KR20130119875A - Automatic calculation of two- or three-dimensional ct-images - Google Patents

Abstract

The present invention relates to a method for automatically calculating image data (PIC) of an examination object from measurement data (MEAS) previously detected during a relative rotational movement between radiation sources (C2, C4) of a computed tomography system (C1) and the examination object. The image data (PIC) to be calculated are intended to show a section along a certain plane defined with respect to the examination object. At least a temporary image (PIC PLAN) captured by the computed tomography system is examined on the basis of the positions of several landmarks (ADAPT). On the basis of the landmark study, a change in position is measured. From the measurement data (MEAS), one or more cross-sectional images are reconstructed and show the examination object in planes perpendicular to the axis of rotation of the computed tomography system. Finally, the image data (PIC) is calculated using the one or more cross-sectional images and the change in position (RECON).

Description

Automatic calculation of two- or three-dimensional CT-images {AUTOMATIC CALCULATION OF TWO- OR THREE-DIMENSIONAL CT-IMAGES}

The present invention relates to a method for automatically calculating image data of an examination subject from measured data detected during relative rotational movement between a radiation source and an examination subject of a computed tomography system.

The tomography imaging method is characterized in that the internal structures of the examination subject can be examined without the need for invasive intervention on the examination subject. One possible tomographic imaging method is to obtain multiple projections of varying angles from the object to be inspected. From these projections, a two-dimensional cross-sectional image or a three-dimensional volume image of the inspection object may be calculated.

One example of such a tomography imaging method is computed tomography . Various methods are known for scanning a test subject using a CT-device. For example, circular scanning, continuous circular scanning or helical scanning with forward movement is applied. Absorption data of the examination subject is recorded at various imaging angles using at least one X-ray source and at least one opposing detector, and the absorption data or projections collected in this way are obtained by a corresponding reconstruction method. It is calculated from the cross-sectional images of the inspection object.

The cross-sectional images of the inspection object are reconstructed from the measurement data of the computed tomography apparatus. These cross-sectional images show the inspection object in planes, which planes lie perpendicular to the axis of rotation of the computed tomography device; The cross-sectional images are represented as axial images. From the plurality of axial images, cross-sectional images of inclined planes can be calculated. This situation is particularly necessary when the inspection object is not symmetrically positioned in the computed tomography device during measurement, or when the parts of the inspection object, in particular, the object to be photographed, are difficult to see in the axial images.

It is an object of the present invention to present a method for automatically calculating CT-images, wherein the image data to be produced shows a cross section along a specific plane defined in relation to the examination object. In addition, the present invention provides a corresponding computing device, CT device, computer program and data medium for a computer program.

The problem is solved by the method having the features of claim 1 and by the computing device, the CT device, the computer program and the data medium having the features of the dependent claims. Preferred embodiments and refinements are the subject of the dependent claims.

In the method according to the invention for automatically calculating the image data of the inspection object from the measurement data, the measurement data has been previously detected in the relative rotational movement between the radiation source of the computed tomography apparatus and the inspection object. The image data to be produced shows a cross section along a specific plane defined with respect to the inspection object. At least one preliminary image detected by the computed tomography apparatus is inspected based on the plurality of landmark positions, and the position variation value is determined with reference to the landmark inspection. From the measurement data, one or more cross-sectional images are shown which show the inspection object in planes perpendicular to the axis of rotation of the computed tomography device. Image data is calculated using the one or more cross-sectional images and position variation values.

The method may be implemented by an image reconstruction apparatus. This method implementation process is automatic, i.e. the mentioned steps do not require user interaction.

As a final image, an image corresponding to a specific cross section of the inspection object should be derived. Examples are axial cross-sectional images, sagittal cross-sectional images or coronal cross-sectional images; Inclined, ie obliquely inclined planes are also possible. The planes are independent of the computed tomography device because they are defined in relation to the inspection object.

In order to obtain the desired image, one or more preliminary images are examined. As the preliminary images, one or a plurality of topograms and / or one or a plurality of cross-sectional images of a test subject may be used. These preliminary images were also obtained by measurement of the computed tomography apparatus, that is, the preliminary images were the same as during the detection process of the measurement data (from which the image data is calculated) relative to the computed tomography apparatus. Position the target to be examined. The expression preliminary images is in that the images are not used for the direct calculation of the image data, but rather only for the preparation step of this calculation, i.e., the position variation value determination step.

The preliminary image (s) are cited in the landmark inspection. As landmarks, prominent points are used that can be automatically found within the images, for example distinct structures. Which landmarks are used depends on the cut-out of the observed subject. Preferably, basically the same landmarks are quoted regardless of the object being inspected. Landmark inspection aims to determine the position variation value. The position variation value can be handled with movement and / or rotation. Preferably the positional variation is three dimensional.

The image data to be calculated is obtained from one or more cross-sectional images of the inspection object, each of which corresponds to a cross section perpendicular to the axis of rotation. In calculating the image data as described above, a position variation value is inserted. For example, if the position variation value corresponds to a specific tilting, the same tilting can be executed in the cross-sectional image likewise for calculating the image data.

It is particularly desirable that during landmark inspection two landmarks are interconnected and the orientation of the connecting line is compared with one particular orientation. Such measures are preferably applied in connection with multiple pairs of landmarks. The specific orientation is preferably a predetermined orientation and is irrelevant to the inspection object. In a refinement of the invention, the position variation of the connecting line is made parallel to the specific orientation in order to determine the position variation value. In practice, this movement does not have to be made; It is enough if it is determined what movement is necessary to reach parallelism. This applies correspondingly to forming connecting lines, ie the lines do not actually need to be displayed in the image; If a line exists, it is sufficient to compare how such a line lies in relation to a particular orientation.

Preferably the specific plane defined in relation to the inspection object can be determined in advance. Such planar predetermination may be made by, for example, a user request. Alternatively there may basically be one particular plane.

The computing device according to the invention is used for the purpose of reconstructing the image data of the inspection object from the measurement data of the CT device. The computing device has means for implementing the method described above. In particular, the computing device may comprise a program memory for storing program code, wherein program code of a computer program is present in the program memory, in some cases, among other things, the program code being the computer program. When executed on this computer it is suitable for carrying out or causing or controlling such a method as described above. The computing device can also be implemented by a number of devices that are coupled together and present in different locations from each other. This process corresponds to the process of assigning a function of a computing device to a plurality of components. Preferably, the computing device may additionally control the measurement process of the CT device.

The CT device according to the invention comprises such a computing device. The CT device may also comprise other components necessary for the detection of the measurement data, for example.

The computer program according to the present invention has a program code, which causes the computer program to carry out the method of the type described above when the computer program is executed on a computer.

The data medium according to the present invention, which can be read by a computer, stores program code of a computer program, which program code causes to execute the method of the type described above when the computer program is executed on a computer.

The invention is explained in more detail below with reference to examples.
1 is a first schematic diagram of an embodiment of a computed tomography apparatus having an image reconstruction component,
2 is a second schematic diagram of an embodiment of a computed tomography apparatus having an image reconstruction component;
3 is a diagram of a series of processes for image generation,
4 shows two topograms,
5 is one topogram and three CT-section images, and
6 is four CT-section images.

1 schematically shows a first computed tomography apparatus C1 having an image reconstruction apparatus C21 first. The computed tomography device is associated with a so-called third generation CT-device, but the invention is not limited to the CT-device. Inside the gantry housing C6 is a closed gantry, which is invisible in this drawing, with a detector C3 facing the first X-ray tube C2 on the gantry. It is. Optionally, a second X-ray tube C4 is disposed with the opposite detector C5 inside the CT device shown in this figure, so that better time resolution can be achieved by an additionally provided radiator combination / detector combination. Alternatively, a "dual-energy" -inspection may also be performed inside the emitter system / detector system when using different X-ray energy spectra.

The CT-device C1 also has a patient bed C8, on which the patient can be moved into the measurement field along the axis C9 of the CT-device, also indicated by the z-axis at the time of examination. However, as a pure circular scan, the injection itself may only occur in the examination area to be taken without the patient moving. Movement of the patient bed C8 relative to the gantry is caused by suitable motorization. During this movement, the X-ray source C2 or C4 rotates around the patient, respectively. At this time, the detectors C3 or C5 rotate together in parallel with the X-ray source C2 or C4 to detect the projection measurement data, in which case the projection measurement data is used for reconstruction of the cross-sectional images. Alternatively, there is, of course, the possibility of a helical scan, in which the patient passes through the examination field step by step between the individual scan processes, in which case the CT-device can be used during the rotational scan by X-ray radiation. Along the axis C9, it passes continuously through the inspection field between the X-ray tube C2 or C4 and the detector C3 or C5. Helix relative to the patient during the measurement for the X-ray source C2 or C4 during a spiral scan by the movement of the patient along the axis C9 and by the rotation of the X-ray source C2 or C4 which occurs simultaneously. A helix path is created. This path can also be achieved by moving the gantry along axis C9 when the patient is not moving. Furthermore, the patient may reciprocate between two points continuously and in some cases periodically.

The CT device C1 is controlled by the control and computing device C10 having computer program codes Prg ₁ to Prg _n present in the memory. As mentioned, of course, the computer program codes Prg ₁ to Prg _n may also be included in an external memory medium and, if necessary, also in the control and computing device C10.

 In order to drive control the CT device according to a particular measurement protocol, acquisition control signals AS are transmitted from the control and computing device C10 via a control interface 24. Can be. Acquisition control signals AS in this case are associated with, for example, X-ray tubes C2 and C4, gantry and table advancement movements, in which case the power of the X-ray tube and its switch-on and switch-off points will be defined. And the rotational speed of the gantry can be defined.

Since the control and arithmetic device C10 has an input console, the measurement parameters can be input by a user or an operator of the CT device, in which case the measurement parameters are captured control signals AS. Control data detection in the form of). Information about the measurement parameters currently being used can be displayed on the screen of the control- and computing device C10; In addition, additional information important to the operator can be displayed.

The projection measurement data p or raw data obtained by the detector C3 or C5 is transferred to the control- and computing device C10 via a raw data interface C23. In this case, the raw data p is optionally processed in the image reconstruction part C21 after appropriate preprocessing. In this embodiment the image reconstruction component C21 is implemented in software form, for example in the form of one or a plurality of computer program codes Prg ₁ to Prg _n , on a process in the control- and computing device C10. Regarding image reconstruction, computer program codes Prg ₁ to Prg _n can also be included in the external memory means as described previously in connection with the measurement process control and, if necessary, also in the control- and computing device C10. have. In addition, measurement process control on the one hand and image reconstruction on the other hand can be implemented by different computing devices.

In this case the image data f reconstructed by the image reconstruction component C21 is stored in the memory C22 of the control- and computing device C10 and / or in a conventional manner. Is displayed on the screen. The image data can also be supplied to a power supply, for example a radiation information system (RIS), connected to a computer tomography apparatus C1 via an interface not shown in FIG. It may be stored in measurement memory accessible from an information system or may be output as an image.

The control and computing device C10 may additionally perform an electrocardiogram (ECG) function, in which case line C12 is used to derive the ECG-potential between the patient and the control and computing device C10. In addition, the CT-device C1 shown in FIG. 1 also has a contrast agent injector C11, through which the contrast agent can be further injected into the patient's circulating blood, for example, in a patient's blood vessels, In particular, the ventricles of the pulsating heart can be better represented. In addition to this, perfusion measurement may be performed, and the proposed method is suitable for the perfusion measurement.

The control- and computing device C10 does not have to be located close to the remaining parts of the CT device C1-as shown in FIG. 1. Rather, the control- and computing device C10 can be installed in another space or in a farther place. The transfer of raw data p and / or acquisition signal AS and / or ECG-data may be via a line or alternatively via a wireless system.

FIG. 2 shows a C-arm-system, in which case the housing C6 supports the C-shaped arm C7, unlike the CT-device of FIG. On the arm is fixed an X-ray tube C2 on the one hand and a detector C3 opposite the X-ray tube on the other hand. The C-shaped arm C7 likewise pivots about the device axis C9 for scanning, so that scanning of multiple scanning angles can occur and corresponding projection data p of multiple projection angles can be detected. Can be. The C-shaped arm device C1 of FIG. 2 has a control and arithmetic device C10 of the type shown in FIG. 1, like the CT device of FIG. 1.

The present invention can be used in the two systems shown in FIGS. 1 and 2. The invention can also be used for other CT-systems which are fundamentally different, eg CT-systems with detectors forming one complete ring.

The following starts from the fact that the present invention refers to a patient as a human without limiting generality.

By CT-image reconstruction, the cross-sectional images are formed in a plane perpendicular to the z-axis of the measuring device. This content is referred to below as 2D reconstruction. From such multiple 2D images cross-sectional images of any orientation can be calculated, which is denoted as 3D reconstruction. A suitable method for this reconstruction is for example Multi Planar Reformatting (MPR).

The operator of the CT-device typically seeks to photograph an axial cross-sectional image, a sagittal cross-section image or a coronal cross-sectional image of a patient. The coronal plane, also referred to as the frontal plane, is a plane parallel to the patient's front view; The sagittal plane lies perpendicular to the coronal plane and parallel to the side view of the body; The axial plane, also referred to as the transverse plane or horizontal plane, lies perpendicular to the longitudinal axis of the body. These provisions are independent of the geometric measurement structure, i.e. the position of the z-axis of the CT-device, but rather the geometry or anatomy of the patient's body.

However, a situation often arises during which the orientation of the patient is not symmetrical with respect to the measuring device, ie the longitudinal axis of the patient is not parallel to the z-axis. In this case, when the cross-sectional image is calculated from the measurement data, the cut plane is inclined at an angle to the patient's axial cut plane, sagittal cut plane or coronal cut plane. Thus, the above results do not correspond to the results desired by the user. The user must reconstruct the image anew, with the image plane lying obliquely with respect to the image plane of the original image.

The same situation occurs if the user wants a particular cross section of the trachea, but the trachea is inclined obliquely due to the patient's anatomical body structure. Even in such a case, one image is first reconstructed, in which case the user observes the image and confirms that the organ has not been imaged as desired in order to cause a new image calculation of the plane inclined at an angle to the original cut plane.

It should be noted that there may be a particular input image in the form of a cutting plane that is inclined at an angle to the z-axis, ie a thin film image having a soft core, for image calculation. Because of this, the user must decide whether an image in the form of an obliquely inclined cutting plane is required before image reconstruction, i.e. 2D or 3D reconstruction should occur. In other words, the user must make this determination when information on whether or not such a type of obliquely slanted cut surface is needed is generally not provided.

One possibility of matching native CT incisions to the patient's anatomical body structure is mechanical tilting of the gantry. However, tilting is generally only possible in certain directions-forward and backward when looking towards the gantry-and also only in certain ranges. Since the determination as to whether or not to be measured using a tilted gantry must already be made before the measurement, the above-mentioned problems with nonsymmetrical placement and unpredictable patient anatomical body structure cannot be solved.

Therefore, in such a situation, it is necessary to determine in advance which image reconstruction mode the user prefers, ie, 2D or 3D. Obtained images often have to be manually matched to anatomical body structures.

3 shows a diagram of a series of procedures for image generation described below. In this process, the determination of which type of reconstruction is to be used, i.e. whether 2D or 3D reconstruction is to be made is related to the image reconstruction part 21 (see Figs. Irrelevant The decision is related to the patient's positioning during the measurement and the patient's anatomical body structure.

First, CT-measurement data is detected (MEAS: measurement). For this purpose a CT-device according to FIG. 1 or 2-as already mentioned-can be used. The user designates what image the user wants to capture at the USER level, i.e., designates the axial section, sagittal section or coronal section of a particular part of the patient. Such input may be made before or after detection of the measurement data.

Picture planning (PIC PLAN) of the patient is provided. In this case, topograms and / or CT-images may be used, as described in detail later with reference to FIGS. 4 to 6. The detection of the measurement data required for the topogram is typically done before the detection of CT-measurement data (MEAS). Thus, before each CT measurement, an overview of the patient, the so-called topogram, is taken. For this purpose, the X-ray tube does not move and the patient passes the X-ray tube. The result is an image that looks similar to a typical X-ray image.

In the (ADAPT: adaptation) phase, an image design (PIC PLAN) is examined based on the location of a particular landmark. Which landmarks are used in this regard depends on the cut-out of the patient being observed. Each two landmarks are interconnected by lines. Examples of suitable landmarks are the eye, both pelvis or lumbar spine, two vertebral bodies of the spine, both clavicles, two points inside the heart, and the like.

It is known what orientation the connecting lines should have in the correct positioning of the patient and in the "normal" anatomical body structure of the patient, which is indicated as "normal orientation" in the following. Thus, this normal orientation is the same for all patients. If the actual orientation of the connecting lines has this normal orientation in the image design (PIC PLAN), no position adjustment is necessary. In this case, in the (RECON: reconstruction) step, a CT-image (PIC: picture) is calculated as required by the user and derived as the final image. This means that 2D image calculation is easily achieved when the user requires an axial image.

In contrast, if the lines connecting the landmarks deviate from their normal orientation, it is determined how the image design (PIC PLAN) should be rotated and / or moved to match the normal alignment. Instead of rotating and / or moving the entire image design (PIC PLAN), it is possible to carry out the position change only with reference to the cut-out containing the area to be photographed. For example, the cuboid described in FIGS. 4 to 6 may be rotated.

If there is a difference between the normal orientation and the connecting lines in the image design (PIC PLAN), an image calculation that does not take into account the detected positional variation can lead to unsatisfactory results for the user. For this reason, in the RECON step, the position variation is taken into consideration and the image PIC is detected. In other words, 3D image calculation is performed in any case. The user obtains an axial image, sagittal image, coronal image (PIC) in relation to the patient's anatomical body structure and irrespective of the measurement situation. The cut plane of the final image PIC is inclined at an angle with respect to the axial plane, sagittal plane and coronal planes of the measurement geometry. Thus, anatomically correct images are represented.

The ADAPT stage also analyzes which areas of the image do not project the patient. One cuboid is formed around the relevant part of the patient, ie around anatomical regions, and the image calculation is only inside the cuboid. By doing so, the field of view is automatically adjusted.

4 shows a case where two topograms are used as the image design (PIC PLAN). The left part of the figure shows an anteroposterior topogram and the right part shows a transverse topogram. Two topograms depict the cross-section of a field of view cube. The comparison of the aforementioned landmarks determines how to change the position of the cuboid to obtain a normal orientation. Landmarks in the observed cut-out are particularly suitable for the vertebrae and pelvis.

5 shows a case where a topogram and two CT-images are used as the image design (PIC PLAN). The topogram is shown in the upper left corner. In the upper right, a sagittal CT image is seen, and in the lower left, an axial CT image is shown. Each of the three image designs (PIC PLAN) depicts a cross section of a cuboid, and the positional variation of the cross section is determined by landmark comparison. The only two CT-images mentioned are image design (PIC PLAN), which are distinguished from the final image (PIC) in terms of their image quality. Preferably, a so-called RTD (Real Time Display) image is used. The final image PIC can be seen at the bottom right; In this figure, an axial image is used.

6 shows the case where three CT-images are used as the image design (PIC PLAN). Coronary images (top left), sagittal images (top right) and axial images (bottom left) are used in this figure. Each cross section of the field of view cuboid is newly depicted. An axial image is used as the final image PIC (bottom right).

In the image design (PIC PLAN) at least two images each corresponding to different planes are used. Thereby, the cuboid from which the final image is calculated can be moved into the space. Alternatively, singular topograms (front and rear or transverse directions) may be used. In this case, however, it is only possible to move the field of view cube into the plane of the topogram.

The above-described measures enable the calculation of an image adapted to the patient's anatomical body structure and the patient's positioning during the measurement without the user having to calculate the values manually. The device automatically determines which type of reconstruction to use, that is, whether to use 2D or 3D reconstruction. This significantly improves difficult 3D image generation for many users, resulting in faster and more accurate design of complex anatomical body structures and reduced operational errors.

Of course, the calibration of the device, ie the position calibration and the determination of the field of view, can both be checked by the user.

The present invention has been described above in one embodiment. Many modifications and variations are possible without departing from the scope of the invention.

Claims (11)

As a method for automatically calculating the image data PIC of the inspection object from the measurement data MEAS,
The measurement data MEAS was detected during the relative rotational movement between the radiation sources C2 and C4 of the computed tomography apparatus C1 and the inspection target.
The image data PIC to be calculated shows a cross section along a specific plane defined in relation to the inspection object,
At least one preliminary image (PIC PLAN) detected by the computed tomography device is examined based on the positions of the plurality of landmarks (ADAPT),
Based on the landmark inspection, the position shift value is determined.
One or more cross-sectional images are reconstructed from the measurement data MEAS, and the one or more cross-sectional images show the inspection object in a plane perpendicular to the axis of rotation of the computed tomography apparatus,
The image data PIC is calculated using one or more cross-sectional images and position variation values (RECON),
A method for automatically calculating image data of an inspection object from measurement data. The method of claim 1,
In the landmark inspection, two landmarks are interconnected, and the orientation of the connecting line is compared with a specific orientation.
A method for automatically calculating image data of an inspection object from measurement data. 3. The method of claim 2,
In order to determine the position variation value, the position variation of the connecting line is made to be parallel to the specific orientation,
A method for automatically calculating image data of an inspection object from measurement data. The method according to any one of claims 1 to 3,
As the at least one preliminary image (PIC PLAN), one or more topograms and / or one or more cross-sectional images of an object to be inspected are used.
A method for automatically calculating image data of an inspection object from measurement data. The method according to any one of claims 1 to 4,
As the position variation value, movement and / or rotation are used,
A method for automatically calculating image data of an inspection object from measurement data. 6. The method according to any one of claims 1 to 5,
As the image data PIC to be calculated, an axial cross-sectional image or a sagittal cross-sectional image or a coronal cross-sectional image of an inspection target is used.
A method for automatically calculating image data of an inspection object from measurement data. 7. The method according to any one of claims 1 to 6,
The specific plane defined in relation to the inspection subject can be determined in advance,
A method for automatically calculating image data of an inspection object from measurement data. As the computing device C10 for calculating the image data PIC of the inspection target from the measurement data MEAS of the CT device C1,
With means for carrying out the method according to any one of claims 1 to 7,
Computing device. As CT-device C1,
A computing device (C10) according to claim 8
CT-device. A computer program having program codes (Prg ₁ -Prg _n ),
To carry out the method according to claims 1 to 7, when the computer program is executed on a computer,
Computer program having program codes (Prg ₁ -Prg _n ). A data medium having program codes (Prg ₁ -Prg _n ) of a program,
When the computer program is executed on a computer, it has a program code (Prg ₁ -Prg _n ) of a computer program for implementing the method according to claims 1 to 7,
Data medium.

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