X-ray imaging method, x-ray imaging system and computer program product

Abstract

In the X-ray imaging method, a first time duration (T1) and a second time duration (T2) are determined, the first time duration being a time duration of a flow of contrast agent from a predetermined contrast agent injection location to a predetermined location near a body midline (8) of a hollow organ (7), the second time duration being a time duration of a flow of contrast agent from the location near the body midline (8) of the hollow organ (7) to a predetermined location away from the body midline (9). A first sequence of X-ray projection images is generated in a first acquisition phase (A1), wherein each projection image of the first sequence at least partially shows the hollow organ (7) in a respectively predetermined different projection direction. The first acquisition phase (A1) is started after a first time duration (T1) after an injection start instant of an injection of contrast agent at the contrast agent injection location, and a duration of the first acquisition phase (A1) is equal to the second time duration (T2). A time resolved three-dimensional reconstruction of the hollow organ (7) is generated from the projection images of the first sequence.

Description

TECHNICAL FIELD

[0001] The invention relates to an X-ray imaging method for the time-resolved three-dimensional display of at least one hollow organ of a person and to an X-ray imaging system for the time-resolved three-dimensional display of at least one hollow organ of a person, wherein the X-ray imaging system has an X-ray source, an X-ray detector, a drive device for positioning the X-ray source and the X-ray detector relative to a recording region in accordance with different projection directions, and at least one computing unit. Furthermore, the invention also relates to a corresponding computer program product. BACKGROUND

[0002] In order to generate a three-dimensional reconstruction of an organ to be imaged by means of X-ray imaging, a large number of X-ray projection images are recorded, for example in different projection directions, and a three-dimensional reconstruction is obtained by means of the re-projection of the corresponding projection images. By this means, for example, a three-dimensional reconstruction of a hollow organ, in particular of a vascular system, can also be generated. In this case, a three-dimensional angiography is meant.

[0003] It is furthermore possible to generate X-ray projection images on the one hand before the administration of a contrast agent and on the other hand after or during the administration of a contrast agent and to subtract the X-ray projection images imaged with and without contrast agent in the same projection direction from one another, so that in the generated subtraction images the hollow organ and, if necessary, the tool can be better recognized. The subtraction images can likewise be based on a three-dimensional reconstruction. In this case, a 3D-DSA (three-dimensional digital subtraction angiography) is meant. There are also methods in which the subtraction is carried out in the three-dimensional image from the outset.

[0004] If a plurality of projection images are recorded during the diffusion of a contrast agent in a hollow organ, a plurality of time-resolved three-dimensional reconstructions can be generated, which enable the observation of a contrast agent bolus at a plurality of different times and from different perspectives. If this is combined with subtraction techniques, this is referred to as 4D-DSA. In the article "4D-DSA: Development and Current Applications in Neurovascular Imaging" by K. L. Ruedinger et al., published in the American Journal of Neuroradiology, Vol. 42 (2) 214-220, 2021, the authors describe the development, acquisition, reconstruction and current applications of 4D-DSA.

[0005] For generating a time-resolved 3D reconstruction (also called 4D reconstruction or time-resolved three-dimensional imaging or 4D image) of one or more hollow organs of a person by means of this method, a conventional three-dimensional reconstruction is first generated from two-dimensional reconstruction images generated during the contrast agent administration. For this purpose, for example, there need to be projection images of the hollow organ completely filled with contrast agent in a sufficient number of projection directions, respectively. The two-dimensional reconstruction images provide the contrast agent flow in at least one hollow organ in the form of sections of the hollow organ partially filled with contrast agent, which are integrated in the three-dimensional reconstruction generated beforehand by means of re-projection.

[0006] It is a prerequisite here that, on the one hand, there is a sufficient number of two-dimensional projection images for establishing a three-dimensional reconstruction with a hollow organ completely filled with contrast agent, and, on the other hand, there is a time-resolved administration of the contrast agent mass in the entire region of interest. If this is not the case, it can lead to artifacts or holes in the time-resolved image, in which, for example, the propagation of the contrast agent mass cannot be imaged in specific critical regions of the hollow organ. SUMMARY

[0007] The technical problem addressed by the present application is to at least partially overcome the disadvantages in X-ray imaging of at least one hollow organ of a person for time-resolved three-dimensional display.

[0008] The technical problem is solved according to the present application by an X-ray imaging method for time-resolved three-dimensional display of at least one hollow organ of a person, wherein

[0009] - a first time duration is determined, which is a person-specific flow duration of contrast agent from a predetermined contrast agent injection location of the person to a predetermined location near the body midline of the at least one hollow organ;

[0010] - a second time duration is determined, which is a person-specific flow duration of contrast agent from the location near the body midline of the at least one hollow organ to a predetermined location away from the body midline;

[0011] - a first sequence of projection images is generated in a first recording phase, wherein each projection image of the first sequence at least partially displays the at least one hollow organ in a respectively preset different projection direction;

[0012] - the first recording phase is started after the first time duration has elapsed after an injection start time of an injection of contrast agent at the contrast agent injection location, and the duration of the first recording phase is equal to the second time duration; and

[0013] - a time-resolved three-dimensional reconstruction of the at least one hollow organ is generated from the projection images of the first sequence.

[0014] The technical problem is also solved according to the application by an X-ray imaging system for time-resolved three-dimensionally displaying at least one hollow organ of a person, the X-ray imaging system having an X-ray source, an X-ray detector, a drive device for positioning the X-ray source and the X-ray detector relative to a recording region in accordance with different projection directions, and at least one computing unit, the computing unit being configured to

[0015] - determine a first time duration, which is a person-specific flow duration of contrast agent from a predetermined contrast agent injection location of the person to a predetermined location of the at least one hollow organ near the body midline,

[0016] - determine a second time duration, which is a person-specific flow duration of contrast agent from the location of the at least one hollow organ near the body midline to a predetermined location away from the body midline,

[0017] - control the drive device, the X-ray source and the X-ray detector so as to generate a first sequence of projection images in a first recording phase, wherein each projection image of the first sequence at least partially displays the at least one hollow organ in accordance with a respectively pre-set different projection direction, wherein the first recording phase is started after the first time duration has elapsed after an injection start time at which contrast agent is injected at the injection location, and the duration of the first recording phase is equal to the second time duration; and

[0018] - generate a time-resolved three-dimensional reconstruction of the at least one hollow organ from the projection images of the first sequence.

[0019] The technical problem is also solved according to the application by a computer program product having instructions which, when executed by an X-ray imaging system of the aforementioned type, carry out an X-ray imaging method of the aforementioned type.

[0020] The idea underlying the application is that a recording phase for generating a series of projection images, which at least partially image the at least one hollow organ from different projection directions, is delayed by a first time duration after an injection start time at which contrast agent is injected, the first time duration being a person-specific flow duration of contrast agent from a pre-set injection location to a pre-set location of the at least one hollow organ near the body midline (or inside), wherein the duration of the recording phase is equal to a second time duration, which is a person-specific flow duration of contrast agent from the pre-set location near the body midline to a pre-set location of the at least one hollow organ away from the body midline (or outside).

[0021] According to an aspect of the application, an X-ray imaging method for time-resolved three-dimensionally displaying at least one hollow organ of a person is provided. A first time duration is obtained, in particular by at least one computing unit of an X-ray imaging system, the first time duration being a person-specific contrast agent flow time duration, in particular from a pre-specified contrast agent injection location to a pre-specified location of the at least one hollow organ close to a body midline. A second time duration is obtained, in particular by the at least one computing unit, the second time duration being a person-specific contrast agent flow time duration from the location of the at least one hollow organ close to the body midline to a location away from the body midline.

[0022] A first sequence of X-ray projection images is generated in a first imaging phase, wherein each projection image of the first sequence at least partially displays the hollow organ in a respectively pre-specified different projection direction. The first imaging phase is started after a first time duration has elapsed after an injection start time, that is to say after the first time duration has elapsed after the injection start time, and the first imaging phase has a duration equal to the second time duration, that is to say the first imaging phase is ended after the sum of the first time duration and the second time duration has elapsed after the injection start time. A time-resolved three-dimensional reconstruction of the at least one hollow organ is generated from the projection images of the first sequence, in particular by means of the at least one computing unit.

[0023] The first and second time durations are in particular obtained in that the first and second time durations are stored in a storage medium of the at least one computing unit and are read by the at least one computing unit. The at least one computing unit in particular also obtains the injection start time, that is to say the time at which the injection of the contrast agent is started at the contrast agent injection location. To this end, an information signal is generated, for example by means of a user input or automatically at the start of the injection, and is passed to the at least one computing unit. The injection of the contrast agent itself, however, is not part of the X-ray imaging method.

[0024] The first and second time durations are in particular time durations which are specific to the person whose at least one hollow organ is displayed by means of the X-ray imaging method. According to the application, the first and second time durations can be determined before the X-ray imaging method or, in some embodiments, also before the imaging phase as part of the X-ray imaging method.

[0025] The first shooting phase starting after a first time period after the injection start time can be understood in particular as meaning that the shooting of the initial projection image of the first sequence is restarted after a first time period after the injection start time. The duration of the first shooting phase being equal to the second shooting duration can be understood in particular as meaning that the final projection image of the first sequence is generated after a second time period after the start of the first shooting phase. Here, in particular, tolerances in terms of the time required for generating the projection images, the time required for setting the respective projection direction, the time required for data detection, etc. are taken into account. The projection images of the first sequence then consist in particular of the initial projection image and the final projection image and a large number of further projection images which are shot between the initial and final projection images.

[0026] The first sequence is in particular a temporal sequence or chronological order of projection images, wherein the total number of projection images of the first sequence is predetermined. The projection images of the first sequence show at least one hollow organ at least partially according to different projection directions which are each predetermined. This can be understood in particular as meaning that each individual projection direction is predetermined for all projection images of the first sequence and is different from one another for all projection images of the first sequence. The projection directions of two different projection images of the first sequence are therefore always different from one another.

[0027] The description relating to the first sequence can likewise be transferred analogously to further sequences of projection images.

[0028] The contrast agent injection location is in particular a site in the vascular system, in particular the blood vessel system, of a person, at which the contrast agent is injected, in particular in a vein of a person. The contrast agent injection location is not necessarily shown by the projection images of the first sequence and is generally not shown in the first sequence either. The first time period is therefore generally greater than zero and is in the order of magnitude of tenths of a second to seconds.

[0029] The first sequence of projection images shows in particular a predetermined region of interest, in which at least one hollow organ is at least partially located. The contrast agent injection location is not necessarily located in the region of interest and is generally located outside the region of interest. The position close to the body midline can be understood as meaning a site of the region of interest which is first reached by the contrast agent bolus after the injection at the contrast agent injection location. That is to say, the position close to the body midline can be understood in this case as meaning the site which is closest to the contrast agent injection location. Correspondingly, the position far from the body midline can be a site inside the region of interest which is last reached by the contrast agent bolus or at which the contrast agent bolus leaves the region of interest. That is to say, the position far from the body midline can be understood in this case as meaning the site which is farthest from the contrast agent injection location.

[0030] The time-resolved three-dimensional reconstruction of the at least one hollow organ is generated from the projection images of the first sequence, which can be understood in particular as meaning that at least the projection images of the first sequence are used for generating the time-resolved three-dimensional reconstruction. In general, further projection images are also used for this purpose, which are not generated during the first acquisition phase, but rather after the first acquisition phase. Since the first acquisition phase begins at a time T1, with the time of the contrast agent injection being set equal to zero, and T1 denotes a first time duration, and the first acquisition time duration ends at a time T1+T2, T2 denoting a second time duration, the first acquisition phase covers the entire relevant time range, during which the contrast agent bolus moves from a position close to the body midline to a position far from the body midline.

[0031] During the second acquisition phase, which follows the first acquisition phase, further projection images can be generated, for example, which image the at least one hollow organ during the filling of the at least one hollow organ with contrast agent in the entire region of interest. The projection images of the second acquisition phase are likewise used for generating the time-resolved three-dimensional reconstruction.

[0032] The projection images of the second acquisition phase can be used, for example, for generating a static three-dimensional reconstruction of the at least one hollow organ, and the projection images of the first sequence from the first acquisition phase can be re-projected into this static three-dimensional reconstruction in order to achieve the time resolution.

[0033] As already mentioned, the process of the contrast agent injection itself is generally not part of the X-ray imaging method according to the application. However, it should be noted that the contrast agent injection, for example in known methods for time-resolved three-dimensional imaging, is carried out over a time range which enables a sufficient number of projection images in which the at least one hollow organ is completely filled with contrast agent in the region of interest. In particular, the contrast agent administration can be carried out over the entire first acquisition phase and, if necessary, over the entire second acquisition phase.

[0034] In some embodiments, the method according to the application can also be implemented as a 4D-DSA method. In this case, the projection images of the first sequence and, if necessary, the projection images of the second acquisition phase and the corresponding second sequence of projection images correspond to so-called object images or vessel images or full images (in English: fill images). Further mask images which are required for the DSA, in particular those which are generated before or after the first acquisition time range when the contrast agent is no longer in the at least one hollow organ, show the at least one hollow organ without contrast agent.

[0035] The length of time of the contrast agent flow from the contrast agent injection site to the position near the body midline can vary depending on the blood flow speed or the anatomy of the specific person. The same applies to the length of time of the contrast agent flow from the position near the body midline to the position away from the body midline. Since the first length of time and the second length of time are obtained or determined for the specific person according to the application and the first recording phase is controlled such that it begins at the time T1 and ends at the time T1 + T2, it is ensured that on the one hand no undesired projection images of a specific projection direction are recorded before the contrast agent bolus has reached the region of interest in general, or that the first recording phase is not ended as soon as the contrast agent bolus has reached the position away from the body midline, so that the time-resolved information is incomplete.

[0036] In particular, it is thereby achieved that the time-resolved reconstruction can show the time-resolved flow of the contrast agent bolus in the entire region of interest from the position near the body midline to the position away from the body midline. This cannot be reliably achieved, for example, if the beginning and end times of the first recording phase are determined according to assumed delay times or empirical values or the like.

[0037] According to at least one embodiment, a preliminary sequence of projection images is generated in a preliminary phase before the injection start time, wherein each projection image of the preliminary sequence shows the position near the body midline and the position away from the body midline. Here, the preliminary sequence is started simultaneously with a further injection start time for injecting contrast agent at the contrast agent injection site. The first length of time and the second length of time are determined according to the projection images of the preliminary sequence.

[0038] Accordingly, at other injection start times before the injection start time, contrast agent is injected in advance in order to determine the first length of time and the second length of time. That is, a test contrast agent bolus can be observed in order to determine the first length of time and the second length of time. At the injection start time, in particular, no contrast agent of the preliminary sequence is present in the at least one hollow organ.

[0039] The projection images of the preliminary sequence do not necessarily have to be taken from different projection directions. It is also possible, however, that the projection images of the preliminary sequence are taken from two or more different projection directions, so that the preliminary sequence comprises two or more different sub-sequences each with a constant projection direction. In this way, the first time duration or the second time duration can be determined more reliably, in particular in the case of a position of the position of the body away from the median line and a position of the body near the median line not lying in the same plane. However, the number of different projection directions in the preliminary sequence does not necessarily have to be similar or equal to the number of different projection directions in the first recording phase. In particular, the projection images of the preliminary sequence do not necessarily have to be suitable for a three-dimensional reconstruction. The number of projection images in the preliminary phase can be smaller, in particular significantly smaller, than the number of projection images in the first recording phase. Alternatively or additionally, the X-ray intensity and / or the frame rate in the preliminary sequence can also be lower than the X-ray intensity and / or the frame rate used for generating the first sequence during the first recording phase. The radiation burden on the person is thereby reduced in the preliminary phase.

[0040] Since the projection images of the preliminary sequence are generated in a time- defined manner, each projection image of the preliminary sequence can correspond to a time after the injection time. In this way, it can be determined when the test contrast agent reaches the position of the body away from the median line and the position of the body near the median line, and the first time duration and the second time duration can accordingly be determined.

[0041] In order to determine the first time duration and the second time duration in the preliminary sequence phase on the basis of the projection images of the preliminary sequence, known methods in terms of image intensity can be applied to the projection images of the preliminary sequence (intensity thresholding). That is to say, for example, a predetermined region around the position of the body near the median line can be evaluated in order to determine those projection images of the preliminary sequence in which the image intensity in the region around the position of the body near the median line first exceeds or is equal to a predetermined limit value. The recording time of the projection image thus identified then corresponds, for example, to the first time duration.

[0042] Furthermore, for example, a predetermined region around the position of the body away from the median line can also be evaluated in order to determine those projection images of the preliminary sequence in which the image intensity in the region around the position of the body away from the median line first exceeds or is equal to a further predetermined limit value. The recording time of the projection image thus identified then corresponds, for example, to the sum of the first time duration and the second time duration.

[0043] It is also possible to use other image evaluation algorithms, for example based on machine learning trained algorithms, in order to identify the respective projection images in which the test contrast agent bolus first reaches the position close to the body midline or the position away from the body midline. It is also possible, in particular, for the position close to the body midline or the position away from the body midline not to be specifically selected by the user in the respective X-ray images. Rather, for example, the user can name a characteristic vessel structure of the at least one hollow organ or a characteristic point in the vessel structure and apply a correspondingly trained algorithm to the projection images of the preparation sequence in order to automatically identify the relevant projection images corresponding to the first or second time length.

[0044] Here, the position close to the body midline and the position away from the body midline can differ depending on the specific application or depending on the specific hollow organ to be imaged or to be shown. For example, the position close to the body midline can correspond to the bifurcation of the internal carotid artery, for example. The distal position can be a point on the sigmoid sinus, for example, or also a point at a distance from a venous malformation, an aneurysm or an arteriovenous fistula, for example.

[0045] According to at least one embodiment, each projection image of the preparation sequence shows the position close to the body midline and the position away from the body midline in the same predetermined projection direction. Alternatively, the preparation sequence consists of two or more subsequences, each subsequence comprising two or more projection images, wherein each projection image of the preparation sequence shows the position close to the body midline and the position away from the body midline and the respective projection direction is identical in each subsequence and different from each other for different subsequences.

[0046] In this way, the preparation sequence can be implemented simply and quickly, wherein T1 and T2 can still be reliably determined.

[0047] In different embodiments, on the basis of the projection images of the preparation sequence, it is also possible to generate corresponding subtraction images in a known manner and then to determine the first and second time lengths accordingly from these subtraction images.

[0048] According to at least one embodiment, a first preliminary sequence of projection images is generated in a preliminary phase before the injection start time, wherein each projection image of the first preliminary sequence shows a position close to the body midline. A second preliminary sequence of projection images is generated in the preliminary phase, wherein each projection image of the second preliminary sequence shows a position away from the body midline. The first preliminary sequence is started simultaneously with a first other injection start time for injecting contrast agent at the contrast agent injection position. The second preliminary sequence is started simultaneously with the first other injection time or with a second other injection start time for injecting contrast agent at the contrast agent injection position. The first time duration is determined from the projection images of the first preliminary sequence and the second time duration is determined from the projection images of the second preliminary sequence.

[0049] The projection images of the first preliminary sequence show in particular no position away from the body midline and the projection images of the second preliminary sequence show in particular no position close to the body midline. In other words, the first and second time duration are determined on the basis of different preliminary sequences. This enables a more accurate determination of the respective time duration by more accurately determining a position close to the body midline or a position away from the body midline, in particular when they are spatially relatively far away from each other.

[0050] For example, the projection direction is constant for all projection images of the first preliminary sequence and the projection direction can likewise be constant for the projection images of the second preliminary sequence. The projection direction of the first preliminary sequence can be the same or different from the projection direction of the second preliminary sequence. It is also possible that the first preliminary sequence and / or the second preliminary sequence have two or more subsequences which are distinguished from each other by a constant projection direction within the respective subsequence.

[0051] According to at least one embodiment, the x-ray imaging method is a method for 4D-DSA.

[0052] According to at least one embodiment, a first mask sequence of projection images is generated in a first mask recording phase, wherein each projection image of the first mask sequence at least partially shows the at least one hollow organ according to a respective different projection direction. Each projection image of the first mask sequence corresponds to exactly one projection image of the first sequence, so that the projection direction of the projection images of the first mask sequence is identical to the projection direction of the respectively corresponding projection image of the first sequence. For each projection image of the first mask sequence, a first subtraction image is generated, in particular by means of at least one computing unit, by subtracting the projection image of the first mask sequence from the respectively corresponding projection image of the first sequence. A time-resolved three-dimensional reconstruction is generated from the first subtraction images, in particular all generated first subtraction images.

[0053] The projection images of the first mask sequence are taken, in particular, when the contrast agent is not yet or no longer in the at least one hollow organ. This embodiment, in particular, relates to an x-ray imaging method for 4D-DSA. The exact assignment of the projection images of the first mask sequence to one projection image of the first sequence means that the number of projection images of the first mask sequence is equal to the number of projection images of the first sequence.

[0054] It should be noted that the duration of the first mask taking phase can be equal to the duration of the first taking phase, however, this is not necessarily the case. It should furthermore be noted that the subtraction of the individual projection images of the first mask sequence from the associated projection images of the first sequence can be carried out in a known DSA method, in particular, can also include a pre-processing or processing step of the individual projection images before the actual subtraction and / or a post-processing step of the resulting subtraction images.

[0055] In this way, the time-resolved display of the at least one hollow organ can be displayed more detailed, more accurately and according to the application completely and reliably.

[0056] According to at least one embodiment, a second sequence of projection images is generated in the second taking phase, wherein each projection image of the second sequence at least partially displays the at least one hollow organ in a respectively pre-set different projection direction. The second taking phase starts at or opens at the end of the first taking phase. A time-resolved three-dimensional reconstruction is generated from the projection images of the first sequence and from the projection images of the second sequence.

[0057] For example, in a corresponding embodiment, a time-resolved three-dimensional reconstruction is generated from the first subtraction images and from the second subtraction images generated from the corresponding projection images of the second sequence.

[0058] The duration of the second taking phase is generally related to the x-ray imaging system used, the frame rate, the required image quality, etc. It is, in particular, selected so that it is possible to take all projection directions required for the generation of a static three-dimensional reconstruction.

[0059] The projection directions of the individual projection images of the second sequence are different, respectively, as set out for the projection directions of the projection images of the first sequence. Furthermore, the projection directions of the projection images of the second sequence can also be different from all projection directions of the projection images of the first sequence. The latter case, however, is not necessary. In particular, the projection directions of the individual or all projection images of the second sequence can coincide with the corresponding projection directions of the projection images of the first sequence.

[0060] As already mentioned before, the injection time length covers not only the time length of the first acquisition phase but also the time length of the second acquisition phase. The injection time length may, for example, be equal to the sum of the time lengths of the first and second acquisition phases. In such an embodiment, a static three-dimensional reconstruction of the at least one hollow organ may, for example, be generated on the basis of the projection images of the second sequence, if necessary on the basis of the corresponding second subtraction images. The projection images of the first sequence or the first subtraction images, respectively, can be re-projected, and the combined re-projections can be inserted into the static three-dimensional reconstruction, respectively.

[0061] That is, by this approach, a sequence of three-dimensional reconstructions is allowed to be generated, wherein each reconstruction of the sequence corresponds to a combination of a static three-dimensional reconstruction with a reconstruction of a corresponding projection image of the first sequence or a corresponding first subtraction image. The three-dimensional reconstructions of the sequence can then be considered as time-resolved three-dimensional reconstructions or four-dimensional reconstructions of the at least one hollow organ.

[0062] According to at least one embodiment, a stop signal for automatically ending the contrast agent injection of the contrast agent is generated at a time instant which precedes the end time instant of the second acquisition phase by the first time length. In particular, the contrast agent injection is automatically ended on the basis of the stop signal.

[0063] The stop signal may, for example, be transmitted to a contrast agent pump for injecting the contrast agent, and the contrast agent pump can automatically end the contrast agent injection in accordance with the stop signal.

[0064] In such an embodiment, the injection time length covers the time length of the first acquisition phase, however, not completely the time length of the second acquisition phase. The injection time length may, for example, be equal to the sum of the time lengths of the first and second acquisition phases minus the first time length. Thereby, it is facilitated that even after the completion of the contrast agent injection the at least one hollow organ of the entire region of interest is still filled with contrast agent for the first time. Thus, a static three-dimensional reconstruction can be generated. Thereby, a saving of contrast agent is achieved, and the physical burden on the patient is reduced by this approach.

[0065] According to at least one embodiment, a second mask sequence of projection images is generated in a second mask acquisition phase, wherein each projection image of the second mask sequence at least partially shows the at least one hollow organ in a respective different projection direction. Each projection image of the second mask sequence corresponds to exactly one projection image of the second sequence, such that the projection direction of the projection images of the second mask sequence is identical to the projection direction of the respectively corresponding projection image of the second sequence. For each projection image of the second mask sequence, a second subtraction image is generated by subtracting the projection image of the second mask sequence from the respectively corresponding projection image of the second sequence, in particular by means of at least one computing unit. A time-resolved three-dimensional reconstruction is generated on the basis of the second subtraction images and on the basis of the first subtraction images.

[0066] The description and interpretation of the first mask sequence can be similarly applied to the second mask sequence.

[0067] According to at least one embodiment, the projection direction of the projected images of the first sequence and the second sequence is characterized by various angles within a predetermined, particularly coherent, angular range in a predetermined plane. The projection direction passes through a first sub-region, particularly a coherent sub-region, of the angular range during a first shooting phase for capturing the first sequence, and through a second sub-region, particularly a coherent sub-region, of the angular range adjacent to the first sub-region during a second shooting phase for capturing the second sequence.

[0068] In other words, the second subregion follows the first subregion and does not overlap with the first subregion.

[0069] For example, the angle characterizing each projection direction can be given by the angle between the straight line connecting the X-ray source and the X-ray detector and a predetermined reference direction in the plane, such as perpendicular to the detector surface of the X-ray detector. Here, the X-ray source and the X-ray detector are arranged and supported relative to each other so that they can rotate about a common axis of rotation perpendicular to the plane. This can be achieved, for example, by arranging the X-ray source and the X-ray detector on a so-called C-arm. In this way, each projection direction can be defined by a corresponding angle from 0° to 360°.

[0070] It should be noted that only rotation about the axis of rotation is observed here. However, in corresponding X-ray imaging systems, it is also feasible for the X-ray source and the X-ray detector to rotate in different planes. This leads to a corresponding improvement to the X-ray imaging method according to the present invention.

[0071] Without limiting generality, it can be assumed, for example, that the angle corresponding to the projection direction of the initial projected image of the first sequence is 0°. This angle range can then be described as [0°, α...]. max ], where α is applicable max <360°. The first subregion is defined by [0°, α1], and the second subregion is defined by [α1, α2], where 0° < α1 < α2 < α1. max .

[0072] The projection images of the first sequence are distributed at multiple angles, for example, uniformly or approximately uniformly, within a first sub-region. The projection images of the second sequence are also distributed at multiple angles, for example, uniformly or approximately uniformly, within a second sub-region.

[0073] The first and second subregions extend adjacently and sequentially, for example, in the same direction.

[0074] By this means, it is possible to realize the first and second recording phases with only one angular stroke of the angular range.

[0075] According to at least one embodiment, the projection direction of the projection images of the first and second mask sequences is characterized by the respective angle within the angular range in the plane. The first sub-region is passed through in the first mask recording phase for recording the first mask sequence, and the second sub-region is passed through in the second mask recording phase for recording the second mask sequence.

[0076] Here, the first and second sub-regions extend in particular in the same direction.

[0077] By this means, it is also possible to detect the first and second mask sequences with only one angular stroke through the entire angular range.

[0078] According to at least one embodiment, the entire angular range is passed through, in particular completely, in the first recording phase for recording the first sequence, and the angular range is passed through, in particular anew, for example completely, in the second recording phase for recording the second sequence.

[0079] In this way, the total angular range can be smaller than in the above-described embodiments in which two sub-regions of the angular range extend in the same direction for detecting the projection images of the first and second sequences.

[0080] For example in the above-described embodiments, in which the angular range is completely passed through in the first and second recording phases, it is possible to pass through the angular range in the first recording phase in a first direction and in the second recording phase in a second direction opposite to the first direction. This reduces the time delay between the first and second recording phases.

[0081] According to at least one embodiment, the angular range is completely passed through in the first and second recording phases, and the duration of the second recording phase is equal to the second duration.

[0082] By this means, it is possible to use the same rotational speed or frame rate for generating the second recording sequence as for generating the first recording sequence. However, it is also possible in alternative embodiments to use a different duration for the second recording phase than the second duration. In this case, the respective requirements for generating a static three-dimensional reconstruction and time-resolved information can be considered independently of one another.

[0083] According to at least one embodiment, wherein the angle range is completely passed through, respectively, in the first recording phase and in the second recording phase, the first mask sequence is generated in a first mask recording phase and the second mask sequence is generated in a second mask recording phase. According to at least one such embodiment, in the first mask recording phase in which the first mask sequence is recorded, the angle range, in particular the complete angle range, is passed through, and in the second mask recording phase in which the second mask sequence is recorded, the angle range, in particular anew, e.g. completely, is passed through.

[0084] According to at least one embodiment, the angle range is passed through in the first mask recording phase in a first direction and in the second mask recording phase in a second direction or oppositely.

[0085] According to at least one embodiment, the duration of the first mask recording phase and / or the duration of the second mask recording phase is equal to the second duration. That is, for example, the duration of the first mask recording phase, the second mask recording phase, the first recording phase and the second recording phase, respectively, is equal to the second duration.

[0086] According to at least one embodiment, the projection direction of the projection images of the first sequence is characterized by the respective angle within a predetermined angle range in a predetermined plane. In the first recording phase, the angle range is passed through, wherein the parameters for generating the projection images of the first sequence are adapted in dependence on the second duration and the angle range, in particular the size of the angle range.

[0087] In other words, the parameters are determined in dependence on the second duration and in dependence on the angle range, and the projection images of the first sequence are generated in dependence on the parameters thus determined.

[0088] For example, the parameters can be the frame rate, the number of projection images of the first sequence, the X-ray dose per projection image, etc. For example, the parameters can also be calculated in dependence on one or more of the above-mentioned variables. In setting the parameters, in particular, it is ensured that the respective three-dimensional reconstruction quality within the angle range is sufficiently high.

[0089] According to another aspect of the application, an X-ray imaging system for time-resolved three-dimensionally displaying at least one hollow organ of a person is provided. The X-ray imaging system has an X-ray source, an X-ray detector and a drive device for positioning the X-ray source and the X-ray detector relative to a recording region according to different projection directions. The X-ray imaging system further has at least one computing unit which is designed to determine a first time duration, in particular by reading the first time duration from a storage medium, wherein the first time duration is a person-specific contrast agent flow time duration from a contrast agent injection position of the person to a predetermined position near a body midline of the at least one hollow organ. The at least one computing unit is designed to determine a second time duration, in particular by reading the second time duration from at least one storage medium, which is a person-specific contrast agent flow time duration from the position near the body midline of the at least one hollow organ to a predetermined position away from the body midline.

[0090] The at least one computing unit is designed to control the drive device, the X-ray source and the X-ray detector in order to generate a first sequence of projection images in a first recording phase, wherein each projection image of the first sequence at least partially displays the at least one hollow organ according to a respectively pre-set different projection direction. Here, the first recording phase is started after the first time duration has elapsed after an injection start time at which a contrast agent is injected at a contrast agent injection position, and the duration of the first recording phase is equal to the second time duration. The at least one computing unit is designed to generate a time-resolved three-dimensional reconstruction of the at least one hollow organ from the projection images of the first sequence.

[0091] A computing unit can in particular be understood as a data processing device which comprises a processing circuit. The computing unit can in particular process data for performing a computing operation. The computing operation can also include an operation for performing a search access to a data structure, for example a look-up table LUT (English: "look-up table"), if necessary.

[0092] The computing unit can in particular comprise one or more computers, one or more microcontrollers and / or one or more integrated circuits, for example one or more application-specific integrated circuits ASIC (English: "application-specific integrated circuit") and / or one or more field-programmable gate arrays FPGA and / or one or more system on a chip SoC (English: "system on a chip"). The computing unit can also comprise one or more processors, for example one or more microprocessors, one or more central processor units CPU (English: "central processing unit"), one or more graphics processor units GPU (English: "graphics processing unit") and / or one or more signal processors, in particular one or more digital signal processors DSP. The computing unit can also comprise a physical or virtual complex of computers or other mentioned units.

[0093] In different embodiments, the computing unit comprises one or more hardware and / or software interfaces and / or one or more storage units.

[0094] The storage unit can be designed as a volatile data memory, for example a dynamic random access memory DRAM (English: "dynamic random access memory") or a static random access memory SRAM (English: "static random access memory"), or as a non-volatile data memory, for example a read-only memory ROM (English: "read-only memory"), a programmable read-only memory PROM (English: "programmable read-only memory"), an erasable programmable read-only memory EPROM (English: "erasable programmable read-only memory"), an electrically erasable programmable read-only memory EEPROM (English: "electrically erasable programmable read-only memory"), a flash memory or flash EEPROM, a ferroelectric random access memory FRAM (English: "ferroelectric random access memory"), a magnetoresistive random access memory MRAM (English: "magnetoresistive random access memory") or a phase-change random access memory PCRAM (English: "phase-change random access memory").

[0095] The X-ray source and the X-ray detector are always positioned and / or oriented identically independently of the respective projection direction. The X-ray source and the X-ray detector can be rigidly connected to each other by means of, for example, a C-arm or the like. The drive device comprises, for example, one or more motors or gear mechanisms for moving, in particular simultaneously, the X-ray source and the X-ray detector in order to set the respective individual projection direction.

[0096] Further embodiments of the X-ray imaging system according to the application directly result from the different design options of the X-ray imaging method according to the application and vice versa. Individual features and the respective explanations and advantages relating to the various embodiments of the X-ray imaging method according to the application can be transferred analogously, in particular, to the respective embodiments of the X-ray imaging system according to the application. The X-ray imaging system according to the application is designed or programmed, in particular, to carry out the X-ray imaging method according to the application. The X-ray imaging system according to the application carries out, in particular, the X-ray imaging method according to the application.

[0097] According to another aspect of the application, a computer program having instructions is provided. When the instructions are executed by at least one computing unit of an X-ray imaging system according to the application, in particular, the instructions cause the X-ray imaging system to carry out the X-ray imaging method according to the application.

[0098] The instructions can be present, for example, as program code. The program code can be provided, for example, in the form of binary code or assembly program and / or source code in a programming language, such as C, and / or program scripts, such as Python.

[0099] According to another aspect of the application, a computer-readable storage medium storing the computer program according to the application is provided.

[0100] The computer program and the computer-readable storage medium according to the application can each be understood as a computer program product having instructions.

[0101] Further features of the application result from the description, the figures and the description of the figures.

[0102] The features and combinations of features mentioned in the description above and the features and combinations of features mentioned in the description of the figures below and / or shown in the figures can each be implemented individually or in any combination with each other. In particular, embodiments and combinations of features not explicitly described are also included in the application. Furthermore, embodiments and combinations of features that go beyond or deviate from the described combinations of features are also included in the application. BRIEF DESCRIPTION OF DRAWINGS

[0103] The application is explained in more detail below with the help of specific embodiments and the accompanying schematic drawings. In the drawings, identical or functionally identical elements can be provided with the same reference signs. Where possible, a repeated description of identical or functionally identical elements is not necessary.

[0104] In the drawings:

[0105] Figure 1 schematic diagram showing an exemplary embodiment of an X-ray imaging system according to the application;

[0106] Figure 2 schematic diagram showing an exemplary embodiment of an X-ray imaging method according to the application;

[0107] Figure 3 schematic diagram showing at least one hollow organ of a person and a position close to the body midline and a position away from the body midline;

[0108] Figure 4 schematic diagram showing a curve of the image intensity variation on the position close to the body midline and the position away from the body midline of the at least one hollow organ;

[0109] Figure 5 schematic diagram showing an exemplary embodiment of an X-ray imaging method according to the application; and

[0110] Figure 6 schematic diagram showing an exemplary embodiment of an X-ray imaging method according to the application. DETAILED DESCRIPTION

[0111] In Figure 1 schematic diagram showing an exemplary embodiment of an X-ray imaging system 1 according to the application for showing a time-resolved three-dimensional image of at least one hollow organ 7 (see Figure 3 ) of a person 6. The X-ray imaging system 1 has an X-ray source 2 and an X-ray detector 3 and a drive device for positioning the X-ray source 2 and the X-ray detector 3 relative to a recording region in order to position the person 6 or the hollow organ 7 according to different projection directions. The recording region can for example correspond to a region on a patient couch 5 which can be recorded by means of the X-ray source 2 and the X-ray detector 3.

[0112] Here, the projection direction is for example characterized by an angle a which is enclosed by a line connecting the X-ray source 2 and the X-ray detector 3 and an x-axis of a coordinate system which subtends a plane in which the X-ray source 2 and the X-ray detector 3 can be rotated by means of the drive device about a rotation axis which is in particular parallel to one of the x-axis and the y-axis and perpendicular to the z-axis.

[0113] Furthermore, the X-ray imaging system 1 has at least one computing unit 4, which on the one hand controls the X-ray source 2 to emit X-rays, and on the other hand enables the X-ray detector 3 to receive corresponding detector data, which corresponds to a projected image according to the current projection direction. The at least one computing unit 4 can also control a driving device to set different projection directions.

[0114] The X-ray imaging method according to the present invention can be performed using the X-ray imaging system 1. Figure 2 A flowchart illustrating an exemplary implementation of this X-ray imaging method is shown.

[0115] In the preparation phase V, a first duration T1 and a second duration T2 are determined for the human 6. Here, the first duration T1 is the time from the predetermined injection site of the contrast agent in the human 6 to a predetermined location 8 near the midline of the body for at least one hollow organ 7 (see [link to relevant documentation]). Figure 3 The second duration, T2, is the individual-specific flow duration of the contrast agent from at least one hollow organ 7 at a position 8 near the body midline to a predetermined position 9 away from the body midline (see...). Figure 3 The duration of movement varies from person to person. Figure 3 The image schematically illustrates two X-ray images, particularly subtraction images, of the vascular tree in the venous and arterial stages after contrast agent administration, as well as an exemplary location 8 near the body midline and an exemplary location 9 away from the body midline. In embodiments of the corresponding X-ray imaging method, the vascular tree corresponds to at least one hollow organ 7.

[0116] In the first imaging phase A1, a first sequence of X-ray projection images is generated, wherein each projection image in the first sequence represents the hollow organ 7 at least partially according to a separately preset projection orientation. Here, the first imaging phase A1 begins after a first duration T1 following the injection start time, at which time the contrast agent is injected at the contrast agent injection site. The duration of the first imaging phase A1 is equal to the second duration T2.

[0117] For example, a second imaging stage A2, following the first imaging stage A1, generates a second sequence of projected images, wherein each projected image in the second sequence at least partially shows at least one hollow organ 7 according to a correspondingly different projection orientation. Here, the second imaging stage A2 begins at the end of the first imaging stage A1.

[0118] From the projection images of the first sequence and, if necessary, also from the projection images of the second sequence, a time-resolved three-dimensional reconstruction of the at least one hollow organ 7 is generated by means of at least one computing unit 4. For example, a static three-dimensional reconstruction of the at least one hollow organ 7 can be generated on the basis of the projection images of the second sequence, and the projection images of the first sequence can each be re-projected into the static three-dimensional reconstruction in order to generate the time-resolved three-dimensional reconstruction as a whole.

[0119] For example, in some embodiments, the X-ray imaging method is also implemented as a 4D-DSA method. In this case, a first mask sequence of projection images is generated in a first mask recording phase M1, wherein each projection image of the first mask sequence at least partially shows the at least one hollow organ 7 in a respectively pre-set different projection direction. Each projection image of the first mask sequence here corresponds to exactly one projection image of the first sequence, such that the projection direction of the projection images of the first mask sequence is identical to the projection direction of the respectively corresponding projection image of the first sequence. For each projection image of the first mask sequence, a first subtraction image is generated by subtracting the projection image of the first mask sequence from the respectively corresponding projection image of the first sequence.

[0120] For example, a second mask sequence of projection images is generated in a second mask recording phase M2, wherein each projection image of the second mask sequence at least partially shows the at least one hollow organ 7 in a respectively different projection direction. Here, each projection image of the second mask sequence corresponds to exactly one projection image of the second sequence, such that the projection direction of the projection images of the second mask sequence is identical to the projection direction of the respectively corresponding projection image of the second sequence. For each projection image of the second mask sequence, a second subtraction image is generated by subtracting the projection image of the second mask sequence from the respectively corresponding projection image of the second sequence.

[0121] Subsequently, a time-resolved three-dimensional reconstruction is generated from the first subtraction images and, for example, all generated second subtraction images. A static three-dimensional reconstruction of the at least one hollow organ 7 can be generated from the second subtraction images, and the first subtraction images can each be re-projected into the static three-dimensional reconstruction in order to generate the time-resolved three-dimensional reconstruction.

[0122] In a preliminary phase V, for example, a preliminary sequence of projection images can be generated, wherein each projection image of the preliminary sequence shows the position close to the body midline 8 and the position away from the body midline 9. The preliminary phase is started at the same time as a further injection start time for injecting contrast medium at the contrast medium injection position, and the first time duration T1 and the second time duration T2 are determined from the projection images of the preliminary sequence.

[0123] Figure 4For this, a time-dependent variation curve 10 of the image intensity of the projection image of the preliminary sequence is schematically shown at the position 8 close to the body midline, and a time-dependent variation curve 11 of the image intensity is correspondingly shown at the position 9 away from the body midline. The first time duration T1 and the second time duration T2 can be determined, for example, in such a way that the respective rising edges of the time-dependent variation curves 10, 11 intersect a horizontal line, which is given by a predetermined limit intensity I t . The first time duration T1 then corresponds to the time at which the time-dependent variation curve 10 at the position 8 close to the body midline first reaches the limit intensity I t . The second time duration T2 corresponds to the time period between the intersection of the time-dependent variation curve 10 with the limit intensity I t and the time at which the time-dependent variation curve 11 first reaches the limit intensity I t . In further embodiments, different limit intensities can also be used for the two time-dependent variation curves 10, 11. However, T1 and T2 are not necessarily determined on the basis of the same preliminary sequence either. For T1 and T2, in particular, different preliminary phases can be used.

[0124] The respective number of projection images in the first and second recording phases A1, A2 and the angular increment between the directly successive projection images of the first recording phase A1 and, if a time duration is set, of the second recording phase A2 is in particular given by the desired image quality.

[0125] In Figure 5 , a flowchart of a further exemplary embodiment of the X-ray imaging method according to the application is schematically shown.

[0126] After the injection start time, after an X-ray delay time equal to the first time duration T1, a first subregion 12a of the angular range 12 is passed through in the first recording phase A1 at the angle a. Here, the first subregion 12a is passed through over a second time duration T2. Subsequently, in the second recording phase A2, a second subregion 12b of the angular range 12 is passed through over a further time duration AT. The first subregion 12a and the second subregion 12b together make up the angular range 12 and are passed through in succession in the same direction. The first sequence and the second sequence are generated, including the X-ray delay time, that is to say, for example, the time T1+T2+AT.

[0127] The second subregion 12b can, for example, correspond to an angular range of 200° overall, and the first subregion of this angular range can correspond to, for example, 60°. That is to say, the angle a in the angular range 12 then overall exceeds 260°. Angular ranges different therefrom can be chosen. As shown, for an angular range of 200°, a reliable static three-dimensional reconstruction can be achieved. The additional 60° of the first subregion 12a is then used to detect time-resolved information.

[0128] If the X-ray imaging method is implemented as a 4D-DSA method, the mask phases M1, M2 likewise pass the entire angle range 12 as a whole, for example (but not necessarily) within the same overall time T2+ΔT. Here, for example, the first sub-range 12a is passed within the first mask phase M1, and subsequently the second sub-range 12b is passed within the second mask phase M2. In an optional step M' between the second mask phase M2 and the first phase A1, the angle a can be reset by corresponding positioning of the X-ray source 2 and the X-ray detector 3.

[0129] Figure 6 A further flow diagram illustrating an exemplary embodiment of such an X-ray imaging method is shown. Here, the first phase A1 is started after a first time duration T1 after the injection start. In the first phase A1, the angle a is passed through the angle range 13 in a first direction within a second time duration T2. In a subsequent second phase A2, the angle a is passed through the angle range 13 again, for example in a second direction opposite to the first direction. This is likewise carried out within the second time duration T2, although this is not mandatory.

[0130] Since the angle range 13 is passed through completely both in the first phase A1 and in the second phase A2, this angle range can be chosen to be smaller than the angle range 12 shown in Fig. 1, for example. For example, the angle range 13 can be 200°. If the second phase A2 likewise has the time duration T2, the time period from the injection start to the end of the second phase A2 is T1 +2*T2. Figure 5

[0131] In the case of 4D-DSA, the angle range 13 is likewise passed through twice completely before the injection start, once in the first mask phase M1 in the first direction and once in the second mask phase M2 in the second direction. The mask phases M1, M2 can likewise each be the second time duration T2. In this case, the overall imaging time is given by T+4*T2. However, this is not mandatory either.

[0132] A person includes a male or female, irrespective of the grammatical gender of the particular term.​

Claims

1. An X-ray imaging method for time-resolved three-dimensionally displaying at least one hollow organ (7) of a person (6), wherein - a first time duration (Tl) is determined, which is a person-specific flow time duration of a contrast agent from a predetermined contrast agent injection site of the person (6) to a predetermined body midline proximity site (8) of the at least one hollow organ (7); - a second time duration (T2) is determined, which is a person-specific flow time duration of the contrast agent from the body midline proximity site (8) of the at least one hollow organ (7) to a predetermined body midline distance site (9); - a first sequence of projection images is generated in a first acquisition phase (Al), wherein each projection image of the first sequence at least partially displays the at least one hollow organ (7) in a respectively pre-set different projection direction; - the first acquisition phase (Al) is started after the first time duration (Tl) after an injection start time of an injection of the contrast agent at the contrast agent injection site, and the duration of the first acquisition phase (Al) is equal to the second time duration (T2); and - a time-resolved three-dimensional reconstruction of the at least one hollow organ (7) is generated from the projection images of the first sequence.

2. The X-ray imaging method according to claim 1, wherein - a preliminary sequence of projection images is generated in a preliminary phase (V) before the injection start time, wherein each projection image of the preliminary sequence displays the body midline proximity site (8) and the body midline distance site (9); - the preliminary sequence is started simultaneously with a further injection start time for an injection of the contrast agent at the contrast agent injection site; and - the first time duration (Tl) and the second time duration (T2) are determined from the projection images of the preliminary sequence.

3. The X-ray imaging method according to claim 2, wherein - each projection image of the preliminary sequence displays the body midline proximity site (8) and the body midline distance site (9) in the same predetermined projection direction; or - the preliminary sequence consists of two or more subsequences, each subsequence comprising two or more projection images, wherein each projection image of the preliminary sequence displays the body midline proximity site (8) and the body midline distance site (9), and the respective projection direction is the same in each subsequence and is different from each other for different subsequences.

4. The X-ray imaging method according to claim 1, wherein - a first preliminary sequence of projection images is generated in a preliminary phase (V) before the injection start time, wherein each projection image of the first preliminary sequence displays the body midline proximity site (8); - a second preliminary sequence of projection images is generated in the preliminary phase (V), wherein each projection image of the second preliminary sequence displays the body midline distance site (9); - the first preliminary sequence is started simultaneously with a first further injection start time for an injection of the contrast agent at the contrast agent injection site; and - the second preliminary sequence is started simultaneously with a second further injection start time for an injection of the contrast agent at the contrast agent injection site. - the second preliminary sequence is started simultaneously with a first further injection moment or with a second further injection start moment for injecting contrast medium at the contrast medium injection position; - the first time duration (T1) is determined from projection images of the first preliminary sequence and the second time duration (T2) is determined from projection images of the second preliminary sequence.

5. The method according to claim 1, wherein - a first mask sequence of projection images is generated in a first mask taking phase (M1), wherein each projection image of the first mask sequence at least partially shows the at least one hollow organ (7) in a respective different projection direction; - each projection image of the first mask sequence corresponds to exactly one projection image of the first sequence, so that the projection direction of a projection image of the first mask sequence is identical to the projection direction of the respectively corresponding projection image of the first sequence; - for each projection image of the first mask sequence, a first subtraction image is generated by subtracting the projection image of the first mask sequence from the respectively corresponding projection image of the first sequence; and - a time resolved three-dimensional reconstruction is generated from the first subtraction images.

6. The method according to claim 5, wherein - a second sequence of projection images is generated in a second taking phase (A2), wherein each projection image of the second sequence at least partially shows the at least one hollow organ (7) in a respectively pre-set different projection direction; - the second taking phase (A2) starts at an end moment of the first taking phase (Al); and - a time resolved three-dimensional reconstruction is generated from the projection images of the second sequence.

7. The X-ray imaging method according to claim 6, wherein - a second mask sequence of projection images is generated in a second mask taking phase (M2), wherein each projection image of the second mask sequence at least partially shows the at least one hollow organ (7) in a respective different projection direction; - each projection image of the second mask sequence corresponds to exactly one projection image of the second sequence, so that the projection direction of a projection image of the second mask sequence is identical to the projection direction of the respectively corresponding projection image of the second sequence; - for each projection image of the second mask sequence, a second subtraction image is generated by subtracting the projection image of the second mask sequence from the respectively corresponding projection image of the second sequence; and - a time resolved three-dimensional reconstruction is generated from the second subtraction images.

8. The X-ray imaging method according to claim 7, wherein - the projection directions of the projection images of the first and second sequences are characterized by respective angles (a) within a pre-determined angular range (12, 13) in a pre-determined plane; and - a first sub-region (12a) of the angular range (12, 13) is passed through in the first taking phase (Al) and a second sub-region (12b) of the angular range (12, 13) adjoining the first sub-region (12a) is passed through in the second taking phase (A2).

9. The X-ray imaging method of claim 8, wherein - the projection directions of the projection images of the first and second mask sequences are characterized by individual angles (a) within the angular range (12, 13) in the plane; - the first sub-region (12a) is passed through in the first mask phase (Ml) and the second sub-region (12b) is passed through in the second mask phase (M2).

10. The X-ray imaging method of claim 7, wherein - the projection directions of the projection images of the first sequence are characterized by individual angles (a) within a predetermined angular range (12, 13) in a predetermined plane; and - the angular range (12, 13) is passed through in the first phase (Al) and the angular range (12, 13) is passed through in the second phase (A2).

11. The method of x-ray imaging according to claim 10, wherein, The angular range (12, 13) is passed through in a first direction in the first phase (Al) and in a second direction opposite the first direction in the second phase (A2).

12. The X-ray imaging method of claim 10, wherein - the projection directions of the projection images of the first mask sequence are characterized by individual angles within the angular range (12, 13) in the plane; and - the angular range (12, 13) is passed through in the first mask phase (Ml) and the angular range (12, 13) is passed through in the second mask phase (M2).

13. The x-ray imaging method according to any one of claims 6 to 12, wherein, A stop signal for automatically ending a contrast agent injection of contrast agent is generated at a time which precedes an end time of the second phase (A2) by a first time duration (Tl).

14. The X-ray imaging method of any one of claims 1 to 7, wherein - the projection directions of the projection images of the first sequence are characterized by individual angles (a) within a predetermined angular range (12, 13) in a predetermined plane; and - the angular range is passed through in the first phase (Al), wherein parameters for generating the projection images of the first sequence are adjusted in accordance with the second time duration (T2) and the angular range.

15. An X-ray imaging system (1) for time-resolved three-dimensionally displaying at least one hollow organ (7) of a person (6), the X-ray imaging system (1) having an X-ray source (2), an X-ray detector (3), a drive device for positioning the X-ray source (2) and the X-ray detector (3) relative to an imaging region in accordance with different projection directions, and at least one computing unit (4), the computing unit being configured to - determine a first time duration (Tl), which is a person-specific flow time duration of contrast agent from a predetermined contrast agent injection location of the person (6) to a predetermined location (8) near a body midline of the at least one hollow organ (7); - determining a second time duration (T2) which is a person-specific flow time duration of the contrast agent from a position (8) close to the body midline to a predetermined position (9) away from the body midline of the at least one hollow organ (7); - controlling the drive device, the X-ray source (2) and the X-ray detector (3) in order to generate a first sequence of projection images in a first recording phase (Al), wherein, each projection image of the first sequence at least partially shows the at least one hollow organ (7) in a respectively pre-set different projection direction, wherein the first acquisition phase (Al) starts after the first time duration (Tl) has elapsed after an injection start time at which the contrast agent is injected at the injection position, and the duration of the first acquisition phase (Al) is equal to the second time duration (T2); and generating a time-resolved three-dimensional reconstruction of the at least one hollow organ (7) from the projection images of the first sequence.

16. A computer program product having instructions which, when executed by the X-ray imaging system according to claim 15, carry out the X-ray imaging method according to one of claims 1 to 14.

Images