Method for determining material information, x-ray machine and computer program

Abstract

The invention relates to a method for determining material information of a material in a region of interest (5) of an examination object (4) by means of an imaging X-ray machine (18) having an X-ray emitter (1), an X-ray detector (2) and a collimator (7), the invention relates to a method for collimating X-ray radiation regions (3, 3 ') of an X-ray emitter (1), characterised in that it comprises the following steps:-adjusting a collimator (7) in order to capture only a region of interest (5),-capturing a scattered radiation image in a collimator shadow (9) on an X-ray detector (2), and-evaluating the scattered radiation image in order to determine material information.

Description

Technical Field

[0001] The invention relates to a method for determining material information of a material, which is located in a region of interest of an object under examination, using an imaging X-ray machine, the X-ray machine having an X-ray radiator, an X-ray detector and a collimator for collimating the X-ray radiation area of ​​the X-ray radiator. In addition, the invention also relates to an X-ray machine and a computer program. Background Art

[0002] In the context of medical examinations, and in particular also in the context of medical interventions, it may be desirable to be able to distinguish between various materials in the object of examination, in particular in the patient, during X-ray imaging, which materials appear at least similar, in particular identical, in a conventional X-ray machine. A typical field of application is the detection of calcifications during medical interventions, in particular under imaging monitoring, and this distinction may also be associated with blood and contrast agents. When a patient undergoes neurological surgery, it may happen that the contrast agent breaks through the blood-brain barrier after the operation, but no clinically significant bleeding occurs. In other words, only the surrounding brain tissue is contaminated with the contrast agent. After such medical interventions, it is known that three-dimensional control images are usually taken, such as C-arm CT (also known as cone beam CT). In single-energy computed tomography images (CT images) and two-dimensional projection images, it is not possible to distinguish between the intensity of contrast agent impurities and actual bleeding.

[0003] However, for such cases where a plurality of different materials must also be distinguished in medical interventions, it is known to use multi-energy X-ray machines, in particular dual-energy X-ray machines, to use different X-ray energies and / or to perform imaging using photon counting X-ray detectors. However, this means extreme expenditure in order to integrate more energy X-ray imaging into the clinical workflow of medical examinations and / or interventions. This is true both in terms of costs and in terms of workflow and complexity. Summary of the invention

[0004] The object of the present invention is therefore to provide a possibility for differentiating between different materials by means of X-ray imaging which can be implemented particularly cost-effectively and / or can be used in the context of interventions.

[0005] To solve this technical problem, the invention provides a method, an X-ray machine and a computer program according to the independent claims. Advantageous developments of the invention are given by the dependent claims.

[0006] According to the invention, a method of the above type, in particular a computer-implemented method, comprises the following steps:

[0007] - Adjust the collimator to image only the area of ​​interest,

[0008] - taking an image of the scattered radiation in the collimator shadow on an X-ray detector, and

[0009] -Evaluating the diffuse radiation image to determine material information.

[0010] In this context, the collimator shadow is understood to be those regions on the x-ray detector in which the radiation from the x-ray radiation source is attenuated or suppressed by the collimator on its way to the x-ray detector.

[0011] The method is preferably implemented by a computer, in particular by a control device of an X-ray machine. Here, the collimator and the recording device consisting of an X-ray radiator and an X-ray detector are controlled accordingly by a control device, and an evaluation unit of the control device is used to evaluate the scattered radiation image to determine material information. The X-ray machine preferably uses a cone beam geometry. It can, for example, have a C-arm on which an X-ray radiator and an X-ray detector are arranged opposite each other. This type of C-arm X-ray machine is currently used in the scope of medical intervention, in particular for patients as examination objects. Generally, the method according to the present invention is preferably used in the scope of medical intervention, in particular image monitoring of minimally invasive surgery, in particular in the scope of postoperative postoperative monitoring. For example, after or during a neurological intervention, the method according to the present invention is used to distinguish between hemorrhage in the brain and simple contrast agent discharge.

[0012] That is, the material information generally describes the material in the region of interest (ROI). For example, the material information may include at least one characteristic value and / or allow distinguishing at least two possible materials in the region of interest.

[0013] The basic idea of ​​the present invention is to shoot an X-ray image of scattered radiation, which is formed by the material in the area of ​​interest. To this end, the collimator of the X-ray machine is first adjusted in a first step so that the X-ray radiation area only covers the area of ​​interest. If the X-ray detector is currently to be read in the area of ​​the collimator shadow, only the scattered radiation can provide a signal, so that the scattered radiation image is subsequently shot by the X-ray machine in a second step. Based on the scattered radiation pattern in the collimator shadow, material information about the material in the area of ​​interest is derived. In other words, material information can be derived through information about the scattering properties of the material in the area of ​​interest given by the two-dimensional scattered radiation image, and different materials or material categories can be distinguished in particular. In general, the situation that different materials, especially materials with different densities and / or effective atomic numbers have different scattering properties is utilized. Conditions can be purposefully established by collimation to measure these scattering properties in the form of scattered radiation images, so that material information is determined by analyzing the scattered radiation images.

[0014] In this way, the implementation of three-dimensional multi-energy imaging, in particular multi-energy CT, can be advantageously omitted. By recording two-dimensional scattered radiation images, materials can be classified based on their scattering properties. In this case, the measurement can be carried out with little effort.

[0015] In order to determine the position information relative to the region of interest, it should be provided that the position of the region of interest is determined by user input of a user and / or by a segmentation process in at least one two-dimensional or three-dimensional previous image data set recorded by an X-ray machine in the located examination area.

[0016] In this case, the three-dimensional position of the region of interest should be determined. In a two-dimensional prior image data set, in particular a projection image, different shooting geometries, in particular mutually perpendicular shooting geometries and / or a three-dimensional prior image data set acquired for this purpose and / or background information, in particular at least one image of the object to be examined taken at an earlier time, can be used to determine the position in three dimensions. In particular, user input can also be taken into account for this. The at least one background information can also include knowledge about the region in which the intervention on the object to be examined is carried out. In this case, a position parallel to the image plane of the scattered radiation image, in particular together with a position perpendicular to the image plane (distance from the X-ray radiator), is used for collimation.

[0017] That is to say, a variety of possibilities can also be considered to define the position of the region of interest. Thus, this aspect is at least partially achieved by user input. For example, it can be provided that the user marks the region of interest with the help of a two-dimensional or three-dimensional view, in particular in at least one previous image data set that has been taken by an X-ray machine. Such a previous image data set can be, for example, a C-arm CT or a general CT image array, which has been taken after the end of the medical intervention for surgical monitoring. If the user is currently interested in the material in the region of interest, he can mark the region of interest by means of a corresponding input device, which can be assigned to the display device of the previous image data set. When using the previous image data set of the X-ray machine, alignment naturally occurs.

[0018] It is also possible to carry out the segmentation process in a two-dimensional prior image data set (projection images) and / or in a three-dimensional prior image data set (e.g. CT volume). This can be based on user input, but can also be fully automated, especially depending on the application, for example when searching for specific anomalies that need to be clarified in terms of material. The three-dimensional prior image data set is preferably an image data set recorded for monitoring a medical intervention. Preferably, a semantic segmentation can be performed.

[0019] When determining the position of the region of interest, background information can also be incorporated, for example when the patient's anatomy as the examination object has an influence on the possible position or possible position of the region of interest. For example, bleeding can only occur near blood vessels and usually does not enter individual tissue types, such as bones.

[0020] In the transmission direction, i.e. at least substantially perpendicular to the image plane of the scattered radiation image, the region of interest at least generally does not completely pass through the object to be measured, but rather occupies a small part of the total attenuation length between the X-ray radiation source and the X-ray detector. This applies in particular to patients with a variety of structures as examination objects. After other transmitted materials located outside the region of interest also emit scattered radiation, a suitable design of the invention also provides that the desired scattered radiation emitted by the region of interest is measured as completely as possible, while the remaining scattered radiation is suppressed. For this purpose, in particular, a scattered radiation grid that is present in any case can be used in many X-ray machines.

[0021] Therefore, in a particularly advantageous design of the present invention, it can be provided that the X-ray machine also has a scattered radiation grid on the detector side, and an adjustment device is configured for it to orient the scattered radiation grid to the area of ​​interest as the focus. That is to say, in principle, the scattered radiation grid is oriented to the focus of the X-ray radiator during normal operation, thereby reducing the scattered radiation in other parts, and in a particularly preferred design, it is provided that the scattered radiation grid is oriented to the area of ​​interest as the source of the X-ray image to be measured, so that the scattered radiation from the area of ​​interest is measured in a targeted manner. Here, the center of the area of ​​interest is selected as the focus of the area of ​​interest at least in the direction along the central beam. The position information that preferably describes the position of the area of ​​interest in three dimensions discussed above can be used to provide a basis for controlling the adjustment device. In this way, interference factors caused by scattered radiation sources can be greatly reduced.

[0022] In this context, in a first specific embodiment, it can be provided that the self-focusing scattered radiation grid has an adjustable absorption element, in particular a sheet, on which an adjustment device acts in order to orient it at least partially toward the region of interest. Such flexibly focusable scattered radiation grids have already been proposed in the prior art and have in particular different adjustable and thus focusable sheets, which can be adjusted, for example, mechanically, in particular by means of microactuators and / or in other ways, for example by means of an orientation in a magnetic field.

[0023] However, in a second specific embodiment, it is also conceivable that the adjustment device has adjustment means for changing the position of the scattered radiation grid in the direction of the central beam, wherein the scattered radiation grid is positioned in the direction of the central beam for at least partial orientation to the region of interest. Different designs are conceivable here, depending on whether the scattered radiation grid itself is at least partially movable or whether the scattered radiation grid is movable, for example, with the X-ray detector to which the scattered radiation grid is fixed. In this case, the adjustment device can include a linear actuator as an adjustment means, for example a so-called lifting mechanism. The adjustment means can also be used to establish different SIDs (source image distances) in normal operation, in particular when moving together with the X-ray detector.

[0024] For a scattered radiation grid with a fixed focus, which is oriented in a base position to the focal point of the X-ray radiator during normal operation, it can be provided in a second embodiment that the scattered radiation grid is moved from the base position by the distance between the region of interest and the focal point of the X-ray radiator. In this way, the focal point of the scattered radiation grid is located in the region of interest.

[0025] It should be noted here that in an embodiment, the distance between the region of interest and the focus of the X-ray radiator can be selected, for example by moving the examination object and / or the recording device consisting of the X-ray radiator and the X-ray detector, so that the movement space of the scattered radiation grid is sufficient to allow the movement of this distance. Of course, the collimation can also be adjusted accordingly for this purpose.

[0026] It should also be noted here that embodiments are also conceivable in which the first and second embodiments are combined, for example in order to further compensate for an at least partially given adjustability of the scattered radiation grid itself by a shift in the direction of the central beam or the like.

[0027] In principle, it can also be provided that when no adjustment device is present, the scattered radiation image is recorded without the scattered radiation grid, in particular the scattered radiation grid is removed from the beam path for recording the scattered radiation image. This is because if the scattered radiation grid cannot be directed to the region of interest, the measurement of the scattered radiation of the region of interest is reduced or even completely prevented, so that it can be conveniently removed when recording the scattered radiation image.

[0028] Suitably, the material information includes the effective atomic number and / or density of the material and / or the category of one of at least two candidate materials. The effective atomic number (usually referred to as the effective atomic number, Zeff) and / or density of the material are parameters that determine the scattering of the material. The characteristic values ​​are usually used as material information in multi-energy imaging. In particular, when the main purpose is to distinguish materials, the material information can also include the classification of the corresponding material category. For example, in one application, blood and contrast agent are distinguished or blood and calcification are distinguished.

[0029] In one expedient embodiment, it can be provided that the evaluation of the scattered radiation image includes the use of at least one trained function which is based on the scattered radiation image as input data and / or on material information as output data.

[0030] Generally speaking, trained functions map the cognitive functions that humans associate with other human brains. Through training based on training data (machine learning), trained functions have the ability to adapt to new environments and can discover and infer patterns.

[0031] Generally speaking, the parameters of the training function can be adjusted by training. In particular, supervised learning, semi-supervised learning, unsupervised learning, reinforcement learning and / or active learning can be used. In addition, representation learning (also called "feature learning") can also be used. In particular, the parameters of the training function can be repeatedly adjusted through multiple training steps.

[0032] For example, the training function may include a neural network, a support vector machine (SVM), a decision tree and / or a Bayesian network, and / or the training function may be based on mean clustering, Q-learning, a genetic algorithm and / or an association rule. In particular, the neural network may be a deep neural network, a convolutional neural network (CNN) or a deep CNN. In addition, the neural network may also be an adversarial network, a deep adversarial network and / or a generative adversarial network (GAN). For this application area, CNN has been shown to be very suitable.

[0033] Therefore, direct evaluation and interpretation of the scattered radiation pattern shown by the scattered radiation image can be achieved by training functions, i.e. by machine learning, where preferably the scattered radiation image is obtained as input data and the material information is obtained as output data. For example, in applications where it is necessary to distinguish between two materials or material classes, a binary classifier can be used.

[0034] In this case, the training can preferably be carried out on a large number of training data sets containing different scattered radiation patterns and relevant material information. In other words, it can be provided that annotated training images are used to train the training function using the ground truth. In this case, the training database can be expanded by determining further training data sets by simulation. For example, in an advantageous improvement, it can be provided that the imaging process of the scattered radiation image is simulated for different regions and / or relevant materials in order to determine the training data for the predetermined examination object. Thus, it is possible to use the actually captured images as a starting point and generate a plurality of training data sets by virtually inserting materials and simulating in at least one ROI.

[0035] However, in the context of the present invention, a similarly good evaluation can also be achieved by simulating the imaging process of the scattered radiation image under corresponding assumptions and comparisons.

[0036] In general, it can be assumed that, for determining the material information, the similarity of the scattered radiation image to the comparison images of the different contrasting material information is determined, and the material information is determined based on at least one greatest similarity. Generally, empirically determined and / or representative comparison images can be used. However, if a three-dimensional prior image data set of the object to be examined is available, the comparison image can be determined specifically for the object to be examined.

[0037] It can therefore also be provided that the contrast image is at least partially determined by simulating an imaging process for a scattered radiation image of a model of the examination object, wherein the material of the respective contrast material information is inserted into the region of interest in the model. The model is preferably established here from a three-dimensional prior image data set of the examination object. The prior image data set can be, for example, a computed tomography image, in particular a C-arm CT image. In this case, the material of the contrast material information is virtually set in the region of interest for the generation of the model, rather than a real material, and a simulation is carried out in order to obtain the contrast image. In order to simulate the imaging process of the scattered radiation image to obtain the contrast image (preferably also including a model of the X-ray machine in the simulation), preferably the acquisition parameters and / or the acquisition geometry, in particular the collimation, of the scattered radiation image are used accordingly. The simulation can involve a statistical method, for example as a Montreal simulation, and / or a deterministic method, for example by solving the Boltzmann transport equation. By determining a specific contrast image and a scattered radiation image of the examination object, a good basis is provided for the comparison and thus a reliable basis for determining the material information.

[0038] In a further development of the invention, it can also be provided that a plurality of scattered radiation images are recorded with different recording geometries and are evaluated for determining the material information, in particular by statistical and / or plausible summaries of the individual material information for each scattered radiation image. If an X-ray machine is used which allows different recording geometries in a simple manner, the scattered radiation images can be recorded accordingly with different recording geometries in order to obtain an extended basis for determining the material information. In this case, it is particularly expedient if the region of interest is positioned at the isocenter of the X-ray machine, since different recording geometries can thereby be set by a simple rotation of a recording device, for example a recording device arranged on a C-arm.

[0039] In addition to the implementation method, the present invention also relates to an X-ray machine, which has an X-ray radiator, an X-ray detector, a collimator for collimating the X-ray radiation area of ​​the X-ray radiator, and a control device, wherein the control device is used to determine material information of a material located in a region of interest of an inspection object, and the control device has:

[0040] - an adjustment unit for adjusting the collimator so that only the area of ​​interest is imaged,

[0041] - an image acquisition unit for acquiring an image of the scattered radiation in the shadow of the collimator on an X-ray detector, and

[0042] - an evaluation unit for evaluating the scattered radiation image to determine material information.

[0043] The control device can preferably have at least one processor and at least one memory. Functional units can be formed by software and / or hardware to implement the steps of the method according to the present invention. In other words, the control device can be configured to execute the method according to the present invention.

[0044] Here, the adjustment unit and the recording unit themselves can also be used for adjusting the collimator and for recording images in other specific applications. In addition to the functional units, further functional units can also be provided for implementing other conceivable steps. For example, the control device can include a determination unit for determining the position of the region of interest and / or a control unit for controlling the adjustment device (or for removing the scattered radiation grid). In some embodiments, the functional unit can have subunits so that, for example, a simulation subunit of the evaluation unit can be provided.

[0045] As mentioned above, the imaging X-ray machine can be in particular an X-ray machine with a C-arm, on which an X-ray emitter and an X-ray detector are fixed opposite each other. It is also conceivable that the X-ray machine is a computed tomography device.

[0046] The computer program according to the invention can be directly loaded into the memory of the control device and has a program content which, when the computer program is executed on the control device, causes the control device to carry out the method according to the invention. The computer program can be stored on an electronically readable data carrier, which thus comprises control information stored thereon, which includes at least one computer program according to the invention and enables the control device to carry out the method according to the invention when the data carrier is used in the control device of the X-ray device. The data carrier can in particular be a non-transitory data carrier. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Further advantages and details of the invention are apparent from the exemplary embodiments described below and with reference to the accompanying drawings. In the drawings:

[0048] Figure 1 The recording geometry for recording a two-dimensional X-ray image of an object under examination is schematically shown.

[0049] Figure 2 Schematically showing the Figure 1 The X-ray image generated by the shooting geometry,

[0050] Figure 3 A flow chart showing an embodiment of the method according to the present invention,

[0051] Figure 4 Schematic representation of the acquisition geometry with collimation for the region of interest,

[0052] Figure 5 shows a schematic diagram for generating scattered radiation in an examination object,

[0053] Figure 6 shows a schematic diagram for using a focusable scattered radiation grid,

[0054] Figure 7 shows a schematic diagram for using a movable scattered radiation grid,

[0055] Figure 8 An X-ray machine according to the present invention is shown, and

[0056] Fig. 9 A functional block diagram of a control device for an X-ray machine is shown. DETAILED DESCRIPTION

[0057] In the following, specific embodiments of the invention are described, with reference to the context of a medical intervention, here a neurological intervention, purely by way of example. In general, different materials should be distinguished in the region of interest. For example, the task when monitoring the outcome of an intervention in a neurological intervention is to distinguish between contrast agents that (bleed-free) cross the blood-brain barrier and actual bleeding (i.e. blood) as a candidate material.

[0058] In this case, Figure 1 The shooting geometry of the projection images shot by an imaging X-ray machine is schematically shown, and the X-ray machine has a shooting device with an X-ray radiator 1 and an X-ray detector 2. The X-ray radiator 1 emits an X-ray radiation zone 3 from a focal point to penetrate an examination object 4, for example, an examination area of ​​a patient. In the example of a neurological interventional procedure, the examination area may be, for example, the head of a patient. An area of ​​interest 5 is shown in the examination area in the examination object 4, in which a certain material exists, which cannot be clearly identified in the corresponding projection image or in a three-dimensional image group reconstructed from a plurality of projection images due to its view. In the above example, blood and contrast agents of contaminated tissue are shown identically.

[0059] Figure 2 Such a two-dimensional projection image 6 is schematically shown, which within the scope of the present invention can be regarded as a two-dimensional prior image data set because it was recorded before the method was carried out. The projection image 6 shows a region of interest 5 within the examination object 4 .

[0060] In order to be able to determine which material is present in the region of interest 5, it is provided that the scattered radiation from the region of interest 5, that is, the scattered radiation of the material, is examined. Figure 3 In the method described, firstly, position information is determined in step S1, and the scattered position information three-dimensionally describes the position of the region of interest 5 in the coordinate system of the X-ray machine. Specifically, the position information can, for example, describe the extension of the region of interest 5 in at least some spatial directions and / or the position of the center of gravity and / or the approximate shape when necessary. For example, from the perspective of the extension in three mutually perpendicular spatial directions, the region of interest can be regarded as spherical or ellipsoidal.

[0061] To determine the position information, user input can be used on the one hand. For example, the user can mark the region of interest 5 in the view of the projection image 6, which can also take place in other projection images of the recording geometry in order to determine the three-dimensional position. The marking can also be performed in the three-dimensional previous image data set.

[0062] As an alternative or in addition, it is also possible to segment the region of interest 5 in the two-dimensional and / or three-dimensional preceding image data set by means of a segmentation process, wherein this can start from a seed point predetermined by the user, for example.

[0063] The position information determined in step S1 can be used to control the collimator of the x-ray machine in step S2 so that the x-ray radiation zone 3 effective for imaging is lowered parallel to the image plane to the region of interest 5 . In other words, the region of interest 5 is collimated.

[0064] This is Figure 4 , which also shows a collimator 7 arranged on the X-ray radiator 1. It can be seen that the effective, collimated X-ray radiation area 3' remaining after the collimator 7 is limited so that it surrounds the region of interest 5 as narrowly as possible. In the image recording with the effective X-ray radiation area 3', the region of interest 5 should be imaged in the central area 8 of the X-ray detector 2, while the scattered radiation is measured in the surrounding collimator shadow 9.

[0065] To achieve this, in step S3 (refer to Figure 3 ) so that the scattered radiation grid, which is fixedly and unvariably aligned with the focal point of the x-ray radiator 1 , is removed, but the scattered radiation of the material can still be measured along the entire attenuation length in the examination object 4 .

[0066] This question is answered through Figure 5 Here it can be seen that the region of interest 5 has only a small portion of the attenuation length in the transmission direction, ie along the central beam, so that in addition to the detected scattered radiation 10, undesired scattered radiation 11 is also generated by other transmitted materials.

[0067] Therefore, in order to avoid undesired scattered radiation 11 as thoroughly as possible, it is preferred to use a scattered radiation grid whose focus can be aligned with the region of interest 5. Generally speaking, it is also preferred to configure the scattered radiation grid with an adjustment device, which is controlled in step S3 to align the focus of the scattered radiation grid with the region of interest 5, and thus to measure the scattered radiation 10 in a targeted manner and suppress the scattered radiation 11.

[0068] pass Figure 6 A first embodiment is explained. In this case, a self-focusing scattered radiation grid 12a is used, to which an adjustment device 13a is provided, which is able to adjust the orientation of a sheet 14 (only partially illustrated here) of the scattered radiation grid 12a so as to select a new focus, here the position of the region of interest 5. The adjustability of the sheet 14 is indicated by the arrow 15. The sheet 14 is an absorbing element.

[0069] pass Figure 7The second embodiment is explained in detail. Here, the orientation of the plate 14 of the scattered radiation grid 12b is fixed. In this case, however, the component unit consisting of the X-ray detector 2 and the scattered radiation grid 12b (or alternatively only the scattered radiation grid 12b itself) can be moved along the central beam by corresponding adjustment means of the adjustment device 13b, as shown by the arrow 16. If the scattered radiation grid 12b is oriented to the focus 17 of the X-ray machine 1 in normal operation, the scattered radiation grid 12b can be moved by controlling the adjustment device 13b so that it is away from the region of interest 5 at the distance of the focus 17 of the X-ray radiator 1, thereby achieving an orientation with the region of interest 15 as the focus.

[0070] In principle, a combination of the first embodiment with the second embodiment is also conceivable, for example when the insufficient adjustability of the lamellae 14 is supplemented by a displacement along the central beam.

[0071] If adjustments are made to the collimator 7 and the scattered radiation grids 12a, 12b by controlling the corresponding components, it is possible to Figure 3 As shown, in step S4 a two-dimensional scattered radiation image is recorded with the aid of the x-ray radiator 1 and the x-ray detector 2 , which image shows the scattered radiation from the region of interest 5 in the collimator shadow 9 .

[0072] The scattered radiation image is then evaluated in step S5 in order to determine material information describing the material in the region of interest 5. The material information may include characteristic values ​​of the material, such as an effective atomic number and / or density. Alternatively or additionally, the material information may also include the classification of the material in at least two material classifications, which is suitable for situations where different materials should be distinguished.

[0073] For evaluating the scattered radiation image, a trained function can be used in a first embodiment of step S5, which uses the scattered radiation image as input data and outputs material information as output data, for example, the class of a candidate material. The trained function has been trained with a training data set, wherein the corresponding material information is assigned to the scattered radiation image as ground truth. The training data set can be determined at least partially by simulation, in that different materials occupy different regions of interest.

[0074] In a second specific embodiment, a three-dimensional prior image data set of the object to be examined 4, which was previously recorded by an X-ray machine, is used as a basis in order to determine comparison images for different materials by simulation. Starting from the three-dimensional prior image data set, the material is virtually inserted into the region of interest according to the material information that matches the comparison image, in order to obtain a model, and the simulation is carried out. This is done, for example, for at least two material classes and / or candidate materials to be distinguished. Subsequently, for each comparison image, a similarity to the scattered radiation image is determined. The material information that matches the comparison image with the highest similarity is then determined as the evaluation result.

[0075] In step S6, the material information may be output to the user, for example, on a display device of an X-ray machine, or may be stored for later use.

[0076] It should be noted that in the described embodiment, it is also conceivable to record more two-dimensional scattered radiation images with different recording geometries and evaluate them together to determine the material information. In this case, steps S2 to S4 are repeated accordingly for each recording geometry.

[0077] Figure 8 The schematic diagram of the principle of an X-ray machine 18 according to the invention is shown. The X-ray machine 18 comprises a C-arm 19, on which an X-ray radiator 1 with a collimator 7 and an X-ray detector 2 with scattered radiation grids 12a, 12b are arranged opposite each other. The operation of the X-ray machine 18 is controlled by a control device 20, which is also designed to carry out the method according to the invention.

[0078] Fig. 9 The functional block diagram of the control device 20 is shown. The control device firstly has a memory 21 in which, for example, previous image data sets, scattered radiation images, material information etc. can be stored.

[0079] In order to control the recording operation in general and in order to control the recording of the scattered radiation image in particular (step S4), the control device 20 first has a recording unit 22. Accordingly, an adjustment unit 23 is provided for controlling the collimator 7 (in particular in step S2), and a control unit 24 is provided for controlling the adjustment devices 13a, 13b (in particular in step S3). The determination unit 25 allows the determination of position information of the region of interest 5 according to step S1. Finally, an evaluation unit 26 is also provided in order to determine material information according to step S5.

[0080] Optionally, when implementing the second specific embodiment, the evaluation unit 26 can also have a simulation unit 27 for carrying out a corresponding simulation.

[0081] In addition to the C-arm X-ray machine shown here, the X-ray machine 18 can also be a computed tomography device, in particular an invasive computed tomography device.

[0082] Although the details of the present invention have been illustrated and described in detail through the preferred embodiments, the present invention is not limited to the disclosed examples, and those skilled in the art may derive other different variations therefrom without departing from the scope of protection of the present invention.

Claims

1. A method for determining material information of a material using an imaging X-ray machine (18), the material being located in a region of interest (5) of an object to be examined (4), the X-ray machine comprising an X-ray radiator (1), an X-ray detector (2) and a collimator (7), the collimator (7) being used for collimating an X-ray radiation zone (3, 3') of the X-ray radiator (1), characterized in that: The method comprises the following steps: - adjusting the collimator (7) to image only the region of interest (5), - recording an image of the scattered radiation in the collimator shadow (9) on the X-ray detector (2), and -Evaluating the diffuse radiation image to determine material information.

2. The method according to claim 1, characterized in that The position of the region of interest (5) is determined by user input and / or by a segmentation process in at least one two-dimensional or three-dimensional prior image data set recorded by an X-ray machine (18) in the located examination region (4).

3. The method according to claim 1 or 2, characterized in that: The X-ray machine (18) also has a scattered radiation grid (12a, 12b) on the detector side, and an adjustment device (13a, 13b) is provided for the scattered radiation grid to orient the scattered radiation grid (12a, 12b) to the region of interest (5) as a focus.

4. The method according to claim 3, characterized in that The self-focusable scattered radiation grid (12a) has an adjustable absorption element, in particular a plate (14), on which adjustment means (13a, 13b) act in order to direct it at least partially to the region of interest (5).

5. The method according to claim 3 or 4, characterized in that: The adjustment device (13a, 13b) has adjustment means for changing the position of the scattered radiation grid (12a, 12b) in the direction of the central beam, wherein the scattered radiation grid (12a, 12b) is positioned in the direction of the central beam for at least partial orientation to the region of interest (5).

6. The method according to claim 5, characterized in that For a fixed-focus scattered radiation grid (12b), which is oriented in normal operation in a basic position to the focus (17) of an X-ray machine (18), the scattered radiation grid (12b) is moved from the basic position at a distance between the region of interest (5) and the focus (17) of the X-ray radiator (1).

7. The method according to claim 1 or 2, characterized in that: A scattered radiation image is recorded without a scattered radiation grid (12a, 12b), in particular the scattered radiation grid (12a, 12b) is removed from the beam path for recording the scattered radiation image.

8. The method according to any one of the preceding claims, characterized in that The material information includes an effective atomic number and / or density of the material and / or a category that is one of at least two candidate materials.

9. The method according to any one of the preceding claims, characterized in that The evaluation of the scattered radiation image comprises the use of at least one trained function which is based on the scattered radiation image as input data and / or on material information as output data.

10. The method according to claim 9, characterized in that Annotated training images are used to train the trained function with ground truth and / or a simulation of the imaging process is carried out for scattered radiation images for different regions of interest and / or materials to determine training data for a predetermined examination object.

11. The method according to any one of the preceding claims, characterized in that To determine the material information, similarities between the scattered radiation image and comparison images of different comparison material information are determined, and the material information is determined based on at least one greatest similarity.

12. The method according to claim 11, characterized in that The contrast image is at least partially determined by simulating an imaging process for a scattered radiation image of a model of the object to be examined (4), wherein the material of the respective contrast material information is inserted into the region of interest (5) in the model.

13. The method according to any one of the preceding claims, characterized in that A plurality of scattered radiation images are acquired using different acquisition geometries and are evaluated to determine the material information, in particular by means of a statistical and / or plausible summary of a single material information item for each scattered radiation image.

14. An X-ray machine (18) comprising an X-ray radiator (1), an X-ray detector (2), a collimator (7) for collimating an X-ray radiation zone (3, 3') of the X-ray machine (1), and a control device (20), wherein: The control device (20) is used to determine material information of a material located in a region of interest (5) of an inspection object (4), and the control device has: - an adjustment unit (23) for adjusting the collimator (7) so as to image only the region of interest (5), - a recording unit (22) for recording an image of the scattered radiation in the collimator shadow (9) on the X-ray detector (2), and - an evaluation unit (26) for evaluating the scattered radiation image to determine material information.

15. A computer program which, when executed in a control device (20) of an imaging X-ray machine (18), causes the control device to carry out the steps of the method according to any one of claims 1 to 13.

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