The control device is configured to determine a spectral X-ray absorption property of at least one volume element that is arranged inside the fill volume of the at least one truncated 2D projection image as a function of the supplemented 2D projection images. The control device is configured to generate virtual 2D projection images of the X-ray spectra of the object under examination from the preliminary volume model of the object under examination as a function of the spectral X-ray absorption property of the at least one volume element. The control device is configured to reconstruct the volume model of the object under examination from the virtual 2D projection images or from the supplemented 2D projection images and the virtual 2D projection images.

The control device may contain one or more computers, one or more microcontrollers, and/or one or more integrated circuits, (e.g., one or more application-specific integrated circuits (ASIC), one or more field-programmable gate arrays (FPGA), and/or one or more systems on a chip (SoC)). The computing unit may also contain one or more processors, (e.g., one or more microprocessors), one or more central processing units (CPU), one or more graphics processing units (GPU), and/or one or more signal processors, (e.g., one or more digital signal processors (DSP)). The computing unit may also contain a physical or a virtual group of computers or other of the units mentioned.

A third aspect of the disclosure relates to an X-ray apparatus. The X-ray apparatus has at least one control device in accordance with the second aspect of the disclosure. The X-ray apparatus is configured to capture first 2D projection images of an object under examination, created in a first X-ray spectrum, and second 2D projection images of the object under examination, created in a second X-ray spectrum, wherein a respective one of the 2D projection images maps a respective object projection of a respective projection volume of the object under examination. The respective projection volume is a partial volume of a total volume of the object under examination that is arranged in a respective field of view of the respective 2D projection image. The X-ray apparatus is configured to provide a data set of the 2D projection images of the object under examination to the control device to generate a volume model of the object under examination.

A fourth aspect of the disclosure relates to a computer program that may be loaded directly into a memory of a control device, with program means for executing the acts of the above-mentioned method if the program is executed in the control device. The method described herein may therefore also be present in the form of a computer program product that implements the method on a control device if it is executed on the control device.

A fifth aspect of the disclosure relates to an electronically readable data medium with electronically readable control information stored thereon, which includes at least one described computer program and is configured such that when the data medium is used in a control device it performs a described method.

Further features of the disclosure emerge from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and/or shown in the figures may be included by the disclosure not only in the combination indicated in each case, but also in other combinations. In particular, embodiments and combinations of features may also be included by the disclosure that do not have all the features of an originally formulated claim. In addition, the disclosure may include embodiments and combinations of features that go beyond or deviate from the combinations of features set out in the back-references of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is explained in greater detail below using concrete embodiments and associated schematic drawings. Identical or functionally identical elements may be provided with the same reference characters in the figures. The description of identical or functionally identical elements is likewise not necessarily repeated in respect of different figures. In the figures:

FIG. 1 shows a schematic representation of an example of a capture of 2D projection images of an object under examination by an X-ray apparatus.

FIG. 2 shows a schematic representation of examples of 2D projection images of an object under examination.

FIG. 3 shows a schematic representation of an example of a reconstructed volume model.

FIG. 4 shows a schematic representation of an example of an operational sequence of a method.

DETAILED DESCRIPTION

FIG. 1 shows a schematic representation of a capture of 2D projection images of an object under examination by an X-ray apparatus.

The X-ray apparatus 1 may have an acquisition device 2 that may include an X-ray source 3 and an acquisition screen 4. The X-ray source 3 may be configured to emit X-ray beams along a conical volume toward the acquisition screen 4. The X-ray apparatus 1 may be configured for the performance of a dual-energy cone beam computed tomography method and/or a limited-angle tomography method. To this end, the X-ray apparatus 1 may output the X-ray beams in two different X-ray spectra.

An object under examination 5 may be arranged between the X-ray source 3 and the acquisition screen 4. The X-ray beams are absorbed by the object under examination 5 so that the acquisition screen 4 captures a two-dimensional projection image 7, 8 of the object under examination 5. The absorption of the X-ray beams in the object under examination 5 may depend on the X-ray spectrum of the X-ray beams. The X-ray beams of the first X-ray spectrum may be captured in first 2D projection images 7, and the X-ray beams of the second X-ray spectrum may be captured in second 2D projection images 8.

A reconstruction of a volume model 11 of the object under examination 5 requires an acquisition of a plurality of the 2D projection images 7, 8 of the object under examination 5 from different directions. For this, the X-ray apparatus 1 may be configured to move the X-ray source 3 and the acquisition screen 4 along a trajectory 6, (e.g., a circular trajectory 6), around the object under examination 5. In predetermined directions, the respective 2D projection images 7, 8 of the object under examination 5 may be captured in the respective X-ray spectrum and may be added to a data set 9. A control device 10 of the X-ray apparatus 1 may be configured to reconstruct the volume model 11 of the object under examination 5 from the first 2D projection images 7 and the second 2D projection images 8.

For a complete reconstruction of the volume model 11 of the object under examination 5, it is necessary for a total volume 14 of the object under examination 5 to be captured completely during a respective measurement. To this end, the total volume 14 is arranged inside the cone during each acquisition of the respective 2D projection images 7, 8 so that the object under examination 5 is irradiated completely, and the projection image 7, 8 includes the object under examination 5 over a total respective dimension. However, it may also be the case that, in at least some positions of the acquisition device 2, missing areas 28 of the object under examination 5 lie outside the cone and are thus not captured by the respective projection image 7, 8. In this case, there is a so-called truncation. As a result, errors may occur in the volume model 11 of the object under examination 5.

An area that is sufficiently irradiated is referred to as a primary reconstruction volume 27. The other area is referred to as a truncation volume 25. The truncation volume 25 may include the volumes that were located outside the field of view during at least one acquisition of one of the projection images 7, 8. For a reconstruction, it may be necessary to supplement the 2D projection images 7, 8 with fill projections 15. The control device 10 may be configured to supplement the 2D projection images 7, 8 with the fill projections 15 and/or to supplement a preliminary volume model 19 created from the non-supplemented 2D projection images 7, 8 with fill volumes 16. To supplement the fill projections 15, a standard model of the object under examination 5 may be assumed, which may map a water cylinder. In this case, the truncation volume 25 may be supplemented by a water cylinder as a fill volume 16.

Partial objects 23 may be arranged in the object under examination 5 and may have respective partial object volumes 24. The partial object volumes 24 may also be located partially inside the primary reconstruction volume 27 and partially outside the primary reconstruction volume 27. To generate the fill volume 16, image features 21 of the partial objects 23 may be identified in the 2D projection images 7, 8, and their positions determined in the 2D projection images 7, 8. From this, the control device 10 may determine a position of the partial object volume 24 of the partial object 23 in the volume model 11. The partial object volume 24 of the partial object 23 may be stored in a database of the control device 10. As a result, the control device 10 may identify the partial object 23 in the 2D projection images 7, 8 of the object under examination 5 based on the image features 21. Part of the partial object volume 24 in the truncation volume 25 that is not mapped in one of the 2D projection images 7, 8 may be supplemented as a fill projection 15 in the other projection image 7, 8. The missing part may be determined or estimated from the partial object volume 24 stored in the database.

The partial object volumes 24 may also be identified in a preliminary volume model 19 of the object under examination 5, which may be determined from the non-supplemented 2D projection images 7, 8. An X-ray absorption property may be determined for at least one volume element 18 of the preliminary volume model 11. The X-ray absorption property may be ascertained based on a material 22, which may be recognized based on a structure in a partial area of one of the 2D projection images 7, 8. The X-ray absorption property of the material 22 may be stored in a database of the control device 10.

After the preliminary volume model 11 is generated, virtual 2D projection images 20 may be created from the preliminary volume model 18 by the control device 10.

FIG. 2 shows a schematic representation of 2D projection images 7, 8 of an object under examination 5.

The 2D projection images 7, 8 may have object projections 12 that map the projection volume 13 of the object under examination 5 of the respective measurement. The projection volume 13 may describe the part of the total volume 14 of the object under examination 5 located inside the cone and thus the field of view 17 of the respective measurement. The missing area 28 outside the object projection 12 may show the part of the 2D projection images 7, 8 that has been supplemented.

The 2D projection images 7, 8 of the object under examination 5 may be created from two positions for the respective X-ray spectra. Due to the X-ray absorption property of materials, intensity values of the 2D projection images 7, 8 may be distinguished from one another as a function of the X-ray spectrum. As a result, a material may be identified. The outlines of the partial objects 23 may represent the image features 21 of the partial objects 23 that may be identified by the control device 10. The position of the partial object 23 in the volume model 11 may be determined from the position of the image features 21.

FIG. 3 shows a schematic representation of a reconstructed volume model 11.

The truncation volume 25 outside the primary reconstruction volume 27 may be supplemented by the fill volume 16. By way of example, a volume element 18 is shown whose X-ray absorption property is determined.

FIG. 4 shows a schematic representation of an operating sequence of a method.

In act S1, a DE-CBCT scan of an object under examination 5 may be performed by an X-ray apparatus 1. During the DE-CBCT scan, 2D projection images 7, 8 with a first and a second X-ray spectrum may be acquired. The DE-CBCT scan may be acquired using known dual-energy methods such as for example dual source, fast kV switching, fast filter switching, or dual layer & photon counting detectors. Both the X-ray spectra may be distinguished from one another in at least one wavelength range. A truncation may have occurred, as a result of which there are 2D projection images 7, 8 in which a missing area 28 of the object under examination 5, (e.g., a lateral area), is cut off. The cut-off missing area 28 may have been located outside the field of view 17 when the projection image 7, 8 was captured. The 2D projection images 7, 8 of the object under examination 5 of the X-ray spectra may be added to a data set 9 that may be provided to a control device 10 to generate a volume model 11.

In act S2, a first image reconstruction for the reconstruction of a preliminary volume model 19 may optionally be performed by the control device 10 by known acts in accordance with the prior art for the reconstruction of the primary reconstruction volume 27. The non-truncated area may describe the total volume 14 of the object under examination 5 in the primary reconstruction volume 27. The reconstruction may optionally take place separately for the 2D projection images 7 of the first X-ray spectrum and the 2D projection images 8 of the second X-ray spectrum. The truncation volume 25 shown in the 2D projection images