Computer-implemented method for processing X-ray images

Abstract

The invention relates to a computer-implemented method for processing X-ray images (2), comprising the steps of: providing a sequence (1) of X-ray images (2) of an image region (3) in which at least one segment of a vascular system (4) of an object to be examined (28) is mapped, wherein the sequence describes a temporal trend of the X-ray intensity detected in the image region (3) due to a change in the distribution of a contrast agent in the segment of the vascular system; determining a contrast agent parameter (20) related to the contrast agent distribution based on the temporal trend (14) of a parameter related to the X-ray intensity in a selected subregion (7) of the X-ray image (2); determining an image (21, 24) of the segment of the vascular system based on at least one of the X-ray images of the sequence; and modifying (22) the image (21, 24) of the segment of the vascular system based on the contrast agent parameter (20) to provide output data (23).

Description

Technical Field

[0001] The invention relates to a computer-implemented method for processing X-ray images. The invention also relates to a processing device, an X-ray device for medical imaging, a computer program and a computer-readable data carrier. Background Art

[0002] In the field of contrast-agent-based X-ray imaging, in particular within the framework of angiographic imaging, blood is made visible in X-ray images by injecting a contrast agent into the vascular system of the patient being examined. For example, contrast agents containing iodine or gadolinium can be used as contrast agents. The respective contrast agent temporarily replaces the blood in the respective blood vessels at least partially or even completely. A series of X-ray images are acquired during or immediately after the injection of the contrast agent. Since the X-ray absorption of the respective contrast agent is significantly higher than the X-ray absorption of the blood or the surrounding tissue, the part of the vascular system affected by the contrast agent is depicted darker than the background in the individual images.

[0003] In order to show a larger vascular system segment, an image can be selected in which there is substantially enough contrast agent in the entire imaged vascular system segment, or different X-ray images of a sequence can be combined in such a way that, for example, for each image point the value of the image point of the X-ray image is selected in which the corresponding image point is depicted darkest, i.e., the strongest absorption is present in the corresponding image point. The entire vascular system segment located in the image area can thus be clearly highlighted. Alternatively, the background can be subtracted by recording without the administration of contrast agent, whereby the background can be subtracted from the image of the vascular system. This is called digital subtraction angiography (DSA).

[0004] The contrast formed by this imaging of the vascular system depends on the imaging parameters; on the characteristics of the object of examination, such as weight; and on the parameters of the contrast agent administration, i.e., for example, how much contrast agent is used or with what pressure the injection is performed; and on the concentration of iodine or gadolinium in the contrast agent; the viscosity of the contrast agent; the mixing ratio of contrast agent to blood and / or the diameter of the injection catheter.

[0005] Various methods are known for contrast improvement. For example, the imaging of the vascular system can be split into different frequency bands, and the amplitudes of these frequency bands can be varied individually, so that frequency bands that are particularly relevant for displaying vascular details are emphasized, while the amplitudes of frequency bands that primarily display noise or large background structures can be reduced. In this case, the scaling of the individual frequency bands can be fixedly predetermined or depend on the vascular imaging itself, that is, on its image data.

[0006] Despite these possibilities for improving the contrast, there remains the problem that images of the vascular system of different patients are hardly comparable, since the resulting contrast depends on a large number of parameters. For example, even images of the vascular system of the same patient cannot be easily compared if different recording parameters or contrast agent injections are used.

[0007] For example, if a fixed predetermined algorithm for contrast optimization is used, low contrast may be formed, for example, when injecting with low pressure or a small amount of contrast agent. On the contrary, if an adaptive method that takes into account the image content is used, the difference may be actually concealed. For example, an implanted stent may lead to a significantly higher blood flow in a part of the vascular system. However, the contrast changes formed by this will be eliminated again by adaptive contrast optimization. In both cases, as in the case of using vascular system images without contrast improvement, only very limited comparability of vascular system images acquired for different examination objects, with different imaging parameters and / or under different contrast agent administration can be achieved.

[0008] In order to solve this problem, document WO 2019 / 002 560 A1 proposes to take into account the imaging parameters used in contrast improvement. In addition, document EP 3 420 906 A1 proposes to take into account the parameters of automatic contrast agent injection in contrast improvement. The two documents discussed use relatively complex models to take into account the mentioned parameters and therefore require relatively complex calculations. In addition, the parameters of contrast agent administration can only be taken into account if the parameters of contrast agent administration are accurately known, which on the one hand increases the cost and on the other hand is ultimately only possible in the case of automatic contrast agent injection.

[0009] However, in many applications manual contrast agent injection is used, so that for example the exact pressure profile of the contrast agent injection is unknown. In these cases, the corresponding changes cannot be compensated, so that only limited comparisons of differently imaged vascular systems are possible. Summary of the invention

[0010] The object of the present invention is therefore to provide a method for processing x-ray images which allows good comparability of images of the vascular system with low computational effort and during manual injection of contrast agent.

[0011] According to the invention, the above technical problem is solved by a computer-implemented method for processing X-ray images, the method comprising the following steps:

[0012] - providing a sequence of X-ray images of an image region in which at least one section of a vascular system of the examination subject is mapped, wherein the sequence describes the temporal course of the detected X-ray intensity in the image region due to a change in the distribution of the contrast agent in the section of the vascular system,

[0013] - determining a contrast agent variable related to the contrast agent distribution based on the time profile of the variable related to the X-ray intensity in a selected sub-region of the X-ray image,

[0014] - determining an image of the segment of the vascular system from at least one of the X-ray images of the sequence,

[0015] - modifying the image of the segment of the vascular system in dependence on the contrast agent parameter to provide output data.

[0016] The invention is based on the idea of ​​monitoring the time course of a variable related to the X-ray intensity, for example the time course of the detected X-ray intensity or X-ray absorption, in a sub-region of an X-ray image and inferring a contrast medium variable related to the contrast medium distribution or the contrast medium administration from this time course. In this case, use can be made of the knowledge that, within the framework of an image sequence, the contrast medium is usually initially present only in relatively small sections of the catheter or the vascular system, for example in the section of the vascular system through which the contrast medium flows into the image region. Therefore, even if there is initially no information about the parameters of the contrast medium administration, the characteristics of the contrast medium administration and the contrast to be expected from this time course, in particular the increase or decrease of the contrast medium concentration in the sub-region and the intensity change of the X-ray intensity that accompanies it, can be inferred.

[0017] The proposed computer-implemented method is therefore particularly suitable for processing sequences of X-ray images that have been recorded during manual contrast medium administration, since in this case only incomplete information about the contrast medium administration is available. Since in the method according to the invention the modification of the images, including the determination of the contrast medium parameters, as will be explained in more detail below, can be realized by relatively simple algorithms, the method can be performed with low computational effort.

[0018] The individual X-ray images can be two-dimensional X-ray images in particular. However, it is also possible to use three-dimensional X-ray images, which are determined, for example, by a reconstruction method from a plurality of corresponding two-dimensional images. This may be suitable, for example, for the use of this method in the field of computed tomography angiography. In particular, the individual X-ray images each show the same image region with the same recording geometry. This makes it possible to immediately find a subregion of a once selected X-ray image in all X-ray images of the sequence, for example by considering the same image points in each case.

[0019] The parameter related to the X-ray intensity can be, for example, the gray value of the corresponding image point. Optionally, preprocessing can be performed in order to, for example, subtract an offset value or a similar value. It may also be advantageous to use absorption values, because the absorption values ​​can be directly related to the contrast agent concentration in the corresponding image area. A sequence of X-ray images can be provided via an input interface, and output data can be output via an output interface. The input or output interface can be a pure software interface, but they can also be a physical interface, such as a network interface or an interface of a data bus. The provision of a sequence of X-ray images can be performed, for example, via a database or the like. However, the sequence of X-ray images can also be provided directly by a medical imaging device. This may be advantageous, for example, to directly use a computer-implemented method to analyze the data of the corresponding image acquisition device.

[0020] To determine the image of the segment of the vascular system, the methods already explained above and known from the prior art can be used. The problems described there with regard to the influence of different parameters on the resulting contrast can be compensated at least to a large extent by the method according to the invention.

[0021] As the selected subregion, an image segment can be selected which maps a catheter and / or a blood vessel through which a contrast agent is or has been guided into the mapped section of the vascular system within the framework of the acquisition sequence, or a subsegment of this image segment can be selected. The subsegment can be taken into account in particular without taking into account the edge regions of the image segment. For example, the subsegment can be the central segment of the image segment or only include a few central image points of the image segment. The subsegment can also include only a single image point, for example an image point which is substantially located in the center of the image segment.

[0022] If the selected subregion includes a plurality of pixels, the temporal curve can be determined, for example, for the minimum, maximum, median or average value of the values ​​of the considered pixels.

[0023] As already explained, the time course of a variable related to the X-ray intensity in a region, such as the time course of the X-ray absorption, can provide information about the time course of the concentration of the contrast agent in this region. By analyzing the contrast agent concentration or a variable related thereto in the region of a catheter or a vessel through which the contrast agent is guided into the imaging region of the vascular system, the time course of the contrast agent feed can be taken into account without having to know the parameters of the contrast agent administration, such as the injection volume or the injection pressure, for this purpose.

[0024] The selection of the selected sub-area can depend on only one of the x-ray images or on a subsequence of x-ray images that does not include all x-ray images. Here, the x-ray images or subsequences can in particular map the section of the contrast agent entering the mapped vascular system.

[0025] For example, this may be an X-ray image or a subsequence of X-ray images acquired immediately after the injection of a contrast agent into the object under examination or after the contrast agent has entered the mapped segment of the vascular system. In such an early X-ray image, the contrast agent is essentially only present in the catheter feeding the contrast agent or in the blood vessels through which the contrast agent is introduced into the mapped segment of the vascular system. As a result, a strong contrast is formed for the region through which the contrast agent is introduced into the mapped segment of the vascular system, so that, for example, this region can be easily segmented in order to use it as a subregion or in order to select a subregion within this region.

[0026] In order to select the selected sub-regions, the relevant image segmentation can be determined by comparing the image data in an X-ray image or in an intermediate image determined according to the subsequence with a limit value. As explained, a high contrast agent concentration leads to a strong X-ray absorption and thus to a low X-ray intensity. Thus, for example, a region with a high contrast agent concentration can be segmented by selecting all coherent image points whose grayscale value or detected X-ray intensity is below a limit value. If the parameter related to the X-ray intensity is selected so that it increases with the increase of the contrast agent concentration, that is, for example, if the X-ray absorption is analyzed, then alternatively, the coherent region exceeding the limit value can also be segmented.

[0027] The relevant segment can in particular be an image fragment of the mapping catheter and / or blood vessel discussed above, through which, within the framework of the recording sequence, a contrast agent has been guided into the mapped segment of the vascular system. As explained above, this can be achieved by analyzing an X-ray image or a subsequence of X-ray images, which has been acquired after the contrast agent has been administered or immediately after the contrast agent has entered the mapped segment of the vascular system. The selected subregion can be a relevant image segment or a subsegment of a relevant image segment. For example, as explained above, a central region or a single image point within the relevant image segment can be selected, for which the time trend of a variable related to the X-ray intensity is analyzed.

[0028] The determination of the intermediate image can be used in particular to identify all regions in which a high contrast agent concentration and therefore a low X-ray intensity is present in at least one X-ray image of the analyzed subsequence. This can be achieved, for example, by setting the grayscale value of each image point of the intermediate image to the minimum grayscale value of this image point occurring in the subsequence. This is suitable if the grayscale value increases with increasing detected X-ray intensity. The minimum grayscale value thus corresponds to the highest occurring contrast agent concentration. If, on the other hand, absorption or other variables which increase with increasing contrast agent concentration have already been mapped to a variable describing the X-ray intensity in the individual X-ray images, then instead for each image point the maximum value occurring for this image point within the subsequence is selected.

[0029] In addition, the contrast agent concentration in the mapped segment of the vascular system also depends on how large the diameter of the catheter used for feeding is. The same applies when the contrast agent is fed to the mapped segment of the vascular system via a blood vessel. It is therefore advantageous to take into account not only the X-ray attenuation formed by the contrast agent feeding and thus essentially the integral of the contrast agent concentration perpendicular to the image plane, but also the diameter of the blood vessel or catheter through which the contrast agent is introduced into the mapped segment of the vascular system. As will be explained below, this diameter can be determined with good accuracy from the X-ray image itself.

[0030] In the method according to the invention, the diameter of a selected subregion or the diameter of the relevant image segment or the diameter of a vessel or duct through which a contrast agent is or has been introduced into the mapped segment of the vascular system within the framework of an acquisition sequence can be determined, wherein the image of the segment of the vascular system is modified as a function of the determined diameter. In particular, the diameter can be determined based on image data or at least based on image data of at least one of the X-ray images of a sequence or of a portion of the X-ray images.

[0031] The possibility of segmenting a vessel or duct for feeding has already been explained above. If the analyzed X-ray images or subsequences have shown that contrast agent has penetrated into the vascular system over a certain length, or if a certain length of duct has been mapped, the longitudinal direction of the vessel or duct can already be determined from the shape of the determined segment, so that, for example, the diameter can be determined as the dimension perpendicular to the determined longitudinal direction or as the shortest dimension.

[0032] As explained at the outset, a sequence of three-dimensional X-ray images can also be processed by the method according to the invention. In this case, as explained above, the diameter can be taken into account. However, in particular, it is also possible to determine the cross-sectional area of ​​a subregion or an associated image segment or a vessel or duct based on the current three-dimensional X-ray image, thereby modifying the image of the segment of the vascular system in accordance with the determined cross-sectional area.

[0033] In order to modify the image of the segment of the vascular system, in particular after subtraction of the offset, all image data of the image or image data of the image that are within a predetermined value range can be multiplied by a scaling factor that depends on the contrast medium parameter. For example, the overall scale of the image data can be compressed or stretched depending on the contrast medium parameter in order to increase or reduce the contrast. However, in some cases, it may also be advantageous to stretch or compress only a portion of the value scale, for example in order to achieve a targeted contrast increase for a specific range of grayscale values ​​and, for example, to compress less relevant scale areas.

[0034] In addition or alternatively, the scaling factor can depend on the diameter or cross-sectional area of ​​the selected subregion or the relevant image segment, or on the diameter or cross-sectional area of ​​the blood vessel or catheter through which the contrast agent is fed. The value range and / or the offset to be scaled can also depend on the contrast agent parameter and / or the diameter or cross-sectional area.

[0035] The scaling factor may be inversely proportional to the contrast agent parameter and / or the determined diameter. In particular, the scaling factor may be inversely proportional to the product of these two parameters. In other words, the scaling factor may be proportional to the inverse of the contrast agent parameter and / or to the inverse of the determined diameter, in particular proportional to the inverse of the product of the contrast agent parameter and the diameter.

[0036] Thus, a larger scaling factor is formed as a function of a smaller contrast parameter (which describes, for example, a less used amount of contrast medium or a smaller contrast medium feed pressure) or as a function of a smaller diameter of the catheter or blood vessel used for feed, whereby the contrast is increased in these cases, and vice versa. In this way, by the described selection of scaling factors, changes in the amount of contrast medium used, changes in the type of contrast medium administration and changes in the contrast medium feed diameter can be compensated at least to a large extent. Since the contrast medium parameters can also depend on the parameters of the imaging or examination object, deviations in this respect can also be compensated at least to a large extent.

[0037] The contrast agent parameter can be determined from the maximum or minimum value of the time profile of the variable related to the X-ray intensity in the selected sub-region or from the integral over this time profile. In the simplest case, the variable related to the X-ray intensity is related to the X-ray absorption and is therefore at least approximately related to the contrast agent concentration or to the product of the contrast agent concentration and the thickness of the contrast agent perfusion region perpendicular to the image plane. The maximum value thus occurs at the time of the maximum contrast agent density.

[0038] If relatively high flow rates are to be expected in the mapped segment of the vascular system, it can be assumed, at least approximately, that the diffusion of the contrast agent bolus can be neglected, and the maximum value of the detected contrast agent concentration can therefore be shifted through the vascular system. If, as explained above, the imaging of the segment of the vascular system is performed by mapping the maximum absorption or the minimum X-ray intensity occurring for each image point, the contrast in the entire image is scaled with the maximum value over time, so that the maximum value represents a suitable contrast agent parameter for the method according to the invention. If the variable related to the X-ray intensity is, for example, directly related to the detected X-ray intensity, the maximum absorption value explained above corresponds to the minimum value of the detected X-ray intensity.

[0039] If, on the other hand, a relatively low flow velocity is to be expected in the mapped segment of the vascular system, the contrast formed in the image of the segment of the vascular system depends primarily on the total amount of contrast agent fed in. Due to the diffusion of the contrast agent, the dispersion of the contrast agent in the vascular system cannot be neglected, so that short-term local maxima of the contrast agent concentration that occur during the contrast agent feed, for example due to pressure fluctuations during the contrast agent feed, are dispersed during the propagation of the contrast agent into the vascular system.

[0040] If in this case X-ray absorption is used as a variable related to the X-ray intensity, the integral over the time course is a good measure for the amount of contrast medium used given a given diameter or a given cross-sectional area of ​​the blood vessel or catheter to be fed. It can be easily recognized from the absorption law that the corresponding variable can also be determined, for example, from the integral of the logarithmic X-ray intensity.

[0041] Depending on the predicted flow rate and / or duration of contrast agent injection, one of a plurality of determination methods for determining contrast agent parameters can be selected. In the case of high flow rates or short injection durations, the maximum or minimum values ​​of the time trend can preferably be used to determine the contrast agent parameters as explained above. In this case, a compact contrast agent bolus moves through the vascular system, so the total amount of contrast agent injected is very unimportant. Anyway, if a longer injection time and / or a slower flow rate is assumed, it may be advantageous to use an integral-based method to determine the contrast agent parameters as explained above. In this case, it is expected that the entire mapped segment of the vascular system is essentially perfused with contrast agent within the framework of the sequence, so that the contrast that occurs depends primarily on the total amount of contrast agent injected.

[0042] The flow rate or the duration of the contrast agent injection can be manually predetermined for a specific sequence, or, for example, depend on the examined body region. Thus, for example, it is known that a significantly slower flow rate will occur in the vascular system of the brain than in the surrounding areas of the body. However, the corresponding parameters can also be obtained or at least estimated from the image data itself. If a catheter or a blood vessel has been identified as described above, through which the contrast agent is guided to the segment of the mapped vascular system in the framework of the shooting sequence, then, for example, it can be determined at different times in the sequence how far the contrast agent has penetrated into the vascular system, which is determined, for example, by: in a specific segment of the vascular system, whether a parameter related to the X-ray intensity exceeds or falls below a limit value predetermined for a specific X-ray image. Thus, at least a rough estimate of the flow rate can be made.

[0043] The duration of the contrast agent injection can be determined, for example, by determining the x-ray image and thus the point in time at which the contrast agent concentration in the feeding catheter or blood vessel or in a part of the vascular system directly adjacent thereto continues to decrease.

[0044] The selection of the determination method for determining the contrast medium quantity and / or the determination of the contrast medium quantity can also depend on other parameters. For example, the volume of the vascular system or at least the volume of the mapped segment of the vascular system or the area occupied by the mapped segment of the vascular system in the image can be taken into account. For this purpose, for example, the segment of the vascular system can be segmented in the image of the segment based on grayscale value thresholds in order to obtain at least a rough estimate of the volume or area.

[0045] In addition to the method according to the invention, the invention also relates to a processing device which is designed to carry out the computer-implemented method according to the invention.

[0046] Furthermore, the invention also relates to an X-ray device for medical imaging, comprising a processing device according to the invention. Furthermore, the X-ray device may also comprise an acquisition device for acquiring a sequence of X-ray images, such as an X-ray source and an X-ray detector. Additionally, the processing device may be designed to acquire a sequence by means of the acquisition device or to control the acquisition device.

[0047] As an alternative to integrating the processing device into the X-ray device, the processing device can also be designed as a separate device. For example, the processing device can be a workstation computer, a local server, a server connected via a network, such as a server in another building, or a cloud-based processing device for decentralized processing data.

[0048] Furthermore, the invention relates to a computer program for a data processing device, the computer program having program instructions which, when executed on the data processing device, perform a computer-implemented method according to the invention, and to a computer-readable data carrier comprising such a computer program.

[0049] The processing device according to the invention and the X-ray device according to the invention as well as the computer program according to the invention and the computer-readable data carrier according to the invention can be further developed with the features explained with respect to the computer-implemented method and with the advantages mentioned there, and vice versa. In general, the individual features disclosed with respect to the subject matter of the invention can be transferred to the other subject matter of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Further advantages and details of the present invention are obtained from the following embodiments and the related drawings. Here, schematically in the drawings:

[0051] Figure 1 A flowchart showing an embodiment of a computer-implemented method according to the present invention is shown.

[0052] Figure 2 It shows that it can be Figure 1 Algorithms and data structures used in exemplary implementations of the methods shown,

[0053] Figure 3 shows an X-ray image,

[0054] Figure 4 shows the time profile of a variable related to the X-ray intensity in a selected sub-region of a sequence of X-ray images,

[0055] Figure 5 An image of a segment of a vascular system is shown, and

[0056] Figure 6 An embodiment of an X-ray device according to the invention is shown which comprises an embodiment of a processing device according to the invention. DETAILED DESCRIPTION

[0057] Figure 1 A flow chart of a computer-implemented method for processing an X-ray image is shown. Figure 2 Explain in more detail the possibilities of implementing the individual method steps, Figure 2 Algorithms and data structures that can be used to implement the method are shown.

[0058] In step S1, a Figure 31 shows a sequence 1 of X-ray images 2 of an image region 3 schematically shown in FIG. 1 , wherein at least one section of a vascular system 4 of the object under examination is projected in the image region 3 . The sequence 1 describes the time course of the detected X-ray intensity in the image region 3 due to a change in the contrast agent distribution in the section of the vascular system 4 . Figure 3 In the example shown, the contrast agent is introduced into the image region 3 from the image edge 26 side, and Figure 3 An X-ray image relatively early in the sequence is shown, whereby the contrast agent is essentially present only in the blood vessels 27 through which the contrast agent was fed into the vascular system 4, whereby the X-ray intensity reduction or absorption increase in the image segment 5 which maps the contrast agent is shown. Further sections 6 of the vascular system 4 are initially essentially free of contrast agent and therefore produce only a low image contrast.

[0059] The sequence 1 can be provided via an input interface and read from a database, for example. However, the sequence can also be provided by providing and processing the X-ray images immediately after their acquisition.

[0060] In step S2, a contrast medium variable 20 related to the contrast medium distribution is determined from the time profile 14 of the variable related to the X-ray intensity in the selected subregion 7 of the X-ray image 2. For this purpose, the subregion 7 is first selected so that it is located in the region of the mapped catheter or vessel 27, through which the contrast medium is guided into the mapped section of the vascular system 4 within the framework of the acquisition sequence 1. For this purpose, the relevant image segments 8 in the X-ray image 2 can be segmented at the beginning of the sequence 1. This procedure is suitable, for example, if it is known that the catheter feeding the contrast medium is located in the image region 3, thereby ensuring that a contrast medium-filled region is already present in these early X-ray images 2.

[0061] If, on the other hand, contrast agent was introduced into the vascular system 4 from outside the image region 3, the contrast agent may not yet be mapped in the individual images of the x-ray images 2. In order to ensure that the vessels 27 or catheters feeding the contrast agent can be robustly identified, it is therefore advantageous to use a subsequence 9 of x-ray images 2 first, in particular at the beginning of the sequence 1, to generate the intermediate image 10. In this case, for each image point of the intermediate image 10, the value of the corresponding image point in the x-ray images 2 of the subsequence 9 which corresponds to the lowest received x-ray intensity or the highest absorption can be selected. This makes it possible to map the highest contrast agent concentration occurring in the subsequence 9 in the intermediate image 10.

[0062] The intermediate image 10 is then segmented by a segmentation algorithm 11 in order to determine an image segment 5 in which a blood vessel 27 is mapped, through which a contrast agent is conducted into the mapped section of the vascular system 4 within the framework of the acquisition sequence 1. For this purpose, the image data in the intermediate image 10 are compared with limit values ​​in order to determine a relevant image segment 8 corresponding to the image segment 5 sought. In this process, a region containing contrast agent is sought, i.e., a region in which a particularly high absorption or a particularly low detected X-ray intensity is present. Thus, if the image data describe the detected X-ray intensity, a coherent segment can be selected as a relevant image segment, in which the image data is below a predefined limit value. Conversely, if the image data describe X-ray absorption, a coherent, relevant image segment 8 can be selected in which a predefined limit value is exceeded for all image points, i.e., a particularly high absorption is present.

[0063] In other methods, the entire relevant image segment 8 can be used as the selected subregion 7. Alternatively, only a part of the relevant image segment 8, in particular the central area, i.e., one or more image points located in the center of the relevant image segment 8, can be selected as the selected subregion 7.

[0064] For the sub-region thus selected, the time profile 14 of a variable related to the X-ray intensity is then determined by an evaluation algorithm 13. In particular, the X-ray absorption or a variable proportional thereto can be used as the variable. If an at least approximately constant emitted X-ray dose can be assumed, the X-ray absorption is indirectly proportional to the logarithm of the X-ray intensity incident on the detector.

[0065] The time course 14 is determined in that, for each X-ray image 2 of the sequence 1, the evaluation algorithm 13 takes into account points located in the previously determined selected sub-region 7, i.e., for example, in the relevant image segment 8. The corresponding values ​​of the variable related to the X-ray intensity are determined for these image points. Since the X-ray images 2 are recorded in a chronological sequence, the time course of the X-ray intensity in each image point of the image region 3 is described overall, so that the variable related to the X-ray intensity determined for the individual X-ray images 2 in turn results in the time course of the variable related to the X-ray intensity in the selected sub-region.

[0066] For the case where the variable related to the X-ray intensity is proportional to the X-ray absorption and therefore substantially proportional to the contrast agent concentration in the selected sub-region 7, Figure 4An exemplary time curve 14 is shown in FIG. 1 . Here, the X-axis 16 represents time and the Y-axis 15 represents the value of the variable. At the beginning of contrast agent injection, the concentration of contrast agent in the selected sub-area 7 is still relatively low at first, since not enough contrast agent has entered the mapped image area 3. In a typical contrast agent injection, for example Figure 4 As shown in FIG. , the contrast agent concentration and thus the X-ray absorption in the selected sub-region 7 increases relatively quickly over time and decreases again after a certain time, ie, in particular after the end of the contrast agent injection. Figure 4 The time trend shown in 14.

[0067] As already explained, for the expected relatively high flow velocities in the mapped section of the vascular system 4, the maximum contrast agent concentration reached in the selected sub-region and therefore the maximum value 18 of the time curve 14 are important for the contrast of the vascular system. Therefore, in this case, the value of the variable at the maximum value 18 can be determined as the contrast agent variable.

[0068] As has also been explained, for long injection times and / or slow flow rates, how much contrast agent is injected overall may also be important for the contrast in the images 21, 24 of the section of the vascular system 4. In the example explained, since the amount of contrast agent present in the selected subregion 7 at the time of the corresponding x-ray image 2 is related to the x-ray absorption and thus to the variable related to the x-ray intensity, in this case the integral 17 of the time curve 14 of the variable, i.e. the area 19 under the curve describing the variable, can be used as the contrast agent variable 20.

[0069] In step S3, images 21, 24 of the vascular system 4 are determined from the X-ray images 2 of the sequence 1, as in Figure 5 The images 21, 24 are generated by selecting for each image point of the images 21, 24 the value of the associated image point in the X-ray image 2 which corresponds to the minimum detected X-ray intensity or the highest absorption and therefore to the highest contrast agent concentration in the region of these image points. This allows an optimal mapping of the vascular system 4.

[0070] To facilitate comparison of images 21 , 24 of the same or different vascular systems 4 , the images 21 , 24 are modified for contrast correction in step S4 . To this end, the images 21 , 24 are modified as a function of the contrast agent parameter 20 to provide output data 23 .

[0071] As already explained, a large contrast medium quantity 20 can be associated with a high contrast in the images 21, 24. Therefore, for small contrast medium quantities 20, a contrast increase should be performed, and for large contrast medium quantities 20, a possible contrast reduction should be performed in order to achieve a uniform image impression. In other words, the image data of the images 21, 24, or at least the image data of the images 21, 24 that are located within a predetermined value range within which the contrast should be adjusted, can be scaled or multiplied by a scaling factor that is inversely proportional to the contrast medium quantity.

[0072] In addition, it has been recognized that Figure 3 The diameter 12 of the blood vessel 27 or catheter shown in the figure for feeding the contrast agent also influences the contrast of the images 21, 24. In this case, a larger diameter 12 leads to a stronger contrast of the images 21, 24. Therefore, the diameter 12 is preferably determined in addition, for example by determining the minimum size of the relevant image segment 8. In this case, the scaling factor used within the framework of the modification 22 can be in particular inversely proportional to the product of the determined contrast agent parameter 20 and the determined diameter 12. In other words, the image data of the images 21, 24 can be divided by the determined contrast agent parameter 20 and by the determined diameter 12, in particular after subtracting the offset, and then multiplied, for example, by a fixed predetermined factor.

[0073] Figure 6 An X-ray device 25 for medical imaging is shown. X-ray radiation provided by an X-ray source 29 penetrates an examination object 28, and an X-ray detector 30 detects the X-ray radiation that has passed through the examination object 28. Part of the incident X-ray radiation is absorbed by the examination object 28 and by a contrast agent (not shown) introduced into the vascular system of the examination object 28, whereby in particular the distribution of the contrast agent in the examination object 28 can be identified in the X-ray images acquired by the X-ray detector 30. If a sequence of X-ray images of a region 32 of the examination object 28 is acquired with the same acquisition geometry during the administration of the contrast agent, the X-ray images of this sequence can be processed by the previously explained computer-implemented method to obtain a contrast-suitable image of a section of the vascular system of the examination object 28.

[0074] The explained computer-implemented method is implemented by a processing device 31 which is integrated into the X-ray device 25 in the example shown, but can also be designed as a separate processing device. The processing device 31 can be implemented, for example, by corresponding programming of a programmable data processing device 33, wherein the data processing can be performed, for example, by a microprocessor, a microcontroller, an FPGA, etc. Optionally, the processing device can additionally be designed to control the X-ray source 29 to acquire a sequence of X-ray images and to acquire corresponding X-ray images via the X-ray detector 30.

[0075] In the case of a processing device that is designed independently of the X-ray device (not shown), it can be implemented, for example, by a workstation computer, in particular for image data analysis, or by a local server or a server connected via a network and / or in a decentralized manner, for example as a cloud solution.

[0076] Although the present invention has been illustrated and described in more detail through preferred embodiments, the present invention is not limited to the disclosed examples and those skilled in the art may derive other variations therefrom without departing from the scope of protection of the present invention.

Claims

1. A computer-implemented method for processing an X-ray image (2), the method comprising the following steps: - providing a sequence (1) of X-ray images (2) of an image region (3) in which at least one section of a vascular system (4) of an object to be examined (28) is mapped, wherein the sequence (1) describes the time course of the detected X-ray intensity in the image region (3) due to a change in the distribution of a contrast agent in the section of the vascular system (4), - determining a contrast agent variable (20) related to the contrast agent distribution based on the time profile (14) of a variable related to the X-ray intensity in a selected sub-region (7) of the X-ray image (2), - determining an image (21, 24) of a section of the vascular system (4) based on at least one of the X-ray images (2) of the sequence (1), - modifying (22) an image (21, 24) of a segment of the vascular system (4) in dependence on the contrast agent parameter (20) in order to provide output data (23), In this case, an image segment (5) of a vessel (27) in a catheter in which a contrast agent is first located and / or in a segment of a vascular system in which a contrast agent is first located is selected, or a sub-segment of the image segment (5) is selected as the selected sub-region (7), and within the framework of photographing the sequence (1), the contrast agent is guided through the catheter or the vessel into the segment of the mapped vascular system (4).

2. The computer-implemented method of claim 1, wherein: The selection of the selected sub-area (7) depends only on one of the X-ray images (2) or on a subsequence (9) of the X-ray images (2) which does not include all X-ray images (2), wherein the X-ray image (2) or the subsequence (9) maps a section of the contrast agent entering the mapped vascular system (4).

3. The computer-implemented method of claim 2, wherein: In order to select the selected sub-region (7), the relevant image segment (8) is determined by comparing image data in an x-ray image (2) or in an intermediate image (10) determined according to the sub-sequence (9) with a limit value.

4. The computer-implemented method according to any one of claims 1 to 3, characterized in that: The diameter of a blood vessel (27) or a catheter in a selected sub-region (7) or a relevant image segment (8) is determined, through which a contrast agent is introduced into a segment of the mapped vascular system (4) within the framework of recording the sequence (1), wherein the image (21, 24) of the segment of the vascular system (4) is modified as a function of the determined diameter (12).

5. The computer-implemented method according to any one of claims 1 to 3, characterized in that: In order to modify (22) an image (21, 24) of a segment of a vascular system (4), all image data of the image (21, 24) of the segment of the vascular system (4) or image data of the image (21, 24) of the segment of the vascular system (4) that are within a predetermined value range are multiplied by a scaling factor that depends on the contrast agent parameter (20).

6. The computer-implemented method of claim 5, wherein: The diameter of a blood vessel (27) or a catheter in a selected sub-region (7) or a relevant image segment (8) is determined, through which a contrast agent is introduced into a segment of the mapped vascular system (4) within the framework of recording the sequence (1), wherein the image (21, 24) of the segment of the vascular system (4) is modified as a function of the determined diameter (12), the scaling factor being inversely proportional to the contrast agent parameter (20) and / or the determined diameter (12).

7. The computer-implemented method according to any one of claims 1 to 3, characterized in that: The contrast agent variable (20) is determined based on a maximum (18) or minimum value of a time profile (14) of a variable related to the x-ray intensity in the selected sub-region (7), or based on an integral (17) over the time profile (14).

8. The computer-implemented method according to any one of claims 1 to 3, characterized in that: Depending on the predicted flow rate and / or duration of the contrast agent injection, one of a plurality of determination methods for determining a contrast agent quantity (20) is selected.

9. A processing device, characterized in that: The processing device is designed to perform a computer-implemented method according to any one of claims 1 to 8.

10. An X-ray device for medical imaging, comprising a processing device (31) according to claim 9.

11. A computer-readable data carrier comprising a computer program for a data processing device (33), the computer program having program instructions which, when executed on the data processing device (33), execute a computer-implemented method according to any one of claims 1 to 8.

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