DE102018006763A1 - Method for recording a scan of an object with a C-arm with a focus ejectory with one rotary and two translational sections and C-arm X-ray diagnostic system for implementing the method - Google Patents

Abstract

The method for recording a scan of an object with a scan center in the POI and a focus ejectory with one rotary and two translational sections, which can be implemented using a C-arm x-ray diagnostic system, provides for converting a selected focus ejectory into polar coordinates (r, α) with the scan center as the coordinate origin and the target focus positions on the focus ejector, at which x-ray projection recordings are to be taken, with the stipulation that the angular distances Δα between two focus target positions are constant over the entire focus ejectory. The x-ray projection recordings that are used for the reconstruction are recorded at focus positions in the vicinity of the defined focus target positions on the focus projection by means of a trigger signal or an image recording frequency signal that is adapted to the focus speed on the focus projection.

Description

In known cone beam computed tomographs (CBCT, Cone Beam Computer Tomography), an x-ray image recording unit consisting of an x-ray emitter and an x-ray detector, preferably a flat panel detector (FPD), rotates around a scanning center, the trajectories of the focus of the x-ray source and an arbitrary point on the FPD being concentric Have circles or arcs of different radii with the scan center as the center. The x-ray image recording unit preferably runs around the scan center at a constant angular velocity and x-ray projection images are recorded at a constant clock frequency. Each time an x-ray projection image is recorded, the x-ray radiation parameters, in particular the tube current, are regulated by means of a dose rate control in such a way that the images recorded by the FPD have a predetermined signal-to-noise ratio. The scan angle intervals between two successive focus positions, at which a projection image is taken, should on the one hand be small enough to avoid artifacts in the reconstructed 3D images, and on the other hand, the scan angle intervals should be constant over the entire scan area so that no projection direction is preferred , If the angular distances between the focus positions at which a projection image is taken are chosen too large, artefacts occur in the volume reconstruction because of the missing projection angle. If the angular distances between the focus positions at which a projection image is taken are selected to be increasingly smaller, the dose applied to the patient will increase without an improvement in the quality of the reconstruction being expected. Provided the dose hygiene for the patient is too high, oversampling should be avoided.

In order to obtain a complete projection data set in the scan plane, the scan angle range must be 180 degrees plus the angular width of the FPD in the scan plane. C-arm x-ray devices which are intended to record scans often have a limited scanning angle range of less than 180 degrees and are not suitable for generating a complete projection data set with a rotation scan. However, it is known to generate complete scans with such C-arm devices if translational trajectory sections are added to the end points of the rotation scan. Trajectories of this type, which have rotary and translational sections, are generally not traversed at a constant path speed, since at the transitions between the rotary section and a translational section, a change in the speed of the C-arm adjustment axes involved in the movement (in particular the orbital axis, the Horizontal and the vertical adjustment axis of the C-arm holder), which also occurs at the beginning and end of a trajectory, because the C-arm can only be brought to the desired path speeds of the scan with the X-ray emitter and the FPD with a limited acceleration become.

In particular, if the rotary sections of the trajectories are non-circular, the path speeds of the X-ray focus and the X-ray detector and the distance of the X-ray focus from the scanning center change over the entire scanning area with a constant rotational speed of the C-arm. In conjunction with this, an image sequence is recorded at a constant image acquisition rate over the entire scan angle range, the individual images of which do not have a constant angular distance from one another. In particular, in the transition areas between rotary and translational movement and at the beginning and end of the trajectories, almost redundant, closely adjacent projection recordings (oversampling) are recorded, which unnecessarily increases the radiation exposure of a patient to be examined and distributes them unevenly over the entire angular range.

Mobile C-arm x-ray devices and associated operating methods are known, which have images of plane scans each with one rotary and at least two translational sections in the focus and detector trajectories. For weight and ergonomic reasons, the C-arm in mobile C-arm X-ray devices is preferably designed as a non-isocentric C-arm, in which the mechanical center of rotation and thus the center of the circular C-arm do not lie on the one through the connecting line of the focus with the center of the X-ray detector input window formed central beam vector. In order to be able to record a rotation scan of an examination object with a region of interest (ROI), the holder of the C-arm has to be adjusted in correlation with the orbital movement in the plane of the C-arm during the scan in such a way that the central beam vector always passes through the scan center runs.

The volume to be reconstructed has the shape of a cylinder, the cylinder axis being perpendicular to the plane of the C-arm. In the plane of the C-arm, the section through the cylindrical volume to be reconstructed represents a preferably circular ROI and the point of penetration of the cylinder axis through the plane of the C-arm represents the scanning center located in the center of the circle of the ROI. The plane of the C-arm remains during the Recording the X-ray projections fixed in space. In particular, for the space requirement of a C-arm X-ray device during the recording of a scan, it is advantageous if the plane of the C-arm is vertical in the room. However, other positions of the spatially fixed plane of the C-arm are also provided, in particular when a section plane of the examination object that is not perpendicular in space is to be reconstructed without artefacts and the examination object cannot be aligned in such a way that the desired section plane with the ROI contained therein stands vertically in the room.

The C-arm x-ray device is intended to provide a projection data set for an ROI with a scanning center, which is complete with regard to a Feldkamp 3D reconstruction of a disk-shaped ROI. The one from the document DE102013013552B3 The method known to the applicant for recording a scan is known for a non-isocentric mobile C-arm x-ray diagnostic system in which the central beam vector does not run through the mechanical rotation center of the C-arm. When the C-arm is shifted in its holder along the circumference of the C-arm, the resulting central beam vectors do not run through a fixed point, but rather each touch a circle around a scanning center. An isocentric C-arm is simulated by synchronous tracking of the C-arm in a horizontal movement axis and a vertical movement axis during orbital movement. The movement in the horizontal movement axis, in the vertical movement axis and in the orbital movement axis is motorized, the movements being controlled by a movement control unit.

Known mobile, non-isocentric C-arm x-ray devices usually have a limited range of rotation in the orbital movement axis of less than 180 °. With such a limited range of rotation, it is not possible to record a complete projection data set for an analytical reconstruction of a disc-shaped cylindrical X-ray volume of the Feldkamp type. In order to generate a complete projection data record for the disk-shaped ROI of the central layer lying in the plane of a C-arm with the thickness of a voxel, the missing projection data must be recorded with further non-rotatory, for example translatory, flat trajectory sections.

In 2 is a focus ejection and a detector trajectory of the center of the radiation entry window of the X-ray detector for a method for recording a projection data set complete in the central layer within an ROI 50 with a scan center 51 shown. The from the sections 181 . 182 . 183 Existing focus ejectory of the focus is traversed in the direction of the arrow. The associated detector trajectory has the sections 203 . 202 . 201 that are passed through one after the other. If the focus is moved along a focus ejectory, which results from the first section 191 the second focus ejector, the second section 182 the focus ejector and the third section 193 of the second focus ejectory, the center point of the beam entry window of the FPD and thus the central beam vector initially move on the first section 213 the second detector trajectory, then on the second section 202 the first detector trajectory and finally on the third section 211 the second detector trajectory

In the individual movement phases, parallel displacements of the central beam vector are provided along its direction, for example to avoid obstacles and to avoid collisions.

The process of taking a scan of an area of interest ROI 50 with one at the center of the ROI 50 lying scan center 51 has a scan that consists of a series of x-ray projection images that contain a complete set of x-ray projection data of the ROI 50 in the central layer in the plane of the C-arm 2 for a 3D reconstruction. The series of X-ray projection images is recorded using a C-arm x-ray device, which has a C-arm with a fixed plane, in which the C-arm can be moved in parallel with a holder that can be adjusted by multiple motors and in the holder along its circumference an orbital axis of movement between a first and a second extreme position is mounted so that it can move in a motorized manner, and wherein the C-arm has an X-ray image recording system with an X-ray source arranged at one end of the C-arm and an FPD arranged opposite at the other end of the C-arm, in the first Extreme position engages the holder on one end of the C-arm with the X-ray source and in the second extreme position the holder engages on the other end of the C-arm with the FPD and the X-ray imaging system is an X-ray source from the focus to the center of the radiation step window of the FPD extending and perpendicular to the beam entry window of the FPD is characterized by a central beam vector and generates a cone beam which contains a fan beam with a fan angle in the plane of the C-arm, the focus taking the series of x-ray projection recordings along a plane connected Focus ejectory is moved between a start point and an end point in any direction.

At the starting point of the focus ejector, the C-arm is positioned in the orbital movement axis in the first extreme position and the adjustable holder of the C-arm is positioned such that a first limiting beam of the fan beam lying on the side of the central beam vector facing away from the C-arm detects the ROI 50 affected.

In a first section 181 . 191 . 195 In the focus ejector, the holder is moved in the plane of the C-arm in parallel until the central beam vector passes through the scan center 51 runs and the ROI 50 is completely within the fan beam.

In a second section 182 . 196 In the focus ejector, the C-arm is moved in the orbital movement axis from the first extreme position into a second extreme position, in which the holder engages with the X-ray detector at the other end of the C-arm, the angular range of the orbital movement between the first and the second extreme position at least 180º minus fan angle and the holder in the plane of the C-arm is displaced parallel so that the central beam vector 11 . 12 . 13 . 14 through the scan center 51 runs and the ROI 50 is completely within the fan beam.

In a third section 183 . 193 . 197 In the trajectory, the C-arm remains positioned in the second extreme position in the orbital movement axis and the holder is shifted parallel in the plane of the C-arm until a second limiting beam of the fan beam lying on the side of the central beam vector facing the C-arm detects the ROI 50 affected.

In the 2 shown trajectories, the orbital angle adjustment range of the C-arm is fully utilized. The first projection of a scan is taken in a first extreme position of the orbital angle and the last projection of the scan is taken in the other extreme position of the orbital angle. Before the start and after the end of the scan, all adjustment axes of the C-arm are in a rest position. The first projection of a scan is taken with the C-arm at rest; the C-arm is then set in motion and braked again at the end of the scan, so that the last projection image of the scan is taken again in a rest position of the C-arm adjustment axes. In the area of the transitions of the trajectories from a rotary to a translatory section, the trajectories of focus and FPD are traversed at a reduced path speed in order to limit accelerations that occur. If the projection recordings were taken at a constant image recording rate or frame rate during such a scan, the recording density would be increased in the transition and end regions of a scan without a diagnostic benefit being obtained therefrom.

From the German patent DE102013013552B3 and the family member US20170265821A1 The applicant is aware of a method for recording a 3D projection data set complete in the central layer with a C-arm x-ray device with a limited orbital adjustment range, in which the trajectories of the focus of the x-ray tube and a point on the input window of the FPD each have a rotary component and then have two translational portions.

From the document DE202017002625U1 an X-ray system with a cone-beam C-arm X-ray device is known for generating a complete 3D data set for volume reconstruction in the central layer, in which the rotational components of the trajectories of the X-ray focus and a point on the input window of the FPD are non-circular during a scan , In particular, provision is made to assemble the rotary part of the trajectories in sections from super ellipses.

From the document DE102009020400B4 A method and a device for image determination from X-ray projections recorded when passing through a flat, rotary trajectory is known. It is provided, for example, for the rotary detector trajectory to be traversed at a path speed that is constant in terms of magnitude, the recording times at which an X-ray projection is recorded not being equidistant in time.

From the document DE102009042922A1 A method and a device for image determination from X-ray projections recorded when passing through a flat, rotary trajectory is known. For example, it is provided that the rotary detector trajectory is traversed at a path speed that is constant in terms of magnitude, the recording positions at which an X-ray projection is recorded in each case being determined with the aid of filter lines.

From the document DE102009052453A1 a 3D reconstruction from projection data of a spiral scan based on a filtered back projection without rebinning is known. The redundant projections obtained during the scan are treated separately during the reconstruction.

From the document EP1737346B1 dynamic dose control in a CT scan is known. The dose is modulated over the scan angle range.

In the area of the transitions of the trajectories from a rotary to a translatory section, the trajectories of focus and FPD are traversed at a reduced path speed in order to limit accelerations that occur. If the projection recordings were taken at a constant image recording rate or frame rate during such a scan, the recording density would be increased in the transition and end regions of a scan. In the case of a subsequent 3D reconstruction from the recorded 2D projection recordings, a higher density of line integrals of the attenuation data to be evaluated would be available for the transition and end regions of the scan, without the image information and thus the diagnostic use of the 3D reconstruction being increased thereby , Rather, contrary to the rules of dose hygiene, the dose would be applied to the examination object without diagnostic benefit. The density of the projection recordings to be recorded during a scan must also have a minimum density over the entire scan area in order to achieve a satisfactory reconstruction result; otherwise streak artifacts would occur during volume reconstruction.

There is a need for a scanning method which, in the case of trajectories for the x-ray focus composed of rotatory and translatory parts to improve the dose hygiene for an examination object with a scanning center located in the POI, oversampling by means of almost redundant, closely adjacent and therefore superfluous projections when taking x-ray projection recordings avoids.

It is the object of the invention to create a method for recording a scan with a scan center in a POI of an object, which avoids oversampling during a scan with rotational and translational parts of a focus ejection and improves the dose hygiene for the examination object without sacrificing the reconstruction quality.

The object is solved by the features of claim 1. The object of the invention is achieved in particular in that the focus target positions on the focus ejectory are calculated at the time the X-ray projection recordings of a scan are taken, provided that the angular distances Δα between two focus target positions over the entire focus ejectory in polar coordinates (r, α) with the scan center as Coordinate origin are constant and the x-ray projection recordings that are used for the reconstruction will be taken at focus positions in the vicinity of the defined focus target positions on the focus ejection.

For this purpose, positions on a selected or a currently driven focus ejectory are determined at which x-ray projection recordings are to be triggered in accordance with the uniformity condition for the density of the projection recordings. This determination can take place before the start of the scan, or in real time during a scan, if a particular focus ejection has been selected. The triggering of the individual projection recordings is triggered by a control.

It is provided within the scope of the invention to record the projection recordings in a video mode and to control the image recording rate or frame rate depending on the position or the current movement parameters of the focus projection such that the uniformity condition for the density of the projection recordings is fulfilled at every point of the focus projection.

It is intended to determine the course of the image recording rate via the scan course before the start of a scan and to store it in a memory. At the start of the scan, it is intended to read out the values for the acquisition rate from the memory and to record the projection recordings at the pre-calculated acquisition rate.

It is further provided within the scope of the invention to calculate and control the acquisition rate along the trajectories in real time during a scan, the control providing the trajectory and the instantaneous speed of the X-ray focus.

The invention is illustrated by the figures.
In 1 is a C-arm X-ray diagnostic system 1 schematically shown, which is provided for the implementation of the method for recording projection recordings of a scan.

An arcuate C-arm 2 carries the X-ray tube at one end 3 , the collimator 5 and at least parts of the high voltage generator 4 and at its other end and the x-ray tube 3 an X-ray image detector opposite 6 , especially a flat panel detector FPD. The C-arm 2 can be moved in several axes in a motor-controlled manner in space, the axes having sensors for detecting the extent of the adjustment. In particular, the C-arm is in a holder along its circumference guided by a motor. This movement is called the orbital movement / orbital axis. The C-arm holder, not shown, is motor-displaceable in at least one horizontal and one vertical axis. A C-arm x-ray device equipped with these 3 motorized axes is set up to perform a scan with a series of 2D x-ray projection recordings for a subsequent reconstruction of an x-ray volume with flat trajectories of the focal point 8th around a scan center 20 realizable. The focus ejectors are circular or non-circular. It is known to use non-circular trajectories that have rotary and translational sections. The runs between the focus 8th and the center of the FPD 6 running central beam 22 always in a rotary section through the scan center 20 , whereas the distance of the central beam 22 from the scan center 20 is continuously changed. An example of a scan with rotary and translational sections is an arc shift scan, such as that from the document DE102013013552B3 is known to the applicant. If the C-arm x-ray device has at least one further motor-controllable axis which has a movement component of the C-arm holder perpendicular to the orbital plane, non-planar scans, such as spiral scans or arc-line scans, can also be implemented.

An x-ray tube 3 creates a focus 8th and is preferably designed as a rotating anode x-ray tube and preferably has a cooling device for removing the amount of heat generated during operation. Sensors for detecting temperatures are provided, the measured values of which are used in the X-ray tube control to protect a high-voltage generator 4 and the x-ray tube 3 processed and an energy management unit 118 to provide.

An oil filled high voltage generator 4 provides all for the operation of the x-ray tube 3 required parameters such as acceleration voltage, tube current, cathode heating current, rotating anode motor current, pulse frequency, pulse width are available.

Is preferably between the focus 8th and the object 21 a controllable collimator 5 to show the focus 8th outgoing X-ray beam provided. It is planned to change the aperture depending on the scanning angle.

On the C-arm 2 is an X-ray image detector, in particular a flat panel detector FPD 6 at a certain distance and in a certain orientation to the focus 8th and the C-arm 2 arranged. It is envisaged the distance and orientation of the FPD 6 to make it reproducible and controllable changeable.

The image data read out from the FPD during a projection recording becomes in a projection image generation unit 7 generates a raw image of a projection of the object and an image processing and storage unit 106 fed.

A scan center 20 represents the center of the region of interest ROI to be reconstructed inside the object 21 represents.

As a central jet 22 becomes the connecting line between the focus 8th and the center of the input window of the FPD 6 or another X-ray receiver. It lies in the orbital plane of the C-arm perpendicular to the entrance window of the FPD 8th ,

An object to be examined 21 is on a patient couch 23 placed. The patient bed 23 can be designed so that after an initial alignment with the C-arm 2 during the x-ray examination of the object 21 remains rigid. There is also provision for the patient bed 23 equipped with motor-controlled, adjustable axes and the movement of the patient bed 23 by means of a couch motor control unit 25 synchronized with the movement of the C-arm 2 to control. The motorized axes of the patient bed 23 can at least partially have the same degrees of freedom as the C-arm 2 exhibit. For example, a relative adjustment of the scan center 20 towards the focus 8th in the vertical direction by adjusting the height of the C-arm 2 and / or by adjusting the height of the patient bed 23 respectively. Is the patient bed perpendicular to the orbital plane of the C-arm that defines the scan plane in the case of a plane focus ejector 2 Motor-adjustable, so a non-level focus ejector can be realized.

A C-arm motor control unit 24 controls all motor-adjustable axes of the C-arm X-ray device and provides the motion control unit with measured values from position sensors of non-motor-adjustable axes.

A couch motor control unit 24 and a C-arm motor control unit 25 are from the motion control unit 103 of the X-ray diagnostic system 1 controlled synchronously.

A higher-level system control unit 100 preferably has a bus system with a large number of control, computing and storage components.

An x-ray control unit 101 controls the high voltage generator 4 who have favourited X-ray tube 3 and the collimator 5 , It has a dose rate control or Automatic Emission Control AEC, which takes the parameters of the X-ray tube when taking an X-ray image 6 controls in such a way that with the FPD 6 an X-ray image with a predetermined quality, for example with a predetermined signal / noise ratio, is generated.

It is provided that in the X-ray control unit 101 after each projection exposure, it is determined whether the projection exposure has been adequately exposed, ie whether there was sufficient energy reserve to regulate the exposure. Is by the X-ray control unit 101 determines that an image was not adequately exposed, an AEC low status signal is generated after such an insufficient exposure with the consequence of an excessively high noise component and an image quality insufficient for reconstruction and the system control unit 100 and the image pickup control unit 104 made available. As a result of the presence of an AEC low status signal, it can be provided that a further projection recording is taken at the next possible time or at the next possible recording location of the focus ejectory.

The C-arm X-ray diagnostic system 1 preferably has a collision monitoring unit 102 to monitor the movement of the C-arm 2 on. The signals from and not shown on the C-arm 2 , the housing of the FPD 6 or / and the housing of the X-ray tube 3 and the collimator 5 arranged distance measuring sensors and collision detection sensors processed. Is used by the collision monitoring unit 102 If a risk of collision is determined, the system control unit is provided with signals for reducing the C-arm speed or for stopping the movement and for switching off the X-ray radiation.

A motion control unit 103 receives the in the scan parameter generating device 107 determined focus ejectory and the position of the scan center with respect to the focus ejectory. When the patient bed and the C-arm are referenced to one another, the position of the scan center is received by the scan parameter generating device. If the C-arm and patient bed are not referenced to one another, the scan center is determined and ascertained and stored using at least two calibration settings of the C-arm in the coordinate system of the C-arm device.

An image acquisition control unit 104 triggers the recording of a projection recording, unless a prevention signal prevents the recording from being triggered. A prevention signal is generated, for example, by a collision recognized immediately beforehand or by an emergency stop of the x-ray system triggered by an operator. After triggering a projection recording, the control of the tube current and / or the exposure time in an exposure control of the X-ray control unit 101 applied a dose in the FPD 6 generates a projection image of a selected quality. The signal-to-noise ratio, for example, can be specified as a measure of the image quality. The tube current and the exposure time are limited by the system, namely on the one hand by the limited load capacity of the rotating anode and on the other hand by the stipulation that motion blur should be prevented by exposure times that are too long. If a predetermined image quality is not achieved even with maximum tube current and with maximum exposure time, for example with a long transmission length, the image recording control triggers at least one further projection image immediately after the projection image with insufficient quality. It is intended to limit the number of additional exposures and to trigger the next projection exposure at the next desired position after the maximum number of additional exposures has been reached.

An FPD control unit 105 controls and controls all functions of the FPD 6 , such as image acquisition, image reading, dark current correction and removal of residual charges after the end of the exposure time.

In an image processing and storage unit 106 the raw image data from the projection image generation unit 7 corrected, filtered or edited and saved according to specified image processing algorithms. You are then the reconstruction unit 117 available for volume reconstruction.

In a scan parameter generation unit 107 all parameters for a scan are generated. The scan parameter generation unit 107 receives the position of the scan center 20 in the coordinate system of the C-arm x-ray device, a focus and a detector trajectory, a total number of the provided x-ray projection recordings of the scan and a provided tube voltage for the scan. The generated scan parameters are in the motion control unit 103 , the X-ray control unit 101 and the image pickup control unit 104 and other units, for example a collision monitoring unit 102 made available.

The scan parameter generation unit 107 is set up the position of a scan center 20 in the coordinate system of the C-arm X-ray device. The scan center can be, for example, by manual alignment of the central beam 22 to the scan center 20 determined in two mutually independent spatial directions and entered into the system control unit by an operator.

The scan parameter generation unit 107 is further set up to focus trajectories 8th and the FPD 23 in the coordinate system of the C-arm X-ray device. The trajectories are kept by an organ program database 115 received after these have been selected by an operator and, if necessary, adapted to the given examination situation, for example to the patient dimensions.

In a focus target position determination unit 108 the positions of the points on a focus trajectory received by the scan parameter generation unit, on which an x-ray projection image is to be generated, are determined according to a predefinable rule. Image acquisition is performed by the image acquisition control unit 103 then triggered when the focus 8th is on the determined target position.

It is at least a display 111 provided for the output of image, control and patient data. Via an input unit 112 instructions of an operator are entered into the system control unit. It is intended to design at least one display as a graphical user interface GUI.

An input device unit 112 is used to enter operator commands / an operator 113 and the import of system programs into the system if they are not via a network 140 are importable.

The control panel 100 has a mass storage 116 and an output unit 114 on. Under an output unit 114 is understood to be any device by means of which test results or / and system parameters can be output on any information carrier.

The control panel 100 has an organ program database 115 in which X-ray and scan parameters for different diagnostic tasks can be called up. The individual organ programs are from one operator 113 adaptable to the existing circumstances, for example the patient dimensions and the current diagnostic task.

The system control unit 100 has a reconstruction unit 117 on, in which the processed and stored projection data from the image processing and storage unit 106 together with the corrected data for the projection geometries of the respective projection recordings from the motion control unit 103 are received and a 3D volume is reconstructed.

It is an energy management unit 118 provided in which parameters such as the state of charge of the battery and capacitor storage, available network power, heat loading of the rotating anode and the generator oil filling are used to determine whether a planned diagnostic task can be carried out. In particular, in the energy management unit 118 determines whether a scan with a predetermined number of projection recordings can be carried out without reaching an overload condition. The scan parameters of a planned scan are used for this. A safety buffer is preferably taken into account. For example, if a scan with 400 individual projections is to be recorded for a certain selected organ program, the scan is released by the energy management unit 118 for example, if it is possible to computationally record an increased number of projection recordings that is 10% higher than the target number. If a complete scan with the selected scan parameters does not appear possible, the operator is shown this on a display 111 signaled. The system control then expects the operator to intervene. The latter can then change the scan parameters, for example, by reducing the total number of projection recordings during the scan. This would ensure the acquisition of a 3D data set suitable for reconstruction.

The system control unit 100 preferably has a DICOM interface 130 to a network 140 on, by means of the inputs and outputs between the C-arm X-ray diagnostic system 1 and for example a HIS hospital information system 142 , a radiology information system RIS 141 and a global network. DICOM input is intended to transfer patient data and patient-specific scan parameters from previous examinations.

Within the scope of the invention it is provided with the image recording control unit 104 to control the projection image recording with an image recording rate in the rotary areas of the focus ejectory, which comes from that of the system control unit 100 provided data about the size of the volume to be reconstructed and the number of voxels in the volume is calculated as a measure of the resolution of the reconstructed volume, assuming a circular scan. The determined image acquisition rate can be directly assigned to an angular distance between two target focus positions.

For a cube-shaped volume to be reconstructed with an edge length of 16cm, for example, a voxel volume of 320x320x320 voxels is selected; for a cube-shaped volume to be reconstructed with an edge length of 20cm, for example, a voxel volume of 512x512x512 voxels is selected.

Der Scanwinkel ϕ ist dabei der Orbitalwinkel des C-Bogens.
Auf der kreisförmigen Trajektorie des Fokus werden in diesem Fall Projektionsaufnahmen nach jeweils durchlaufenen gleichen Winkelintervallen Δφ aufgenommen.The scanning frequency dn / dϕ, namely the number of x-ray projection images per scanning angle ϕ is kept constant over the entire area of the circular scan $$\text{dn}/\text{d}\mathrm{\phi }=\text{const},$$

The scan angle ϕ is the orbital angle of the C-arm.
In this case, projection recordings are taken on the circular trajectory of the focus after the same angular intervals .DELTA..phi.

wobei der Winkel ϕ im rotatorischen Bereich der Fokustrajektorie dem Orbitalwinkel der C-Bogen-Rotation entspricht.In the case of non-circular rotation scans, the distances between the focus ejectory from the scan center change depending on the angle ϕ. It is provided within the scope of the invention to adapt the acquisition rate calculated on the assumption of a circular scan to the distance of the focus ejectory from the scan center. The recording rate is chosen to be lower the greater the distance of the focus ejectory from the scan center. It is provided that the acquisition rate calculated assuming a circular focus ejectory with a radius r ₀ is multiplied angle-dependent by a correction factor K ₁ which is linearly dependent on the current distance r of the focus ejectory, whereby $${\text{K}}_1\left(\mathrm{\phi }\right)=\text{r}\left(\mathrm{\phi }\right)/{\text{<figure-callout id="0" label="t" filenames="DE102018006763A1\_0012.png,DE102018006763A1\_0013.png" state="{{state}}">t</figure-callout>}}_0$$

where the angle ϕ in the rotary area of the focus ejection corresponds to the orbital angle of the C-arm rotation.

The inventor has recognized as advantageous to represent the complete focus ejectory with a rotary component and two translatory components in polar coordinates with the scan center as the coordinate origin, with a radius r as the distance of a point on the focus ejectory from the scan center and with a polar angle α. The polar angle α can be viewed as a synthetic scan angle for the entire focus ejection; in the rotary section of the focus ejector, this angle α corresponds to the orbital angle of the C-arm orbital movement.

The inventor has also recognized that oversampling when recording a scan with a rotary and translational section of the focus ejection is avoided by fulfilling a uniformity condition for the density of the projection recordings along the focus ejection of the scan. The uniformity condition is met when the angular distances Δα between the target focus positions on the focus ejectory are the same over the entire scan area. The angular distance between the individual exposure positions is calculated from the angular range of the focus ejectory between the start angle α _beginning , the _end angle α _end and the total number N of the proposed projection exposures: $$\mathrm{\Delta \alpha }=\left({\mathrm{\alpha }}_{\text{The End}}-{\mathrm{\alpha }}_{\text{Beginning}}\right)/\left(\text{N}-\text{1}\right)$$

The recording density of the projection recordings, ie the number of recordings per angular interval dα, are constant over the entire scan area. This condition is called the uniformity condition: $$\text{dn}/\text{d}\mathrm{\alpha }=\text{const},$$

The constant depends on the total number N of projection projections provided. In the case of a scan with an undefined focus ejectory, in particular a focus ejectory with an unknown total angular range, instead of the total number N, it is provided to specify the angular distance between two projection recordings or the equivalent number of projection recordings per angular interval α.

It is advantageous if the representation of the focus ejectory in the movement control unit and / or in the organ program database 115 exists in polar coordinates. As a result, transformations between a Cartesian and a polar coordinate system can be avoided, which in particular in the case of dynamic calculations leads to savings in computing capacity and computing time.

The uniformity condition can also be applied to circular scans. In this case, the angular intervals Δα correspond to the angular intervals of the orbital movement of the C-arm.
Furthermore, it is envisaged to apply the uniformity condition to non-planar scans which have rotary and translational sections in the focus ejectory. An example here is an “arc-line” scan, in which a linear circular scan is followed by a linear movement of the focus perpendicular to the plane.

In the case of non-planar focus ejectors, the respective focus ejectory is provided in spatial polar coordinates with respect to the scan center 20 to calculate and the Determine the total scan angle by integrating the angular distances d (α, θ) between the radius vectors.
The uniformity condition for non-flat focus ejectors then corresponds to the condition in the case of a flat focus ejectory $$\text{dn}/\text{d}\left(\mathrm{\alpha }.\mathrm{\theta }\right)=\text{const},$$

It is provided to determine the angular velocity dα / dt from the chronological sequence of the positions of the adjustment axes of the X-ray imaging system during a scan in real time, and from this to calculate the target image acquisition rate dn / dt (number of projection exposures per second) together with the uniformity condition. Furthermore, it is provided in the image recording control during a scan to determine the angle α in real time from the positions of the adjustment axes of the X-ray recording system and to record a projection recording each time an angle interval Δα is passed. The focus extractor is used in advance for the image recording control by the motion control unit 103 made available.

It is provided within the scope of the invention that the focus ejectory in the currently in the motion control unit 103 to calculate existing positions of the X-ray imaging unit.

In the memory of the motion control unit of the C-arm x-ray system, the path speeds on the focus ejectory are preferably also determined as a function of the angle α of the focus ejectory; they become together with the focus ejectory of the scan parameter generation unit 107 for calculating the image recording rate or the target focus position on the focus ejectory. Has the C-arm X-ray system next to the C-arm 2 a patient table that can be adjusted simultaneously by motor 23 on, so in the motion control unit 103 the C-arm motor control unit 24 and the couch motor control unit 25 controlled according to a stored rule in such a way that the focus ejectory in accordance with the transmitted data from the scan parameter generation unit 107 with respect to the scan center. In this case, the scan center is not fixed in space because it is with the object 21 on the adjustable patient table 23 connected is. A combined adjustment of the C-arm and patient bed has the advantage that, for example, there are limitations in the C-arm movement around the scanning center 20 can be expanded around by the movements of the patient bed.

In addition to the provision of a trigger signal at a point in time when the focus is on a target target position of the focus ejectory, an x-ray projection recording can also be triggered by recording a video stream with a clock frequency and adapting this clock frequency to the focus ejectory in such a way that the video frames are recorded at the focus target positions. It is known to record the x-ray projection recordings of a scan with constant frame rates, which are generated from a V-Sync-like signal of constant frequency (hereinafter referred to as V-Sync). This V-Sync generally represents a periodic signal, on the rising or falling edge of which an image trigger signal is generated. In a method according to the invention for recording x-ray projection recordings of a scan, two alternative strategies for changing the V-sync frequency are provided.

It is intended to keep the V-Sync frequency constant and to reduce the image recording frequency by blanking out V-Sync signals. If, for example, there is a frequency of 25 Hz, it can be provided to record projection images only every three periods, i.e. constantly with an image recording frequency of 8.3 Hz. According to the invention, it is provided that the image recording frequency is varied during the recording scan so that it has discrete values of f = 25Hz / m, where m is a natural number that is varied dynamically during the scan.

It is also provided that the V-Sync frequency is dynamically adjusted during the scan so that the V-Sync signal can be used directly as an image trigger signal, the image triggering taking place at the target focus positions on the focus extractor. At the end of a scan or if the X-ray recording unit is inactive, the V-Sync signal is switched off, so that no image is taken.

In the described methods for adapting the image acquisition rates, the V-sync frequencies can be calculated after selecting a path curve, but before starting a scan. Alternatively, it is provided to calculate and set the required frame rates in real time during the recording of the scan.

Depending on the organ program selected and especially in the case of a fat patient, the absolute value of the image acquisition rate dn / dα or the total number of X-ray projection images per scan can be increased in order to achieve an acceptable signal-to-noise ratio in the reconstructed volume. So if the user chooses a corresponding patient, the scan parameter generation unit 107 dn / dα increased accordingly if an energy management unit 118 a sufficient power reserve for the energy supply of the C-arm X-ray diagnostic system has recognized. This ensures that a specific recording density dn / dα can be achieved without the recording having to be stopped prematurely because of an then empty energy store. The patient orientation selected by the user and the organ program can be taken into account in order to estimate the angular interval in which an increase in dn / dα will probably be necessary.

For a scan with a shot of a number of projection shots and a scan center 20 Individual sections of the focus ejectory should be differentiated as follows:

Rotatory sections of the focus ejectory are those in which the central beam always moves through the scan center when the C-arm is displaced 20 runs. The distance of the focus ejector from the scan center 20 is irrelevant. It can be a circular arc scan, an elliptical scan or, for example, a super-elliptical scan.

Translatory sections of the focus ejectory are those in which the central beam continuously changes the distance to the scan center when the C-arm is displaced. The shape of the focus ejector is irrelevant; it can take a linear, arcuate or any other form.

If, in addition to the three controllable adjustment axes described above, a C-arm X-ray diagnostic system has another with an adjustment component perpendicular to the orbital plane or if a patient couch is provided that is adjustable synchronously with the C-arm, it is possible to use a non-level focus ejector, for example a so-called arc-line trajectory with a flat circular arc and a linear section extending perpendicular to the circular surface and starting at one end of the circular arc. In the case of a non-planar focus ejectory, the focus ejectory would be converted from a Cartesian coordinate system into spatial polar coordinates (r, α, θ) to determine the target focus positions. The total angular range in an arc-line scan would be the angular range of the rotary section (α _enderot - α _beginning ), the angular range of the translational section perpendicular to the scan plane with the condition for the vertical line α = const. and the condition for the scan plane θ = 0 is θ _end -0 = θ _end . The total angular range is made up of the total angular range of the rotary section and the total angular range of the translational section. The uniformity condition for spatial polar coordinates is $$\mathrm{\Delta \alpha }\mathrm{,\; \Theta \; =}\left({\mathrm{\alpha }}_{\text{enderot}}-{\mathrm{\alpha }}_{\text{Beginning}}+{\mathrm{\theta }}_{\text{The End}}\right)/\left(\text{N}-1\right)$$

If, for the sake of simplicity, the angular section is linearly removed from the angled focus trajectory of an arc-line trajectory in order to determine the target focus positions, an error occurs in the angular range in a single angular step; the angular distance there is chosen to be too small by a maximum of 30%, which has a negligible influence on the total dose given a total of 400 projection images of a scan.

If you look at the trajectories 2 , you can see that these trajectories cannot be traversed at a constant path speed because the time derivative of the path curve is inconsistent. In order to avoid impermissibly high accelerations of the C-arm, the path speed near the transitions of the trajectory between a rotary part and a translatory part is reduced. To prevent the focus from coming to a complete standstill, measures to adapt the trajectories in these areas are from the document DE102013013552B3 known to the applicant.

Within the scope of the invention, the recording of the projection recordings is recorded at a constant image recording rate, characterized by a constant V-sync frequency, and the image recording rate is changed discretely by omitting or blanking out individual trigger signals at individual target focus positions or individual target trigger times.

It is known that the image recording system is operated, for example, with a V-sync frequency of 25 Hz. A projection image recording frequency of 8.3 Hz is realized in that a projection recording is only taken at every third trigger time.

m

Bildaufnahmefrequenz/Hz bei V-Sync-Frequenz (Triggerfrequenz) von 25 Hz

1

25

2

12,5

3

8,3

4

6,2

5

5

6

4,2

7

3,6

8

3,1

···

···

The invention provides for the x-ray projections to be recorded during the scan with a variable recording rate of f = f _V-Sync / m, where f _{V-Sync represents} the V-Sync frequency and m is a natural number which is changed during the scan. The first image acquisition frequencies of the series that can be achieved with this method are given below.

m

Image acquisition frequency / Hz at V-sync frequency (trigger frequency) of 25 Hz

1

25

2

12.5

3

8.3

4

6.2

5

5

6

4.2

7

3.6

8th

3.1

···

···

The described method for varying the image recording rate leads to changes in the image recording frequency of different sizes in the upper and in the lower frequency range. If, based on an image recording frequency of 8.3 Hz in the area of a circular section of a trajectory, the image recording frequency is to be reduced when the detector approaches the transition area to a translatory section, this is done via the frequency steps 6.2 Hz, 5 Hz, 4.3 Hz. Etc.

The parameter m is calculated from the focus ejectory, the path speed, from the scan angle range and the number of projection recordings N to be recorded in real time or before the start of a scan or is taken from a pre-calculated and stored LUT.

Alternatively, it is provided to adapt the image recording rate during the recording of a scan by dynamically changing the V-sync frequency and recording a projection image at every trigger point in time and without missing trigger signals.

A trigger signal referred to as an image trigger signal preferably triggers the activation of the X-ray source and the exposure of the FPD. There is no V-sync signal and therefore no trigger signal in the radiation pauses, especially even when the x-ray generator is inactive for a long time.

In 4 the course of the angle-dependent image acquisition rate f is shown schematically as a function of the angle α of the target focus positions. It can be seen that in the transition areas between the rotary section (area α _{red beginning} to α _rotating ) and the translational sections of the focus ejection, the image recording rate is reduced.

In 5 the course of the angle-dependent weighting function g (α) of the target focus positions is shown schematically. It can be seen that the weighting function differs from 1 only in a region of the rotary section of the focus ejection. The effect of the weighting function is developed by multiplying it by the image acquisition rate f (α). As a result, certain spatial directions preferred from the organ program or by input of the operator are recorded in the rotary section of the focus ejectory with a higher recording density in order to compensate for a reduced projection image quality caused by an estimated focus position-dependent patient absorption.

In order to determine the trigger signal times and thus the current V-sync frequency, the following method according to the invention is used: A focus ejector selected by the user of the C-arm x-ray diagnostic system is made available to the system controller. The provision of the focus trajectory is preferably preceded by the selection of an organ program that is dependent on the patient's dimensions. The focus ejectory, which is present in a Cartesian coordinate system of the C-arm X-ray diagnostic system, is converted into polar coordinates, the origin of the polar coordinate system being in the scan center. The focus ejectory is determined by the distance r (α) from the coordinate origin. The radii r (α) only fall in the rotary section of the focus ejectory with the direction of the central beam 22 together.

The endpoints of the _initial Fokustrajektorie are the polar angles α and α associated _end. In polar coordinates, a scanning area angle = (α _end - α _beginning ) is introduced, over which the total number N of projection images is initially evenly distributed. This results in equal angular spacings of the polar angle α between the target focus positions on the focus ejector, namely $$\mathrm{\Delta \alpha \; =}\left({\mathrm{\alpha }}_{\text{The End}}-{\mathrm{\alpha }}_{\text{Beginning}}\right)/\left(\text{N}-1\right)$$

mit n=0 bis n=N-1 befindet.Projection recordings are thus generated when the focus on the focus ejectory is at the desired positions $$\text{Fn}\left(\text{r}.\mathrm{\alpha }\right)=\text{F}\left(\text{r}.{\mathrm{\alpha }}_{\text{Beginning}}+\text{n}\mathrm{\Delta \alpha }\right)$$

with n = 0 to n = N-1.

In order to achieve projection recordings with a predeterminable signal-to-noise ratio, it is provided to regulate the dose in real time in a known manner via the tube current for each projection recording.

Within the scope of the invention, it is provided that the trajectories for the detector and the X-ray focus and scan center are determined by the user from the start of a scan, the trajectories initially being present in Cartesian coordinates in the coordinate system of the C-arm X-ray diagnostic system. Each pair of a point on the detector trajectory and a point on the focus trajectory is on the one hand a unique position and orientation of the x-ray unit and on the other hand, a triple of position values assigned to the at least 3 adjustment axes, namely the horizontal adjustment axis, the vertical adjustment axis and the orbital axis of the C-arm device. The position values of the adjustment axes are in turn clearly linked to the position values of the drive motors in these adjustment axes.

The relationship between the position values of the drive motors and the pair of points on the detector and focus ejectors can theoretically be calculated from knowledge of the kinematics of the C-arm, but is known to be checked by means of a calibration run; Deviations from the theoretical kinematics are corrected in the course of a calibration run and stored as calibrated kinematics, preferably in LUTs, in a memory of the C-arm x-ray diagnostic system.

For a volume reconstruction, the projection geometries of the calibrated kinematics are used for each projection image.
To determine the recording angles of the recording positions, the selected focus ejectory, which is made available to the control of the C-arm, is converted into polar coordinates. The projection recordings are taken when the calculated target focus positions are reached on the focus ejectory by the trigger of an image trigger signal. The method is advantageous because no knowledge of the current speeds of the adjustment axes or of the speed of the focus on the focus ejectory is required to determine the times at which a calculated target focus position was reached.

If the point in time for the recording of a projection recording, which is determined by an image trigger signal, is determined by the condition of reaching the angular position of a target focus position on the focus ejection, this is done regardless of the speeds at which the trajectories are traversed. In particular, even if the speed on the trajectories of FPD and X-ray focus is reduced by the movement control unit of the C-arm X-ray diagnostic system when a risk of collision of a part of the C-arm (FPD or X-ray emitter) is reduced.

The angle of view positions can be calculated before the start of a scan or in real time during the scan.

Within the scope of the invention it is provided to determine the frequency of the recording of the x-ray projections (recording rate or frame rate) during the scan in the rotary and translational trajectory section as a function of the current position or the current angular velocity of the polar angle α before the start of the scanning trajectory or in real time during it to calculate the scan. The acquisition rate depends on the time in which an angular interval Δα is traversed or on the angular velocity dα / dt at which the trajectories are traversed.

Within the scope of the invention, it is further provided not to determine the target focus position, but rather the frame rate as a function of the time at which a projection recording is triggered and the swept polar angle Δα.

In accordance with the legally required requirements for dose hygiene in an X-ray examination with subsequent volume reconstruction, on the one hand, every patient dose should be avoided that generates no or no additional information value for the diagnostic task, and on the other hand, a scan with a sufficient density and number of projection recordings must be carried out to ensure a predetermined reconstruction quality of the x-ray volume. Such a reconstruction quality cannot be achieved and may lead to the fact that no diagnostic information can be obtained from the x-ray projections if the scan can be completed, for example, because the energy supply of the high-voltage generator is too low. It is therefore provided that a planned scan with a planned number of projection recordings and a dose estimated for the diagnostic task in an energy management unit 118 to check whether it can be safely driven through completely. This means in particular that an energy reserve of, for example, 10% of the estimated energy requirement must be available for a scan. The energy reserve is partially exhausted if, for example, due to an excessively long transmission length at one or more target focus positions, a recording cannot be corrected and more than one x-ray projection recording must be taken in order to use these multiple projection recordings to produce a synthetic projection recording at the target focus position generate, which is used for the reconstruction.

If an unexpected case occurs during a scan that it can be foreseen that the scan cannot be completed with the scan parameters provided, then it is provided that the angular intervals Δα be increased until the end of the scan and thus the remaining number of the projection recordings to be recorded is reduced ,

It is provided within the scope of the invention to calculate the conditions for the recording times or for the recording locations on the focus ejector in advance or dynamically.

trigger procedures

The method according to the invention for recording a scan with the triggering of the recording of a projection recording by means of an image trigger signal is described below on the basis of individual, numbered method steps.

Step 3.1

Receive trajectories of focus and FPD in the coordinate system of the C-arm X-ray diagnostic system in the scan parameter generation unit 107 and go to step 3.2

Step 3.2

Receive the position of the scan center in the coordinate system of the C-arm X-ray diagnostic system in the scan parameter generation unit 107 and go to step 3.3

Step 3.3

Receive the total number N of the intended x-ray projection recordings of the scan in the scan parameter generation unit 107 and go to step 3.4

Step 3.4

Calculate in the scan parameter generation unit 107 the start and end points of the Fokustrajektorie in polar coordinates (r, α) to the scan center as the coordinate origin and determine the path swept by the Fokustrajektorie angular range (α _end - α _start) and go to step 3.5

Step 3.5

Calculate in the scan parameter generation unit 107 the positions of the receiving locations for projection images Fn (r, α) = F (r, α _start + n Δα) with n = 0 to n = N-1 on the Fokustrajektorie in polar coordinates satisfying the uniformity condition Δα = (α _end - α _beginning ) / (N-1) and calculation of the coordinates of the recording locations in the coordinate system of the C-arm X-ray diagnostic system 1 and outputting the positions of the recording locations on the focus trajectory to the movement control unit 103 and go to step 3.6

Step 6.6

Receive in the motion control unit 103 the focus ejector, the scan center and the positions of the recording locations on the focus ejector and go to step 3.7

Step 3.7

Calculate the adjustment parameters of the adjustment axes of the C-arm X-ray diagnostic system in the motion control unit 103 and pass the motion control data to the C-arm motor control unit 24 and if necessary to the couch motor control unit 25 and go to step 3.8

Step 3.8

Monitor the receipt of a scan start signal and start the movement of the C-arm and, if necessary, the patient couch to go through the focus ejector and go to step 3.9

Step 3.9

Move the C-arm and, if necessary, the patient bed with the focus along the focus ejectory and go to step 3.10

Step 3.10

Decide whether the focus is on a target shooting position of the focus ejection.
If so: go to step 3.11 ; if no: go to step 3.9

Step 3.11

Decide whether the focus target position is the last intended position on the focus ejection.
If yes: transmit an image trigger signal to the image acquisition control unit, work in parallel there the steps from step 3.12 and give an end of motion signal to the system control unit; if not: transmit an image trigger signal to the image acquisition control unit, work in parallel there the steps from step 3.12 and go to step 3.9 ,

Step 3.12

Receive an image trigger signal in the image capture control unit 104

Step 3.13

Decide whether an image trigger signal is pending.
If yes: go to step 3.14 ; if no: check repeatedly until the end of one maximum waiting time to receive an image trigger signal. If there is no image trigger signal after the maximum waiting time has expired, abort the method step and send an abort signal with an abort log to the system control unit 100 ,

Step 3.14

Receive a prevention signal from one of the units: collision monitoring control unit, energy management unit, input unit (emergency stop).

Step 3.15

Decide whether there is a prevention signal.
If so: cancel the process step and send an abort signal with an abort log to the system control unit 100 ; if no: go to step 2.16 ,

Step 3.16

Control of the tube control unit 101 and the FPD control unit 105 to trigger a projection recording

Step 3.17

Decide whether the projection recording meets the specified requirements (e.g. with regard to the signal-to-noise ratio).
If so: go to step 3.13 ; if not: go to step 3.18 ,

Step 3.18

Decide whether the maximum number of repetitions of projection recordings at the same location has been reached.
If so: and send a retry status log to the control panel 100 and go to step 3.13 ; if not: go to step 3.19 ,

Step 3.19

Trigger the capture of another projection image and go to step 3.15 ,

After completing the process steps, the system control is available N Projection recordings with focus positions that meet the uniformity condition for further processing in the reconstruction unit 117 to disposal. Repeat or additional images can be available at one or more focus positions. An X-ray projection is synthesized from the originally recorded projection image and the repeat or additional images, which is used for the reconstruction.

A further solution to the problem are methods in which the projection image recording frequency is variably controlled over the course of the focus ejection (“frequency calculation method” or “focus position calculation method”)

Preliminary frequency calculation method

A projection image recording method according to the invention, taking into account the course of the angular velocity dα / dt in a preliminary calculation, has the following method steps:

Step 4.1

Receive a selected focus ejection

Step 4.2

Receiving an angular velocity dα / dt for each point of the focus ejection

Step 4.3

Receiving dn _to a selected constant desired recording density / d.alpha, namely the number of projection images per angular interval Δα from the memory of the system control unit 100 ,

Step 4.4

Calculation of the acquisition rate dependent on the angle alpha $$\text{dn}/\text{dt}=\text{dn}/\text{d}\mathrm{\alpha }*\text{d}\mathrm{\alpha }/\text{dt}$$

Step 4.5

Receiving a minimum and maximum image acquisition rate f _min and f _max and an optional start image acquisition rate f _start from the memory of the system control unit 100 ,

Step 4.6

Calculate the desired image acquisition rate dn / dt depending on the angle α, taking into account f _min and f _max as well as an optional start image acquisition rate f _start .

Step 4.7

Triggering the start of the scan and varying the recording frequency f depending on the angle α at which the focus is on the focus ejection located according to the pre-calculated and saved frequency response

Step 4.8

Continuous increase of the projection image acquisition rate compared to the target image rate at each angular position of the focus ejectory when an AEC low status signal is received and steady return of the image acquisition frequency to the target image rate when no AEC low status signal signal is received.

Dynamic frequency calculation method

A projection image recording method according to the invention, taking into account the course of the angular velocity dα / dt in a dynamic calculation, has the following method steps:

Step 5.1

Receiving a target sampling rate dn _soll / dα from the memory of the system control unit 100 and calculating the dn (α) / dt = dn (α) / dα * dα / dt

Step 5.2

Receiving a minimum and maximum image acquisition rate fmin and fmax and an optional start image acquisition rate f _start from the memory of the system control unit 100 ,

Step 5.3

Start the scan at the start image acquisition rate f _start .

Step 5.4

Continuous calculation of the current angular velocity dα / dt and the target image acquisition rate dn (α) / dt = dn (α) / dα * dα / dt and application of the image acquisition rate taking into account fmin and fmax.

Step 5.5

Optional at any time: steady increase of the projection image acquisition rate compared to the target image rate at every angular position of the focus ejectory, steady increase of the projection image acquisition rate compared to the target image rate at every angular position of the focus ejectory if an AEC low status signal is received and steady return of the projection image acquisition rate if no AEC low status signal is received.

Pre-focus position calculation method

A projection image recording method according to the invention, taking into account the current position of the focus on the focus trajectory with a pre-calculation, has the following method steps:

Step 6.1

Receiving dn _to a selected Fokustrajektorie as well as a desired recording density / d.alpha from the memory of the system control unit 100 ,

Step 6.2

Receive a minimum and maximum image acquisition rate fmin and fmax

Step 6.3

Select the starting position on the focus trajectory as the first recording position.

Step 6.4

Calculate the polar angle α of the recording locations of the focus on the focus ejectory at which the projection images are to be recorded, taking into account fmin and fmax.

Step 6.5

Carrying out the recording and triggering the individual projections at the calculated locations with the polar angle α.

Step 6.6

• - Wechsel in den dynamischen Modus, wobei die vorberechneten Positionen der Aufnahme der Projektionsaufnahmen dem Speicher gelöscht werden/verworfen werden
• - Wechsel in den Vorberechnungsmodus, wobei die vorberechneten Aufnahmepositionen aus dem Speicher gelöscht werden/verworfen werden und eine neue Vorberechnung entsprechend aktueller Anforderung erfolgt, wobei diese neu berechneten Positionen wieder verworfen werden und entsprechend aktueller Anforderung wiederum neu berechnet werden, wenn ein AEC-low-Statussignal empfangen wird und dann wieder Vorberechnung und Auslösen an den vorberechneten Positionen, solange kein AEC-low-Statussignal anliegt oder die Endposition der Fokustrajektorie erreicht ist; andernfalls Neuberechnung bis zur nächsten Anforderung oder bis Aufnahmeende.
• - Wechsel in den regulären V_sync-Modus mit Auslösen zusätzlicher Projektionsaufnahmen bei Vorliegen eines AEC-low-Statussignals in den sonst ausgelassenen Slots und Fortsetzung des Scans mit Auslösen von Projektionsaufnahmen an den abgespeicherten vorbestimmten Winkelpositionen, wenn kein AEC-low-Statussignal anliegt.

Optionally, a steady increase in the recording density dn / dα compared to the target recording density at each angular position of the focus projection is carried out at every recording location (r, α) when an AEC low status signal is received, and there is a constant return of the recording density to that Target recording density is carried out when no AEC low status signal is received, the control system switching to a predetermined one of the three modes described below when an AEC low status signal is present:

• - Switch to dynamic mode, whereby the pre-calculated positions of the recording of the projection recordings are deleted / discarded in the memory
• - Change to the precalculation mode, the precalculated recording positions being deleted / discarded from the memory and a new precalculation taking place in accordance with the current requirement, wherein these recalculated positions are rejected and, according to current requirements, are recalculated when an AEC low status signal is received and then recalculation and triggering at the precalculated positions as long as no AEC low status signal is present or the end position of the focus ejection is reached is; otherwise recalculation until the next request or until the end of admission.
• - Change to the regular V _sync mode with triggering additional projection recordings when an AEC-low status signal is present in the otherwise omitted slots and continue the scan with triggering projection recordings at the stored predetermined angular positions if there is no AEC-low status signal.

Dynamic focus position calculation method

A projection image recording method according to the invention, taking into account the current position of the focus on the focus trajectory in a dynamic calculation, has the following method steps:

Step 7.1

Dn _to receiving a Fokustrajektorie and a desired recording density / d.alpha from the memory of the system control unit 100 .

Step 7.2

Position the C-arm in such a way that the focus is at a starting point of the focus ejection

Step 7.3

Triggering a projection recording before the start of the movement of the C-arm.

Step 7.4

Continuously calculate the angular interval Δα since the last exposure.

Step 7.5

Continuously calculate the dimensionless quantity k = Δα * dn / dα, where dn / dα is the specified recording density and transmit a projection image trigger signal to the image recording control unit if k≥1 and trigger a projection image recording if an AEC low status signal is present and follow up Trigger the projection recording to step 7.4 and repeat the steps 7.4 to 7.5 until the end position of the focus ejector is reached.

Step 7.6

Increasing steadily dn the projection image recording density / d.alpha when an AEC-low-state signal has been received and steady return _to dn-recording density set by the current recording density to the / d.alpha if no AEC-low-status signal is received.

A control device according to the invention for a C-arm X-ray diagnostic system is designed in such a way that the C-arm X-ray device is first activated in order to record a scan from a predetermined number of projection recordings,
that the x-ray projection recordings are taken at target focus positions on the focus ejectory that have a constant polar angle distance.

The control method for recording a scan is preferably implemented in software. A largely software-based implementation of the control method has the advantage that previously used control devices for C-arm X-ray diagnostic systems can also be easily upgraded by a software update in order to work in the manner according to the invention. In this respect, the object is also achieved by a corresponding computer program product with a computer program which can be loaded directly into a memory device of a control device of a C-arm x-ray diagnostic system, with program sections, in order to carry out all steps of the method according to the invention when the computer program is executed in the control device. In addition to the computer program, such a computer program product can optionally include additional components such as documentation and / or additional components, including hardware components for using the software.

For transport to the control device and / or for storage on or in the control device, a computer-readable medium, for example a memory stick, a hard disk or another portable or permanently installed data carrier, can be used, on which the program sections of the computer program that can be read and executed by a computer unit of the control device can be stored are. A connection to a hospital information system connected to a network, to a radiology information system or to a global network can also serve for the transport, in which systems the program sections of the computer program that can be read and executed by a computer unit of the control device are stored. The computing unit can e.g. B. this one or have several cooperating microprocessors or the like.

Further, particularly advantageous refinements and developments of the invention result from the dependent claims and the description, the independent claims of one claim category also being able to be developed analogously to the dependent claims of another claim category, and in particular also individual features of different exemplary embodiments or variants of new exemplary embodiments or variants can be combined.

• Empfange eine von einem Benutzer aus einer Vielzahl von in einer Organprogramm-Datenbank (115) zur Verfügung stehenden Fokustrajektorien ausgewählte Fokustrajektorie mit rotatorischem und translatorischen Anteilen im Koordinatensystem des C-Bogen-Röntgendiagnostiksystems (1) durch die Scanparameter-Erzeugungseinheit (107),
• empfange eine Information über die Lage des gewünschten Scanzentrums (20, 51) im Koordinatensystem des C-Bogen-Röntgendiagnostiksystems (1) durch die Scanparameter-Erzeugungseinheit (107),
• empfange eine Information über die Soll-Aufnahmedichte der Röntgenprojektionsaufnahmen, wobei die Information eine der Information ist aus der Gesamtzahl N der Aufnahmen über die gesamte Länge der Fokustrajektorie und dem mittleren Winkelabstand Δα_soll im rotatorischen Teil der Fokustrajektorie zwischen zwei Fokuspositionen bezogen auf das Scanzentrum durch die Scanparameter-Erzeugungseinheit (107),
• übermittle die Scanparameter an die Fokus-Sollpositionsermittlungseinheit (108),
• rechne die Fokustrajektorie mit dem Scanzentrum (20, 51) als Koordinatenursprung in Polarkoordinaten um,
• errechne die Fokussollpositionen F_i(r_i,α_i) auf der Fokustrajektorie, an denen jeweils eine Röntgenprojektionsaufnahme aufgenommen werden soll mit der Vorgabe einer konstanten Aufnahmedichte dn/dα der Projektionsaufnahmen, wobei die Polarwinkel α_i der Fokussollpositionen zwischen dem Polarwinkel α_anfang=α₁ am Startpunkt der Fokustrajektorie und dem Polarwinkel α_ende am Endpunkt der Fokustrajektorie bei gegebenem N der Bedingung α_i=α₁+(i - 1) *Δα mit 1=1 bis i=N, wobei Δα= (α_ende-α₁) / (N-1) und bei gegebenem Δα_soll der Bedingung α_i=α₁+(i-1) *Δα_soll mit i=1 bis i=M, wobei M= (α_ende-α₁) /Δα_soll,
• stelle die Fokussollpositionen der Bewegungssteuerungseinheit (103) zur Verfügung,
• berechne aus der in der Scanparameter-Erzeugungseinheit (107) hinterlegten Fokustrajektorie, einem kinematischen Modell des C-Bogens und damit verknüpften Geschwindigkeits- und Beschleunigungsprofilen die Motoransteuersignale für die motorisierten Achsen (x(t), y(t), ϕ(t)), die die zeitabhängige Bewegung des Fokus auf der Fokustrajektorie beschreiben sowie den zeitlichen Verlauf des Polarwinkels α(t),
• erzeuge eine Information über das Erreichen einer Fokussollposition und übermittle diese an die Bildaufnahmesteuerungseinheit (103),
• veranlasse die Bildaufnahmesteuerungseinheit (104), zum nächstmöglichen Zeitpunkt eine Röntgenprojektionsaufnahme auszulösen, nehme sukzessive die Reihe der Röntgenprojektionsaufnahmen auf und stelle die Bilddaten der Röntgenprojektionsaufnahmen mit den Koordinaten des Fokus zum Aufnahmezeitpunkt, der Fokustrajektorie und der Lage des Scanzentrums der Rekonstruktionseinheit (117) zur Verfügung.

The invention provides a method for recording a scan of an area of interest ROI ( 50 ) with a focus on ROI ( 50 ) lying scan center ( 20 . 51 ) in an object ( 21 ) available, with the scan consisting of a series of x-ray projection images that contain a complete set of x-ray projection data of the ROI ( 50 ) in the orbital plane of a C-arm X-ray device ( 2 ) for a 3D reconstruction and the recording of the scan using a C-arm X-ray diagnostic system ( 1 ) success with
a motor-adjustable C-arm in a holder along the circumference around an orbital movement axis ϕ and in the C-arm plane in two independent axes x and y, the C-arm an X-ray image recording system with an X-ray tube arranged at one end of the C-arm ( 3 ) with a focus and an FPD X-ray image detector arranged opposite one another at the other end of the C-arm ( 6 ) and with the focus of the X-ray tube ( 3 a system control unit, taking a series of cone-beam x-ray projection recordings with a predetermined image quality along a coherent, plane and monotonous focus ejectory with a rotatory section and two translational sections adjoining the ends of the rotatory section, 100 )
a motion control unit ( 103 ), which detects all movements of the C-arm X-ray device ( 2 ) to move through the focus on the focus ejectory taking into account in the motion control unit ( 103 ) controls stored kinematics with speed and acceleration profiles,
an image acquisition control unit ( 104 )
a scan parameter generation unit ( 107 )
a reconstruction unit ( 117 ), a focus target position determination unit ( 108 )
the method comprising the following steps:

• Receive one from a variety of users in an organ program database ( 115 ) available focus ejectors selected focus ejectors with rotary and translational components in the coordinate system of the C-arm X-ray diagnostic system ( 1 ) by the scan parameter generation unit ( 107 )
• receive information about the location of the desired scan center ( 20 . 51 ) in the coordinate system of the C-arm X-ray diagnostic system ( 1 ) by the scan parameter generation unit ( 107 )
• receive information about the target recording density of the x-ray projection recordings, the information being one of the information from the total number N of the recordings over the entire length of the focus ejectory and the mean angular distance Δα _{should be} in the rotary part of the focus ejectory between two focus positions in relation to the scan center by the scan parameter generation unit ( 107 )
• transmit the scan parameters to the focus target position determination unit ( 108 )
• calculate the focus ejector with the scan center ( 20 . 51 ) as a coordinate origin in polar coordinates,
• calculate the focus target positions F _i (r _i , α _i ) on the focus ejectory, at each of which an X-ray projection image is to be recorded with the specification of a constant recording density dn / dα of the projection recordings, the polar angles α _{i of} the focus target positions between the polar angles α _beginning = α ₁ at the start point of the focus ejectory and the polar angle α _end at the end point of the focus ejectory given N the condition α _i = α ₁ + (i - 1) * Δα with 1 = 1 to i = N, where Δα = (α _end -α ₁ ) / (N-1) and at a given Δα _to the condition α _i = α ₁ + (i-1) * Δα _to i = 1 to i = M, where M = (α _end -α ₁₎ / Δα _to .
• set the focus target positions of the motion control unit ( 103 ) to disposal,
• calculate from the in the scan parameter generation unit ( 107 ) deposited focus ejectory, a kinematic model of the C-arm and the associated speed and acceleration profiles, the motor control signals for the motorized axes (x (t), y (t), ϕ (t)), which show the time-dependent movement of the focus on the focus ejectory describe and the time course of the polar angle α (t),
• generate information about reaching a focus target position and transmit it to the image recording control unit ( 103 )
• initiate the image acquisition control unit ( 104 ) to trigger an x-ray projection picture as soon as possible, take the series of x-ray projection pictures successively and compose the image data of the x-ray projection pictures with the Coordinates of the focus at the time of recording, the focus ejectory and the position of the scan center of the reconstruction unit ( 117 ) to disposal.

The focus positions at which x-ray projection recordings are to be taken are determined according to the invention on the basis that the angular distances Δα between two focus target positions are constant over the entire focus ejectory. The focus positions, at which X-ray projection recordings are actually taken to obtain the projection data for a 3D reconstruction, differ from the focus target positions due to the system. The focus positions at which x-ray projection images were actually taken are used for the reconstruction.

It is provided that the information about reaching a target focus position in feature i) is obtained by calculating the polar angular velocity dα / dt of the focus on the focus projection and together with the polar angle distance Δα between two target target positions a time-dependent target image recording frequency signal f ( t) = dα / dt * 1 / Δa is calculated and the target image recording frequency signal synchronously to the image recording control unit ( 104 ) is transmitted. If, for example, the speed of the focus on the focus ejectory is changed in the orthoradial direction during a scan, the polar angular speed also changes and, at a constant image recording frequency, projection recordings would be taken with a recording density that is too high or too low compared to the desired recording density. The inventive adaptation of the image recording frequency signal to the orthoradial speed of the focus achieves x-ray projection recordings at focus positions with the same polar angle distance.

It is further contemplated that the information is generated on the achievement of a focus target position in the feature i) by monitoring the polar angle α (t), wherein on reaching a polar angle _i of a focus target position, a trigger signal to the α, the image pickup control unit ( 104 ) is transmitted to promptly trigger an x-ray projection image.

It is envisaged that the image acquisition control unit ( 104 ) Values for a minimum target image acquisition frequency f _min , a maximum target image acquisition frequency f _max and an optional start-target image acquisition frequency f _start from the system control unit memory ( 100 ) is received and the calculated target image recording frequency signal f (t) is constantly changed when the limit values are imminent and there is a deviation in the starting target image recording frequency. The specification of a minimum target image acquisition frequency f _min has the result that, for example, at points in the focus ejectory where the focus comes to a standstill, projection recordings continue to be recorded with the minimum target image recording frequency.

It is further provided that the system control unit ( 100 ) is also designed to generate a signal ("AEC low status signal") and to the image acquisition control unit ( 104 ) to be made available when an x-ray projection image with insufficient exposure has been generated and image data with an excessively high noise component have been recorded, a further x-ray projection image being recorded at the next possible time if an AEC low status signal is present. If the Doisis power control AEC cannot regulate a projection image, at least one further projection image is recorded at almost the same position in order to reduce the noise in the image data set for this focus position.

It is further provided that the projection image recording density dn / dα is continuously increased when in the image recording control unit ( 104 ) an AEC low status signal was received and the projection image recording density dn / dα is steadily lowered from the current recording density to the target recording density dn _soll / dα if no AEC low status signal was received.

It is further provided that the image acquisition control unit ( 104 ) is set up to steadily increase the projection image recording rate dn / dt at any time compared to the target image rate at any angular position of the focus ejectory when an AEC low status signal from the image recording control unit ( 104 ) has been received and the projection image recording rate has to be steadily reduced to the target image rate if no AEC low status signal is received.

It is also envisaged that the C-arm X-ray diagnostic system ( 1 ) also a simultaneous with the C-arm X-ray device ( 2 ) motor-controlled patient couch ( 23 ) and the control method for the motion control unit ( 103 ) the C-arm X-ray machine ( 2 ) and the patient bed ( 23 ) according to a movement instruction for guiding the focus along the focus ejectory around the scan center ( 20 . 51 ) in the coordinate system of the C-arm X-ray diagnostic system ( 1 ) controls synchronously.

It is further provided that the scan parameter generation unit ( 107 ) the focus target positions to the motion control unit ( 103 ) transmitted and there a blanking signal is determined by comparison with the current focus position, which in the image recording control unit ( 104 ) generates an angle-dependent image recording frequency f (α) in that pulses are blanked out from a V-sync image recording trigger signal of constant frequency when in the motion control unit ( 103 ) the current focus position did not match the target focus position.

It is further provided that the scan parameter generation unit ( 107 ) also receives, together with the focus ejectory, a weighting function dependent on an estimated focus position-dependent patient absorption, which after conversion into polar coordinates g (α) for weighting the image recording frequency f _wt . (α) = f (α) * g (α) is used.

• eine Scanparameter-Erzeugungseinheit (107) die eingerichtet ist, eine von einem Benutzer aus einer Vielzahl von in einer Organprogramm-Datenbank (115) zur Verfügung stehenden Fokustrajektorien ausgewählte Fokustrajektorie mit rotatorischem und translatorischen Anteilen im Koordinatensystem des C-Bogen-Röntgendiagnostiksystems (1), eine Information über das gewünschte Scanzentrum (20, 51) im Koordinatensystem des C-Bogen-Röntgendiagnostiksystems (1), eine Information über die Soll-Aufnahmedichte zu empfangen, wobei die Information eine der Information über die Gesamtzahl N der Aufnahmen über die gesamte Länge der Fokustrajektorie und über den mittleren Winkelabstand Δα_soll im rotatorischen Teil der Fokustrajektorie zwischen zwei Fokuspositionen bezogen auf das Scanzentrum darstellt und weiterhin eingerichtet ist, die Scanparameter der Fokus-Sollpositionsermittlungseinheit (108) zur Verfügung zu stellen,
• eine Fokus-Sollpositionsermittlungseinheit (108), die eingerichtet ist, die Fokustrajektorie mit dem Scanzentrum (20, 51) als Koordinatenursprung in Polarkoordinaten umzurechnen, die Fokussollpositionen F_i(r_i,α_i) auf der Fokustrajektorie, an denen jeweils eine Röntgenprojektionsaufnahme aufgenommen werden soll, zu berechnen, wobei die Polarwinkel α_i der Fokussollpositionen zwischen dem Polarwinkel α_anfang=α₁ am Startpunkt der Fokustrajektorie und dem Polarwinkel α_ende am Endpunkt der Fokustrajektorie bei gegebenem N der Bedingung α_i=α₁+(i-1)*Δα mit 1=1 bis i=N, wobei Δα=(α_ende- α₁)/(N-1) und bei gegebenem Δα_soll der Bedingung α_i=α₁+(i-1) * Δα_soll mit i=1 bis i=M, wobei M= (α_ende-α₁)/Δα_soll und weiterhin eingerichtet ist, die Fokussollpositionen der Bewegungssteuerungseinheit (103) zur Verfügung zu stellen,
• eine Bewegungssteuerungseinheit (103), die eingerichtet ist, eine aus der in der Scanparameter-Erzeugungseinheit (107) hinterlegten Fokustrajektorie, einem kinematischen Modell des C-Bogens und damit verknüpften Geschwindigkeits- und Beschleunigungsprofilen die Motoransteuersignale für die motorisierten Achsen (x(t), y(t), ϕ(t)), die die zeitabhängige Bewegung des Fokus auf der Fokustrajektorie beschreiben, zu berechnen sowie den zeitlichen Verlauf des Polarwinkels α(t) zu berechnen und eine Information über das Erreichen einer Fokussollposition an die Bildaufnahmesteuerungseinheit (103) abzugeben,
• eine Bildaufnahmesteuerungseinheit (104), die eingerichtet ist, nach Erhalt einer Information zum nächstmöglichen Zeitpunkt eine Röntgenprojektionsaufnahme auszulösen und die Bewegungssteuerungseinheit (103) zu veranlassen, die Koordinaten des Fokus zum Zeitpunkt der Bildaufnahme zu ermitteln und der Rekonstruktionseinheit (117) zur Verfügung zu stellen.

The C-arm X-ray diagnostic system suitable for implementing the method ( 1 ) has the following control components:

• a scan parameter generation unit ( 107 ) which is set up by a user from a multitude of in an organ program database ( 115 ) available focus ejectors selected focus ejectors with rotary and translational components in the coordinate system of the C-arm X-ray diagnostic system ( 1 ), information about the desired scan center ( 20 . 51 ) in the coordinate system of the C-arm X-ray diagnostic system ( 1 ) to receive information about the target recording density, the information being one of the information about the total number N of the recordings over the entire length of the focus ejectory and over the mean angular distance Δα _{should represent} in the rotary part of the focus ejectory between two focus positions in relation to the scan center and is also set up the scan parameters of the focus target position determination unit ( 108 ) to provide,
• a focus target position determination unit ( 108 ), which is set up, the focus ejector with the scan center ( 20 . 51 ) as the origin of the coordinates to convert into polar coordinates, to calculate the focus target positions F _i (r _i , α _i ) on the focus ejectory, at which an x-ray projection image is to be taken, the polar angle α _{i of} the focus target positions between the polar angle α _beginning = α ₁ am Starting point of the focus ejectory and the polar angle α _end at the end point of the focus ejectory for a given N of the condition α _i = α ₁ + (i-1) * Δα with 1 = 1 to i = N, where Δα = (α _end - α ₁ ) / (N-1) and at a given Δα the condition α _i = α ₁ + (i-1) * Δα _{is intended to} i = 1 to i = M, where M = (α _end -α ₁₎ / Δα _should and continue to is set up, the focus target positions of the motion control unit ( 103 ) to provide,
• a motion control unit ( 103 ), which is set up, one from the in the scan parameter generation unit ( 107 ) deposited focus ejectory, a kinematic model of the C-arm and the associated speed and acceleration profiles, the motor control signals for the motorized axes (x (t), y (t), ϕ (t)), which show the time-dependent movement of the focus on the focus ejectory describe, calculate and calculate the temporal course of the polar angle α (t) and information about reaching a focus target position to the image recording control unit ( 103 ) to deliver
• an image acquisition control unit ( 104 ), which is set up to trigger an x-ray projection recording as soon as possible after receiving information, and the movement control unit ( 103 ) to determine the coordinates of the focus at the time of the image acquisition and the reconstruction unit ( 117 ) to provide.

The method according to the invention is preferably implemented by means of a computer with a computer program product containing a computer program, which is stored directly in a memory unit of the control unit of the C-arm x-ray diagnostic system ( 1 ) can be loaded with program sections in order to carry out all steps of the method according to the invention when the computer program is executed in the control unit of the C-arm x-ray diagnostic system

list of figures

• 1 : C-arm X-ray diagnostic system
• 2 : Focus ejector and detector trajectory for recording a complete projection data set with rotary and translational sections.
• 3 : Focus ejectory with a non-circular rotary and translational sections in polar coordinate representation r, alpha
• 4 : The course of image recording frequency f (α) over _{the beginning of} the scan area of α to α _end.
• 5 : History of the weighting function g (α) over the scanning range of α α _beginning to _end.

LIST OF REFERENCE NUMBERS

1

C-arm X-ray diagnostic system

2

C-arm

3

X-ray tube

4

High voltage generator

5

collimator

6

X-ray image detector FPD

7

Projection image generation unit

20, 51

scan center

21

object

22

central beam

23

patient support

24

C-arm motor control unit

25

Are engine control unit

50

Area of interest / ROI

100

Control unit

101

X-ray control unit

102

Collision monitoring unit

103

Motion control unit

104

Image capture control unit

105

FPD control unit

106

Image processing and storage unit

107

Scan parameter generation unit

108

Focus set position determining unit

111

display

112

Input device unit

113

Operator / Operator

114

output unit

115

Organ program database

116

mass storage

117

reconstruction unit

118

Energy management unit

130

DICOM Interface

140

network

141

RIS radiology information system

142

HIS hospital information system

181

First section of the first focus ejector

182

second section of the first focus ejector

183

third section of the first focus ejector

191

first section of the second focus ejector

193

third section of the second focus ejector

201

third section of the first detector trajectory

202

second section of the first detector trajectory

203

first section of the first detector trajectory

211

third section of the second detector trajectory

213

first section of the second detector trajectory

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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

• DE 102013013552 B3 [0006, 0016, 0031, 0085]
• US 20170265821 A1 [0016]
• DE 202017002625 U1 [0017]
• DE 102009020400 B4 [0018]
• DE 102009042922 A1 [0019]
• DE 102009052453 A1 [0020]
• EP 1737346 B1 [0021]

Claims (13)

Method for recording a scan of an area of interest ROI (50) with a scanning center (20, 51) lying in the center of the ROI (50) in an object (21), the scan consisting of a series of X-ray projection recordings which comprise a complete set of Provides X-ray projection data of the ROI (50) in the orbital plane of a C-arm X-ray device (2) for a 3D reconstruction and the recording of the scan takes place using a C-arm X-ray diagnostic system (1), with • one in one Bracket along the circumference around an orbital movement axis ϕ and in the C-arm plane in two independent axes x and y motor-adjustable C-arm, the C-arm an X-ray imaging system with an X-ray tube (3) arranged at one end of the C-arm. having a focus and an FPD x-ray image detector (6) arranged opposite one another at the other end of the C-arm, and wherein the focus of the x-ray tube (3) while recording de r A series of cone-beam x-ray projection recordings with a predetermined image quality is moved along a coherent, plane and monotonous focus ejectory with a rotary section and two translational sections adjoining the ends of the rotary section between a starting point and an end point, • a system control unit (100), • a motion control unit (103) which controls all movements of the C-arm x-ray device (2) for moving through the focus on the focus ejectory taking into account the kinematics stored in the motion control unit (103) with speed and acceleration profiles, • an image recording control unit (104), • a scan parameter generation unit (107), • a reconstruction unit (117), • a focus target position determination unit (108), the method comprising the following steps: a) receiving one from a user from a plurality of in a In the organ program database (115) available focus ejectors selected focus ejectory with rotary and translational components in the coordinate system of the C-arm X-ray diagnostic system (1) by the scan parameter generation unit (107), b) receive information about the location of the desired scan center ( 20, 51) in the coordinate system of the C-arm x-ray diagnostic system (1) by the scan parameter generation unit (107), C) receive information about the target recording density of the x-ray projection recordings, the information being one of the information from the total number N of recordings Over the entire length of the focus ejectory and the mean angular distance Δα _, the scan parameter generation unit (107), d) in the rotary part of the focus ejectory between two focus positions in relation to the scan center should transmit the scan parameters to the focus target position determination unit (108), e) the focus ejector with the S can center (20, 51) as the origin of the coordinates in polar coordinates, f) calculate the focus target positions Fi (ri, (Xi) on the focus ejectory, at which an x-ray projection image is to be recorded with the specification of a constant recording density dn / dα of the projection images, the Polar angle α _i of the focus target positions between the polar angle α _start = α ₁ at the start point of the Fokustrajektorie and the polar angle α _end at the end point of the Fokustrajektorie at a given N the condition α _i = α ₁ + (i - 1) * Δα 1 = 1 to i = N, where Δα = (α _end -α ₁₎ / (N-1) and at a given Δα the condition α _i = α ₁ + (i-1) * Δα _{is intended to} i = 1 to i = M, wherein M = (α _end -α ₁ ) / Δα _soll , g) make the focus target positions available to the motion control unit (103), h) calculate from the focus ejectory stored in the scan parameter generation unit (107), a kinematic model of the C-arm and associated speed and acceleration profile the motor control signals for the motorized axes (x (t), y (t), ϕ (t)), which describe the time-dependent movement of the focus on the focus ejection and the time course of the polar angle α (t), i) generate information on reaching a focus target position and transmit this to the image acquisition control unit (103), j) cause the image acquisition control unit (104) to trigger an x-ray projection image at the next possible time, k) successively record the row of x-ray projection images and set the image data of the x-ray projection images with the coordinates of the Focus at the time of recording, the focus ejectory and the location of the scan center of the reconstruction unit (117). Procedure for taking a scan for Claim 1 , characterized in that the information about reaching a target focus position in feature i) is obtained by calculating the polar angular velocity dα / dt of the focus on the focus projection and together with the polar angle distance Δα of two target target positions a time-dependent target image recording frequency signal f ( t) = dα / dt * 1 / Δα is calculated and the desired image recording frequency signal is transmitted synchronously to the image recording control unit (104). Procedure for taking a scan for Claim 1 , characterized in that the information about reaching a target focus position in feature i) by monitoring the polar angle α (t) is generated, a trigger signal being transmitted to the image recording control unit (104) for prompt triggering of an x-ray projection recording when a polar angle α _{i of} a target focus position is reached. Procedure for taking a scan for Claim 2 , characterized in that the image acquisition control unit (104) receives values for a minimum target image acquisition frequency fmin, a maximum target image acquisition frequency fmax and an optional start-target image acquisition frequency f _start from the memory of the system control unit (100) and the calculated target image acquisition frequency signal f (t) is constantly changed when the limit values are imminent and there is a deviation in the start-target image recording frequency. Procedure for taking a scan according to one of the Claims 1 - 4 , characterized in that the system control unit (100) is further designed to generate a signal (“AEC low status signal”) and to make it available to the image recording control unit (104) if an X-ray projection image generates with insufficient exposure and image data with an excessively high one Noise component were recorded, with an X-ray projection recording being taken as soon as possible when an AEC low status signal is present. Procedure for taking a scan for Claim 5 , characterized in that the projection image recording density dn / dα is continuously increased if an AEC low status signal has been received in the image recording control unit (104) and the projection image recording density dn / dα is continuously decreasing from the current recording density to the target recording density dn _soll / dα if no AEC low status signal was received. Procedure for taking a scan for Claim 5 , characterized in that the image recording control unit (104) is set up to steadily increase the projection image recording rate dn / dt at any point in time compared to the target image rate at any angular position of the focus ejection when an AEC low status signal has been received by the image recording control unit (104) and that Decrease projection image acquisition rate steadily to the target image rate if no AEC low status signal is received. Method according to one of the preceding claims, characterized in that the C-arm x-ray diagnostic system (1) furthermore has a patient couch (23) which can be controlled simultaneously with the C-arm x-ray device (2) and the control method for the movement control unit (103) does this C-arm x-ray device (2) and the patient couch (23) according to a movement instruction for guiding the focus along the focus ejectory around the scan center (20, 51) in the coordinate system of the c-arm x-ray diagnostic system (1) synchronously. Method according to one of the preceding claims, characterized in that the scan parameter generation unit (107) transmits the focus target positions to the motion control unit (103) and there a blanking signal is determined by comparison with the current focus position, which is a in the image recording control unit (104) angle-dependent image recording frequency f (α) is generated in that pulses are blanked out from a V-sync image recording trigger signal of constant frequency if no match between the current focus position and the target focus position has been determined in the motion control unit (103). Method according to one of the preceding claims, characterized in that the scan parameter generation unit (107) also receives, together with the focus jjectory, a weighting function which is dependent on an estimated focus position-dependent patient absorption and which, after conversion into polar coordinates g (α) for weighting the image recording frequency f _wt. (α) = f (α) * g (α) is used. C-arm X-ray diagnostic system for implementing the method Claim 1 , characterized in that the C-arm x-ray diagnostic system (1) has: a) a scan parameter generation unit (107) which is set up to select one of a number of focus ejectors available in a organ program database (115) by a user Focus ejectory with rotary and translational components in the coordinate system of the C-arm X-ray diagnostic system (1), information about the desired scan center (20, 51) in the coordinate system of the C-arm X-ray diagnostic system (1), information about the target recording density wherein the information includes a information on the total number N of recording over the entire length of the Fokustrajektorie and the average angular distance Δα of Fokustrajektorie between two focal positions with respect _to showing on the scan center and is further arranged, the scan parameters of the focus target position detection unit in the rotary part (108) available to provide supply, b) a focus target position detection unit (108) is established, the Fokustrajektorie with the scanning center (20 to convert 51) as the coordinate origin in the polar coordinate, the focus target positions F _i (r _i, α _i) on the Fokustrajektorie to which each need to take an x-ray projection image, the Polar angle α _i of the focus target positions between the polar angle α _start = α ₁ at the start point of the Fokustrajektorie and the polar angle α _end at the end point of the Fokustrajektorie at a given N the condition α _i = α ₁ + (i-1) * Δα 1 = 1 to i = N, where Δα = (α _end - α ₁₎ / (N-1) and at a given Δα the condition α _i = α ₁ + (i-1) * Δα _{is intended to} i = 1 to i = M, wherein M = (α _end -α ₁ ) / Δα _should and is furthermore set up to make the focus target positions available to the movement control unit (103), c) a movement control unit (103) which is set up, one of those in the scan parameter generation unit ( 107) deposited focus ejectory, a kinematic model of the C-arm and the associated speed and acceleration profiles, the motor control signals for the motorized axes (x (t), y (t), ϕ (t)), which show the time-dependent movement of the focus on the Describe focus ejectory, calculate and the time course of the polar angle ls α (t) and to provide information about reaching a focus target position to the image recording control unit (103), d) an image recording control unit (104) which is set up to trigger an x-ray projection recording after receiving information as soon as possible and the motion control unit (103 ) to determine the coordinates of the focus at the time of the image acquisition and to make it available to the reconstruction unit (117). Computer program product with a computer program, which can be loaded directly into a memory unit of a control unit of a C-arm x-ray diagnostic system (1), with program sections to complete all steps of the method according to one of the Claims 1 to 10 to be executed when the computer program is executed in the control unit of the C-arm X-ray diagnostic system Computer-readable medium on which program sections that can be read and executed by a computer unit are stored, in order to carry out all steps of the method according to one of the Claims 1 to 10 to be executed when the program sections are executed by the computer unit.

Images