Method and apparatus for post-processing x-ray film

Abstract

The invention relates to a method for post-processing an X-ray film in X-ray data comprising a spectral photograph of a subject of an object, the method comprising the following steps: creating a first image from the X-ray film, in which first material of the object is highlighted and second material is suppressed, and creating a second image from the X-ray film, in which second material of the object is suppressed; the first material has a different spectral attenuation characteristic compared to a second material of the object,-creating a second image from the X-ray sheet, in which the second material is highlighted and the first material is suppressed,-post-processing the created image by means of a filter module, wherein the first image is post-processed by means of the first filter module and the second image is post-processed by means of the second filter module, the first material and the second material being shown,-outputting a total image. The invention also relates to a control device for an X-ray radiography system and an X-ray radiography system having such a control device.

Description

Technical Field

[0001] The invention relates to a method and an apparatus for post-processing an X-ray film, as well as a control device for an X-ray radiography system and an X-ray radiography system having such a control device. Background Art

[0002] Radiography is a common method used in medicine to take pictures of the inside of the body. X-rays radiate through the body onto a detector (formerly film) and produce an X-ray film or X-ray image, which is a projection of the body onto a flat surface. In addition to the original picture, it is also possible to record after the administration of a contrast medium (usually iodine), for example during angiography.

[0003] In order to enable a visual interpretation of an X-ray film, several image processing steps are usually performed. A rough separation of the image processing pipeline can be made by dividing it into natural law-based corrections (e.g. log(I / I0) or scattered beam correction), dynamic range compression (DRC) and (high frequency) detail enhancement (HFE).

[0004] The main motivation of the DRC step is to eliminate the low-frequency brightness modulation of the image caused by the varying projection thickness of the object. Here, the relative bone contrast within the object must be preserved. The standard method for this is to apply a low-pass filter (Gaussian filter or bilateral filter) and perform a nonlinear transformation on the image, which reduces its dynamic range, for example by applying an S-shaped transformation function. After the transformation, the remaining high frequencies are added again.

[0005] If the low-pass filter cannot completely separate the bone from the soft tissue structure, then the DRC automatically removes the low-frequency bone contrast in areas with less object thickness, which is a serious problem. Here, images of the limbs, such as images of the foot including toes, are particularly challenging because the background that must be balanced can vary greatly.

[0006] The main motivation for the HFE step is to improve diagnostically relevant structures compared to the anatomical noise and quantum noise background.

[0007] The following problem arises in both filtering methods: at the transition from areas with high contrast to areas with low contrast, systematic errors can occur during automatic filtering. This problem has not been solved to date. The only remedy is to reduce the intensity of the DRC or HFE, which usually results in a typical "analog" or "film-like" image appearance. Summary of the invention

[0008] The object of the present invention is to propose an alternative, more comfortable method for post-processing X-ray films and a corresponding device, by means of which the above-mentioned disadvantages are avoided.

[0009] This object is achieved by a method according to the invention, an apparatus according to the invention, a control device according to the invention and an X-ray radiography system according to the invention. The method according to the invention is used for post-processing X-rays in X-ray radiography data, which include spectral photographs of the subject of an object, for example a body region of a patient. X-ray systems that are capable of recording such spectral data are in particular X-ray systems with photon counting detectors, X-ray systems with double-layer detectors or multi-layer detectors, X-ray systems that record two consecutive images with different beam energies (kV) and / or filters.

[0010] The method comprises the following steps:

[0011] - creating a first image from the X-ray film, in which a first material of the object is highlighted and a second material is suppressed, the first material having different spectral attenuation characteristics than the second material of the object,

[0012] - creating a second image from the X-ray film, in which second image the second material is highlighted and the first material is suppressed,

[0013] - post-processing the created images by means of filter modules, wherein the first image is post-processed by means of a first filter module and the second image is post-processed by means of a second filter module,

[0014] - merging the post-processed images into an overall image in which the first material and the second material are shown,

[0015] - Output the total image.

[0016] The creation of images is known in principle to a person skilled in the art. In the case described here, X-rays are present as raw data (e.g., projection images) and the material decomposition is performed based on these X-rays. In a simplified manner, it can be assumed here, for example, that the object consists of only two materials. Two images are then created (material-decomposed).

[0017] Usually, there are two or more original images in the spectral photograph of the subject, and the original images show the subject at different beam energies. There can also be a data set, which has a vector consisting of two or more image values ​​at each pixel position. When creating an image, the image value of each pixel of the created image is usually calculated by linking the corresponding pixels based on the original image (or vector entry). However, it is also possible to observe the pixel group around the corresponding pixel of the original image for each pixel of the generated image. Preferably, the calculation includes weighted subtraction, in which, for example, from the values ​​A and B of the pixels corresponding to each other of the two original images, the value X of the corresponding pixel of the created image is calculated with coefficients a and b by means of the formula X=aA-bB. The coefficients are preferably weights here. In addition to subtraction, nonlinear merging of input values ​​can also be calculated. Optionally, a lookup table can also be used instead of an analysis function.

[0018] In this case, (at least) two images are created, which differently show the two materials of the recorded object. The two materials differ in that the first material has different spectral attenuation properties than the second material (e.g. absorbs more radiation). Preferably, the first material is bone material or a contrast agent (e.g. iodine) and the second material is tissue.

[0019] In the first image, a first material (e.g. bone) is highlighted and a second material (e.g. surrounding tissue) is suppressed, in the second image, in contrast, the second material (e.g. tissue) is highlighted and the first material (e.g. bone) is suppressed. In the example of bone or tissue, the first image can be referred to as a "bone image" and the second image can be referred to as a VNBC image (VNBC: "Virtual Non-Bone Contrast"). In this context, it should be noted that, in contrast to a "Virtual Non-Calcium" image (VNCa image), with regard to the present invention, the following decomposition is preferably shown, in which the local calcium contrast is replaced by water and is not set to 0. A setting of "0" (as is usually done in the prior art) usually shows a negative contrast in the projected image, which can be disadvantageous here.

[0020] Since we are discussing images here, it goes without saying that "highlighting" or "suppressing" a material corresponds to "highlighting" or "suppressing" the image information of the material. For example, the pixel values ​​of an image can be reduced to suppress a material or enhanced to highlight the material. In an inverted image, the opposite may be true.

[0021] The created images (the first image and the second image and optionally the other images) are then post-processed with the aid of a filter module. The filter module preferably comprises the above-mentioned DRC filter and HFE filter, i.e. a compressor and a filter for detail enhancement. As described in the introduction, the application of these filters to images is known in the prior art. The difference from the prior art is that the two images are generated by (physical) material decomposition (rather than by image-based decomposition) and the first image is post-processed with the aid of a first filter module and the second image is post-processed with the aid of a second filter module. Therefore, these filter modules can be optimized for the type of image, i.e. differentiated. For example, the first filter module can comprise a DRC filter and an HFE filter that have been optimized for bone images, and the second filter module comprises a DRC filter and an HFE filter that have been optimized for VNBC images. In addition, other images can also be post-processed with the aid of other filter modules, wherein each filter module should be used for an image (preferably for an image type) for which the filter module has been optimized.

[0022] After each image has been post-processed and thus subjected in particular to optimal filtering, the post-processed images are merged into a total image. The post-processed image represents at least the first image and the second image after their post-processing. Further post-processed images can be added, which can however also be merged into a further total image. Since the first material (e.g. bone) is highlighted in the first image and the second material (e.g. tissue) is highlighted in the second image, the total image shows the first material as well as the second material (i.e. bone with surrounding tissue). The total image is then output, for example for evaluation by a person.

[0023] The device according to the invention is used for post-processing of radiographs in radiographic data, said radiographic data comprising a spectrograph of a subject of an object. Preferably, said device is designed to carry out the method according to the invention and comprises the following components:

[0024] an imaging unit designed to create a first image from an X-ray film, in which a first material of the object is emphasized and a second material is suppressed, the first material having different spectral attenuation characteristics than the second material of the object, and the imaging unit designed to create a second image from the X-ray film, in which the second material is emphasized and the first material is suppressed,

[0025] a post-processing unit designed to post-process the created images by means of filter modules, wherein the first image is post-processed by means of a first filter module and the second image is post-processed by means of a second filter module,

[0026] a merging unit designed to merge the post-processed images into an overall image, in which the first material and the second material are shown,

[0027] An output unit, which is designed to output the overall image.

[0028] The functions of the components have already been described above within the scope of the method. The device is particularly preferably (specifically) designed to carry out the method according to the invention.

[0029] A control device according to the invention for controlling an x-ray radiography system comprises the device according to the invention and / or is designed to carry out the method according to the invention.

[0030] The X-ray radiography system according to the invention comprises a control device according to the invention.

[0031] Most of the aforementioned components of the device can be implemented completely or partially in the form of software modules in a processor of a corresponding computing system, for example by a control device of an X-ray radiography system. The implementation using software to a large extent has the advantage that computing systems that have been used so far can also be converted in a simple manner by a software upgrade in order to operate in the manner according to the invention. In this regard, the object is also achieved by a corresponding computer program product with a computer program that can be directly loaded into a computing system and has program steps so that when the program is run in the computing system, the steps of the method according to the invention are implemented, at least the steps that can be implemented by a computer. Such a computer program product can optionally include additional components such as documentation and / or additional components in addition to the computer program and also hardware components such as a hardware key (dongle, etc.) for using the software.

[0032] For transport to a computing system or control device and / or for storage at or in a computing system or control device, a computer-readable medium can be used, such as a memory stick, a hard disk or other transportable or permanently mounted data carrier, on which program segments of a computer program that can be read in and run by a computing system are stored. For this purpose, a computing system can, for example, have one or more cooperating microprocessors or the like.

[0033] Further particularly advantageous designs and improvements of the invention are apparent from the following description, in which embodiments of one embodiment category can also be improved in a similar manner to embodiments and description parts of another embodiment category, and in particular individual features of different embodiments or variants can also be combined into new embodiments or variants.

[0034] According to a preferred method, the first material is bone and / or a contrast agent, in particular iodine. The second material is preferably (surrounding) tissue. Preferably, the first image is constructed to highlight the patient's bone and / or the contrast agent and suppress information about the patient's surrounding tissue. Preferably, the second image is constructed to highlight the patient's tissue and suppress information about the patient's bone and / or the contrast agent.

[0035] As previously described, when highlighting a material, the image value of the pixel showing the material is increased (or decreased in an inverted image). When suppressing a material, the image value of the pixel showing the material is decreased (or increased in an inverted image).

[0036] According to a preferred method, in a spectrophotograph of a subject (e.g. a body region of a patient), a plurality of raw images are present as X-rays or are created. The first image and the second image are then calculated by a plurality of weighted subtractions of the two raw images, wherein the weighting coefficients each define which material is highlighted and which is suppressed in these images. This can be done, for example, for individual pixels by means of the above-mentioned function X=aA-bB, where a and b are weighting coefficients. The two images are created here from the same raw image.

[0037] According to a preferred method, the second image shows a decomposition of the original image, wherein local contrast, in particular calcium contrast and / or contrast agent contrast, in particular iodine contrast, is virtually replaced by water. This has the advantage, as described above, that negative contrast is prevented.

[0038] According to a preferred method, at least two different beam energies of the spectrogram are generated by a plurality of accelerating voltages, which differ by at least 30 kV, in particular by at least 50 kV. Alternatively or in addition (for example when irradiating with a broad X-ray spectrum), the average beam energy preferably differs by at least 30 keV, in particular by at least 50 keV.

[0039] According to a preferred method, the filter module comprises a compressor (DRC filter) which compresses the dynamic range of the image. The compressor eliminates low-frequency brightness modulations of the image, which are caused by the varying projection thickness of the object. The standard method for this is to apply a low-pass filter (Gaussian or bilateral) and perform a nonlinear transformation on the image, for example by applying a sigmoid transformation function, which reduces its dynamic range. After the transformation, the remaining high frequencies are added again.

[0040] According to a preferred method, the filter module comprises a detail enhancement filter ("HFE filter", which stands for "High Frequency Feature Enhancement"). The HFE filter improves the diagnostically relevant structure compared to the anatomical noise and quantum noise background. Preferably, the serial application (Serienanwendung) of the compressor (DRC filter) and the detail enhancement filter (HFE filter) is also preferred.

[0041] According to a preferred method, the filter module comprises a denoising filter. Such filters are known in the art.

[0042] According to a preferred method, the first filter module is different from the second filter module. The filter modules should be optimized for the images to which they are applied. Therefore, the first filter module for the first image should be optimized for the first structure, that is, optimized for the structure with relatively strong absorption. The second filter module for the second image should be optimized for the second structure, that is, optimized for the structure with relatively weak absorption. It is preferred that the filter modules have filters of the same type and / or filters of the same architecture, but the parameters of the filters are different. A preferred example is that both filters have a DRC filter and an HFE filter (and optionally also a denoising filter), and the filters are also applied in the same order in particular.

[0043] For the method according to the invention, preferably an AI-based method (AI: "artificial intelligence") is used. Artificial intelligence is based on the principle of machine learning and is usually performed with the aid of correspondingly trained learning algorithms. The English expression "Machine Learning" is often used for machine learning-based methods, which also includes the principle of "deep learning". For example, a deep convolutional neural network (DCNN) is trained in the following aspects: a first image and a second image are created from two X-ray films as original images. However, the filter module or the filter of the filter module can also be realized by AI.

[0044] Preferably, the components of the present invention, in particular the image unit and / or the post-processing unit, are present as a "cloud service". Such a cloud service is used to process data, in particular with the aid of artificial intelligence, but can also be a service based on conventional algorithms or a service that is evaluated by a person in the background. In general, a cloud service (hereinafter referred to as "the cloud") is an IT infrastructure in which, for example, storage space or computing power and / or application software are provided via a network. The communication between the user and the cloud takes place here with the aid of a data interface and / or a data transmission protocol. In the present case, it is particularly preferred that the cloud service provides both computing power and application software.

[0045] Within the scope of a preferred method, data are provided to a cloud service via a network. The cloud service includes a computing system, such as a computer cluster, which usually does not include a local computer of the user. The cloud can be provided in particular by a medical device that also provides a medical technology system. For example, the data of the image recording is sent to a (remote) computer system (cloud) via a RIS (Radiology Information System) or a PACS. Preferably, the computing system, the network and the (medical technology) system of the cloud are a complex in the sense of data technology. The method can be implemented in the network with the help of an instruction cluster (Befehlskonstellation). The data calculated in the cloud ("result data") are then sent again to the local computer of the user via the network. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Below, the present invention is described in detail again according to an embodiment with reference to the drawings. In the different drawings, the same components are provided with the same reference numerals. The drawings are generally not to scale. The drawings show:

[0047] Figure 1 An example of an X-ray radiography system having a control device according to the present invention is shown;

[0048] Figure 2 A simplified diagram showing image post-processing according to the prior art;

[0049] Figure 3 A simplified diagram shows image post-processing according to the method according to the invention. DETAILED DESCRIPTION

[0050] Figure 1 A roughly schematic diagram shows an X-ray radiography system 1 having a control device 2. The control device is equipped with a device 5 designed to carry out the method according to the invention. The X-ray radiography system 1 usually has a radiation source 3, which here represents an X-ray source, and during the X-ray recording, the patient P is fluoroscopically imaged so that the radiation impinges on a detector 4 which is respectively opposite the radiation source 3. The X-ray radiography system 1 is designed here to produce spectroscopic images and is, for example, a system which can generate two different accelerating voltages for the radiation or has a detector 4 which can measure energy-resolved. The X-ray radiography system 1 can also include a selective filter which can be used to filter the two different beam energies.

[0051] Only the components that are essential for explaining the present invention are shown in the control device 2. In principle, the x-ray system 1 and the associated control device 2 are known to a person skilled in the art and do not require a detailed explanation.

[0052] The control device 2 comprises a device 5 for post-processing radiographs R in radiographic data, which comprise spectral radiographs of a subject M of an object P, for example a body region M of a patient P shown here, at two different beam energies.

[0053] The device comprises an image unit 6, a post-processing unit 7, a merging unit 8 and an output unit 9, which can be implemented via a simple data interface. Figure 3 .

[0054] The imaging unit 6 is designed to create at least two different images B1, B2 from the X-ray film R. The first image B1 here prominently shows the bones of the patient P, while the tissue is suppressed. In contrast, the second image B2 shows the tissue and less bones. However, instead of bones, contrast agents such as iodine can also be used.

[0055] The post-processing unit 7 is designed to post-process the created patterns B1, B2 with the aid of filter modules F1, F2, wherein the first image B1 is post-processed with the aid of the first filter module F1 and the second image B2 is post-processed with the aid of the second filter module F2. The filter modules F1, F2 can be completely different here, which is a special advantage of the present invention. That is, each of the images B1, B2 can be post-processed with the aid of filter modules F1, F2 optimized for these images B1, B2. It is preferred that the filter modules F1, F2 have filters D1, D2, H1, H2 of the same type and / or filters D1, D2, H1, H2 of the same architecture, but the parameters of the filters D1, D2, H1, H2 are different.

[0056] The merging unit 8 is designed to merge the post-processed images B1 , B2 into a total image G. The first material and the second material are shown in the total image.

[0057] The output unit 9 is used to output the overall image G, for example, for diagnosis.

[0058] Figure 2 A simplified diagram of image post-processing according to the prior art is shown. In the example shown, an X-ray film R (all recorded images) is post-processed with the aid of the same filters D, H.

[0059] Figure 3 An example of a method according to the invention for post-processing a spectral radiograph R in radiographic data is shown schematically, for example by means of a Figure 1The X-ray system 1 records at two different beam energies. Two raw images R1 , R2 are generated as X-ray films R, which are shown on the far left. The beam energies should be far apart and not overlap, so that different information is present in the raw images R1 , R2 .

[0060] Now, a first image B1 and a second image are created from the original images R1, R2 by means of the image unit 6, and a specific material is suppressed or highlighted in this case. In the present example, the first material is bone and the second material is surrounding tissue. The first image B1 is constructed in this case so that the bone is highlighted and the information of the surrounding tissue of the patient P is suppressed, and the second image B2 is constructed so that the tissue is highlighted and the information of the bone is suppressed.

[0061] Subsequently, the created images B1, B2 are post-processed by means of filter modules F1, F2 of the post-processing unit 7. In the present example, each filter module F1, F2 comprises a compressor D1, D2 (or a DRC filter D1, D2) and a detail enhancement filter H1, H2 (or an HFE filter H1, H2), wherein the compressor D1, D2 compresses the dynamic range of the pattern. Here, the first image B1 is post-processed by means of the first filter module F1 and the second image B2 is post-processed by means of the second filter module F2.

[0062] After the post-processing, the post-processed images B1 , B2 are merged into a whole image G by means of a merging unit 8 and output.

[0063] Finally, it should be pointed out again that the drawings described in detail above only relate to embodiments, which can be modified in various 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" or "an" does not exclude that the relevant features can also exist multiple times. Similarly, the terms "unit" and "device" do not exclude that the relevant components can be composed of multiple co-acting subcomponents, which can optionally also be spatially distributed. The expression "multiple" is understood to mean "at least one". Regardless of the grammatical part of speech of a particular term, people with male or female gender are included.

Claims

1. A method for post-processing radiographs (R) in radiographic data, the radiographic data comprising a spectrogram of a subject (M) of an object (P), the method comprising the following steps: - creating a first image (B1) from the X-ray film (R), in which a first material of the object (P) is highlighted and a second material is suppressed, the first material having different spectral attenuation characteristics compared to the second material of the object (P), - creating a second image (B2) from said X-ray film (R), in which said second material is highlighted and said first material is suppressed, - post-processing the created images (B1, B2) by means of filter modules (F1, F2), wherein the first image (B1) is post-processed by means of a first filter module (F1) and the second image (B2) is post-processed by means of a second filter module (F2), - merging the post-processed images (B1, B2) into a total image (G) in which the first material and the second material are shown, - Outputting the total image (G).

2. A method according to claim 1, wherein the first material is bone and / or a contrast agent and the second material is surrounding tissue, wherein the first image (B1) is constructed so as to highlight the bone of the patient (P) and / or the contrast agent and suppress information about the surrounding tissue of the patient (P), and wherein the second image (B2) is constructed so as to highlight the tissue of the patient (P) and suppress information about the contrast agent and / or the bone of the patient (P).

3. A method according to any of the above claims, wherein multiple original images (R1, R2) exist or are created as X-ray films (R) in a spectral photograph of the subject (M), and the first image (B1) and the second image (B2) are calculated by multiple weighted subtractions of the two original images (R1, R2), wherein the weight coefficients respectively define which materials are highlighted and which materials are suppressed in these images (B1, B2).

4. The method according to claim 1, wherein the second image (B2) shows a decomposition of the original image (R1, R2), wherein local contrast, in particular calcium contrast and / or contrast agent contrast, is virtually replaced by water.

5. The method according to claim 1 , wherein the X-ray film (R) is recorded by means of an X-ray system, the X-ray system - have a photon counting detector, and / or -Having dual-layer detectors, and / or - having multiple layers of detectors, and / or - the X-ray system records two consecutive images with different beam energies, and / or The X-ray system records two consecutive images by means of different filters.

6. A method according to any one of the above claims, wherein the filter module (F1, F2) includes a compressor (D1, D2) and / or includes a detail enhancement filter (H1, H2) and / or includes a denoising filter, the compressor (D1, D2) compresses the dynamic range of the image, and preferably the filter module includes a series application of a compressor (D1, D2) and a detail enhancement filter (H1, H2).

7. A method according to any one of the above claims, wherein the first filter module (F1) is different from the second filter module (F1), preferably, wherein the filter module (F1) has the same type of filters (D1, D2, H1, H2) and / or filters of the same architecture (D1, D2, H1, H2), but the parameters of the filters (D1, D2, H1, H2) are different.

8. A device (5) for post-processing radiographs (R) in radiographic data, the radiographic data comprising a spectrograph of a subject (M) of an object (P), the device comprising: - an imaging unit (6) designed to create a first image (B1) from the X-ray film (R), in which a first material of the object (P) is highlighted and a second material is suppressed, the first material having different spectral attenuation characteristics than the second material of the object (P), and the imaging unit (6) is designed to create a second image (B2) from the X-ray film (R), in which the second material is highlighted and the first material is suppressed, a post-processing unit (7) designed to post-process the created images (B1, B2) by means of filter modules (F1, F2), wherein the first image (B1) is post-processed by means of a first filter module (F1) and the second image (B2) is post-processed by means of a second filter module (F2), a merging unit (8) designed to merge the post-processed images (B1, B2) into a total image (G) in which the first material and the second material are shown, - an output unit (9), which is designed to output the overall image (G).

9. A control device (2) for controlling a radiographic system (1), comprising an apparatus (5) according to claim 8 and / or being designed to carry out a method according to any one of claims 1 to 7.

10. A radiographic system (1) comprising a control device (2) according to claim 9.

11. A computer program product comprising instructions which, when the program is run by a computer, cause the computer to carry out the steps of the method according to any one of claims 1 to 7.

12. A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to implement the steps of the method according to any one of claims 1 to 7.

Images