Automatic navigation echo placement detection

Abstract

The invention relates to a method for determining the position of a body landmark in a tomographic image slice of an object, and a method of determining the location of navigation echoes in a three-dimensional preview image of an object by continuously applying a method of determining the position of a body landmark in at least three tomographic image slices of the object in different viewing directions.

Description

Technical Field

[0001] The present invention relates to a computer-implemented method for determining the position of a body landmark in a tomographic image slice of an object, a computer-implemented method for determining the positioning of a navigation echo, and a method for acquiring a tomographic image of an object using a tomographic scanner. Background Art

[0002] "Automated Navigator Tracker Placement for MRI Liver Scans" by Goto Takao et al., December 11, 2014, ISBN: 978-3-030-90436-4 describes a method for automatically placing a navigation tracker for MRI liver scans. The authors proposed using a set-based classifier to detect pixels and correct landmarks on the upper edge of the liver, and then identifying regions containing edge pixels in the up / down direction. After fitting to a quadratic function, the navigation tracker position is calculated from the peak position of the upper convex shape formed by the edge pixels.

[0003] Magnetic resonance imaging (MRI) is a widely used diagnostic tool that preferably requires navigation echoes during image acquisition to correct for motion artifacts. A navigation echo is a method employed in magnetic resonance imaging to mitigate the effects of motion artifacts that occur during the image acquisition process due to patient movement. This technique involves capturing a low-resolution image of the region of interest (ROI) prior to obtaining a high-resolution image. The navigator sequence requires obtaining one or more slices of the ROI in a plane perpendicular to the main imaging sequence using parameters similar to or different from those of the main sequence. Typically, the navigator image can be quickly acquired within a few seconds, and the navigator image is used to monitor the motion of the ROI during the acquisition of the high-resolution image. Throughout the high-resolution image acquisition, the navigator sequence is continuously obtained to track the motion of the ROI. Then, the motion data extracted from the navigator sequence can be utilized to modify the imaging parameters of the high-resolution sequence, such as gradient and RF pulse timing, to account for the motion of the ROI. This parameter modification is performed in real time to ensure that the acquired images are free of any motion-related artifacts. The navigation echo technique is particularly valuable when imaging the chest and abdominal regions, where respiratory motion can significantly affect image quality. Motion caused by other factors, such as patient movement and cardiac motion, can also be considered. Ultimately, the navigation echo technique enhances image quality and reduces the need for repeated scans, thereby saving time and reducing the overall cost of the MRI procedure. A simple and commonly used version of the navigation echo can be to graphically place a navigator pencil beam having dimensions of approximately 30×30×100 mm on the dome of the liver using a scout image.

[0004] However, manually placing navigation echoes on a scout image can be a complex task. Automatic detection of navigation echoes can improve efficiency and reduce the expertise required for placing navigation echoes in MRI image acquisition, thus facilitating the diagnosis and treatment of various medical conditions.

[0005] Accordingly, the inventors of the present invention have found that an improved method for determining the positioning of navigation echoes would be advantageous, which method ensures that the navigation echoes are placed in an optimal position, thereby resulting in better image quality. Summary of the Invention

[0006] An object of the present invention is to provide an improved method for determining the positioning of navigation echoes, which provides reliable and accurate positioning.

[0007] The object of the present invention is solved by the subject matter of the independent claims, wherein further embodiments are incorporated in the dependent claims.

[0008] The described embodiments similarly relate to a computer-implemented method for determining the position of a body landmark in a tomographic image slice of an object, a computer-implemented method for determining the positioning of navigation echoes, and a method for acquiring tomographic images of an object using a tomographic scanner. The further described embodiments can be combined in any possible way. Synergistic effects can be produced by different combinations of the embodiments, although they may not be described in detail.

[0009] According to one aspect of the present invention, there is provided a computer-implemented method for determining the positioning of navigation echoes. The method comprises:

[0010] Receiving a three-dimensional preview image of an object acquired by a tomographic scanner, the preview image including a region of interest of the object;

[0011] Determining a first tomographic image slice of the three-dimensional preview image, the first tomographic image slice being a central slice relative to the center of the region of interest of the object in a preferred coronal view of the object;

[0012] Performing segmentation on the first tomographic image slice, thereby segmenting the first tomographic image slice into at least two body regions;

[0013] Applying an edge detection algorithm to the segmented first tomographic image slice, thereby determining a first outer shape of at least one of the at least two body regions;

[0014] Determining the position of the center point of the first outer shape of at least one of the at least two body regions as a first position of a body landmark in the first tomographic image slice;

[0015] Determine a second tomographic image slice of the three-dimensional preview image, the second tomographic image slice being an image slice of the region of interest of the object in a preferred sagittal view of the object, the second tomographic image slice being perpendicular to the first tomographic image slice and containing the first position of the determined body landmark;

[0016] Perform segmentation on the second tomographic image slice, thereby segmenting the second tomographic image slice into at least two body regions;

[0017] Apply the edge detection algorithm to the segmented second tomographic image slice, thereby determining a second outer shape of at least one of the at least two body regions;

[0018] Determine the position of the center point of the second outer shape of at least one of the at least two body regions as the second position of the body landmark in the second tomographic image slice;

[0019] Determine a third tomographic image slice of the three-dimensional preview image, the third tomographic image slice being an image slice of the region of interest of the object in a preferred coronal view of the object, the third tomographic image slice being perpendicular to the second tomographic image slice and parallel to the first tomographic image slice, and containing the second position of the determined body landmark;

[0020] Perform segmentation on the third tomographic image slice, thereby segmenting the third tomographic image slice into at least two body regions;

[0021] Apply the edge detection algorithm to the segmented third tomographic image slice, thereby determining a third outer shape of at least one of the at least two body regions;

[0022] Determine the position of the center point of the third outer shape of at least one of the at least two body regions as the third position of the body landmark in the second tomographic image slice; and

[0023] Provide the positioning of the navigation echo based on the second position of the body landmark and the third position of the body landmark as an output of the method.

[0024] The use of navigation echoes has proven crucial for monitoring respiration and defining the position of the heart. This in turn helps to enhance the imaging of the coronary arteries and other cardiac regions. To localize the navigation tracker, it may be necessary to know, for example, the shape of the dome of the liver. To achieve this, a three-step image processing method is proposed, which utilizes the successive application in different image slices in different viewing directions. A sequence of coronal, sagittal, and coronal views is preferred for many applications. However, other combinations of the first and third parallel tomographic image slices perpendicular to the second imaging slice are also possible.

[0025] After determining the first tomographic image slice in the coronal view (which may be the central slice of the region of interest), the position of a body landmark (e.g., the dome of the liver) is determined in this slice in the coronal view, and the x coordinate of the determined position is used to select the correct image slice in the sagittal view, which in turn is used to determine the position of the body landmark in the sagittal view. The corresponding coordinates of the determined body landmark in the sagittal view are again used to determine the correct final image slice in the coronal view. In the case where this correct coronal image slice is available, the final position of the body landmark can be determined, and thus the localization of the navigation echo can be determined.

[0026] Performing the "navigator placement process" as described above three times in the preferred coronal view, sagittal view, and again in the coronal view is advantageous for finding the correct position in all three dimensions to determine the correct localization of the navigator. This provides improved robustness for the localization of the navigator.

[0027] Thus, according to this method, automatic navigation echo detection and placement is possible. In addition, in cardiac imaging, automatic navigation echo placement detection can be used to detect the navigation echo and place it in the optimal position for cardiac gating, which may be crucial for acquiring high-quality cardiac images. The placement of the navigator can be challenging, especially in patients with irregular breathing patterns. Automatic navigation echo placement detection can help overcome this. In addition, the scan time can be reduced because automatic navigation echo placement detection can be performed in just a few seconds.

[0028] In an embodiment of the present invention, the localization of the navigation echo in the anterior-posterior direction of the object is determined based on the second position of the body landmark, and the localization of the navigation echo in the left-right and up-down directions is determined based on the third position of the body landmark.

[0029] In an embodiment of the present invention, the central slice is determined to be located in the middle of the range of the three-dimensional preview image, in the middle of the region of interest of the object, and / or in the middle of the object.

[0030] The navigator placement process method performed three times as described above includes determining the position of a body landmark in a tomographic image slice of an object. The method includes the following steps: receiving a tomographic image slice of the object in a predefined view of the object, the tomographic image slice including a region of interest of the object; performing segmentation on the tomographic image slice, preferably based on a threshold, so as to segment the tomographic image slice into at least two body regions; and applying an edge detection algorithm to the segmented tomographic image slice, so as to determine the outer shape of at least one of the at least two body regions. The method further includes the following steps: determining the position of the center point of the outer shape of the at least one of the at least two body regions; and providing the position of the center point of the outer shape as the position of the body landmark in the tomographic image slice, as the output of the method. The outer shape may also be referred to as an edge shape, a contour, or a curve.

[0031] Thus, according to this method, the position of a body landmark in a tomographic image slice of an object can be determined. The body landmark may be the highest point of the dome of the liver, or at least the highest point of the dome of the liver in the corresponding image slice included in a given view of the image slice. Therefore, a threshold-based segmentation algorithm is preferably applied to segment, for example, the lungs and / or the liver, and an edge detection algorithm can be applied to the segmented tomographic image slice, so as to determine the outer shape of at least one of the lungs and the liver. Next, a custom filter can be used to locate the lower edge of the lungs, which corresponds to the dome of the liver. Thus, when the contour of the dome of the liver is determined in this image slice, the topmost point of the contour can be determined, which may correspond to the dome of the liver, as long as the dome of the liver is included in this corresponding image slice. Thereafter, the navigator beam can be placed on the median of the dome curve of the liver as the required body landmark. However, it should be noted that the proposed method can only work when the correct image slice that already contains the dome of the liver is selected. Therefore, a novel three-stage image processing-based method is proposed, which is used to automatically locate the dome of the liver in three dimensions in an MRI image and place a navigation tracker above it, which will be described in more detail below.

[0032] In an embodiment of the present invention, the step of applying an edge detection algorithm to the segmented first, second, and / or third tomographic image slices includes the following sub-steps: applying an edge detection algorithm to the segmented tomographic image slice, so as to determine the contour of at least one of the at least two body regions; and applying at least one filter to the determined contour, so as to determine the outer shape of at least one of the at least two body regions.

[0033] In an embodiment of the present invention, the step of applying an edge detection algorithm to the segmented tomographic image slices further includes the following sub-steps: performing positioning of the outer shape of at least one of the determined at least two body regions relative to the region of interest of the object; and discarding a part of the outer shape of at least one of the determined at least two body regions as a result of performing the positioning, the part being considered not to be part of the region of interest of the object.

[0034] In an embodiment of the present invention, the body landmark is the highest point of the dome of the liver in the first, second, and / or third segmented tomographic image slices.

[0035] In an embodiment of the present invention, the region of interest includes at least part of the chest of the object, in particular the interface between the lungs and the liver of the object.

[0036] In an embodiment of the present invention, the segmentation separates the tissue of the lungs from the tissue of the liver.

[0037] In an embodiment of the present invention, the center point of the first, second, and / or third outer shape of at least one of the at least two body regions is the highest point of the outer shape in the up-down direction of the object.

[0038] According to another aspect of the present invention, there is provided a method of acquiring tomographic images of an object using a tomographic scanner. The method includes the following steps: acquiring a three-dimensional preview image of the object; determining the positioning of the navigation echo in the preview image according to the method of any one of the foregoing embodiments; and acquiring tomographic images of the object while correcting the movement of the object based on the positioning of the navigation echo.

[0039] According to another aspect of the present invention, there is provided a data processing device including a module for performing the steps of the method according to any one of the foregoing embodiments.

[0040] According to another aspect of the present invention, there is provided a computer program including instructions which, when executed by a computer, cause the computer to perform the steps of the method according to any one of the foregoing embodiments.

[0041] According to another aspect of the present invention, there is provided a computer-readable storage medium including instructions which, when executed by a computer, cause the computer to perform the steps of the method according to any one of the foregoing embodiments.

[0042] Therefore, the benefits provided by any of the above aspects equally apply to all other aspects, and vice versa.

[0043] In summary, the present invention relates to a method for determining the positioning of navigation echoes in a three-dimensional preview image of an object by continuously applying a method for determining the positions of body landmarks in at least three tomographic image slices of the object in different viewing directions.

[0044] One of the advantages of the embodiments of the present invention is that it can effectively automate the placement of navigation echoes in MRI scans. Another advantage can be that the automatic navigation echo placement detection can ensure that the navigation echoes are placed in the optimal position, thereby producing better image quality, because the placement of navigation echoes is crucial for accurately correcting motion-induced artifacts in MRI scans. Another advantage can be that the automatic placement of navigation echoes ensures consistency among different operators, because the manual placement of navigation echoes can vary among operators, resulting in inconsistent image quality. Another advantage can be that the automatic navigation echo placement detection reduces the need for manual labor and experts and can be more cost-effective.

[0045] These advantages are non-limiting, and other advantages can be envisioned in the context of the present application.

[0046] The above aspects and embodiments will become apparent and will be elucidated with reference to the exemplary embodiments described below. The exemplary embodiments of the present invention will be described below with reference to the following drawings: BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A block diagram showing a computer-implemented method for determining the positions of body landmarks in tomographic image slices of an object according to an embodiment of the present invention.

[0048] Figure 2 A block diagram showing a computer-implemented method for determining the positioning of navigation echoes according to an embodiment of the present invention.

[0049] Figure 3 A flowchart showing a method for determining the positions of body landmarks in tomographic image slices of an object according to an embodiment of the present invention.

[0050] Figure 4 A flowchart showing a method for determining the positioning of navigation echoes according to an embodiment of the present invention.

[0051] LIST OF REFERENCE NUMERALS:

[0052] 110 Tomographic image slice

[0053] 111 First tomographic image slice

[0054] 112 Second tomographic image slice

[0055] 113 Third tomographic image slice

[0056] 120 Body landmark

[0057] 130 Region of interest

[0058] 140 Two body regions Detailed implementation manner

[0059] Regarding Figure 1 , a block diagram of a computer-implemented method for determining the position of a body landmark 120 in a tomographic image slice 110 of an object according to an embodiment of the present invention is illustrated. This method is also referred to as a navigator placement process. The method includes step S110 of receiving a tomographic image slice 110 of an object in a predefined view of the object, wherein the tomographic image slice includes a region of interest 130 of the object. The method further includes the following step S120: performing threshold-based segmentation on the tomographic image slice 110, thereby segmenting the tomographic image slice into at least two body regions 140. The method further includes step S130: applying an edge detection algorithm to the segmented tomographic image slice 110, thereby determining the outer shape of at least one of the at least two body regions 140. The method further includes: step S140 of determining the position of the center point of the outer shape of at least one of the at least two body regions; and step S150 of providing the position of the center point of the outer shape as the position of the body landmark 120 in the tomographic image slice 110 as an output of the method.

[0060] Figure 2 A block diagram of a computer-implemented method for determining the positioning of a navigation echo according to an embodiment of the present invention is shown. The method includes: step S210 of receiving a three-dimensional preview image of an object acquired by a tomographic scanner, the preview image including a region of interest 130 of the object; and step S220 of determining a first tomographic image slice 111 of the three-dimensional preview image, the first tomographic image slice 111 being a central slice with respect to the region of interest 130 of the object in the coronal view of the object. The method further includes: step S230 of determining a first position of the body landmark 120 in the first tomographic image slice 111 according to the navigator placement process as described above regarding Figure 1 ; and step S240 of determining a second tomographic image slice 112 of the three-dimensional preview image, the second tomographic image slice 112 being an image slice with respect to the region of interest 130 of the object in the sagittal view of the object, the second tomographic image slice 112 being perpendicular to the first tomographic image slice 111 and including the determined first position of the body landmark 120. The method further includes according to as described above regarding Figure 1Step S250 of determining the second position of the body landmark 120 in the second tomographic image slice 112 by the navigator placement process described above. The method further includes step S260 of determining a third tomographic image slice 113 of the three-dimensional preview image, the third tomographic image slice 113 being an image slice of the object's region of interest 130 in the coronal view of the object, the third tomographic image slice 113 being perpendicular to the second tomographic image slice 112 and parallel to the first tomographic image slice 111, and including the determined second position of the body landmark 120. The method further includes: step S270 of determining the third position of the body landmark 120 in the third tomographic image slice 113 by the navigator placement process as described above; and step S280 of providing the positioning of the navigation echo based on the second position of the body landmark 120 and the third position of the body landmark 120 as the output of the method. Figure 1 Step S270 of determining the third position of the body landmark 120 in the third tomographic image slice 113 by the navigator placement process as described above; and step S280 of providing the positioning of the navigation echo based on the second position of the body landmark 120 and the third position of the body landmark 120 as the output of the method.

[0061] Figure 3 A flowchart of a method for determining the position of a body landmark 120 in a tomographic image slice 110 of an object according to an embodiment of the present invention is shown. As Figure 3 shown in this exemplary illustration, a sagittal view of the chest of the object is used as the tomographic image slice 110, which includes the lungs and liver of the object as the region of interest 130. After step S120 of applying threshold-based segmentation to distinguish the lungs from the liver, the lungs and liver of the object can be easily distinguished in the image slice as two body regions 140 to be detected, especially the boundary regions of these two body regions 140. After step S130 of performing edge detection on the output of the threshold-based segmentation to capture the edge shape of the lungs, the boundary region between the lungs and the liver as the two body regions 140 is clearly highlighted. Optionally, a customized defined filter can be applied to the contour of the lungs to only retain the shape of the dome of the liver, and more positioning can be performed to avoid the situation where the filter detects both the dome of the liver and the top of the lungs (which usually can have a similar shape). Therefore, the extra noise in the image can be eliminated. In addition, the processing step applied to the corresponding tomographic image slice 110 includes step S140 of determining the position of the center point of the contour of the boundary between the lungs and the liver and providing the coordinates of the center point as the body landmark 120 as the output.

[0062] Figure 4The flowchart of a method for determining the localization of navigation echoes according to an embodiment of the present invention is shown. Thus, according to the proposed method, the following steps may be required. For example, an MRI scanner can acquire a three-dimensional smart scout image with good image quality. The scout scan can be free-breathing or breath-hold. The region of interest 130 can be determined, which can be the left half of the scan and generally includes the dome of the liver in the coronal view.

[0063] To localize the dome of the liver as a navigation echo as a body landmark in the region of interest, first, the correct dome placement in the sagittal view can be determined. Thus, it may be necessary to find potential image slices to predict the dome of the liver in the sagittal view. For this purpose, several processing steps are performed on the central or middle slice of the coronal view. After the middle slice of the coronal view has been determined as the first tomographic image slice 111, these steps are as follows, as described above.

[0064] The processing steps applied to the middle slice of the coronal view as the first tomographic image slice 111 at least include performing (threshold-based) segmentation to distinguish the lungs from the liver, and performing edge detection on the output of the (threshold-based) segmentation to capture the edge shape of the lungs. Optionally, a custom-defined filter can be applied to the contour of the lungs to retain only the shape of the dome of the liver, and more localization can be performed to avoid the case where the filter detects both the dome of the liver and the top of the lungs (which can generally have a similar shape). Thus, the extra noise in the image can be eliminated. In addition, the processing steps applied to the middle slice of the coronal view can include picking the center of the pixels left in the final output of the shape of the boundary between the lungs and the liver.

[0065] After applying these steps to the middle slice in the coronal view, the x-coordinate value of the center or the most vertex of the determined contour found in the above process will be the slice number for predicting the dome of the liver in the sagittal view.

[0066] Now that the potential image slice for predicting the dome of the liver in the sagittal view has been defined as the second tomographic image slice 112, the above processing steps are applied to this image slice in the sagittal view. In particular, (threshold-based) segmentation is performed to distinguish the lungs from the liver, edge detection is applied to the output of the threshold-based segmentation to capture the edge shape of the lungs, and the center of the pixels left in the final output of the shape of the boundary between the lungs and the liver is selected. This will result in the correct navigator placement in the sagittal view.

[0067] Now, to correctly place the position of the navigation echo in the correct slice in the sagittal view, the correct x - coordinate value of the point found from the above - mentioned steps in the sagittal view is used to determine the correct image slice in the coronal view as the third tomographic image slice 113, and is used to perform a final detection of the position of the liver dome in this correct slice of the coronal view. Now, having determined the correct slice of the coronal view, the above - mentioned steps are applied to this coronal third tomographic image slice 113. In particular, (threshold - based) segmentation is performed to distinguish the lungs from the liver, edge detection is applied to the output of the threshold - based segmentation to capture the edge shape of the lungs, and the centers of the pixels remaining in the final output of the shape of the boundary between the lungs and the liver are selected.

[0068] The output of the application of the described steps in the correct coronal view will be the final estimate of the body landmark 120 to be determined as the navigation echo placement.

[0069] Performing the "navigator placement process" as described above three times, in the coronal view, in the sagittal view, and again in the coronal view, is beneficial for finding the correct position in all three dimensions to robustly determine the correct positioning of the navigation echo. The proposed method was evaluated on 60 clinical MRI datasets, and it achieved 96.7% accuracy in detecting the correct placement of the navigation echo.

[0070] Although the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. By studying the drawings, the disclosure, and the dependent claims, those skilled in the art can understand and implement other variations of the disclosed embodiments when practicing the claimed invention.

[0071] In the claims, the word "comprising" does not exclude other elements or steps, and the quantifier "a" or "an" does not exclude a plurality. The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used advantageously. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A computer-implemented method for determining the location of a navigator echo, the method comprising the following steps: receiving (S210) a three-dimensional preview image of an object acquired by a tomography scanner, the preview image including a region of interest (130) of the object; determining (S220) a first tomographic image slice (111) of the three-dimensional preview image, the first tomographic image slice (111) being a central slice relative to a region of interest (130) of the object in a preferred coronal view of the object; performing (S120) segmentation on the first tomographic image slice (111), thereby segmenting the first tomographic image slice into at least two body regions (140); applying (S130) an edge detection algorithm to the segmented first tomographic image slice (111) to thereby determine a first external shape of at least one of the at least two body regions (140); determining (S140) a position of a center point of the first outer shape of the at least one body region of the at least two body regions as a first position of a body landmark (120) in the first tomographic image slice; determining (S240) a second tomographic image slice (112) of the three-dimensional preview image, the second tomographic image slice (112) being an image slice relative to the region of interest (130) of the object in a preferred sagittal view of the object, the second tomographic image slice (112) being perpendicular to the first tomographic image slice (111) and containing the determined first position of the body landmark (120); performing (S120) segmentation on the second tomographic image slice (112), thereby segmenting the second tomographic image slice into at least two body regions (140); applying (S130) the edge detection algorithm to the segmented second tomographic image slices (112) to thereby determine a second outer shape of at least one of the at least two body regions (140); determining (S140) a position of a center point of the second outer shape of the at least one body region of the at least two body regions as a second position of the body landmark (120) in the second tomographic image slice; determining (S260) a third tomographic image slice (113) of the three-dimensional preview image, the third tomographic image slice (113) being an image slice relative to the region of interest (130) of the object in a preferred coronal view of the object, the third tomographic image slice (113) being perpendicular to the second tomographic image slice (112) and parallel to the first tomographic image slice (111) and containing the determined second position of the body landmark (120); performing (S120) segmentation on the third tomographic image slice (113), thereby segmenting the third tomographic image slice into at least two body regions (140); applying (S130) the edge detection algorithm to the segmented third tomographic image slice (113) to thereby determine a third outer shape of at least one of the at least two body regions (140); determining (S140) the position of the center point of the third outer shape of the at least one body region of the at least two body regions as a third position of the body landmark (120) in the second tomographic image slice; and The positioning of the navigator echo is provided (S280) as an output of the method based on the second position of the body landmark (120) and the third position of the body landmark (120).

2. The method according to claim 1, wherein: The step of applying the edge detection algorithm to the segmented first, second and / or third tomographic image slices (111, 112, 113) comprises the following sub-steps: applying the edge detection algorithm to the segmented tomographic image slices (111, 112, 113) to thereby determine the contour of at least one of the at least two body regions (140); and At least one filter is applied to the determined contour to thereby determine the outer shape of at least one of the at least two body regions (140).

3. The method according to claim 2, wherein: The step of applying an edge detection algorithm to the segmented tomographic image slices (111, 112, 113) further comprises the following sub-steps: performing a positioning of the determined outer shape of the at least one body region of the at least two body regions (140) relative to the region of interest (130) of the subject; as well as Parts of the determined outer shape of at least one of the at least two body regions (140) are discarded which, as a result of the performed positioning, are considered not to be part of the region of interest (130) of the object.

4. A method according to any one of the preceding claims, wherein: The body landmark (120) is the highest point of the dome of the liver in the segmented first, second and / or third tomographic image slices (111, 112, 113).

5. A method according to any one of the preceding claims, wherein: The region of interest includes at least a portion of the subject's chest, in particular the interface between the subject's lungs and liver.

6. A method according to any one of the preceding claims, wherein: The segmentation is threshold based.

7. A method according to any one of the preceding claims, wherein: The segmentation distinguishes tissue of the lungs from tissue of the liver.

8. A method according to any one of the preceding claims, wherein: The center point of the first external shape, the second external shape and / or the third external shape of at least one of the at least two body regions (140) is the highest point of the external shape in the up-down direction of the object.

9. A method according to any one of the preceding claims, wherein: The positioning of the navigation echo in the front-to-back direction of the object is determined based on the second position of the body landmark (120), and the positioning of the navigation echo in the left-right direction and the up-down direction is determined based on the third position of the body landmark (120).

10. The method according to any one of the preceding claims, wherein: The central slice is determined to be located in the middle of the range of the three-dimensional preview image, in the middle of the region of interest (130) of the object and / or in the middle of the object.

11. A method for acquiring a tomographic image of an object using a tomographic scanner, the method comprising the following steps: Acquiring the three-dimensional preview image of the object; Determining the location of a navigator echo in the preview image according to the method of any of the preceding claims; as well as The tomographic image of the object is acquired while correcting for motion of the object based on the movement of the location of the navigator echo.

12. A data processing device comprising means for performing the steps of the method according to any one of claims 1 to 10.

13. A computer program comprising instructions which, when executed by a computer, cause the computer to perform the steps of the method according to any one of claims 1 to 10.

14. 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 any one of claims 1 to 10.

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