Controller for a CT scanner

Abstract

A controller and method are used to configure the operation of a kVp switching spectral CT imaging apparatus, which in at least one mode is intended to mimic the user-side operational workflow of a conventional non-spectral CT scanner. The controller receives user-defined settings associated with the operation of a non-spectral CT system, including a desired peak tube voltage and a desired tube current. Based on these user-specified inputs, the controller performs a conversion procedure to derive a set of spectral CT operating parameters estimated to administer the same dose of X-ray radiation within a single kVp switching cycle as would be administered by a conventional scanner within the same time duration. Thus, a user can acquire CT projection and image data using a spectral CT scanner without needing to change their own operational workflow and moreover in a manner that will administer the same radiographic density as they would expect to achieve on a conventional scanner with the same user-specified settings.

Description

Technical Field

[0001] The present invention relates to a controller for a CT imaging apparatus (particularly for a kVp-switched CT imaging apparatus). Background Technology

[0002] A computed tomography (CT) scanner includes an X-ray radiation generator mounted on a rotatable gantry opposite one or more detectors. The X-ray generator rotates around an examination area located between the X-ray generator and the one or more detectors, emitting (typically multicolor) radiation that passes through the examination area and onto objects and / or targets positioned within it. The one or more detectors detect the radiation passing through the examination area and generate signals (or projection data) indicative of the examination area and the objects and / or targets positioned therein. Projection data refers to the raw detector data and can be used to form a projection sine curve, a visual representation of the projection data captured by the detectors(s).

[0003] In the field of CT imaging technology, two types of CT imaging can be distinguished: spectral CT imaging and non-spectral CT imaging.

[0004] Non-spectral computed tomography (CT) scanners typically consist of an X-ray tube mounted on a rotatable gantry opposite one or more rows of detectors. The X-ray tube rotates around the area being examined and emits broadband radiation that passes through that area. A key parameter is the peak kilovolt (kVp), which is the maximum voltage applied across the X-ray tube during X-ray generation.

[0005] For example, at a peak (maximum) tube voltage of 120 keV (i.e., 120 kVp), the energy spectrum of the emitted radiation (filtered with low-energy photons) can range from 40 keV to 120 keV. One or more rows of detectors detect the radiation passing through the inspection area and generate projection data (line integral) indicating it. The projection data is reconstructed to generate volumetric image data.

[0006] The voxels of the reconstructed volumetric image data are typically displayed using grayscale values ​​corresponding to relative radiometric density. These grayscale values ​​reflect the attenuation characteristics of the scanned object and often reveal structure, such as anatomical structures within the object. Since the attenuation of a material to photons depends on the energy of the photons passing through the material, the detected radiation also includes energy spectral information that provides additional information about the elemental or material composition (e.g., atomic number) of the scanned material. However, the values ​​of the projected data are proportional to the energy flux integrated over the energy spectrum (e.g., 40 keV to 120 keV), and the volumetric image data does not reflect energy-related information.

[0007] Spectral (multi-energy) CT scanners are configured to generate projection data at multiple different energy spectrum locations. Multiple measurements with different energy spectra allow for the acquisition of information about the energy-related attenuation of X-rays. This is known as spectral X-ray imaging. Spectral X-ray data allows for the identification and quantification of the material contained within the scanned object.

[0008] One method for performing energy spectrum imaging is kVp switching, in which the tube voltage is periodically switched between or through at least two different tube voltages. A single X-ray tube can be switched by different operating peak voltages, or two or more X-ray tubes can be used, which are configured to emit radiation with different average energy spectra and are driven sequentially.

[0009] By way of example, in a dual-energy configuration, a first voltage (e.g., lower kVp) is applied across the X-ray tube voltage during a first integration period, a second voltage (e.g., higher kVp) is applied across the X-ray tube voltage during a second integration period, the first voltage is applied across the X-ray tube voltage during a third integration period, the second voltage is applied across the X-ray tube voltage during a fourth integration period, and so on.

[0010] Lower kV projection data and higher kV projection data can be decomposed into, for example, photoelectric effect components and Compton scattering components, which can then be individually reconstructed and then combined to produce virtual single-energy volumetric image data.

[0011] Switching CT scanners at kVp is more complex than operating conventional non-spectral CT scanners. Therefore, operators with experience only in operating conventional scanners may find using spectral CT scanners difficult and unfamiliar. Such practitioners may find it harder to apply their experience and expertise intuitively when operating CT scanners, potentially leading to poorer image quality, longer scan times, and potential errors in configuring scanner settings, which could expose patients to radiation without providing usable images. Consequently, the ultimate clinical outcome and patient risk are reduced. Summary of the Invention

[0012] The inventors have recognized the need for a means to enable operators with experience operating conventional non-spectral CT scanners to directly apply their operational skills to the operation of spectral CT scanners. It has also been recognized that operators will be able to acquire spectral CT scan data and the additional information that this can provide, even without detailed expertise on configuring operating parameters for spectral CT scanning.

[0013] This invention is defined by the claims.

[0014] According to an example of an aspect of the invention, a controller is provided for use in controlling the operation of an energy spectrum computed tomography (CT) X-ray imaging apparatus.

[0015] The imaging device is a kVp switching device, which includes an X-ray generator having at least one X-ray tube, and the generator is controlled during operation to periodically switch between at least two different X-ray tube voltages (representing kVp switching cycles) for acquiring energy-spectral CT scan data. The device has a first set of adjustable operating parameters.

[0016] The device is capable of selectively operating in an assisted (pseudo-conventional) acquisition mode, in which the controller is adapted to receive user input instructing user-defined settings for a set of second operating parameters, wherein the second operating parameters are parameters associated with the operation of non-spectral CT imaging, which includes the use of a radiation source operating with a fixed X-ray tube voltage. The second operating parameters include at least the values ​​of the tube current I and the fixed tube voltage kVp.

[0017] The controller is adapted to apply a conversion process for converting the user-defined settings for the second operating parameter into a set of values ​​for the first operating parameter, the set of values ​​being determined to achieve an estimated X-ray radiation dose delivered within a single kVp switching cycle time interval that is the same as the X-ray radiation dose delivered by a fixed voltage radiation source operated using the user-defined second operating parameter within the same time interval.

[0018] The controller is also adapted to generate control instructions for causing the spectral X-ray imaging apparatus to perform a CT scan procedure according to determined settings for the first operating parameters, thereby obtaining a set of spectral CT scan data. The scan data may be spectral projection data. This can also be processed to derive image data or other information, as explained later.

[0019] Therefore, embodiments of the present invention enable users to input operating parameters they will use for a conventional (non-spectral) CT scanner, wherein the scanner converts these operating parameters into an equivalent set of parameters for a spectral CT scanner, designed to match the X-ray dose to be generated using conventional settings. This allows users to perform CT scans directly using a spectral CT scanner, even if they only have knowledge of operating a non-spectral scanner. Furthermore, by calculating the spectral CT parameters to achieve the same X-ray dose as the user anticipates from a conventional scan, the resulting scan data will produce reconstructed image data with similar visual properties in terms of radiographic density.

[0020] For example, in a routine scan, tube voltage and current are used to balance the expected image quality (in terms of contrast and noise) with the patient's radiation dose, and operators are trained to follow the ALARA (lowest reasonably achievable) principle for X-ray dose. Therefore, the combination of tube voltage and current in a routine scan affects both patient dose and image appearance.

[0021] In a preferred embodiment, the first operating parameters determined by the controller may include at least a higher tube voltage and a lower tube voltage. This means that when an application is used to translate user-defined settings for the second operating parameters into a set of values ​​for the first operating parameters, the controller is adapted to determine at least the higher (maximum) tube voltage and the lower (minimum) tube voltage values ​​for the kVp switching scan protocol based on a user-input set of second operating parameters. These are free parameters in the fitting process. Therefore, the method involves at least adjusting the upper and lower voltage limits of the kVp switching protocol to identify (first) operating parameters of the scanner that provide the same dose as the user-defined second operating parameters.

[0022] Higher and lower transistor voltages refer to the maximum and minimum transistor voltages among a set of two or more transistor voltages that the generator is adapted to periodically switch between during operation.

[0023] In some embodiments, the first operating parameter may additionally or alternatively include tube current. In some cases, the value of the tube current can be freely adjusted over time within one or more kVp switching cycles. For example, the switching process may involve fitting a tube current waveform to meet desired dosing characteristics. Upper and lower voltage limits can also be freely adjusted over time in such a way that they dynamically adjust over multiple switching cycles. In other cases, the first operating parameter may include average tube current.

[0024] In some embodiments, the first operating parameters may additionally or alternatively include the duty cycle (i.e., the ratio of lower to higher voltage periods (durations)) and / or the switching frequency of the kVp switching protocol.

[0025] A controller can be a single control unit, or it can be a control device that includes multiple control modules or processors. For example, it can be a processing device.

[0026] Spectral CT scan data can correspond to, for example, spectral projection data, or in some examples, spectral imaging data.

[0027] According to one or more embodiments, the controller may be adapted to generate virtual non-spectral image data based on the processing of the acquired spectral CT scan data and based on a user-defined fixed tube voltage.

[0028] The tube voltage during a conventional scan determines the radiographic contrast of the resulting reconstructed image. In some embodiments, the controller can be configured to construct image data based on acquired spectral CT projection data that mimics the appearance of a non-spectral image to be acquired from a conventional CT scanner using user-defined operating parameters.

[0029] This achieves the following technical effect: the image output presented to the user is constructed to replicate the appearance of scan image data generated by a conventional CT scanner device.

[0030] According to one or more embodiments, the controller may be adapted to:

[0031] Determine the time period T of a single kVp switching cycle of the energy spectrum CT device;

[0032] Calculate the estimated X-ray dose delivered by a fixed-voltage radiation source operating with the user-defined settings for the second operating parameters within a time period equal to the determined time period T; and

[0033] The settings for the first operating parameters are determined, and when implemented on the energy spectrum CT scanning device, the settings are estimated to deliver an X-ray dose equal to the estimated X-ray dose during each kVp switching cycle.

[0034] The estimated X-ray dose refers to the X-ray dose that will be delivered by the non-spectral CT scanning device when configured with user-defined settings for the second operating parameters.

[0035] In some examples, calculations can be based on predefined equations or lookup tables.

[0036] There are different possible definitions for X-ray dose, depending on whether it is defined as energy per unit mass, energy per unit area, or various other definitions. In all cases, it relates to the total amount of radiation energy delivered over a given period of time.

[0037] In a favorable set of examples, it is defined as the total beam energy per unit of irradiated mass (abbreviated as 'Kerma').

[0038] In some examples, the dosage definition can be user-configurable, for example, based on user input provided at the user interface.

[0039] According to one or more embodiments, the controller may be adapted to calculate the total beam energy K per irradiation mass unit of the fixed voltage radiation source based on the following equation. conv :

[0040]

[0041] Wherein, P(E,U,I) is the estimated energy spectrum of the X-ray beam entering the object being scanned from the fixed voltage radiation source (e.g., possibly after passing through any beamforming element or material), where E is the radiation energy, U is the X-ray tube voltage, I is the X-ray tube current, and T is the duration of a single switching cycle of the energy spectrum imaging device.

[0042] In some examples, the controller may be adapted to calculate the energy spectrum of the beam entering the object based on the following equation:

[0043]

[0044] Where X(E,U,I) is the assumed X-ray tube output energy spectrum, f is an estimated set of all materials (or target depth level within the object) that the X-ray beam must pass through between the X-ray source and the object, μ(i,E) is the linear absorption coefficient of material i, l(i) is the thickness of each material, E is the radiation energy, U is the X-ray tube voltage, and I is the X-ray tube current.

[0045] According to one or more embodiments, determining the settings for the first operating parameter may include a fitting process for fitting the first operating parameter based on a target X-ray dose equal to a calculated X-ray dose for the fixed-voltage X-ray source.

[0046] Compared to non-spectral imaging, there are a greater number of operating parameters associated with spectral CT imaging. Many of these scanning parameters (such as rotation time, collimation, etc.) can remain the same between non-spectral and spectral CT devices. However, the fixed tube voltage and current settings cannot be kept the same because the tube voltage and current vary during each switching cycle in the kVp switching device. Therefore, there is no one-to-one mapping between non-spectral voltage and current parameters and spectral parameters.

[0047] Therefore, reconstructing the operating parameters of spectral CT to achieve the desired dose can be advantageously performed as an optimization problem, for example, based on seeking to fit the voltage change waveform during the switching cycle so that the total delivered X-ray dose matches the target dose.

[0048] The fitting or optimization process can be based, for example, on minimizing a predetermined cost function.

[0049] The controller can be configured to generate energy spectrum image data based on the obtained energy spectrum projection data in at least one operating mode.

[0050] In one or more embodiments, the controller may be adapted to receive user input indicating a desired image reconstruction mode, and to selectively operate in the following modes based on the user input:

[0051] The first image reconstruction mode, wherein only the virtual non-spectral image data is generated;

[0052] A second image reconstruction mode, wherein both the virtual non-spectral image data and the spectral image data are generated; or

[0053] The third image reconstruction mode generates only the energy spectrum image data.

[0054] Therefore, this allows users to selectively operate in a fully pseudo-normal mode, a hybrid mode (generating both energy spectrum image data and non-energy spectrum image data), or a pure energy spectrum mode.

[0055] An example of another aspect of the present invention provides a system comprising:

[0056] A spectral CT X-ray imaging apparatus includes an X-ray generator having at least one X-ray tube, and said generator being controlled during operation to periodically switch between at least two different X-ray tube voltages for generating spectral CT scan data, and said apparatus having a first set of adjustable operating parameters; and

[0057] The controller, based on any example or embodiment outlined above or described below, or according to any claim of this application, is operatively coupled to the spectral CT X-ray imaging apparatus.

[0058] The system may also include a user interface operatively coupled to the controller, wherein the controller is configured to receive user-defined settings for a set of second operating parameters from the user interface.

[0059] The system may further include a display unit, wherein the controller is adapted to reconstruct volumetric image data based on energy spectrum CT image data and output the volumetric image data to the display unit for presentation to a user.

[0060] An example of another aspect of the present invention provides a method for controlling the operation of an energy spectrum computed tomography (CT) X-ray imaging apparatus.

[0061] The energy spectrum X-ray imaging device is a kVp switching device, which includes an X-ray generator having at least one X-ray tube, and the generator is controlled during operation to periodically switch between at least two different X-ray tube voltages to generate energy spectrum CT scan data, and the device has a first set of adjustable operating parameters.

[0062] The method includes receiving user input indicating user-defined settings for a set of second operating parameters, wherein the second operating parameters are parameters associated with different non-spectral CT imaging devices configured to operate using a radiation source operating at a fixed X-ray tube voltage, and the second operating parameters include at least the values ​​of tube current I and the fixed tube voltage kVp.

[0063] The method further includes applying a conversion process for converting the user-defined settings for the second operating parameter into a set of values ​​for the first operating parameter, the set of values ​​being determined to deliver the same X-ray radiation dose within a single kVp switching cycle as would be delivered by a fixed-voltage radiation source operated using the user-defined second operating parameter within the same time period.

[0064] The method further includes generating control instructions for causing the X-ray imaging apparatus to perform a CT scan procedure according to determined settings for the first operating parameters, thereby obtaining a set of energy spectral CT scan data.

[0065] An example of another aspect of the invention provides a computer program product comprising computer program code that is executable on a processor or computer.

[0066] When the processor or the computer is operatively coupled to an energy-dispersive computed tomography (CT) X-ray imaging apparatus, the code is configured to cause the processor to perform a method according to any example or embodiment outlined above or described below, or according to any claim of this application.

[0067] These and other aspects of the invention will become apparent from the embodiments described below and will be set forth with reference to the embodiments described below. Attached Figure Description

[0068] To better understand the invention and to more clearly illustrate how it can be implemented, reference will now be made to the accompanying drawings by way of example only, wherein:

[0069] Figure 1A CT imaging system according to one or more embodiments is schematically illustrated;

[0070] Figure 2 The processing flow of a controller according to one or more embodiments is illustrated schematically;

[0071] Figure 3 The processing flow according to one or more embodiments is also schematically illustrated;

[0072] Figure 4 The figure shows the voltage waveform for the kVp switching cycle of the energy spectrum CT imaging device;

[0073] Figure 5 An example method is shown for reconstructing non-spectral imaging data and spectral imaging data from acquired spectral projection data to form a virtual non-spectral image; and

[0074] Figure 6 Another example method is shown for reconstructing non-spectral imaging data and spectral imaging data from acquired spectral projection data to form a virtual non-spectral image. Detailed Implementation

[0075] The invention will be described with reference to the accompanying drawings.

[0076] It should be understood that the detailed descriptions and specific examples, while indicating exemplary embodiments of the apparatus, system, and method, are intended for illustrative purposes only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, system, and method of the invention will be better understood from the following description, the appended claims, and the accompanying drawings. It should be understood that the drawings are merely schematic and not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to denote the same or similar parts.

[0077] This invention provides a controller and method for configuring the operation of a kVp-switched spectral CT imaging device, which is designed to mimic the user-side operating workflow of a conventional non-spectral CT scanner in at least one mode. The controller receives user-defined settings associated with the operation of a non-spectral CT system, including desired peak tube voltage and desired tube current. Based on these user-specified inputs, the controller performs a conversion process to derive a set of spectral CT operating parameters estimated to achieve the same dose of X-ray radiation applied within a single kVp-switching cycle as would be applied by a conventional scanner for the same duration. Therefore, users can acquire CT projection and image data using the spectral CT scanner without altering their own operating workflow and in a manner that applies the same radiographic density they would expect to achieve on a conventional scanner using the same user-specified settings.

[0078] The following describes an example spectral CT X-ray imaging system configured to acquire spectral projection data using kVp-switched multi-energy acquisition. First, refer to... Figure 1 The image schematically illustrates an imaging system 100, such as a computed tomography (CT) scanner. The imaging system 100 includes a scanning or imaging device 150, which typically includes a fixed gantry 102 and a rotating gantry 104, the rotating gantry 104 being rotatably supported by the fixed gantry 102 and rotating about the examination area 106 about the z-axis.

[0079] A radiation source 108 (such as an X-ray tube) is rotatably supported by a rotating gantry 104, rotates with the gantry 104, and emits broadband radiation through an examination area 106. A radiation source voltage controller (kVp CTRL) 110 controls the peak emission voltage of the radiation source 108. The kVp CTRL 110 is configured to switch the X-ray tube voltage between at least two voltages (e.g., 80 kVp and 140 kVp, etc.). Thus, the radiation source 108 alternately produces at least a first radiation beam having a first energy spectrum and a second radiation beam having a different second energy spectrum.

[0080] Note that in some examples, radiation source 108 may include a single X-ray tube configured to switch between at least two different emission voltages (e.g., 80 kVp and 140 kVp) during scanning. However, in other examples, radiation source 108 may include two or more X-ray tubes configured to emit radiation with different average energy spectra. In still further examples, radiation source 108 may include a combination thereof.

[0081] Detector 112 comprises a one-dimensional or two-dimensional array of detector elements 114, wherein each row extends in the xy-plane and multiple rows are arranged along the z-direction. Detector 112 is rotatably supported by a rotating frame 104 along an angular arc opposite to the radiation source 108 across the inspection region 106. Detector 112 rotates in coordination with the radiation source 108 to detect radiation passing through the inspection region 106 and generate different sets of projected data for each energy spectrum in different energy spectra.

[0082] In one example, the kVp CTRL110 alternates the X-ray tube voltage between integration periods (IP). Typically, IP is the time period during which the detector 112 probes radiation while rotating through a predetermined angular increment for measurement. For each IP, each detector element 114 generates an attenuation line integral. The set of line integrals used for IP / angular increments are views. The projection data comprises a set of views acquired at at least 180° plus a sector angle for each energy spectrum in different energy spectra.

[0083] Reconstructor 116 is typically also included, and it reconstructs projection data for different energy spectra and generates volumetric image data.

[0084] As described in more detail below, this can include generating spectral volumetric image data and / or non-spectral volumetric image data based on (spectral) projection data. Non-limiting examples of spectral volumetric image data include low-energy and high-energy, single-energy / monochromatic, virtual non-contrast, effective Z (atomic number), and iodine-only spectral image data.

[0085] Non-spectral volumetric image data corresponds to a predetermined X-ray tube kVp. In one instance, the reconstructor 116 is implemented using a processor (e.g., a central processing unit or microprocessor) configured to execute computer-executable instructions stored, embedded, or encoded on a computer-readable storage medium (such as physical memory and / or other non-transient memory). In some embodiments, the reconstructor 116 includes dedicated hardware such as a graphics processing unit (GPU) and / or an application-specific integrated circuit (ASIC). The reconstructor 116 may be part of system 100 and / or may be located remotely from system 100.

[0086] An object support 118 (such as a couch) supports an object or device in the inspection area 106. The object support 118 can move in coordination with the imaging process to guide the object or device relative to the inspection area 106 for loading, scanning, and / or unloading the object or device.

[0087] The controller 120 is operatively linked to the CT scanning apparatus 150. Specifically, it is operatively coupled to the reconstructor 116 and to an X-ray imaging assembly including a kVp CTRL 110 and a detector 112. The controller may include one or more processors 122. In other examples, the reconstructor may be part of the controller.

[0088] The user interface (such as an operator console) includes input devices 132 that allow the operator to control the system 100 (such as inputting operating parameters). Input devices may include, for example, a mouse and / or a keyboard. User output devices 134 may also be included, such as a display monitor. This can be used to display reconstructed image data and / or can form part of the operator console used for configuring and controlling the system.

[0089] As discussed, the X-ray imaging apparatus 150 is a kVp switching device. It has a first set of adjustable operating parameters. By way of example, these may include at least, for example, higher tube voltage, lower tube voltage, average tube current, and / or kVp duty cycle.

[0090] The controller 120 is configured to receive, for example, a set of user-specified second operating parameters 142 from a user input device 132. The second operating parameters are parameters associated with the operation of a different non-spectral CT imaging apparatus using a fixed radiation source (tube) voltage. For example, the input device 132 may be part of a user interface that prompts the user to input values ​​for a set of second operating parameters via a display. The second operating parameters include at least the values ​​of the fixed tube voltage (kVp) and the fixed radiation tube current (I).

[0091] The combination of tube voltage and current in a routine scan affects the patient's X-ray dose and the appearance of the image. For example, current and voltage settings together affect X-ray intensity and the applied patient dose. Therefore, image noise will also be affected (in an inverse relationship).

[0092] The controller 120 is configured to calculate the conversion or mapping between these user-specified second operating parameters 142 and the first operating parameters required by the spectral CT imaging system 100. Specifically, the controller 120 is configured to apply a conversion process to convert user-defined settings for the second operating parameters into a set of values ​​for the first operating parameters, said set of values ​​being determined to achieve the same X-ray radiation dose delivered within a single kVp switching cycle as would be delivered by a fixed-voltage radiation source operated using the user-defined second operating parameters within the same time period.

[0093] Once the conversion has been performed, the controller is then configured to generate control instructions for causing the X-ray imaging apparatus 100 to perform a CT scan procedure according to settings determined for the first operating parameter 144, and thereby derive a set of energy spectral CT scan data (e.g., projection data).

[0094] In some embodiments, the reconstructor 116 may then generate spectral image data based on the obtained spectral projection data. In some embodiments, non-spectral image data may be generated additionally or alternatively. This is described in further detail below.

[0095] Figure 2The processing workflow of controller 120 is schematically outlined. A second (non-spectral) operating parameter 142 is received at the controller. The controller applies a conversion procedure. The conversion procedure may be a set of one or more algorithms encoded in one or more processors of the controller. Algorithms in a simple example may include referencing one or more reference lookup tables that enumerate appropriate first operating parameters 144 for the spectral imaging apparatus 100 based on the input second operating parameter 142. For example, these may be pre-calculated and pre-stored in a local data storage device. In other examples, the controller may apply one or more algorithms configured to calculate appropriate second operating parameters 144 for a kVp switching device in real time. This may involve calculating an estimated X-ray dose associated with a user-specified second operating parameter and deriving the first operating parameter based on seeking to match that X-ray dose.

[0096] The first operating parameter 144 derived for the kVp switching device is transmitted to the energy spectrum CT imaging device 100 for the implementation of CT scan operation.

[0097] exist Figure 3 The controller's processing flow is described in more detail below. As indicated, the second set of (non-spectral) operating parameters 142 includes at least the values ​​of the tube current I and the fixed tube peak voltage kVp. These relate to parameters for multi-energy non-spectral CT devices, where the X-ray source operates at a single fixed tube voltage and current.

[0098] These user-specified parameters 142 are received at controller 120.

[0099] The controller can calculate an estimated X-ray dose, which will be delivered by a fixed-voltage radiation source operating with user-defined settings for a second operating parameter 142 over a time period T, equal to the time period of a single kVp switching interval of the spectral CT imaging apparatus 100. A switching interval refers to the period during which a complete sequence of two or more kVp tube voltages has been switched through. The time period T may be known and stored in local memory, or it may be calculated by the controller.

[0100] In some examples, X-ray dose can be defined as the total beam energy per irradiated mass unit (abbreviated as Kerma). Kerma can be defined for different depths within the body. For example, Kerma at the object's entrance indicates the skin dose. Inside the object (below the skin), the X-ray dose may vary due to different absorption characteristics. Another dose definition can use the Kerma at the object's center, or even a weighted sum of the skin and center doses. Yet another dose definition can be based on dose measurements using a patient phantom and calorimeters, which are pre-stored in a lookup table and consulted during operation to determine the estimated dose.

[0101] The definition of the dose to be used can be stored in local data storage or memory, or encoded in the controller's programming and retrieved when dose calculation is performed. This can include functions, equations or algorithms, or lookup tables to be applied to calculate the dose.

[0102] The controller determines a setting for a first operating parameter, which, when implemented on the energy spectrum CT scanning device 100, is estimated to deliver an X-ray dose equal to the estimated X-ray dose within each switching cycle time period T.

[0103] These determined first operating parameters are then passed to the CT scanning device 100, which implements the scanning protocol based on these settings.

[0104] The energy spectrum CT scanning device thus obtains energy spectrum projection data 152.

[0105] In some embodiments, the reconstructor 116 receives energy spectrum projection data 152 and generates reconstructed image data of the scanned object, such as volumetric image data.

[0106] In a favorable example, this includes generating virtual non-spectral image data (or pseudo-non-spectral image data) based on the processing of the obtained spectral CT projection data and based on a user-defined value of a fixed radiation source voltage.

[0107] In particular, the appearance of an image in a conventional CT scanner depends on the X-ray tube voltage because the CT contrast of biological tissue depends on the X-ray energy spectrum. If the user selects a specific tube voltage value, he or she will expect to obtain an image with a multicolor energy spectrum appearance according to the selected tube voltage. Therefore, the derived energy spectrum projection data 152 can optionally be processed to obtain virtual non-spectral image data based on a user-specified fixed voltage setting kVp. This process will be explained in more detail below.

[0108] In some embodiments, in at least one operating mode, the reconstructor 116 may additionally or alternatively generate energy spectrum image data based on the obtained energy spectrum projection data 152.

[0109] In some embodiments, the controller may be adapted to receive user input indicating a desired image reconstruction mode, and to operate selectively in the following modes based on the user input:

[0110] In the first reconstruction mode, only the virtual non-spectral image data is generated;

[0111] The second reconstruction mode involves generating both the virtual non-spectral image data and the spectral image data; or

[0112] The third reconstruction mode generates only the energy spectrum image data.

[0113] Note that although the reconstructor 116 is shown as a separate unit from the controller 120, the reconstructor can be part of the controller. The controller can be a distributed controller, comprising multiple processing modules that may or may not form a single physical unit.

[0114] As discussed above, in some embodiments, controller 120 is configured to calculate an estimated X-ray dose, which will be delivered over a period of time in a single switching cycle by a fixed-voltage radiation source operating with user-defined settings for a second (non-spectral) operating parameter 142. This will now be described in more detail.

[0115] As mentioned above, different possible definitions of X-ray dose can exist. In all cases, dose refers to the amount of X-ray energy applied to an object during at least a portion of a CT scan. In some cases, this can be the amount of X-ray radiation over the entire volume of the object. In other cases, it can be the energy per unit volume or unit area. In still other cases, it can be the energy per unit mass. This definition can be predefined and explicitly or implicitly stored in the controller. In some examples, it can be user-configurable, allowing the user to select a preferred definition of the dose used in performing conversion calculations.

[0116] Preferably, the dose of X-ray radiation is calculated for only a single kVp switching cycle of the energy spectrum X-ray device. This simplifies the calculation.

[0117] For the purposes of this example, the X-ray dose will be defined as the total beam energy per unit of irradiated mass (abbreviated as Kerma).

[0118] The controller can be configured to first calculate the estimated X-ray dose, which will be delivered by a fixed-voltage radiation source operating with user-defined settings for a second operating parameter over a time period T equal to a single kVp switching cycle.

[0119] Therefore, the Kerma of the central X-ray beam as it enters the object can be calculated. For a given user-defined tube voltage U and current I, it is possible to calculate the central beam power by integrating the (filtered) X-ray energy spectrum of the X-ray tube over energy. Filtering refers to the energy spectrum of the beam after it has passed through the material forming the object.

[0120] Assume the tube output energy spectrum of X(E,U,I), where E is the energy, U is the tube voltage, and I is the tube current. The energy spectrum P of the (filtered) X-ray beam from a single-voltage radiation source entering the object (e.g., possibly after passing through any beamforming element or material) can be estimated as:

[0121]

[0122] Where f is an estimated set of all materials that the X-ray beam must pass through between the X-ray source and the object (or the target depth level within the object), μ(i,E) is the linear absorption coefficient of material i, and l(i) is the thickness of each material.

[0123] X() and P() are usually expressed in terms of the number of photons per energy interval, per unit time, or per solid angle.

[0124] For conventional (non-spectral) scanning, the X-ray dose (K) during a time period equal to the switching period of length T is... conv The following energy integral can be used to calculate:

[0125]

[0126] For kVp switching devices, the dose (Kerma) calculation requires further integration over time because the tube voltage and current change during the switching period T. Taking U(t) and I(t) as voltage and current waveforms over one switching period, the dose (Kerma) for a kVp switching device within a single switching period T is calculated. kVp-S It can be estimated as:

[0127]

[0128] As discussed above, the controller is configured to determine the settings for the first (spectral CT) operating parameters, which, when implemented on the spectral CT imaging apparatus, are estimated to deliver an X-ray dose equal to the estimated X-ray dose calculated for the second operating parameters input by the user during each switching cycle.

[0129] Since the tube voltage and current vary over time during the switching cycle of the spectral CT imaging device, it is necessary to determine the voltage and current waveforms to be implemented by the spectral CT scanner, which delivers the same equivalent X-ray dose as a conventional scan over a time period equal to a single switching period.

[0130] Equations (2) and (3) above provide equations for estimating the dose during a switching cycle for non-spectral CT scanners and spectral CT scanners, respectively, based on the definition of dose as total beam energy (Kerma) per unit of irradiated mass.

[0131] The estimation of the first operating parameters used to achieve the calculated target X-ray dose can be understood as an optimization procedure, where the free parameters of the spectral CT apparatus are optimized to minimize the deviation between the obtained dose and the target dose. The constraints for optimization are individual hardware constraints on the scanner apparatus and the target X-ray dose. Typically, the number of free parameters in the optimization is greater than one, as required to match the dose requirements. Therefore, optimization objectives can be defined to more narrowly constrain or guide the optimization process. Practical objectives can be estimated using the spectral separation power or sensitivity to photon insufficiency from the spectral CT scanning protocol.

[0132] The term energy spectrum separation power refers to the quality of the energy spectrum attenuation information obtained. If two energy spectra (at two different kVp switching voltages) are similar or have very different noise levels, the task of obtaining energy spectrum information (often called material separation) becomes less stable, and material separation becomes noisy.

[0133] If the total X-ray flux becomes very low within an integration period (IP), the number of photons detected by the detector may become very small or even zero. This effect is called photon insufficiency. Photon insufficiency will cause problems in image reconstruction and may lead to streak artifacts.

[0134] An example is now presented for an example spectral (kVp switching) CT imaging device. Figure 4 The voltage waveform for one kVp switching cycle of total duration T is shown. The total switching period T consists of a higher voltage period T. 较高 Low voltage period T 较低 and two transition periods T 上升 T 下降 Composition, during the higher voltage period T 较高 During the period when the tube is powered by a higher voltage, and during the period when the voltage is lower, T 较低 During the period, the tube is powered by a lower voltage, during the two transition periods T 上升 T 下降 During this period, the voltage ramps up from a lower voltage to a higher voltage and then ramps down from a higher voltage to a lower voltage. In the illustrated example, the initial ramp transition period T is shown. 上升 The switching cycle is defined, but this cycle can be understood as starting at any time.

[0135] In this case, the optimized free parameters (first operating parameters) are the lower voltage level, the higher voltage level, and the duty cycle (the ratio of the lower voltage period to the higher voltage period). Additionally, the tube current can be controlled. The duration of the transition period is typically fixed by the CT scanner hardware and depends on the voltage level and current. For tubes with thermionic emission, the emitter temperature is typically controlled. Since the emitter heats up and cools down relatively slowly, the temperature will remain almost constant and cannot be changed during the cycle. Therefore, for a constant emitter temperature and a controlled tube voltage, the resulting emission current will follow the tube characteristics.

[0136] The effective current waveform depends on the temperature and voltage waveforms. This dependence is assumed to be known or predetermined and is used in the constrained optimization process.

[0137] Optimization can be performed based on minimizing a cost function, where the cost function defines the optimization objective, such as optimal spectral separation power. This optimization objective is pursued within defined constraints, including the target X-ray dose and other hardware constraints such as device power limits.

[0138] By way of a non-restrictive example, an exemplary optimization algorithm can be as follows:

[0139] Optimization Algorithm

[0140] Search for all first operating parameters of a CT device except for one of the first operating parameters of the CT device:

[0141] Use system constraints and behavior to compute dependency parameters (such as rise and fall times).

[0142] Calculate the remaining free parameters (e.g., duty cycle) to meet the dose equivalence requirement (X-ray dose matching the target dose).

[0143] Calculate the cost function (e.g., energy spectrum separation power).

[0144] When a set of initial operating parameters for the experiment exceeds optimization constraints (e.g., power level), the cost function should be set to infinity.

[0145] Steps 1, 2, and 3 can be repeated repeatedly to minimize the cost function.

[0146] As noted above, there are typically more degrees of freedom in spectral CT devices to match dose constraints compared to the required one. Only one of the entire set of parameter settings that meet the dose requirements is needed. The cost function adds further guidance to the optimization, allowing for the implementation of a set of parameters that maximizes a certain advantageous characteristic. As an example, the cost function can be configured to select settings that achieve the optimal spectral separation power.

[0147] For example, and by way of non-limiting explanation, a cost function can be considered as follows for estimating the energy spectrum separation power. Given a first set of operating parameters, it is possible to estimate the effective energy spectrum for the low-voltage and high-voltage phases of the switching cycle. An energy spectrum imaging task can be considered using a 30 cm phantom with a water-iodine solution (to simulate a human body with injected contrast agent (iodine)). This allows for the estimation of the expected detector signal and noise. A certain material decomposition can be assumed, and the water and iodine absorptions can be estimated based on these measurements. The covariance matrix of the decomposition results can be estimated using statistical methods (e.g., the so-called Cramer-Rao lower bound estimation). The variance of the water signal can be used as the cost function.

[0148] Therefore, in the example above, the cost function is minimized when the image noise in the water image is minimized. The Cramer-Rao lower bound makes it possible to estimate this noise based on the signal characteristics of the projected data.

[0149] Note that in other embodiments, dose definitions other than total beam energy (Kerma) per unit of irradiated mass may be used instead.

[0150] For example, the skin dose can be estimated as the component of P() absorbed in the patient's skin (discussed above). Alternatively, the central dose absorbed at the body center can be estimated. In some examples, a weighted sum of the patient and body doses can be used. In each case, a similar method to the definition of total beam energy per unit of irradiated mass for dose, as outlined above, can be used.

[0151] If a dose definition corresponding to a level deeper than the skin is used, equations (1)-(3) can be directly adjusted by simply adjusting f in equation (1) to define all material layers between the X-ray source and the target depth level. Therefore, it can be adjusted to include the tissue layers between the skin surface and the target level (e.g., the center of the body). The rest of the dose calculation can remain the same. By way of a non-limiting example, the central dose can be approximately adjusted by adding the equivalent of 15 cm of water attenuation (for a patient with a diameter of approximately 30 cm).

[0152] Instead of calculating the dose, it is also possible to obtain the dose value in advance from experiments. For example, the dose can be measured or determined in advance for different constant kVp values ​​and recorded in a lookup table. During the operation of the CT device, the dose at a specific kVp can be determined simply by using the lookup table.

[0153] As discussed above, according to one or more embodiments, controller 120 or reconstructor 116 can generate virtual non-spectral image data based on the obtained energy spectrum projection data. Alternatively or additionally, energy spectrum image data can be obtained from energy spectrum projection data.

[0154] Now refer to Figure 5 and Figure 6 This section outlines example methods for reconstructing spectral image data and virtual non-spectral image data from spectral projection data.

[0155] Figure 5 An example of a reconstructor 116 according to one or more embodiments is schematically illustrated. For illustrative purposes, this example is described in conjunction with dual-energy scanning, wherein the voltage of the radiation source 108 switches between two voltages (lower and higher) between views, and the detector 112 generates low-kV projection data and high-kV projection data.

[0156] Angle rebinding unit 202 receives a set of low and high kV energy spectrum projection data and angle rebinds them to produce a set of low and high kV parallel line integrals. In a non-limiting instance, this is achieved by known or other angle rebinding methods. An example of a suitable method is described in US6963631B2.

[0157] Decomposer 204 decomposes the set of low and high kV parallel line integrals into distinct bases or contributions, such as the photoelectric effect and Compton scattering or other bases. Non-limiting methods include: creating a lookup table (LUT) with the contribution of each base as a function of energy; storing the LUT; and using the values ​​in the LUT to decompose the line integral into contributions of both bases. An example of a suitable method for creating and using a LUT for decomposition is described in US9324142B2.

[0158] Another method models the low-kV parallel line integral and the high-kV parallel line integral as: I h,l =∫S h,l (E)D(E)exp(-∫μ(E)dl)dE, where indices h and l refer to high and low, respectively, and S h,l (E) represents the tube energy spectrum for both high and low energy levels, and exp(-∫μ(E)dl)dE denotes the line integral. The two-energy treatment separates μ(E)dl into fundamental components, such that, for example, I... h,l =∫S h,l (E)D(E)exp(-L B1 B1(E)-L B2 B2(E))dE, where L B1 and L B2 There are two basis pairs contributing, D(E) represents the energy spectrum response of the detector, and B1(E) and B2(E) are their corresponding decay energy dependencies. The decomposition solves for the two unknowns L for each pixel. B1 and L B2 Mapping to measurement result I h and I lNonlinear systems.

[0159] When the contributions of the two basis pairs are the photoelectric effect and the Compton scattering contribution, I h,l =∫S h,l (E)D(E)exp(-L p P(E)-L s S(E))dE, where L p and L s The contributions are from the photoelectric effect and Compton scattering, and P(E) and S(E) are their corresponding decay energy dependencies. Furthermore, the decomposition solves for each pixel, removing the two unknowns L. p and L s Mapping to measurement result I h and I l Nonlinear systems. Other basis pairs are also considered in this paper. Another example is described in Alverez et al., “Energy-selective Reconstructions in X-ray Computerized Tomography” (Phys. Med. Biol. 1976, Vol. 21, No. 5, 733-744). Other methods are also anticipated in this paper.

[0160] The reconstructor 116 includes two processing chains 206 and 208 that process the two contributions. The processing (spectral) chain 206 processes the contribution and generates spectral volumetric image data. The processing (non-spectral) chain 208 processes the contribution and generates non-spectral volumetric image data.

[0161] Processing chain 206 includes a radial rebinator 210 that receives two contributions and radially rebinds the parallel-line integral (e.g., by interpolation) to produce equally spaced parallel-line integrals. In a non-limiting instance, this is achieved by known or other angular rebinding methods. Examples of suitable methods are described, for example, in US6963631B2.

[0162] Processing chain 206 also includes image processor 212, which reconstructs the decomposed projection data of the radial repartition bins to generate first volumetric image data and second volumetric image data for the first and second contributions. Image processor 212 employs filtered backprojection, iteration, and / or other reconstruction methods.

[0163] Processing chain 206 also includes an energy spectrum processor 214, which combines (e.g., using weighted summation) the first volumetric image data and the second volumetric image data to produce energy spectrum volumetric image data. For example, image processor 212 is capable of producing single-energy volumetric image data. As described herein, other energy spectrum volumetric image data include virtual non-contrast, effective Z, or iodine-only energy spectrum volumetric image data as non-limiting examples. A single-energy image is an image acquired using an X-ray source that emits photons with only a single energy.

[0164] Processing chain 208 includes a reconstructor 216 that reconstructs the decomposed projection data against a predetermined reference tube voltage 218. The predetermined reference tube voltage 218 is considered to be a user-specified value of a fixed radiation source voltage (input as one of the second operating parameters) in kVp.

[0165] Example refactoring is: I user_kVp =∫D(E)S user_kVp (E)exp(-L p P(E)-L s S(E))dE, where S user_kVp (E) is the tube energy spectrum for a user-specified value with a fixed tube voltage. For example, with low kVp and high kVp values ​​of 80 kVp and 140 kVp respectively, and a user-specified fixed tube voltage of 120 kVp for tube voltage 218, the reconstruction is: I 120_kVp =∫D(E)S 120_kVp (E)exp(-L p P(E)-L s S(E))dE. In one instance, this is implemented by multiplying the material attenuation at a specific energy by the portion of the energy spectrum at that specific energy for all energies of the energy spectrum, and then summing the products, for a user-specified tube voltage 218.

[0166] Processing chain 208 also includes a radial rebinator 220, which receives the reconstructed projection data and radially rebinds the parallel line integrals to produce equally spaced parallel line integrals, for example, as discussed in conjunction with radial rebinator 210. In one example, radial rebinators 210 and 220 are separate radial rebinators, as shown. In a variant, radial rebinators 210 and 220 are part of the same radial rebinator or the same radial rebinator.

[0167] Processing chain 208 also includes image processor 222, which receives and reconstructs the projected data from the radial resplicing bins, for example, as discussed in conjunction with image processor 212. In one instance, image processors 212 and 222 are separate image processors, as shown. In a variant, image processors 212 and 222 are part of the same image processor or the same image processor.

[0168] Typically, processing chain 208 processes interleaved acquisitions at different source spectra and generates non-spectral volumetric image data that appears to be reconstructed using projection data from a specific kVp acquisition. As an example, in a non-limiting instance, processing chain 208 processes interleaved acquisitions at 80 kVp and 140 kVp and generates volumetric image data that appears to be reconstructed using projection data from a single 120 kVp acquisition.

[0169] Note that in different embodiments, or in different reconstruction modes, the reconstructor can be configured to generate only non-spectral image data, only spectral image data, or both spectral and non-spectral image data. Therefore, according to one set of embodiments, the radial resplitter 210, image processor 212, and spectral processor 214 of the first processing chain 206 can be omitted, such that only non-spectral volumetric image data is constructed from the spectral projection data. In another embodiment, the entire second processing chain 208 can be omitted, such that only spectral volumetric image data is generated. In yet another embodiment, both processing chains 206 and 208 are implemented such that both spectral and non-spectral image data are generated.

[0170] Figure 6 Another example of reconstructor 116 is illustrated schematically. This example includes... Figure 5 The example includes the angle resplitter 202, the resolver 204, and the entire first processing chain 206 (including the radial resplitter 210, the image processor 212, and the energy spectrum processor 214). These components have been discussed above and will not be repeated here. In this example, the energy spectrum processor 214 generates energy spectrum image data in the form of single-energy images of the energy spectrum across the radiation beam (e.g., from 40 keV to 120 keV).

[0171] In this example, the second processing chain 208 includes a reference kVp (a user-specified value for a fixed tube voltage) 218 ​​(as described above) and a non-spectral processor 302. The non-spectral processor 302 generates non-spectral volumetric image data by calculating a weighted average of single-energy images across the radiation beam energy spectrum (e.g., from 40 keV to 120 keV), where the relative weights are derived from the effective tube energy spectrum at the user-specified tube voltage (e.g., 120 kVp) filtered by the object or average object. This weighting will mimic the contrast shown in the non-spectral volumetric image data.

[0172] As discussed above, the embodiments utilize a controller. A controller can be implemented in a variety of ways using software and / or hardware to perform a variety of desired functions. A processor is an example of a controller employing one or more microprocessors, which can be programmed using software (e.g., microcode) to perform desired functions. However, a controller can be implemented with or without a processor, and can also be implemented as a combination of dedicated hardware performing some functions and processors (e.g., one or more programmed microprocessors and associated circuitry) performing other functions.

[0173] Examples of controller components that may be employed in various embodiments of this disclosure include, but are not limited to, conventional microprocessors, application-specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

[0174] In various implementations, the processor or controller may be associated with one or more storage media, such as volatile and non-volatile computer memories, such as RAM, PROM, EPROM, and EEPROM. The storage media may be encoded with one or more programs that, when run on one or more processors and / or controllers, perform the desired functions. The various storage media may be fixed within the processor or controller, or may be transportable, allowing one or more programs stored thereon to be loaded into the processor or controller.

[0175] Those skilled in the art, through studying the accompanying drawings, the disclosure, and the claims, will be able to understand and implement variations of the disclosed embodiments when practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the words "a" or "an" do not exclude a plurality.

[0176] A single processor or other unit can implement the functions of several items as described in the claims.

[0177] Although some measures are described in different dependent claims, this does not mean that combinations of these measures cannot be used advantageously.

[0178] Computer programs may be stored / distributed on suitable media, such as optical storage media or solid-state media supplied together with or as part of other hardware, but computer programs may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

[0179] If the term “suitable” is used in the claims or description, it should be noted that the term “suitable” is intended to be equivalent to the term “configured as”.

[0180] No reference numerals in the claims should be construed as limiting the scope.

Claims

1. A controller for use in controlling the operation of an X-ray-based energy-spectral computed tomography (CT) imaging apparatus. in, The spectral CT imaging device is a kVp switching device, which includes an X-ray generator having at least one X-ray tube, and the generator is controlled to periodically switch between a lower tube voltage and a higher tube voltage during operation in kVp switching mode for acquiring spectral CT scan data, and the spectral CT imaging device has a set of adjustable first operating parameters, which include at least the higher tube voltage, the lower tube voltage, and the duty cycle; The energy-dispersive CT imaging device is capable of selectively operating in an auxiliary acquisition mode, wherein in the auxiliary acquisition mode, the controller is adapted to: The system receives user input indicating user-defined settings for a set of second operating parameters, which are parameters associated with non-spectral CT imaging, including the use of a radiation source operated using a fixed X-ray tube voltage. The set of second operating parameters includes at least the values ​​of the tube current I and the fixed X-ray tube voltage kVp. An application conversion process is used to convert the user-defined settings for the set of second operating parameters into a set of values ​​for the set of adjustable first operating parameters, the set of values ​​being determined to deliver the same X-ray radiation dose within a single kVp switching cycle as would be delivered by a fixed-voltage radiation source operated using the user-defined set of second operating parameters for the same duration; and Generate control instructions to cause the spectral CT imaging device to perform a CT scan procedure according to determined settings for the set of adjustable first operating parameters, and thereby obtain a set of spectral CT scan data.

2. The controller according to claim 1, wherein, The controller is adapted to generate virtual non-spectral image data based on the processing of the acquired spectral CT scan data and based on the fixed X-ray tube voltage defined by the user.

3. The controller according to claim 1 or 2, wherein, The controller is adapted to: Determine the duration T of a single kVp switching cycle of the energy spectrum CT imaging device; Calculate the estimated X-ray radiation dose to be delivered by a fixed-voltage radiation source operating with the user-defined settings for the set of second operating parameters over a determined duration T. and A setting for the set of adjustable first operating parameters is determined, which, when implemented on the spectral CT imaging apparatus, is estimated to deliver an X-ray radiation dose equal to the estimated X-ray radiation dose during each switching cycle.

4. The controller according to claim 1 or 2, wherein, The X-ray radiation dose is defined as the total beam energy per irradiated mass unit.

5. The controller according to claim 4, wherein, The controller is adapted to calculate the total beam energy per irradiation mass unit for the fixed-voltage radiation source based on the following equation. : in, It is the estimated energy spectrum of the X-ray beam entering the object being scanned from the fixed voltage radiation source, where E is the radiation energy, U is the fixed X-ray tube voltage, I is the X-ray tube current, and T is the duration of a single kVp switching cycle of the energy spectrum CT imaging device.

6. The controller according to claim 5, wherein, The controller is adapted to calculate the energy spectrum of the filtered beam entering the scanned object based on the following equation: in, Here, f is the assumed X-ray tube output energy spectrum, f is an estimated set of all materials that the X-ray beam must pass through between the fixed voltage radiation source and the scanned object, µ(i,E) is the linear absorption coefficient of material i, l(i) is the thickness of each material, E is the radiation energy, U is the fixed X-ray tube voltage, and I is the X-ray tube current.

7. The controller according to claim 3, wherein, Determining the settings for the set of adjustable first operating parameters includes a fitting process for fitting the set of adjustable first operating parameters based on a target X-ray radiation dose equal to the calculated X-ray radiation dose for the fixed voltage radiation source.

8. The controller according to any one of claims 1, 2 and 5-7 is also capable of operating in at least one operating mode to generate spectral image data based on the obtained spectral CT scan data.

9. The controller according to any one of claims 1 and 5-7, wherein, The controller is adapted to receive user input indicating a desired image reconstruction mode, and to selectively operate in the following modes based on the user input: In the first reconstruction mode, only virtual non-spectral image data is generated, wherein the virtual non-spectral image data is generated by the controller based on the processing of the obtained spectral CT scan data and based on the fixed X-ray tube voltage defined by the user. The second reconstruction mode generates both the virtual non-spectral image data and the spectral image data, wherein the spectral image data is generated by the controller based on the obtained spectral CT scan data; or The third reconstruction mode generates only the energy spectrum image data.

10. A spectral computed tomography (CT) imaging system utilizing X-rays, comprising: An X-ray spectral CT imaging apparatus includes an X-ray generator having at least one X-ray tube, and the generator is controlled during operation to periodically switch between at least two different X-ray tube voltages for generating spectral CT scan data, and the spectral CT imaging apparatus has a set of adjustable first operating parameters. as well as The controller according to any one of claims 1-9 is operatively coupled to the spectral CT imaging device.

11. The spectral CT imaging system of claim 10, further comprising a user interface operatively coupled to the controller, and the controller being arranged to receive, from the user interface, the user-defined settings for the set of second operating parameters.

12. The spectral CT imaging system according to claim 10 or 11, further comprising a display unit, wherein, The controller is adapted to reconstruct volumetric image data based on energy spectrum CT image data and output the volumetric image data to the display unit for presentation to the user.

13. A method for controlling the operation of an X-ray-based energy-spectral computed tomography (CT) imaging device. in, The spectral CT imaging device is a kVp switching device, which includes an X-ray generator having at least one X-ray tube, and the generator is controlled to periodically switch between a lower tube voltage and a higher tube voltage during operation in kVp switching mode to generate spectral CT scan data, and the spectral CT imaging device has a set of adjustable first operating parameters, which at least include the higher tube voltage and the lower tube voltage and the duty cycle; The method includes: The system receives user input indicating user-defined settings for a set of second operating parameters, wherein the set of second operating parameters are parameters associated with different non-spectral CT imaging devices configured to operate using a radiation source operating at a fixed X-ray tube voltage, and the set of second operating parameters includes at least the values ​​of tube current I and the fixed X-ray tube voltage kVp. An application conversion process is used to convert the user-defined settings for the set of second operating parameters into a set of values ​​for the set of adjustable first operating parameters, the set of values ​​being determined to deliver the same X-ray radiation dose within a single kVp switching cycle as would be delivered by a fixed-voltage radiation source operated using the user-defined set of second operating parameters for the same duration; and Generate control instructions to cause the spectral CT imaging device to perform a CT scan procedure according to determined settings for the set of adjustable first operating parameters, and thereby obtain a set of spectral CT scan data.

14. A computer program product comprising computer program code, said computer program code being executable on a processor or computer. in, When the processor or the computer is operatively coupled to an X-ray-based spectral computed tomography (CT) imaging apparatus, the code is configured to cause the processor to perform the method according to claim 13.

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