Methods for performing scans using a computed tomography system

Abstract

Method for performing scans using a computed tomography system (1), the method comprising the following steps: - Moving a rotor (3) of a gantry (2) of the computed tomography system (1) into a rotation relative to a patient (6), - Performing a topogram scan (T) using the computed tomography system (1), acquiring projection data (D) that provide an overview of at least part of the patient (6), defining an examination area (U) before performing the topogram scan (T) and determining during the topogram scan (T) whether the examination area (U) has been reached based on the projection data (D) of the topogram scan (T), - Determining parameter settings (P) for a main scan (H) based on the projection data (D), wherein the parameters (P) define at least one radiation power and / or examination area (U) for the main scan (H), wherein, prior to reaching the examination area (U), the parameter settings (P) for the main scan (H) are determined using the projection data (D) of the topogram scan (T) and a model of the patient (6), and upon reaching the examination area (U), the main scan (H) is started based on the parameters (P) as soon as the topogram scan (T) has arrived at the examination area (U). - Performing the main scan (H) of the patient (6) using the computed tomography system (1) based on the parameters (P), whereby both the topogram scan (T) and the main scan (H) are performed during the rotation of the rotor (3).

Description

[0001] The invention relates to a method for performing scans using a computed tomography system. The invention further relates to a control device for controlling a computed tomography system and to a computed tomography system itself.

[0002] The state of the art in this context includes DE 10 2007 033 883 A1 and DE 103 01 891 B3.

[0003] In a CT scan (CT: "computed tomography"), a topogram is often created before the main scan to determine the parameters for the main scan. These parameters include, for example, the patient's position, height, and body volume, and are referred to as "SSDE information." This serves to protect the patient, as the radiation dose expected during the main scan must be at least roughly estimated, and the main scan must be planned to prevent errors, such as receiving too low a dose or scanning in the wrong position. Essentially, the parameters that must be applied during the main scan must be determined to ensure a successful and optimal scan for the patient and to obtain usable results.

[0004] This is done as part of a separate topogram scan (or topo-scan) and is conventionally performed with a stationary rotor of the CT system's gantry.

[0005] For the topogram scan, the X-ray source and aperture are set to 0°, 90°, 180°, or 270°, switched on, and then the patient table is moved with the rotor stationary to image a section of the patient or even the entire patient. The topogram scan is performed with a constant voltage and current for the X-ray source, for example, with a power output of approximately 5.5 kW at a voltage of 100 kV and a current of 55 mA, or with 7 kW (50 mA at 140 kV). A single topogram scan can be performed, for example, at an angle of 0°, or two topogram scans at different angles, or more topogram scans can be performed. It should be noted that each topogram scan requires a certain amount of time and results in a certain radiation exposure for the patient.

[0006] For a 500 mm long topogram, at a table feed rate of 20 cm, setting the angles and acquiring the images would take approximately 3 to 5 seconds per topographic scan. This would result in approximately 2000 to 3000 images being acquired per second, each representing a sub-area (corresponding to the detector width) of, for example, 10 mm to 60 mm of the scanned area, with significant overlap. Erroneous images can then be eliminated by averaging.

[0007] Once the topogram has been created and the parameters for the main scan are known, the gantry rotor must be accelerated to a specific rotational speed for the main scan. When the rotor reaches its target rotational speed (e.g., 2 to 4 revolutions per second), the main scan, such as a spiral scan, can be performed. The acceleration process between the topogram scan and the main scan can take 30 to 40 seconds. This means there is a pause of 30 to 40 seconds between the topogram scan and the main scan. During this time, the patient must lie still on the table and must not move.

[0008] After the main scan (or multiple main scans of this patient), the gantry rotor must be braked and brought to a standstill for the next topogram scan. This braking process typically takes between 30 and 40 seconds. After braking, the CT scanner must be moved to the target position for the next topogram scan.

[0009] This means that the gantry rotor must be braked after each main scan and then accelerated again for the next one. This not only results in waiting times, which are particularly disadvantageous when a CT system is operating at high capacity, but also in mechanical wear of the gantry due to the acceleration forces (especially during braking) and increased power consumption during the acceleration processes.

[0010] It is an object of the present invention to provide an alternative to the conventional method of performing CT scans. This object is achieved by a method according to claim 1, a control device according to claim 9, and a CT system according to claim 12. Regardless of the grammatical gender of a particular term, persons of male, female, or other gender identities are included.

[0011] The invention relates to a method for performing scans using a computed tomography system, wherein the method comprises the following steps: - Setting a rotor of a gantry of the computed tomography system into rotation relative to a patient, - Performing a topogram scan using the computed tomography system, capturing projection data that provides an overview of at least part of the patient, - Determining settings for parameters for a main scan based on the projection data, wherein the parameters define at least an irradiance and / or a scan area for the main scan, - Performing the main scan of the patient using the computed tomography system based on the parameters, in particular based on the parameter settings, whereby both the topogram scan and the main scan are performed during the rotation of the rotor.

[0012] In particular, it may be provided that the parameters for the main scan are set based on the determined settings for the main scan parameters. Specifically, it may be provided that the gantry of the computed tomography system comprises the rotor, a support structure, a rotary bearing, and a rotary drive, that the rotor is rotatably mounted relative to the support structure about an axis of rotation by means of the rotary bearing, and that the rotary drive is configured to drive the rotation of the rotor about the axis of rotation.

[0013] In particular, the rotor may be provided with an X-ray source for generating X-rays and a detector for detecting the X-rays, and / or the projection data may be acquired based on the X-rays. Furthermore, it may be provided that, during the main scan of the patient using the computed tomography system, computed tomography imaging data are acquired, in particular data acquired based on the X-rays.

[0014] The fundamentals for controlling a computed tomography system are known in the art, in particular the execution of a scan and the data acquisition performed during that scan. It is also known which beam powers and acceleration voltages must be used for a specific type of scan. For example, it is known which beam parameters a topogram scan should have for acquiring projection data that provides an overview of at least part of a patient. Although further embodiments are outlined below, this topogram scan can be performed with a conventionally used X-ray beam power.

[0015] Determining the parameters for a main scan from the projection data of the topogram scan is a well-known procedure and is currently performed in examinations. These parameters typically include radiation intensity and / or an examination area for the main scan. While the area of ​​the patient to be examined (e.g., lungs or heart) is always predetermined, the precise location of this examination area within the patient and the patient's correct positioning are not always known. Therefore, the examination area must be adapted to the position of the organ being examined within the patient and to the patient's position on the examination table (its isocenter).

[0016] Performing the main scan of the patient using a computed tomography system is also known in the prior art. The special feature of the invention is that both the topographic scan and the main scan are performed with a rotating rotor of the computed tomography system's gantry. This eliminates waiting time for acceleration or deceleration between scans and also reduces wear.

[0017] Spiral scans are frequently performed, in which the gantry and patient table are moved relative to each other, particularly at a constant speed, while the gantry rotor rotates. Here, the rotation of the gantry rotor should be coordinated with the feed rate of the patient table and the detector size to produce a continuous image. For example, with a gantry rotor rotation of 4 revolutions per second, a feed rate of no more than approximately 20 cm / s should be chosen. This ensures sufficient overlap between individual scans at the same angular position, especially with a 6 cm wide detector, allowing the images to be properly stitched together into a single image. This applies to both the topogram scan and the main scan. However, this is not absolutely necessary for the topogram scan, as will be explained in more detail below.With a smaller detector, the table speed can be adjusted to the rotation of the gantry rotor, or the parameters can also be determined from disjointed stripe images.

[0018] As an alternative to a spiral scan, the patient can be scanned with the patient lying down and the patient lying down can be moved relative to the gantry between scans.

[0019] A topogram scan is performed during the rotation of the gantry rotor. The X-ray source is preferentially triggered only at predefined source / aperture positions (at the acquisition angles). If the user selects a 90° position, the source will, for example, start emitting at 85° and stop emitting at 95°. The patient table should travel the same distance as the detector width with each rotation. An image reconstruction unit preferentially evaluates the values ​​for the current generator current. If these values ​​exceed a certain threshold (e.g., "Full Dose" and / or "Parameterized Angle"), it is assumed that continuous X-ray radiation is being used, and the acquired data is then reconstructed as CT images by the image reconstruction unit.

[0020] It should also be noted that conventional topogram scans often do not utilize the full detector width, but only a thin strip (due to overlapping images). The method presented here prefers to use the full detector width, i.e., the entire detector, for the topogram scan.

[0021] The invention further relates to a control device for controlling a computed tomography system based on the method according to the invention, which has a detection unit, wherein the detection unit is configured to determine settings for parameters for the main scan based on the projection data, wherein the parameters define at least the irradiation power and / or the examination area for the main scan.The control unit is designed to control the rotation of the gantry rotor of the computed tomography system relative to the patient, the performance of the topogram scan using the computed tomography system, capturing the projection data that provides an overview of at least part of the patient, and the performance of the main scan of the patient using the computed tomography system based on the parameters, with both the topogram scan and the main scan being performed during the rotation of the rotor.

[0022] A computed tomography system according to the invention comprises a control device according to the invention and / or is equipped to carry out a method according to the invention.

[0023] Components of the control device according to the invention can be implemented wholly or partially as software modules in a processor of a corresponding computing system, in particular a computer. A largely software-based implementation has the advantage that even previously used computing systems can be easily retrofitted by a software update to operate in the manner of the invention. In this respect, the problem is also solved by a corresponding computer program product with a computer program that can be directly loaded into a computing system, containing program sections to execute the steps of the method according to the invention, at least those steps that can be executed by a computer, when the program is run in the computing system. It should be noted that performing a scan of the output of corresponding control data and the acquisition of projection data corresponds to receiving the corresponding detector signals.In addition to the computer program itself, such a computer program product may include additional components such as documentation and / or additional hardware components, such as hardware keys (dongles, etc.) for using the software.

[0024] For transport to the computer system or control unit and / or for storage on or in the computer system or control unit, a computer-readable medium, e.g., a memory stick, a hard drive, or other 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 system are stored. The computer system may, for example, include one or more cooperating microprocessors or similar components.

[0025] It should be noted that process steps such as performing a scan can correspond to the output of corresponding control commands. Further, particularly advantageous embodiments and developments of the invention will become apparent from the dependent claims and the following description, wherein the claims of one claim category may also be further developed analogously to the claims and parts of the description of another claim category, and in particular, individual features of different embodiments or variants may be combined to form new embodiments or variants.

[0026] According to a preferred method, the topogram scan is performed within a predetermined angular range around a number of predefined acquisition angles of the rotor. The acquisition angles are preferably the previously used angles at the zenith above the patient, at the nadir below the patient, or from the side. The acquisition angles of the rotor can, in particular, be acquisition angles of the rotor relative to the supporting structure around the axis of rotation.

[0027] In particular, a first imaging angle can be an angle at which the image is taken from the zenith above the patient or from the nadir below the patient. In particular, a second imaging angle can be 90° or 180° to this, preferably with fewer images being taken and / or images being taken with a lower X-ray power than at the first imaging angle.

[0028] One could also say the angles are 0°, 90°, 180°, or 270°, although theoretically, either the gantry's or the patient's coordinate system can be used, since the patient can be scanned lying on their back, side, or stomach. The angle range W specifies the area around this scan angle. The scan angle lies in the middle of the angle range; thus, for a scan angle A, the scan angle range is from AW / 2 to A+W / 2. With a preferred angle range of 10° around the scan angles of 0° and 90°, the topogram scan would be performed in the angle ranges of 355° to 5° and 85° to 95°.

[0029] It is preferred that one of the imaging angles is an angle from which the image is taken at the zenith above the patient or at the nadir below the patient. Depending on the type of examination, however, an imaging angle of 90° or 270° may also be advantageous. A combination of 0° / 180° with an image taken at 90° or 270° may also be preferred. Here, a balance must be struck between the importance of, for example, correct patient positioning and the additional radiation exposure from an additional topogram scan. Often, the imaging angle also depends on the type of image being viewed. For example, the lungs are preferably imaged from above or below, while the head is preferably imaged from the side.

[0030] In the following, the term "shooting angle" should always be understood to also include the "shooting angle range". The shooting angle is the center of the shooting angle range. Shots taken at a given shooting angle are taken within that shooting angle range.

[0031] When images are taken from different angles, it is particularly advantageous to use one angle for the topogram scan and the other angle for fewer images and / or images taken with a lower radiation dose. For example, the topogram scan is performed from an angle of 0° (within a 10° range), and a few images (possibly at a lower radiation dose) are taken from a second angle rotated 90° to precisely determine the correct position of the isocenter. It should be noted that the starting position for the main scan and parameters relating to organ positions can be derived from a topogram scan. However, the isocenter or additional information about the patient's volume can also be determined simply from the shadows cast by the body.

[0032] According to a preferred embodiment of the preceding design, the topogram scan is performed using only one imaging angle. In combination with this, a camera image in the visible or infrared spectrum is acquired from an imaging angle rotated 90° relative to the first, which at least reproduces the contours of the patient. To prevent the camera from being exposed to radiation, its position can be shifted along the rotation axis of the gantry rotor relative to the X-ray source, i.e., it can be positioned in front of or behind the X-ray source. Even when patients are sometimes surrounded by blankets or mats during imaging, a camera is particularly advantageous for, for example, making a rough estimate of the patient's size and organ position. For instance, the head is usually clearly visible in camera images. The topogram can also correct the camera images.

[0033] Camera images can also supplement a topogram. It's important to note that a topogram scan should not take longer than 10 seconds. With very narrow detectors, e.g., 1 cm thick, this time could be exceeded at a fixed rotor speed (e.g., 2 rpm), or only "strip images" of the patient could be captured, where areas between the stripes are not represented in the topogram. Using the camera images, it's then possible to extrapolate a complete topogram from the strip images, particularly with the aid of a model. In a preferred scenario, where an additional camera (stationary, mounted above, below, or to the side of the patient) records the patient during the topogram scan, even with a fast table rotation, at least a kind of outer contour of the patient could be reproduced, and internal structures would then be available in strips or added from the model.The result would be sufficient, however, to at least estimate the patient's isocenter and volume, and also to indicate the spatial starting point of the main scan. Therefore, the additional use of a camera represents an option where the procedure can be carried out without problems even with inexpensive devices (with small detectors and / or low rotor speeds).

[0034] It is therefore preferable for the patient to be photographed simultaneously with the topogram scan and for the camera images to be combined with the topogram scan. The previously described methods are considered "combination." It should be noted that checking the isocenter does not necessarily require using images rotated by 90°; a size comparison can also be made between images taken at 180° angles to each other. The images should overlap to allow for comparisons with the same body region.

[0035] According to a preferred method, the angular range is less than 20° (e.g., the recording angular range for a recording angle of 0° would then be the range from 350° to 10°), preferably less than 10°, particularly less than 5° or even less than 2° (i.e., from 359° to 1°). Although the angular range can be different for each recording angle, it is preferred that, when recording from multiple recording angles, the angular ranges around all recording angles are the same.

[0036] Preferably, multiple images are acquired within a given angular range, preferably more than two, but preferably fewer than 50. This has the advantage that if an image is faulty, it can be replaced by another image, or the images can be averaged to reduce errors. For example, three images can be acquired at an angle of 0°: one at 359°, one at 0°, and one at 1°, so the angular range would be 2°. Ultimately, the number of images can be determined from the error probability of a CT system.

[0037] According to a preferred method, when the rotor's rotation angles deviate from the respective angular ranges by the number of acquisition angles, the X-ray source of the computed tomography system used for acquisition is switched off. This has the significant advantage of reducing the radiation exposure for the patient. The same accelerating voltage and current as in a conventional topographic scan can be used for the X-ray source. However, in a conventional topographic scan, the X-ray source is continuously switched on. In the embodiment described here, only "flash images" are taken in the relevant angular ranges, and the X-ray source is otherwise switched off when no images are being acquired (outside the angular ranges). It is preferred that the X-ray source is only switched on to acquire a number of images in the respective angular ranges.If images are taken within a specific angular range (N), the X-ray source should be switched off between images. However, the time required for the X-ray source to achieve stable emission of X-rays should be taken into account. If the angular range is traversed within this time due to the rotor's rotation, it would be advantageous to keep the X-ray source switched on within the angular range. Even with reduced X-ray power, the quality of a topogram acquired in this way is comparable to that of conventional topograms. The rotor's rotation angles can be, in particular, rotation angles of the rotor relative to the supporting structure around the axis of rotation.

[0038] According to a preferred method, both the topographic scan and the main scan are performed in the form of a spiral scan by means of a patient table of the computed tomography system by performing a translational movement of the patient relative to the gantry of the computed tomography system, in particular continuously, i.e. at constant speed, while the rotor rotates.

[0039] According to the invention, an examination area is defined before the topogram scan is performed, and during the topogram scan, it is determined, based on the projection data of the topogram scan, whether the examination area has been reached. For this purpose, each image can, for example, be searched for a predetermined structure. For instance, before the topogram scan, it is known which area of ​​the patient is to be examined. Now, each individual image of the topogram can be automatically examined after its acquisition, and it can be determined which part of the patient this image shows. Since the basic anatomy of a patient does not differ from that of other patients, it is possible to estimate when the examination area might be reached, or at least whether the examination area has been reached. In practice, this can be done, for example, by means of automated image recognition and a comparison with a model of the patient's anatomy.

[0040] Upon reaching the examination area, the X-ray power for the topogram scan is preferably increased. It should be noted that even based on images showing only rough features of the patient, such as the outline, it is possible to estimate whether the examination area has been reached. Therefore, the topogram scan could initially be performed at a reduced power level, and once the examination area has been reached, at a (predefined) normal power level. The reduced power level is preferably less than 80% of the normal power level, particularly less than 60% or even less than 50%. This approach is especially advantageous when using a spiral scan as a topogram scan, as it allows for a more precise examination.

[0041] According to the invention, the parameters for the main scan are determined using a model of the patient and the projection data of the topogram scan before the examination area is reached. Upon reaching the examination area, the main scan is started based on these parameters as soon as the topogram scan has arrived at the examination area. It should be noted that the main scan is performed with a continuous beam. If the beam is temporarily switched off during the topogram scan, it should then be operated continuously for the main scan.

[0042] The parameters can be determined in particular using a model of the patient, whereby the model can be derived from a previous examination and / or calculated by modifying a basic model using the projection data of the topogram scan.

[0043] For example, during a lung examination using a spiral scan, the topographic scan can determine whether the bronchi have been reached. Until the bronchi are reached, the patient's size and position can be estimated from the previously scanned area (head and shoulders). This allows for determining whether the patient is correctly positioned and which preset beam parameters should be used for the main scan. Once it is clear that the topographic scan has reached the examination area, particularly through the recognition of characteristic structures or by evaluating the previously scanned structures and the patient table's movement speed, the main scan is initiated. This involves setting the appropriate X-ray power and acquiring images from numerous different angles.

[0044] Preferably, individual images from the main scan are used as (projection) images for a subsequent topogram scan. These are the images taken within the angular ranges surrounding the original topographic scan angles. These images are then used to determine when to end the main scan. This subsequent topographic scan allows the system to determine when the entire survey area has been covered. It's important to note that information can be calculated more quickly from topograms (i.e., projection images) than from tomograms (i.e., reconstructed 3D images). With smaller detectors, such as those with a strip width of 1 cm, representations of the currently captured portion of the topogram are possible almost in real time.

[0045] It should be noted that the patient table can be stopped and moved back during a scan. Therefore, if it is discovered during the topographic scan that the boundary of the examination area has already been crossed, the patient table could be moved back a short distance, especially with the X-ray source switched off, and then the main scan started in the correct position.

[0046] According to a preferred method, a model of a patient or a part of a patient is selected based on the projection data of the topogram scan and / or created by modifying a base model. A selection can be made from a large number of patient models that have been created beforehand. The most similar model is then chosen. Alternatively, a base model can be used, which is then adapted to the patient through geometric changes, in particular scaling, rotations, stretching, or compression. A combination of methods is also conceivable, in which the model that most closely matches the patient's stature is selected from a number of models and then used as the base model for modification.

[0047] It is preferred that the model is created during the topogram scan (i.e., not afterwards) based on the projection data recorded so far, and that this created model is modified with further projection data recorded as part of the topogram scan.

[0048] A preferred control device comprises a model unit, wherein the model unit is configured to - Selecting a model of a patient or a part of a patient (possibly as a base model) and / or for - Modifying a base model based on the projection data is set up.

[0049] Regarding a patient model, a simple basic model can be used in which body regions are represented by basic geometric shapes such as ellipsoids or spheres, general cylinders or barrels, or possibly even cubes. The size of the individual basic shapes can be determined by fitting the model to the topogram. However, it is not necessarily required to adjust all parts of the model. For example, the length of the legs is not very important for a lung scan, but the shape and volume of the upper body are. Often, it is possible to adjust the entire model using partial scans of a patient's body, at least in a way that is essential for the main scan (and for determining presets for its parameters).

[0050] According to a preferred method, several examinations, each comprising a topogram scan and a main scan, are performed sequentially. The rotor preferably rotates at a constant speed from the first to the last examination. Preferably, several patients are examined. The special feature is that the rotor rotates continuously throughout the entire procedure, e.g., from the start of the examinations in the morning until the end of the examinations in the evening.

[0051] It is preferred that during a break between two tests, the rotor rotates in an idle mode, in which the rotation is maintained and / or no energy is expended for acceleration or deceleration. In particular, it could be discussed when the next test should take place and an estimate of the energy that would be required for acceleration if the rotor were rotating in idle mode, as well as how much energy would be required to maintain the rotation. Whether the rotor is left in idle mode or maintained could depend on the result of this estimate.

[0052] A preferred control device comprises an idle unit configured to maintain the rotation of the gantry rotor between two tests essentially without energy input and without initiating braking. The term "essentially" means that at most, only enough energy should be expended to keep the rotational speed of the rotor constant, and in particular, no energy should be expended for acceleration.

[0053] One advantage of the invention is that the rotor no longer needs to be braked and accelerated between scans. This saves time, reduces wear and tear, and lowers power consumption. Continuous rotation of the CT scanner is possible. After a topogram scan, the main scan can be started immediately without delay. The patient needs to lie in the scanning position for a shorter time. Furthermore, a significant reduction in radiation exposure can be achieved by switching off the X-ray source during the topogram scan. Despite the lower radiation dose, the same or even better image quality can be achieved with the topogram scan.

[0054] The invention is explained in more detail below with reference to the accompanying figures and exemplary embodiments. The same components are designated with identical reference numerals in the various figures. The figures are generally not to scale. They show: Fig. 1. A rough schematic representation of a CT system with an exemplary embodiment of a control unit for carrying out the procedure, Fig. 2 possible positions for a topogram scan, Fig. 3 a topogram scan, Fig. 4. A sketch for a spiral scan, Fig. 5 two ways to use the topogram scan for a main scan, Fig. Figure 6 shows a block diagram of a preferred embodiment of a method according to the invention.

[0055] Fig. Figure 1 shows an embodiment of a computed tomography (CT) system 1 with a detector 4 and an X-ray source 5. The X-ray source 5 is configured to expose the detector 4 to X-rays. The CT system 1 shown comprises a gantry 2 with a rotor 3. The rotor 3 includes the X-ray source 5 and the detector 4. The detector 4 is configured to detect the X-rays.

[0056] The rotor 3 is rotatable about the axis of rotation 8, which can also be considered the patient's longitudinal axis. The patient 6 is positioned on the patient table 7 and can be moved along the axis of rotation 8 by the gantry 2. The control unit 9 is provided for controlling the computed tomography system 1.

[0057] In a main scan, computed tomography imaging data of object 6 are typically acquired from a variety of angular directions using detector 4 at a specific beam energy. Subsequently, a final image dataset ("CT images") can be reconstructed from the computed tomography imaging data using a mathematical procedure, for example, including filtered back projection or an iterative reconstruction method.

[0058] The control unit 9 can also include an image reconstruction unit for reconstructing an image dataset based on the computed tomography imaging data. Furthermore, an input device 10 and an output device 11 are connected to the control unit 9. The input device 10 and the output device 11 can, for example, enable user interaction, display a generated image dataset, or output a determined solution to a problem.

[0059] The control unit 9 here includes a determination unit 12, set up to determine settings for parameters P for a main scan H from the projection data D of a topogram scan T, wherein the parameters P define at least an irradiation power and / or an examination area U for the main scan H.

[0060] The control unit 9 is configured to perform a topogram scan T and a main scan H while the rotor 2 is rotating. The topogram scan T is used to acquire projection data D, which provide an overview of at least part of a patient 6. The main scan H is used to acquire computed tomography imaging data, which can, for example, be reconstructed into an image dataset.

[0061] The control unit 9 also includes a model unit 13, which is configured to select a base model of a patient 6 and to modify this base model. Both the selection and the modification are based on projection data D of the topogram scan T.

[0062] In addition, the control device 9 here includes an idle unit 14, which is designed to maintain the rotation of the rotor 3 of the gantry 2 between two tests essentially without energy input and without initiating braking.

[0063] Fig. Figure 2 shows possible positions for a topogram scan T. A top-down view is indicated, with the X-ray source 5 of the gantry 2 positioned directly above the patient 6 and the detector 4 directly below. This position can be considered, for example, 0°. The X-ray beam R is intended to illuminate the entire patient 6 in a cone shape, within a strip corresponding to the detector area. Two further possible positions are shown with dashed lines: one where the X-ray source 3 is positioned next to the patient 6 (90°) and the other where it is positioned below the patient 6 (180°).

[0064] Fig. Figure 3 outlines a topogram scan T. Here, the rotor 3 rotates in the direction of the arrow, and the images are taken from the side at an angle of less than 90°. The acquisition angle A of 90° to a perpendicular is indicated (dashed lines). The projection data D is acquired within an angular range W around the acquisition angle A (dotted lines). One position of the X-ray source 3 and detector 4 at the acquisition angle A is shown, and two further possible positions within the angular range W for two additional acquisitions are indicated by dashed lines.

[0065] Fig. Figure 4 shows a sketch for a spiral scan in which the X-ray source 3 together with detector 4 is part of the rotor 3 (szB Fig. 1) The X-ray source rotates around the patient 6 while the patient is moved along the arrow on a movable patient table 7 through the gantry 2. From the patient's perspective, the X-ray source then describes a spiral path S. The patient's movement can, for example, occur at 20 cm / s while the rotor 3 rotates at four revolutions per second.

[0066] Fig. Figure 5 shows two possibilities for using the topogram scan T for a main scan H. The upper figure uses arrows to illustrate that the topogram scan T first covers the entire body of the patient 6, and then the main scan H is performed over the examination area U. The lower figure uses arrows to illustrate that the topogram scan T first covers a portion of the patient 6, and the main scan H is performed upon reaching the examination area U. The topogram scan T can be extended with projection images from the main scan H, which were acquired at the acquisition angles A of the topogram scan T.

[0067] Fig. Figure 6 shows a block diagram of a preferred embodiment of a method according to the invention for controlling a computed tomography system 1 (see Figure 6). Fig. 1).

[0068] In step I, a rotor is set in rotation so that the subsequent steps can be carried out with a rotating rotor.

[0069] In step II, a topogram scan T is performed to acquire projection data D while the rotor 3 is rotating. This projection data D should provide an overview of at least part of a patient 6.

[0070] The topogram scan T is performed in a predetermined angular range W around a number of predetermined recording angles A of the rotor 3 (see Fig. 3) Several images are taken in each angular range, e.g., three to ten. For example, the topogram scan T is performed at an angle of 0° and a few images are taken at a reduced dose of 90° to determine the isocenter of patient 6.

[0071] To reduce the dose to patient 6, the X-ray source 5 of the gantry 2 used for imaging is switched off when the rotor 3 rotates outside the respective angular ranges W around the imaging angles A.

[0072] Based on the projection data D of the topographic scan T, a base model can now be selected for patient 6 and this base model modified to fit patient 6. This allows the determination of the examination area U (e.g., Fig. 5) should be in patient 6 and what radiation dose can and should be administered.

[0073] In step III, such settings for parameters P for a main scan H are determined from the projection data D of the topographic scan T. These parameters P define an irradiance and an examination area U for the main scan H.

[0074] In this step, it can be determined, particularly based on the projection data D of the topogram scan T, whether the investigation area U has been reached and, if applicable, how in Fig. As shown below in point 5, in the positive case the main scan H will be started.

[0075] In step IV, the main scan H of patient 6 is then performed using the computed tomography system 1, whereby the computed tomography imaging data B are recorded.

[0076] Steps II to IV can be performed multiple times in succession for several patients 6, as indicated by the dashed arrow below. During this time, the rotor 3 rotates continuously without being slowed down and accelerated between examinations.

[0077] Finally, it should be noted once again that the figures described in detail above are merely exemplary embodiments, which can be modified in various ways by a person skilled in the art without departing from the scope of the invention. Furthermore, the use of the indefinite articles "a" or "an" does not preclude the possibility that the features in question may be present multiple times. Likewise, the terms "unit" and "device" do not preclude the possibility that the components in question may consist of several interacting sub-components, which may also be spatially distributed. The expression "a number" is to be understood as "at least one."

Claims

[1] Method for performing scans using a computed tomography system (1) wherein the method comprises the following steps: - Moving a rotor (3) of a gantry (2) of the computed tomography system (1) into a rotation relative to a patient (6), - Performing a topogram scan (T) using the computed tomography system (1), acquiring projection data (D) that provide an overview of at least part of the patient (6), defining an examination area (U) before performing the topogram scan (T) and determining during the topogram scan (T) whether the examination area (U) has been reached based on the projection data (D) of the topogram scan (T), - Determining parameter settings (P) for a main scan (H) based on the projection data (D), wherein the parameters (P) define at least one radiation power and / or examination area (U) for the main scan (H), wherein, prior to reaching the examination area (U), the parameter settings (P) for the main scan (H) are determined using the projection data (D) of the topogram scan (T) and a model of the patient (6), and upon reaching the examination area (U), the main scan (H) is started based on the parameters (P) as soon as the topogram scan (T) has arrived at the examination area (U). - Performing the main scan (H) of the patient (6) using the computed tomography system (1) based on the parameters (P), whereby both the topogram scan (T) and the main scan (H) are performed during the rotation of the rotor (3). [2] Method according to claim 1, wherein the topogram scan (T) is performed in a predetermined angular range (W) around a number of predetermined recording angles (A) of the rotor (3). [3] Method according to claim 2, wherein the angular range (W) is less than 20°, preferably less than 10°, in particular less than 5° or even less than 2°. [4] Method according to claim 2 or 3, wherein when the rotation angles of the rotor (3) are outside the respective angular ranges (W) by the number of recording angles (A) an X-ray source (5) of the computed tomography system (1) used for recording is switched off. [5] Method according to any of the preceding claims, wherein both the topogram scan (T) and the main scan (H) are each performed in the form of a spiral scan by means of a patient table (7) performing a translational movement of the patient (6) relative to the gantry (2) of the computed tomography system (1) during the rotation of the rotor (3) of the gantry (2). [6] Method according to one of the preceding claims, wherein upon reaching the examination area (U) an X-ray beam power is increased for the topogram scan (T). [7] Method according to any of the preceding claims, wherein a model of the patient (6) or of a part of the patient (6) is selected based on the projection data (D) of the topogram scan (T) and / or created by modifying a basic model. [8] Method according to one of the preceding claims, wherein several investigations, each comprising a topogram scan (T) and a main scan (H), are carried out successively and the gantry (2) rotates at a constant speed from the first to the last investigation. [9] Control device (9) for controlling a computed tomography system (1) based on a method according to one of the preceding claims, - wherein the control device (9) has a detection unit (12), wherein the detection unit (12) is configured to determine settings for the parameters (P) for the main scan (H) based on the projection data (D), wherein the parameters (P) define at least the irradiation power and / or the examination area (U) for the main scan (H), - wherein the control device (9) is configured to, - to control the movement of the rotor (3) of the gantry (2) of the computed tomography system (1) into rotation relative to the patient (6), - to control the execution of the topogram scan (T) using the computed tomography system (1), wherein the projection data (D) that provide an overview of at least part of the patient (6) are acquired, wherein an examination area (U) is defined before the topogram scan (T) is performed, and wherein, during the topogram scan (T), it is determined whether the examination area (U) has been reached based on the projection data (D) of the topogram scan (T), wherein, before reaching the examination area (U), the settings for the parameters (P) for the main scan (H) are determined using a model of the patient (6) based on the projection data (D) of the topogram scan (T), and upon reaching the examination area (U), the main scan (H) is started based on the parameters (P) as soon as the topogram scan (T) has arrived at the examination area (U), and - to control the performance of the main scan (H) of the patient (6) using the computed tomography system (1) based on the parameters (P), where both the topogram scan (T) and the main scan (H) are performed during the rotation of the rotor (3). [10] Control device according to claim 9, comprising a model unit (13), wherein the model unit (13) is used for - Selecting a model of the patient (6) or a part of the patient (6) and / or to - Modifying a base model based on the projection data (D) is set up. [11] Control device according to claim 9 or 10, comprising an idle unit (14), wherein the idle unit is configured to maintain the rotation of the rotor (3) of the gantry (2) between two tests essentially without energy input and without initiating braking. [12] Computed tomography system (1) comprising the control unit (9) according to any one of claims 9 to 11 and / or configured to perform a method according to any one of claims 1 to 8. [13] Computer program product comprising instructions which, when the program is executed by a computer, cause it to perform the steps of the method according to any one of claims 1 to 8, wherein setting the rotor (3) of the gantry (2) into rotation, performing the topogram scan (T) and performing the main scan (H) are carried out by sending appropriate control commands from the computer to appropriate components of the computed tomography system (1). [14] Computer-readable storage medium comprising instructions which, when executed by a computer, cause it to perform the steps of the method according to any one of claims 1 to 8, wherein setting the rotor (3) of the gantry (2) into rotation, performing the topogram scan (T) and performing the main scan (H) are carried out by sending appropriate control commands from the computer to appropriate components of the computed tomography system (1).

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