3-D MEASUREMENTS GRID TOOL FOR X-RAY IMAGES

Abstract

Method of calculating a scaled virtual grid for x-ray projection images, comprising providing at least a first and a second co-registered x-ray projection image Ij—j=1, 2, . . . of a desired anatomy of a patient (step S1), defining two points P.sub.1 and P.sub.2 of the desired anatomy in 3-D space and determining 3-D coordinates of the two points P.sub.1 and P.sub.2 thereby using the x-ray projection images (step S2), calculating the scaled virtual grid based on the determined 3-D coordinates of the two points P.sub.1 and P.sub.2 (step S3), and projecting and displaying the calculated grid to a user on at least one of the first and the second co-registered x-ray projection image (step S4).

Claims

1. Method of calculating a scaled virtual grid for x-ray projection images, comprising providing at least a first and a second co-registered x-ray projection image I.sub.j—j=1,2, . . . of a desired anatomy of a patient (step S1), defining at least two points P.sub.1 and P.sub.2 of the desired anatomy in 3-D space and determining 3-D coordinates of the two points P.sub.1 and P.sub.2 thereby using the x-ray projection images (step S2), calculating the scaled virtual grid based on the determined 3-D coordinates of the two points P.sub.1 and P.sub.2 (step S3), and projecting and displaying the calculated grid to a user on an x-ray projection image, preferably on at least one of the first and the second co-registered x-ray projection image (step S4).

2. Method according to claim 1, wherein the step of calculating the scaled virtual grid (step S3) comprises: calculating at least two control points c.sub.i; i=1,2, . . . on a line connecting the defined points P.sub.1 and P.sub.2 (step S3a); calculating for each co-registered image cross lines d.sub.ij; i=1,2, . . . ; j=1,2, . . . (step S3b), wherein each cross line d.sub.ij crosses the line connecting the defined points P.sub.1 and P.sub.2 at control point c.sub.i, wherein each cross line d.sub.ij is parallel with a detector, with which image I.sub.j was captured, and preferably each cross line d.sub.ij is perpendicular to the line connecting the defined two points P.sub.1 and P.sub.2.

3. Method according to claim 2, comprising calculating on each cross line d.sub.ij control points k.sub.ijm(S3c), wherein the control points k.sub.ijm define the scaled virtual grid for each image I.sub.j.

4. Method according to claim 3, comprising projecting and displaying the scaled virtual grid being defined by control points k.sub.i1m on the first co-registered x-ray projection image I.sub.1 to the user, and projecting and displaying the scaled virtual grid being defined by control points k.sub.i2m on the second co-registered x-ray projection image I.sub.2 to the user.

5. Method according to claim 3, comprising calculating the distance in 3-D space between the two points P.sub.1 and P.sub.2, and using the calculated distance to determine the distance between at least two control points k.sub.ijm.

6. Method according claim 5, comprising displaying the determined distance between the at least two control points k.sub.ijm together with the control points k.sub.ijm on the image I.sub.j to the user.

7. Method according to claim 1, wherein the first and second co-registered x-ray projection images show the desired anatomy of the patient from different perspectives.

8. Method according to claim 1, comprising localizing an x-ray imaging device in six degrees of freedom, wherein the provided first and second co-registered x-ray projection images were generated with said x-ray imaging device.

9. Method according claim 8, wherein the localization is carried out using a Ripple marker, using optical tracking of the x-ray imaging device, using internal encoders of the x-ray imaging device, and/or using other image-based markers.

10. Method according to claim 1, wherein the step of defining two points P.sub.1 and P.sub.2 of the desired anatomy in 3-D space (step S2) comprises identifying a first landmark of the desired anatomy in the first x-ray projection image (step S2a), determining a first line on which the first landmark lays between an x-ray source and an x-ray detector that were used for generating the first x-ray projection image (step S2b), identifying a second landmark of the desired anatomy in the second x-ray projection image (step S2c), determining a second line on which the second landmark lays between the x-ray source and the x-ray detector that were used for generating the second x-ray projection image (step S2d), and calculating 3-D coordinates of an intersection of the determined first and second lines (step S2e), wherein the calculated 3-D coordinates define point P.sub.1 in 3-D space; identifying a third landmark of the desired anatomy in the first x-ray projection image (step S2f), determining a third line on which the third landmark lays between the x-ray source and the x-ray detector that were used for generating the first x-ray projection image (step S2g), identifying a fourth landmark of the desired anatomy in the second x-ray projection image (step S2h), determining a fourth line on which the fourth landmark lays between the x-ray source and the x-ray detector that were used for generating the second x-ray projection image (step S2i), and calculating 3-D coordinates of an intersection of the determined third and fourth lines (step S2j), wherein the calculated 3-D coordinates define point P.sub.2 in 3-D space.

11. Method according to claim 10, comprising projecting the determined first line onto the second x-ray projection image, and/or projecting the determined third line onto the second x-ray projection image.

12. Method according to claim 11, wherein the projection of the determined first and/or third line is used as a constraint on a Human Machine Interface (HMI), which constrains user input possibilities for identifying a landmark in the second x-ray projection image on the HMI.

13. Device for calculating a scaled virtual grid for x-ray projection images, comprising a calculation unit configured for: receiving at least a first and a second co-registered x-ray projection image I.sub.j of a desired anatomy of a patient, calculating two points P.sub.1 and P.sub.2 in the x-ray projection images and in the desired anatomy thereby determining 3-D coordinates of the two points P.sub.1 and P.sub.2, calculating the scaled virtual grid based on the determined 3-D coordinates of the two points P.sub.1 and P.sub.2, and causing a projection and a displaying of the calculated grid to a user on at least one of the first and the second co-registered x-ray projection image.

14. System for calculating a scaled virtual grid for x-ray projection images, comprising a device according to claim 13, and a Human Machine Interface (HMI) configured for displaying the received first and a second co-registered x-ray projection images and configured for receiving input signals from the user for identifying landmarks in the displayed images of the desired anatomy.

15. System according to claim 14, comprising an x-ray imaging device, preferably a mobile C-arm CT, comprising an x-ray source and an x-ray detector for generating the x-ray projection images.

16. Program element, which, when run on a processor or computer, is configured to carry out the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In the following, the disclosure is described exemplarily with reference to the enclosed figures, in which

[0054] FIG. 1 shows a flow diagram of the method for calculating a scaled virtual grid for x-ray projection images according to an embodiment.

[0055] FIG. 2 shows another embodiment of the method for calculating a scaled virtual grid by means of a flow diagram.

[0056] FIG. 3 shows a schematic view of a system for calculating a scaled virtual grid for x-ray projection images according to an embodiment.

[0057] FIG. 4 schematically shows how the definition of one point P.sub.1 of the desired anatomy in 3-D space and the determination of the 3-D coordinates of the point P.sub.1 are carried out in an exemplary embodiment.

[0058] FIG. 5 shows exemplary x-ray projection images with a respectively overlaid scaled virtual grid according to an embodiment.

[0059] FIG. 6 shows exemplary x-ray projection images with a respectively overlaid scaled virtual grid with a change in magnification of the scale according to an embodiment.

[0060] Notably, the figures are merely schematic representations and serve only to illustrate embodiments of the present disclosure. Identical or equivalent elements are in principle provided with the same reference signs.

DETAILED DESCRIPTION OF EMBODIMENTS

[0061] FIG. 1 shows a flow diagram of the method for calculating a scaled virtual grid for x-ray projection images according to an embodiment of the present invention. The steps comprise the provision of at least a first and a second co-registered x-ray projection image of a desired anatomy of a patient (step S1), defining two points P.sub.1 and P.sub.2 of the desired anatomy in 3-D space and determining 3-D coordinates of the two points P.sub.1 and P.sub.2 thereby using the x-ray projection images (step S2), calculating the scaled virtual grid based on the determined 3-D coordinates of the two points P.sub.1 and P.sub.2 (step S3), and projecting and displaying the calculated grid to a user on at least one of the first and the second co-registered x-ray projection image (step S4).

[0062] In other words, in step S1 at least two co-registered x-ray projections of a desired anatomy from different perspectives are be provided and further used for the calculation the scaled grid. The co-registered x-ray projections serve as data basis for the following steps. The different perspectives of the co-registered x-ray projections are necessary, for the second step S2, wherein two points are defined respectively selected in the region of interest in the co-registered x-ray projection image. For determining the 3-D coordinates of these two points an alignment of each selected point with the corresponding position in the other co-registered x-ray projection image is carried out. With this position information of each point in both co-registered x-ray projection images it is possible to determine the 3-D coordinates of each point in the 3-D space of the desired anatomy. These 3-D coordinates of the two points serve as base for a scale grid of the anatomy, which is designed in step S3. In the last step S3 the designed scale grid is projected on co-registered x-ray projections, which means it is overlaid on the co-registered x-ray projections. Hence, there is a calibrated scale grid overlaid on both co-registered x-ray projections, which is displayed to a user.

[0063] Note that the calculation of the scaled virtual grid can be carried out by various mathematical methods, as will be elucidated with two embodiments explained in the context of FIG. 2. Moreover, projecting and displaying the calculated grid to a user on at least one of the first and the second co-registered x-ray projection image can be carried out on one or more/various displays, e.g. using an HMI of a CT, and/or static screens and portable smart glasses using Augmented Reality technologies.

[0064] This method is based on the insight of the inventors that the use of objects, which are placed on the desired anatomy during CT-imaging only provides exact measurement data for regions, which lay parallel in the plane of object of known size, wherein the object of known size also has to lay in a plane parallel to the x-ray detector. Hence, every measurement of a distance outside of the plane of the object of known size, wherein the object of known size lays in a plane parallel to the x-ray detector, leads to an unavoidable inaccuracy. These disadvantages is overcome by the method of FIG. 2. For example, in an especially preferred embodiment of the invention it is possible to measure the distances in x-ray projection images without the use of an additional object of known size for any perspective of the anatomy. The distances in regions of interest to be measured can lay outside a plane parallel to the detector without losing measurement accuracy. Hence, with the use of the grid calculated according to the method of FIG. 2, the physician can always derive reliable measurement values from the x-ray projection image without an explicit calibration step.

[0065] FIG. 2 shows another embodiment of the method for calculating a scaled virtual grid by means of a flow diagram. In this embodiment, step S3 is further divided in the following sub-steps: calculating at least two control points c.sub.i, i=1,2, . . . on a line connecting the defined points P.sub.1 and P.sub.2 (step S3a); calculating for each co-registered image cross lines d.sub.ij; i=1,2, . . . ; j=1,2, . . . (step S3b), wherein each cross line d.sub.ij crosses the line connecting the defined points P.sub.1 and P.sub.2 at control point c.sub.i, wherein each cross line d.sub.ij is parallel with a detector, with which image I.sub.j was captured, and preferably each cross line d.sub.ij is perpendicular to the line connecting the defined two points P.sub.1 and P.sub.2 and calculating on each cross line d.sub.ij control points k.sub.ijm (S3c), wherein the control points k.sub.ijm define the scaled virtual grid for each image I.sub.j.

[0066] In other words, a line is drawn between the two points P.sub.1 and P.sub.2, wherein the line serves a center line in the grid. The line is further divided in part sections, defined by the point c.sub.i (step S3a). These part sections define the grid size in one direction. The calculated crosslines d.sub.ij run through the points c.sub.i and are perpendicular to the center line and parallel to each other (step S3b). Each cross line d.sub.ij shows calculated points k.sub.ijm(step S3c). These points define the mesh size in the second direction. As a result, you gain the calibrated scale grid for x-ray projection images for the desired anatomy.

[0067] Alternatively, the grid can also be defined with three selected points P.sub.1, P.sub.2 and P.sub.3, which define a plane, in which the cross lines d.sub.ij lie. The cross lines di are perpendicular to the line connecting the defined points P.sub.1 and P.sub.2, but not parallel to the detector. This can be an advantage if your region of interest is located in special plane of the object. In other words, another way to define the grid is to define/select a third anatomical point P.sub.3 in the two x-ray images. P.sub.3 together with P.sub.1 and P.sub.2 define a plane. Then we one use steps S1-S3a, as has been explained in detail hereinbefore and will be elucidated even more hereinafter, to define c.sub.i. Then one can uniquely build cross lines d.sub.ij in the plane defined by the three points P.sub.1, P.sub.2 and P.sub.3. Such a d.sub.ij crossline is perpendicular on P.sub.1P.sub.2, but it is not parallel anymore with the detectors, as was the case in the embodiment described before. In this approach, the grid is calibrated and attached to the plane defined by P.sub.1P.sub.2P.sub.3, as is clear to person skilled in the art from this disclosure.

[0068] FIG. 3 shows a schematic view of the system 10 for calculating a scaled virtual grid for x-ray projection images according to the preferred embodiment. The system 10 comprises a mobile C-arm CT, comprising an x-ray source 11 and an x-ray detector 12, which are mounted on C-arm 13. The C-arm 13 can move in six directions, i.e. three translatory directions and three rotatory directions. The desired anatomy is positioned in the center of the C-arm such that the x-ray source 11 can emit radiation on the desired anatomy and the corresponding x-ray detector 12 can detect the emitted radiation, which is influenced by the desired anatomy. In this way the x-ray projection images of the desired anatomy are acquired. With the information of the position of the C-arm 13 the x-ray projection images can be co-registered through various calculation methods (not shown). The information of the position respectively the six space coordinates of the C-arm are acquired by so called ripple marker (not shown). The system further comprises a Human Machine Interface (HMI) 14 configured for displaying the received first and a second co-registered x-ray projection images and configured for receiving input signals from the user for identifying landmarks in the displayed images of the desired anatomy. The nature and use of the landmarks will become apparent from the description of the embodiment shown in FIG. 4.

[0069] The system further comprises a calculation unit 15, which is configured for receiving at least a first and a second co-registered x-ray projection image I.sub.j of a desired anatomy of a patient, calculating two points P.sub.1 and P.sub.2 in the x-ray projection images and in the desired anatomy thereby determining 3-D coordinates of the two points P.sub.1 and P.sub.2. The calculation unit can calculate the scaled virtual grid based on the determined 3-D coordinates of the two points P.sub.1 and P.sub.2, and causes projection and a displaying of the calculated grid to a user on at least one of the first and the second co-registered x-ray projection image. In other words the calculation unit 15 is responsible for all steps of the calculation of the grid and the control of the projection and displaying the grid to a user.

[0070] FIG. 4 shows a schematic view 20 of defining one point 29 of the desired anatomy 23 in 3-D space and determining 3-D coordinates of the point 29. Identifying a first landmark 29 of the desired anatomy 23 in the first x-ray projection image 26 (step S2a), determining a first line 35 on which the first landmark 29 lies between an x-ray source 22 and an x-ray detector 24 that were used for generating the first x-ray projection image 26 (step S2b), identifying a second landmark 28 of the desired anatomy 23 in the second x-ray projection image 27 (step S2c), determining a second line 31 on which the second landmark 28 lies between the x-ray source 21 and the x-ray detector 25 that were used for generating the second x-ray projection image 27 (step S2d), and calculating 3-D coordinates of an intersection of the determined first and second lines 31, 35 (step S2e), wherein the calculated 3-D coordinates define point P.sub.1 in 3-D space 32.

[0071] In other words the desired anatomy 23 lies between x-ray sources 21, 22 and corresponding x-ray detectors 24, 25. The lines 33, 34, 36 and 37 shall give information about the optical path between the x-ray sources 21, 22 and the corresponding x-ray detectors 24, 25. The two x-ray sources 21, 22 and corresponding x-ray detectors 24, 25 are in reality one x-ray source and one x-ray detector of the same C-arm CT, which merely differ in their perspectives of desired anatomy. On the position of the x-ray detector 24 the x-ray projection image 26 from a first perspective is shown, which shall clarify that the x-ray projection image always correlates with a corresponding x-ray source/x-ray detector position, which is gained via a ripple marker 32. In reality, the user selects via HMI (not shown) on which the x-ray projection image 26 is displayed a point/landmark 29. In a next step the calculation unit (not shown) calculates a first line 35 between the point/landmark 29 and the x-ray source 22. In a next step a part of the first line 35, which lies between the lines 33 and 34, is projected on the second x-ray projection image 27. The second x-ray projection image corresponds to the x-ray source 21 and the x-ray detector 25 in the second perspective of the desired anatomy 23. The projected line 30 on the second x-ray projection image 27 serves as constraint, on which the landmark/point 28 can lie, for the user's selection of the landmark/point 28. The two landmarks/points 28, 29 represent the same feature of the desired anatomy only from different perspectives. After the selection of the landmark/point 28 in the second x-ray projection image 27, a line 31 is calculated between the x-ray source 21 and the landmark/point 28. The 3-D coordinates of the landmark/point in 3-D space are derived from the intersection of the lines 31 and 35.

[0072] FIG. 5 shows exemplary a section of x-ray projection images 40 with overlaid scaled virtual. The section of x-ray projection images 40 comprises a first x-ray projection image 41 and a second x-ray projection image 42, which show the same desired object from two different perspectives. The desired object lies respectively below the grid 51, 61. Further an implant 46, 58 with an overlaid orientation line 48, 62 is displayed. Point 43, 55 and point 44, 56 represent the selected points from user input, which define the region interest and are used for the construction of the scale grid. Lines 49, 63 are defined by the points 43, 55 and 44, 56. The scale grid 50 comprises cross lines and longitudinal lines and has millimeter scale in cross direction 50, 59 and longitudinal direction 51, 60. Points 43, 44 and 47 serve also as orientation assistance for the user in second x-ray projection image 42 and represent the top view the orientation lines 54, 53 and 52. As a result it is easier for the user to imagine the change of perspective corresponding x-ray projection images.

[0073] FIG. 6 shows an exemplary section 70 of x-ray projections images 71, 72 with overlaid scaled virtual grids with a change in magnification of the scale. Further an implant is also displayed in both x-ray projections images 71, 72. The grid comprises as above mentioned two points 73, 74 which defines the line 75 and are further used for the scaled grid construction. On the contrary to FIG. 5, grid 76 changes its magnification from the bottom 78 to top 79, which means the grid has no equidistant grid size. This is caused by the selection of the points 73, 74 which are not parallel to the detector (not shown).

[0074] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from the study of the drawings, the disclosure, and the appended claims. In the claims the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfill the functions of several items or steps recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope of the claims.

LIST OF REFERENCE SIGNS

[0075] 10 system [0076] 11, 21, 22 x-ray source [0077] 12, 24, 25 x-ray detector [0078] 13 C-arm [0079] 14 HMI [0080] 15 calculation unit [0081] 20 schematic view of defining one point [0082] 23 object [0083] 26, 27, 41, 42, 71, 72 x-ray projection image [0084] 28, 29, 38, 43, 44, 47, 55, 56, 57, 73, 74 point, landmark, intersection [0085] 30 projected line [0086] 31,35 line [0087] 32 ripple marker [0088] 33, 34, 36, 37 optic path [0089] 40, 70 section of x-ray projection images [0090] 45, 50, 59, 60, 78, 79 scale [0091] 46, 58, 77 implant [0092] 48, 62 orientation line implant [0093] 49, 75 center line [0094] 51,61,76 grid [0095] 52, 53, 54 orientation line