Generating a volumetric image of an elongated object under investigation.

Abstract

A tomography system (R) configured to perform a first scan along a first helical segment of a trajectory (BA1) and a second scan along a second helical segment of a trajectory (BA2), wherein the tomography system (R) comprises a beam source (Q1, Q2) and a detector (RD1, RD2) associated with the beam source (Q1, Q2), wherein a sensor surface (SF1, SF2) of the detector (RD1, RD2) has the shape of a parallelogram, the interior angle of which is adapted to a slope of the helical segment of a trajectory (BA1, BA2) on which the beam source (Q1, Q2) is active, and wherein the tomography system (R) is configured to acquire a first data set (DS1) during the first scan and a second data set (DS2) during the second scan and to generate a fused data set (DS12) from the two data sets (DS1, DS2).which is sufficiently complete for the reconstruction of a three- or four-dimensional volume image (V) without partial rotation artifacts, whereas both the first (V1) and the second (V2) data set, taken individually, are too incomplete for the reconstruction of a volume image (V) without partial rotation artifacts.

Description

[0001] The invention relates to a tomography system that is prepared to carry out a first scan along a first helical-segment-shaped trajectory section and a second scan along a second helical-segment-shaped trajectory section. A first data set is obtained from the first scan and a second data set is obtained from the second scan.

[0002] The invention also relates to a corresponding method for operating a tomography system.

[0003] A data set is preferably understood here as a data set from a volume scan from which a complete three- or four-dimensional volume image can be reconstructed. A data set of a volume scan includes the captured image data of the associated projection image for each projection angle used. A four-dimensional volume image is usually understood to be a sequence of at least two three-dimensional volume images that follow one another in time. A first of the at least two three-dimensional volume images shows, for example, an inflow phase and a second of the at least two three-dimensional volume images shows, for example, an outflow phase. The tomography system can be, for example, an x-ray tomography system or a fluorescence tomography system.

[0004] In diagnostics and therapy in particular, increasing demands are being made on the performance of medical devices. In particular, the aim is to avoid health hazards and personal injury as a result of incorrect diagnosis or treatment.

[0005] DE 10 2006 040 934 A1 describes a method for imaging arteries and / or veins of a vascular system using a C-arm biplane system that includes two C-arms. During a filling run, a sequence of X-ray images is recorded from different projection angles for each C-arm. The x-ray images of the filling course from the first and the second C-arm from an arterial phase are combined into a first data set. The reconstruction into a three-dimensional image data record can be carried out before the data from the X-ray images of the two C-arms are combined or on the data record of the extracted arterial vascular system.

[0006] With known C-arm angiography systems, it is not possible to capture an entire body or large parts of a body of a normal-sized adult using a single scan trajectory. This is because in known C-arm tomography systems, cable feeds for the C-arms limit the range of rotation angles (about the orbital axis) of the beam source-detector pair of the respective C-arm to approximately 400°.

[0007] It is an object of the present invention to provide a tomography system and a method for operating a tomography system which overcomes this design problem of conventional tomography systems.

[0008] According to the invention, this object is achieved by a tomography system that is prepared to carry out a first scan along a first helical segment-shaped trajectory section and a second scan along a second helical-segment-shaped trajectory section. The tomography system is prepared to acquire a first data set for the first scan and a second data set for the second scan and to generate a merged data set from the two data sets that is sufficiently complete for a reconstruction of a three- or four-dimensional volume image without a partial circulation artifact. Taken on their own, both the first and the second data set are too incomplete for a reconstruction of a volume image without a partial circulation artifact.

[0009] The method according to the invention for operating a tomography system includes the following actions. A first scan is carried out along a first helical-segment-shaped path curve section and a second scan along a second helical-segment-shaped path curve section. A first data set is obtained during the first scan and a second data set is obtained during the second scan, with both the first and the second data set being too incomplete for a reconstruction of a volume image without a partial rotation artifact. A merged data set is generated from the two data sets, which is sufficiently complete for a reconstruction of a three- or four-dimensional volume image without a partial circulation artifact.

[0010] A concept of the present invention can be seen in the fact that the tomography system is prepared to generate a merged data set from the two data sets that is sufficiently complete for a reconstruction of a three- or four-dimensional volume image without a partial rotation artifact, each taken on its own both the first as well as the second data set is too incomplete for a reconstruction of a volume image without a partial circulation artifact. For example, each rotation angle range can be limited to 180° or 100° for the individual scan without having to accept partial rotation artifacts. This results in considerable design advantages (in particular with regard to the cable feeds for each individual C-arm). A three-dimensional or four-dimensional image can be reconstructed from the merged data set using a known reconstruction method (for example using a filtered back-projection method according to Feldkamp, ​​Davis, Kress). The reconstructed image can be two-, three- or four-dimensional, with its dimension being at most as large as the dimension of the merged dataset. Typically, both trajectories have an identical shape (although typically with a rotation angle difference and / or an offset in the direction of the orbital axis). Typically, the second helical-segment-shaped trajectory is arranged concentrically to the first helical-segment-shaped trajectory. Irrespective of this, it is also preferred if a radius of the first helical-segment-shaped trajectory is the same size as a radius of the second helical-segment-shaped trajectory. Applications are also conceivable in which it is advantageous if the slope of the helical segment-shaped trajectories is zero. In the degenerate case, the helical segment-shaped trajectories can therefore be in the form of segments of a circle.

[0011] One embodiment provides that the first helical-segment-shaped trajectory section extends over a first rotation angle range and the second helical-segment-shaped trajectory section extends over a second rotation angle range, the sum of the first and second rotation angle ranges being 360°. In this case, a minimum rotational angle position of the second helical-segment-shaped trajectory section is offset relative to a minimum rotational angle position of the first helical-segment-shaped trajectory section in the direction of rotation by the first rotational angle span. Alternatively, the minimum rotational angle position of the first helical-segment-shaped trajectory section can be offset relative to the minimum rotational angle position of the second helical-segment-shaped trajectory section in the direction of rotation by the second rotational angle span. A merged data set can be generated from the data sets of two scans, which were carried out over mutually complementary rotation angle spans of 180°, from which a complete volume image can be reconstructed without partial rotation artifacts.

[0012] This is especially true when both scans are run as large volume scans. In a large volume scan, a center point of a sensor surface of the detector is shifted by half a detector width in the direction of rotation or opposite to the direction of rotation relative to a central ray of the beam of rays of the beam source. As a result, a diameter of the recording area that can be evaluated is increased by a factor of approximately two in the direction of rotation.

[0013] A further embodiment provides that the first helical-segment-shaped trajectory curve section extends over a first rotation angle range and the second helical-segment-shaped trajectory curve section extends over a second rotation angle range RS C2 extends, wherein the first rotation angle span RS C1 calculated as follows: RS C1 = 180° + SW − RS C2 .

[0014] The second rotation angle range RS C2 is at least half as large as a width SW of a beam angle in the direction of rotation. A minimum rotational angle position of the second helical-segment-shaped trajectory section is arranged offset in the direction of rotation by the first rotational angle range relative to a minimum rotational angle position of the first helical-segment-shaped trajectory section. Alternatively, the minimum rotational angle position of the first helical-segment-shaped trajectory section is offset relative to the minimum rotational angle position of the second helical-segment-shaped trajectory section in the direction of rotation by the second rotational angle span. A merged data set can be generated from the data sets of two scans, which are carried out over mutually adjacent rotation angle ranges, from which a complete volume image can be reconstructed without partial circulation artifacts, as in the case of a short scan. For a short scan, it is assumed that a center point of a sensor surface of the detector is arranged in a central ray of the radiation beam of the radiation source.

[0015] To perform a large volume scan, it is also possible that the rotation angle spans for the first and second scan are identical and each cover 90° plus one half of the beam angle, with the sensor surface being shifted in opposite directions between the two scans such that the The center point of a sensor surface of the detector is shifted in the opposite direction by half a detector width in relation to a central ray of the radiation beam of the beam source.

[0016] Particular advantages arise when the tomography system is prepared to acquire a first part of the second data set with a second radiation spectrum that differs from a first radiation spectrum with which a first part of the first data set is acquired. A development provides that the first part of the first data set includes the entire first data set and the first part of the second data set includes the entire second data set. An alternative development provides that the tomography system is prepared to obtain a remaining part of the first data set with the second radiation spectrum and a remaining part of the second data set with the first radiation spectrum. If a different anode voltage and / or a different anode material is used for generating the second radiation spectrum than for generating the first radiation spectrum, for example density measurements can be carried out. In this embodiment, the first data set typically includes the projection image data of two helical-segment-shaped path sections, of which the first is traversed with the first radiation spectrum and the second with the second radiation spectrum, wherein the second data set also includes the projection image data of two helical-segment-shaped path sections, of which the first with the second radiation spectrum and the second with the first radiation spectrum. A first complete data set for the first radiation spectrum and a second complete data set for the second radiation spectrum can be obtained by exchanging the data of the second helical segment-shaped path section between the two data sets.

[0017] It is also advantageous if the first data set is recorded only on first helical segment-shaped path curve sections that run in a first direction of rotation. This has the advantage, among other things, that a small or a large perpendicular bisector of a first (rectangular) sensor surface of the first detector can be aligned parallel to the first helical segment-shaped trajectory section, without this alignment having to be changed during the gradual passage through the helix turns. During the step-by-step passage through the helical windings, the sensor surface does not need to be rotated around the central ray of the beam of rays of the beam source, so that when the first data set is recorded, a yaw angle between the small or large median perpendicular of the first sensor surface and the first helical-segment-shaped trajectory section is zero degrees.

[0018] Alternatively or additionally, the second data set is recorded only on second helical segment-shaped path curve sections that run in a direction of rotation that is opposite to or in the same direction as the first direction of rotation. If the first data set is obtained only on first helical-segment-shaped trajectory sections that run in a first direction of rotation, and the second data set is obtained only on second helical-segment-shaped trajectory sections that run in a direction of rotation that is opposite to the first direction of rotation, this can help influencing of the first data set by a beam source intended for acquiring the second data set and / or helping to avoid influencing the second data set by a beam source intended for acquiring the first data set.

[0019] It is particularly advantageous if the first scan is recorded when a perpendicular bisector of a first sensor surface of the first detector is aligned parallel to the first helical segment-shaped path curve section. Alternatively or additionally, the second scan can be recorded when a perpendicular bisector of the second sensor surface of the second detector is aligned parallel to the second helical segment-shaped path curve section. As a result, the sensor surfaces are aligned in such a way that their use for the scan according to the invention is optimal. An even better use of the respective sensor surface can be achieved if the sensor surface of the respective detector has the shape of a parallelogram, the internal angle of which is adapted to the slope of the helical segment-shaped trajectory section on which the associated beam source is active.

[0020] Irrespective of this, the tomography system can be prepared to carry out the first scan when a center point of a sensor surface of the first detector is shifted by half a detector width in the direction of rotation or by half a detector width in the opposite direction to the direction of rotation relative to a central ray of a beam of rays from the first beam source. Alternatively, the tomography system can be prepared to carry out the first scan when a center point of a sensor surface of the first detector is shifted by half a detector width in a direction of the first helical segment-shaped path curve section relative to a central ray of a beam of rays of the first beam source. Each of these measures is suitable for increasing a diameter of a recording area that can be evaluated in the direction of rotation.

[0021] Alternatively or additionally, an expansion of the field of view in the direction of rotation can also be achieved by reducing the source-to-sensor distance SID (source to image distance).

[0022] Depending on the tomography system used, it can be expedient if a minimum rotational angle position of the second helical-segment-shaped trajectory section is spaced apart from a minimum rotational angle position of the first helical-segment-shaped trajectory section in the orbital direction. This measure may contribute to a device that is required for the first scan not interfering (obstructed) with a device that is required for the second scan and / or a device that is required for the second scan , does not interfere with any device required for the first scan. This can be relevant in particular when the two scans (for example using a C-arm each) are carried out synchronously in a biplane tomography system.

[0023] It is particularly preferred if the tomography system has a first beam source and a first detector assigned to the first beam source for the first scan, and a second beam source and a second detector assigned to the second beam source for the second scan. A distance from the first beam source to the first detector typically remains constant while the first detector is guided along the helical segment-shaped first trajectory around the orbital axis. This also applies to a distance between the second beam source and the second detector.

[0024] If the tomography system is a monoplane tomography system, the second scan is performed with the same detector as the first scan, either before or after the first scan.

[0025] The first beam source and the first detector can be attached to a common movable carrier, for example the same first C-arm, or to different movable carriers, for example each to a robot arm. The same also applies to the second beam source and the second detector. Both beam source-detector pairs can even be attached to a common movable carrier, for example the same C-arm. Optionally, an image intensifier can be connected to the first detector. This also applies to the second beam source and the second detector. An option that is independent of this provides that the first detector includes an image intensifier and / or the second detector includes an image intensifier. The concepts according to the invention can also be transferred to a tomography system with more than two beam sources, for example a triplan or quattroplan tomography system.

[0026] The invention is explained in more detail with reference to the accompanying drawings, in which show:

[0027] figure 1 schematically a biplane tomography system according to the invention,

[0028] figure 2 schematically shows a scan of a first embodiment of a biplane tomography system,

[0029] figure 3 schematically, in relation to a volume that can be completely reconstructed, either an arrangement of two pairs of radiation sources and detectors or two positions of the same pair of radiation sources and detectors at two different points in time,

[0030] figure 4 schematically a data flow of a tomography system according to the invention,

[0031] figure 5 schematically shows a scan of a second embodiment of a biplane tomography system,

[0032] figure 6 schematically shows a scan of a third embodiment of a biplane tomography system,

[0033] figure 7 schematically shows a scan of a fourth embodiment of a biplane tomography system, and

[0034] figure 8 shows schematically a sequence of a method for operating a tomography system.

[0035] The exemplary embodiments described in more detail below represent preferred embodiments of the present invention.

[0036] In the figureThe biplane tomography system R shown in FIG. 1 has a first C1 and a second C2 C-arm and a patient support PA. A first beam source Q1 and a first detector RD1 are attached to the first C-arm C1. A second beam source Q2 and a second detector RD2 are attached to the second C-arm C2. To perform a comprehensive scan on an object ZO to be examined, the first C-arm C1 performs an orbital rotation RO about an orbital axis OA, while the second C-arm C2 synchronously also performs an orbital rotation RO about the same orbital axis OA. At the same time, the patient support PA is moved along the orbital axis OA. This typically happens at a constant speed in the direction of the orbital axis z. During the orbital rotation RO of the first C-arm C1, the (imaginary) plane in which the first C-arm C1 is located usually remains unchanged. The same also applies to the second C-arm C2. In principle, however, it is also conceivable that, alternatively or additionally, both C-arms are moved along the orbital axis OA during the scan. If the tomography system R is a monoplan tomography system, ie only one C-arm C1 is present, the second scan is carried out with the same detector RD1 as the first scan, specifically before or after the first scan. Otherwise, the same concepts and considerations can be used as are known and / or described for a biplane tomography system.

[0037] the figure 2 shows a first rotation angle range RS C1 , in which the first detector RD1 can be positioned, and a second rotation angle range RS C2 , in which the second detector RD2 can be positioned. The first detector RD1 performs a zigzag movement over the entire first rotation angle range RS C1 from 180° through. Each time the first detector RD1 reaches one or the other end of the first rotation angle range RS C1 reached, it changes the direction of rotation RR1, RR2 together with the beam source Q1, which is assigned to it. In relation to the object ZO to be examined, the first detector RD1 runs through helical segment-shaped trajectories BA1 with alternating directions of rotation RR1, RR2. The same applies to the second detector RD2. Each time the second detector RD2 reaches one or the other end of the second rotation angle range RS C2 reached, it changes the direction of rotation RR1, RR2 together with the beam source Q2, which is assigned to it. In relation to the object ZO to be examined, the second detector RD2 also runs through helical segment-shaped trajectory sections BA2 with alternating directions of rotation RR1, RR2.

[0038] Scans of any length are possible by periodically lining up the helical segment-shaped trajectory curve sections. In this case, each of the two beam source-detector pairs Q1 / RD1, Q2 / RD2 executes a zigzag movement over a rotation angle range RSC1 or RSC2. The beginning of the period T of the back and forth movement of the second beam source-detector pair Q2 / RD2 can coincide with the beginning of the period of the back and forth movement of the first beam source-detector pair Q1 / RD1 or (as in the example of figure 6) may be offset in time by a fraction (e.g. half) of the period T from the start of the period of reciprocation of the first beam source-detector pair Q1 / RD1. This applies to all of the embodiments described here.

[0039] In the embodiment of figure 2, the first radiation source Q1 generates a first radiation spectrum in the first direction of rotation RR1 and a second radiation spectrum in the second direction of rotation RR2. The second radiation source Q2 generates the first radiation spectrum in the second direction of rotation RR2 and the second radiation spectrum in the first direction of rotation RR1. In this figure, scan portions in which the first radiation spectrum is used are framed with solid lines, and scan portions in which the second radiation spectrum is used are framed with broken lines. This also applies to the following figures. the figure2 illustrates that over the entire area that is scanned in the direction z of the orbital axis, every angle is scanned over 360° with the intended angular resolution (of, for example, 1°). This applies to both the first and the second radiation spectrum.

[0040] Alternatively, one in the figure 2 to figure 7 constellation not explicitly shown is possible, in which the second beam source Q2 generates the first and second radiation spectrum in the same direction of rotation RR1, RR2 as the first beam source Q1, i.e. the first radiation spectrum in the first direction of rotation RR1 and the second radiation spectrum in the second direction of rotation RR2. As a result, for each of the two radiation spectra, every angle is scanned over 360° with the intended angular resolution (of, for example, 1°). This applies to the entire area that is scanned in the orbital axis direction z.

[0041] the figure 3 shows the boundaries of a volume RV that can be completely reconstructed and an arrangement of two beam source-detector pairs Q1 / RD1, Q2 / RD2 of a biplane tomography system R and their pyramid-shaped beam cones SK1, SK2. Optionally, the arrangement can also be viewed as the positions of a single beam source-detector pair Q1 / RD1 at two different points in time. The first beam cone SK1 intersects the lateral surface MF of the completely reconstructable volume RV on both the entry and exit sides.

[0042] As the secondary figure illustrates, it follows from the step angle theorem and the center angle theorem that the exit surface AF is three times as wide in the direction of rotation RR1 as the entry surface EF. The lengthening of the exit surface AF in the direction of the orbital axis OAR is calculated as 4*ZR*sin(SW / 2), where ZR denotes the cylinder radius of the completely reconstructable volume RV. In the in the figure 3, the isocenter lies on an isoaxis IA, which coincides with the orbital axis of the tomography system R and with the axis of symmetry of the cylindrical, fully reconstructable volume RV. Depending on the specifically selected embodiment, the difference in the dimensions of the entry surface EF and exit surface AF must be taken into account when designing a scan scheme. In order to avoid a partial revolution artifact, at least one of the two beam source-detector pairs Q1, Q2 must be in at least one Position of the beam source-detector pair Q1 / RD1, Q2 / RD2 are irradiated. The rotation angle range can also be non-contiguous, in which case diametrically opposite rotation angle positions are not to be counted twice but only once.

[0043] the figure 4 shows a fuser FU for generating a merged data set DS12 from the first DS1 and second DS2 data set and a reconstructor RE for generating a three- or four-dimensional volume image VB. In the simplest case, the merger FU is used for a purely aggregative combination of the first DS1 and the second DS2 data set (for example by means of a union query). The reconstructor RE generates the three- or four-dimensional volume image VB from the merged data set DS12 using a known reconstruction method (for example using a filtered back-projection method according to Feldkamp, ​​Davis, Kress).

[0044] Also in the embodiment of figure 5, both beam source-detector pairs carry out synchronous zigzag movements over a rotation angle span of 180° each. However, the first beam source Q1 is active here only in a first direction of rotation RR1 and the second beam source Q2 is only active in a second direction of rotation RR2, which is opposite to the first direction of rotation RR1.

[0045] An embodiment not shown in the figures provides that both beam source-detector pairs carry out synchronous zigzag movements over a rotation angle span of 180° each, with both beam sources Q1, Q2 being active in the same direction of rotation RR1 or RR2.

[0046] the figure5 shows that over the entire area that is scanned in the direction z of the orbital axis, every angle is scanned over 360° with the intended angular resolution (of, for example, 1°). In this case, the same radiation spectrum is typically always used.

[0047] The respective detector can always remain in a position in which a small MSk or a large MSg perpendicular bisector of the (rectangular) sensor surface SF1, SF2 of the respective detector is aligned with (the gradient) of the helical segment-shaped trajectory sections BA1 during such time periods in which the associated beam source Q1, Q2 is active (i.e. along the "leading" trajectory sections). This also applies to the embodiments described below. By aligning a perpendicular bisector MSk, MSg of the sensor surface SF1, SF2 with (the slope) of the helical segment-shaped trajectory sections BA1, unnecessary overlapping of adjacent scan sections can be avoided and thus dose efficiency improved and acquisition speed optimized. If the beam sources Q1, Q2 are inactive (i.e. along the "returning" trajectory sections), the respective detector RD1, RD2 is not required for data acquisition, it can therefore remain twisted about the central beam ZS, as is necessary for the subsequent data acquisition along the "advancing" Curve sections is appropriate.

[0048] In the embodiment of figure 6, the two beam source-detector pairs perform synchronous zigzag movements over a rotation angle range RS C1 , RS C2 of 180° each. Here, both beam sources Q1, Q2 are active in a first direction of rotation RR1, while both beam sources Q1, Q2 are not active in a second direction of rotation RR2, which is opposite to the first direction of rotation RR1. The figure shows that over the entire area that is scanned in the direction z of the orbital axis, every angle is scanned over 360° with the intended angular resolution (of, for example, 1°). In this case, the same radiation spectrum is typically always used. For the embodiment of figure 6, the offset of the beginning of the period T of the to-and-fro movement of the second beam source-detector pair Q2 / RD2 with respect to the beginning of the period of to-and-fro movement of the first beam source-detector pair Q1 / RD1 is optional.

[0049] the figure 7 shows an embodiment with a fused helix short scan. In this case, each of the two beam source-detector pairs carries out zigzag movements over a rotation angle range of 1 / 2*(180°+SW), where SW designates a beam angle of the beam sources Q1, Q2. If partial rotation artifacts are to be avoided in a short scan for all locations (pixels, voxels) that lie within a convex envelope of the trajectory (path curve), the total rotation angle of the central beams ZS of the two radiation sources Q1, Q2 must be at least 180 for each of these locations ° plus beam angle (in the plane of rotation, i.e. perpendicular to the orbital axis) total. This beam angle can also be referred to as a fan angle. For example, if the beam angle is 20°, each of the two rotation angle spans has RS C1 , RS C2 a width |RS C1 |, |RS C2 | from 100°. Both beam sources Q1, Q2 are active in a first direction of rotation RR1, but inactive in a second direction of rotation RR2, which is opposite to the first direction of rotation RR1. For the embodiment of figure 7, the rotation of the detector RD1, RD2 shown about the central beam ZS is optional.

[0050] The figure shows that over the entire area that is scanned in the direction z of the orbital axis, over 180° plus beam angle SW of, for example, 20°, each angle is scanned with the intended angular resolution (of, for example, 1°). In this case, the same radiation spectrum is typically always used.

[0051] In all of the embodiments, the scan can be carried out either with a monoplane system or with a biplane system R. If the scan is carried out with a monoplane system, it is particularly efficient if the helical segment-shaped trajectory sections BA1 of the first rotation angle range RS C1are scanned in a first operation and the helical segment-shaped trajectory sections BA2 of the second rotation angle range RS C2 be scanned in a second operation (for example, while moving back the patient support PA).

[0052] This in figure 8 procedures shown 100 for operating a tomography system R includes the following actions. A first scan is carried out along a first helical-segment-shaped path curve section BA1 and a second scan along a second helical-segment-shaped path curve section BA2. A first data set DS1 is obtained in the first scan and a second data set DS2 in the second scan, with both the first DS1 and the second DS2 data set being too incomplete on their own for a reconstruction of a volume image VB without a partial circulation artifact. A merged data set DS12 is obtained from the two data sets DS1, DS2, which is sufficiently complete for a reconstruction of a three- or four-dimensional volume image VB without a partial circulation artifact.

[0053] With the present invention, a new trajectory is proposed which enables helix acquisition using a biplane system R. By lining up helical segment-shaped path sections (to which the figure 2 and figure 5 to figure 7 illustrate exemplary embodiments) scans of any length are possible. This acquisition can be combined with one or more displacements of the detector(s) RD1, RD2, so that a diameter of the reconstructable area is up to doubled. In this way, volume images VB of volumes of any length can be generated in a structurally advantageous manner using a monoplan or biplan C-arm tomography system R.

[0054] A preferred embodiment of the method according to the invention 100 provides that both planes of a biplane tomography system R are rotated synchronously in order to achieve a continuous helix acquisition together. The two levels rotate synchronously forwards and backwards again and again. As a result, each individual plane scans a reversing helix (reverse helix) whose rotation angle span RS C1 , RS C2 is limited. This creates a double scan that includes two helices Ha, Hb with opposite winding directions (rotational directions opposite to one another). With the data acquired by means of the double scan, a fast and dose-efficient acquisition and generation of a volume image VB is possible using known reconstruction algorithms.

[0055] Dual-energy scans can also be implemented in this way by setting different anode voltages for both planes and swapping the anode voltages of the beam sources Q1, Q2 (at least in terms of value) between the planes at the turning points of the respective trajectory. This creates two complete helices H1, H2 for one anode voltage each. There are basically the following alternatives for exchanging the value of the anode voltages: Changing the voltage of a voltage source that is (fixedly) assigned to the respective beam source Q1, Q2; interchanging the assignment of the two voltage sources to the two beam sources Q1, Q2 by means of a cross switch; Swapping the assignment of the two beam sources (C-arms) to the two planes.

[0056] In order to avoid a self-collision, the two planes can be offset in the direction of rotation RR1, RR2 and / or along the orbital axis direction z. Alternatively, the trajectory can also be realized on monoplan systems by recording the two partial trajectories one after the other.

[0057] In some embodiments of the tomography system R according to the invention, parts of the object ZO to be examined are recorded multiple times by the double scan. This redundancy can be used to achieve one or a combination of the following goals, for example: noise reduction, motion compensation, determination of density information by switching one or more radiation parameters (e.g. to generate a complete dual-source tomogram), enlargement a distance (pitch) of the helix turns (e.g. from 22.5 cm to 45 cm). With the same radiation intensity, a faster advance is possible with the last-mentioned measure (under otherwise the same conditions), as a result of which a recording time can be reduced and dose efficiency can be improved.

[0058] For all embodiments, the feed can be activated either by moving the object to be examined ZO (e.g. by means of the patient support PA) and / or by moving the beam source-detector pairs Q1 / RD1, Q2 / RD2 in the direction of the orbital axis OAR (or in the opposite direction ) can be effected.

[0059] A check of the completeness of the trajectories using simulations has shown that using the method according to the invention 100 a volume image VB can be generated which has a data coverage of 100% along the entire volume and 5 cm away from the isocenter and is therefore comparable to conventional helix images. In contrast to conventional helix imaging, this data coverage is given up to a distance of 45 cm between the helix turns, which means that a shorter imaging time and therefore lower dose are possible. In a conventional helical recording, the distance between the helical turns is 22.5 cm.

[0060] A detector height DL of 30 cm, a source-to-detector distance SID of 1200 mm and a source-to-object distance SOD (source to object distance) of 600 mm were assumed, with the detector height DL being the width of the sensor area SF1, SF2 in the direction of the orbital axis OA. Those skilled in the art usually refer to this direction OA as the v-direction (if the detector is in portrait mode or in landscape mode, ie is not rotated about the beam axis).

[0061] The width h is calculated from the law of rays ISO of a cone beam on the isoaxis IA, with which the sensor surface SF1, SF2 just covers its entire detector height DL, as follows: H ISO = DL SOD / SID.

[0062] Correspondingly it follows for the width w ISO a cone beam perpendicular to the isoaxis IA, which covers the sensor surface SF1, SF2 just over its entire width 2DH in the direction of rotation RR1, RR2: w ISO = 2DH*SOD / SID (where DH is half the width of the sensor area in the direction of rotation RR1, RR2). If it were not a short scan, all voxels on the isoaxis IA are recorded twice with a rotation of 360°. This results in a maximum gradient of the helical segment-shaped trajectory BK1, BK2 of 2*h ISO . However, this would only scan half of the volume to be reconstructed. For complete reconstructability, the maximum feed (the slope) of the helical segment-shaped trajectory BK1, BK2 around the radius w ISO / 2 of the volume can be corrected as follows: P helix = 2 h ISO – w ISO / 2 = (2DL - DH)SOD / SID.

[0063] For the parameters used in the simulation, the maximum helix feed at SOD / SID = 0.5 is: P helix ≈ 2·15cm – 20cm 2 = 20cm.

[0064] The maximum feed P is calculated with the selected dimensions helix to 20 cm and not to 22.5 cm as found in the numerical simulation. The deviation is not surprising since the above formula for P helix is an estimate based on simplifications. The following feed can be selected for the proposed double helix: P helix = 2P helix .

[0065] With the present disclosure, for the first time a three- or four-dimensional volume image of a volume of any length can be generated by means of a C-arm angiography system. The acquisition takes place on zigzag-shaped trajectories, which are composed of helical segment-shaped trajectory sections (BA1 or BA2) and which can be of any length in the direction of the orbital axis z. In this way, a three-dimensional volume image VB (without a partial rotation artifact) of an adult of normal size can be generated in one operation. This is not possible with known C-arm systems. Since the acquisition can be resorted to at least one non-reversing complete helix Ha, Hb, all reconstruction methods (in particular all known and / or exact reconstruction methods) that are suitable for computed tomography can be used. This applies in particular to spiral CT and helical CT procedures. In addition, a recording time can optionally be shortened, dose efficiency can be improved and / or dual-energy methods can be used.

[0066] The invention relates to a tomography system R, which is prepared for the following: performing a first scan along a first helical segment-shaped trajectory section BA1 and a second scan along a second helical-segment-shaped trajectory section BA2. In the first scan, a first data set DS1 and in the second scan a second data set DS2 is obtained and a merged three- or four-dimensional data set DS12 is generated from the two data sets DS1, DS2, which is sufficiently complete for a reconstruction of a volume image VB without a partial circulation artifact, while each taken alone, both the first DS1 and the second DS2 data set are too incomplete for a reconstruction of a volume image VB without a partial circulation artifact. Reference List AF exit surface AP1 Minimum rotation angle position of the first helical segment-shaped trajectory section AP2 Minimum rotation angle position of the second helical segment-shaped trajectory section BA1 first helical segment shaped trajectory section BA2 second helical segment shaped trajectory section C1 first C-arm C2 second C-arm DH half the detector width in the direction of rotation DL Detector width in orbital axis direction DR Detector height in the direction of the axis of rotation DS1 first record DS2 second record DS12 merged three or four dimensional data set EF entry surface Ha first helix Hb second helix IA isoaxis MF lateral surface MP1 Center of the first detector MP2 Center of the second detector MSk Bisector of a short side of the sensor area MSg Bisector of a long side of the sensor area MP2 Center of the second detector OA orbital axis OAR orbital axis direction PA patient support Q1 first beam source Q2 second beam source R tomography system RD1 first detector RD2 second detector RO rotation RR1 first direction of rotation RR2 second direction of rotation RS C1 first rotation angle span RS C2 second rotation angle span RV fully reconstructable volume RWD rotation angle difference SB bundle of rays SF1 Sensor area of ​​the first detector SF2 Sensor area of ​​the second detector SID Distance between beam source and sensor surface SK1 beam cone of the first beam source SK2 beam cone of the second beam source SOD distance between beam source and object SW beam angle T period u Detector coordinate in the direction of rotation v Detector coordinate in orbital axis direction VB volumetric image z orbital axis direction ZR cylinder radius ZS central ray of the bundle of rays 100 procedures 110 Performing a first and a second scan 120 Obtaining a first and a second set of data 130 Creation of a merged three- or four-dimensional data set QUOTES INCLUDED IN DESCRIPTION

[0067] This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Patent Literature Cited

[0068] DE 102006040934 A1

[0005]

Claims

[1] A tomography system (R) prepared to perform a first scan along a first helical segment of a trajectory (BA1) and a second scan along a second helical segment of a trajectory (BA2), wherein the tomography system (R) is prepared to acquire a first data set (DS1) during the first scan and a second data set (DS2) during the second scan and to generate a fused data set (DS12) from the two data sets (DS1, DS2) which is sufficiently complete for the reconstruction of a three- or four-dimensional volume image (VB) without partial rotation artifact, wherein each of the first (DS1) and second (DS2) data sets taken individually is too incomplete for the reconstruction of a volume image (VB) without partial rotation artifact. [2] Tomography system (R) according to claim 1, characterized bythat the first helical segment-shaped trajectory section (BA1) extends over a first rotation angle span (RS) C1 ) extends and the second helical segment-shaped trajectory section (BA2) extends over a second rotation angle span (RS) C2 ) extends, where the sum of the first (RS C1 ) and the second (RS C2 ) Rotation angle span is 360°, wherein a minimum rotation angle position (AP2) of the second helical segment-shaped trajectory section (BA2) relative to a minimum rotation angle position (AP1) of the first helical segment-shaped trajectory section (BA1) in the direction of rotation (RR1, RR2) around the first rotation angle span (RS) C1) is arranged offset or wherein the minimum rotation angle position (AP1) of the first helical segment-shaped trajectory section (BA1) is offset relative to the minimum rotation angle position (AP2) of the second helical segment-shaped trajectory section (BA2) in the direction of rotation (RR1, RR2) by the second rotation angle span (RS) C2 ) is arranged in a staggered pattern. [3] Tomography system (R) according to claim 1, characterized by that the first helical segment-shaped trajectory section (BA1) extends over a first rotation angle span (RS) C1 ) extends and the second helical segment-shaped trajectory section (BA2) extends over a second rotation angle span RS C2 extends, with the first rotation angle span RS C1 calculated as follows: RS C1 = 180° + SW – RS C2 , where the second rotation angle span (RS) C2) is at least half as large as a width SW of a beam angle in the direction of rotation (RR1, RR2), wherein a minimum rotation angle position (AP2) of the second helical segment-shaped trajectory section (BA2) relative to a minimum rotation angle position (AP1) of the first helical segment-shaped trajectory section (BA1) in the direction of rotation (RR1, RR2) by the first rotation angle span (RS) C1 ) is arranged offset or wherein the minimum rotation angle position (AP1) of the first helical segment-shaped trajectory section (BA1) is offset relative to the minimum rotation angle position (AP2) of the second helical segment-shaped trajectory section (BA2) in the direction of rotation (RR1, RR2) by the second rotation angle span (RS) C2 ) is arranged in a staggered pattern. [4] Tomography system (R) according to one of the preceding claims, characterized bythat the tomography system (R) is prepared to acquire a first part of the second data set (DS2) with a second radiation spectrum that differs from a first radiation spectrum with which a first part of the first data set (DS1) is acquired. [5] Tomography system (R) according to one of the preceding claims, characterized by that the tomography system (R) is prepared to record the first data set (DS1) only on first helical segment-shaped trajectory sections (BA1) that run in a first direction of rotation (RR1), and / or to record the second data set (DS2) only on second helical segment-shaped trajectory sections (BA2) that run in a direction of rotation (RR2) that is opposite to or in the same direction as the first direction of rotation (RR1). [6] Tomography system (R) according to one of the preceding claims, characterized bythat the tomography system (R) is prepared to activate the first beam source (Q1) when a perpendicular center (MSk, MSg) of a first sensor surface (SF1) of the first detector (RD1) is aligned parallel to the first helical segment of the trajectory (BA1), and / or to activate the second beam source (Q2) when a perpendicular center (MSk, MSg) of a second sensor surface (SF2) of the second detector (RD2) is aligned parallel to the second helical segment of the trajectory (BA2). [7] Tomography system (R) according to one of the preceding claims, characterized bythat the tomography system (R) is prepared to perform the first scan when a center point (MP1) of a sensor area (SF1) of the first detector (RD1) is displaced relative to a central ray (ZS) of a beam (SB) of the first beam source (Q1) by half a detector width (DH) in the direction of rotation (RR1, RR2) or by half a detector width (DH) opposite to the direction of rotation (RR1, RR2), and / or that the tomography system (R) is prepared to perform the first scan when a center point (MP1) of a sensor area (SF1) of the first detector (RD1) is displaced relative to a central ray (ZS) of a beam (SB) of the first beam source (Q1) by half a detector width (DH) in one direction of the first helical segment of the path (BA1). [8] Tomography system (R) according to one of the preceding claims, characterized bythat a minimum rotation angle position (AP2) of the second helical segment-shaped trajectory section (BA2) is spaced apart from a minimum rotation angle position (AP1) of the first helical segment-shaped trajectory section (BA1) in the orbital axis direction (z). [9] Tomography system (R) according to any one of the preceding claims, characterized by that the tomography system (R) for the first scan has a first beam source (Q1) and a first detector (RD1) assigned to the first beam source (Q1), and for the second scan has a second beam source (Q2) and a second detector (RD2) assigned to the second beam source (Q2). [10] Procedure ( 100 ) for operating a tomography system (R), wherein the method ( 100 ) includes the following actions: - Carry out ( 110) of a first scan along a first helical segment-shaped trajectory section (BA1) and a second scan along a second helical segment-shaped trajectory section (BA2); - Win ( 120 ) of a first data set (DS1) during the first scan and acquisition of a second data set (DS2) during the second scan, whereby, taken individually, both the first (DS1) and the second (DS2) data set are too incomplete for a reconstruction of a volume image (VB) without partial rotation artifacts; and - Generate ( 130 ) of a fused three- or four-dimensional dataset (DS12) from the two datasets (DS1, DS2) that is sufficiently complete for the reconstruction of a volume image (VB) without partial rotation artifact.

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