RIB UNFOLDING FROM MAGNETIC RESONANCE IMAGES

Abstract

In a method and an apparatus for rib unfolding in an MR image, a computer is provided with an input data file formed of volumetric MR data that represent a 3D image of the rib cage and the lungs of a subject. A view is selected wherein the ribs in the rib cage are in approximated as curves, such as a transverse slice through the 3D image, or an oblique view of the 3D image. The lungs in the selected view are used in order to define a first smooth curved surface representation that is inside of the rib cage. Further ellipses are selectively defined starting from the first ellipse and moving outwardly from the first smooth curved surface representation that respectively proceed through rib pairs in the rib cage in the selected image. These further smooth curved surface representations are then used to unfold the 3D image, by cutting and straightening these further smooth curved surface representations, thereby obtaining an unfolded 3D image, which is then displayed at a display.

Claims

1. A method for rib unfolding from a magnetic resonance (MR) image, comprising: providing a computer with an input data file comprising volumetric MR data representing a 3D image of the rib cage and lungs of a subject; in said computer, selecting a view through said 3D image; in said computer, using said lungs in said 3D image to define a first smooth curved surface representation that is inside of said rib cage; in said computer, successively defining further smooth curved surface representations, starting from and moving outwardly from said first smooth curved surface representation, that each proceed through at least one pair of ribs in said rib cage; in said computer, unfolding said 3D image by cutting and straightening said further smooth curved surface representations, to obtain an unfolded MR image; and at a display in communication with said computer, displaying said unfolded MR image.

2. A method as claimed in claim 1 comprising identifying said lungs in said selected view by executing a lung segmentation algorithm in said computer.

3. A method as claimed in claim 2 comprising generating a segmentation mask in said segmentation algorithm, and generating a mesh of a surface of the lungs, and defining said further smooth curved surface representations by predicting said further smooth curved surface representations in said computer using said lung surface.

4. A method as claimed in claim 3 comprising generating said mesh of said lung surface using an algorithm selected from the group consisting of marching cubes and marching tetrahedra.

5. A method as claimed in claim 1 comprising identifying said lungs in said selected view by displaying said selected view at a user interface and receiving a designation of said lungs into said computer by manual interaction with said user interface that designates said lungs in said displayed selected view.

6. A method as claimed in claim 1 comprising, in said computer, defining each of said first smooth curved surface representation and said further smooth curved surface representations as a surface defined by an ellipse.

7. A method as claimed in claim 1 comprising, in said computer, defining each of said first smooth curved surface representation and said further smooth curved surface representations as a surface defined by an B-spline.

8. A method as claimed in claim 1 comprising, in said computer, defining each of said first smooth curved surface representation and said further smooth curved surface representations as a surface defined by a 3D Bezier curve.

9. An apparatus for rib unfolding from a magnetic resonance (MR) image, comprising: a source of volumetric MR data representing a 3D image of the rib cage and lungs of a subject; a computer provided with an input data file comprising said volumetric MR data; said computer being configured to select a view through said 3D image; said computer being configured to use said lungs in said 3D image to define a first smooth curved surface representation that is inside of said rib cage; said computer being configured to successively define further smooth curved surface representations, starting from and moving outwardly from said first smooth curved surface representation, that each proceed through at least one pair of ribs in said rib cage; said computer being configured to unfold said 3D image by cutting and straightening said further smooth curved surface representations, to obtain an unfolded MR image; and a display in communication with said computer, said computer being configured to display said unfolded MR image at said display.

10. An apparatus as claimed in claim 9 wherein said computer is configured to identify said lungs in said selected view by executing a lung segmentation algorithm in said computer.

11. An apparatus as claimed in claim 10 wherein said computer is configured to generate a segmentation mask in said segmentation algorithm, and generating a mesh of a surface of the lungs, and defining said further smooth curved surface representations by predicting said further ellipses in said computer using said lung surface.

12. An apparatus as claimed in claim 11 wherein said computer is configured to generate said mesh of said lung surface using an algorithm selected from the group consisting of marching cubes and marching tetrahedra.

13. An apparatus as claimed in claim 9 wherein said computer is configured to identify said lungs in said selected view by displaying said selected view at a user interface at said display and to receive a designation of said lungs into said computer by manual interaction with said user interface that designates said lungs in said displayed selected view.

14. An apparatus as claimed in claim 9 wherein said computer is configured to define each of said first smooth curved surface representation and said further smooth curved surface representations as a surface defined by an ellipse.

15. An apparatus as claimed in claim 9 wherein said computer is configured to define each of said first smooth curved surface representation and said further smooth curved surface representations as a surface defined by an B-spline.

16. An apparatus as claimed in claim 9 wherein said computer is configured to define each of said first smooth curved surface representation and said further smooth curved surface representations as a surface defined by a 3D Bezier curve.

17. A non-transitory, computer-readable data storage medium encoded with programming instructions, said storage medium being loaded into a computer and said programming instructions causing said computer to: receive a computer with an input data file comprising volumetric magnetic resonance data representing a 3D image of the rib cage and lungs of a subject; select a view through said 3D image; use said lungs in said 3D image to define a first smooth curved surface representation that is inside of said rib cage; successively define further smooth curved surface representations, starting from and moving outwardly from said first smooth curved surface representation, that each proceed through at least one pair of ribs in said rib cage; unfold said 3D image by cutting and straightening said further smooth curved surface representations, to obtain an unfolded MR image; and at a display in communication with said computer, display said unfolded MR image.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 schematically shows a conventional CT image of a rib cage, a conventional CT image of a rib cage, and the resulting processed image that shows the ribs in a flattened view.

[0015] FIG. 2 schematically illustrates a known technique for achieving rib flattening in a processed image, using a CT image of the rib cage.

[0016] FIG. 3 schematically illustrates the basis of rib flattening in an MR image in accordance with the present invention.

[0017] FIG. 4 is a flowchart of an embodiment of the method according to the present invention.

[0018] FIG. 5 shows an image with rib flattening that is achieved in accordance with the present invention.

[0019] FIG. 6 is a block diagram of an apparatus for implementing the inventive method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] FIG. 1 shows the result of a conventional procedure for rib flattening or rib straightening, starting from a conventional CT image of a rib cage, shown at the left in FIG. 1. The result of the use of a conventional rib flattening algorithm is shown at the right in FIG. 1, wherein the ribs are all represented in a plane, unfolded from the view shown at the left in FIG. 1.

[0021] FIG. 2 schematically illustrates one conventional procedure for rib flattening wherein, in an image such as shown at the left in FIG. 1, each individual rib is sampled at the locations illustrated by the open circles, and a known algorithm is then employed to create a straight line from those curved samples. This known procedure requires that the ribs be clearly shown in the starting image, which is a criterion that is satisfied in a CT image, but which may not be the case in an MR image.

[0022] FIG. 3 schematically illustrates the principles of the present invention for rib flattening starting from an MR image. A suitable MR image that can be used to implement the procedure in accordance with the invention is shown in FIG. 3. This image may be a selected view of a volumetric 3D MR data set acquired from the torso of a subject, and thus shows the rib cage in its natural (curved) form, surrounding the lungs, which are also shown in FIG. 3.

[0023] Using the lungs as a reference, a first smooth curved surface representation, in this embodiment indicated by the innermost ellipse with the open circles, is defined in a computer using the image shown in FIG. 3. The sample points may be successively determined around the ellipse, such as by proceeding in the direction of the innermost arrow relative to a selected centerpoint C.

[0024] Starting from this innermost ellipse, further ellipses are defined that are concentric with the innermost ellipse, but that progressively proceed outwardly from the lungs, toward the rib cage.

[0025] Since the individual ribs exhibit different curvatures, the successively defined concentric ellipses will approximate the curvature of different ones, or different groups, of the ribs. In the example shown in FIG. 3, the ellipse designated with reference numeral 2 approximate the ribs having the innermost curvature, and the ellipse designated with reference numeral 3 approximates the rest of the ribs. These respective ellipses are then cut in the computer, and straightened, so as to produce the straight lines designated as 1.sub.straight, 2.sub.straight and 3.sub.straight.

[0026] Although this embodiment has been described using ellipses, any smoothed curved surface can be used, such as surface defined by a B-spline or a 3D Bezier curve.

[0027] The result of the inventive procedure is shown in FIG. 4. In comparison to the conventional approach shown in FIG. 1, it can be seen that the ribs in the result of the inventive procedure are not completely straightened, but their interior surfaces are still visible in the flattened image that is achieved in accordance with the invention. In many types of diagnoses, it is not of significant consequence that the individual ribs are not shown as being straight since the flattened rib view is used for navigation rather than as the basic for the actual diagnosis, and so the departure from a straight rib presentation is offset by the advantage that, in accordance with the invention, only a coarse detection of the rib cage is necessary, which is a condition that can be fulfilled by most MR images of the torso. The result shown in FIG. 4 still allows all ribs to be assessed in a single glance, and to be traversed with very few scroll actions.

[0028] A flowchart that shows the basic steps of the method in accordance with the invention is shown in FIG. 5. In a first step S1, a computer is provided with an input data file that includes volumetric MR data representing a 3D image that includes the rib cage and the lungs of a subject. This may be, for example, a volumetric MR data set of the torso of the subject.

[0029] In a second step S2, the computer selects a view through the 3D image, in which the rib cage and the lungs are visible. If it is desired to show only the lungs (and not other internal organs) in this view, these lungs can be segmented using known techniques, such as active contours, graph cuts, etc. One known procedure for lung segmentation is described in the article by Ray et al., Merging Parametric Active Contours Within Homogeneous Image Regions for MRI-Based Lung Segmentation, IEEE Trans. on Medical Imaging, Vol. 22, No. 2, pages 189-198 (2003).

[0030] This can be followed by generating a mesh of the lung surface from the segmentation mask, such as by using the known techniques of marching cubes or marching tetrahedra. The basic marching cube or marching square technique is described in U.S. Pat. No. 4,710,876.

[0031] The segmentation and generation of a suitable representation of the lung in the image that is used in accordance with the present invention can also be implemented manually or semi-automatically, by displaying the selected view and with a physician or technician interacting with an interface, such as a touch screen, to outline the lungs in the displayed image.

[0032] In step S3, once the lungs have been suitably designated in the image, the shape of the rib cage is predicted using the lung surfaces by fitting a smooth curved surface representation (which in turn defines a corresponding curved cylinder in the 3D data set) that best approximates the outline or shape of the lungs in the selected image. Using the lung-based smooth curved surface representation as a first smooth curved surface representation, further smooth curved surface representations (ellipse cylinders) are fitted to the rib cage, by proceeding outwardly from the lung-based smooth curved surface representation. This can be done automatically by pattern recognition that identifies when an ellipse proceeds through a number of image points that represent a pair of ribs in the rib cage that exceeds a predetermined threshold, for example. Since the pairs of ribs in the rib cage will exhibit respectively different curvatures, more than one such smooth curved surface representation may be identified, as illustrated in the example shown in FIG. 3 using ellipses as the smooth curved surface representations.

[0033] In step S4, once the one or more rib-based ellipses have been identified, the MR volume can be re-sampled based on cylinders associated therewith, by cutting and straightening the smooth curved surface representations, so that an image of the type shown in FIG. 4 results. This image is then displayed in step S5.

[0034] FIG. 6 is a block diagram showing the basic components of an apparatus for performing the inventive method. The apparatus includes a computer 4 with an input/output interface 5 that includes a display screen. The display screen can be an interactive screen, such as a touch-sensitive screen, that allows the aforementioned user interaction.

[0035] The computer 4 is in communication with a source 6 of an MR torso image. The source 6 may be an MR apparatus that includes an MR data acquisition scanner for acquiring such an image, or the source 6 may be a database in which a previously-acquired image has been entered and stored.

[0036] The computer 4 is provided with a non-transitory, computer readable data storage medium that is included with programming instructions that configure the computer 4 in order to perform the method according to the invention.

[0037] Although modifications and changes may be suggested by those skilled in the art, it is the intention of the Applicant to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of the Applicant's contribution to the art.