Method and device for virtually determining baseline image during CT perfusion measurement

Abstract

The present invention describes a method for determining CT perfusion data. In the method, raw X-ray data (RD) affected by contrast agent generated by a spectral or multi-energy CT image recording method is acquired from an examination region, wherein a plurality of images are recorded from the examination region at consecutive time points. A virtual baseline image (GVBLB) is determined based on the acquired raw X-ray data (RD) by calculating virtual native image data (VNB) with the aid of material decomposition. Finally, the temporal variation of the contrast agent concentration in the examination region is determined based on the raw X-ray data (RD) affected by contrast agent and the virtual baseline image (BLB). The present invention also describes a method for measuring CT perfusion. Furthermore, a device for determining CT perfusion data is described. Furthermore, a computer tomography system (1) is described.

Description

Technical Field

[0001] The invention relates to a method for determining CT perfusion data. In the method for determining CT perfusion data, raw X-ray data influenced by a contrast agent are acquired from an examination region by a spectral or multi-energy CT image recording method, wherein a plurality of images are recorded from the examination region at consecutive time points. The invention also relates to a CT perfusion measurement method. In addition, the invention also relates to a CT perfusion data determination device. In addition, the invention also relates to a computer tomography system. Background Art

[0002] X-ray imaging devices, such as computed tomography devices (CT devices for short), are increasingly being used to clarify medical questions.

[0003] One possibility for determining the blood flow through an organ (eg the brain or liver) and thus being able to examine its function more precisely is to perform a perfusion measurement. Such a perfusion measurement can be performed, for example, using a CT device.

[0004] In CT perfusion measurement, a large number of CT recordings are performed successively in time in order to detect the flow characteristics of the contrast agent flowing through the examination area. Such an examination area can include, for example, the brain, liver or heart. For example, within the scope of such a perfusion scan, 50 images of an examination area are recorded continuously in time while the contrast agent flows through the examination area. In order to be able to determine the concentration of the contrast agent in the examination area with spatial resolution, in addition to the contrast of the contrast agent, the original contrast in the examination area or at all parts of the examination area must also be known, which will be measured without contrast agent in the examination area. For this purpose, the original image is recorded in advance without contrast agent. Usually, five original images, also called pre-contrast images, are recorded in the scope of the so-called baseline scan or baseline recording. Then, the amount of contrast injected is proportional to the difference between the attenuation values ​​of the contrast agent image and the image recorded without contrast agent (i.e., the original image). Therefore, in order to be able to evaluate the perfusion measurement, the original image is absolutely necessary.

[0005] In order to be able to carry out a baseline recording, it is usually necessary to carry out a baseline recording shortly before the contrast agent bolus reaches the examination area. However, this is at the expense of a higher X-ray dose, since part of the X-ray dose must be used for the additional recording before the contrast agent bolus reaches the examination area. In addition, this can complicate the workflow. For example, a test bolus is required to determine the time between injection and bolus arrival.

[0006] Typically, the baseline volume is calculated by averaging the first volume of the CT perfusion images. In order to have an image without contrast at least when measuring the first volume, different techniques are usually used. For example, a fixed time period, also called a "delay", can be specified between the injection of contrast agent and the start of the first image recording. However, this method requires a longer total recording time in order to take into account the variability of human physiology and to ensure that the baseline recording is performed without contrast agent. Test boluses can also be used to determine the time when the contrast agent required for an individual person arrives in the examination area. However, this will complicate the entire workflow and increase the time cost. Alternatively, a separate recording is usually performed before the start of the original perfusion recording, and the perfusion recording is only then started using the bolus trigger. In this variant, more time and an increased X-ray dose are also required to perform a separate CT recording of the examination area. Summary of the invention

[0007] It is therefore an object of the present invention to develop a CT perfusion measurement which can be performed with less effort and preferably in a shorter time and at a lower X-ray dose than conventional methods.

[0008] According to the invention, this object is achieved by a CT perfusion data determination method, a perfusion measurement method, a CT perfusion data determination device and a computer tomography system according to the invention.

[0009] In the CT perfusion data determination method according to the present invention, first, X-ray raw data affected by contrast agent are acquired from the examination region. The X-ray raw data affected by contrast agent are generated by a spectral or multi-energy CT image recording method. The X-ray raw data affected by contrast agent should be understood as X-ray raw data recorded in the presence of X-ray contrast agent. Here, compared with the image recording without contrast agent, at least at a suitable X-ray energy, the X-ray attenuation value or the CT attenuation value will change. In the scope of raw data acquisition, multiple images are recorded from the examination region at consecutive time points. Based on the X-ray raw data acquired for multiple spectral ranges of X-ray energy, virtual native image data are calculated by directly applying material decomposition to the acquired X-ray raw data in the raw data space or by applying material decomposition to the reconstructed image data after reconstructing the image data based on the X-ray raw data in the image data space, thereby determining a virtual baseline image.

[0010] For example, when using a contrast medium, preferably iodine, not only the X-ray edge, i.e. the K-edge of the contrast medium, is taken into account, but also generally the different properties of the contrast medium and water in the X-ray spectrum. If there are two images for different parts of the X-ray spectrum, for example in the spectral range of 20 to 50 keV and 100 to 150 keV, the content of water and contrast medium can be calculated by solving a linear 2x2 system, i.e. the basic material decomposition. The water content is then approximated to a virtual native image or virtual baseline image, since fat and soft tissue behave similarly to water with respect to X-ray attenuation or in this respect differ significantly from the attenuation properties of the contrast medium or the contrast medium, in particular iodine.

[0011] Alternatively, the material components can also be combined to form virtual monoenergetic image data. In this case, the material components of the X-ray attenuation are combined in the raw data space or in the image data space in such a way that image data with a predetermined higher X-ray energy are generated. The virtual image data are then calculated for the predetermined higher X-ray energy above the X-ray edge. This means that the X-ray energy is selected in such a way that a native image is created and the properties of the contrast agent do not play a role at the selected energy.

[0012] Finally, the temporal change of the contrast agent concentration in the examination region is determined based on the X-ray raw data affected by the contrast agent acquired at different times or in succession and the determined virtual baseline image. For this purpose, the X-ray contrast of the image affected by the contrast agent can be determined, for example, by subtracting the contrast value or the X-ray attenuation value of the virtual baseline image from the X-ray attenuation value of the corresponding image affected by the contrast agent, so that the location-dependent X-ray attenuation value in the corresponding image reflects or represents the location-dependent contrast agent concentration, whereby the location-dependent and time-dependent occurrence of the X-ray contrast agent concentration in the examination region can be determined from the images acquired in time succession.

[0013] Therefore, raw X-ray data affected by contrast agents from the examination area will be processed, which are generated by spectral or multi-energy CT image recording methods. Spectral CT image recording methods should be understood as CT image recording methods in which the X-ray spectrum is detected in a resolved manner according to at least two X-ray energy intervals. This spectrally resolved detection of X-ray radiation can be performed, for example, by a so-called photon counting X-ray detector. In the multi-energy CT image recording method, X-rays with at least two different spectra are detected separately, for example by two separate detectors, which respectively detect different spectral components of the X-ray radiation transmitted through the examination area during CT imaging. In an alternative multi-energy CT image recording method, X-rays with at least two different spectra are detected separately, for example, which can be generated by periodic changes in the voltage of the X-ray source (so-called kV switching). Virtual native image data are generated based on the acquired X-ray raw data. As mentioned above, virtual native image data are obtained by means of material decomposition. For example, a method for obtaining image data by material decomposition is described in US 7 778 454 B2. The calculation of virtual image data based on dual-energy and multi-energy CT recordings is also explained in McCullough et al., "Principles and Applications of Multi-Energy CT" (report of AAPM Task Group 291).

[0014] One advantage of the method according to the invention is that a separate image recording does not have to be carried out for the baseline image, but the baseline image can be generated simultaneously based on the image generated during the perfusion measurement, approximately as a by-product without additional time expenditure. Advantageously, the recording time of the perfusion measurement can be reduced. In addition, the method according to the invention makes it possible to trigger the perfusion measurement by observing the contrast agent concentration in the patient's body at a distance from the actual examination area in the patient's body. However, in conventional perfusion measurements, such perfusion measurements must be started very early, because after the trigger signal, a corresponding separate native image must also be generated, so that the triggering based on the contrast agent concentration occurring in the patient's body or detected there would occur too late. Therefore, more generally speaking, the termination of the perfusion measurement or the time adjustment of the contrast agent bolus and the actual perfusion measurement can be carried out significantly more accurately in the examination area.

[0015] In the CT perfusion measurement method according to the invention, a spectral or multi-energy CT image recording method is first performed, wherein X-ray raw data affected by contrast agent are generated from the examination region, and a plurality of images are recorded from the examination region at successive time points. Furthermore, the CT perfusion data determination method according to the invention is performed based on the recorded X-ray raw data affected by contrast agent. The CT perfusion measurement method according to the invention also has the advantages of the CT perfusion data determination method according to the invention.

[0016] The CT perfusion data determination device according to the present invention comprises a data acquisition unit. The data acquisition unit is configured to acquire X-ray raw data affected by contrast agents generated by a spectral or multi-energy CT image recording method from an examination region. Here, the acquisition of X-ray raw data includes the acquisition of multiple X-ray raw data sets, wherein multiple images are recorded from the examination region at consecutive time points. A part of the CT perfusion data determination device according to the present invention is also an image determination unit, which is used to calculate virtual native image data by material decomposition based on the acquired X-ray raw data so as to determine a virtual baseline image. The CT perfusion data determination device according to the present invention also includes a concentration determination unit, which is used to determine the time change of the contrast agent concentration in the examination region based on the X-ray raw data affected by the contrast agent and the virtual baseline image. In addition, the CT perfusion data determination device may also include an image reconstruction unit, which may be part of the concentration determination unit or may be connected upstream of the concentration determination unit and is configured to reconstruct an image data set based on the acquired X-ray raw data set, which is the basis for perfusion measurement or determines the contrast agent concentration in the examination region based on the image data set. The CT perfusion data determination device according to the present invention also has the advantages of the CT perfusion data determination method according to the present invention.

[0017] The computer tomography system according to the invention has an X-ray emission unit, a detector unit for acquiring spectral or multi-energy raw data and a CT perfusion data determination device according to the invention. The computer tomography system according to the invention also has the advantages of the CT perfusion data determination device according to the invention.

[0018] The main components of the CT perfusion data determination device according to the invention can be designed for the most part in the form of software components. This applies in particular to the image determination unit and the concentration determination unit.

[0019] However, in principle, these components can also be implemented partially in the form of software-supported hardware, such as FPGAs, etc., especially when particularly fast calculations are involved. For example, if only data are to be received from other software components, the required interfaces can also be designed as software interfaces. However, the interfaces can also be designed as hardware-based interfaces controlled by suitable software.

[0020] A largely software-based implementation has the advantage that control devices of computed tomography systems that are already in use can also be easily retrofitted by means of a software update so as to operate in the manner according to the invention. In this respect, the object is also achieved by a corresponding computer program product having a computer program, which can be directly loaded into a storage device of a computed tomography system or into a storage device of a control device of a computed tomography system, and which includes program segments that execute all steps of the method according to the invention for determining CT perfusion data and / or the method according to the invention for measuring CT perfusion data when the computer program is run in the control device of the computed tomography system.

[0021] In addition to the computer program, such a computer program product may optionally include additional components such as documentation and / or additional components, and may also include hardware components, such as a hardware key (dongle, etc.) for using the software.

[0022] By means of software implementation, the method can be executed reproducibly and error-free on different computers.

[0023] For transmission to a storage device of a control device of a computed tomography system and / or for storage on a control device of a computed tomography system, a computer-readable medium such as a memory stick, a hard disk or another removable or fixedly mounted data carrier can be used, on which program segments of a computer program that can be read and executed by a computing unit of the computed tomography system are stored. For this purpose, the computing unit can have, for example, one or more cooperating microprocessors or the like.

[0024] The following descriptions all contain particularly advantageous designs and improvements of the invention. In particular, claims of one claim category may also be improved in a similar manner to dependent claims of another claim category. Furthermore, within the scope of the invention, different embodiments and different features of the claims may also be combined into new embodiments. In particular, the features and advantages described in conjunction with the method according to the invention may also be embodied as corresponding subunits or modules of the determination device according to the invention or of the computer program product according to the invention. Conversely, the features and advantages described in conjunction with the determination device according to the invention or of the computer program product according to the invention may also be embodied as corresponding method steps of the method according to the invention.

[0025] According to one embodiment of the method for determining CT perfusion data according to the invention, the CT image recording method is performed using a spectrally resolving X-ray detector, preferably a photon counting X-ray detector. Such an X-ray detector has the following advantages over a dual-energy CT system or a multi-energy CT system: X-ray raw data of the examination area can thereby be recorded or acquired for different spectra from the same direction. If there are two differently positioned X-ray sources, slightly different objects are detected from different directions or an examination area is detected from different viewing angles. In addition, the X-ray attenuation, i.e. the enhancement of the different recordings, is also slightly different. These problems are advantageously overcome by means of a spectrally resolving X-ray detector, preferably a photon counting X-ray detector, since in this case the same source is used for different images with different X-ray spectra.

[0026] For CT image recording, the X-ray tube is preferably operated with a tube voltage of 120 kV and a low tube current. Recording with an X-ray tube voltage of 120 kV allows reliable calculation of iodine-water decomposition, i.e., basic material decomposition, particularly in the case of iodine as a contrast agent. And for the conventional preferred 70 kV or 80 kV, the width of the X-ray spectrum is no longer sufficient to perform such separation of spectral components according to contrast agents (preferably iodine) and water. The low tube current is only because the patient cannot receive too much radiation or should not be exposed to too high a radiation dose, which would occur in the case of a higher tube current. Because such perfusion recording requires a very long duration of 40 to 70 seconds. In addition, the image quality reduced by reducing the tube current is sufficient to create a native image that is now collected or generated simultaneously with the perfusion measurement according to the present invention, because the knowledge of the larger area with contrast agent accumulation and its distribution is sufficient for perfusion measurement. The typical value of the tube current in the conventional CT imaging method with a tube voltage of 120 kV is about 320 mAs of exposure. In the method according to the present invention, a relatively weak tube current can be advantageously used. The exposure corresponding to these weaker tube currents preferably has values ​​of less than 200 mAs, more preferably of 100 mAs, quite particularly preferably of about 40 mA, which is associated with a significantly lower radiation exposure than in the prior art.

[0027] In the CT perfusion data determination method according to the present invention, virtual native image data is preferably determined by material decomposition into several images of a plurality of perfusion images, thereby generating a plurality of virtual native images for different time points of perfusion measurement. In this variant, a baseline image is determined based on a plurality of virtual native images. The statistical error occurring when determining the baseline image is advantageously reduced because the data basis of the baseline image is expanded compared to the method that uses only a single virtual native image as the basis for calculating the baseline image. Thus, a higher accuracy and reliability of the baseline image is achieved.

[0028] Particularly preferably, the baseline image is determined as an average image based on a plurality of virtual native images. Averaging makes it possible to reduce statistically induced errors when recording the X-ray raw data for the virtual native images.

[0029] Furthermore, the averaged baseline image forms a particularly advantageous contrast average value for the native image pixels, so that contrast deviations due to temporal changes in the examination region or in the image recording parameters or resulting errors in the determination of the perfusion image contrast can be reduced or minimized when recording or generating images or image data sets generated continuously over time for perfusion measurements.

[0030] It is also preferred that, within the scope of the CT perfusion measurement according to the invention, the CT perfusion measurement is performed in a first organ of the patient, the concentration of the contrast agent is monitored in another region outside the examination region, and the start of the perfusion method is triggered when contrast agent is detected in the region outside the examination region. Advantageously, the start of the actual perfusion measurement can be precisely synchronized with the arrival of the contrast agent bolus in the examination region. This process is possible because, due to the omission of additional pre-recording, the time period during which the contrast agent bolus moves between the region outside the examination region and the examination region is sufficient to start the actual CT perfusion measurement.

[0031] The method is particularly advantageous if, within the scope of the CT perfusion measurement according to the invention, the CT perfusion measurement is carried out in the brain of the patient and the concentration of the contrast agent is monitored in another region outside the examination region, for example in an organ, preferably in the heart region of the patient, and the start of the perfusion method is triggered when contrast agent is detected in the region outside the examination region, preferably in the heart region of the patient. In this case, the start of the actual perfusion measurement can also advantageously be precisely synchronized with the arrival of the contrast agent bolus in the examination region. As already mentioned, this process is possible because, due to the omission of additional pre-recording, the time period during which the contrast agent bolus moves between the region outside the examination region, for example in the heart region, and the examination region, i.e. in particular the brain, is sufficient to start the actual CT scan perfusion measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be described and explained in more detail below with reference to the embodiments shown in the accompanying drawings, in which:

[0033] Figure 1 FIG. 4 is a flowchart illustrating a method for determining CT perfusion data according to an embodiment of the present invention.

[0034] Figure 2 FIG. 4 is a flow chart illustrating a CT perfusion measurement method according to an embodiment of the present invention.

[0035] Figure 3FIG. 4 is a schematic diagram showing a CT perfusion data determination device according to an embodiment of the present invention.

[0036] Figure 4 A schematic diagram of a computer tomography system according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0037] exist Figure 1 1 is a flowchart 100 illustrating a method for determining CT perfusion data according to an embodiment of the present invention.

[0038] In step 1.I, raw data RD influenced by contrast agent are received from the examination region of the patient, which raw data RD are detected in a spectrally resolved manner in a CT image recording method. Figure 1 In the embodiment shown, the examination region is a brain region. The raw data RD are spectrally resolved and are therefore suitable for material decomposition. The raw data RD include 50 raw data sets, which are assigned to 50 images or image data sets, which were recorded from the examination region at successive times.

[0039] In step 1.II, a material decomposition is performed based on the received raw data RD according to the materials of the contrast medium and water. Alternatively, the material decomposition can also be performed in the image data space.

[0040] Then, in step 1.III, a virtual native image VNB is generated based on the water content of the material decomposition.

[0041] Alternatively, the material components can also be combined to form virtual monoenergetic image data VNB. In this case, the material components of the X-ray attenuation are combined in the raw data space or in the image data space in such a way that image data with a predetermined higher X-ray energy are generated. The virtual image data VNB are then calculated for the predetermined higher X-ray energy above the X-ray edge. This means that the X-ray energy is selected in such a way that a native image is created and the properties of the contrast agent do not play a role at the selected energy. Figure 1 In the illustrated embodiment, a native image VNB is calculated for each of the 50 received images.

[0042] In step 1.IV, an average virtual baseline image GVBLB is calculated by averaging the 50 native images VNB calculated in step 1.III. The average baseline image forms a particularly advantageous contrast average value of the pixels of the native images, so that contrast deviations due to temporal changes in the examination area or in the image recording parameters will be reduced or minimized when recording or generating 50 image data sets generated successively in time.

[0043] Furthermore, in step 1.V, 50 images BD affected by the contrast agent are reconstructed likewise based on the raw data RD.

[0044] Finally, in step 1.VI, the change in the contrast medium concentration in the examination region, i.e. the spatially and temporally variable contrast medium concentration, is determined based on the 50 contrast medium-affected image data sets BD and based on the average virtual baseline image GVBLB. In this case, the average virtual baseline image GVBLB is subtracted from the contrast medium-affected image data set BD in order to determine the X-ray attenuation caused only by the contrast medium (e.g. iodine) in the examination region.

[0045] Figure 2 A flow chart 200 is shown which illustrates a CT perfusion method according to an exemplary embodiment of the invention. In step 2.I, a CT image recording UB is first performed on the heart of the patient, or a plurality of such CT image recordings are performed in succession in time. In step 2.II, it is determined with the aid of the CT image recording UB or the image data generated therein whether the contrast agent concentration KK has exceeded a predetermined value SW in the heart region. Such monitoring of the contrast agent concentration can be performed, for example, by means of a plurality of CT recordings performed in succession in time. In addition to the heart region, a small section of the aorta or a section of the carotid artery is also suitable for this.

[0046] If it is determined in step 2.II that the contrast agent K has reached the heart, this Figure 2 If the contrast agent K is marked with "j" in step 2.III, then the procedure is transferred to step 2.III. If it is determined in step 2.II that the contrast agent K has not yet reached the patient's heart, this is Figure 2 If the number is marked with "n", return to step 2.I.

[0047] In step 2.III, the actual perfusion measurement now begins, since the time at which the contrast agent reaches the brain can be determined or estimated based on the knowledge of its arrival in the cardiac region, and thus the start time of the perfusion measurement in the brain will be determined. Furthermore, within the scope of this perfusion measurement, a method for recording spectral CT images of the patient's brain is performed, wherein 50 raw X-ray data sets RD affected by the contrast agent are generated, or at the time points t1, ..., t 50 Perform 50 image recordings.

[0048] In step 2.IV, based on the obtained X-ray raw data set RD, Figure 1 The illustrated method for determining CT perfusion data involves determining 50 contrast agent images BD which display the temporal profile of the contrast agent concentration or the spatially and temporally variable distribution of the contrast agent in the brain of a patient.

[0049] exist Figure 3 FIG. 4 is a schematic diagram of a CT perfusion data determination device 30 according to an embodiment of the present invention.

[0050] The CT perfusion data determination device 30 comprises an X-ray data acquisition unit 31. The X-ray data acquisition unit 31 receives 50 raw data sets RD of a total of 50 images acquired in the presence of a contrast agent, which were acquired by an X-ray detector during a CT image acquisition of a patient examination region.

[0051] The CT perfusion data determination device 30 further includes an image determination unit 32 for determining a virtual baseline image based on the acquired X-ray raw data set RD.

[0052] A part of the image determination unit 32 also includes a material decomposition unit 32a. The material decomposition unit 32a generates virtual native image data VNB for a plurality of acquired X-ray raw data sets RD (preferably each acquired X-ray raw data set RD) based on material decomposition of the acquired X-ray raw data RD, for example, to generate a virtual baseline image.

[0053] The CT perfusion data determination device 30 further comprises an averaging unit 33 which is arranged to calculate an average virtual baseline image GVBLB by averaging the generated virtual native image datasets VNB or virtual baseline images based thereon.

[0054] The CT perfusion data determination device 30 further comprises an image reconstruction unit 34 which is arranged to reconstruct an image dataset BD based on the acquired X-ray raw dataset RD, the image dataset BD being the basis for the perfusion measurement.

[0055] The average virtual baseline image GVBLB is transmitted to a concentration determination unit 35, which is likewise part of the CT perfusion data determination device 30. The concentration determination unit 35 is configured to determine the temporal variation of the contrast agent concentration KK in the examination region, i.e. the location- and time-dependent contrast agent concentration, based on the reconstructed image data set BD and the average virtual baseline image GVBLB. The determined perfusion measurement data PD are then output, for example, for display or further processing.

[0056] exist Figure 4 FIG. 4 shows a CT system 1 according to an embodiment of the present invention.

[0057] The CT system 1 is designed as a CT system with a photon counting detector 16, which consists essentially of a conventional scanner 10, wherein a projection measurement data acquisition unit 5 having a photon counting detector 16 and an X-ray source 15 opposite the photon counting detector 16 is rotated around a measurement space 12 on a gantry 11. A patient support device 3 or a patient table 3 is arranged in front of the scanner 10, the upper part 2 of which can be moved with the patient O to the scanner 10 in order to move the patient O through the measurement space 12 relative to the detector system or the detector 16. The scanner 10 and the patient table 3 are controlled by a control device 40, from which acquisition control signals AS are sent via a conventional control interface 42 in order to control the entire system in a conventional manner according to a preset measurement protocol. In the case of a spiral acquisition, a spiral path is generated during the measurement in that the patient O is moved in the z direction, which corresponds to the system axis z running longitudinally through the measurement space 12, and the X-ray source 15 is simultaneously rotated relative to the patient O. In this case, the detector 16 is always operated in parallel opposite the X-ray source 15 in order to acquire spectrally resolved projection measurement data RD, which are then used for the reconstruction of volume and / or slice image data. It is also possible to carry out a sequential measurement method, in which a fixed position is approached in the z direction and then the required spectrally resolved projection measurement data RD are acquired at the corresponding z position during one rotation, part of a rotation or several rotations in order to reconstruct a cross-sectional image at this z position or to reconstruct image data from projection measurement data of several z positions. The CT perfusion data determination method according to the invention and the perfusion measurement method according to the invention can in principle also be used or carried out on other CT systems, for example systems with several X-ray sources or detectors forming a complete ring. For example, the method according to the invention can also be applied to systems with a stationary patient table and a gantry that moves in the z direction (so-called sliding gantry).

[0058] The spectrally resolved projection measurement data RD (hereinafter also referred to as raw data) acquired by the detector 16 are transmitted to the control device 40 via a raw data interface 43. These raw data RD are then further processed, if necessary after appropriate preprocessing, in the CT perfusion data determination device 30, which in this exemplary embodiment is implemented in the form of software on a processor in the control device 40. The perfusion data determination device 30 is implemented as in the embodiment of the present invention. Figure 3 The perfusion measurement data PD are constructed as shown in FIG. 1 and are generated from the acquired raw data RD.

[0059] The perfusion measurement data PD generated by the perfusion data determination device 30 are then stored in a memory 44 of the control device 40 and / or output in a conventional manner on a screen of the control device 40. The perfusion measurement data PD can also be obtained by Figure 4The data are fed into a network connected to the computed tomography system 1, such as a radiology information system (RIS), via an interface (not shown) and stored in a mass storage device accessible therefrom or output as an image on a printer or recording station connected thereto. The data can thus be further processed in any desired manner and then stored or output.

[0060] In addition, Figure 4 4 shows a contrast agent injection device 45, by which a contrast agent K is injected into the patient O in advance (i.e. before starting the CT perfusion measurement method) in order to prepare for the perfusion measurement. Then, within the scope of the perfusion measurement, the area through which the contrast agent K flows can be acquired in the form of images by means of the computed tomography system 1.

[0061] The components of the perfusion data determination device 30 can be implemented mainly or completely in the form of software elements on a suitable processor. In particular, the interfaces between these components can also be designed purely on the basis of software. All that is required is the ability to access suitable storage areas, in which data can be appropriately temporarily stored and can be called up again and updated at any time.

[0062] Finally, it should be pointed out again that the above-described method and device are only preferred embodiments of the invention and that the skilled person may modify the invention without departing from the scope of the invention, as long as this scope is specified by the claims. For the sake of completeness, it should also be pointed out that the use of the indefinite article "a" or "an" does not exclude the possibility that the relevant feature may also appear several times. Likewise, the term "unit" does not exclude the possibility that it consists of a plurality of components that are spatially distributed if necessary.

Claims

1. A method for determining CT perfusion data, comprising the following steps: - acquisition of X-ray raw data (RD) influenced by a contrast agent from an examination region, which is generated by a spectral or multi-energetic CT image recording method, wherein a plurality of images are recorded from the examination region at successive points in time, - determining a virtual baseline image based on the acquired X-ray raw data (RD) by determining virtual native image data (VNB) by material decomposition, - determining a temporal variation of a contrast agent concentration in the examination region based on the contrast agent affected X-ray raw data (RD) and the virtual baseline image.

2. The method according to claim 1, wherein the CT image recording method is performed using a photon counting X-ray detector (16).

3. The method according to claim 1 or 2, wherein an X-ray tube is operated at 120 kV and a low tube current for CT image recording.

4. The method according to claim 1 or 2, wherein a virtual native image (VNB) is determined for each of several images of the plurality of images based on material decomposition, and the virtual baseline image is determined based on the plurality of virtual native images (VNB) thus generated. The method of claim 4 , wherein the virtual baseline image is determined as an average image based on the plurality of virtual native images (VNBs).

6. A CT perfusion measurement method, comprising the following steps: - performing a spectral or multi-energetic CT image recording method, in which X-ray raw data (RD) influenced by a contrast agent are generated from an examination region and a plurality of images are recorded from said examination region at successive points in time, - performing the CT perfusion data determination method according to any one of claims 1 to 5 based on the recorded X-ray raw data (RD) affected by the contrast agent.

7. The method according to claim 6, wherein - performing a perfusion measurement in a first body region of a patient (O), - monitoring the concentration of contrast agent in said first body region, and - triggering the start of the perfusion measurement method according to claim 6 in a second body region of the patient (O) when the contrast agent is detected in the first body region of the patient (O).

8. The method of claim 7, wherein the first body region is the patient's heart and the second body region is the patient's brain.

9. A CT perfusion data determination device (30), comprising: a data acquisition unit (31) for acquiring raw X-ray data (RD) influenced by a contrast agent from an examination region, which is generated by a spectral or multi-energetic CT image recording method, wherein a plurality of images are recorded from the examination region at successive points in time, - an image determination unit (32, 33) for determining a virtual baseline image based on the acquired X-ray raw data (RD) by calculating virtual native image data (VNB) by material decomposition, - a concentration determination unit (35) for determining the temporal variation of the contrast agent concentration in the examination region based on the contrast agent-affected X-ray raw data (RD) and the virtual baseline image.

10. A computer tomography system (1), comprising: - an X-ray emitting unit (15), - a detector unit for collecting spectral or multi-energy raw data (RD), - A CT perfusion data determination device (30) according to claim 9.

11. A computer program product comprising a computer program that can be directly loaded into a storage device of a computed tomography system (1), the computer program having a plurality of program segments so that when the computer program is run in the computed tomography system (1), all steps of the method according to any one of claims 1 to 8 are performed. 12 . A computer-readable medium on which a program segment that can be read and executed by a computing unit is stored, so that when the program segment is run by the computing unit, all steps of the method according to claim 1 are executed.

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