Imaging system and method for recording projection images

Abstract

The invention relates to an imaging system (1) for recording projection images, comprising a detector unit (4) and a radiation source (3), the detector unit (4) having two detector elements (4.1, 4.2) arranged one behind the other, which both cover the same recording area (A), the radiation source (3) is designed and / or the detector unit (4) is designed in such a way that the second detector element (4.2) is not saturated for a portion of the recording region (A) in which the first detector element (4.1) is saturated during irradiation, and wherein the imaging system (1) additionally comprises a data acquisition unit (6), which is designed to acquire data from the first detector element (4.1) and the second detector element (4.2). A first data set (D1) of the first detector element (4.1) and a second data set (D2) of the second detector element (4.2) are recorded such that the two data sets (D1, D2) can be separated from each other. The invention also relates to a method.

Description

Technical Field

[0001] The invention relates to an imaging system and a method for recording a projected image. Background Art

[0002] In an X-ray image, i.e. a projection image recorded with the aid of an X-ray beam, there is an area outside the object area which is illuminated with primary radiation and scattered radiation from the object. Since this area decreases with increasing lateral distance from the object, the highest beam intensity can usually be found at the skin-air transition.

[0003] If the intensity of the incident X-ray radiation (primary radiation) exceeds the dynamic range of the detector, the X-ray detector is saturated. The saturated pixel area can no longer be used for image analysis or diagnosis. Often, saturated pixels are even cropped. Due to electronic limitations (bit depth, maximum storage capacity), the dynamic range is limited by the minimum required sensitivity (digital resolution of the incident X-ray signal) and the maximum acceptable X-ray signal.

[0004] In mammography, this situation is exacerbated by the increased object attenuation at the X-ray photon energies below 50 kVp used here compared to radiography. The intensity in the skin-air transition region can vary by several orders of magnitude. The dynamic range of the detector is not sufficient to detect all intensities for all observed object thicknesses and densities in the image.

[0005] It is advantageous to be able to measure this "skin-to-air transition" since useful information can be obtained from it, for example about the degree of scattering or the intensity of the incident X-rays. The greatest challenge is that the skin-to-air transition is typically not imaged, that is, cannot be clearly visualized, since the saturation region of the detector extends into the actual image region.

[0006] Another important aspect is to determine the total applied dose with high precision. This is currently not possible due to detector saturation. This leads, for example, to large errors in the inferred iodine accumulation in specific object areas in contrast-enhanced dual-energy examinations.

[0007] Higher pixel storage capacity in the detector can extend the range of incident X-ray signals available for digitization. However, this is accompanied by a disadvantageous increase in pixel noise.

[0008] It is also possible to use multiple images of the same object in order to divide the total clinically used dose into smaller parts that can still be covered by the detector. However, this is also disadvantageously affected by increased image noise during multiple readouts and possible motion artifacts due to the longer total detection duration. Summary of the invention

[0009] The object of the present invention is to provide an imaging system and a method for recording projection images, with which the above-mentioned disadvantages are avoided.

[0010] This object is achieved by the imaging system according to the invention and the method according to the invention.

[0011] The imaging system according to the invention is used to record projection images. The imaging system comprises a detector unit and a radiation source, wherein the detector unit has two detector elements arranged in succession, both of which cover the same recording area. In addition, the radiation source is set and / or the detector unit is configured so that for a portion of the recording area in which the first detector element is saturated during the irradiation, the second detector element is not saturated. In addition, the imaging system comprises a data acquisition unit, which is designed to record a first data set of the first detector element and a second data set of the second detector element, so that the two data sets can be separated from each other.

[0012] Basically, conventional radiographic systems, fluoroscopic systems or urological systems can be used as imaging systems, but also systems for tomography or tomosynthesis. However, a detector unit having two detector elements arranged in succession must be provided. Basically, the invention is advantageous for all applications in which projection images are recorded, regardless of whether these projection images are the result or are used for the reconstruction of an image.

[0013] In this case, the detector elements must be arranged so that the X-ray beam strikes both detector elements simultaneously, i.e. both detector elements cover the same recording area. In this case, the influence of the cone beam on the differences in the recordings of the two detector elements can be corrected. Such corrections are known in the prior art.

[0014] In order to be able to advantageously apply the method, data from the second detector element are required. Therefore, the second detector element must not be saturated, at least in the area where its data is used. Whether the second detector element will be saturated depends on the intensity of the primary radiation on the one hand, and on the shielding effect of the first detector element and, if necessary, a further absorber on the other hand. For the reasons described, the radiation source must be set or the detector unit must be constructed so that the second detector element is not saturated for the part of the recording area in which the first detector element is saturated during irradiation. As described, this does not have to be all areas of the second detector element, but it should be the area of ​​the transition from the object to the air, because this area is the most interesting.

[0015] Thus, by using a second detector element behind the first detector element, an X-ray beam that penetrates the first detector element can be detected. The radiation that strikes the second detector element has a lower intensity due to absorption in the first detector element, so that the second detector element receives fewer, mainly high-energy photons. In the case of a correctly set X-ray source, the second detector element can fully detect direct and scattered radiation modes and compensate for the saturation of the first detector element without having to accept a loss in the quality of the original image.

[0016] Suitable data acquisition units for imaging systems are generally known. However, for the present invention, the data acquisition unit must be designed so that a first data set of a first detector element can be separated from a second data set of a second detector element. In this case, the data sets should be stored separately from one another or at least have markings that enable a one-to-one association.

[0017] The method according to the invention is used for recording a projection image using an imaging system according to the invention. The method comprises the following steps:

[0018] - irradiating the body part of the patient with a radiation source, wherein two detection elements of the detector unit are irradiated through the body part,

[0019] - reading out two detector elements and forming a first data set by reading out the first detector element and a second data set by reading out the second detector element,

[0020] A projection image is generated from the two data sets, wherein image values ​​in the projection image at which the first detector element was saturated during the readout are based on data from the second data set.

[0021] The recording of projection images by radiation is sufficiently known. The method is characterized in that two detector elements are read out and in the region in which the first detector element is saturated, information is ascertained, for example supplemented, with the second data set.

[0022] Other particularly advantageous designs and improvements of the present invention are revealed in the following description, wherein the claims of one claim category can also be improved similarly to the description parts and claims of other claim categories, and the individual features of different embodiments or variants can also be combined into new embodiments or variants.

[0023] In a preferred embodiment, the radiation source is an X-ray source or a particle radiation source. The imaging system is preferably an imaging system for medical technology, such as a radiological imaging system, in particular an imaging system for mammography.

[0024] The preferred imaging system comprises a correction unit, which is designed to correct at least one of the data sets. Here, the correction unit is preferably designed for at least one of the following corrections: noise suppression, pixel registration, cone beam magnification correction and / or spectral correction. Such correction units, in particular correction units in the form of software modules, are known per se. They are advantageous for use in the method according to the invention. If the correction is not applied to the first data set where the first detector module is saturated, computing time can be saved. It can also be advantageous that the correction is not applied to the second data set where the first data set is used to generate the projection image, at least when the second data set is not used at this time.

[0025] The preferred imaging system includes an image generation unit, which is designed to generate a projection image. It is more precisely designed to generate a first region, especially a central region, of the projection image by the data of the first data group. However, for example, when the data of the second data group contains other spectral information, the data of the second data group can also be used for this purpose. The second region, especially the edge region of the projection image is generated by the data of the second data group or by the data of the two data groups. Here, it is preferred to reconstruct the image data in which the first detector element is saturated by means of the data of the second data group, that is, the data of the second detector element. For this purpose, the data of the second data group can be simply used. However, the data of the second data group is scaled differently from the data of the first data group because the second detector element experiences different intensities. However, the data of the second data group can be scaled so that it matches the data of the first data group. For this purpose, the information of the first data group, such as changes in the region of the object, is used to determine a scaling function for the data and apply the scaling function to all data of the second data group (i.e., where the first detector element is saturated).

[0026] Preferably, the second detector element is designed to receive radiation with higher energy than the first detector element. This is advantageous because in the first detector element, mainly the radiation with low energy is completely absorbed. In addition, spectral information is obtained that can be used to generate a projection image.

[0027] Preferably, the first detector element is designed as an absorber. To this end, it should be noted that all materials in the beam path have an absorbing effect. This means that the detector element is designed as an absorber in addition to its function as a detector, for example in that the substrate for the detector material is designed to be thicker than a normal substrate. In particular, the detection layer of the detector element or the surface in or at the detection layer is designed so that the second detector element is not saturated at a predetermined beam intensity for image acquisition.

[0028] Preferably, the detector unit comprises an absorber plate between the first detector element and the second detector element, said absorber plate at least partially covering the second detector element, wherein the absorber plate is preferably removable or replaceable. As a result, the second detector element can be shielded in a targeted manner so that it does not saturate.

[0029] According to a preferred embodiment of the method, a first region of the projection image is generated from the first data set (information of the upper detector element). The first region shows the object, for example a body part, and in particular the central region of the projection image. In particular, the first region can also be generated with the aid of the second data set, if the second data set includes further spectral information.

[0030] The second region is in particular an edge region surrounding the central region and is generated from the second data set or a combination of both data sets. In the latter case, the first data set is preferably used to adapt the second data set to the first data set.

[0031] Preferably, the second region, in particular the edge region, is formed by weighted convolution of the two data sets or by scaling. This can be done in particular by using a convolution kernel to perform spectral filtering with subsequent weighting of the data of the second data set with the corresponding data of the first data set.

[0032] Particularly preferably, the total dose over the entire image is determined from the second data set and the first data set. This can be done, for example, by first matching the intensity measured by the second detector element in the second region, i.e., where the first detector element is saturated, to the first data set using the data of the first data set. The data in the second region then reflects the situation in which the first detector element is not saturated there. The total intensity can now be inferred from the curve of the data in the second region and extrapolated over the entire detector surface. This can be done using a formula determined by test measurements without a subject or using a system correction table.

[0033] According to a preferred embodiment of the method, the position and the signal profile at the surface of the recorded object are extracted from the second data set. This is in particular the position and the signal profile of the skin-air transition, for example at the chest. This information is then used to determine the corresponding signal profile from the first data set. Preferably, for this purpose, the lateral limits of the recorded object, in particular the skin-air transition, are determined and / or corrected based on the second data set. It should be noted here that the saturation of the first detector element "blurs" the information about the skin-air transition there.

[0034] Preferably, at least one of the data sets is corrected for geometric effects associated with the double-layer technique. In this case, preferably a pixel registration of the first data set to the second data set or vice versa is performed. Alternatively or in addition, a correction of the cone beam magnification can also be performed. It should be noted that the two detector elements are at different distances from the object and the source and that a cone beam is typically used.

[0035] Preferably, the recorded data set is spectrally corrected, in particular based on previously detected calibration data. Preferably, a correction for beam hardening is performed here. In this way, beam hardening effects due to the double-layer design of the detector unit can be compensated. For this purpose, in particular a priori knowledge can be used. Since the beam hardening of the detector unit is known, this can be used for the correction. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be described in detail again according to the embodiments with reference to the accompanying drawings. In this case, the same components are provided with the same reference numerals in different drawings. The drawings are usually not to scale. The drawings show:

[0037] Figure 1 An imaging system for recording a projection image is shown,

[0038] FIG. 2 shows recorded data according to the prior art,

[0039] Figure 3 shows a data set recorded according to the invention,

[0040] Figure 4 A method for recording a projection image using an imaging system according to the invention is shown. DETAILED DESCRIPTION

[0041] Figure 1 An imaging system 1 for recording projection images in the form of a radiography system 1 with a control device 2 is roughly schematically shown. The radiography system 1 usually has a radiation source 3, which is an X-ray source in this case, and during the radiographic recording irradiates a patient P so that the radiation impinges on a detector unit 4 located opposite the radiation source.

[0042] The detector unit 4 comprises two detector elements 4.1, 4.2 arranged in succession, which both cover the same recording area A. The radiation source 3 is set and the detector unit 4 is designed in such a way that the second detector element 4.2 is not saturated for the part of the recording area A in which the first detector element 4.1 is saturated during the irradiation. This can be done, for example, using a pre-recording of the patient P.

[0043] Only the components that are essential for explaining the present invention are shown in the control device 2. In principle, the radiography system 1 and the associated control device 2 are known to a person skilled in the art and therefore do not need to be explained in detail.

[0044] Control device 2 comprises a data acquisition unit 6 which is designed to record a first data set D1 of first detector element 4 . 1 and to record a second data set D2 of second detector element 4 . 2 , so that the two data sets D1 , D2 can be separated from one another.

[0045] In addition, the control device 2 comprises a correction unit 7 which is designed to correct at least one of the data sets D1 , D2 . The correction unit 7 is designed, for example, for noise suppression, pixel registration, correction of cone beam enlargement and / or spectral correction.

[0046] In addition, the control device 2 includes an image generation unit 8, which is designed to generate a projection image, a first area of ​​the projection image, in particular a central area, is generated by data from the first data group D1, and in particular also by data from the second data group D2, and a second area of ​​the projection image, in particular an edge area, is generated by data from the second data group D2 or by data from both data groups D1, D2.

[0047] FIG. 2 shows data recorded according to the prior art. A body region K, for example a breast, is irradiated from above with X-ray radiation. The radiation impinges on a detector unit 4, which consists of a single element, and detects a signal S, the profile of which is presented in graphical form. At the body part K, the detected signal S is low and rises towards the edge. In the region of the skin-air transition T, the signal S then rises so strongly that the detector unit saturates, which is indicated by the level profile of the signal.

[0048] Figure 3 2 shows a data set recorded according to the invention, in which the same body part as in FIG. 2 is recorded. However, in contrast to FIG. 2 , the data set is now recorded using the same method as in FIG. Figure 1 The detector unit 4 visible in FIG. 4 records and comprises two detector modules 4.1, 4.2. The upper image portion with the first detector module 4.1 shows the same signal S as in FIG. 2 as the first signal S, which is also to be expected since the intensity of the radiation is the same.

[0049] However, the lower image section with the second detector module 4 . 2 shows a significantly reduced intensity profile as the second signal S1 . It can be clearly seen that the intensity in the region of the air-skin transition T rises strongly until beyond this region and then drops.

[0050] If it is now assumed that the two signals S, S1 should show the same curve in the area of ​​the body part (more precisely, the two inner dashed lines), the second signal S1 can now be scaled so that it shows the same curve between the two inner dashed lines. If the other part of the second signal is scaled accordingly, it shows the curve that the first signal should actually have if the detector elements were not saturated.

[0051] Figure 4 Shown for use as in Figure 1 A method for recording a projection image using an imaging system such as that shown in FIG.

[0052] In step I, a body part K of a patient P is irradiated with a radiation source, wherein the two detector elements 4 . 1 , 4 . 2 of the detector unit 4 are irradiated through the body part K.

[0053] In step II, both detector elements 4 . 1 , 4 . 2 are read out and a first data set D1 is formed by reading out first detector element 4 . 1 and a second data set D2 is formed by reading out second detector element 4 . 2 .

[0054] In step III, a projection image is generated from the two data sets D1 , D2 , wherein the first data set D1 forms a central region in which the body part is imaged and the second data set D2 forms an edge region in which the first detector element is saturated.

[0055] Finally, it should be pointed out again that the invention described in detail above is only an embodiment, which can be modified in different ways by a person skilled in the art without departing from the scope of the invention. In addition, the use of the indefinite article "a" does not exclude that the features involved can also appear multiple times. Similarly, terms such as "unit" do not exclude that the components involved are composed of multiple co-acting subcomponents that can also be distributed spatially if necessary. The term "a certain number" should be interpreted as "at least one". Regardless of the grammatical gender of a particular term, people with male or female gender are included.

Claims

1. An imaging system (1) for recording a projection image, the imaging system (1) comprising a detector unit (4) and a radiation source (3), wherein the detector unit (4) has two detector elements (4.1, 4.2) arranged in succession, the two detector elements (4.1, 4.2) both covering the same recording area (A), and the radiation source (3) is set and / or the detector unit (4) is constructed so that for a portion of the recording area (A) in which the first detector element (4.1) is saturated during irradiation, the second detector element (4.2) is not saturated, wherein the imaging system (1) additionally comprises a data acquisition unit (6), the data acquisition unit (6) being designed to record a first data set (D1) of the first detector element (4.1) and a second data set (D2) of the second detector element (4.2) so that the two data sets (D1, D2) can be separated from each other.

2. An imaging system according to claim 1, wherein the radiation source (3) is an X-ray source or a particle radiation source, wherein the imaging system (1) is preferably an imaging system (1) for medical technology, in particular an imaging system for mammography.

3. The imaging system according to claim 1 , comprising a correction unit ( 7 ) designed to correct at least one of the data sets ( D1 , D2 ), preferably wherein the correction unit ( 7 ) is designed to perform at least one of the following corrections: - Noise suppression, - Pixel registration, - correction of cone beam magnification, and / or - Spectral correction.

4. An imaging system according to any one of the above claims, comprising an image generating unit (8), which is designed to generate a projection image, a first area of ​​the projection image, in particular a central area, is generated by data of the first data group (D1), and in particular also by data of the second data group (D2), and a second area of ​​the projection image, in particular an edge area, is generated by data of the second data group (D2) or data of both data groups (D1, D2), preferably wherein image data in which the first detector (4.1) is saturated is reconstructed with the aid of the second data group (D2).

5. The imaging system according to any of the preceding claims, wherein the second detector element (4.2) is designed to receive radiation of higher energy than the first detector element (4.1).

6. An imaging system according to any of the preceding claims, wherein the first detector element (4.1) is designed as an absorber and in particular wherein a detection layer of the first detector element (4.1) or a surface in or at the detection layer is designed such that, at a predetermined beam intensity for image recording, the second detector element (4.2) is not saturated, Preferably, the detector unit (4) comprises an absorber plate between the first detector element (4.1) and the second detector element (4.2), the absorber plate at least partially covering the second detector element (4.2), wherein the absorber plate is preferably removable or replaceable.

7. A method for recording a projection image using an imaging system (1) according to any one of the preceding claims, the method comprising the following steps: - irradiating a body part (K) of a patient with a radiation source (3), wherein two detector elements (4.1, 4.2) of the detector unit (4) are irradiated through the body part (K), - reading out two detector elements (4.1, 4.2) and forming a first data set (D1) by reading out the first detector element (4.1) and a second data set (D2) by reading out the second detector element (4.2), - generating a projection image from the two data sets (D1, D2), wherein the image values ​​in the projection image at which the first detector element (4.1) was saturated during the readout are based on data from the second data set (D2).

8. The method according to claim 7 , wherein a first, in particular central region of the projection image showing the body part (K) is generated from the first data set (D1) and in particular also from the second data set (D2), and a second region, in particular an edge region surrounding the central region, is generated from the second data set (D2) or a combination of the two data sets (D1, D2), wherein the second data set (D2) preferably matches the first data set (D1), Preferably, the second region, in particular the edge region, is formed by weighted convolution of the two data sets (D1, D2), or the second data set (D2) is scaled, in particular by spectral filtering using a convolution kernel or by subsequent weighting of the data of the second data set (D2) with the corresponding data of the first data set (D1), In this case, the total dose over the entire image is particularly preferably ascertained from the second data set (D2) and the first data set (D1).

9. The method according to claim 7 or 8, wherein the recorded positions and signal curves at the surface of the object, in particular the positions and signal curves of the skin-air transition (T), are extracted from the second data set (D2) and the information is used to determine the corresponding signal curve from the first data set (D1), In this case, preferably based on the second data set (D2) a lateral limit of the recorded object, in particular a skin-air transition (T) is determined and / or corrected.

10. A method according to any one of claims 7 to 9, wherein at least one of the data sets (D1, D2) is corrected with respect to geometrical effects associated with the double-layer technique, wherein preferably a pixel alignment of the first data set (D1) to the second data set (D2) or vice versa is performed, and / or a correction of cone beam magnification is performed.

11. The method according to claim 7, wherein the recorded data set (D1, D2) is spectrally corrected, in particular based on previously detected calibration data, preferably wherein a correction for beam hardening is performed.

12. A computer program product comprising instructions which, when the program is executed by a computer, cause the computer to perform the steps of the method according to claims 7 to 11, wherein the steps for irradiating or reading correspond to sending corresponding control commands.

13. A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to perform the steps of the method according to claims 7 to 11, wherein the steps for irradiating or reading correspond to sending corresponding control commands.

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