CONTRAST AGENT-BASED VESSEL IMAGE

Description

[0001] The invention relates to an X-ray contrast agent. Furthermore, the invention relates to an X-ray imaging method in which the aforementioned X-ray contrast agent is used. The invention also relates to an image reconstruction device. Finally, the invention relates to an X-ray imaging system.

[0002] Modern imaging techniques are often used to generate two- or three-dimensional image data, which can be used to visualize a depicted object of investigation and also for other applications.

[0003] Imaging techniques are often based on the detection of X-rays, generating so-called projection measurement data. For example, projection measurement data can be acquired using a computed tomography (CT) system.

[0004] X-ray imaging often involves the use of contrast agents, which are injected into the patient to enhance image contrast and thus facilitate diagnosis. One example of the application of contrast agents is the visualization of blood vessels using X-rays. X-ray procedures can be performed with conventional systems, C-arm systems, angiography systems, or CT systems. Traditionally, iodine is used as the X-ray contrast agent in such imaging.

[0005] However, a problem arises with iodine angiography: bones, calcifications, and partially calcified plaques in the vessels exhibit similar density values ​​to the contrast-filled vessel. Therefore, particularly in complex anatomical structures, such as in the skull, iodine-filled vessels, bones, and calcifications overlap within the vessels and can no longer be precisely distinguished in the image. Consequently, especially in small-diameter vessels, the vessel diameter, also known as the lumen, can often no longer be determined using CT angiography in cases of severe calcification. This phenomenon limits the application of CT angiography to coronary arteries and peripheral leg vessels.

[0006] Traditionally, attempts were made to differentiate bones and calcifications or partially calcified plaques in vessels from the areas visualized by iodine contrast by subtracting a pre-image of the area to be imaged, which was taken without contrast agent. However, the time lag between the pre-image and the main image leads to registration problems due to patient movement. Furthermore, the additional image acquisition increases the radiation dose for the patient.

[0007] The application of software-based methods for separating image information relating to vessels from that relating to bones is also prone to errors. These errors occur particularly in complex representations, such as the skull base. Furthermore, eliminating (partially) calcified plaques from the vascular representation is not possible due to the blooming effect. This is because the blooming effect causes the partially calcified plaques to appear larger than they actually are. If the plaque representations are removed from the image, areas remain without image information due to the excessively large areas previously covered by the plaques.

[0008] One way to separate bone and iodine-containing contrast agent pixels is to use dual-energy or multi-energy imaging techniques. These techniques involve acquiring images of the same examination area using at least two different average X-ray energies. However, simpler versions, where pixels are assigned to contrast agent or bone material through classification, experience similar problems to those encountered with software-based methods. Incorrect separation of iodine-containing areas and plaque-containing areas also occurs, particularly in complex vascular structures. Furthermore, this approach also results in the magnification of calcified areas. If these areas are subsequently extracted to visualize the vessels, it is unclear how the areas obscured by the magnified view should be represented in the image.

[0009] In another relatively new method, dual-energy imaging is used to calculate two different images based on this acquisition. One of the two images depicts the calcium-containing structures, while the other shows areas treated with contrast medium. Consequently, neither bones nor calcifications of the vessels are visible in the contrast-enhanced image. While this avoids magnified representations of the calcifications in the image and provides information about areas otherwise obscured by the magnified structures, the problem remains that previously used contrast agents, such as iodine, and bone or calcifications are very similar with respect to their spectral absorption behavior in the energy range of X-ray images (40 keV to 140 keV). That is, the X-ray absorption of both materials increases sharply at lower energies.FIG 1 The absorption is shown for a low-energy image (denoted E(1)) and a high-energy image (denoted E(2)). Due to the similar behavior of the conventional contrast agent iodine and calcium, the resulting material images exhibit very high image noise and imprecise material separation. While the problem of high image noise and imprecise material separation can be resolved by significantly increasing the radiation dose, this approach places an increased health burden on the patient and is not feasible for some examination types, such as coronary angiography, due to technical limitations.

[0010] WO 2016 / 172 256 A1 describes the use of a bowel contrast agent. This bowel contrast agent is a suspension containing capsule-like particles with a gas-filled or vacuum-sealed interior. The spectral absorption profile of the bowel contrast agent is selected to differ significantly from that of a second contrast agent used in a neighboring area, such as blood vessels or an adjacent organ.

[0011] US 2008 / 0 137 803 A1 describes a medical imaging system designed to separately depict body areas exposed to contrast agents with different absorption edges for X-rays.

[0012] In WO 2017 / 027 547 A1, a system for image-guided radiotherapy is described. To reduce the radiation dose, the contrast agents used for imaging and radiotherapy are selected to exhibit strong absorption of the radiation used for therapy and to enable imaging and delineation of the area of ​​the body to be treated from its surroundings.

[0013] The problem, therefore, is to achieve high-quality vascular imaging with a low radiation dose.

[0014] This problem is solved by an X-ray contrast medium for visualizing blood vessels permeated with the X-ray contrast medium according to claim 1, an X-ray imaging method for visualizing blood vessels permeated with an X-ray contrast medium according to claim 5, an image reconstruction device according to claim 9 and an X-ray imaging system according to claim 10.

[0015] The X-ray contrast medium according to the invention for visualizing blood vessels permeated with the X-ray contrast medium exhibits an X-ray absorption whose change between at least two different X-ray photon energies differs significantly from the change in the X-ray absorption of calcium between the at least two different X-ray photon energies.

[0016] Ideally, the absorption of the X-ray contrast medium according to the invention should remain almost constant between the at least two different X-ray photon energies. In this context, "significant" means that the change is less than half the change in calcium at the selected different X-ray photon energies.

[0017] If the X-ray absorption of the X-ray contrast medium is not significantly different for the at least two X-ray photon energies, it is advantageously achieved that the X-ray contrast medium according to the invention differs significantly in its absorption behavior depending on the photon energy compared to materials such as calcium, which occur particularly in angiography.

[0018] The spectrally distinct behavior of the contrast agent according to the invention can advantageously be used to distinguish areas permeated by the contrast agent from other image areas that are calcified or partially calcified. Particularly in the angiographic imaging of vessels, more precise values ​​for the opening width of the depicted vessels are obtained, and the accuracy of the imaging is improved compared to conventionally used contrast agents. Therefore, the X-ray contrast agent according to the invention is advantageously applicable in the imaging of blood vessels, as it allows the inner diameter of vessels to be depicted with particular accuracy.

[0019] In the X-ray imaging method according to the invention for visualizing blood vessels permeated with an X-ray contrast medium, a contrast medium according to the invention is first selected. Furthermore, raw X-ray data from an area of ​​the examination object permeated by the contrast medium are acquired using a multi-energy imaging technique. The X-ray imaging method according to the invention can be carried out as a computer-implemented method based on the acquired data.

[0020] Based on the raw X-ray data, a material breakdown is performed into data that can be assigned either to the contrast agent according to the invention or to calcium.

[0021] In the material decomposition method, which is known in principle, the underlying assumption is that an X-ray attenuation value measured by an X-ray imaging device can be described as a linear combination of X-ray attenuation values ​​of so-called base materials with respect to the aforementioned X-ray quantum energy distribution or X-ray photon energy. Measured X-ray attenuation values ​​result from at least two raw data sets or image data sets reconstructed from them, representing different X-ray quantum energy distributions. In the application according to the invention, the material or base material consists of calcium on the one hand and the X-ray contrast agent according to the invention on the other. The X-ray attenuation of a base material as a function of the energy of the X-ray radiation is generally known or can be determined by prior measurements on phantoms and stored in the form of tables for retrieval during the material decomposition process.The result of the material decomposition is a spatial density distribution of the at least two materials, i.e., the contrast agent according to the invention and calcium in the patient, from which the base material proportions or the base material combination can be determined for each volume element in the patient's body region to be imaged. The material decomposition can be performed directly on the raw data or on reconstructed image data. In any case, at least two image datasets are generated within the framework of the method based on spectrally decomposed data, whether raw data or image data: The at least two image datasets comprise a first image dataset, which represents a first image region illuminated by the contrast agent according to the invention, and a second image dataset, which represents a second image region, preferably complementary to the first image region, in which calcium-containing structures are visualized.

[0022] In the case of a complementary representation of the first and second image data sets, areas affected by the contrast agent according to the invention and calcium-containing structures can be illustrated together in one image, for example by superimposing the two image data sets, whereby the relative position of the different structures or materials as well as the spatial separation or interfaces between these different structures or materials are clearly recognizable.

[0023] If there is a mixture of the different materials represented by the two image data sets, then, in order to illustrate the different materials separately, the first and second image data sets can each be presented separately in two separate images.

[0024] The X-ray imaging method according to the invention enables separate visualization of calcium-containing image areas and those affected by the contrast agent according to the invention. This allows, for example, a more precise representation of the inner diameter of vessels, which contributes to a more reliable diagnosis based on angiographic image data. Furthermore, due to the different spectral absorption properties of the contrast agent according to the invention and the other materials to be visualized, the X-ray dose can be selected to be lower than in conventional imaging methods.

[0025] The image reconstruction device according to the invention has a detection unit for determining at least two different X-ray photon energies at which a contrast agent according to the invention differs significantly from the change in the X-ray absorption of calcium between the at least two different X-ray photon energies.

[0026] The choice of energy values ​​can be considered within a multi-energy imaging technique when selecting the energies or average energy values ​​of the X-ray sources used for imaging. If counter-measuring detectors are used to detect the X-ray radiation, energy thresholds or intervals can be selected to encompass the aforementioned energy values.

[0027] Part of the image reconstruction device according to the invention is also a raw data receiving unit for receiving raw X-ray data from an area of ​​an object under investigation that is at least partially flooded with the contrast agent using a multi-energy imaging method.

[0028] The image reconstruction device according to the invention also comprises a decomposition unit for performing a material decomposition based on the raw X-ray data with respect to the contrast agent and calcium, and a reconstruction unit for reconstructing at least two image datasets based on the material decomposition. Such material decompositions are generally known in the imaging of multiple materials using dual-energy or multi-energy imaging, as already explained.

[0029] The at least two image data sets comprise a first image data set, which represents a first image area illuminated by the contrast agent, and a second image data set, which preferably represents a second image area complementary to the first image area. The image reconstruction device according to the invention shares the advantages of the X-ray imaging method according to the invention.

[0030] The X-ray imaging system according to the invention comprises an image reconstruction unit according to the invention. The X-ray imaging system according to the invention may preferably include a CT angiography unit. The X-ray contrast medium according to the invention is particularly advantageous for imaging blood vessels, as it allows the inner diameter of vessels to be depicted with exceptional accuracy.

[0031] The essential components of the image reconstruction device according to the invention can be predominantly implemented as software components. This applies in particular to the decomposition unit and the reconstruction unit of the image reconstruction device according to the invention. However, these components can also be partially implemented as software-supported hardware, such as FPGAs or the like, especially when particularly fast calculations are required. Likewise, the necessary interfaces, for example, when it is only a matter of transferring data from other software components, can be implemented as software interfaces. Alternatively, they can be implemented as hardware interfaces controlled by suitable software.

[0032] A largely software-based implementation has the advantage that existing medical imaging systems or image reconstruction devices can be easily retrofitted via a software update to operate according to the invention. In this respect, the problem is also solved by a corresponding computer program product with a computer program that can be directly loaded into a storage device of an X-ray imaging system. This program contains sections for executing the software-implemented steps of the X-ray imaging method according to the invention when the program is run in the X-ray imaging system. In addition to the computer program itself, such a computer program product may optionally include additional components such as documentation and / or additional components, including hardware components such as hardware keys (dongles, etc.) for using the software.

[0033] For transport to and / or storage on or within the subsystem, a computer-readable medium, such as a memory stick, a hard drive, or other portable or permanently installed data carrier, can be used. This medium stores the program sections of the computer program that can be read and executed by a computing unit. The computing unit may, for example, comprise one or more cooperating microprocessors or similar components. The computing unit may be, for example, part of a terminal or control unit of an imaging system, such as a CT scanner, or it may be part of a remotely located server system within a data transmission network that communicates with the imaging system.

[0034] The dependent claims and the subsequent description each contain particularly advantageous embodiments and further developments of the invention. In particular, the claims of one claim category may also be further developed analogously to the dependent claims of another claim category. Furthermore, within the scope of the invention, the various features of different embodiments and claims may also be combined to form new embodiments.

[0035] It is particularly advantageous if the X-ray absorption spectrum of the X-ray contrast medium according to the invention is similar to the X-ray absorption spectrum of water or soft tissue. This is because water or soft tissue exhibit behavior in an energy range relevant for angiography that is independent of the X-ray photon energy and can therefore be easily separated from other body materials, such as calcium.

[0036] In a particularly advantageous embodiment of the invention, the X-ray contrast medium according to the invention comprises one of the following materials: Tungsten, tantalum, hafnium, gold.

[0037] The aforementioned materials all advantageously exhibit water-like absorption behavior and can therefore be easily separated from calcium-containing materials in an area under investigation or presented separately.

[0038] In one embodiment of the X-ray imaging method according to the invention, it comprises a multi-energy imaging method, preferably a dual-energy imaging method. In the multi-energy imaging method, at least two different X-ray tube voltages are defined, at which the change in the X-ray absorption of the contrast agent according to the invention differs significantly from the X-ray absorption of calcium. Furthermore, at least two X-ray images are acquired using the at least two different X-ray tube voltages to acquire a first raw data set and at least a second raw data set. The material decomposition is then performed based on the at least two raw data sets.In this variant, X-rays with different X-ray spectra are generated using different X-ray tube voltages, which are used to generate at least two raw data sets that are used to separate different materials in imaging.

[0039] In an alternative embodiment of the X-ray imaging method according to the invention, raw X-ray data, acquired with energy resolution using a photon-counting detector, are recorded. The energy thresholds of the photon-counting detector are set such that, at the different energy ranges defined by the energy thresholds, the change in the X-ray absorption of the contrast agent according to the invention differs significantly from the change in the X-ray absorption of calcium. Furthermore, material decomposition is performed based on the energy-resolved raw data. Advantageously, in this variant, only one X-ray tube is required to irradiate a single examination area.

[0040] The invention is explained in more detail below with reference to the accompanying figures and exemplary embodiments. The figures show: FIG 1 a diagram illustrating the absorption properties of the contrast agent iodine and the bone material calcium as a function of the energy of the X-ray photons, FIG 2 a diagram illustrating the absorption values ​​of the contrast agent iodine and the material tungsten as a function of the tube voltage of an X-ray machine, FIG 3 a diagram showing the absorption properties of the contrast agents iodine and tungsten, as well as calcium and water, as a function of the energy of the X-ray photons, FIG 4 a flowchart illustrating an X-ray imaging procedure according to an embodiment of the invention, FIG 5 a schematic representation of an image reconstruction device according to an embodiment of the invention, FIG 6 a schematic representation of a CT system according to an embodiment of the invention.

[0041] In FIG 1 Figure 10 illustrates the absorption properties of the contrast agent iodine (I) and the bone material calcium (Ca) as a function of the energy EPH of the X-ray photons. To illustrate the absorption of these materials, the mass absorption coefficient κ is plotted as a function of the energy EPH of the X-ray photons. Furthermore, in FIG 1 A typical mean energy E(1) of a low-energy image acquisition and the mean energy E(2) of a high-energy image acquisition of a dual-energy image acquisition are shown. As in FIG 1 As can be seen, the curves of the mass absorption coefficients of iodine (I) and calcium (Ca) are quite similar. It must be taken into account that iodine and calcium can be present in different densities and concentrations. This leads to the fact that the FIG 1 In the worst case, the absorption curves shown may completely overlap. A visual separation of the two materials is then no longer possible.

[0042] In FIG 2 Figure 20 illustrates the absorption values ​​Is of the contrast agent iodine (Ic) and the material tungsten (Wc) as a function of the tube voltage (VT) of an X-ray unit. While the X-ray absorption of iodine decreases with increasing energy, the X-ray absorption of tungsten (Wc) changes only slightly with energy. In particular, during dual-energy imaging at a low energy of 80 kV and a higher energy of 140 kV or 150 kV with a tin filter, the X-ray absorption Is of tungsten (Wc) remains practically unchanged compared to the X-ray absorption of iodine. Therefore, image points where the two individual images are generated with different tube voltages can easily be assigned to one of the two contrast agents.For example, a point where the absorption is the same in both images can clearly be attributed to the material tungsten, and a point where the absorption is very different in both images can clearly be attributed to the material iodine.

[0043] In FIG 3 Figure 30 illustrates the absorption properties of the contrast agents iodine (I) and tungsten (W), as well as calcium (Ca) and water (H₂O), as a function of the energy EPH of the X-ray photons. For each of these materials, the mass absorption coefficient κ is plotted as a function of the energy EPH of the X-ray photons. FIG 3 It is clearly visible that the absorption of the contrast agent iodine (I) and the bone material calcium (Ca) decreases sharply with increasing photon energy (EPH) in the range of 40 to 80 keV. It should be noted that the absorption is shown logarithmically. In contrast, tungsten (W) behaves more like water (H2Oh). The absorption of tungsten (W) for a first photon energy (E1), which is approximately 45 keV, is the same as the absorption for a second photon energy (E2), which is approximately 80 keV. Due to the significantly different behavior of tungsten (W) compared to calcium (Ca), image areas containing tungsten (W) can be easily separated from areas where calcium (Ca) predominates.

[0044] In FIG 4 Figure 400 shows a flowchart illustrating an X-ray imaging method according to an embodiment of the invention. In step 4.I, a tungsten-based contrast agent is first selected for angiographic imaging of an examination area of ​​a patient, for example, the patient's skull. Furthermore, in step 4.II, raw X-ray data RD, acquired from an area of ​​an examination object O flooded with the selected contrast agent using a dual-energy imaging method, are recorded. In the diagram shown in FIG 4 In the illustrated method, raw X-ray data is acquired using X-rays recorded with two different energy values, E(1) and E(2). The energy values ​​are selected such that the absorption behavior of the chosen contrast agent, in this embodiment a tungsten-based contrast agent, is the same for both energy values. This process can be achieved, for example, by using two spatially separated detectors, with a filter placed in the beam path in front of one of the detectors to filter out a portion of the X-ray spectrum. Thus, two sets of raw data are acquired, each with different X-ray energies, E(1) and E(2).

[0045] In step 4.III, two image datasets, BD1 and BD2, are reconstructed based on the two raw datasets generated in step 4.II. A first image dataset, BD1, is generated, representing the first image region treated with the contrast agent tungsten. A second image dataset, BD2, is generated, representing a second image region complementary to the first, in which calcium-based structures are visualized. The generation of the two image datasets, BD1 and BD2, can be achieved, for example, by means of material decomposition based on the raw data acquired in step 4.II.

[0046] In FIG 5 A reconstruction device 50 is shown. The reconstruction device 50 has a detection unit 51. The detection unit 51 receives information regarding the contrast agent K to be used and determines values ​​E(1), E(2) for two different X-ray photon energies at which a selected contrast agent K behaves like water, i.e., the absorption is the same for both energy values. In contrast, the image areas containing calcium, which are to be separated from the contrast agent K, exhibit a clear spectral dependence of absorption in energy ranges usable by X-ray devices and can therefore be easily distinguished from the selected contrast agent K at the determined energy values ​​E(1), E(2). The selection of the energy values ​​E(1), E(2) can, for example, be based on energy-dependent absorption values ​​of the selected contrast agent K stored in a data storage device.

[0047] The choice of energy values ​​E(1) and E(2) can be taken into account in a multi-energy imaging procedure when selecting the energies or average energy values ​​of the X-ray sources used for imaging. If counter detectors are used to detect the X-ray radiation, energy thresholds or intervals can be selected to encompass the aforementioned energy values.

[0048] The reconstruction device 50 also includes a raw data receiving unit 52 for receiving raw X-ray data RD. The raw data RD were acquired using a dual-energy CT procedure from an area of ​​the examination object that was at least partially saturated with the contrast agent K.

[0049] The raw data RD are forwarded to a decomposition unit 53, which performs a material decomposition of the raw data RD based on the X-ray raw data RD with respect to the contrast agent K and calcium. The material-specific components MA1, MA2 of the raw data, assigned to the individual absorption spectra of the different materials, are transmitted to a reconstruction unit 54, which reconstructs at least two image data sets BD1, BD2 based on the material-specific components MA1, MA2. A first image data set BD1 illustrates a first image region treated with the contrast agent, and a second image data set BD2 illustrates a second image region complementary to the first, in which calcium-containing structures or iodine-contrasted structures predominate.The generated image data sets BD1, BD2 are output via an output interface 55, for example to a display unit, a data storage unit or a control computer with image display.

[0050] In FIG 6 Figure 60 illustrates an X-ray imaging system, in this case a CT system, according to an embodiment of the invention.

[0051] The CT system 60, which is designed as a dual-energy CT system, essentially consists of a conventional scanner 9. A projection measurement data acquisition unit 5 with two detectors 16a, 16b and two X-ray sources 15a, 15b opposite the detectors 16a, 16b is mounted on a gantry 11 and rotates around a measurement chamber 12. In front of the scanner 9 is a patient positioning device 3 or a patient table 3. The upper part 2 of the table, with a patient O on it, can be moved towards the scanner 9 to move the patient O through the measurement chamber 12 relative to the detector system 16a, 16b. The scanner 9 and the patient table 3 are controlled by a control unit 31, from which acquisition control signals AS are received via a conventional control interface 34 to control the entire system in the standard manner according to predefined measurement protocols.In the case of spiral acquisition, a helical path is formed by the movement of the patient O along the z-direction, which corresponds to the system axis z through the measuring chamber 12, and the simultaneous rotation of the X-ray sources 15a, 15b relative to the patient O during the measurement. The detectors 16a, 16b always move in parallel with the X-ray sources 15a, 15b to acquire projection measurement data PMD1, PMD2, which are then used to reconstruct volume and / or tomographic image data. A sequential measurement procedure can also be performed, in which a fixed position in the z-direction is approached, and then, during one or more rotations, the necessary projection measurement data PMD1, PMD2 are acquired at the respective z-position to reconstruct a cross-sectional image at this z-position or to reconstruct image data from the projection measurement data of several z-positions.The method according to the invention can, in principle, also be used on other CT systems, e.g., with only one X-ray source or a detector forming a complete ring. For example, the method according to the invention can also be applied to a system with a stationary patient table and a gantry moving in the z-direction (a so-called sliding gantry).

[0052] The projection measurement data PMD1, PMD2 (hereinafter also referred to as raw data) acquired by the detectors 16a, 16b are transferred to the control unit 31 via a raw data interface 33. This raw data is then further processed, optionally after suitable preprocessing, in a reconstruction unit 50, which in this embodiment is implemented in the control unit 31 as software on a processor. Based on the raw data PMD1, PMD2, this reconstruction unit 50 reconstructs two image data sets BD1, BD2, of which a first image data set BD1 illustrates vascular structures exposed to a contrast agent K according to the invention, and a second image data set BD2 depicts bone structures as well as calcified or partially calcified areas in the vessels.

[0053] The exact structure of such a reconstruction facility 50 is described in FIG 5 Explained in detail.

[0054] The image data BD1, BD2 generated by the reconstruction unit 50 are then stored in a memory 32 of the control unit 31 and / or displayed on the screen of the control unit 31 in the usual manner. They can also be accessed via a FIG 6 The data can be fed into a network connected to the computed tomography system 60, for example a radiological information system (RIS), via an interface not shown, and stored in a mass storage device accessible there or output as images on connected printers or filming stations. The data can then be further processed and subsequently stored or output in any desired manner.

[0055] Additionally, in FIG 6A contrast agent injection device 35 is also shown, with which a contrast agent K is injected into the patient O in advance, i.e., before the start of the CT imaging procedure. The areas permeated by the contrast agent K, as well as bone structures and (partially) calcified areas, can then be imaged using the computed tomography system 60 and the X-ray imaging method according to the invention.

[0056] The components of the reconstruction device 50 can be implemented predominantly or entirely as software elements on a suitable processor. In particular, the interfaces between these components can also be purely software-based. The only requirement is access to suitable memory areas where the data can be appropriately temporarily stored and retrieved and updated at any time.

[0057] Finally, it should be noted once again that the methods and devices described above are merely preferred embodiments of the invention and that the invention can be varied by a person skilled in the art without departing from the scope of the invention, insofar as it is defined by the claims. For the sake of completeness, it should also be noted that the use of the indefinite articles "a" or "an" does not preclude the possibility that the features in question may be present multiple times. Likewise, the term "unit" does not preclude the possibility that it consists of several components, which may also be spatially distributed.

Claims

1. X-ray contrast agent (K) for the representation of blood vessels flooded with the X-ray contrast agent (K), having an X-ray absorption the change of which between at least two different X-ray photon energies (E(1), E(2)) differs significantly from the change in the X-ray absorption of calcium between the at least two different X-ray photon energies (E(1), E(2)), wherein the X-ray absorption for the at least two X-ray photon energies (E(1), E(2)) is not significantly different.

2. X-ray contrast agent according to claim 1, wherein the spectrum of the X-ray absorption of the X-ray contrast agent (K) is similar to the spectrum of the X-ray absorption of water or soft tissue.

3. X-ray contrast agent according to one of the preceding claims, having one of the following materials: - tungsten, - tantalum, - hafnium, - gold.

4. X-ray imaging method for the representation of blood vessels flooded with an X-ray contrast agent (K), having the steps: - selecting a contrast agent (K) according to one of the preceding claims, - capturing X-ray raw data (RD, PMD1, PMD2) from a region of an examination object (0) which is flooded by the contrast agent (K), with the aid of a multi-energy recording method, - carrying out a material decomposition on the basis of the X-ray raw data (RD, PMD1, PMD2) in relation to the contrast agent (K) and calcium, - reconstructing at least two image datasets (BD1, BD2) on the basis of the material decomposition, comprising: - a first image dataset (BD1) which represents a first image region affected by the contrast agent (K), - a second image dataset (BD2) which represents a second image region which is preferably complementary to the first image region.

5. X-ray imaging method according to claim 4, having a multi-energy imaging method with the steps: - specifying at least two different X-ray tube voltages (VT) at which a change in the X-ray absorption of the contrast agent (K) significantly differs from calcium, - capturing at least two datasets of X-ray image recordings that have been recorded with the at least two different X-ray tube voltages (VT) for acquisition of a first raw dataset (PMD1) and at least one second raw data set (PMD2), - carrying out the material decomposition on the basis of the at least two raw datasets (PMD1, PMD2).

6. X-ray imaging method according to claim 4, having the steps: - capture of X-ray raw data (RD, PMD1, PMD2) with the aid of a photon-counting detector in an energy-resolved manner, wherein the energy thresholds of the photon-counting detector are set such that therewith, the change in the X-ray absorption of the X-ray contrast agent (K) differs significantly from the change in the X-ray absorption of calcium, - carrying out the material decomposition on the basis of the energy-resolved raw data (RD, PMD1, PMD2).

7. X-ray imaging method according to one of claims 4 to 6, having a CT angiographic imaging method.

8. Image reconstruction facility (50), having: - an ascertaining unit (51) for ascertaining at least two different X-ray photon energies (E(1), E(2)) at which an X-ray contrast agent (K) according to one of claims 1 to 3 differs significantly from the change in the X-ray absorption of calcium between the at least two different X-ray photon energies (E(1), E(2)), - a raw data receiving unit (52) for receiving X-ray raw data (RD) from a region of an examination object (0) which is partially flooded by the X-ray contrast agent (K), with the aid of a multi-energy recording method, - a decomposition unit (53) for carrying out a material decomposition on the basis of the X-ray raw data (RD, PMD1, PMD2) in relation to the X-ray contrast agent (K) and calcium, - a reconstruction unit (54) for reconstructing at least two image datasets (BD1, BD2) on the basis of the material decomposition, comprising: - a first image dataset (BD1) which represents a first image region affected by the X-ray contrast agent (K), - a second image dataset (BD2) which represents a second image region which is preferably complementary to the first image region.

9. X-ray imaging system (60), having an image reconstruction facility (50) according to claim 8.

10. X-ray imaging system according to claim 9, having a CT angiography facility.

11. Computer program product having a computer program which can be directly loaded into a storage facility of an X-ray imaging system (60), having program portions in order to carry out all the steps of a method according to one of claims 4 to 7 when the computer program is executed in the X-ray imaging system (60).

12. Computer-readable medium on which program portions that can be read in and executed by a computer unit are stored, in order to carry out all the steps of a method according to one of claims 4 to 7 when the program portions are executed by the computer unit.