WO2009149991A1

WO2009149991A1 - Method and device for producing an overall x-ray image that is composed of partial images

Info

Publication number: WO2009149991A1
Application number: PCT/EP2009/055293
Authority: WO
Inventors: Andrea Zandegiacomo; Thomas Pohl; Helmuth Schramm
Original assignee: Siemens Ag Österreich; Siemens Aktiengesellschaft
Priority date: 2008-06-09
Filing date: 2009-04-30
Publication date: 2009-12-17

Abstract

A method for producing a series of partial images that, when put together, provide an overall x-ray image of an object to be examined (2), a drive system moving an x-ray radiation source (1) incrementally in successive imaging positions (P1, P2, P3, P4) in order to emit an x-ray radiation beam (4), which is detected by a detector system (3) as a radiation image (11) after penetrating a partial region of the object to be examined, characterized in that a linear movement and a rotational movement are carried out by the x-ray radiation source (1) when moved into an imaging position.

Description

description

Method and apparatus for creating an overall X-ray image composed of sub-images

Technical area

The present invention relates to a method and an apparatus for producing a sequence of partial images, which in an assembled form yield an overall X-ray image of an examination object, wherein a drive system moves an X-ray source stepwise into recording positions in order to emit in each case an X-ray beam , which is detected by a detector system as a radiation image after penetration of a sub-region of the examination subject.

In order to represent a whole spine or a whole leg in a single X-ray image, in radiological examinations, the examination area is displayed stepwise, and the individual partial images are combined by means of a digital image processing system to form an X-ray overall image. The quality of this calculated total X-ray image depends crucially on the receiving position in which the X-ray source is located when a partial image is taken.

In DE 102 44 609 A1, for example, an X-ray device is described in which a radiation source is displaced vertically with respect to a standing patient into successive acquisition positions in order to form partial images create digitally merged into an overall picture. In this case, it is disadvantageous that the x-rays lying in the beam cone impinge on the recording plane of the detector at an acute angle. It comes to a so-called parallax effect: a point of

Examined object is illuminated from different directions and is thus projected at different positions on the recording plane of the detector. As a consequence, distortions, i. a blurring at the seams of the individual partial images. The distortion is the greater, the sharper the angle of entry of the X-rays is on the receiving plane, that is, the smaller the distance between the X-ray source and the detector. Of particular disadvantage is that this distortion can be computationally difficult to correct.

In another known method, as disclosed, for example, in DE 101 09 754 B4, the X-ray source for taking the individual X-ray partial images is pivoted by a certain angle, but is fixed locally. The disadvantage here is that the pivoting causes a slanting radiation, which again in particular in the edge regions of the beam cone, the objects lying one above the other in the examination object lying on the detector as lying side by side. Follow this

Projection error is again a distortion, which is the greater, the smaller the distance between the X-ray source and the recording plane.

Both artifacts are of course undesirable because they are the

Affect image quality of the overall X-ray image and represent a source of error that may lead to incorrect diagnostics. For the acquisition of partial images, which are carried out in a lying patient, the smallest possible distance between the radiation source and the detector is desirable, since the available room height in a treatment room is usually limited to less than 300 cm.

Presentation of the invention

It is an object of the present invention to provide a method and a device for generating a composite of partial images X-ray overall image so that when recording high-quality partial images of the distance between the X-ray source and detector can be kept as low as possible.

This object is achieved for a method by the features of patent claim 1 and for a device having the features of claim 15. Advantageous embodiments of the invention are defined in the respective dependent claims.

According to the invention, it is provided that a drive system, for the production of the individual partial recordings, respectively positions the X-ray source in recording positions, the positioning movement being composed of a linear movement and of a pivoting movement of the X-ray source. The X-ray source is thus displaced laterally relative to the examination subject in several steps by a predeterminable distance and rotated by a predeterminable rotational or pivotal angle. This ensures that the parallax effect is less strong effect. By suitably specifying the distance and the swivel angle, it is possible to substantially reduce the distance between the X-ray source and the detector, without the quality of the overall X-ray image being greatly impaired. Ceiling mounting of the X-ray machine in conventional treatment rooms is possible.

In a preferred embodiment of the invention, the drive system automatically predefines the step size and the angle of rotation when the X-ray source moves into a pickup position. As a result, no manual actions for taking the sub-picture sequence are required.

It may be advantageous if the geometric dimensions of the examination object are taken into account when specifying the step size and the angle of rotation. This can for example be done so that the size of the area of interest to be examined is input to controls of the drive system. The drive system then calculates from the distance between the X-ray source and the examination subject, as well as from the travel paths of the X-ray source and the detector, a favorable angle of rotation with regard to the quality of the overall image.

Short movement times can be achieved in particular if the linear movement and the rotational movement are performed simultaneously.

It may be expedient if the linear movement takes place in the direction of a longitudinal axis, which is substantially parallel to a longitudinal axis of the examination subject. Preferably, the rotational movement about a pivot axis, which is arranged perpendicular to the longitudinal axis.

The specification of the angle of rotation is computationally simpler if the pivot axis by the focus of the X-ray

Radiation source runs. Less corrections are required.

In a preferred embodiment of the invention adjacent receiving positions each differ by an equal step size. The specification of an equal step size is technically simple.

On the other hand, it may also be favorable if the distance between adjacent receiving positions is not equal but is set to a different size. This allows a particular area of interest, such as a particular portion of the spine, to be shifted out of a fuzzy interface area into a central area of a partial image. This can do that

Area of interest in the overall x-ray image to be accurately represented.

With regard to the timing when creating a sequence of sub-images, it may be beneficial if the

Pivoting operation of the X-ray source with the same direction of rotation.

In terms of design, it may be favorable if the detector system has a flat detector which can be displaced by means of the drive system in a receiving plane. With regard to short positioning times, it may be favorable if the displacement in detector recording positions is carried out synchronously, ie simultaneously with the positioning movement of the x-ray source.

In the reconstruction of the overall X-ray image, it is favorable if the movement of the flat detector takes place in such a way that the individual consecutive partial images overlap. The overlap width is chosen so that the individual partial images can be merged to form an overall picture.

For a vibration-free sequence when taking the sub-images, it may be advantageous if the drive device is given a driving profile that continuously rises or falls, so that the reaction torque during the acceleration phase or during the deceleration phase of the X-ray source is as low as possible ,

Brief description of the drawings

To further explain the invention, reference is made in the following part of the description to the drawings, from which further advantageous embodiments, details and further developments of the invention can be found.

Show it:

FIG. 1 shows a three-dimensional sketch of a first embodiment of the invention, in which the X-ray radiation directed onto an examination subject is shown. Radiation source can be seen in three recording positions, each of these recording positions is approached by a positioning movement, which is composed of a linear movement and a rotational or pivotal movement of the X-ray source;

Figure 2 is a representation of the beam path of an X-ray source in four receiving positions, according to a second embodiment of the invention;

Figure 3 is an illustration of the beam path of an X-ray source in four recording positions, wherein the recording positions are respectively occupied by a local displacement of the X-ray source, according to the prior art;

4 shows a representation of the beam path of an X-ray source in four recording positions, wherein the recording positions are taken by a pivoting movement of a stationary X-ray source, wherein the distance between X-ray source and detector is 300 cm, according to the prior art;

Figure 5 is a view according to Figure 4, wherein the distance between the X-ray source and detector is 180 cm. Embodiment of the invention

The method according to the invention will first be explained with reference to the spatial sketch in FIG. 1 shows an X-ray source 1 in three recording positions Pl, P2 and P3, in each of which a conical X-ray beam 4 is emitted. The examination beam 2 is located in a receiving plane 12. The X-ray source 1 is displaceable by means of an electric drive system 14 not shown here along the axis 6 (double arrow 8) and about the axis 5 pivotally mounted. The axis 6 is approximately parallel to the longitudinal axis 9 of the examination subject 2 and passes through the focal point (focus) of the X-ray source 1. The distance between the X-ray source 1 and the receiving plane 12 is indicated by the arrow SID. The detector system 3 consists of a flat detector which is displaceable in the direction of the arrow 15. The step size of the detector system 3 is in this example the same size with the step size of the linear displacement of the X-ray source 1 (Δsl or Δs2). The sequence of partial images can be recorded according to the arrow 8 from left to right or from right to left.

According to the invention, the displacement of the X-ray source 1 between adjacent pick-up positions, eg between Pl and P2, or between P2 and P3 involves a translation and a rotation. This type of stepwise displacement of the X-ray source 1 combines, so to speak, the movement processes of the above-mentioned known methods, in which either only one translation or only one rotation of the X-ray source 1 is performed.

The sequence according to the invention when creating a sequence of X-ray partial recordings is as follows:

If, for example, a first radiation image 11 of a subarea of the examination subject 2 was recorded in the position P1, then the x-ray radiation source 1 for the purpose of recording a second partial image in the

Pickup position P2 shifts (linear movement according to the arrow 8 to the right). This displacement takes place by the drive system 14. The distance traveled in this translation is the step size Δsl. A rotary movement comes to this linear movement: the X-ray source 1 is rotated by the angle Δφl clockwise. The longitudinal movement and the rotational movement preferably occur simultaneously during the positioning process; however, the two movements can also be performed one behind the other. As soon as the X-ray source 1 is in the position P2, a cone-shaped X-ray beam 4 is emitted again for the purpose of taking a second partial image. This X-ray beam 4 is now directed to a central sub-area of the examination object 2. The x-rays of the bundle 4 penetrate this central subarea and again cause a two-dimensional shadow image 11 on the flat detector of the detector system 3. In the next step, the X-ray source 1 is shifted from the pickup position P2 to the pickup position P3. During this movement process, the X-ray emitter 1 again covers a linear movement with the step size Δs2 and the emitter 1 with respect to the rotational position in P2 by the angle of rotation Δφ2 in FIG Pivoted clockwise. Compared to Pl now the X-ray source 1 is tilted by the angle Δφl + Δφ2. The angle between the longitudinal axis 6 and the axis 7 (central ray) of the radiation beam 4 is shown in FIG. 1 with φ 1, φ 2, φ 3. Adjacent recording positions are laterally offset by the step size .DELTA.sl or .DELTA.s2 and rotated by the rotational angle .DELTA..phi..sub.1 or .DELTA..phi.2.

The detector system 3 detects the individual partial images 11 of the examination object 2. As already mentioned above, the image information provided by the detector system 3 is generated in a conventional manner by means of an image processing device, not shown here, an overall X-ray image 13 (see FIG. 2) of the examination subject 2 created. The reconstruction of a two-dimensional overall image from a sequence of overlapping two-dimensional partial images takes place digitally. Both methods and devices of the digital image composition are well known and need not be further explained here for the understanding of the present invention.

The technical design of the detector system 3 may be different, for example, a sheet-shaped solid state detector (scintillator), which is slidably mounted in the plane 12 and synchronously with the

Movement of the radiator 1 enters different detector positions. However, the detector system 3 can also comprise a DLR cassette, an X-ray storage film, a conventional X-ray film, or another suitable sheet-like recording medium.

The step size and angle of rotation can vary from one position to another. Is advantageous in particular an adaptation to the size of the examination subject 2, or to areas of particular anatomical interest, which can be done by corresponding input to controls not shown here, the drive system 14.

The drawing of Figure 2 shows a representation of the beam path of an X-ray source in four recording positions Pl, P2, P3, P4, according to a second embodiment of the invention.

In a comparison thereto, FIG. 3, FIG. 4 and FIG. 5 each show a representation of the beam path according to the prior art.

The specified dimensions correspond to the real geometry.

In Figure 2, the examination object 2 is shown as an elongated body, which should have a thickness of OS = 15 cm and a length OS = 120 cm in the present example. At the top and at the bottom of the object 2 distinctive points are marked (on the top of the X-ray beam 1 lying with the sign "φ", on the side facing the table 10 bottom with the character "D"). The projection ("shadow") of these marking points in the recording plane 12 will be explained in more detail below. The size of the image on the detector is labeled IS = 35 cm; the step size of the detector is designated here with ISS = 28 cm. The distance between X-ray emitter 1 and detector (plane) 12 is SID = 180 cm. The detector system 3 consists essentially of a planar detector, which is displaceable in the direction of the recording plane 12, that is, in the present example for recording the partial images in four recording positions einfährt. This retraction into the recording positions is effected synchronously with the displacement of the x-ray source 1 shown above into the respective recording positions Pl, P2, P3, P4. By way of illustration, these four sub-images below the representation of the beam path are shown offset again with each other. In the lowermost illustration, the composite X-ray overall image 13 is shown after composing. (Under the examination object 2, a table 10 is drawn, whose position is irrelevant for the representation of the beam path.)

FIG. 2 shows four receiving positions P1, P2, P3, P4 of the X-ray source 1 which, according to the present invention, are respectively approached by a translation and a rotation. Of course, depending on the size of the object 2, the areal dimension of the detector may vary as well as the number of approached positions. Adjacent shooting positions are spaced by the pitch Δs (designated SSS = 15.9 cm in FIG. 2). Starting with the first position Pl, the cone of rays 4 is pivoted counterclockwise in each additional position by a respective angle of rotation Δφ. The maximum angle of incidence (max rad. Angle) is 11.31 °; the parallax effect is 0.91 cm. (The distance TOD between the table 10 and the examination subject 2, and the distance TID between the table and the detector is TOD = 25 cm and TID = 6.5 cm, respectively, in the drawings of FIGS. 2, 3, 4 and 5. ) FIG. 3 shows the beam path of a prior art recording method in which the X-ray source 1 moves sideways but is not pivoted. X-ray source 1 and detector 3 are moved parallel to each other. However, due to the lateral movement of the X-ray source 1, the already mentioned undesired parallax effect occurs, that is, an object is illuminated from different directions and thus projected onto the detector at different positions. For example, superposed marking points (φ and D) in the center of the examination object 2 in FIG. 3 interchange their position, depending on whether they lie on the right or on the left edge of the two detector positions. This leads in the composite

Overall picture 13 inevitably leads to a faulty image at the seams of the partial images. In Figure 3, the parallax effect (parallax offset) is 1.61 cm. The extent of this parallax effect and the associated blurring are directly related to the distance a point has in two different projections on the (flat) detector. This distance on the detector doubles, for example, from about 0.8 cm at a SID = 300 cm to 1.61 cm at a SIS = 180 cm. Accordingly, the blurring increases. 3, the maximum angle of incidence (maximum rad. Angle) with a 5.60 ° is relatively small; the parallax effect but with 1.61 cm high.

If one compares the result of the invention (FIG. 2) with the first method known from the prior art, the lateral "displacement of the radiation source" (FIG. 3), the advantage of the invention can be clearly seen: FIG Parallax effect, which alienates the composite part recordings by a blur that is difficult to correct computationally, is reduced by half: 0.91 cm according to the invention in Figure 2 (compared with 1.61 cm according to the prior art in FIG 3). The maximum incidence of 11.31 ° in FIG. 2 (invention) has increased compared with FIG. 3 (prior art), but is still within an acceptable range.

However, the advantages of the invention also appear in a further comparison with the second known from the prior art method, the "rotation or pivoting method". Here, the X-ray source 1 is not changed with respect to the local situation, but the swing angle: in Figure 4 and in Figure 5, an X-ray source 1 can be seen, the beam cone 4 is pivoted to create the partial images in four pivot positions , The distance between the X-ray source 1 and the receiving plane 12 of the detector system 3 in FIG. 4 is SID = 300 cm, in FIG. 5 SID = 180 cm. Although no parallax effect occurs in the "rotation or swivel method" (FIG. 4 and FIG. 5 parallax offset: 0.0 cm), there is a projection error: in FIG. 4, the oblique irradiation of up to 11.27 ° (max 4), in particular in the edge regions, that marking points (φ above or D below) located above one another in the examination object 2 are projected next to one another in the plane 12. This projection error reaches a value of 18.43 ° for a SID = 180 cm (FIG. 5). This high value leads to severe distortions and can lead to misdiagnosis. The "rotation or pivoting method" is therefore no longer suitable in radiology with a SID of 180 cm, on the other hand, the projection error according to the invention (Figure 2] with 11.31 ° still in an acceptable range.

In summary, at a distance between the X-ray source and the detector which is greater than 300 cm, the artifacts which are known in both prior art methods ("moving the radiation source" (FIG. 3) and "rotating or Panning the radiation source "(Figure 4 and Figure 5)) occur in radiology still acceptable. (The "rotation or panning method" has the advantage that it leads to comparatively good composing results due to the lack of parallax effect.) However, as soon as the SID is reduced to 180 cm or less, the invention has shown

Approach significant advantages over the prior art, since the parallax effect is lower, which reduces the blurring at the joints of the composite recordings. This increases the quality and acceptance of the overall recording. The risk of a misdiagnosis is reduced.

Thanks to the invention, the X-ray device fits in treatment rooms conventional height.

Since the recording of the sub-picture sequence is carried out by an automatic specification of step size or angle of rotation, the handling of the X-ray device is simple. Compilation of the reference numbers used

1 X-ray source

2 examination object

3 detector system

4 X-ray beams

5 pivot axis

6 longitudinal axis

7 axis of the beam, central ray

8 direction of longitudinal movement

9 longitudinal axis of the examination subject

10 table

11 radiation image, partial image

12 recording level

13 overall picture

14 drive system

15 arrow

SID distance between X-ray source and detector

TOD distance between table and examination object

TID distance between table and detector

OS size of the examination object

IS size of the image on the detector Δs, SSS step size of the X-ray source

(Route)

Δφ rotation angle

ISS step size of the detector

Max. Wheel angle. Maximum angle of incidence with respect to X-rays and detector

Parallax offset Size of the parallax effect

Claims

claims

1. A method for creating a sequence of partial images, which result in a composite form an overall X-ray image of an examination subject (2), wherein a

Drive system (14) an X-ray source (1) gradually in successive recording positions (Pl, ..., PN) moves to emit in each of these an X-ray beam (4), which after penetration of a sub-region of the object to be examined (2) is detected by a detector system (3) as a radiation image (11), characterized in that when moving into a recording position of the X-ray source (1) a linear movement and a rotational movement is performed.

2. The method according to claim 1, characterized in that the drive system (14) during movement into a receiving position (Pl, ..., PN), a step size (Δs) and a rotation angle (Δφ) are automatically specified.

3. The method according to claim 2, characterized in that in the specification of the step size (Δs) and / or the rotation angle (Δφ) a geometric size of the examination object (2) is taken into account.

4. The method according to claim 1, 2 or 3, characterized in that the linear movement and the rotational movement are performed simultaneously.

5. The method according to any one of claims 1 to 4, characterized in that the linear movement in the direction of a Longitudinal axis (6) takes place, which is substantially parallel to a longitudinal axis (9) of the examination object (2).

6. The method according to claim 5, characterized in that the rotational movement about a pivot axis (5), which is arranged substantially perpendicular to the longitudinal axis (6).

7. The method according to claim 6, characterized in that the pivot axis (5) through a focal point of the X-ray

Radiation source (1) extends.

8. The method according to claim 6 or 7, characterized in that the distance between adjacent receiving positions is the same.

9. The method according to claim 6 or 7, characterized in that the distance between adjacent receiving positions is different.

10. The method according to any one of claims 2 to 7, characterized in that during the movement in successive recording positions, the rotational movement is in each case carried out with a same direction of rotation.

11. The method according to any one of claims 1 to 10, characterized in that the detector system (3) comprises a flat detector, which in a receiving plane

(12) is slidably mounted and is moved to receive a partial image in each case in a detector-receiving position.

12. The method according to claim 11, characterized in that the flat detector is moved synchronously with the movement of the X-ray source (1).

13. Method according to claim 11, characterized in that the recording positions (Pl,.

14. The method according to any one of claims 1 to 13, characterized in that the drive system comprises an electric positioning drive (14) which uses a driving profile containing monotonically rising and / or monotonically falling edges.

15. X-ray machine with a drive system which moves an X-ray source (1) in successive recording positions (Pl, ..., PN) in order to emit in each case an X-ray beam (4), which after penetration of a sub-area of Examination object (2) by a detector system (3) as a radiation image (11) is detected, characterized in that the movement of the X-ray source (1) is formed in a receiving position by a longitudinal movement and a rotational movement.

16. X-ray apparatus according to claim 15, characterized in that during a movement in one

Recording position (Pl, ..., PN) by the drive system, a step size (Δs) and a rotation angle (Δφ) is automatically specified.

17. X-ray apparatus according to claim 15 or 16, characterized in that the linear movement and the rotational movement are performed simultaneously.

18. X-ray device according to one of claims 15 to 17, characterized in that the linear movement in the direction of a longitudinal axis (6), which is substantially parallel to a longitudinal axis (9) of the examination object (2).

19. X-ray device according to one of claims 15 to 18, characterized in that the rotational movement about a pivot axis (5), which is arranged perpendicular to the longitudinal axis (6).

20. X-ray apparatus according to claim 19, characterized in that the pivot axis (5) is arranged in a focal point of the X-ray source (1).

21. X-ray device according to one of claims 15 to 20, characterized in that the distance between adjacent recording positions is the same.

22. X-ray device according to one of claims 15 to 20, characterized in that the distance between adjacent receiving positions is different

23. X-ray device according to one of claims 15 to 22, characterized in that during the movement in successive recording positions the direction of rotation is the same.