Self-validating elastic fusion

Abstract

Disclosed is a computer-implemented method of validating a determined deformation of an image rendering of an anatomical structure between digital medical images. The disclosed method encompasses a comparison of the position of corresponding image constituents representing the same moving anatomical structure throughout a set of 4D-CT slices as determined by 1) elastic fusion from a reference slice to the other slices and 2) segmentation of a contour of the anatomical structure in each of the slices, for example (only) the other slices. This procedure allows determining the validity of the fusion results. This allows improving the quality of determining the movement of the anatomical structure for planning radiation treatment of the anatomical structure.

Description

[0001] SELF-VALIDATING ELASTIC FUSION

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a computer-implemented method of validating a determined deformation of an image rendering of an anatomical structure between digital medical images, a corresponding computer program, a computer-readable storage medium storing such a program and a computer executing the program, as well as a medical system comprising an electronic data storage device and the aforementioned computer.

[0004] TECHNICAL BACKGROUND

[0005] The disclosed method can be used for planning radiation treatment of a moving target by specifically supporting the elastic fusion (between reference bin and remaining bins) that is used to create the trajectory of every voxel that in turn is required to pick out voxels moving the same way the target does. A four-dimensional computed X-ray tomography (4D-CT) is a computed X-ray tomography taken of the moving target over time. A 4D-CT comprises several tomographies (also called “bins”), each bin representing a different respiratory state of the scanned patient. Elastic fusion is used to make determine movement of the target between bins.

[0006] To validate the result of such an elastic fusion time consuming visual inspection has to be performed. Goal of the new approach is to be able to automatically provide a quality score of the fusion result.

[0007] The present invention has the object of providing a method of determining the quality of tracking a movement target. The present invention can be used for radiation treatment planning procedures e.g. in connection with a system for image-guided radiotherapy such as VERO® and ExacTrac®, both products of Brainlab AG.

[0008] 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.

[0009] EXEMPLARY SHORT DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] The disclosed method encompasses a comparison of the position of corresponding image constituents representing the same moving anatomical structure throughout a set of 4D-CT bins, i.e. slices, as determined by 1 ) elastic fusion from a reference slice to the other slices and 2) segmentation of a contour of the anatomical structure in each of the slices, for example (only) the other slices. This procedure allows determining the validity of the fusion results. This allows improving the quality of determining the movement of the anatomical structure for planning radiation treatment of the anatomical structure.

[0012] GENERAL DESCRIPTION OF THE INVENTION

[0013] 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.

[0014] In general, the invention reaches the aforementioned object by providing, in a first aspect, a computer-implemented medical method of validating a determined deformation of an image rendering of an anatomical structure between digital medical images. The method comprises executing, on at least one processor of at least one computer (for example at least one computer being part of a radiation treatment planning system), the following exemplary steps which are executed by the at least one processor.

[0015] In a (for example first) exemplary step, first medical image data is acquired which describes a first medical image of the anatomical structure in a first vital state. The term of vital state encompasses at least one of a physiological state and a pathological state of the anatomical structure. For example, the physiological state, for example the size and / or position of the anatomical structure, changes due to a vital movement of the patient to whom the anatomical structure belongs. A vital movement is for example at least one of a breathing motion which influences the size and position of the lung as the anatomical structure, and a heartbeat which influences the size and position of the heart as the anatomical structure. The size and / or position of the anatomical structure may also be influenced by a state of the pathological state of the anatomical structure, for example due to a tumour growing or shrinking (for example, by radiation treatment or surgery) in or close to the anatomical structure. For example, the tumour development may increase or reduce the size of the anatomical structure and therefore positions of its constituents. The first medical image is for example a digital image and for example a three-dimensional image (i.e. an image defined by image data in which positions of image constituents are defined in three dimensions) such as a tomographic image such as a computed X-ray tomography or a magnetic resonance tomography or an ultrasound tomography. In an example, the first medical image is a two-dimensional image (i.e. an image defined by image data in which positions of image constituents are defined in two dimensions) such as a radiography or a digitally reconstructed radiograph.

[0016] In a (for example second) exemplary step, second medical image data is acquired which describes a second medical image of the anatomical structure, in a second vital state, the second vital state being different from the first vital state. For example, the first medical image and the second medical image are defined in a common reference system, i.e. have the same reference system in which the positions of their image constituents are defined. For example, at least one of the size and the position of the anatomical structure in the first medical image differs from the respective one of size and position of the anatomical structure in the second medical image. The second medical image is for example a digital image and for example a three-dimensional image (i.e. an image defined by image data in which positions of image constituents are defined in three dimensions) such as a tomographic image such as a computed X- ray tomography or a magnetic resonance tomography or an ultrasound tomography. In an example, the second medical image is a two-dimensional image (i.e. an image defined by image data in which positions of image constituents are defined in two dimensions) such as a radiography or a digitally reconstructed radiograph.

[0017] In a (for example third) exemplary step, image deformation data is determined based on the first medical image data and the second medical image data. For example, the image deformation data describes a deformation between the image rendering of the anatomical structure in the first medical image and the image rendering of the anatomical structure in the second medical image. The deformation is determined for example as a deformation field. The deformation is for example represented by a transformation, for example a positional transformation (also called mapping), between position in the first medical image and position in the second medical image defining image constituents of the respective images representing corresponding parts of the anatomical structure. For example, the image deformation data is determined by applying an image fusion algorithm to the first medical image and the second medical image. For example, the transformation is determined by performing an elastic fusion between the first medical image and the second medical image, or by applying an optical flow algorithm to the first medical image and the second medical image.

[0018] In a (for example fourth) exemplary step, deformed first medical image data is determined based on the first medical image data and the image deformation data. For example, the deformed first medical image data describes a deformed first medical image being the result of applying the deformation to the first medical image. For example, the transformation between the first medical image and the second medical image is applied to the first medical image, and the result of applying the transformation is stored in and therefore represented by the first medical image data.

[0019] In a (for example fifth) exemplary step, deformation position data is determined based on the deformed first medical image data. For example, the deformation position data describes a position of the image representation of the anatomical structure in the deformed first medical image. For example, the deformation position data is determined by segmenting the contour of the image rendering of the anatomical structure described by the deformed first medical image. For example, the deformation position data is determined based on the image contour data, for example by using the position of a segmentation of the contour of the image representation of the anatomical structure in the second medical image as a boundary condition for determining the image deformation data, for example in a feed-back loop for grey value and contourbased fusion of the first and second medical images.

[0020] In a (for example sixth) exemplary step, image contour data is determined based on the second medical image data, wherein the image contour data describes the position of a segmentation of the contour of the image representation of the anatomical structure in the second medical image. The kind of contour is chosen for the segmentation for example in dependence on the medical indication present for the individual patient. For example, the contour is an outer contour of the image representation of the anatomical structure, i.e. its represents its circumference. For example, the image contour data is determined by at least one of segmenting a contour of the image rendering of the anatomical structure in the second medical image, for example by using an automatic segmentation algorithm, for example a machine learning-based segmentation algorithm, and by acquiring atlas data which describes a digital model of the anatomical structure and determining the image contour data based on the second medical image data and the atlas data. For example, the atlas data is compared to, for example elastically fused with, the second medical image data in order to determine the position of the contour from a corresponding contour contained in the atlas data.

[0021] In a (for example seventh) exemplary step, similarity data is determined based on the image deformation data and the image contour data. For example, the similarity data describes a value of a measure of similarity between the position of a contour of the image representation of the anatomical structure in the deformed first medical image described by the deformation position data and the position of the segmentation of the contour of the image representation of the anatomical structure described by the image contour data. For example, the value of the measure of similarity is determined between the position of anatomical structure as determined from the deformation of the first medical image and as determined from the segmentation of the contour in the second medical image. For example, the contour of the image representation of the anatomical structure in the first medical image, for example in the deformed first medical image, is or has been determined by segmenting the contour in the first medical image. For example, the contour of the image representation of the anatomical structure in the first medical image, for example in the deformed first medical image, is or has been determined by at least one of segmenting a contour of the image rendering of the anatomical structure in the second medical image, for example by using an automatic segmentation algorithm, for example a machine learning-based segmentation algorithm and acquiring atlas data which describes a digital model of the anatomical structure and determining the image contour data based on the second medical image data and the atlas data. For example, the atlas data is compared to, for example elastically fused with, the first medical image data in order to determine the position of the contour from a corresponding contour contained in the atlas data. For example, the measure of similarity is determined by applying a least squares distance determination algorithm to the position of a contour of the image representation of the anatomical structure in the deformed first medical image described by the deformation position data and the position of the segmentation of the contour of the image representation of the anatomical structure described by the image contour data.

[0022] In an example of the method according to the first aspect, the first medical image data describes a contour of the image representation of the anatomical structure in the first medical image and the deformed first medical image describes a result of applying the deformation to the contour of the image representation of the anatomical structure in the first medical image, and the deformation position data describes a position of the contour of the image representation of the anatomical structure in the first medical image.

[0023] In a second aspect, this disclosure is directed to a method of determining control data for controlling a radiation treatment system. The method according to the second aspect comprises executing, on at least one processor of at least one computer (for example at least one computer being part of a radiation treatment planning system), the following exemplary steps which are executed by the at least one processor: a) executing the method according to the first aspect; b) acquiring similarity threshold data describing a threshold of the value of the measure of similarity; c) determining validation data based on the similarity data and the similarity threshold data describing whether the position of the image rendering of the anatomical structure in the second medical image described by the deformation position data shall be used as a basis for determining the control data.

[0024] For example, the validation data is determined by comparing the value of the measure of similarity to the threshold. For example, the method according to the second aspect comprises determining, if the value of the measure of similarity and the threshold have a predetermined relationship to each other, the control data based on the deformation position data, for example for irradiating the anatomical structure with treatment radiation.

[0025] In a third aspect, the invention is directed to a computer program comprising instructions which, when the program is executed by at least one computer, causes the at least one computer to carry out method according to the first aspect. The invention may alternatively or additionally relate to a (physical, for example electrical, for example technically generated) signal wave, for example a digital signal wave, such as an electromagnetic carrier 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 steps of the method according to the first aspect. The signal wave is in one example a data carrier signal carrying the aforementioned computer program. A computer program stored on a disc is a data file, and when the file is read out and transmitted it becomes a data stream for example in the form of a (physical, for example electrical, for example technically generated) signal. The signal can be implemented as the signal wave, for example as the electromagnetic carrier wave which is described herein. For example, the signal, for example the signal wave is constituted to be transmitted via a computer network, for example LAN, WLAN, WAN, mobile network, for example the internet. For example, the signal, for example the signal wave, is constituted to be transmitted by optic or acoustic data transmission. The invention according to the second aspect therefore may alternatively or additionally relate to a data stream representative of the aforementioned program, i.e. comprising the program.

[0026] In a fourth aspect, the invention is directed to a computer-readable storage medium on which the program according to the second aspect is stored. The program storage medium is for example non-transitory.

[0027] In a fifth aspect, the invention is directed to at least one computer (for example, a computer), comprising at least one processor (for example, a processor), wherein the program according to the second aspect is executed by the processor, or wherein the at least one computer comprises the computer-readable storage medium according to the third aspect.

[0028] In a sixth aspect, the invention is directed to a medical system, comprising: a) the at least one computer according to the fifth aspect, wherein the instructions cause the computer to carry out the method according to the second aspect; b) at least one electronic data storage device storing the control data; and c) a radiation treatment apparatus, wherein the at least one computer is operably coupled to

[0029] - the at least one electronic data storage device for acquiring, from the at least one data storage device, the control data, and

[0030] - the radiation treatment apparatus for issuing a control signal to the radiation treatment apparatus for controlling the operation of the radiation treatment apparatus on the basis of the control data.

[0031] In an example of the system according to the sixth aspect, the radiation treatment apparatus comprises a treatment beam source (for example, for emitting ionizing radiation) and a patient support unit, wherein the at least one computer is operably coupled to the radiation treatment apparatus for issuing a control signal to the radiation treatment apparatus for controlling, on the basis of the control data, at least one of the operation of the treatment beam source or the position of the patient support unit.

[0032] Alternatively or additionally, the invention according to the sixth aspect is directed to a for example non-transitory computer-readable program storage medium storing a program for causing the computer according to the fourth aspect to execute the data processing steps of the method according to the first aspect or the method according to the second aspect.

[0033] For example, the disclosed method is not a method for treatment of the human or animal body by surgery or therapy. 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.

[0034] For example, the invention does not comprise a step of treating a patient with treatment radiation. More particularly, the invention does not involve or in particular comprise or encompass any surgical or therapeutic activity. The invention is instead directed for example supporting planning radiation treatment 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.

[0035] The present invention also relates to the use of the device / system or any embodiment thereof for planning radiation treatment. The use comprises for example execution of at least one of the method of the first aspect or the method according to the second aspect.

[0036] DEFINITIONS

[0037] In this section, definitions for specific terminology used in this disclosure are offered which also form part of the present disclosure.

[0038] 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.

[0039] 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-sem iconductor 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 "sub-computers", 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 computer includes a server resource. 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.

[0040] The invention also relates to a computer program comprising instructions which, when on the program is executed by a computer, cause the computer to carry out the method or methods, for example, the steps of the method or methods, described herein and / or to a computer-readable storage medium (for example, a non-transitory computer- readable storage medium) on which the program is stored 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, such as an electromagnetic carrier 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. The signal wave is in one example a data carrier signal carrying the aforementioned computer program. The invention also relates to a computer comprising at least one processor and / or the aforementioned computer-readable storage medium and for example a memory, wherein the program is executed by the processor.

[0041] 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 instructionexecuting 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 instruction-executing 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.

[0042] 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. A step of “determining” as described herein for example comprises or consists of issuing a command to perform the determination described herein. For example, the step comprises or consists of issuing a command to cause a computer, for example a remote computer, for example a remote server, for example in the cloud, to perform the determination. Alternatively or additionally, a step of “determination” as described herein for example comprises or consists of receiving the data resulting from the determination described herein, for example receiving the resulting data from the remote computer, for example from that remote computer which has been caused to perform the determination. 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.

[0043] 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: 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

[0044] 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.

[0045] 3. Yaniv Z., Joskowicz L., Simkin A., Garza-Jinich M., Milgrom C. (1998) Fluoroscopic image processing for computer-aided orthopaedic surgery. In: Wells W.M., Colchester A., Delp S. (eds) Medical Image Computing and Computer-Assisted Intervention — MICCAI’98. MICCAI 1998. Lecture Notes in Computer Science, vol 1496. Springer, Berlin, Heidelberg

[0046] 4. EP 08 156 293.6

[0047] 5. US 61 / 054,187

[0048] Preferably, atlas data is acquired which describes (for example defines, more particularly represents and / or is) a general three-dimensional shape of the anatomical body part. The atlas data therefore represents an atlas of the anatomical body part. An atlas typically consists of a plurality of generic models of objects, wherein the generic models of the objects together form a complex structure. For example, the atlas constitutes a statistical model of a patient’s body (for example, a part of the body) which has been generated from anatomic information gathered from a plurality of human bodies, for example from medical image data containing images of such human bodies. In principle, the atlas data therefore represents the result of a statistical analysis of such medical image data for a plurality of human bodies. This result can be output as an image - the atlas data therefore contains or is comparable to medical image data. Such a comparison can be carried out for example by applying an image fusion algorithm which conducts an image fusion between the atlas data and the medical image data. The result of the comparison can be a measure of similarity between the atlas data and the medical image data. The atlas data comprises image information (for example, positional image information) which can be matched (for example by applying an elastic or rigid image fusion algorithm) for example to image information (for example, positional image information) contained in medical image data so as to for example compare the atlas data to the medical image data in order to determine the position of anatomical structures in the medical image data which correspond to anatomical structures defined by the atlas data.

[0049] The human bodies, the anatomy of which serves as an input for generating the atlas data, advantageously share a common feature such as at least one of gender, age, ethnicity, body measurements (e.g. size and / or mass) and pathologic state. The anatomic information describes for example the anatomy of the human bodies and is extracted for example from medical image information about the human bodies. The atlas of a femur, for example, can comprise the head, the neck, the body, the greater trochanter, the lesser trochanter and the lower extremity as objects which together make up the complete structure. The atlas of a brain, for example, can comprise the telencephalon, the cerebellum, the diencephalon, the pons, the mesencephalon and the medulla as the objects which together make up the complex structure. One application of such an atlas is in the segmentation of medical images, in which the atlas is matched to medical image data, and the image data are compared with the matched atlas in order to assign a point (a pixel or voxel) of the image data to an object of the matched atlas, thereby segmenting the image data into objects.

[0050] For example, the atlas data includes information of the anatomical body part. This information is for example at least one of patient-specific, non-patient-specific, indication-specific or non-indication-specific. The atlas data therefore describes for example at least one of a patient-specific, non-patient-specific, indication-specific or non-indication-specific atlas. For example, the atlas data includes movement information indicating a degree of freedom of movement of the anatomical body part with respect to a given reference (e.g. another anatomical body part). For example, the atlas is a multimodal atlas which defines atlas information for a plurality of (i.e. at least two) imaging modalities and contains a mapping between the atlas information in different imaging modalities (for example, a mapping between all of the modalities) so that the atlas can be used for transforming medical image information from its image depiction in a first imaging modality into its image depiction in a second imaging modality which is different from the first imaging modality or to compare (for example, match or register) images of different imaging modality with one another.

[0051] The present invention relates to the field of controlling a treatment beam. The treatment beam treats body parts which are to be treated and which are referred to in the following as "treatment body parts". These body parts are for example parts of a patient's body, i.e. anatomical body parts.

[0052] The present invention relates to the field of medicine and for example to the use of beams, such as radiation beams, to treat parts of a patient's body, which are therefore also referred to as treatment beams. A treatment beam treats body parts which are to be treated and which are referred to in the following as "treatment body parts". These body parts are for example parts of a patient's body, i.e. anatomical body parts. Ionising radiation is for example used for the purpose of treatment. For example, the treatment beam comprises or consists of ionising radiation. The ionising radiation comprises or consists of particles (for example, sub-atomic particles or ions) or electromagnetic waves which are energetic enough to detach electrons from atoms or molecules and so ionise them. Examples of such ionising radiation include X-rays, high-energy particles (high-energy particle beams) and / or ionising radiation emitted from a radioactive element. The treatment radiation, for example the treatment beam, is for example used in radiation therapy or radiotherapy, such as in the field of oncology. For treating cancer in particular, parts of the body comprising a pathological structure or tissue such as a tumour are treated using ionising radiation. The tumour is then an example of a treatment body part.

[0053] The treatment beam is preferably controlled such that it passes through the treatment body part. However, the treatment beam can have a negative effect on body parts outside the treatment body part. These body parts are referred to here as "outside body parts". Generally, a treatment beam has to pass through outside body parts in order to reach and so pass through the treatment body part.

[0054] Reference is also made in this respect to the following web pages: http: / / www.elekta.com / healthcare_us_elekta_vmat.php and http: / / www.varian.com / us / oncology / treatments / treatment_techniques / rapidarc. A treatment body part can be treated by one or more treatment beams issued from one or more directions at one or more times. The treatment by means of the at least one treatment beam thus follows a particular spatial and temporal pattern. The term "beam arrangement" is then used to cover the spatial and temporal features of the treatment by means of the at least one treatment beam. The beam arrangement is an arrangement of at least one treatment beam.

[0055] The "beam positions" describe the positions of the treatment beams of the beam arrangement. The arrangement of beam positions is referred to as the positional arrangement. A beam position is preferably defined by the beam direction and additional information which allows a specific location, for example in three- dimensional space, to be assigned to the treatment beam, for example information about its co-ordinates in a defined co-ordinate system. The specific location is a point, preferably a point on a straight line. This line is then referred to as a "beam line" and extends in the beam direction, for example along the central axis of the treatment beam. The defined co-ordinate system is preferably defined relative to the treatment device or relative to at least a part of the patient's body. The positional arrangement comprises and for example consists of at least one beam position, for example a discrete set of beam positions (for example, two or more different beam positions), or a continuous multiplicity (manifold) of beam positions.

[0056] For example, one or more treatment beams adopt(s) the treatment beam position(s) defined by the positional arrangement simultaneously or sequentially during treatment (for example sequentially if there is only one beam source to emit a treatment beam). If there are several beam sources, it is also possible for at least a subset of the beam positions to be adopted simultaneously by treatment beams during the treatment. For example, one or more subsets of the treatment beams can adopt the beam positions of the positional arrangement in accordance with a predefined sequence. A subset of treatment beams comprises one or more treatment beams. The complete set of treatment beams which comprises one or more treatment beams which adopt(s) all the beam positions defined by the positional arrangement is then the beam arrangement.

[0057] 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 radiography, 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 (SPECT), as mentioned by Wikipedia. The image data thus generated is also termed “medical imaging data”. Analytical devices for example are used to generate the image data in apparatusbased 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.

[0058] 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).

[0059] BRIEF DESCRIPTION OF THE DRAWINGS

[0060] 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

[0061] Fig. 1 illustrates the basic steps of the method according to the first aspect;

[0062] Fig. 2 shows an embodiment of the present invention, specifically the method according to the first aspect;

[0063] Fig. 3 is a flow representation of three embodiments of the invention;

[0064] Figs. 4a to 4g illustrate the matching of the anatomical structure between images; and

[0065] Fig. 5 is a schematic illustration of the system according to the sixth aspect. DESCRIPTION OF EMBODIMENTS

[0066] Fig. 1 illustrates the basic steps of the method according to the first aspect, in which step S11 encompasses acquisition of the first medical image data, step S12 encompasses acquisition of the second medical image data and subsequent step S13 encompasses determination of the image deformation data. This is followed in step S14 by determining the deformed first medical image data. Step S15 then determines the deformation position data, and step S16 the image contour data. Finally, step S17 determines the similarity data.

[0067] Fig. 2 illustrates an embodiment of the present invention that includes all essential features of the invention. In this embodiment, the entire data processing which is part of the method according to the first aspect is performed by a computer 2. Reference sign 1 denotes the input of data acquired by the method according to the first aspect into the computer 2 and reference sign 3 denotes the output of data determined by the method according to the first aspect.

[0068] Fig. 3 illustrates three algorithms Alg 1 , Alg2 and Alg3 which each form an embodiment of the invention. According to Alg1 (flow diagram “Alg1”), elastic fusion is used to determine a contour of the representation of the anatomical structure in the first medical image (1st contour), and subsequently Alg2 max be executed which segments the contour in the second medical image (2nd contour), and the two resulting contours are compared and the resulting value of the measure of similarity is used as a basis to determine whether the second contour is valid. In another embodiment shown in flow diagram “Alg2 (Alg1 + Alg3)”, if the result of the validation is bad (i.e. there is only low similarity), the 2nd contour is fed back into the elastic fusion algorithm as a boundary condition for re-iterating the fusion between the first medical image and the second medical image. In a further embodiment shown in flow diagram “Alg3”, the second contour is determined first and unconditionally used as a boundary condition for conducting the aforementioned elastic fusion.

[0069] As quality score - for computing the similarity between the objects in the image representing the anatomical structure as propagated over time and the objects as determined in place, the Root Mean Square can be used. The Root Mean Square Error (RMSE) is defined as follows, with P and P’ being a point correspondence to compute the Euclidian distance from:

[0070] Alternatively, the similarity between the objects in the image representing the anatomical structure as propagated over time and the objects as determined in place can be determined by computing their Hausdorff distance.

[0071] Fig. 4a shows a 4D-CT of a moving target inside of the breathing lung. As shown in Fig. 4b, the first slice (“bin”) is used as a reference for determining the movement of the target throughout the other slices. Figs. 4c and 4d illustrate determination of movement of the contour of the lung and the target as the anatomical structure by fusing it to the other slices. The resulting deformation filed allows determining the position of the anatomical structure in the other slices, as exemplified by Figs. 4e and 4f. The similarity determination is illustrated by Fig. 4g which shows calculation of the RMSE error between the fusion results (upper row of images) and the segmentation results for the contour (lower row of images), for each of the slices.

[0072] Fig. 5 is a schematic illustration of the medical system 4 according to the sixth aspect. The system is in its entirety identified by reference sign 4 and comprises a computer 5, an electronic data storage device (such as a hard disc) 6 for storing at least the patient data and a medical device 7 (such as a radiation treatment apparatus). The components of the medical system 4 have the functionalities and properties explained above with regard to the sixth aspect of this disclosure.

Claims

CLAIMS1. A computer-implemented medical method of validating a determined deformation of an image rendering of an anatomical structure between digital medical images, the method comprising the following steps: a) first medical image data is acquired (S11 ) which describes a first medical image of the anatomical structure in a first vital state; b) second medical image data is acquired (S12) which describes a second medical image of the anatomical structure, in a second vital state, the second vital state being different from the first vital state; c) image deformation data is determined (S13) based on the first medical image data and the second medical image data, wherein the image deformation data describes a deformation between the image rendering of the anatomical structure in the first medical image and the image rendering of the anatomical structure in the second medical image; d) deformed first medical image data is determined (S14) based on the first medical image data and the image deformation data, wherein the deformed first medical image data describes a deformed first medical image being a result of applying the deformation to the first medical image; e) deformation position data is determined (S15) based on the deformed first medical image data, wherein the deformation position data describes a position of the image representation of the anatomical structure in the deformed first medical image; f) image contour data is determined (S16) based on the second medical image data, wherein the image contour data describes the position of a segmentation of the contour of the image representation of the anatomical structure in the second medical image; g) similarity data is determined (S17) based on the image deformation data and the image contour data, wherein the similarity data describes a value of a measure of similarity between the position of a contour of the image representation of the anatomical structure in the deformed first medicalimage described by the deformation position data and the position of the segmentation of the contour of the image representation of the anatomical structure described by the image contour data.

2. The method according to the preceding claim, wherein the deformation position data is determined by segmenting the contour of the image rendering of the anatomical structure described by the deformed first medical image.

3. The method according to claim 1 , wherein the first medical image data describes a contour of the image representation of the anatomical structure in the first medical image and the deformed first medical image describes a result of applying the deformation to the contour of the image representation of the anatomical structure in the first medical image, and the deformation position data describes a position of the contour of the image representation of the anatomical structure in the first medical image.

4. The method according to the preceding claim, wherein the contour of the image representation of the anatomical structure in the first medical image is or has been determined by segmenting the contour in the first medical image.

5. The method according to any one of the preceding claims, wherein the image deformation data is determined by applying an image fusion algorithm to the first medical image and the second medical image.

6. The method according to any one of the preceding claims, wherein the image contour data is determined by segmenting a contour of the image rendering of the anatomical structure in the second medical image, for example by using an automatic segmentation algorithm, for example a machine learning-based segmentation algorithm, or by acquiring atlas data which describes a digital model of the anatomical structure and determining the image contour data based on the second medical image data and the atlas data.

7. The method according to any one of the preceding claims, wherein the first medical image data and the second medical image data is two- or three- dimensional digital image data, for example describes, for example comprises of consists of, radiographies, digitally reconstructed radiographs, or tomographic images such as magnetic resonance tomographies or computed X-ray tomographies or ultrasound tomographies.

8. The method according to any one of claims 1 to 5, wherein the deformation position data is determined based on the image contour data, for example by using the position of a segmentation of the contour of the image representation of the anatomical structure in the second medical image as a boundary condition for determining the image deformation data, for example in a feed-back loop for grey value and contour-based fusion of the first and second medical images.

9. A method of determining control data for controlling a radiation treatment system, comprising a) executing the method according to any one of the preceding claims; b) acquiring similarity threshold data describing a threshold of the value of the measure of similarity; c) determining validation data based on the similarity data and the similarity threshold data describing whether the position of the image rendering of the anatomical structure in the second medical image described by the deformation position data shall be used as a basis for determining the control data.

10. The method according to the preceding claim, wherein the validation data is determined by comparing the value of the measure of similarity to the threshold.

11. The method according to any one of the two immediately preceding claims, comprising determining, if the value of the measure of similarity and the thresholdhave a predetermined relationship to each other, the control data based on the deformation position data, for example for irradiating the anatomical structure with treatment radiation.

12. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any one of the preceding claims.

13. A computer-readable storage medium on which the program according to the preceding claim is stored.

14. A computer comprising at least one processor, wherein the program according to claim 10 is executed by the processor.

15. A data carrier signal carrying the program according to claim 10.

16. A data stream carrying the program according to claim 10.

17. A medical system (4), comprising: d) the at least one computer (5) according to the claim 10, wherein the instructions cause the computer to carry out the method according to claim 7; e) at least one electronic data storage device (6) storing the control data; and f) a radiation treatment apparatus (7), wherein the at least one computer is operably coupled to the at least one electronic data storage device for acquiring, from the at least one data storage device, the control data, and the radiation treatment apparatus (7) for issuing a control signal to the radiation treatment apparatus (7) for controlling the operation of the radiation treatment apparatus (7) on the basis of the control data.

18. The system according to the preceding claim, wherein the radiation treatment apparatus comprises a treatment beam source and a patient support unit,wherein the at least one computer is operably coupled to the radiation treatment apparatus for issuing a control signal to the radiation treatment apparatus for controlling, on the basis of the control data, at least one of- the operation of the treatment beam source or - the position of the patient support unit.

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