WO2010052628A2

WO2010052628A2 - Device and method for adjusting anode angle and anode-to-anode distance

Info

Publication number: WO2010052628A2
Application number: PCT/IB2009/054847
Authority: WO
Inventors: Rolf K. O. Behling
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N. V.
Priority date: 2008-11-07
Filing date: 2009-11-02
Publication date: 2010-05-14
Also published as: WO2010052628A3

Abstract

The present invention is an X-ray device (10, 51, 52) with two rotatable anodes each having a target area for emitting an X-ray beams. The anodes are spaced with an adjustable distance (31) from each other, and the rotational axis of each anode is tiltable with an adjustable tilt angle (32) relative to a detector field plane of a detector (14), detecting each X-ray beam in a common detector field (33).

Description

DEVICE AND METHOD FOR ADJUSTING ANODE ANGLE AND ANODE-TO- ANODE DISTANCE

FIELD OF THE INVENTION

The present invention relates generally to X-ray devices and more particularly to computed tomography (CT) scanners and a method to operate said devices.

BACKGROUND OF THE INVENTION

In current X-ray devices in a CT system an X-ray tube is rotating around an object of interest, for example a patient or, for industrial applications, around a good to be inspected. Opposite to the X-ray tube and with it on a gantry rotor rotates a detector, which converts the X-rays, attenuated by the object of interest, into electrical signals for later processing. During processing a computer system reconstructs an image of the object of interest, a patients body for instance. US 5,822,395 discloses an x-ray apparatus wherein an X-ray tube can be used with a focal spot having a suitable size and geometry for different applications. The anode disk of the x-ray tube is tiltable with respect to the connecting axis between the focal spot and the center of a detector.

SUMMARY OF THE INVENTION

It is one object of the invention to provide an X-ray device, a CT apparatus and an accompanying method capable of improving image quality and reducing patient dose for medical applications. Further it is another object of the invention to provide said means capable to modifying the field or volume of irradiation according to a region of interest (ROI), between the X-ray device and the detector changing in seize and/or position.

In order to achieve the above objects, the present invention provides an X-ray device, a CT scanner and a method according to the independent claims. The X-ray device comprising: a first and a second rotatable anode each having a target area for emitting an X-ray beam, wherein the anodes are spaced with an adjustable distance from each other, and wherein the rotational axis of each anode is tiltable with an adjustable tilt angle relative to a detector field plane of a detector, detecting each X-ray beam in a common detector field. As the X-ray optical focal spot appears brighter for decreasing view angles, view angle and anode angle should be minimal. The anode angle is the angle spanning between a target area or focal spot plane of the anode, particularly the anode disk and a normal of a detector plane crossing the focal spot of the said anode target area. The effective anode angle is the said anode angle plus a tilt angle. The tilt angle may be defined as the angle spanning between an anode-centered rotational axis in a first normal position and the rotational axis shifted around a pivot axis through the focal spot of the anode, wherein the pivot axis is orientated perpendicular to said shifted rotational axis. According to the invention a continuously changing of said tilt angle with a predefined absolute angle value have the same effect for the deflection of the anode's optical focal spot plane and thus for the effective anode angle.

Further, penumbra and beam hardening effects may restrict the useful radiation field to minimum angles between 1° and 5°. Here, the invention enables to choose a minimal effective anode angle by a respective tilting of the anode disk or X-ray tube around a predefined tilt angle to have an optimal ratio of thermal loadability and brightness (~1 /angle) of the focal spot. Further, for a symmetric radiation field Φ, the effective anode angle αeff may be designed to αeff= Φ/2 + υ, wherein υ is the view angle adjacent to the radiation field Φ with the X-ray device of the invention. In other words, according to the invention, the effective anode angle αeff for the focal spot plane of each anode can be adjusted for optimal brightness and loadability, which is preferably achieved by tilting the anodes and/or the tubes with respect to the detector plane/ or a CT gantry. According to another embodiment of the invention, a CT scanner comprising: a rotating gantry, an X-ray device with a first and a second rotatable anode each having a target area for emitting an X-ray beam, wherein the X-ray device rotably mounted to said gantry, wherein the anodes are spaced with an adjustable distance from each other, and wherein the rotational axis of each anode is tiltable with an adjustable tilt angle relative to a plane of a detector field of a detector for detecting each X-ray beam in a common detector field and a detector mounted to said gantry opposite to said X-ray device for receiving X-rays from the X-ray device.

It yet another embodiment of the invention a method of generating two X-ray beams is proposed, the method comprising the steps of: adjusting the distance between a first anode and a second anode, adjusting a tilt angle of the first anode relative to a detector field plane of a detector, adjusting a tilt angle of the second anode relative to the detector field plane, generating a first electron beam from a first cathode facing a target area of the first anode, generating a second electron beam from the first cathode or a second cathode facing a target area of a second anode, generating a first X-ray beam by the first anode, generating a second X-ray beam by the second anode and receiving X-radiation generated from the first and second anode by a the detector.

In other aspects an X-ray device, wherein each anode having a back face and the target area on a front face is achieved in several configurations: In a first face-to- face anode configuration the front face of the first anode is facing the front face of the second anode. In a back-to-back anode configuration the back face of the first anode is facing the back face of the second anode. Finally, in a parallel anode configuration the back face of the first anode is facing the front face of the second anode.

In one aspect it proposed, particularly for the face-to-face and back-to- back anode configuration, that the first anode having a first cathode adjacent thereto and the second anode having a second cathode adjacent thereto. Further it may be preferred to use just one cathode for both anodes in the parallel anode configuration, wherein the first anode or anode disk having at least one slit or cavity within the target area to enable the electron beam of the cathode passing through to the target area of the second anode. In one aspect a common X-ray tube may enclose the first and second anode and the first and second cathode.

In yet another aspect, a first X-ray tube enclosing the first anode and the first cathode. a second X-ray tube enclosing the second anode and second cathode, wherein the adjustable distance and/or the adjustable tilt angle are adjustable by adjusting the respective X-ray tube.

In yet another aspect, the X-ray device comprises at least one focusing system for generating an electro -magnetic field, particularly comprising a magnetic quadrupole field, for varying the cross-sectional shape of the electron beam from at least one of the cathodes to at least one of the anodes in conformity with the adjusted tilt angle, particularly by varying the radial extension of the electron beam (length), while maintaining the azimuth extension (width).

According to yet another aspect it may the adjustment of the tilt angle of each anode and the adjustment of the distance between the anodes may be carried out by at least one mechanical device comprising at least one motor drive, using rails, pivot points and actuators. The mechanical devices enabled to adjust the tilt angle properly in accordance to a varying distance between the anodes/focal spots.

In another aspect, the adjustment of the tilt angle of each anode and the adjustment of the distance between the anodes is carried out by using at least one bellows system. In one preferred embodiment the CT device comprises an adjustable collimator mounted to the rotating gantry in between the said X-ray device and said detector, said collimator for collimating X-ray generated by said X-ray source so as to obtain a fan- shaped beam of adjustable thickness for irradiating an object space, the region of interest (ROI). In one aspect the method according to the invention comprises the steps of adjusting a collimator and collimating the first and second X-ray beam.

Further, the method may comprise: generating a focusing electromagnetic field, preferably a magnetic quadrupole filed to vary the cross-sectional shape of the first and second electron beam from the cathodes to the anodes in conformity with the adjusted tilt angle.

According to one embodiment of the invention, the adjusting of the distance between the anodes is carried out continuously.

It may be another embodiment if the adjusting of both tilt angles is carried out with the same absolute value.

Other objects and advantages of the present invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this invention, reference should now be had to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention. In the drawings:

Fig. 1 is a schematic diagram of an X-ray device in a CT;

Fig. 2 is a view of a cathode, an anode, and focal spots for different anode angles;

Fig. 3 is a schematic view of two different arrangements of two anodes and the respective radiation field;

Fig. 4 is a sectional view to three different anode configurations; Fig. 5 is an expanded back-to-back anode configuration; and Fig. 6 is the back-to-back anode configuration of Fig. 5 with close anode-to-anode distance. DETAILED DESCRIPTION OF EMBODIMENTS

Referring to Fig. 1, there is shown an X-ray device 10 with an X-ray tube containing two anodes not shown here, on a rotating gantry 12, along with a detector 14 as it would be arranged for a volume CT application. A adjustable collimator 16 collimates the X-rays from the focal points into planes of radiation. The gantry 12 rotates about an axis moving the X-ray device 10 and the detector 14 along with. A computer system, not shown here, reconstructs an image of on object of interest, not shown here. Referring to Fig. 2, a cathode 22, an anode 24 in form of an anode disk are schematically shown. Further the respective radiation field Φ, 26, 26', 26" for different effective anode angles αeff are shown, wherein 5°, 0° and 5° are tilt angles for which the anode is tilted around a pivot point, shown in Fig. 5.

In a first unshifted position (tilt angle 0°) the focal spot diagram on the right side of Fig. 2 shown the associated focal spot 28' with a quadratic shape. Tilted or shifted by 5° tilt angle, the focal spot 28 and the associated radiation field 26 are elongated, Tilted by 5° tilt angle, the shape focal spot 28" and the associated radiation field 26" are compressed. Further, Fig. 2 shows a view angle υ and a reserve angle υr adjacent to the radiation field Φ. For a symmetric radiation field Φ (middle row of the focal spot diagram) the anode angle α has to be designed to α=Φ/2 + υ.

Referring to Fig. 3, two different arrangements of two anodes, not shown here, and the respective X-radiation field generated by an electron beam 35 focused by a collimator 38 are shown schematically. In the arrangement A the region of interest 30 is larger than in the arrangement B on the right. Thus, the focal spots FSl and FS2 of the two anodes are spaced with a larger distance 31 from each other in the arrangement A and are adjusted to a smaller distance 31' shown on arrangement B. Further, comparing the arrangements, each anode is tilted around a tilt angle (arrow 32) relative to a detector field plane of a detector 32, detecting each X-ray beam in a common detector field 33. Comparing both arrangements A, B it could be noted, that the anode with focal spot FS 1 is tilted with a smaller tilt angle than the second anode with focal spot FS 2. Further, arrangement B shows a shorter focal distance (central beam line 34) between the focal spots FSl and FS2 than arrangement B.

Referring to Fig. 4, three different X-ray device configurations A, B, and C are shown, wherein each anode having a back face and the target area on a front face. In a first face-to-face anode configuration A the front face 41 of the first anode 42 is facing the front face 43 of the second anode 44. In a back-to-back anode configuration B the back face 45 of the first anode 42 is facing the back face 46 of the second anode 44. Finally, in a parallel anode configuration the front face 41 of the first anode 44 is facing the back face 46 of the second anode 44. Referring to Fig. 5 and 6, two X-ray devices 51, 52 are shown in an expanded configuration (Fig. 5) and a compressed configuration (Fig. 6). In this embodiment tubes are mounted in a back-to-back anode configuration (see Fig. 4, configuration B). The tubes can be moved along an axis 53 using a motor drive 54. Further the tubes, and the anodes 55, 56 respectively, can be tilted around their pivot axis 57, which are perpendicular to the paper plane proceeding through the centers of the focal spots 58, 59. Preferably, the tilting takes place by tilting the rotational axis of the onode disks 55, 56 around a direction perpendicular to their centered rotational axis by a defined tilt angle.

Claims

CLAIMS:

1. An X-ray device (10, 51, 52) comprising: a first and a second rotatable anode (24, 42, 44, 55, 56) each having a target area (FSl, FS2) for emitting an X-ray beam; wherein the anodes (24, 42, 44, 55, 56) are spaced with an adjustable distance (31, 31 ') from each other, and wherein the rotational axis of each anode is tiltable with an adjustable tilt angle (32) relative to a detector field plane of a detector (14) , detecting each X-ray beam in a common detector field (33).

2. An X-ray device (10, 51, 52) according to claim 1, wherein each anode having a back face (45, 46) and the target area on a front face (41, 43), and a) wherein the front face (41) of the first anode (42) is facing the front face (43) of the second anode(44) in a face-to-face anode configuration or b) wherein the back face (45) of the first anode (42) is facing the back face (46) of the second anode (44) in a back-to-back anode configuration or c) wherein the front face (41) of the first anode (42) is facing the back face (46) of the second anode (44) in a parallel anode configuration.

3. An X-ray device (10, 51, 52) according to claim 1 or 2, wherein the first anode having a first cathode (22) adjacent thereto and the second anode having a second cathode adjacent thereto.

4. An X-ray device (10) according to one of the claims 1 to 3, further comprising a common X-ray tube enclosing the first and second anode and the first and second cathode.

5. An X-ray device (10, 51, 52) according to one of the claims 1 to 3, further comprising a first X-ray tube (51) enclosing the first anode and the first cathode. a second X-ray tube (52) enclosing the second anode and second cathode; wherein the adjustable distance (31) and/or the adjustable tilt angle (32) are adjustable by adjusting the respective X-ray tube.

6. An X-ray device (10, 51, 52) according to one of the claims 1 to 5, further comprising at least one focusing system (38) for generating an electro -magnetic field, particularly comprising a magnetic quadrupole field, for varying the cross-sectional shape of the electron beam from at least one of the cathodes to at least one of the anodes in conformity with the adjusted tilt angle, particularly by varying the radial extension of the electron beam (length), while maintaining the azimuth extension (width)

7. An X-ray device (10, 51, 52) according to one of the claims 1 to 6, wherein the adjustment of the tilt angle (32) of each anode and the adjustment of the distance (31) between the anodes is carried out by at least one mechanical device (54) comprising at least one motor drive;

8. An X-ray device (10, 51, 52) according to one of the claims 1 to 7, wherein the adjustment of the tilt angle (32) of each anode and the adjustment of the distance between the anodes is carried out by using at least one bellows system.

9. An CT scanner comprising: a rotating gantry (12); an X-ray device (10, 51, 52) with a first and a second rotatable anode each having a target area for emitting an X-ray beam; wherein the X-ray device (10, 51, 52) rotably mounted to said gantry; wherein the anodes are spaced with an adjustable distance from each other, and wherein the rotational axis of each anode is tiltable with an adjustable tilt angle relative to a plane of a detector field of a detector for detecting each X-ray beam in a common detector field; and a detector (14) mounted to said gantry opposite to said X-ray device (10, 51, 52) for receiving X-rays from the X-ray device(l 0, 51, 52).

10. The CT scanner of claim 9, further comprising: an adjustable collimator (16) mounted to said rotating gantry (12) in between the said X- ray device (10) and said detector (14), said collimator (16) for collimating X-ray generated by said X-ray device so as to obtain a fan-shaped beam of adjustable thickness for irradiating an object space, the region of interest (30).

11. A method of generating two X-ray beams, comprising the steps of: adjusting the distance (30) between a first anode and a second anode; adjusting a tilt angle (32) of the first anode relative to a detector field plane (33) of a detector (14); adjusting a tilt angle (32) of the second anode relative to the detector field plane; generating a first electron beam from a first cathode (22) facing a target area of the first anode (24); generating a second electron beam from the first cathode (22) or a second cathode facing a target area of a second anode; generating a first X-ray beam by the first anode; generating a second X-ray beam by the second anode; receiving X-radiation generated from the first and second anode by a the detector.

12. The method of claim 11, further comprising the step of : adjusting a collimator (16) and collimating the first and second X-ray beam.

13. The method of claim 11 or 12, further comprising the step of : generating a focusing electromagnetic field, preferably a magnetic quadrupole filed (38) to vary the cross-sectional shape of the first and second electron beam from the cathodes to the anodes in conformity with the adjusted tilt angle.

14. The method of one of claims 11 to 13, wherein the adjusting of the distance between the anodes is carried out continuously.

15. The method of one of claims 11 to 14, wherein the adjusting of the tilt angles (32) is carried out with the same absolute value.