COMPUTER-IMPLEMENTED METHOD FOR PROCESSING X-RAY IMAGES

Abstract

A computer-implemented method for processing x-ray images. A sequence of x-ray images is provided of a field of view in which at least one section of a vascular system of an examination subjects is imaged. The sequence describes a variation with time of the detected x-ray intensity in the field of view based on a change in a contrast agent distribution in the section of the vascular system. A contrast agent variable is determined relating to the contrast agent distribution as a function of a variation with time of a variable relating to the x-ray intensity in a selected subregion of the x-ray images. An image of the section of the vascular system is determined as a function of at least one of the x-ray images of the sequence. The image is modified as a function of the contrast agent variable.

Claims

1. A computer-implemented method for processing x-ray images, the method comprising: providing a sequence of x-ray images of a field of view in which at least one section of a vascular system of an examination subject is imaged, wherein the sequence of x-ray images describes a variation with time of a detected x-ray intensity in the field of view based on a change in a contrast agent distribution in the section of the vascular system; determining a contrast agent variable relating to the contrast agent distribution as a function of a variation with time of a variable relating to the detected x-ray intensity in a selected subregion of the sequence of x-ray images; determining an image of the at least one section of the vascular system as a function of at least one x-ray image of the sequence of x-ray images; and modifying the image of the at least one section of the vascular system as a function of the contrast agent variable to provide output data.

2. The computer-implemented method of claim 1, wherein the selected subregion comprises an image section that images a catheter, a vessel, or the catheter and the vessel via which the contrast agent was or is conducted into the imaged section of the vascular system during an acquisition of the sequence or a subsection of the image section.

3. The computer-implemented method of claim 1, wherein the selection of the selected subregion is dependent solely on one x-ray image of the sequence of x-ray images or on a subsequence of x-ray images comprising not all of the x-ray images of the sequence of x-ray images, wherein the one x-ray image or subsequence of x-ray images include an entry of the contrast agent into the imaged section of the vascular system.

4. The computer-implemented method of claim 3, wherein in order to select the selected subregion, a relevant image segment is determined in that image data in the one x-ray image or in an intermediate image determined as a function of the subsequence is compared with a limit value.

5. The computer-implemented method of claim 1, further comprising: determining a diameter of the selected subregion or of a relevant image segment or of a vessel or a catheter via which the contrast agent was or is conducted into the imaged section of the vascular system during acquisition of the sequence of x-ray images, wherein the image of the section of the vascular system is modified as a function of the determined diameter.

6. The computer-implemented method of claim 1, wherein that in order to modify the image of the section of the vascular system, all image data of the image or image data of the image that lies within a predefined value range may be multiplied after deduction of an offset by a scaling factor that is dependent on the contrast agent variable.

7. The computer-implemented method of claim 6, wherein the scaling factor is inversely proportional to the contrast agent variable, the determined diameter, or the contrast agent variable and the determined diameter.

8. The computer-implemented method of claim 1, wherein the contrast agent variable is determined from the maximum or minimum of the variation with time of the variable relating to the x-ray intensity in the selected subregion or from an integral over the variation with time.

9. The computer-implemented method of claim 1, wherein one of a number of methods for determining the contrast agent variable is selected as a function of a predicted flow rate, a duration of a contrast agent injection, or the predicted flow rate and the duration of the contrast agent injection.

10. An x-ray system for medical imaging, comprising: an acquisition device configured for capturing a sequence of x-ray images of a field of view in which at least one section of a vascular system of an examination subject is imaged, wherein the sequence of x-ray images describes a variation with time of a detected x-ray intensity in the field of view based on a change in a contrast agent distribution in the at least one section of the vascular system; and a processing device configured to determine a contrast agent variable relating to the contrast agent distribution as a function of a variation with time of a variable relating to the detected x-ray intensity in a selected subregion of the sequence of x-ray images, determine an image of the at least one section of the vascular system as a function of at least one x-ray image of the sequence of x-ray images, and modify the image of the at least one section of the vascular system as a function of the contrast agent variable to provide output data.

11. The x-ray system of claim 10, wherein the selected subregion comprises an image section that images a catheter, a vessel, or the catheter and the vessel via which the contrast agent was or is conducted into the imaged section of the vascular system during acquisition of the sequence or a subsection of the image section.

12. The x-ray system of claim 10, wherein the selection of the selected subregion is dependent solely on one x-ray image or on a subsequence of the x-ray images comprising not all of the x-ray images of the sequence of x-ray images, wherein the one x-ray image or subsequence of x-ray images include an entry of the contrast agent into the imaged section of the vascular system.

13. The x-ray system of claim 12, wherein in order to select the selected subregion, a relevant image segment is determined in that image data in the one x-ray image or in an intermediate image determined as a function of the subsequence is compared with a limit value.

14. The x-ray system of claim 10, wherein the processing is further configured to determine a diameter of the selected subregion or of a relevant image segment or of a vessel or a catheter via which the contrast agent was or is conducted into the imaged section of the vascular system during acquisition of the sequence, wherein the image of the section of the vascular system is modified as a function of the determined diameter.

15. The x-ray system of claim 10, wherein that in order to modify the image of the section of the vascular system, all image data of the image or image data of the image that lies within a predefined value range may be multiplied after deduction of an offset by a scaling factor that is dependent on the contrast agent variable.

16. The x-ray system of claim 15, wherein the scaling factor is inversely proportional to the contrast agent variable, the determined diameter, or the contrast agent variable and the determined diameter.

17. The x-ray system of claim 10, wherein the contrast agent variable is determined from the maximum or minimum of the variation with time of the variable relating to the x-ray intensity in the selected subregion or from an integral over the variation with time.

18. The x-ray system of claim 10, wherein one of a number of methods for determining the contrast agent variable is selected as a function of a predicted flow rate, a duration of a contrast agent injection, or the predicted flow rate and the duration of the contrast agent injection.

19. A non-transitory computer implemented storage medium that stores machine-readable instructions executable by at least one processor, the machine-readable instructions comprising: acquiring a sequence of x-ray images of a field of view in which at least one section of a vascular system of an examination subject is imaged, wherein the sequence of x-ray images describes a variation with time of the detected x-ray intensity in the field of view based on a change in a contrast agent distribution in the at least one section of the vascular system; determining a contrast agent variable relating to the contrast agent distribution as a function of a variation with time of a variable relating to the x-ray intensity in a selected subregion of the sequence of x-ray images; determining an image of the at least one section of the vascular system as a function of at least one of the x-ray images of the sequence of x-ray images; and modifying the image of the at least one section of the vascular system as a function of the contrast agent variable to provide output data.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0048] FIG. 1 depicts a flowchart of an embodiment of a computer-implemented method according to an embodiment.

[0049] FIG. 2 depicts algorithms and data structures that may be used in an implementation of the method depicted in FIG. 1 according to an embodiment.

[0050] FIG. 3 depicts an x-ray image according to an embodiment.

[0051] FIG. 4 depicts a variation with time of a variable relating to the x-ray intensity in a selected subregion of x-ray images of a sequence according to an embodiment.

[0052] FIG. 5 depicts an image of a section of a vascular system according to an embodiment.

[0053] FIG. 6 depicts an embodiment of an x-ray device including an embodiment of a processing device.

DETAILED DESCRIPTION

[0054] FIG. 1 depicts a flowchart of a computer-implemented method for processing x-ray images. Possible ways of implementing the individual method steps are explained in more detail here with reference to FIG. 2, that depicts algorithms and data structures that may be used to implement the method.

[0055] In step S1, a sequence 1 of x-ray images 2 of a field of view 3 depicted schematically in FIG. 3 is provided, at least one section of a vascular system 4 of an examination subject being imaged in the field of view 3. The sequence 1 describes a variation with time of the detected x-ray intensity in the field of view 3 due to a change in a contrast agent distribution in the section of the vascular system 4. In the example depicted in FIG. 3, the contrast agent is introduced into the field of view 3 from the side of the image edge 26 and the figure depicts an x-ray image that lies relatively early in the sequence, whereby contrast agent is present substantially exclusively in the vessel 27 via which the contrast agent is supplied to the vascular system 4, as a result of which an x-ray intensity in the image section 5 imaging the contrast agent is reduced or an absorption is increased. The remaining section 6 of the vascular system 4 is initially substantially free of contrast agent and consequently produces only low image contrasts.

[0056] The sequence 1 may be provided via an input interface and be read out from a database, for example. However, it is also possible to deliver the sequence by providing and processing the x-ray images immediately after they have been acquired.

[0057] In step S2, a contrast agent variable 20 relating to the contrast agent distribution is determined as a function of a variation with time 14 of a variable relating to the x-ray intensity in a selected subregion 7 of the x-ray images 2. To that end, the subregion 7 is initially selected in such a way that it lies in a region of an imaged catheter or vessel 27 via which the contrast agent is conducted into the imaged section of the vascular system 4 in the course of the acquisition of the sequence 1. For this purpose, the relevant image segment 8 in an x-ray image 2 might be segmented at the start of the sequence 1. This approach may be beneficial, for example, when it is known that a catheter via which contrast agent is supplied lies within the field of view 3, such that it is ensured that a region filled with contrast agent is already present in these early x-ray images 2.

[0058] If the contrast agent is introduced into the vascular system 4 from outside of the field of view 3, it is possible that no contrast agent will yet be imaged on individual images of the x-ray images 2. In order to ensure that a vessel 27 or catheter supplying the contrast agent may be robustly identified, it may therefore be advantageous to use a subsequence 9 of x-ray images 2 initially, for example at the start of the sequence 1, in order to generate an intermediate image 10. In this instance, for each pixel of the intermediate image 10, the value of the corresponding pixel of that image of the x-ray images 2 of the subsequence 9 may be chosen in each case that corresponds to the lowest received x-ray intensity or, as the case may be, the highest absorption. In this way it may be provided that the highest occurring contrast agent concentration within the subsequence 9 is imaged in each case in the intermediate image 10.

[0059] The intermediate image 10 is subsequently segmented by a segmentation algorithm 11 to determine the image section 5 in which the vessel 27 via which the contrast agent was conducted into the imaged section of the vascular system 4 in the course of the acquisition of the sequence 1 is imaged. The image data in the intermediate image 10 is compared with a limit value in order to determine a relevant image segment 8 that corresponds to the image section 5 that is being sought. This entails searching for a region containing contrast agent, specifically a region in which a particularly high absorption or a particularly low detected x-ray intensity is present. Thus, if the image data describes a detected x-ray intensity, a coherent segment in which the image data undershoots a predefined limit value may be chosen as the relevant image segment. If an x-ray absorption is described by the image data, a coherent relevant image segment 8 may be chosen in which the predefined limit value is exceeded for all pixels, specifically a particularly high absorption is present.

[0060] The entire relevant image segment 8 may be taken into account as the selected subregion 7. Alternatively, it would also be possible to choose only a part of the relevant image segment 8, for example a central region, specifically one or more pixels located for example centrally in the relevant image segment 8, as the selected subregion 7.

[0061] A variation with time 14 of a variable relating to the x-ray intensity is subsequently determined by the evaluation algorithm 13 for the thus chosen subregion. For example, an x-ray absorption or a variable proportional thereto may be used as the variable. The x-ray absorption is indirectly proportional to the logarithm of the x-ray intensity incident on the detector as far as an at least approximately constant emitted x-ray dose may be assumed.

[0062] The variation with time 14 is determined in that the evaluation algorithm 13 takes into account in each case, for each of the x-ray images 2 of the sequence 1, the pixels that lie in the previously determined selected subregion 7, specifically for example in the relevant image segment 8. A respective value of the variable relating to the x-ray intensity is determined for each of the pixels. Since the x-ray images 2 are acquired in chronological sequence and therefore overall describe a variation with time of the x-ray intensity in each pixel of the field of view 3, the variables relating to the x-ray intensity that were determined for the individual x-ray images 2 again result in a variation with time of the variable relating to the x-ray intensity in the selected subregion.

[0063] An embodiment with time 14 is depicted in FIG. 4 for the case in which the variable relating to the x-ray intensity is proportional to the x-ray absorption and consequently substantially to the contrast agent concentration in the selected subregion 7. Here, the X-axis 16 depicts the time and the Y-axis 15 the value of the variable. At the start of the contrast agent injection, the concentration of the contrast agent in the selected subregion 7 is initially still relatively low since sufficient contrast agent has not yet entered the imaged field of view 3. With a typical contrast agent injection, the contrast agent concentration in the selected subregion 7, and consequently the x-ray absorption, as shown in FIG. 4, will increase relatively quickly over time and after a certain time, specifically, for example, after the end of the contrast agent injection, will decrease again. This results in the variation with time 14 depicted in FIG. 4.

[0064] As already explained, given a relatively high expected flow rate in the imaged section of the vascular system 4, for example the maximum concentration of the contrast agent achieved in the selected subregion, and consequently the maximum 18 of the variation with time 14, is relevant for the contrast of the vascular system. The value of the variable at the maximum 18 may therefore be determined as the contrast agent variable.

[0065] As likewise already explained, with long injection times and/or at slow flow rates, how much contrast agent has been injected overall may also be important for the contrast in the image 21, 24 of the section of the vascular system 4. Since the amount of contrast agent that is present in the selected subregion 7 at the time of acquisition of the respective x-ray image 2 correlates in the explained example with the x-ray absorption, and consequently with the variable relating to the x-ray intensity, the integral 17 of the variation with time 14 of the variable, specifically the area 19 below the curve describing the variable, may be used as the contrast agent variable 20.

[0066] In step S3, an image 21, 24 of the vascular system 4 is determined as a function of the x-ray images 2 of the sequence 1, as is depicted by way of example in FIG. 5. The image 21, 24 may be generated by choosing, for each pixel of the image 21, 24, the value of the associated pixel of that image of the x-ray images 2 that corresponds to the lowest detected x-ray intensity or, as the case may be, to the highest absorption, and consequently to the highest contrast agent concentration in the region of the pixel. This provides an optimal imaging of the vascular system 4.

[0067] In order to make a comparability of the images 21, 24 of the same vascular system 4 or of different vascular systems 4 easier, a modification of the image 21, 24 for contrast correction is performed in step S4. For this purpose, the image 21, 24 is modified as a function of the contrast agent variable 20 in order to provide output data 23.

[0068] As has already been explained, a high contrast agent variable 20 may correlate with a high contrast in the image 21, 24. Consequently, an increase in contrast should be affected for small contrast agent variables 20 and potentially a reduction in contrast for large contrast agent variables 20 in order to achieve a uniform image impression. In other words, the image data of the image 21, 24, or at least that image data of the image 21, 24 that lies within a predefined value range within which it is aimed to adjust the contrast, may be scaled or multiplied with a scaling factor that is inversely proportional to the contrast agent variable.

[0069] The diameter 12 (shown in FIG. 3) of the vessel 27 or catheter via which the contrast agent is supplied likewise influences the contrast of the image 21, 24. larger diameters 12 lead to stronger contrasts in the image 21, 24. For this reason the diameter 12 may be determined in addition for example by determining a minimum dimension of the relevant image segment 8. The scaling factor used in the course of the modification 22 may be inversely proportional to the product from the determined contrast agent variable 20 and the determined diameter 12. The image data of the image 21, 24 may be divided, for example after deduction of an offset, both by the determined contrast agent variable 20 and by the determined diameter 12 and subsequently multiplied for example by a predefined fixed factor.

[0070] FIG. 6 depicts an x-ray device 25 for medical imaging. X-ray radiation provided by an x-ray source 29 is passed through an examination subject 28 and the x-ray radiation that has passed through the examination subject 28 is detected by the x-ray detector 30. A portion of the emitted x-ray radiation is absorbed by the examination subject 28 as well as by a contrast agent (not shown) introduced into the vascular system of the examination subject 28, as a result of which the contrast agent distribution in the examination subject 28 is identifiable in the x-ray images captured by the x-ray detector 30. If a sequence of x-ray images of the region 32 of the examination subject 28 is acquired using the same acquisition geometry during an administration of contrast agent, the sequence of x-ray images may be processed by the previously explained computer-implemented method in order to obtain a contrast-adjusted image of a section of the vascular system of the examination subject 28.

[0071] A processing device 31, that in the example shown is integrated into the x-ray device 25 but might also be configured as a separate processing device, implements the explained computer-implemented method. The processing device 31 may be implemented for example by appropriate programming of a programmable data processing device 33, in which case the data processing may be carried out for example by a microprocessor, microcontroller, FPGA or similar. The processing device may be additionally configured to control the x-ray source 29 for the acquisition of the sequence of x-ray images and to capture the corresponding x-ray images via the x-ray detector 30.

[0072] In a case not depicted, where the processing device is configured separately from the x-ray device, the same may be implemented for example by a workstation computer, for example for image data evaluation, by a local server or a server connected via a network and/or non-centrally, for example as a cloud solution.

[0073] It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present application. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.

[0074] While the present application has been described above by reference to various embodiments, it may be understood that many changes and modifications may be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.