Method for processing tomosynthesis acquisitions in order to obtain a representation of the contents of an organ

Abstract

A method for processing tomosynthesis images of an object of interest, using an imaging system, the imaging system comprising an X-ray source positioned facing a detector on which the object of interest is positioned. With the method of an embodiment of the invention, it is possible to display a three-dimensional (3D) reconstruction slice, as well as a two-dimensional (2D) image of the object of interest.

Claims

1. A method of processing tomosynthesis images of an object of interest, using an imaging system, the imaging system comprising an X-ray source positioned facing a detector on which the object of interest is positioned, the processing comprising the following steps: acquiring a plurality of 2D projection images of the object of interest according to a plurality of orientations located with respect to a perpendicular to the detector, a zero orientation being the closest to the perpendicular; applying a filter on the acquired 2D projection images so as to obtain filtered projection images of the object of interest; reconstructing slices of the object of interest from at least two of the filtered projection images, the reconstructed slices being a filtered reconstructed volume of the object of interest; reprojecting the reconstructed slices according to a determined orientation direction to obtain an intermediate 2D image of the object of interest; and using a pixel-to-pixel linear combination of the intermediate 2D image obtained by the reprojection and at least one of the acquired plurality of 2D projection images corresponding to the determined orientation to obtain a final 2D image of the object of interest.

2. The method according to claim 1, wherein the reprojection of the reconstructed slices is a Sorted Intensity Pixel (SIP) reprojection in the determined orientation direction, the SIP reprojection comprising, for each pixel of the intermediate 2D image: determining, in the filtered reconstructed volume, an intensity voxel calculated by using sorting of the values of pixels along the ray from the source to the pixel of the intermediate 2D image; and storing, in a memory unit of the imaging system, an identifier of the reconstructed slice in which is found the voxel from the sorting, so as to have in the memory unit, depth information connecting each pixel of the intermediate 2D image to the associated reconstructed slice from which this pixel stems.

3. The method according to claim 1, wherein the reprojection of the reconstructed slices is a Maximum Intensity Pixel (MIP) reprojection in the determined orientation direction, the MIP reprojection comprising, for each pixel of the intermediate 2D image: determining, in the filtered reconstructed volume, the maximum intensity voxel along the ray from the source to the pixel of the intermediate 2D image; and storing, in a memory unit of the imaging system, an identifier of the reconstructed slice in which the maximum intensity voxel is found, so as to have in the memory unit, depth information connecting each pixel of the intermediate 2D image to the associated reconstructed slice from which this pixel stems.

4. The method according to claim 1, wherein the reprojecting of the reconstructed slices is performed by sorting of values of pixels according to their intensity.

5. The method according to claim 4, wherein a voxel having the highest probability of belonging to a lesion along the ray from the source to the pixel is selected.

6. The method according to claim 5, comprising a step for determining a volume, obtained using a system for automatic detection of lesions, wherein each voxel represents a probability of belonging to a lesion.

7. A display method for displaying a set of radiography images of the object of interest by a unit for displaying radiography images, radiography images being the reconstructed slices of the object of interest and a final 2D image of the object of interest obtained by a method of processing tomosynthesis images according to claim 1, the method of processing tomosynthesis images further including the step of: storing depth information (argMax′) in a memory unit, the display method comprising the steps of: displaying the final 2D image on the display unit, selecting a pixel from the final 2D image; searching, among the depth information (argMax′) stored in the memory unit, for an identifier of the reconstructed slice associated with the selected pixel; adjusting the size of the reconstructed slice associated with the selected pixel to the size of the final 2D image; and displaying by means of the display unit, the adjusted reconstructed slice associated with the selected pixel.

8. The method of claim 1 further comprising: displaying the final 2D image obtained from the combination of the tomosynthesis projection image and the reprojection image; selecting a pixel from the final 2D image; searching among a depth information for an identifier of a reconstructed slice associated with the selected pixel; and displaying the reconstructed slice.

9. The method of claim 8, wherein the size of the reconstructed slice is adjusted to the size of the final 2D image.

10. The method of claim 9, wherein an adjustment factor for the adjusting depends on the height of the reconstructed slice.

11. The method of claim 8, wherein the size of the final 2D image is adjusted to the size of the reconstructed slice.

12. The method of claim 11, wherein an adjustment factor for the adjusting depends on the height of the reconstructed slice.

13. The method of claim 8, wherein the final 2D image and the reconstructed slice are displayed concurrently.

14. The method of claim 8 further comprising toggling between the reconstructed slice and the final 2D image.

15. The method of claim 8, wherein the depth information is stored in a memory unit.

16. A method of displaying radiography images of an object of interest using a display unit and a processing unit comprising: displaying a final 2D image; selecting a pixel from the final 2D image, wherein the final 2D image is obtained from the combination of a 2D projection acquired in a determined orientation and a reprojection of reconstructed slices in the corresponding determined orientation; searching among a depth information for an identifier of a reconstructed slice associated with the selected pixel; adjusting the size of the identified reconstructed slice to be the same size as the displayed final 2D image; and displaying the adjusted reconstructed slice.

17. The method of claim 16, wherein the final 2D image and the reconstructed slice of the object of interest were processed using an imaging system, the imaging system comprising an X-ray source positioned facing a detector on which the object of interest is positioned, the processing comprising the following steps: acquiring a plurality of 2D projection images of the object of interest according to a plurality of orientations located with respect to a perpendicular to the detector where at least one of the plurality of orientations includes the determined orientation, a zero orientation being the closest to the perpendicular; applying a filter on the acquired 2D projection images so as to obtain filtered projection images of the object of interest; reconstructing the slices of the object of interest from at least two of the filtered projection images, the reconstructed slices being a filtered reconstructed volume of the object of interest; obtaining an intermediate 2D image of the object of interest by reprojecting the reconstructed slices according to the determined orientation; and using a pixel-to-pixel linear combination of the intermediate 2D image obtained by the reprojection and the at least one of the acquired plurality of 2D projection images corresponding to the determined orientation to obtain the final 2D image of the object of interest.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) Other characteristics, objects and advantages of the invention will become apparent from the description which follows which is purely illustrative and non-limiting, and which should be read with reference to the appended drawings, wherein:

(2) FIG. 1 schematically illustrates an imaging system according to the invention;

(3) FIG. 2 schematically illustrates a few functionalities of the imaging system;

(4) FIG. 3 illustrates, as a block diagram, a method for processing images according to the invention;

(5) FIG. 4 illustrates as a block diagram, a step for re-projecting reconstructed slices of an object of interest according to an embodiment of the invention;

(6) FIG. 5 illustrates, as a block diagram, a step for re-projecting reconstructed slices according to an embodiment of the invention;

(7) FIG. 6 illustrates as a block diagram, a display method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(8) Medical Imaging System

(9) FIG. 1 schematically illustrates a medical imaging system 10 for acquiring projection 2D images for reconstructing a 3D image of a region of interest.

(10) The medical imaging system 10 comprises a unit for acquiring images 12, a unit for processing images 13 and a display system 15.

(11) FIG. 2 schematically illustrates the acquisition unit 12.

(12) The acquisition unit 12 allows acquisition of a plurality of 2D projections of a region of interest O—of an organ—of a patient. The acquisition unit 12 is notably formed by a detector 11 located facing a source 12 of X-rays. The detector 11 for example is a digital camera. The acquisition unit 12 for example is an X-ray acquisition system, the latter comprising any known means allowing emission of X-rays onto the object O and the acquisition of resulting images.

(13) The display unit 15 may be integrated into the image acquisition unit 12 or the image processing unit 13, or be separated from the acquisition unit 12 and from the processing unit 13. The display unit 15 for example, is a computer screen, a monitor, a flat screen, a plasma screen, or any type of display device known commercially. The display unit 15 enables a radiologist practitioner to monitor the reconstruction and/or display of acquired 2D images.

(14) The processing unit 13 is adapted to the application of the processing method (for example for reconstructing a 3D image from 2D images). The processing unit 13 may be integrated into the acquisition unit 12 or be separated from the acquisition unit 12. The processing unit 13 is for example one or more computers, one or more processors, one or more microcontrollers, one or more microcomputers, one or more programmable controllers, one or more application specific integrated circuits, other programmable circuits, or other devices which include a computer such as a workstation.

(15) The processing unit 13 is coupled with memory means 14 which may be integrated to or separated from the processing unit 13. These means may be formed by a hard disk or by any other removable storage means (a CDROM, a diskette, etc.). These storage means may be used for storing a 3D image of the area of the viewed organ, such as an acquired or processed 2D image, this may be a ROM/RAM memory of the processing unit 13, a CDROM, a USB key, a memory of a central server. The processing unit 13 may comprise a reading device (not shown) for example a diskette reader or a CDROM reader, for reading the instructions of the processing method (which will be described subsequently) from a medium of instructions (not shown) such as a diskette or a CDROM. Alternatively, the processing unit 13 executes the instructions of the processing method (which will be described subsequently) stored in micro-software packages (not shown).

(16) Image Processing Method

(17) With the image processing method which we shall describe, an image similar to a mammographic image may be obtained from tomosynthesis images.

(18) It is specified here that by image similar to a mammographic image is meant an image which visually resembles to a full dose standard 2D mammography image.

(19) The image processing method therefore consists of processing radiography images obtained by an imaging system 10 comprising an X-ray source 12 positioned facing a detector 11 on which the object of interest O is positioned.

(20) FIG. 3 illustrates steps of the method for processing images obtained by tomosynthesis.

(21) In a first step S1, a plurality of 2D projection images 30 of the object of interest O is acquired according to a plurality of orientations, a so-called zero orientation being the closest to the perpendicular H.

(22) It is specified here that each orientation is located with respect to the perpendicular H to the detector 11.

(23) During this first step, a 2D image is in particular acquired according to a determined orientation 31. The determined orientation is preferably the so-called zero orientation.

(24) The method then comprises a step S2 for applying a filter on the acquired 2D projection images 30 so as to obtain filtered projection images 40 of the object of interest O.

(25) This filter is preferably of the high-pass type and its cut-off frequency is preferably a function of the thickness of the object of interest O.

(26) During a step S3, slices 50 are determined for reconstructing the object of interest O. This determination S3 in particular consists in a reprojection of the filtered 2D projection images 40. During step S3, the slices 50 may also be simply outputted as illustrated in FIG. 3.

(27) This back projection may in particular be non-linear of the “Order Statistics Based Backprojection” type. In the linear back projection, each voxel of the volume is reconstructed by using N information pixels, each pixel being determined by backprojection of the voxel in each of the N projections. In the non-linear backprojection, the maximum intensity pixel among the N pixels is not used, which allows significant reduction of the replication artifacts caused by the most intense objects.

(28) It is noted that the slices for reconstructing the object of interest O represent the reconstructed volume of the object of interest O.

(29) Next, during a step S4, a reprojection of the reconstructed slices 50 is carried out in the determined direction. With this, it is possible to obtain an intermediate 2D image 60 of the object of interest O. It is noted that reprojection occurs along the same direction as the projection image corresponding to the determined orientation.

(30) Finally, during a step S5, a final 2D image of the object of interest is obtained by combining the intermediate 2D image 60 and the projection image 30 corresponding to the determined orientation 31. The combination is preferably a pixel-to-pixel linear combination.

(31) The final 2D image 70 is an image similar to a mammography image.

(32) In an advantageous alternative, the final 2D image of the object of interest is determined for each orientation.

(33) The step for re-projecting S4 the reconstructed slices 50 is a preferred implementation, an MIP (Maximum Intensity Pixel) reprojection in the determined orientation direction. More generally, any reprojection using sorting of the values of the pixels present along the rays may be used (SIP, for Sorted Intensity Pixel). The sorting consists in classifying the pixels according to their intensity (increasing or decreasing sorting).

(34) FIG. 4 illustrates the steps of the MIP reprojection according to a first embodiment.

(35) This type of MIP reprojection consists, for each pixel of the intermediate 2D image 60, in a determination S41, in the reconstructed volume of the object of interest, of the maximum intensity voxel along the ray from the source to this pixel and in storage S42, in a memory unit 14 of the imaging system, of an identifier of the reconstructed slice in which the maximum intensity voxel is found.

(36) In this way, in the memory unit 14, a depth information argMax is available, connecting each pixel of the intermediate 2D image 60 to the associated reconstructed slice from which this pixel stems.

(37) The reprojection may be applied in a different way from the one shown above.

(38) FIG. 5 illustrates the steps of the reprojection according to a second embodiment.

(39) In this embodiment, the reprojection S4 of the re-construction slices 50 further consists in any pixel of the intermediate 2D image 60 in a selection S43 of the voxel having the highest probability of belonging to a lesion along the ray from the source to this pixel, and in storage S44, in a memory unit 14 of the imaging system, of an identifier of the re-construction slice in which the maximum probability voxel is found.

(40) This assumes that with each voxel is associated a probability of belonging to a lesion. An automatic detection system (3D CAD (Computer Aided Detection)) allows such a volume of probabilities to be obtained.

(41) In this way, in the memory unit 14, depth information argMax is available connecting each pixel of the intermediate 2D image 60 to the associated re-construction slice from which this pixel stems.

(42) The processing method may further comprise a step for local regularization S6, by the processing unit 13, of the depth information argMax. This regularization step consists of uniformizing the information argMax, locally. The result is depth information noted as argMax′.

(43) Advantageously, the method comprises an alternative filtering step S2′ for applying via the processing unit 13, a filter to the image acquired in step S1 resulting in projection image 31 of the object of interest O prior to the elaboration S5 of the final 2D image 70 so as to reduce noise. The applied filter is preferably a low-pass filter.

(44) Additionally, it is possible to apply a step S4′ for determining reconstructed slices 50′ which correspond to the reconstructed volume of the object of interest, in other words this is a volume which is obtained from projection images with the reconstruction methods known from the state of the art, the purpose of which is viewing slices.

(45) Display Method

(46) The processing method described above finds a particular application in a method for displaying radiography images of an object of interest O. The display of the radiography images is carried out by means of a display unit 15 connected to the processing unit 13 applying the display method.

(47) FIG. 5 illustrates steps of the display method.

(48) The display method comprises a step DI for displaying the final 2D image 70 obtained by means of the image processing method described above.

(49) It further comprises a selection of a pixel from the final 2D image 70.

(50) The display method also comprises a search D3 among the depth information argMax or argMax′ stored in the memory unit 14, for an identifier of the reconstruction slice associated with the selected pixel.

(51) Following this search, the method comprises a step D4 for adjusting the size of the reconstructed slice with the same identifier to the size of the final 2D image 70, the adjustment factor preferentially depending on the height of the reconstructed slice.

(52) Finally, by means of the display unit, the thereby adjusted reconstructed slice is displayed. By this means, the reconstructed slice and the final 2D image 70 have the same geometrical properties with structures placed in the same location. It is then easier to toggle between the reconstructed slices and the final 2D image 70 and vice versa. Following the display of the adjusted reconstructed slice, it is also possible to return to a display of the final 2D image D6.

(53) Alternatively, the display method may consist in the succession of the following steps: displaying DI a reconstructed slice by means of the display unit 15; adjusting D4 the size of the final 2D image 70 to the size of the reconstructed slice, the adjustment factor preferentially depending on the height of the reconstructed slice; displaying D5, by means of the display unit 15, the adjusted final 2D image 70.

(54) By this means, the reconstructed slice and the final 2D image 70 have the same geometrical properties with structures placed in the same location. It is then easier to toggle between the reconstructed slices and the final 2D image 70 and vice versa.