WO2012123843A1

WO2012123843A1 - Stereoscopic imaging

Info

Publication number: WO2012123843A1
Application number: PCT/IB2012/050955
Authority: WO
Inventors: Rolf Karl Otto Behling; Bart Pierre Antoine Jozef Hoornaert; Johannes Wilhelmus Maria Jacobs; Steffen Holzapfel
Original assignee: Koninklijke Philips Electronics N.V.; Philips Intellectual Property & Standards Gmbh
Priority date: 2011-03-15
Filing date: 2012-03-01
Publication date: 2012-09-20

Abstract

The present invention relates to an X-ray tube for stereoscopic imaging, an X- ray imaging system for stereoscopic imaging, a method for stereoscopic imaging as well as a computer program element and a computer readable medium for stereoscopic imaging. In order to provide stereoscopic imaging with improved space requirements and enhanced weight characteristics, an X-ray tube (10) for stereoscopic imaging is provided, comprising a cathode (12), an anode (14), means (16) for deflection of an electron beam, an X-ray aperture (18) with at least a first hole (20) and a second hole (22), and an envelope (24) housing the cathode and the anode. The means for deflection are adapted such that the electron beam from the cathode can be deflected such that the electron beam hits the anode in at least two stereo focal spot positions (26) separated from each other with a first distance (28) defining a stereo direction (30). The aperture is fixedly arranged inside the envelope and an X-ray beam (32) is generated at each focal spot emanating in a viewing direction (34) through one of the at least first and second holes in the aperture. The direction of the first distance is perpendicular to the viewing direction, wherein the first distance is adaptable.

Description

STEREOSCOPIC IMAGING

FIELD OF THE INVENTION

The present invention relates to an X-ray tube for stereoscopic imaging, an X- ray imaging system for stereoscopic imaging, a method for stereoscopic imaging as well as a computer program element and a computer readable medium for stereoscopic imaging.

BACKGROUND OF THE INVENTION

Stereoscopic X-ray imaging is used for providing three-dimensional information about a region of interest of an object. For example, for positioning of catheters, a three-dimensional impression of the vessels is provided. In order to achieve a stereo viewing effect, multiple tubes are used for acquiring the image data. For example, in document US 2006/0227936 Al a stereo X-ray system with two grid-controlled X-ray tubes and one detector is described.

SUMMARY OF THE INVENTION

It may be an object of the present invention to provide stereoscopic imaging with improved space weight characteristics.

The objective of the present invention is solved by the subject-matter of the independent claims, wherein further embodiments are incorporated in the dependent claims.

It should be noted that the following described aspects of the invention apply also for the X-ray tube, the X-ray imaging system, the method, the program element and the computer readable medium.

According to an exemplary embodiment of the invention, an X-ray tube for stereoscopic imaging is provided, that comprises a cathode, an anode, means for deflection of an electron beam, an X-ray aperture with at least a first hole and a second hole, and an envelope housing the cathode and the anode. The means for deflection are adapted such that the electron beam from the cathode can be deflected such that the electron beam hits the anode in at least two stereo focal spot positions separated from each other with a first distance defining a stereo direction. The aperture is fixedly arranged inside the envelope. An X-ray beam is generated at each focal spot emanating in a viewing direction through one of the at least first and second holes in the aperture. The direction of the first distance is perpendicular to the viewing direction. The first distance is adaptable. One of the advantages is that only one X-ray tube is necessary for acquiring the stereoscopic image data. A further advantage is that by providing an adaptable distance of the two stereo focal spot positions, it is possible to adapt the stereoscopic effect to the particular needs, for example to different viewing directions and distances between X-ray source, patient and detector.

According to an aspect of the invention, the aperture is provided in addition to an X-ray window provided in the envelope of the X-ray tube.

According to a further exemplary embodiment of the invention, the means for deflection are adapted such that the at least two focal stereo spot positions are adaptable in the viewing direction, and such that the focal spots are each provided with a focal spot shape in which a projected length is larger than a projected width, wherein the projected length and the projected width have a ratio of larger than 3/1.

According to an exemplary embodiment of the invention, the means for deflection are adapted such that the stereo spots can be skewed.

According to another exemplary embodiment of the invention, two stereo spots can be provided by a selection from a set of at least three, in particular from six focal spot positions arranged such that a projection of the focal spot positions in the viewing direction results in a first two-dimensional pattern.

According to an exemplary embodiment of the invention, an X-ray imaging system for stereoscopic imaging is provided, comprising an X-ray tube according to one of the above-mentioned exemplary embodiments, a detector and a processing unit. The processing unit is adapted to control the emission of an electron beam from the cathode and to control the means for deflection. The detector is provided with an asymmetric resolution, which is finer along the stereo direction than in a direction perpendicular to the stereo direction.

According to another exemplary embodiment of the invention, a method for stereoscopic imaging is provided, comprising the following steps:

a) Acquiring first image data with X-rays delivered by a first stereo focal spot; and

b) Acquiring second image data with X-rays delivered by a second stereo focal spot.

According to the method, an X-ray tube for stereoscopic imaging is provided with a cathode, an anode, means for deflection of an electron beam, an X-ray aperture with at least a first hole and a second hole, and an envelope housing the cathode and the anode, wherein the aperture is fixedly arranged inside the envelope. During step a) the means for deflection deflect the electron beam from the cathode such that the electron beam hits the anode in a first stereo focal spot position. During step b) the means for deflection deflect the electron beam from the cathode such that the electron beam hits the anode in a second stereo focal spot position. The first and second stereo focal spot positions are separated from each other with a first distance defining a stereo direction. During step a) an X-ray beam is generated at the first focal spot emanating in a viewing direction through one of the at least first and second holes in the aperture, wherein the direction of the first distance is

perpendicular to the viewing direction. The stereo focal spot positions are adapted in the stereo direction and/or the viewing direction.

It can be seen as the gist of the invention to provide two alternating stereo spots which are created by a deflection of a single electron beam. Further, the focal spot positions can be adapted, for example according to object position, source to image receptor distance SID, field limitation and stereo zone requirements.

These and other aspects of the present invention will become apparent from an elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will be described in the following with reference to the following drawings.

Fig. 1 illustrates an X-ray imaging system for stereoscopic imaging according to an exemplary embodiment of the invention.

Fig. 2 illustrates a schematic perspective view of an X-ray tube for

stereoscopic imaging according to an exemplary embodiment of the invention.

Fig. 3 shows a detail of an exemplary embodiment of an X-ray tube

according to the invention.

Fig. 4 illustrates a further exemplary embodiment of an X-ray imaging

system according to the invention.

Fig. 5 shows a further aspect of the stereoscopic imaging according to the invention.

Fig. 6 shows a further exemplary aspect of stereoscopic imaging according to the invention.

Fig. 7 shows a further exemplary aspect of an example of stereoscopic imaging according to the invention.

Fig. 8 shows a further aspect of an exemplary embodiment of stereoscopic imaging according to the invention.

Fig. 9 shows a further aspect of the stereoscopic imaging according to the invention.

Fig. 10 shows a further exemplary aspect of an embodiment according to the invention.

Fig. 11 schematically shows a further aspect of an exemplary embodiment of stereoscopic imaging according to the invention.

Fig. 12 shows a further aspect of an exemplary embodiment of stereoscopic imaging according to the invention.

Fig. 13 shows a further exemplary embodiment of an X-ray tube for

stereoscopic imaging according to the invention.

Fig. 14 shows a further exemplary embodiment of an X-ray tube for

stereoscopic imaging according to the invention.

Fig. 15 shows a further exemplary embodiment of stereoscopic imaging

according to the invention.

Fig. 16 shows basic steps of an exemplary embodiment of a method for

stereoscopic imaging according to the invention.

Fig. 17 shows a further exemplary embodiment of a method for stereoscopic imaging according to the invention.

Fig. 19 shows a further exemplary embodiment of a method for stereoscopic imaging according to the invention. DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 illustrates an X-ray imaging system 200 comprising an X-ray tube 210, a detector 212 and a processing unit 214. The detector 212 and the tube 210 are arranged at opposite ends of a C-arm 216 which is rotatably mounted to a support 218 suspended from a ceiling 220 of an examination laboratory. The support 218 is also rotatably mounted to the ceiling. Thus, the C-arm can be freely moved around an object 222 arranged on an examination table 224. The table 224 is supported by a base 226 which allows for an adjustment of the table's height. Further, the table is slidable horizontally, which is indicated by a double arrow 228. Further, for a control of the table as well as for other control purposes, an interface 230 is provided in the vicinity of the table 224. As can be seen, a display arrangement 232, for example comprising a number of monitors, is suspended from the ceiling 220 by a display support 234. The latter also allows for a movement of the display arrangement such that the position and the orientation of the displays can be adapted to the particular means.

In the example shown, the C-arm 216 is arranged such that the X-ray tube 210 is located below the table and the detector 212 is located above the table. Thus, an X-ray source of the X-ray tube can provide X-ray beams 236 which are emanating towards the detector 212. In the example shown in Fig. 1, three arrows 236a, 236b, and 236c indicate that according to the invention, different X-ray beam directions are possible.

It is noted that the processing unit 214 is shown to be integrated in the base

226. Of course, the processing unit 214 can also be arranged at another location.

According to the invention, the processing unit 214 is adapted to control the emission of an electron beam from a cathode of the X-ray tube and also to control means for deflection which are also provided at the arm of the C-arm where the X-ray tube is located.

The detector 212 is provided with an asymmetric resolution, which is finer along a stereo direction than in a direction perpendicular to the stereo direction. The aspects of the stereo direction will be explained in the following figures.

The asymmetric detector resolution may be supported or achieved by an asymmetric structure of the scintillator.

According to a further aspect, the asymmetric detector resolution may be supported or achieved by binning of detector cells, i.e. substantially reading the sum of the signals of selected individual cells.

It must be noted that the C-arm is shown exemplary only. Of course, other X- ray image acquisition systems are also possible, either with static X-ray sources of with movable source and detector such as a CT with a circular gantry.

According to a further aspect, the processing unit may be adapted to control the means for deflection such that the stereo spots can be selected automatically by the system based on image data analysis and/or manually by the user; for example, by selecting two stereo spots out of the plurality of stereo spots.

The automatic selection may be based on an analysis of hidden relevant objects, such as vessel bifurcations, or based on other system parameters, e.g. geometric position of the X-ray source in relation to the object, e.g. a patient.

The manual selection by the user may be based on the approach trying to optimize the stereo effect in a shown X-ray image. In Fig. 2, an X-ray tube 10 for stereoscopic imaging is provided comprising a cathode 12, an anode 14, means 16 for deflection of an electron beam (not shown in detail in Fig. 2), an X-ray aperture 18 with at least a first hole 20 and a second hole 22. The first and second hole 20, 22 will be explained in relation to Fig. 7, for example.

Further, an envelope 24 is provided, housing the cathode and the anode.

According to a further aspect, a vacuum is provided inside the envelope 24 for generating X-ray radiation.

According to a further aspect, one of the first and second apertures is provided for mono-scopic viewing.

According to a further aspect, an X-ray beam in the viewing direction can be provided for the mono-scopic viewing.

The means for deflection are adapted such that the electron beam from the cathode towards the anode can be deflected such that the electron beam hits the anode in at least two stereo focal spot positions 26 separated from each other with a first distance 28 defining a stereo direction 30.

The aperture is fixedly arranged inside the envelope.

An X-ray beam, indicated with dotted lines 32, is generated at each focal spot emanating in a viewing direction 34 through one of the at least first and second holes 20, 22 in the aperture.

The direction of the first distance 28, i.e. the direction of the stereo direction

30, is perpendicular to the viewing direction 34.

The first distance 28 is adaptable.

According to an aspect of the invention, not further shown, the aperture is provided in addition to an X-ray window provided in the envelope of the X-ray tube. It is noted that the X-ray window is also not further shown in any of the following drawings.

However, the aperture is arranged inside the envelope whereas the X-ray window is provided within the envelope allowing the radiation to pass through the envelope, which envelope is X-ray opaque except for the X-ray window.

In Fig. 3, the electron beam is indicated with first lines 36a and 36b. As can be seen, the electron beam 36, which is provided by a cathode not shown, is deflected by the means for deflection such that the electron beam hits the anode 14 in two stereo focal spot positions 26 which are indicated with reference numeral SFPl and SFP2.

Of course, the deflection of the electron beam is arranged in an alternating manner, i.e. the electron beam is defiected to the first focal spot position SFPl and in a next situation it is deflected to the second stereo focal spot position SFP2, indicated by the first lines 36a and 36b. In Fig. 3A, the anode 14 is shown as a rotating anode with an inclined focal track area 38. The inclination of the surface of the anode is indicated with an angle 40. In other words, the anode disc has a cone-shaped section 42 in the area of at least one focal track 38.

The generation of X-rays occurring when the electron beam hits the anode, is not further shown.

According to another exemplary embodiment, shown in Fig. 3B, the anode disc 14 has a cross-section with at least two steps 44 in the focal track area to provide at least a first focal track 46 on a first step 48 and a second focal track 50 on a second step 52.

For example, the first and second steps 48, 52 are inclined with respect to a direction perpendicular to the rotation direction, which rotation direction is indicated with a symbolic arrow 54 in Fig. 3A.

Further, a coordinate system with three perpendicular axes is shown in the left half of Fig. 3A. A first axis 56 is indicated with reference numeral "R" and is also referred to as the R-axis. A second axis 58, labelled with indicator "Z" is arranged perpendicular to the R-axis. Both axis 56, 58 are arranged in a plane which is parallel to the printing surface of the figures on the respective sheet of paper. Further, a third axis 60, indicated with reference numeral "X" is arranged perpendicular to the plane which is defined by the first and second axis 56, 58.

In Fig. 4, the X-ray imaging system 200 of Fig. 1 is shown together with an arrow 62 indicating the viewing direction from the X-ray source, i.e. the X-ray tube 210 towards the X-ray detector 212. As can be seen, an object 64 is arranged between the X-ray tube and the detector.

It is noted that the viewing direction 62 is equal to the R-axis, i.e. the first axis

56, of Fig. 3A. Accordingly, the second axis 58 (Z-axis) and the third axis 60 (X-axis) are arranged in a plane which is perpendicular to the viewing direction 62.

For example, the X-axis or X-direction is also referred to as the stereo direction.

In the following, the stereoscopic imaging is explained with reference to the following figures.

Fig. 5 shows a schematic arrangement of a first object 66 and a second object 68. With respect to the coordinate system, in Fig. 5 the viewing direction, i.e. the R-axis, is opposite to the R-axis shown in Fig. 4 for the sake of better explanation. In other words, the R-axis is pointing downwards when viewing Fig. 5 with the page arranged in a landscape orientation. However, an arrow 70 indicates the viewing direction.

With an image projection according to the arrow 70, the second object 68 would be hidden by the first object 66 when projected onto a plane perpendicular to the viewing direction, for example to a plane arranged at the bottom of Fig. 5, indicated with reference numeral 72.

In order to be able to detect also the second object 68, a stereoscopic imaging is applied as projection from two different stereo spots 74 and 76. As can be seen by the respective projection lines 78, connecting the spots 74, 76 with the image plane 72, the projection lines 78 lead to two different projections on the image plane 72. When viewed from spot 74, the first object 66 would be visible by a first projection 80 and the second object 68 would be visible by a second projection 82. Further, when viewed from the second spot 76, the first object 66 would lead to a third projection 84 and the second object would lead to a fourth projection 86.

As can be seen, the respective projections of the first and second object 66, 68 would be arranged in a different order when comparing the projection of the first spot 74 with the projection of the second spot 76.

In Fig. 5, an arrow 88 indicates the source to image receptor distance SID. Further, a second arrow 90 indicates the source to object distance SOD, and a third arrow 92 indicates the distance between the two objects 66, 68. This distance is also referred to as AL, i.e. the difference in length. The first spot 74 and the second spot 76 are arranged with a distance to each other, indicated by a fourth arrow 94, also referred to as reference "d".

Further, a fifth arrow 96 indicates the width W of the first projection spot 74 as an example.

The projected distance between the projection of the first object and the second object, i.e. the distance between the projection 80 and the projection 82 is indicated with a sixth arrow 98.

A seventh arrow 100 further indicates the spatial X-resolution s.

The distance between the two projections, indicated by arrow 98 is also referred to as Δρ which is always larger than s.

For determining the distance between the two objects, i.e. for determining AL, the following equation applies:

AL ~ SID * 2*Δρ / (d*M²)

M = SID / SOD wherein M equals SID/SOD. For example, M is 1.3, SID is 120 cm, d, i.e. the distance of the two projection points, is 4 cm, and the detected Δρ is 0.02 cm. This leads to the result that AL is 0.71 cm.

Fig. 6 shows a further aspect of a stereo effect according to the invention. In the following, the axis directions of the coordinate system indicated in the lower left part of Fig. 6 is used when referring to directions.

The first and second object 66, 68 are shown as being inside a larger object 102. In other words, the object 102 has two sub-objects, namely the first object 66 and the second object 68. The spatial X-resolution s must be sufficient to differentiate the sub-object projections.

The focal spots 74 and 76 having a focal spot width, indicated by the arrow 96 and the distance d, lead to the stereo effect in X-direction.

To achieve a 3D separation with a small distance d of the focal spots, the spatial X-resolution of a detector, arranged in a detection plane 72, but not further shown in Fig. 6, needs to be sufficiently high.

In Fig. 6, a central beam 104 is also shown for mono-scopic viewing.

Another possibility for mono-scopic viewing is provided by using the right or left one of the stereo spots for a central beam.

With respect to the coordinate system in Fig. 6, it is further noted that the R- axis is the radial direction from the centre of the rotating anode along the central beam. The Z-axis is orthogonal to the slide or printing plane of the figure. The X-direction is the line of connection of the focal spots.

According to a general aspect of the invention, the focal spot positions are adaptable. For example, the focal spot positions are adapted to object position, SID, field limitation, and stereo requirements.

In Fig. 7, some of the aspects described in relation to Fig. 2 referring to the X- ray tube are explained in relation with geometrical aspects.

In Fig. 7, two focal spot positions 26, i.e. the first focal spot position 74 and the second focal spot position 76 are shown.

The focal spots are arranged with a distance C to the X-ray aperture 18 with the first hole 20 and the second hole 22, wherein the distance is indicated with a seventh arrow 106. A third hole 108 is also provided in the X-ray aperture. The arrangement of the first, second and third hole is shown in more detail in the right half of Fig. 7. The first and second hole 20, 22 have a first hole width 110, also indicated with reference numeral As. The third hole 108 has a second hole width 112, indicated with reference numeral Ac. Further, the first and second holes 20, 22 are provided with a second total distance 114 between their outer opening edges, which is also referred to by reference numeral A_totai.

The third hole 108 can be provided, for example, at half the distance between the focal stereo spot positions.

According to a further exemplary embodiment, which is also shown in Fig. 7, but which feature can be applied also isolated, the focal stereo spot positions 26 are adaptable in the viewing direction, i.e. in the direction of the R-axis.

In other words, the focal stereo spot positions can be adapted in different directions, which is indicated with double arrows 116.

It is once again noted that the adaption of the focal stereo spot positions is provided by the means for deflection.

As is also shown in Fig. 7, the aperture 18 is positioned close to the focal spots inside the envelope to limit the radiation field of the focal spots.

A further aspect is also shown in Figure 8. According to another exemplary embodiment, a secondary aperture 118 is provided to limit radiation emanating to a sideward direction, which radiation would not hit the detector and would thus mean a superfluous dose impact for the object, which is important when the object is a patient. The limiting of the radiation is indicated with dotted arrows 120.

According to a further aspect of the invention, a detector 122 is arranged in a viewing plane 124 orthogonal to the viewing direction R.

According to a further aspect, the X-axis and the Z-axis are arranged in the viewing plane.

The secondary aperture can also be referred to as a collimator 126.

According to an aspect of the invention, the aperture 18 is a fix triple hole aperture which reduces X-ray radiation during the transition of the focal spots. The radiation field is limited to the active area of the detector by a combination of the triple hole aperture 18 and the main collimator 126.

According to a further aspect, already indicated above, the focal spot positions 26 are provided to be stationary but being able to be adjusted such that the radiation field need the field limitation requirements, including tolerances in the system and variations of the SID, etc.

For example, limitation lines 128 indicate the required field limitation. The active area of the detector is indicated with reference numeral H, indicated with double arrow 130.

A further aspect of relating to the stereoscopic imaging is shown in Fig. 8. A length arrow 132 indicates the minimum distance L_mi_n which has to be kept between the first object 66 and the focal stereo spot positions 26. A dotted line 134 indicates that no stereo effect is available above this limit. In other words, the projection would be off the detector. The distance d of the two focal spot positions 74 and 76 is arranged to be equal to the length Atotai, indicated with an arrow 136. Thus, the projection settings are adjusted for the longest SID. The aperture 18 is arranged with a distance Ci , indicated with an arrow 138, with respect to the focal spot positions 26. The following equation applies with respect to the limit of the stereo effect zone:

di = a_total

(adjusted for longest L (SID)

As can be seen in Fig. 8, a so-called stereo zone 140 is provided, which is a zone in which a stereo effect can be achieved. The stereo zone 140 is indicated with a dashed pattern 142.

A further aspect of a stereoscopic imaging is shown in Fig. 9. In this arrangement, the focal spot positions 26 are arranged with a larger distance compared to Fig. 8 with respect to the aperture 18. The larger distance or second distance is indicated with an arrow 144 and also referred to as C₂. The distance d of the stereo focal spot positions, which are adapted in Z- and X-direction, is larger than the distance a_totai-

The stereo zone is defined to be arranged between a minimum length Lmi_n with respect to a distance from the stereo focal spot positions, indicated with the arrow 132, and the maximum length L_max, indicated with an arrow 146. Thus, the stereo zone has a length in R-direction or in the viewing direction, indicated with arrow 148, which length is also referred to as L_stereozone. In other words, the stereo zone is arranged between the first line 136 and a second line 150, which both lines are shown in a dashed line. As can be seen, the stereo zone 140 is much smaller than the stereo zone in Fig. 8.

Further, a centre spot position 152 is shown, which is adapted in R-direction and which matches with the fixed aperture and the centre radiation field.

With respect to the stereo zone, the following equation applies:

L_min = L * d / (h + d)

d₂ > a_totai

(d₂ widened for smaller SID) L_max = C₂ / [1- (a_total/d₂)]

According to a further exemplary embodiment, shown in Fig. 10, the means for deflection are adapted such that the focal spots are each provided with a focal spot shape 152 in which a projected length Lp is larger than a projected width Wp. The projection of the focal spot shapes 152 are also shown in the right part of Fig. 1 1. Two focal spots are shown with a focal spot shape 152 with respect to the stereoscopic imaging, and a further focal spot with a further focal spot shape 152 is indicating a focal spot for mono-scopic viewing.

According to a further exemplary embodiment of the invention, the projected length and the projected width have a ratio of larger than 3/1.

According to a further aspect, the ratio is larger than 4/1. For example, the ratio is 8/1.

According to an example, the length is 1.6 mm and the width is 0.2 mm.

According to a further aspect, the width and length are projected onto a projection plane which is orthogonal to the viewing direction.

According to a further exemplary embodiment, as a general aspect, the widths are minimized. For example, the width is decreased with larger magnification.

According to a further aspect, the focal spots are provided with an optical width that is smaller than the optical length, wherein the optical width is a projection of a focal spot width on the anode to a plane which is orthogonal to the centre beam of the particular stereo spot through its corresponding hole in the aperture, and the optical length is a projection perpendicular to the optical width.

According to a further exemplary embodiment, which is also shown in Fig. 10, the means for deflection are adapted such that the stereo spots can be skewed.

It is explicitly noted that the features shown in the respective figures can also be applied isolated from other features shown in that respective figure and can thus be freely combined with further features.

As can be seen in Fig. 10, the focal spot shapes 152 are arranged such that their longitudinal axis are arranged in an inclined manner, i.e. the axis meet at a common section point and are thus forming an angle in-between. In other words, skewed stereo spots are not arranged parallel to each other but in an inclined manner.

For example, the means for deflection comprise optical magnetic lenses.

According to a further aspect of the invention, the detector comprises a plurality of cells 156, which is indicated in the left part of Fig. 1 1. According to a further aspect, the control unit is adapted to provide an asymmetric binning of the detector cells.

The asymmetric binning allows for high tube currents, large signal-to-noise ratios in the detector, reduced patient dose, and a high contrast for a proper stereo effect.

As there is no three-dimensional separation in Z-direction, the Y-resolution is less demanding.

For example, the binning comprises a binning of cells in the X- and the Z- direction with a ratio of smaller than 1/3, preferably as small as 1/8.

A binning with a ratio of 1/8 is indicated with a dashed pattern 158 in Fig. 11. According to another aspect of the invention, it is also possible to arrange the orientation of the focal spot shapes to be inclined with respect to the detector grid, which is schematically shown in Fig. 12.

As indicated with a dashed pattern 158, an asymmetric binning is provided which comprises a summarization or addition of a pattern of detector cells which has more detector cells in a first binning direction, indicated with a secondary coordinate system with a binning axis X_B and another binning axis Z_B. The asymmetric binning comprises the summarization of more detector cells in the first binning direction, for example in the Z_B- direction, than in a second binning direction, for example the X_B-direction. The second binning direction is perpendicular to the first binning direction. The second binning direction is having a smaller angle to a perpendicular of the stereo direction than the second binning direction.

According to a further aspect, the asymmetric binning is adapted to the projected length/width ratio of the focal spot pattern.

According to a further aspect, the detector cells are arranged in a grid, as shown in Fig. 12, and the viewing direction is arranged in a skewed or inclined angle in relation to the detector grid. The viewing direction is indicated with dotted lines 160 in Fig. 12.

As already mentioned above, the binning directions are arranged in a skewed or inclined angle in relation to the detector grid.

According to a further aspect, the skewed angle results in a skewed binning pattern, as indicated with the dashed pattern 158.

As can be seen, according to an example, the skewed binning pattern comprises a stepped pattern of detector cells.

According to a further aspect, although not shown, a scintillator is provided with an asymmetric structure. For example, the scintillator material comprises needles with an ellipsoidal cross section.

According to a further exemplary embodiment shown in Fig. 13, the aperture is provided with three holes to provide two stereoscopic focal spot positions and a central focal spot position for mono-scopic viewing.

According to a further exemplary embodiment, the two stereo spots can be provided by a selection from a set of at least three focal spot positions arranged such that a projection of the focal spot positions in the viewing direction results in a first two- dimensional pattern.

For example, at least four focal spot positions are provided.

According to a further exemplary embodiment, six focal spot positions are provided.

According to a further aspect of the invention, the aperture comprises a set of at least three holes 164 arranged in a second two-dimensional pattern, wherein the second two-dimensional pattern is adapted to the first two-dimensional pattern, as indicated in Fig. 14.

According to a further aspect of the invention, six focal spot positions are arranged by providing three focal spot positions in two lines. As can be seen in Fig. 15, the focal spot positions are indicated with circles 166.

Reference 167 schematically indicates two focal tracks.

Thus, a two-dimensional pattern is provided from which the focal spot positions to be applied for the respective stereoscopic viewing can be selected. In Fig. 15 A, the lower left and the upper right positions are selected such that the viewing direction is also inclined. In Fig. 15B, the upper left and the lower right are selected to provide a stereoscopic effect in an inclined manner opposite to the one shown in Fig. 15 A. Further, it is also possible to select the upper left and the lower middle one to provide a further inclined stereoscopic imaging with a stereoscopic direction indicated with a dotted line 168. The selected focal spot positions are indicated with patterned circles 170.

As indicated in Fig. 15D and 15E, it is also possible to select the upper left and right or the lower left and right positions, respectively, to provide further differentiated stereoscopic imaging.

According to a further aspect (not shown), the stereo spots are selected automatically by the system based on image data analysis.

According to an alternative aspect (not shown), the stereo spots are selected manually by the user. According to a further aspect (not shown), both possibilities are provided, i.e. automatic selection and manual selection, for example, the selection of two stereo spots out of a plurality of stereo spots, such as six stereo spots.

According to a further exemplary embodiment of the invention, a method for stereoscopic imaging is provided. A method 500, shown in Fig. 16, comprises the following steps:

In a first acquisition step 510, first image data 112 is acquired with X-rays delivered by a first stereo focal spot. In a second acquisition step 514, second image data 516 is acquired with X-rays delivered by a second stereo focal spot.

The thus acquired image data can then be further processed indicated with a common rectangular box 518.

The first acquisition step is also referred to as step a) and the second acquisition step as step b).

According to the method described above, an X-ray tube for stereoscopic imaging is provided with a cathode, an anode, means for deflection of an electron beam, an X-ray aperture with at least a first hole and a second hole, and an envelope housing the cathode and the anode, wherein the aperture is fixedly arranged inside the envelope.

According to the method, during step a) the means for deflection are deflecting the electron beam from the cathode such that the electron beam hits the anode in a first stereo focal spot position; and during step b) the means for deflection are deflecting the electron beam from the cathode such that the electron beam hits the anode in a second stereo focal spot position, wherein the first and second stereo focal spot positions are separated from each other with a first distance defining a stereo direction. During step a) an X-ray beam is generated at the first focal spot emanating in a viewing direction through one of the at least first and second holes in the aperture. The direction of the first distance is perpendicular to the viewing direction. According to the method, the stereo focal spot positions are adapted in the stereo direction and/or the viewing direction.

According to a further exemplary embodiment, a method is provided, wherein before step a), the first and the second focal spot positions are selected 520 from a set of at least three focal spot positions arranged such that a projection of the focal spot positions in the viewing direction results in a first two-dimensional pattern. This is indicated in Fig. 17.

According to a further exemplary embodiment, shown in Fig. 18, a method is provided wherein the first and second image data are transformed 522 into a first and a second image 524, 526 and wherein the first and second images are presented expanded and edge enhanced at least in the stereo direction, which is indicated by a common box 528.

However, it is also possible to provide the presentation of box 528 into separate boxes for each of the respective images.

According to a further aspect of the invention, a single X-ray tube is attached to a conventional collimator.

According to an aspect of the invention, a centre focal spot in two alternating stereo spots is created by X-deflection of a single electron beam. Additional to a single funnel collimator, the radiation field is defined by a tube intrinsic triple hole aperture. The focal spot positions are adapted to object position, to SID, to field limitation or to stereo zone requirements. For a stereo mode, the focal spot widths (X) are minimized. The larger the magnification, the narrower the focal spots.

According to a further aspect, as a benefit, the three-dimensional effect in centre region of the object is adaptable to the object position in the system. Further, due to only providing a single tube, stereoscopic imaging is provided in a cost-effective, compact, and low-mass including embodiment.

According to a further aspect, a fixed intrinsic aperture is used. Therefore, the focal spot positions need to be flexible to be adjusted for different SIDs.

In another exemplary embodiment of the present invention, a computer program or a computer program element is provided that is characterized by being adapted to execute the method steps of the method according to one of the preceding embodiments, on an appropriate system.

The computer program element might therefore be stored on a computer unit, which might also be part of an embodiment of the present invention. This computing unit may be adapted to perform or induce a performing of the steps of the method described above. Moreover, it may be adapted to operate the components of the above described apparatus. The computing unit can be adapted to operate automatically and/or to execute the orders of a user. A computer program may be loaded into a working memory of a data processor. The data processor may thus be equipped to carry out the method of the invention.

This exemplary embodiment of the invention covers both, a computer program that right from the beginning uses the invention and a computer program that by means of an up-date turns an existing program into a program that uses the invention.

Further on, the computer program element might be able to provide all necessary steps to fulfil the procedure of an exemplary embodiment of the method as described above.

According to a further exemplary embodiment of the present invention, a computer readable medium, such as a CD-ROM, is presented wherein the computer readable medium has a computer program element stored on it which computer program element is described by the preceding section.

However, the computer program may also be presented over a network like the World Wide Web and can be downloaded into the working memory of a data processor from such a network. According to a further exemplary embodiment of the present invention, a medium for making a computer program element available for downloading is provided, which computer program element is arranged to perform a method according to one of the previously described embodiments of the invention.

It has to be noted that embodiments of the invention are described with reference to different subject matters. In particular, some embodiments are described with reference to method type claims whereas other embodiments are described with reference to the device type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters is considered to be disclosed with this application.

However, all features can be combined providing synergetic effects that are more than the simple summation of the features.

While the invention has been illustrated and described in detail in the drawings and 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. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing a claimed invention, from a study of the drawings, the disclosure, and the dependent 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 fulfil the functions of several items re-cited in the claims. The mere fact that certain measures are re-cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. An X-ray tube (10) for stereoscopic imaging, comprising:

- a cathode (12);

an anode (14);

means (16) for deflection of an electron beam;

an X-ray aperture (18) with at least a first hole (20) and a second hole (22); and

- an envelope (24) housing the cathode and the anode;

wherein the means for deflection are adapted such that the electron beam from the cathode can be deflected such that the electron beam hits the anode in at least two stereo focal spot positions (26) separated from each other with a first distance (28) defining a stereo direction (30);

wherein the aperture is fixedly arranged inside the envelope; wherein an X-ray beam (32) is generated at each focal spot emanating in a viewing direction (34) through one of the at least first and second holes in the aperture;

wherein the direction of the first distance is perpendicular to the viewing direction; and

wherein the first distance is adaptable.

2. X-ray tube according to claim 1 , wherein the means for deflection are adapted such that the at least two focal stereo spot positions are adaptable in the viewing direction.

3. X-ray tube according to claim 1 or 2, wherein the means for deflection are adapted such that the focal spots are each provided with a focal spot shape (152) in which a projected length (L_P) is larger than a projected width (Wp).

4. X-ray tube according to claim 3, wherein the projected length and the projected width have a ratio of larger than 3/1.

5. X-ray tube according to one of the preceding claims, wherein the means for deflection are adapted such that the stereo spots can be skewed.

6. X-ray tube according to one of the preceding claims, wherein two stereo spots (74, 76) can be provided by a selection from a set of at least three focal spot positions (26) arranged such that a projection of the focal spot positions in the viewing direction results in a first two-dimensional pattern.

7. X-ray tube according to claim 6, wherein six focal spot positions (166) are provided.

8. An X-ray imaging system (200), comprising

an X-ray tube (210) according to one of the preceding claims; a detector (212); and

a processing unit (214);

wherein the processing unit is adapted to control the emission of an electron beam from a cathode; and to control means for deflection; and

wherein the detector is provided with an asymmetric resolution, which is finer along the stereo direction than in a direction perpendicular to the stereo direction.

9. System according to claim 8, wherein the processing unit is adapted to control the means for deflection such that the stereo spots can be selected automatically by the system based on image data analysis and/or manually by the user.

10. A method for X-ray tube for stereoscopic imaging, comprising the following steps:

a) acquiring (510) first image data (512) with X-rays delivered by a first stereo focal spot;

b) acquiring (514) second image data (516) with X-rays delivered by a second stereo focal spot;

wherein an X-ray tube for stereoscopic imaging is provided with a cathode, an anode, means for deflection of an electron beam, an X-ray aperture with at least a first hole and a second hole, and an envelope housing the cathode and the anode; wherein the aperture is fixedly arranged inside the envelope;

wherein during step a) the means for deflection are deflecting the electron beam from the cathode such that the electron beam hits the anode in a first stereo focal spot position; and wherein during step b) the means for deflection are deflecting the electron beam from the cathode such that the electron beam hits the anode in a second stereo focal spot position; wherein the first and second stereo focal spot positions are separated from each other with a first distance defining a stereo direction;

wherein during step a) an X-ray beam is generated at the first focal spot emanating in a viewing direction through one of the at least first and second holes in the aperture;

wherein the stereo focal spot positions are adapted in the stereo direction and/or the viewing direction.

11. Method according to claim 10, wherein before step a) the first and the second focal spot position are selected (520) from a set of at least three focal spot positions arranged such that a projection of the focal spot positions in the viewing direction results in a first two- dimensional pattern.

12. Method according to claim 11, wherein the selection of the stereo spots is performed automatically by the system based on image data analysis and/or manually by the user.

13. Method according to claim 10, 11 or 12, wherein the first and second image data are transformed (524, 526) into a first and a second image; and wherein the first and second images are presented (528) expanded and edge enhanced at least in the stereo direction.

14. Computer program element for controlling an apparatus according to one of the claims 1 to 9, which, when being executed by a processing unit, is adapted to perform the method steps of one of the claims 10 to 13.

15. Computer readable medium having stored the program element of claim 14.