CONTRAST AGENT-BASED VASCULAR IMAGING

Abstract

Embodiments of the present invention relates to an X-ray contrast agent. The X-ray contrast agent has an X-ray absorption the change of which between at least two different X-ray photon energy levels differs from the change in X-ray absorption of calcium between the at least two different X-ray photon energy level. Embodiments of the present invention also relates to an X-ray imaging method. Embodiments of the present invention additionally relates to an image reconstruction device. Embodiments of the present invention further relates to an X-ray imaging system.

Claims

1. An X-ray contrast agent, having an X-ray absorption the change of which between at least two different X-ray photon energies differs from the change in the X-ray absorption of calcium between the at least two different X-ray photon energies.

2. The X-ray contrast agent as claimed in claim 1, wherein the X-ray absorption for the at least two X-ray photon energies not significantly different.

3. The X-ray contrast agent as claimed in claim 1, wherein the spectrum of the X-ray absorption of the X-ray contrast agent is similar to the spectrum of the X-ray absorption of water or soft tissue.

4. The X-ray contrast agent as claimed claim 1, having one of the following materials: tungsten, tantalum, hafnium, and gold.

5. An X-ray imaging method, comprising: selecting the contrast agent as claimed in claim 1, capturing X-ray raw data from a region of an examination object using a multi-energy recording method, the region of the examination object including the contrast agent, carrying out a material decomposition based on the X-ray raw data in relation to the contrast agent and calcium, and reconstructing at least two image datasets based on the material decomposition, the at least two image datasets including, a first image dataset representing, a first image region affected by the contrast agent, and a second image dataset representing a second image region, the second image region being complementary to the first image region.

6. The X-ray imaging method as claimed in claim 5, further comprising: a multi-energy imaging method including, specifying at least two different X-ray tube voltages at which a change in the X-ray absorption of the contrast agent significantly differs from calcium, capturing at least two datasets of X-ray image recordings that have been recorded with the at least two different X-ray tube voltages for acquisition of a first raw dataset and at least one second raw data set, and carrying out the material decomposition based on the at least two raw datasets.

7. The X-ray imaging method as claimed in claim 5, further comprising: capturing X-ray raw data with using a photon-counting detector in an energy-resolved manner, wherein energy thresholds of the photon-counting detector are set such that therewith, the change in the X-ray absorption of the X-ray contrast agent differs from the change in the X-ray absorption of calcium, carrying out the material decomposition based on the energy-resolved raw data.

8. The X-ray imaging method as claimed in claim 5, further comprising: a CT angiographic imaging method.

9. An image reconstruction facility, having: an ascertaining unit configured to ascertain at least two different X-ray photon energies which an X-ray contrast agent as claimed in one of claims 1 to 4 differs significantly from the change in the X-ray absorption of calcium between the at least two different X-ray photon energies, a raw data receiving unit configured to receive X-ray raw data from a region of an examination object which is partially flooded by the X-ray contrast agent, with the aid of a multi-energy recording method, a decomposition unit configured to carry out a material decomposition based on the X-ray raw data in relation to the X-ray contrast agent and calcium, and a reconstruction unit configured to reconstruct at least two image datasets based on the material decomposition, the at least two image datasets, including, a first image dataset representing a first image region affected by the X-ray contrast agent, and a second image dataset representing a second image region, the second image region being complementary to the first image region.

10. An X-ray imaging system, having the image reconstruction facility as claimed in claim 9.

11. The X-ray imaging system as claimed in claim 10, having a CT angiography facility.

12. A computer program product having a computer program, when exerted by a storage facility of an X-ray imaging system, cause the X-ray imaging system to perform the method of claim 5.

13. A computer-readable medium on which program portions that can be read in and executed by a computer unit are stored, is configured to cause the computer unit to perform the method as claimed in claim 5.

14. The X-ray contrast agent as claimed in claim 2, wherein the spectrum of the X-ray absorption of the X-ray contrast agent is similar to the spectrum of the X-ray absorption of water or soft tissue.

15. The X-ray contrast agent as claimed claim 2, having one of the following materials: tungsten, tantalum, hafnium, and gold.

16. The X-ray contrast agent as claimed claim 3, having one of the following materials: tungsten, tantalum, hafnium, and gold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention will now be described again in greater detail using example embodiments, making reference to the accompanying drawings. In the drawings:

[0044] FIG. 1 shows a graphical representation that illustrates the absorption properties of the contrast agent iodine and the bone material calcium dependent upon the energy of the X-ray photons,

[0045] FIG. 2 shows a graphical representation that illustrates absorption values of the contrast agent iodine and the material tungsten dependent upon the tube voltage of an X-ray device,

[0046] FIG. 3 shows a graphical representation that illustrates the absorption properties of the contrast agent iodine and of calcium and water dependent upon the energy of the X-ray photons,

[0047] FIG. 4 shows a flow diagram that illustrates an X-ray imaging method according to an example embodiment of the present invention,

[0048] FIG. 5 shows a schematic representation of an image reconstruction facility according to an example embodiment of the present invention, and

[0049] FIG. 6 shows a schematic representation of a CT system according to an example embodiment of the present invention.

DETAILED DESCRIPTION

[0050] FIG. 1 shows a graphical representation 10 that illustrates the absorption properties of the contrast agent iodine I and of the bone material calcium Ca dependent upon the energy EPH of the X-ray photons. For the visualization of the absorption of the materials mentioned, the mass absorption coefficient K is shown dependent upon the energy EPH of the X-ray photons. Furthermore, in FIG. 1, a typical mean energy E(1) of an image recording with a low energy and the mean energy E(2) of an image recording with the high energy of a dual-energy image recording is shown. As shown in FIG. 1, the progression of the two curves of the mass absorption coefficient of iodine I and of calcium Ca is very similar. It must therein be taken into account that the materials iodine and calcium can be present in different densities and concentrations. This has the result that, in the most unfavorable case, the absorption curves shown in FIG. 1 overlap one another completely. A pictorial separation of the two materials is then no longer possible.

[0051] FIG. 2 shows a graphical representation 20 that illustrates absorption values Is of the contrast agent iodine I and the material tungsten W dependent upon the tube voltage VT of an X-ray device. Whereas the X-ray absorption of iodine decreases with increasing energy, the X-ray absorption of tungsten W decreases only slightly with increasing energy.

[0052] Particularly in a dual-energy image recording at a low energy of 80 kV and a higher energy of 140 kV or 150 kV with a tin filter, the X-ray absorption Is of tungsten W changes practically not at all as compared with the X-ray absorption of iodine. Therefore, image points at which the two individual recordings are generated with different tube voltages can easily be associated with one of the two contrast agents. For example, a point at which the absorption is the same in the two images is clearly attributable to the material tungsten and a point at which the absorption in the two images is strongly different is clearly attributable to the material iodine.

[0053] FIG. 3 shows a graphical representation 30 that illustrates the absorption properties of the contrast agents iodine I and tungsten W as well as those of calcium Ca and water H2O, dependent upon the energy EPH of the X-ray photons. For each of the materials mentioned, the mass absorption coefficient K is shown dependent upon the energy EPH of the X-ray photons. It is clearly apparent in FIG. 3 that the absorption of the contrast agent iodine I and of the bone material calcium Ca decreases greatly in the region from 40 to 80 keV with increasing photon energy EPH. It should be noted that therein the absorption is shown logarithmically. In contrast thereto, tungsten W behaves more like water H2O. That is, the absorption of tungsten W for a first photon energy E(1), which is at approximately 45 keV, is equal to the absorption at a second photon energy E(2) which is at approximately 80 keV. Due to the strongly differing behavior of tungsten W as compared with calcium Ca, image regions which are laden with tungsten W can readily be separated or separately represented from regions in which calcium Ca prevails.

[0054] FIG. 4 shows a flow diagram 400 which illustrates an X-ray imaging method according to an example embodiment of the present invention. In the step 4.I, initially a contrast agent based upon the element tungsten is selected for an angiographic imaging of an examination region of a patient, for example, the skull of the patient. Furthermore, in the step 4.II, X-ray raw data RD that has been recorded from a region of an examination object O which is flooded with the selected contrast agent with the aid of a dual-energy recording method is captured. In the method visualized in FIG. 4, X-ray raw data that has been recorded with X-rays at two different energy values E(1) and E(2) is captured. The energy values are therein selected such that the absorption behavior of the selected contrast agent based upon the material tungsten is the same for both the energy values in this example embodiment. This process can be realized, for example, by way of the use of two detectors arranged spatially separated from one another, wherein a filter is introduced into the beam path in front of one of the two detectors, said filter filtering out part of the spectrum of the X-rays. Thus, two raw datasets to which different X-ray energies E(1) and E(2) are assigned are captured.

[0055] In step 4.III, a reconstruction of two image datasets BD1, BD2 takes place on the basis of the two raw datasets generated in step 4.II. Therein a first image dataset BD1 is generated which represents a first image region affected by the contrast agent tungsten, and a second image dataset BD2 is generated which represents a second image region, which is complementary to the first image region, and in which calcium-based structures are made visible. The creation of the two image datasets BD1, BD2 can take place, for example, with the aid of a material decomposition on the basis of the raw data acquired in step 4.II.

[0056] FIG. 5 shows a reconstruction facility 50. The reconstruction facility 50 has an ascertaining unit 51. The ascertaining unit 51 receives information regarding the contrast agent K to be used and establishes values E(1), E(2) of two different X-ray photon energies at which a selected contrast agent K behaves like water, i.e. the absorption is the same for both energy values. However, the image regions laden with calcium that are to be separated from the contrast agent K have, in energy regions that can be used by X-ray devices, a clear spectral dependence of the absorption and can therefore easily be differentiated at the established energy values E(1), E(2) from the selected contrast agent K. The selection of the energy values E(1), E(2) can take place, for example, on the basis of energy-dependent absorption values of the selected contrast agent K stored in a data store.

[0057] The selection of the energy values E(1), E(2) can be taken into account, in the context of a multi-energy recording method, in the selection of the energies and/or mean energy values of the X-ray sources used for imaging. If counting detectors are used for capturing the X-ray radiation, then energy thresholds and/or intervals can be selected so that the energy values mentioned are included.

[0058] The reconstruction facility 50 also has a raw data receiving unit 52 for receiving X-ray raw data RD. The raw data RD has been acquired with the aid of a dual-energy CT method from a region of an examination object which is partially flooded by the contrast agent K.

[0059] The raw data RD is passed on to a decomposition unit 53 which carries out a material decomposition of the raw data RD on the basis of the X-ray raw data RD in relation to the contrast agent K and calcium. The material-specific portions MA1, MA2 of the raw data which are associated with the individual absorption spectra of the different materials are transferred to the reconstruction unit 54 which reconstructs at least two image datasets BD1, BD2 on the basis of the material-specific portions MA1, MA2. A first image dataset BD1 visualizes a first image region affected by the contrast agent and a second image dataset BD2 visualizes a second image region which is complementary to the first image region, and in which structures laden with calcium or structures contrasted with iodine prevail. The image datasets BD1, BD2 generated are output by means of an output interface 55, for example, to a display unit, a data storage unit or a control computer with an image display.

[0060] FIG. 6 shows an X-ray imaging system, in this case a CT system 60, according to an example embodiment of the present invention.

[0061] The CT system 60 which is configured as a dual-energy CT system, substantially consists therein of a typical scanner 9 in which a projection measurement data acquisition unit 5 with two detectors 16a, 16b and two X-ray sources 15a, 15b arranged opposite the two detectors 16a, 16b circulates on a gantry 11 round a measurement space 12. Situated in front of the scanner 9 is a patient positioning apparatus 3 and/or a patient table 3, the upper part 2 of which can be displaced with a patient O situated thereon toward the scanner 9, in order to move the patient O through the measurement space 12 relative to the detector system 16a, 16b. The scanner 9 and the patient table 3 are controlled by way of a control facility 31 from which acquisition control signals AS come via a conventional control interface 34 in order to control the whole system in the conventional manner according to predetermined scan protocols. In the case of a spiral acquisition, by way of a movement of the patient O along the z-direction which corresponds to the system axis z through the measurement space 12 and the simultaneous circulation of the X-ray sources 15a, 15b, for the X-ray sources 15a, 15b relative to the patient O during the scan, a helical path results. The detectors 16a, 16b therein always move in parallel relative to the X-ray sources 15a, 15b, in order to capture projection measurement data PMD1, PMD2 which is then used for the reconstruction of volume and/or slice image data. Similarly, a sequential scanning method can also be carried out in which a fixed position in the z-direction is approached and then, during a circulation, a partial circulation or a plurality of circulations at the z-position in question, the required projection measurement data PMD1, PMD2 is captured, in order to reconstruct a sectional image at this z-position or to reconstruct image data from the projection measurement data of a plurality of z-positions. The method according to embodiments of the present invention can also in principle be used with other CT systems, for example, with just one X-ray source or with a detector forming a complete ring. For example, the inventive method can also be used on a system with an unmoved patient table and a gantry moved in the z-direction (a so-called sliding gantry).

[0062] The projection measurement data PMD1, PMD2 (also referred to here as raw data) acquired from the detectors 16a, 16b is transferred via a raw data interface 33 to the control facility 31. This raw data is then further processed, possibly after a suitable pre-processing in a reconstruction facility 50 which, in this example embodiment, is realized in the control facility 31 in the form of software on a processor. This reconstruction facility 50 reconstructs, on the basis of the raw data PMD1, PMD2, two image datasets BD1, BD2 of which a first image dataset BD1 visualizes vessel structures affected by a contrast agent K according to embodiments of the present invention and a second image dataset BD2 visualizes bone structures and calcified or partially calcified regions in the vessels.

[0063] The exact configuration of such a reconstruction facility 50 is illustrated in detail in FIG. 5.

[0064] The image data BD1, BD2 generated by the reconstruction facility 50 is then stored in a memory store 32 of the control facility 31 and/or is output in the usual manner on the screen of the control facility 31. Thus, by means of an interface (not shown in FIG. 6), it can also be fed into a network connected to the computed tomography system 60, for example, a radiological information system (RIS), and stored in a mass memory store accessible there or output as images to printers or filming stations connected there. The data can thus be further processed in any desired manner and then stored or output.

[0065] In addition in FIG. 6, a contrast agent injection facility 35 is shown, with which a contrast agent K is injected into the patient O in advance, that is before the start of the CT imaging method. The regions which are flooded by the contrast agent K and bone structures and (partially) calcified regions can then be captured in image form with the aid of the computed tomography system 60 using the X-ray imaging method according to embodiments of the present invention.

[0066] The components of the reconstruction facility 50 can be realized mainly or entirely in the form of software elements on a suitable processor. In particular, the interfaces between these components can also be configured purely as software. It is required only that access possibilities exist in suitable memory storage regions in which the data can be suitably placed in intermediate storage and called up again and updated at any time.

[0067] Finally, it should again be noted that the methods and apparatuses described above are merely preferred example embodiments of the present invention and that embodiments of the present invention can also be modified by a person skilled in the art without departing from the field of the present invention, to the extent that it is specified by the claims. For the sake of completeness, it should also be mentioned that the use of the indefinite article “a” or “an” does not preclude the relevant features from being present plurally. Similarly, the expression “unit” does not preclude this consisting of a plurality of components which can possibly also be spatially distributed.