapy. In order to distinguish the different data used by the present method, the data are denoted (i.e. referred to) as "XY data" and the like and are defined in terms of the information which they describe, which is then preferably referred to as "XY information" and the like.

[0104] Registering

[0105] The n-dimensional image of a body is registered when the spatial location of each point of an actual object within a space, for example a body part in an operating theatre, is assigned an image data point of an image (CT, MR, etc.) stored in a navigation system. Image registration

[0106] Image registration is the process of transforming different sets of data into one coordinate system. The data can be multiple photographs and / or data from different sensors, different times or different viewpoints. It is used in computer vision, medical imaging and in compiling and analysing images and data from satellites. Registration is necessary in order to be able to compare or integrate the data obtained from these different measurements.

[0107] Marker

[0108] It is the function of a marker to be detected by a marker detection device (for example, a camera or an ultrasound receiver or analytical devices such as CT or MRI devices) in such a way that its spatial position (i.e. its spatial location and / or alignment) can be ascertained. The detection device is for example part of a navigation system. The markers can be active markers. An active marker can for example emit electromagnetic radiation and / or waves which can be in the infrared, visible and / or ultraviolet spectral range. A marker can also however be passive, i.e. can for example reflect electromagnetic radiation in the infrared, visible and / or ultraviolet spectral range or can block x-ray radiation. To this end, the marker can be provided with a surface which has corresponding reflective properties or can be made of metal in order to block the x-ray radiation. It is also possible for a marker to reflect and / or emit electromagnetic radiation and / or waves in the radio frequency range or at ultrasound wavelengths. A marker preferably has a spherical and / or spheroid shape and can therefore be referred to as a marker sphere; markers can however also exhibit a cornered, for example cubic, shape.

[0109] Marker device

[0110] A marker device can for example be a reference star or a pointer or a single marker or a plurality of (individual) markers which are then preferably in a predetermined spatial relationship. A marker device comprises one, two, three or more markers, wherein two or more such markers are in a predetermined spatial relationship. This predetermined spatial relationship is for example known to a navigation system and is for example stored in a computer of the navigation system.

[0111] In another embodiment, a marker device comprises an optical pattern, for example on a two-dimensional surface. The optical pattern might comprise a plurality of geometric shapes like circles, rectangles and / or triangles. The optical pattern can be identified in an image captured by a camera, and the position of the marker device relative to the camera can be determined from the size of the pattern in the image, the orientation of the pattern in the image and the distortion of the pattern in the image. This allows determining the relative position in up to three rotational dimensions and up to three translational dimensions from a single two-dimensional image.

[0112] The position of a marker device can be ascertained, for example by a medical navigation system. If the marker device is attached to an object, such as a bone or a medical instrument, the position of the object can be determined from the position of the marker device and the relative position between the marker device and the object. Determining this relative position is also referred to as registering the marker device and the object. The marker device or the object can be tracked, which means that the position of the marker device or the object is ascertained twice or more over time.

[0113] Marker holder

[0114] A marker holder is understood to mean an attaching device for an individual marker which serves to attach the marker to an instrument, a part of the body and / or a holding element of a reference star, wherein it can be attached such that it is stationary and advantageously such that it can be detached. A marker holder can for example be rod-shaped and / or cylindrical. A fastening device (such as for instance a latching mechanism) for the marker device can be provided at the end of the marker holder facing the marker and assists in placing the marker device on the marker holder in a force fit and / or positive fit.

[0115] Pointer A pointer is a rod which comprises one or more - advantageously, two - markers fastened to it and which can be used to measure off individual co-ordinates, for example spatial co-ordinates (i.e. three-dimensional co-ordinates), on a part of the body, wherein a user guides the pointer (for example, a part of the pointer which has a defined and advantageously fixed position with respect to the at least one marker attached to the pointer) to the position corresponding to the co-ordinates, such that the position of the pointer can be determined by using a surgical navigation system to detect the marker on the pointer. The relative location between the markers of the pointer and the part of the pointer used to measure off co-ordinates (for example, the tip of the pointer) is for example known. The surgical navigation system then enables the location (of the three-dimensional co-ordinates) to be assigned to a predetermined body structure, wherein the assignment can be made automatically or by user intervention.

[0116] Reference star

[0117] A "reference star" refers to a device with a number of markers, advantageously three markers, attached to it, wherein the markers are (for example detachably) attached to the reference star such that they are stationary, thus providing a known (and advantageously fixed) position of the markers relative to each other. The position of the markers relative to each other can be individually different for each reference star used within the framework of a surgical navigation method, in order to enable a surgical navigation system to identify the corresponding reference star on the basis of the position of its markers relative to each other. It is therefore also then possible for the objects (for example, instruments and / or parts of a body) to which the reference star is attached to be identified and / or differentiated accordingly. In a surgical navigation method, the reference star serves to attach a plurality of markers to an object (for example, a bone or a medical instrument) in order to be able to detect the position of the object (i.e. its spatial location and / or alignment). Such a reference star for example features a way of being attached to the object (for example, a clamp and / or a thread) and / or a holding element which ensures a distance between the markers and the object (for example in order to assist the visibility of the markers to a marker detection device) and / or marker holders which are mechanically connected to the holding element and which the markers can be attached to.

[0118] Navigation system

[0119] The present disclosure may be applied in the context of a navigation system for computer-assisted surgery. This navigation system preferably comprises the aforementioned computer for processing the data provided in accordance with the computer implemented method as described in any one of the embodiments described herein. The navigation system preferably comprises a detection device for detecting the position of detection points which represent the main points and auxiliary points, in order to generate detection signals and to supply the generated detection signals to the computer, such that the computer can determine the absolute main point data and absolute auxiliary point data on the basis of the detection signals received. A detection point is for example a point on the surface of the anatomical structure which is detected, for example by a pointer. In this way, the absolute point data can be provided to the computer. The navigation system also preferably comprises a user interface for receiving the calculation results from the computer (for example, the position of the main plane, the position of the auxiliary plane and / or the position of the standard plane). The user interface provides the received data to the user as information. Examples of a user interface include a display device such as a monitor, or a loudspeaker. The user interface can use any kind of indication signal (for example a visual signal, an audio signal and / or a vibration signal). One example of a display device is an augmented reality device (also referred to as augmented reality glasses) which can be used as so-called "goggles" for navigating. A specific example of such augmented reality glasses is Google Glass (a trademark of Google, Inc.). An augmented reality device can be used both to input information into the computer of the navigation system by user interaction and to display information outputted by the computer.

[0120] The invention also relates to a navigation system for computer-assisted surgery, comprising: a computer for processing the absolute point data and the relative point data; a detection device for detecting the position of the main and auxiliary points in order to generate the absolute point data and to supply the absolute point data to the computer; a data interface for receiving the relative point data and for supplying the relative point data to the computer; and a user interface for receiving data from the computer in order to provide information to the user, wherein the received data are generated by the computer on the basis of the results of the processing performed by the computer.

[0121] Surgical navigation system

[0122] A navigation system, such as a surgical navigation system, is understood to mean a system which can comprise: at least one marker device; a transmitter which emits electromagnetic waves and / or radiation and / or ultrasound waves; a receiver which receives electromagnetic waves and / or radiation and / or ultrasound waves; and an electronic data processing device which is connected to the receiver and / or the transmitter, wherein the data processing device (for example, a computer) for example comprises a processor (CPU) and a working memory and advantageously an indicating device for issuing an indication signal (for example, a visual indicating device such as a monitor and / or an audio indicating device such as a loudspeaker and / or a tactile indicating device such as a vibrator) and a permanent data memory, wherein the data processing device processes navigation data forwarded to it by the receiver and can advantageously output guidance information to a user via the indicating device. The navigation data can be stored in the permanent data memory and for example compared with data stored in said memory beforehand.

[0123] Landmarks

[0124] A landmark is a defined element of an anatomical body part which is always identical or recurs with a high degree of similarity in the same anatomical body part of multiple patients. Typical landmarks are for example the epicondyles of a femoral bone or the tips of the transverse processes and / or dorsal process of a vertebra. The points (main points or auxiliary points) can represent such landmarks. A landmark which lies on (for example on the surface of) a characteristic anatomical structure of the body part can also represent said structure. The landmark can represent the anatomical structure as a whole or only a point or part of it. A landmark can also for example lie on the anatomical structure, which is for example a prominent structure. An example of such an anatomical structure is the posterior aspect of the iliac crest. Another example of a landmark is one defined by the rim of the acetabulum, for instance by the centre of said rim. In another example, a landmark represents the bottom or deepest point of an acetabulum, which is derived from a multitude of detection points. Thus, one landmark can for example represent a multitude of detection points. As mentioned above, a landmark can represent an anatomical characteristic which is defined on the basis of a characteristic structure of the body part. Additionally, a landmark can also represent an anatomical characteristic defined by a relative movement of two body parts, such as the rotational centre of the femur when moved relative to the acetabulum.

[0125] Imaging geometry

[0126] The information on the imaging geometry preferably comprises information which allows the analysis image (x-ray image) to be calculated, given a known relative position between the imaging geometry analysis apparatus and the analysis object (anatomical body part) to be analysed by x-ray radiation, if the analysis object which is to be analysed is known, wherein "known" means that the spatial geometry (size and shape) of the analysis object is known. This means for example that three- dimensional, "spatially resolved" information concerning the interaction between the analysis object (anatomical body part) and the analysis radiation (x-ray radiation) is known, wherein "interaction" means for example that the analysis radiation is blocked or partially or completely allowed to pass by the analysis object. The location and in particular orientation of the imaging geometry is for example defined by the position of the x-ray device, for example by the position of the x-ray source and the x-ray detector and / or for example by the position of the multiplicity (manifold) of x-ray beams which pass through the analysis object and are detected by the x-ray detector. The imaging geometry for example describes the position (i.e. the location and in particular the orientation) and the shape (for example, a conical shape exhibiting a specific angle of inclination) of said multiplicity (manifold). The position can for example be represented by the position of an x-ray beam which passes through the centre of said multiplicity or by the position of a geometric object (such as a truncated cone) which represents the multiplicity (manifold) of x-ray beams. Information concerning the above-mentioned interaction is preferably known in three dimensions, for example from a three-dimensional CT, and describes the interaction in a spatially resolved way for points and / or regions of the analysis object, for example for all of the points and / or regions of the analysis object. Knowledge of the imaging geometry for example allows the location of a source of the radiation (for example, an x-ray source) to be calculated relative to an image plane (for example, the plane of an x-ray detector). With respect to the connection between three- dimensional analysis objects and two-dimensional analysis images as defined by the imaging geometry, reference is made for example to the following publications:

[0127] 1. "An Efficient and Accurate Camera Calibration Technique for 3D Machine Vision", Roger Y. Tsai, Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition. Miami Beach, Florida, 1986, pages 364-374

[0128] 2. "A Versatile Camera Calibration Technique for High-Accuracy 3D Machine Vision Metrology Using Off-the-Shelf TV Cameras and Lenses", Roger Y. Tsai, IEEE Journal of Robotics and Automation, Volume RA-3, No. 4, August 1987, pages 323- 344.

[0129] 3. "Fluoroscopic X-ray Image Processing and Registration for Computer-Aided Orthopedic Surgery", Ziv Yaniv

[0130] 4. EP 08 156 293.6

[0131] 5. US 61 / 054,187

[0132] Referencing

[0133] Determining the position is referred to as referencing if it implies informing a navigation system of said position in a reference system of the navigation system.

[0134] Imaging methods

[0135] In the field of medicine, imaging methods (also called imaging modalities and / or medical imaging modalities) are used to generate image data (for example, two- dimensional or three-dimensional image data) of anatomical structures (such as soft tissues, bones, organs, etc.) of the human body. The term "medical imaging methods" is understood to mean (advantageously apparatus-based) imaging methods (for example so-called medical imaging modalities and / or radiological imaging methods) such as for instance computed tomography (CT) and cone beam computed tomography (CBCT, such as volumetric CBCT), x-ray tomography, magnetic resonance tomography (MRT or MRI), conventional x-ray, sonography and / or ultrasound examinations, and positron emission tomography. For example, the medical imaging methods are performed by the analytical devices. Examples for medical imaging modalities applied by medical imaging methods are: X-ray, magnetic resonance imaging, medical ultrasonography or ultrasound, endoscopy, elastography, tactile imaging, thermography, medical photography and nuclear medicine functional imaging techniques as positron emission tomography (PET) and Single-photon emission computed tomography, as mentioned by Wikipedia.

[0136] The image data thus generated is also termed “medical imaging data”. Analytical devices for example are used to generate the image data in apparatus-based imaging methods. The imaging methods are for example used for medical diagnostics, to analyse the anatomical body in order to generate images which are described by the image data. The imaging methods are also for example used to detect pathological changes in the human body. However, some of the changes in the anatomical structure, such as the pathological changes in the structures (tissue), may not be detectable and for example may not be visible in the images generated by the imaging methods. A tumour represents an example of a change in an anatomical structure. If the tumour grows, it may then be said to represent an expanded anatomical structure. This expanded anatomical structure may not be detectable; for example, only a part of the expanded anatomical structure may be detectable. Primary / high-grade brain tumours are for example usually visible on MRI scans when contrast agents are used to infiltrate the tumour. MRI scans represent an example of an imaging method. In the case of MRI scans of such brain tumours, the signal enhancement in the MRI images (due to the contrast agents infiltrating the tumour) is considered to represent the solid tumour mass. Thus, the tumour is detectable and for example discernible in the image generated by the imaging method. In addition to these tumours, referred to as "enhancing" tumours, it is thought that approximately 10% of brain tumours are not discernible on a scan and are for example not visible to a user looking at the images generated by the imaging method.

[0137] Mapping

[0138] Mapping describes a transformation (for example, linear transformation) of an element (for example, a pixel or voxel), for example the position of an element, of a first data set in a first coordinate system to an element (for example, a pixel or voxel), for example the position of an element, of a second data set in a second coordinate system (which may have a basis which is different from the basis of the first coordinate system). In one embodiment, the mapping is determined by comparing (for example, matching) the color values (for example grey values) of the respective elements by means of an elastic or rigid fusion algorithm. The mapping is embodied for example by a transformation matrix (such as a matrix defining an affine transformation).

[0139] Elastic fusion, image fusion / morphing, rigid

[0140] Image fusion can be elastic image fusion or rigid image fusion. In the case of rigid image fusion, the relative position between the pixels of a 2D image and / or voxels of a 3D image is fixed, while in the case of elastic image fusion, the relative positions are allowed to change.

[0141] In this application, the term "image morphing" is also used as an alternative to the term "elastic image fusion", but with the same meaning.

[0142] Elastic fusion transformations (for example, elastic image fusion transformations) are for example designed to enable a seamless transition from one dataset (for example a first dataset such as for example a first image) to another dataset (for example a second dataset such as for example a second image). The transformation is for example designed such that one of the first and second datasets (images) is deformed, for example in such a way that corresponding structures (for example, corresponding image elements) are arranged at the same position as in the other of the first and second images. The deformed (transformed) image which is transformed from one of the first and second images is for example as similar as possible to the other of the first and second images. Preferably, (numerical) optimisation algorithms are applied in order to find the transformation which results in an optimum degree of similarity. The degree of similarity is preferably measured by way of a measure of similarity (also referred to in the following as a "similarity measure"). The parameters of the optimisation algorithm are for example vectors of a deformation field. These vectors are determined by the optimisation algorithm in such a way as to result in an optimum degree of similarity. Thus, the optimum degree of similarity represents a condition, for example a constraint, for the optimisation algorithm. The bases of the vectors lie for example at voxel positions of one of the first and second images which is to be transformed, and the tips of the vectors lie at the corresponding voxel positions in the transformed image. A plurality of these vectors is preferably provided, for instance more than twenty or a hundred or a thousand or ten thousand, etc. Preferably, there are (other) constraints on the transformation (deformation), for example in order to avoid pathological deformations (for instance, all the voxels being shifted to the same position by the transformation). These constraints include for example the constraint that the transformation is regular, which for example means that a Jacobian determinant calculated from a matrix of the deformation field (for example, the vector field) is larger than zero, and also the constraint that the transformed (deformed) image is not self-intersecting and for example that the transformed (deformed) image does not comprise faults and / or ruptures. The constraints include for example the constraint that if a regular grid is transformed simultaneously with the image and in a corresponding manner, the grid is not allowed to interfold at any of its locations. The optimising problem is for example solved iteratively, for example by means of an optimisation algorithm which is for example a first-order optimisation algorithm, such as a gradient descent algorithm. Other examples of optimisation algorithms include optimisation algorithms which do not use derivations, such as the downhill simplex algorithm, or algorithms which use higher- order derivatives such as Newton-like algorithms. The optimisation algorithm preferably performs a local optimisation. If there is a plurality of local optima, global algorithms such as simulated annealing or generic algorithms can be used. In the case of linear optimisation problems, the simplex method can for instance be used. In the steps of the optimisation algorithms, the voxels are for example shifted by a magnitude in a direction such that the degree of similarity is increased. This magnitude is preferably less than a predefined limit, for instance less than one tenth or one hundredth or one thousandth of the diameter of the image, and for example about equal to or less than the distance between neighbouring voxels. Large deformations can be implemented, for example due to a high number of (iteration) steps.

[0143] The determined elastic fusion transformation can for example be used to determine a degree of similarity (or similarity measure, see above) between the first and second datasets (first and second images). To this end, the deviation between the elastic fusion transformation and an identity transformation is determined. The degree of deviation can for instance be calculated by determining the difference between the determinant of the elastic fusion transformation and the identity transformation. The higher the deviation, the lower the similarity, hence the degree of deviation can be used to determine a measure of similarity.

[0144] A measure of similarity can for example be determined on the basis of a determined correlation between the first and second datasets.

[0145] Fixed (relative) position

[0146] A fixed position, which is also referred to as fixed relative position, in this document means that two objects which are in a fixed position have a relative position which does not change unless this change is explicitly and intentionally initiated. A fixed position is in particular given if a force or torque above a predetermined threshold has to be applied in order to change the position. This threshold might be 10 N or 10 Nm. In particular, the position of a sensor device remains fixed relative to a target while the target is registered or two targets are moved relative to each other. A fixed position can for example be achieved by rigidly attaching one object to another. The spatial location, which is a part of the position, can in particular be described just by a distance (between two objects) or just by the direction of a vector (which links two objects). The alignment, which is another part of the position, can in particular be described by just the relative angle of orientation (between the two objects).

[0147] Medical Workflow

[0148] A medical workflow comprises a plurality of workflow steps performed during a medical treatment and / or a medical diagnosis. The workflow steps are typically, but not necessarily performed in a predetermined order. Each workflow step for example means a particular task, which might be a single action or a set of actions. Examples of workflow steps are capturing a medical image, positioning a patient, attaching a marker, performing a resection, moving a joint, placing an implant and the like.

[0149] BRIEF DESCRIPTION OF THE DRAWINGS

[0150] In the following, the invention is described with reference to the appended figures which give background explanations and represent specific embodiments of the invention. The scope of the invention is however not limited to the specific features disclosed in the context of the figures, wherein

[0151] Fig. 1 illustrates a method according to the present disclosure;

[0152] Fig. 2 is a schematic illustration of a system according to the present disclosure;

[0153] Fig. 3 illustrates a first option for combined rotational and translational movement;

[0154] Fig. 4 illustrates a second option for combined rotational and translational movement;

[0155] Fig. 5 illustrates a series of X-ray images for a combined rotational and translational movement;

[0156] Fig. 6 illustrates a reconstructed X-ray image at different depths;

[0157] Fig. 7 illustrates an exemplary imaging ring that may be used for the system according to the present disclosure;

[0158] Fig. 8 illustrates an example according to the present disclosure comprising projecting vessels into a fluoroscopic image. DESCRIPTION OF EMBODIMENTS

[0159] Figure 1 illustrates the basic steps of the method for the computer implemented method for tomosynthesis according to the present disclosure.

[0160] Step S11 encompasses X-ray image data acquisition by means of a 2D X-ray scanner, also referred to as “scanner” below.

[0161] Step S12 encompasses moving a viewing axis of the 2D X-ray scanner relative to a patient table during the X-ray image data acquisition in a movement comprising at least two movement directions.

[0162] The scanner is configured and arranged in such a manner that the movement is independent of guide elements, in particular fixed-position guide elements like rails or the like.

[0163] For example, the movement may comprise a translational movement along a first axis, e.g. by the scanner driving along the patient table, and a superimposed rotational movement around a second axis.

[0164] The second axis may be perpendicular to the first axis. For example, the rotational movement may be around any rotation axis that is in a plane perpendicular to the first axis, i.e., the axis along which the translational movement takes place. This may entail that the C-arm or gantry, on which the X-ray source and X-ray detector are mounted, may tilt in or against the direction of the translational movement.

[0165] Alternatively, the second axis may be parallel to the first axis. For example, the rotational movement may be around any rotation axis that is in a plane comprising to the first axis, i.e., the axis along which the translational movement takes place. The rotation may be considered as being in a traverse or sideways direction relative to the translational movement. Particularly, this may be a rotation around a longitudinal axis of the gantry or C-arm.

[0166] The rotational movement may comprise repeated alternating rotations in opposite directions, for example a wobbling movement. Particularly, the alternating rotations may be alternating tilting movements of the gantry or C-arm in and against the direction of the translational movement or alternating rotations around the gantry or C-arm longitudinal axis, which may be arranged parallel to the translational movement direction.

[0167] As an example for implementing the above-described movements, the scanner may be mounted on a wheeled device, particularly a non-rail-born device to allow for independent translational movement on the floor, and the translational movement may comprise moving the wheeled device relative to the patient table. As an example, the wheeled device may have four independently steerable wheels, some of which having an active drive, e.g., the rear wheels having an active drive. The wheeled device may be automated guided vehicle AGV.

[0168] Step S13 encompasses tomosynthesis image reconstruction from the X-ray image data. Thus, depth information can be obtained by the reconstruction. By the above-described superimposing of two movement directions, it is possible to improve depth information.

[0169] The tomosynthesis image reconstruction may comprise a reconstruction based on filtered backprojection (FBP). Alternatively or in addition, the tomosynthesis image reconstruction may comprise iterative reconstruction, which optionally incorporates for initialization deconvolution using a set of known point spread functions, PSF, that is derived from the geometries of the tomosynthesis data acquisition.

[0170] The method may also comprise optional step S14 of optical tracking, wherein the optical tracking comprises tracking a position of the scanner and / or an orientation of the scanner. This may further improve reconstruction accuracy.

[0171] Figure 2 discloses a system 1 for tomosynthesis according to the present disclosure. The system may be configured to carry out the methods of the present disclosure, particularly as outlined in the context of Figure 1 . Several optional system features are shown for illustration and may be omitted or replaced.

[0172] The system comprises an X-ray imaging system 2 comprising a 2D X-ray scanner configured to carry out X-ray image data acquisition. The 2D X-ray scanner may correspond to the medical imaging system. Accordingly, the 2D X-ray scanner is also referred to as imaging system hereinbelow. Particularly, the imaging system may be a CT imaging system, particularly a cone beam CT (CBCT). As an example, a Loop-X imaging system may be employed for X-ray image data acquisition.

[0173] The system also comprises a processing system 12 configured to carry out tomosynthesis image reconstruction from the X-ray image data and particularly configured to carry out and / or control any of the method steps of the method of the present disclosure, e.g. as illustrated in Figure 1. The processing system is shown as being part of the imaging system comprising the X-ray scanner, but it may also be a separate processing system or partially separate distributed processing system.

[0174] The system is configured to move the X-ray viewing axis of the scanner relative to a patient table during the X-ray image data acquisition in a movement comprising at least two movement directions, and the scanner is configured and arranged in such a manner that the movement is independent of guide elements, in particular fixed-position guide-elements, like rails.

[0175] The system may comprise a wheeled device, for example an automated guided vehicle (AGV), the scanner being mounted on the wheeled device and the wheeled device being configured to move the scanner. For example, the movement of the X-ray viewing axis, specifically a translational movement, may comprise moving the wheeled device relative to the patient table. The wheeled device may, for example, comprise four independently steerable wheels, in particular with rear wheels having active drive / traction. The wheeled device may be non-rail-borne to allow for independent translational movement.

[0176] An exemplary source 2a and exemplary detector 2b arranged on a gantry 2c are shown. The gantry may have a loop shape. However, other configurations of the medical imaging system are conceivable. For example, a C-arm configuration may be adopted instead of such a gantry.

[0177] The imaging system is illustrated, exemplarily, as a system having a tiltable gantry 2c, particularly the gantry having a tiltable rotation plane (which is in this illustration viewed from the side) indicated by dashed line 10.

[0178] The system may optionally further comprise a tracking device 3, in this example an infrared tracking camera. The tracking device may be rigidly attached to the imaging system, optionally in a detachable manner. The Figure also illustrates that the system may optionally comprise a surgical navigation system 4. These optional tools may be used for navigation and for providing spatial information for even further improved image reconstruction. Optional markers 5a to 5e, which may be used together with the tracking device and / or surgical navigation system, are also illustrated, respectively arranged on the floor, attached to a patient bed 6, attached to a portion of the patient 7 inside the region of interest 8 or attached to a portion of the patient outside the region of interest, or attached to a medical tool 9. It is to be understood that any single one of and any combination of at least some of the markers 5a to 5e may be employed. A tracking device of the surgical navigation system is denoted by reference sign 4a. The tracking device 3 and the medical imaging system 2 may communicate via data connection 11a. The surgical navigation system and the medical imaging system may communicate via a data connection 11b. The respective data connection may be wired or wireless. The above features concerning the tracking device, navigation system and markers are advantageous for improved navigation and image reconstruction, yet are optional.

[0179] In the following, more examples and advantages will be described to illustrate the methods and systems of the present disclosure.

[0180] As explained above, by providing the two movement directions, additional image data is obtained as compared to known methods. Said data, when used for tomosynthesis image reconstruction, allows for improved depth information and / or correction of parallax errors.

[0181] When the scanner only carries out a translational movement along the scanning direction, limited depth information in tomosynthesis images will be obtained. The angular coverage range of incident X-rays, in this case, is equivalent to the effective X-ray opening angle that can be captured by the detector. This coverage range of X-rays is important for 3D reconstruction. An entirely correctly reconstructed 3D image can only be reconstructed if the coverage range of incident X-rays is 180°.

[0182] The present application envisions increasing accuracy by combining the translational movement, e.g. along the scanning direction, with a rotational movement. Said additional movement will yield image data allowing to increase the effective coverage range and, when incorporated in the reconstruction, improves depth information. As indicated in Figure 3, coverage range can be increased by a gantry tilt in and / or against the translational direction. Such gantry tilt is supported, for example by some imaging rings like the Loop X. Accordingly, depth reconstruction is improved.

[0183] In other words, increasing the coverage range of incident X-rays to improve the depth reconstruction may entail making use of the gantry tilt that is featured by imaging rings. This may lead to a combined AGV-based longitudinal movement and gantry tilting during (full-size) X-ray acquisition. Source and detector, particularly source and detector arms, are static relative to each other in this case and, in this example, are also not rotated around an axis parallel to the movement direction.

[0184] In Figure 3, on the left, a sagittal view is shown, and, on the right, a trans-axial view is shown.

[0185] Alternatively, as indicated in Figure 4, coverage range can be increased by a rotation in a plane that is essentially perpendicular to the translational movement direction. For example, source and / or detector may rotate around an axis that is parallel to the translational movement direction. In such a scenario, a relative position between source and detector may remain the same, i.e., they may be rotated together, or their relative position may change, e.g., by independent rotation of source and detector. For example, source arm and detector may be independently movable.

[0186] In other words, for example, a source and / or detector movement may be carried out while also traveling with the AGV in main direction. Source and detector (arms) do not necessarily have to move such that their relative angular distance stays constant, but may also vary relative to each other, e.g. in case the imaged volume is located not exactly in the mechanical isocenter's depth level. For example, source and detector arms may be moving alternatingly clockwise and counterclockwise.

[0187] In Figure 4, on the left, a sagittal view is shown, and, on the right, a trans-axial view is shown.

[0188] In Figure 5, a series of X-ray images is shown, with a rotation around an axis that is parallel to a scanning direction, as indicated by the arrows. The scanning direction is along the longitudinal axis of a patient, here along the legs, imaging the legs including the knees. Specifically, the rotation is an alternating rotation in opposite directions, e.g., a wobble. For example, the movement as illustrated in Figure 4 may yield such images.

[0189] In Figure 6, for the sake of illustration, different reconstructed images at different depths are shown, e.g. from top to bottom of the patient. From said images, it becomes apparent that there are slices where the reconstructed images are more in focus and slices that are out of focus. The range of depths in which the images are in focus can be increased by the methods of the present disclosure, as explained above.

[0190] For the sake of illustration Figure 7 shows an example of an imaging ring, e.g. a Loop-X, which allows for an AGV-based movement combined with tilting the gantry and also a source and a flat panel detector that can be rotated together and independently. Such an imaging ring may be employed as the imaging system according to the present disclosure, its source and detector may be comprised in the 2D X-ray scanner of the present disclosure.

[0191] Fig. 8 illustrates an example according to the present disclosure comprising projecting vessels into a fluoroscopic image.

[0192] In the example shown in Fig. 8, a 3D vessel segmentation is projected into a fluoroscopic image, particularly into fluoroscopic image sequences, in particular live / in real time. This can be done at any angle and position due to the nature of the tomosynthesis according to the present disclosure.

[0193] In some examples, adaptive imaging is carried out in the context of 3D vessel segmentation, such as explained above. That is, the projection direction during tomosynthesis may vary dependent on the imaged anatomy during image acquisition. For example, such varying of the projection direction dependent on the imaged anatomy may comprise image-based and / or tracking-based (e.g. using marker-based techniques) detection of an anatomy or part thereof. For example, this may allow for better acquisition and reconstruction of images.

[0194] 3D vessel segmentation obtained from tomosynthesis according to the present disclosure, particularly combined with adaptive imaging, may allow, among others, for overlaying a projection of the vessel (which maybe referred to as a 2D projected vessel mask) with fluoroscopic image sequences (also be referred to as roadmapping) from any angle and, consequently, allows for lower radiation and contrast agent doses. This is not possible with conventional 2D DSA (digital subtraction angiography) approaches, since the 2D fluoroscopy and 2D vessels mask (i.e. roadmap) must have been generated using exactly the same projection I imaging geometry.

[0195] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered exemplary and not restrictive. The invention is not limited to the disclosed embodiments. In view of the foregoing description and drawings it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention, as defined by the claims.

Claims

Brainlab AGAttorney’s File: B17950WO2CLAIMS1. A computer-implemented method for tomosynthesis, the method comprising the steps of:X-ray image data acquisition (S11 ) by means of a cone beam 2D X-ray scanner; and tomosynthesis image reconstruction (S13) from the X-ray image data, wherein an X-ray viewing axis of the cone beam of the 2D X-ray scanner is moved (S12) relative to a patient table during the X-ray image data acquisition in a movement comprising at least two movement directions, and wherein the 2D X-ray scanner is configured and arranged in such a manner that the movement is independent of guide-elements.

2. The method according to claim 1 , wherein the movement comprises a translational movement along a first axis and a superimposed rotational movement around a second axis.

3. The method according to claim 2, wherein the second axis is perpendicular to the first axis, or wherein the second axis is parallel with, in particular coincides with, the first axis.

4. The method according to claim 2 or 3, wherein the first axis is parallel to or coincides with a patient table’s longitudinal axis.

5. The method of any according to any of claims 2 to 4, wherein the rotational movement comprises repeated alternating rotations in opposite directions.

6. The method according to any of claims 2 to 5, wherein the rotational movement is a wobbling movement.

7. The method according to any according to any of claims 2 to 6,wherein the rotational movement comprises a rotational movement of an X-ray source during X-ray image data acquisition and / or a rotational movement of an X-ray detector during X-ray image data acquisition.

8. The method according to claim 7, wherein the rotational movement comprises a rotational movement of a C-arm or ring gantry on which the X-ray source and X-ray detector are mounted.

9. The method according to any of claims 2 to 8, wherein the rotational movement comprises a tilting movement of a gantry during X-ray image data acquisition.

10. The method according to any of claims 2 to 9, wherein the translational movement comprises a translational movement of the 2D X-ray scanner.11 . The method according to any of the preceding claims, wherein the 2D X-ray scanner is mounted on a wheeled device configured to allow for moving the 2D X-ray scanner, the wheeled device particularly being a non- rail-borne wheeled device, and wherein the movement, in particular the translational movement, comprises moving the wheeled device relative to the patient table.

12. The method according to claim 11 , wherein the wheeled device comprises four independently steerable wheels, in particular with rear wheels having an active drive.

13. The method according to claim 11 or 12, wherein the wheeled device is an automated guided vehicle, AGV.

14. The method according to any of the preceding claims, further comprising optical tracking (S14), wherein the optical tracking comprises tracking a position of the 2D X-ray scanner and / or an orientation of the 2D X-ray scanner.

15. The method according to any of the preceding claims, wherein the X- ray image data acquisition is carried out in a manner allowing for non-isocentricity of the 2D X-ray scanner.

16. The method according to any of the preceding claims,wherein the tomosynthesis image reconstruction comprises a reconstruction based on filtered backprojection, FBP, and / or wherein the tomosynthesis image reconstruction comprises iterative reconstruction, which optionally incorporates for initialization the FBP and / or deconvolution, particularly of the projections, using a set of known point spread functions, PSF, that is derived from the geometries of the tomosynthesis data acquisition.

17. The method according to any of the preceding claims, wherein the 2D X-ray scanner is a cone beam computed tomography, CBCT, scanner.

18. A system (1 ) for tomosynthesis, the system comprising an X-ray imaging system (2) comprising a 2D X-ray scanner, configured to carry out X-ray image data acquisition; and a processing system (12) configured to carry out tomosynthesis image reconstruction from the X-ray image data, wherein the system is configured to move an X-ray viewing axis of the 2D X- ray scanner relative to a patient table during the X-ray image data acquisition in a movement comprising at least two movement directions, and wherein the 2D X-ray scanner is configured and arranged in such a manner that the movement is independent of guide-elements.

19. The system (1 ) according to claim 18, the system comprising a wheeled device, the wheeled device particularly being a non-rail-borne wheeled device, wherein the 2D X-ray scanner is mounted on the wheeled device and the wheeled device is configured to move the 2D X-ray scanner, and wherein the movement, in particular a translational movement, of the X-ray viewing axis of the 2D X-ray scanner, comprises moving the wheeled device relative to the patient table.

20. The system (1) according to claim 19, wherein the wheeled device comprises four independently steerable wheels, in particular with rear wheels having active drive.21 . The system (1 ) according to claim 19 or 20, wherein the wheeled device is an automated guided vehicle, AGV.

22. The system (1) according to any according to any one of claims 18 to21 , wherein the system is configured to carry out the method of any according to claims 1 to 17, in particular, wherein the method steps are controlled and / or carried out by the processing system (12).

23. The system (1) according to any according to any one of claims 19 to22, wherein the 2D X-ray scanner is a cone beam computed tomography, CBCT, scanner.

24. A computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out and / or control the method steps of any one according to claims 1 to 17.

25. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out and / or control the method steps of any one according to claims 1 to 17.

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