DE102010040308A1 - Radiography system e.g. angiography system has imaging system for determining radiographic image such as three-dimensional X-ray image from several sub-area images received by X-ray detector - Google Patents

Abstract

The system has X-ray source device (10) comprising several X-ray sources to emit X-rays. A beam shaping device is attached to each x-ray source, for forming the respective X-ray beam. An X-ray detector includes several partial surfaces that are associated with X-ray source, for irradiating the X-ray beam from X-ray source, such that the simultaneously emitted X-rays are in non-overlapping state. A radiographic image such as three-dimensional X-ray image is determined by the imaging system from several sub-area images received by X-ray detector. An independent claim is included for method for receiving projection image by radiographic system.

Description

The invention relates to an X-ray recording system according to claim 1 and to a method for recording a projection image according to patent claim 12.

Cone-beam X-ray systems belong today to the state of the art in medical X-ray imaging and z. As C-arm angiography often in interventional clinical environment in use. Such systems typically have a single X-ray source on a C-arm and an oppositely disposed large area X-ray detector (eg, about 30x40 cm), which typically has a readout frequency of about 30 to 60 frames per second. During a rotational movement about an examination subject, a multiplicity (for example a few hundred) of projection images from different projection directions are recorded within a few seconds using this arrangement. From these projection images, a 3D image is determined by means of a CT reconstruction method, which can then be visualized and evaluated. While such a method for high-contrast imaging has long been established, for. B. off Fahrig et al., Use of a C-arm System to Generate True Three-dimensional Computed Rotational Angiograms: Preliminary In Vitro and In Vivo Results, AJNR American Journal of Neuroradiology, Volume 18, pp. 1507-1514, 1997 , Low-quality imaging has limitations on image quality. In particular, C-arm angiography systems have a less good low-contrast resolution than z. B. diagnostic CT systems, so that z. B. a reliable diagnosis of strokes is not possible.

One of the main reasons for limiting the image quality is the (for example, 14-bit) limited gray value dynamics of a flat X-ray detector. In practice (especially in the case of skull images), this often leads to saturation effects or prevents the resolution of small differences with small attenuation coefficients. These dynamics deficits in the projection image data set have a direct negative effect on the 3D image quality. The achievable low-contrast resolution is also limited by the fact that the imaging geometry (cone beam geometry, circular trajectory of the X-ray source during recording) for theoretical reasons for an accurate 3D reconstruction is insufficient (see, for example HK Tuy, An Inversion formula for cone beam reconstruction, SIAM Journal of Applied Mathmatics, Volume 43 (3), page 546 et seq., 1983 ). In the 3D image, this inadequacy is manifested in the form of so-called cone-beam artifacts, the strength and frequency of which generally increase significantly with a larger cone angle independently of the reconstruction algorithm. The achievable low contrast resolution is also limited by the fact that the projection images taken in the cone beam geometry described above are known to be degraded by scattered radiation effects. Some of these effects can be mitigated, for example, by (partly heuristic) algorithmic methods; however, a fundamental solution to the problem is not to be expected because of the limitations mentioned.

In order to improve the low-contrast image quality in cone-beam X-ray systems, modifications of the recording system are possible in which statically or mechanically adaptable shape filters for modulating the X-ray beam are introduced into the beam path, so that the dynamics of the intensity distribution of the incident radiation over the detector surface is reduced. This leads to an improved gray value dynamics in the acquired projection data set, see, for example, US Pat. B. Mail et al., The influence of bowtie filtration on cone-beam CT image quality, Med. Phys., January 2009, pages 22-32 , The problem, however, is that a static shape filter can only achieve suboptimal dynamics enhancement because it ignores the actual attenuation behavior of the object of interest. An adaptive shape filter is based on mechanical changes and is therefore maintenance-intensive, and can not be changed arbitrarily fast and flexibly. Another suggestion is to perform the X-ray in an inverse geometry. An inverse recording geometry is achieved by directing several X-ray sources onto an X-ray detector with a very small active area. For each mechanical position of the recording system, the individual X-ray sources are activated one after the other and thus several smaller projection images are acquired. The X-ray sources can be operated with different settings, so that a similar effect can be achieved as with a mechanical mold filter. The problem, however, is that the X-ray detector must have a very high frame rate, since the projection image of each individual X-ray source must be individually detected by the total acquisition time compared to the "non-inverse" geometry. to keep constant. Typically, therefore, not only the X-ray source but also the X-ray detector of the system must be replaced, which means a greater interference with the system concept.

It is an object of the present invention to provide an X-ray imaging system which ensures improved low-contrast image quality in conical beam symmetry. Furthermore, it is an object of the invention to provide an X-ray imaging method.

The object is achieved by an X-ray recording system according to claim 1 and a method for receiving a projection image according to claim 12; advantageous embodiments of the invention are the subject of the dependent claims.

The X-ray imaging system according to the invention comprises an X-ray source device, a planar X-ray detector and an image system, which X-ray source device has a plurality of X-ray sources for emitting X-rays and each X-ray source each having a beam shaping device for forming the respective X-ray beam and which X-ray detector has a plurality of partial surfaces, each X-ray source in each case assigned a partial area and the respective associated partial area can be irradiated by means of the X-ray source of the respective X-ray source formed by the respective beam shaping device, whereby simultaneously emitted X-rays in the area of the X-ray detector are free of overlapping, wherein a plurality of partial area images can be recorded by means of the X-ray detector and wherein an X-ray image, in particular a 3D X-ray image, by means of the image system of the plurality of partial area images erm is ittelbar. The X-ray source device and the planar X-ray detector have a cone beam geometry.

The method according to the invention for recording a projection image by means of such an X-ray recording system comprises the following steps: activation of the multiplicity of X-ray sources for irradiation of the respectively assigned partial surfaces, acquisition of partial surface images by means of the X-ray detector, in particular from several projection directions, and optionally the determination of an X-ray image, in particular a 3D X-ray image, from the partial surface images.

Either one 2D projection image can be assembled from the partial surface images and then several projection images can be reconstructed from different projection directions or a 3D image of the volume of the examination object can be reconstructed directly from a data set of several partial surface images created in different projection directions. As projection images, either one or more composite (in group activation) partial area images may be used.

By means of the x-ray recording system or method according to the invention, even with a dynamically limited x-ray detector, a larger dynamic range in the imaging data can be detected correctly. This leads to an increase in the gray value dynamics in the projection image, and it can, for. B. in skull recordings in the detector edge area, saturation effects are avoided. The use of a plurality of X-ray sources results in a modified recording geometry, in which the object to be examined is no longer irradiated with a, very wide-open cone of rays, but with several, narrowly collimated beam cones. The acquired image data then have more information from a theoretical point of view, what z. B. in a 3D reconstruction using a suitable reconstruction algorithm leads to a reduction of the cone beam artifacts. In addition, when shooting projection images, the total X-ray dose may be lowered, e.g. B. when X-ray sources in peripheral areas of the X-ray detector for imaging a lower X-ray dose is needed and the X-ray sources arranged there are operated at lower operating currents. Overall, the invention enables improved low-contrast resolution for 3D reconstruction.

According to one embodiment of the invention, the X-ray recording system has an adjustable holder, in particular a C-arm, on which the X-ray source device and the X-ray detector are arranged, and which is adjustable so that it is rotatable about an examination object. By this adjustment particularly simple and precise projection images can be taken from different projection directions or positions with respect to an examination subject. The x-ray recording system is advantageously designed to receive a multiplicity of projection images recorded at different projection directions during a rotation of the holder about an examination subject. According to a further embodiment of the invention, the x-ray recording system is designed to reconstruct a 3D image from the multiplicity of partial area images or projection images recorded at different positions.

Advantageously, for the lowest possible radiation exposure of the examination object, the partial surfaces have a maximum overlap of 20%. According to a further embodiment of the invention, the partial surfaces adjoin one another flush. In this way, a simple assembly of the partial surface images without additional processing steps is possible. Optionally, the projection image can also be created directly by means of a single image with simultaneous activation of the X-ray sources irradiating all partial surfaces. There may also be gaps between the faces.

Conveniently, the number of X-ray sources and the number of faces is the same size and each X-ray source has an unambiguous assignment to a partial area and vice versa.

According to an advantageous embodiment of the invention, the X-ray sources of field emission emitters, in particular having a nanostructured material with carbon nanotubes, are formed. Such field emission emitters are particularly small, light and energy-saving and allow a very high, easy to control and easily focusable electron beam current. In addition, field emission emitters cause only low heat generation and high efficiency.

Advantageously, the plurality of X-ray sources for irradiating the respectively associated sub-areas is activated simultaneously and the sub-area images are recorded simultaneously. In such a case, no overlapping of the partial surfaces should be provided, but these should adjoin one another flush. To control the x-ray source device, a system control is preferably provided.

According to a further embodiment of the invention, the plurality of X-ray sources for the irradiation of the respectively associated sub-areas is activated in groups and the sub-area images are recorded in groups. In this way, a reduction of the scattered radiation is possible by directly adjacent subareas not simultaneously but z. B. be recorded in succession. The scattered radiation incident on the adjacent subareas can then be ignored for further evaluation and reconstruction; thus the scattering effect for the reconstruction is additionally reduced. Furthermore, one can use the measured scattered radiation for an estimate of the scattering influences for the entire detector surface, and thus improve algorithmic scattered beam correction. The control of X-ray sources and X-ray detector can in turn be carried out by means of the system control.

According to a further embodiment of the invention, each X-ray source can be controlled individually and independently activated. In this way, for example, different operating modes or different operating currents for different X-ray sources can be applied and thus a virtual adaptive shape filter can be formed.

The invention and further advantageous embodiments according to features of the subclaims are explained in more detail below with reference to schematically illustrated embodiments in the drawing, without thereby limiting the invention to these embodiments. Show it:

1 a view of an inventive radiographic system,

2 a view of an x-ray detector with subdivided into groups,

3 a sequence of a method according to the invention and

4 a view of another inventive radiographic system with a articulated robot.

In the 1 is an X-ray imaging system according to the invention with an X-ray source device 10 with eight x-ray sources 10.1 to 10.8 and an x-ray detector 11 with eight faces 11.1 to 11.8 shown. The entire, the X-ray detector irradiating X-rays is thus made of eight X-rays 13.1 to 13.8 together. Each X-ray source is uniquely associated with a partial surface of the X-ray detector: a first X-ray source 10.1 generates a first x-ray beam 13.1 , which is a research object 20 radiates through and onto a first partial surface 11.1 incident, a second X-ray source 10.2 generates a second x-ray beam 13.2 , which is the examination object 20 (at another point) radiates and on a second partial surface 11.2 hits, etc.

Every X-ray source 10.1 to 10.8 This is configured (and adjusted as necessary during automatic exposure control during a recording) in such a way that the partial area illuminated by it is optimally exposed. In this case, for example, the partial surfaces can adjoin flush with two or more further partial surfaces, ie have no overlaps. In such a case, all X-ray sources can be activated at the same time for the emission of X-rays and all partial surfaces can be exposed and recorded simultaneously. In the case of overlaps of the X-rays on adjacent faces, adjacent X-rays are sequentially activated. Simultaneously activated X-rays are non-overlapping with respect to the X-ray detector, ie overlaps are possible in the "air", but not on the X-ray detector.

In the 3 the steps of the method according to the invention are shown. In a first step 14 one or more X-ray sources are activated to emit X-rays and thereby irradiate the examination subject and irradiate one or more partial surfaces. In a second step 15 corresponding sub-area images are recorded, so depending on the mode of operation of the x-ray detector, imaging data are recorded and possibly read out. By means of the arrow 21 is implied that activation and absorption can be done several times, for example, if not all faces are to be irradiated simultaneously.

Either all X-ray sources can be activated simultaneously (for example in the case of flush contiguous X-rays or partial surfaces) or sequentially (for example in the case of overlaps of the partial surfaces) to emit X-rays and corresponding partial surface images or groups of partial surface images can be recorded. With successively activated X-ray sources, partial area images can be read out between the activation; It can also be a readout after recording all image data are performed.

In the case of non-simultaneous activation, the x-ray sources can each be completely separated one after another or z. B. be activated in subgroups simultaneously. In the 2 For example, such sub-groups are shown, wherein the sub-areas designated by A are irradiated by a first sub-group and the sub-areas designated B are irradiated by a second sub-group. Thus, for example, subgroup A can first be activated and the corresponding subareas recorded and then subgroup B activated and the associated subareas recorded. The subgroups may, for example, be selected such that "crosswise" arranged subareas are recorded simultaneously and adjacent subareas are recorded one after the other. Overall, in the method, all areas of the X-ray detector to be irradiated are irradiated at least once.

There may be any trade-off between the number of simultaneously activated X-ray sources and the readout frequency of the X-ray detector. It can z. B. all X-ray sources are activated simultaneously and the detector contents are read only once. Another example would be to first activate the x-ray sources for subgroup A, read them out and then activate those for subgroup B and read them out again. A third example would be to individually activate each X-ray source and read the detector contents.

In order to create a 3D image of the volume of an examination object, one or more partial surface images or groups of partial surface images are respectively recorded during rotation of the recording system around the examination object in different projection directions.

In a third step 16 An X-ray image is determined from the partial surface images or the groups of partial surface images. There are several possibilities here: On the one hand, one 2D projection image per projection direction can be assembled from the partial area images and then several projection images from different projection directions can be reconstructed into a 3D image. On the other hand, a data set of several sub-area images or groups of sub-area images, which were each created in different projection directions, can be reconstructed directly into a 3D volume image. For this purpose, an image system can be used with image processing software.

When composing 2D projection images z. B. in flush contiguous faces the partial images of irradiated by the direct radiation of the X-rays of the X-ray sources faces directly joined and irradiated only by scattered surface areas are removed, so that a complete, gap-free composite projection image of the object under investigation arises. For sub-areas with intersections, the intersection areas are cropped such that no area exists more than once in the projection image.

For a 3D reconstruction, the data of the projection images are converted into line integrals according to the respective X-ray source settings, from which the 3D object volume is reconstructed. The reconstruction takes place, for example, iteratively or by means of analytical methods of filtered backprojection (for example using rebinning methods).

Important advantages of the method according to the invention or the x-ray recording system according to the invention can be found in the reduction of the scattered beam influences on the reconstruction, the reduction of cone beam artifacts during the reconstruction and the implementation of a nonmechanical adaptive shape filter for increasing the detector dynamics. A non-mechanical adaptive shape filter can be achieved by a different control of different x-ray sources z. B. with respect to the operating currents are formed. It can, for. B. adapted to the object to be examined, a part of the X-ray sources with higher and a part of lower operating currents are applied. For example, edge regions can be operated with lower currents. Each individual X-ray source can be operated with an individual operating current and the operating currents can also be changed dynamically adapted.

Overall, the invention eliminates important limitations for 3D low contrast resolution. In comparison z. B. the known X-ray image with inverse geometry, the inventive method / the X-ray recording system according to the invention requires no special detector with high frame rates. Since the individual x-ray sources of the x-ray recording system according to the invention illuminate different partial areas of the large x-ray detector, the associated projection data if necessary, at least partially together (and not successively) are read out. In addition, in the method / the X-ray acquisition system according to the invention, a partial measurement of scattered radiation for improved scattered beam correction can be carried out in a simple manner; this is z. B. not possible with inverse CT systems. In comparison to known adaptive shape filters, the x-ray recording system according to the invention can be operated so that no mechanical movement is necessary to change the filter, is therefore faster, more flexible and less prone to failure.

In the 4 is shown as an example of an X-ray system, a C-arm system. This has one on a articulated robot 18 arranged C-arm 17 on which in turn the x-ray source device 10 and the X-ray detector 11 are arranged. In addition, an additional beam-shaping device 19 for shaping the X-ray source device 10 emitted X-rays provided. The C-arm system can be designed, for example, as an angiography system. The C-arm system is powered by a control panel 22 driven; there is also an image system 23 z. B. provided with an image processing and an input and display unit.

The X-ray source device with the plurality of X-ray sources may be arranged as an addition to a main X-ray source or instead of a main X-ray source (see 4 ) completely replace it. The individual X-ray sources can be formed by field emission emitters, in particular comprising a nanostructured material with carbon nanotubes (so-called carbon nanotubes, CNTs). Usually, CNT-based X-ray sources are not suitable for high currents because of the used static anodes. However, since in the X-ray imaging system according to the invention, each CNT source emits only a narrowly collimated X-ray beam, the anode angle can be optimized accordingly and thus the X-ray current can be increased.

The core idea of the invention is to provide an existing X-ray recording system, in particular a C-arm system, with an X-ray source device having a plurality of individual X-ray sources (eg in the form of an array), wherein each individual X-ray source irradiates only a partial area of a large-area X-ray detector and wherein each individual x-ray source can be individually configured and activated. Furthermore, it is proposed to record a projection data set of an examination object with this system and to reconstruct a 3D image data set therefrom.

The invention may be briefly summarized as follows: For improved low-contrast image quality, an X-ray imaging system comprising an X-ray source device, an X-ray detector and an imaging system, which X-ray source device is a plurality of X-ray sources for emitting X-rays and each X-ray source is a beam shaping device for shaping the respective X-ray beam each X-ray source is assigned a partial area and the respective associated partial area can be irradiated by means of the X-ray beam of the respective X-ray source formed by the respective beam-shaping device, simultaneously emitted X-rays being free of overlap with respect to the X-ray detector, wherein a plurality of partial surface images are receivable by means of the X-ray detector and an X-ray image, in in particular a 3D x-ray image, by means of the image system ( 23 ) can be determined from the multiplicity of partial area images.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Fahrig et al., Use of a C-arm System to Generate True Three-dimensional Computed Rotational Angiograms: Preliminary In Vitro and In Vivo Results, AJNR American Journal of Neuroradiology, Volume 18, pp. 1507-1514, 1997 [0002]
• HK Tuy, An Inversion formula for cone beam reconstruction, SIAM Journal of Applied Mathmatics, Volume 43 (3), page 546 et seq., 1983 [0003]
• Mail et al., The influence of bowtie filtration on cone-beam CT image quality, Med. Phys, January 2009, pages 22-32 [0004]

Claims (17)

X-ray recording system comprising an X-ray source device ( 10 ), a flat X-ray detector ( 11 ) and an image system ( 23 ), which X-ray source device ( 10 ) a plurality of x-ray sources ( 10.1 . 10.2 , ..., 10.8 ) for the emission of X-rays ( 13.1 ) and to each x-ray source ( 10.1 . 10.2 , ..., 10.8 ) in each case a beam-shaping device ( 19 ) for shaping the respective X-ray beam ( 13.1 ) and which X-ray detector ( 11 ) a plurality of partial surfaces ( 11.1 . 11.2 , ..., 11.8 ), wherein each x-ray source ( 10.1 . 10.2 . 10.8 ) in each case a partial area ( 11.1 . 11.2 , ..., 11.8 ) and the respective associated subarea ( 11.1 . 11.2 , ..., 11.8 ) by means of the respective beam shaping device ( 19 ) shaped X-ray beam ( 13.1 ) of the respective X-ray source ( 10.1 . 10.2 , ..., 10.8 ) is irradiated, - whereby simultaneously emitted X-rays ( 13.1 ) are free of overlap in the area of the X-ray detector, wherein a multiplicity of partial area images are determined by means of the X-ray detector (FIG. 11 ) are receivable and - wherein an X-ray image, in particular a 3D X-ray image, by means of the image system ( 23 ) can be determined from the multiplicity of partial area images. An x-ray imaging system according to claim 1, comprising an adjustable support on which the x-ray source device ( 10 ) and the X-ray detector ( 11 ) are arranged, and which is adjustable so that they are around an examination object ( 20 ) is rotatable. X-ray recording system according to claim 2, designed to receive a plurality of projection images recorded at different positions during a rotation of the holder around an examination object ( 20 ). An X-ray imaging system according to claim 3, adapted to reconstruct a 3D image from the plurality of projection images taken at different positions. X-ray imaging system according to one of the preceding claims, wherein the partial surfaces ( 11.1 . 11.2 , ..., 11.8 ) have a maximum overlap of 20%. X-ray imaging system according to one of the preceding claims, wherein the number of X-ray sources ( 10.1 . 10.2 , ..., 10.8 ) and the number of faces ( 11.1 . 11.2 , ..., 11.8 ) are the same size and each x-ray source ( 10.1 . 10.2 , ..., 10.8 ) an unambiguous assignment to a subarea ( 11.1 . 11.2 , ..., 11.8 ) and vice versa. X-ray imaging system according to one of the preceding claims, wherein the X-ray sources ( 10.1 . 10.2 , ..., 10.8 ) of field emission emitters, in particular comprising a nanostructured material with carbon nanotubes. X-ray imaging system according to one of the preceding claims, wherein the partial surfaces ( 11.1 . 11.2 , ..., 11.8 ) are flush with each other. X-ray imaging system according to one of the preceding claims, comprising a system control ( 22 ) for controlling the X-ray source device ( 10 ) and the X-ray detector ( 11 ) such that a simultaneous irradiation of all partial surfaces ( 11.1 . 11.2 , ..., 11.8 ) of the X-ray detector ( 11 ) and recording the partial surface images is feasible. X-ray imaging system according to one of the preceding claims, comprising a system control ( 22 ) for controlling the X-ray source device ( 10 ) and the X-ray detector ( 11 ) such that a stepwise irradiation of all partial surfaces ( 11.1 . 11.2 , ..., 11.8 ) of the X-ray detector ( 11 ) and recording the partial surface images is feasible. X-ray imaging system according to one of the preceding claims, wherein each X-ray source ( 10.1 . 10.2 . 10.8 ) is individually controllable and independently activatable. Method of recording a projection image by means of an X-ray recording system according to one of Claims 1 to 11, comprising the following steps: 14 ) of the plurality of X-ray sources ( 10.1 . 10.2 , ..., 10.8 ) for the irradiation of the respective associated partial surfaces ( 11.1 . 11.2 , ..., 11.8 ), - Admission ( 15 ) of partial surface images by means of the X-ray detector ( 11 ), and - determining ( 16 ) of an X-ray image, in particular a 3D image from the partial surface images. The method of claim 12, wherein the plurality of x-ray sources ( 10.1 . 10.2 , ..., 10.8 ) for the irradiation of the respective associated partial surfaces ( 11.1 . 11.2 , ..., 11.8 ) are activated simultaneously and the partial surface images are recorded simultaneously. The method of claim 12 or 13, wherein said plurality of x-ray sources ( 10.1 . 10.2 , ..., 10.8 ) for the irradiation of the respective associated partial surfaces ( 11.1 . 11.2 , ..., 11.8 ) are activated in groups and the partial surface images are taken in groups. Method according to claim 14, wherein the group (A, B) is designed in such a way that directly adjacent partial surfaces ( 11.1 . 11.2 , ..., 11.8 ) are recorded at different times. Method according to one of claims 12 to 15, wherein the holder around an examination subject ( 20 ) and partial area images are taken in such a way that a 3D image can be reconstructed from the partial surface images. The method of claim 16, wherein a 3D image is reconstructed.

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