Methods and systems for X-ray imaging

Abstract

This invention provides various methods and systems for medical imaging systems. In one example, the imaging system (100) includes: a C-frame (102); an x-ray tube (108) coupled to a first end (152) of the C-frame (102); an x-ray detector (130) coupled to a second end (150) of the C-frame (102) opposite to the x-ray tube (108); and a controller (120) having computer-readable instructions stored in a non-transitory memory, which, when executed, cause the controller (120) to: identify a reference image; determine a target current (306) based on the reference image; determine a correction current (316) based on the target current (306); and transition the current (304) supplied to the x-ray tube (108) to the target current (306) by commanding the current (304) to the correction current (316) while maintaining a constant voltage supplied to the x-ray tube (108).

Description

Technical Field

[0001] The embodiments of the subject matter disclosed herein relate to medical imaging systems, and more specifically to radiological imaging systems. Background Technology

[0002] Radiographic imaging systems can be used in a variety of applications, including medical and industrial applications. In medical settings, radiographic imaging devices can provide a non-invasive way to image a patient's tissues and bones. Imaging devices can have the ability to capture multiple images at specified intervals and display them sequentially to create a single image of the object being examined.

[0003] The imaging apparatus may include a C-arm coupled to a base unit. The C-arm may include an X-ray source positioned at one end of the arm and a detector positioned at the other end of the arm. A gap may be provided between the X-ray source and the detector to receive an object, such as a part of a patient's body, which can be irradiated by radiation from the X-ray source. When the object is irradiated, the X-ray radiation penetrates the object and is captured by the detector. By penetrating the object placed between the source and the detector, the X-rays enable the acquisition of an image of the object, which can then be transmitted to a display monitor, where the image can be later displayed or stored and retrieved. Summary of the Invention

[0004] In one example, the imaging system includes: a C-shaped gantry; an X-ray tube coupled to a first end of the C-shaped gantry; an X-ray detector coupled to a second end of the C-shaped gantry opposite the X-ray tube; and a controller having computer-readable instructions stored in a non-transitory memory, the computer-readable instructions, when executed, causing the controller to: identify a reference image; determine a target current based on the reference image; determine a correction current based on the target current; and transition the current supplied to the X-ray tube to the target current by commanding the current to the correction current while maintaining a constant voltage supplied to the X-ray tube.

[0005] It should be understood that the above brief description is provided to introduce selected concepts further described in the detailed embodiments in a simplified form. This is not intended to identify key or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims following the detailed embodiments. Furthermore, the claimed subject matter is not limited to embodiments that address any shortcomings mentioned above or in any part of this disclosure. Attached Figure Description

[0006] The invention will be better understood by referring to the following description of non-limiting embodiments, in which:

[0007] Figure 1An exemplary medical imaging system including a C-arm is shown according to one embodiment.

[0008] Figure 2 A flowchart illustrating a method for controlling an X-ray tube in a medical imaging system, according to one embodiment, is shown.

[0009] Figures 3 to 4 Different graphs are shown according to one embodiment of an X-ray tube of a medical imaging system, illustrating the current and command correction current.

[0010] Figure 5 A graph showing the current and command correction current of an X-ray tube in a medical imaging system according to one embodiment is presented. Detailed Implementation

[0011] The following description relates to various embodiments for medical imaging systems and methods for controlling medical imaging systems. A 3D mobile C-arm imaging system is provided according to this disclosure. Additionally, control routines for a 3D mobile C-arm imaging system are provided according to this disclosure. Medical imaging systems (such as...) Figure 1 The illustrated medical imaging system includes a C-arm. A radiation source is positioned at a first end of the C-arm, and a radiation detector is positioned at the opposite second end of the C-arm. A subject to be imaged by the medical imaging system can be positioned between the radiation source and the radiation detector. The radiation source emits radiation such as X-rays, and the radiation passes through the subject, where attenuated X-rays that have passed through the subject are intercepted or received by the detector. The current supplied to the radiation source is controlled by the imaging system's electronic controller. Figure 2 The method shown in the flowchart allows the controller to adjust the actual current to a target current with a desired value by commanding the current as a correction current based on imaging parameters. The correction current can be offset from the target current, such as... Figures 3 to 4 As shown, this is to provide a transition from the actual current to the target current within a desired time frame (such as the command transition duration between images in the acquisition sequence). Therefore, during the scanning of the subject, the actual current can be more responsively adjusted (e.g., matched) to the target current, such as... Figure 5 As shown.

[0012] refer to Figure 1An imaging system 100 including a C-arm 102 (which may be referred to herein as a C-gantry) is schematically illustrated. The imaging system 100 may be referred to herein as a medical imaging system and / or a C-arm imaging system. The imaging system 100 includes a radiation source, and in the example described herein, the radiation source is an x-ray unit 108 (which may be referred to herein as an x-ray tube), which is positioned relative to a detector 130 (which may be referred to herein as an x-ray detector) and configured to emit x-ray radiation. In other examples, the radiation source may be configured to emit different types of radiation, such as gamma rays, for imaging (e.g., imaging a subject such as patient 134), and the detector (e.g., x-ray detector 130) may be configured to detect radiation emitted by the radiation source (e.g., x-ray beam 132). The imaging system 100 further includes a base unit 105 that supports the imaging system 100 on the ground surface 190 on which the imaging system 100 is situated (e.g., via a base 122 supported by wheels 124, wheels 126, etc.).

[0013] C-arm 102 includes a C-shaped portion 103 connected to an extension 107, wherein the extension 107 is rotatably coupled to a base unit 105. A detector 130 is coupled to the C-shaped portion 103 at a first end 150, and an X-ray unit 108 is coupled to the C-shaped portion 103 at an opposite second end 152. For example, the C-arm 102 may be configured to rotate at least 180 degrees relative to the base unit 105 in opposite directions. The C-arm 102 may rotate about at least a rotation axis 164 and additionally about an axis 167. The C-shaped portion 103 may be rotated as described above to adjust the X-ray unit 108 and the detector 130 (positioned along axis 166 at opposite ends of the C-shaped portion of the C-arm 102, where axis 166 intersects and extends radially relative to the rotation axis 164) through multiple positions.

[0014] During an imaging operation (e.g., a scan), radiation from the x-ray unit 108 can be used to irradiate a portion of a patient's body placed in an opening formed between the x-ray unit 108 and the detector 130. For example, the patient 134 may be supported by a patient support table 136 (which includes a support surface 138 and a base 140) and may be arranged between the x-ray unit 108 and the detector 130. The x-ray unit 108 includes an x-ray tube insert 109, and x-ray radiation generated by the x-ray tube insert 109 can be emitted from the x-ray unit 108. The radiation can penetrate the portion of the patient's body arranged to be irradiated and can travel to the detector 130, which captures (e.g., intercepts by the detector surface 113 of the detector 130) the radiation. By penetrating the portion of the patient's body placed between the x-ray unit 108 and the detector 130, an image of the patient's body is captured and relayed to the electronic controller 120 of the imaging system 100 (e.g., via an electrical connection, such as a conductive cable 161). The image can be displayed via a display device 118. The images of the subject acquired by the imaging system 100 via the x-ray unit 108 and the detector 130 as described above may be referred to herein as projection images and / or scanned projection images.

[0015] The base unit 105 may include an electronic controller (e.g., a control and computing unit) that processes instructions or commands sent from a user input device during operation of the imaging system 100. The base unit 105 may also include an internal power supply (not shown) that provides power to operate the imaging system 100. Alternatively, the base unit 105 may be connected to an external power source to power the imaging system 100. Multiple connection lines (e.g., cables, such as conductive cable 161) may be provided to transmit power, instructions, and / or data between the x-ray unit 108, the detector 130, and the control and computing unit. These connection lines can transmit power from power sources (e.g., internal and / or external power sources) to the x-ray unit 108 and the detector 130.

[0016] The C-arm 102 can be adjusted to multiple different positions by rotating the C-shaped portion 103 of the C-arm 102. For example, in Figure 1In the initial first position shown, detector 130 is vertically positioned above x-ray unit 108 relative to ground 190 where imaging system 100 is located, wherein axis 166, arranged perpendicular to ground 190, intersects the midpoint of each of the outlet 111 of x-ray unit 108 and detector surface 113 of detector 130. C-arm 102 can be adjusted from the first position to different second positions by rotating C-shaped portion 103. In one example, the second position could be a position where x-ray unit 108 and detector 130 are rotated together by 180 degrees relative to the first position, such that x-ray unit 108 is vertically positioned above detector 130, wherein axis 166 intersects the midpoint of outlet 111 of x-ray unit 108 and the midpoint of detector surface 113 of detector 130. When adjusted to the second position, the X-ray unit 108 can be vertically positioned above the rotation axis 164 of the C-shaped portion 103 of the C-arm 102, and the detector 130 can be vertically positioned below the rotation axis 164. Different rotational positions of the C-arm 102 are possible.

[0017] Detector saturation in cone-beam computed tomography (CBCT) refers to overexposure or exceeding of the detection range in images acquired by a computed tomography imaging system. In cases of detector saturation, the intensity range of X-ray radiation exceeds the detector's detectability range in at least some projections. Consequently, information loss occurs in the saturated regions of the projected image, potentially increasing the likelihood of imaging artifacts, skin line loss, decreased CT number accuracy, reduced contrast-to-noise ratio of the acquired images, and / or image uniformity.

[0018] The dynamic range of X-ray detectors in moving C-arm systems is typically much smaller than that in conventional CT systems (e.g., stationary CT imaging systems without a C-arm). In moving C-arm systems, detector saturation can occur as imaging conditions change from one projection to another due to the varying thickness of the anatomical structures being imaged. This can lead to image quality degradation. Furthermore, moving C-arm systems typically use CMOS X-ray detectors, which offer lower electronic noise, lower electromagnetic interference, shorter latency, faster readouts, lower power consumption, and less temperature-dependent operational variation. However, the dynamic range of CMOS X-ray detectors is only about one-tenth that of amorphous silicon-based X-ray detectors, potentially increasing the likelihood of detector saturation.

[0019] In a moving C-arm system, the cathode-anode voltage of the X-ray tube (e.g., the voltage provided at the X-ray tube insert, such as X-ray tube insert 109) is typically expressed as a kilovolt peak (kVp). The duration for adjusting the cathode-anode voltage of the X-ray tube to a commanded value (e.g., command kVp) is typically in the range of a few milliseconds. The current applied to the X-ray tube is typically expressed in milliamperes (mA), and the current may be referred to as mA herein. However, the duration for adjusting the current (e.g., adjusting mA) is much longer than the duration for adjusting the cathode-anode voltage. Typically, the duration for adjusting the current is about one second. Because the duration for adjusting the cathode-anode voltage is much shorter than the duration for adjusting the current, adjusting imaging parameters during 3D scanning in conventional imaging systems is typically achieved primarily by adjusting the voltage (kVp) rather than the current (mA). However, when the voltage is adjusted during scanning, the X-ray attenuation and CT number of a given voxel can vary with projection as the voltage changes. Variations in X-ray attenuation can reduce the accuracy of the CT number and can additionally increase the likelihood of image artifacts.

[0020] To reduce the possibility of detector saturation according to this disclosure, a constant voltage may be provided at the x-ray tube insert throughout the 3D scan. The constant voltage may be based on the size of a portion of the subject to be imaged (e.g., the size of the patient's anatomical structures). As an example, the voltage value may be determined via a pre-capture performed at the start of the 3D scan (e.g., immediately before acquiring the first projection of the entire projection series acquired during the 3D scan), wherein the pre-captured image may be recognized as a reference image by a controller. For example, the thickness of the subject's anatomical structures to be imaged may vary from subject to subject. Determining the constant voltage to be provided to the x-ray tube insert based on the thickness of the anatomical structures of a given subject to be imaged can increase image quality. Determining the constant voltage based on the pre-captured image may include, for example, determining the constant voltage based on an image level indicator (VLI) of the subject's anatomical structures in the pre-captured image. The VLI may be a measure of the brightness of the subject's anatomical structures in the pre-captured image. As an example, where VLI is low, the controller can command a higher constant voltage to be supplied to the X-ray tube insert throughout the patient's scan, and where VLI is high, the controller can command a lower constant voltage to be supplied to the X-ray tube insert throughout the patient's scan. The constant voltage can be determined via a lookup table stored in the controller's memory. For example, the controller can calculate the constant voltage based on the VLI of a pre-captured image, where the input to the lookup table is VLI, and the output of the lookup table is the constant voltage. In some examples, the constant voltage can be a function of VLI, where the controller calculates the constant voltage with VLI as input. Maintaining a constant voltage increases the ease of use of the imaging system in conjunction with the control routines described herein.

[0021] With the voltage maintained at a constant voltage, the current is adjusted throughout the scan to provide sufficient clarity for imaging the subject due to the varying thickness of the subject's anatomical structures. However, as mentioned above, there may be a delay during the imaging of the subject, in which the current supplied to the X-ray tube insert 109 is adjusted from a first value to a second value.

[0022] During the operation of a conventional C-arm imaging system, adjusting the current from an initial value to a target value involves commanding the current to the target value and waiting for the transition from the initial value to the target value. This duration, or delay, can be relatively long compared to the duration of transitioning the voltage from an initial voltage to a target voltage. This delay can result in undesirable long response times in conventional imaging systems where current is frequently adjusted (e.g., during a scan). As an example, the current may be commanded (e.g., set) to a target current, and during a scan of the subject, it may be expected that the current will transition from a first value (e.g., 2 mA) to the target current (e.g., 3 mA) within a relatively short duration. However, during the transition, the rate of change of the current may decrease as the current approaches the target current (e.g., the rate of change may decay exponentially as the current approaches the target current). Therefore, the duration of the transition can be significantly longer than the expected (e.g., commanded) transition time (e.g., the expected transition time might be 100 milliseconds, and the actual transition time might be 600 milliseconds). This may increase the scan duration and / or degrade the imaging quality of the system.

[0023] However, according to this disclosure, the electronic controller 120 can command the current as a correction current (e.g., a correction value of the current determined by the controller) to transition the actual current supplied to the x-ray tube insert 109 from a first value (e.g., an initial value) to a second value (e.g., a target value) with a shorter transition duration. The correction current can be determined by the controller via a function or lookup table stored in the controller's memory (e.g., calculation), and by commanding the current as a correction current, the speed of current adjustment can be improved. As an example, according to this disclosure, the transition duration between the first and second values ​​can be in the range of 10%-15% of the transition duration in a conventional imaging system. Therefore, the imaging performance of the imaging system can be improved. For example, in a conventional imaging system, the length of the transition duration can be long enough that adjusting the current supplied to the x-ray tube insert during the scanning of the subject may be impractical (e.g., a long transition duration may result in longer scan times, image aberrations or artifacts caused by the subject's breathing or other movements throughout the longer scan time).

[0024] By controlling the operation of the imaging system as described herein, the current supplied to the X-ray tube insert can be more easily adjusted during the scanning of the subject (e.g., the speed of current adjustment can be increased). Therefore, image quality can be improved. For example, by controlling the imaging system as described herein, the current supplied at the X-ray tube insert can be adjusted more quickly to compensate for variations in the thickness of the imaging anatomy for each projection of the scan (e.g., the current can be adjusted from each projection to the corresponding next projection).

[0025] refer to Figure 2 The diagram illustrates a method 200 (referred to herein as an imaging method) for controlling an x-ray tube in a medical imaging system. The x-ray tube and the medical imaging system are respectively referenced above. Figure 1 The x-ray unit 108 and imaging system 100 are similar to or identical. Controlling the operation of the x-ray tube includes controlling the operation of the x-ray tube insert housed within the x-ray tube. For example, as described herein, adjusting the current supplied to the x-ray tube refers to adjusting the current supplied to the x-ray tube insert. The x-ray tube insert may be similar to the one described above. Figure 1 The X-ray tube insert 109 is similar to or the same as described herein. Instructions for performing method 200, included herein, may be provided by a controller (e.g., referenced above). Figure 1 The electronic controller 120 is based on instructions stored in the controller's memory and combined with instructions from sensors of the imaging system (such as those mentioned above). Figure 1 The detector 130 receives signals to perform the operation. According to the method described below, the controller can adjust imaging parameters to adjust the operation of the imaging system (e.g., the operation of the X-ray tube insert).

[0026] At 202, the method includes determining imaging system operating conditions. Determining imaging system operating conditions may include, for example, determining the value of the actual current at the X-ray tube insert, determining the actual voltage at the X-ray tube insert, determining the target scan range of the imaging system (e.g., determining the target angle through which the C-arm of the imaging system rotates during the scanning of the subject), determining the image acquisition rate of the imaging system, etc. As an example, the operator of the imaging system (e.g., a clinician) may input the target scan range of the imaging system before starting the scanning of the subject based on the anatomical structure of the subject to be imaged by the imaging system (e.g., the subject's torso), and the determination at 202 may include determining the angle spanned by the C-arm of the imaging system during the scanning (e.g., the amount of rotation of the C-arm around the imaging isocenter, such as 100 degrees, 150 degrees, 190 degrees, etc.).

[0027] The method optionally continues from 202 to 203, wherein the method includes acquiring a pre-projection image using a pre-projection voltage and a pre-projection current supplied to the X-ray tube insert, and determining a scanning voltage based on the pre-projection image. Acquiring the pre-projection image can occur during a period in which the acquisition of a scanning projection image by the imaging system has not yet occurred. For example, an operator of the imaging system can input a command to the controller of the imaging system to indicate a desired scan of the subject, and thus the imaging system can use the pre-projection voltage and pre-projection current supplied to the X-ray tube insert to acquire a pre-projection image as a single initial projection image of the subject. The pre-projection voltage can be a predetermined default voltage, and the pre-projection current can be a predetermined default current, wherein the values ​​of the pre-projection voltage and pre-projection current are stored in the memory of the controller. As a non-limiting example, the pre-projection voltage can be 100 kVp, and the pre-projection current can be 10 mA.

[0028] Determining the scan voltage based on the pre-captured image may include calculating the scan voltage based on the pre-captured voltage, pre-captured current, and / or image level indicator (VLI) of the pre-captured image. For example, the scan voltage may be determined by converting the VLI value to a scan voltage value via a lookup table stored in the controller's memory (e.g., non-transitory memory), as described above. The VLI of the pre-captured image may be a measure of the brightness of the pre-captured image and may include the average brightness of the pre-captured image in a region of interest (also referred to herein as the interactive region), such as a region of the image corresponding to the center of the detector and / or the center of the subject in the pre-captured image.

[0029] The method continues from 202 or 203 to 204, wherein the method includes identifying a reference projection image and determining an initial scan current based on the reference projection image. The reference projection image is a projection image acquired by the imaging system. As an example, the reference projection image may be a pre-captured image as described above. For example, during a period where a pre-captured image has already been acquired by the imaging system and a first projection image included in the scan of the subject has not yet been acquired, the imaging system may identify the pre-captured image as the reference image. As another example, during a period where the scan of the subject is in progress and at least one projection image following the pre-captured projection image has been acquired by the imaging system during the scan, the reference image may be a most recently acquired projection image (e.g., during a period where the pre-captured image is the only projection image acquired by the imaging system in the scan of the subject, the pre-captured image is the most recently acquired projection image identified as the reference image). The scan of the subject may be defined by a sequence of projection images acquired by the imaging system (e.g., a series of consecutive projection images). Projection images in sequence may be referred to herein as consecutive images.

[0030] In cases where the reference projection image is a pre-captured projection image (e.g., a pre-captured image has been acquired and other projection images have not yet been acquired for scanning), the initial scan current may be the pre-captured current. In other cases where multiple projection images have been acquired during the scan, the initial scan current may be the most recently actual current provided at the x-ray tube insert (e.g., the actual current provided at the x-ray tube insert when acquiring the most recently acquired projection image).

[0031] The current can be a function of the filament temperature, where both the filament temperature and current change over time (e.g., the filament temperature can change according to a first-order time function, and the current can be a function of the filament temperature). The filament temperature determines the number of free electrons in the filament (e.g., electrons that overcome the binding energy of the atomic nuclei forming the filament). The voltage supplied to the X-ray tube insert determines the number of free electrons reaching the anode of the X-ray tube insert (e.g., the percentage of total free electrons transferred to the anode of the filament). The electrons of individual atoms in the filament have different binding energy levels, where each binding energy level of the atom comprises multiple electrons. During periods where the filament temperature increases, the energy of a first group of electrons at a first binding energy level can increase, causing the first group of electrons to become unbound from the atom (e.g., free electrons). During periods where the filament temperature increases even further, the energy of a second group of electrons at a second binding energy level can increase, causing the second group of electrons to become unbound from the atom (e.g., where the bond between the second group of electrons and the nucleus is stronger than the bond between the first group of electrons and the nucleus). Therefore, the total number of free electrons can be based on the temperature of the filament, and the number of free electrons reaching the anode of the X-ray tube insert can be based on the voltage supplied to the X-ray tube insert.

[0032] The number of free electrons reaching the anode can be further increased by increasing the current supplied to the X-ray tube insert, or decreased by decreasing the current supplied to the X-ray tube insert. During periods where the filament temperature is low (e.g., 900 degrees Celsius), an increase in the amount of current supplied to the X-ray tube insert (e.g., increasing the current from 2 mA to 3 mA) results in a lower number of electrons reaching the anode, which in turn results in a lower intensity of X-ray radiation emitted by the X-ray tube insert. During periods where the filament temperature is high (e.g., 1000 degrees Celsius), the same increase in the amount of current supplied to the X-ray tube insert results in a larger number of electrons reaching the anode and a higher intensity of X-ray radiation emitted by the X-ray tube insert. Therefore, the current supplied to the X-ray tube insert can be controlled based on the filament temperature to provide a sufficient intensity of X-ray radiation emitted by the X-ray tube insert.

[0033] The method continues from 204 to 208, wherein the method includes determining a target current to be supplied to the X-ray tube insert based on an image level indicator (VLI) of a reference projection image for acquiring a scan projection image after the reference projection image. The scan projection image is the projection image immediately following the reference projection image in a scan sequence (e.g., in a sequence of scan projection images, the scan projection images are ordered sequentially after the reference projection image). The target current can be a current determined by a controller to provide a scan projection image with a desired (e.g., target) VLI. For example, the target VLI may have a value associated with optimized exposure of the scan projection image (e.g., exposure that results in a subject imaged by the imaging system that is sufficiently clear for subject analysis, diagnosis, etc., without exceeding the detector's maximum saturation level).

[0034] The target current associated with the scanned projection image is based on the VLI of the reference projection image, where the VLI of the reference projection image is defined as the average value of the reference projection image encoded with the square root in a given region of interaction (ROI). For example, the target current of the scanned projection image immediately following the reference projection image can be expressed by the following relationship: and VLI associated with the reference projection image, where It is the VLI value of the reference projection image (where the reference projection image has projection image number k in the order of the scanned image sequence). mA(k) This is the corresponding current supplied at the X-ray tube insert during the acquisition of the reference projection image. k VLI It is a proportionality coefficient, and VLI(k) and mA(k) The square root ratio.

[0035] To configure the scanned projection image immediately following the reference projection image to have a target image level indicator (VLI). VLI T via relational formula Calculate the target current in the projection image immediately following the reference projection image. The number of projection images in the scan is represented by (k + 1), where k is the number of projection images of the reference projection image as described above. By substituting... The relation becomes It can be determined (e.g., selected). VLI T To provide clinically relevant image projection quality (e.g., to provide image contrast suitable for clinicians to analyze the anatomy of a subject, diagnose the subject, etc.). Expression mA ( k +1) is the target current of the scanned projection image that immediately follows the reference projection image, and the relationship is further described below. and mA ( t ) = mA 0 +( mA c – mA 0)(1- In ) it is represented as mA ( t ).

[0036] The method continues from 208 to 210, wherein the method includes determining a correction current to be supplied to the x-ray tube insert based on a target current and a target transition duration for acquiring a scanned projection image after a reference projection image. The controller may use a lookup table or function stored in the controller's memory to determine the correction current. For example, the correction current may be a function of the target current and the target transition duration. As an example according to this disclosure, the target (e.g., desired) current at the x-ray tube insert, as a function of time, may be determined according to the relationship... mA (t) = mA 0 + (mA c – mA 0)(1 – And changes, among which mA 0 It is in time t = Initial scan current at 0 (e.g., the actual measured current). mA c It is in time t = Correction current (e.g., command current) at 0. T mA It is the time constant of the X-ray tube current, and mA(t) The target current is at time t. The current time constant may have a predetermined value stored in the controller's memory, and may be different for different X-ray tube inserts (e.g., the time constant may vary depending on the geometry, material, etc. of the X-ray tube insert). The corrected current is determined by solving... mA c This relationship can be represented as To calculate the correction current used to provide the target current at the X-ray tube insert during the target transition duration. mA c Time t Set the target transition duration (e.g., 100 milliseconds, 33 milliseconds, 7 milliseconds, etc.), and the target current can be set. mA(t) Set to the desired value (e.g., a value determined by the controller based on the VLI of the reference image as described above). Controller mAc The current can then be commanded as a correction current to adjust the system to the target current during the target transition duration, as described below. As another example according to this disclosure, the target current at the x-ray tube insert, as a function of time, can be determined according to the relationship... And the changes, among which mA ( t ) is the target current at time t, and Based on initial current mA 0 and the difference between the initial current and the correction current at time t = 0 δmA The coefficients of the analytical cost function. f(δmA) = In order to calculate the correction current mA c .

[0037] The method at 210 may optionally include, at 212, determining the target transition duration based on the image acquisition rate of the scan. For example, the image acquisition rate may be based on the number of projected images scanned and / or the duration of the scan. As an example, in a case where the scan duration is 30 seconds and the total number of projected images to be included in the scan (e.g., to be acquired by the imaging system during the scan) is 300, the image acquisition rate may be ten projected images per second (e.g., one projected image every tenth of a second). In this case, the target transition duration may be one-tenth of a second (100 milliseconds). The target transition duration may also be a commanded duration based on the rotational speed of the C-arm and the scan range. For example, in a case where the scan range is 200 degrees around the subject (e.g., the C-arm of the imaging system rotates 200 degrees around the subject), the desired number of projections to be acquired during the scan is one projection per degree, and the desired rotational speed (e.g., angular velocity) of the C-arm is 5 degrees per second, the system may acquire 200 images in 40 seconds. In this case, the image acquisition rate may be five projected images per second (e.g., one projected image every fifth of a second). The target transition duration during this situation can be one-fifth of a second (200 milliseconds). Other transition durations are possible.

[0038] The method continues from 210 to 214, wherein the method includes transitioning the actual current supplied to the x-ray tube insert toward a correction current throughout the entire target transition duration to provide a target current to the x-ray tube insert at the end of the target transition duration. Specifically, the controller controls the actual current supplied to the x-ray tube insert by commanding the current to be a correction current. Because once the target transition duration has elapsed, the controller determines that commanding the current to be a correction current will cause the actual current to reach the target current (e.g., the controller commands the target transition duration to elapse between the acquisition of consecutive images of the subject during a scan of the imaging system, wherein the acquisition of a given image and the acquisition of another image immediately following the given image are separated by a commanded target transition duration time interval), the controller provides the target current at the x-ray tube insert at the end of the target transition duration.

[0039] The method continues from 214 to 216, wherein the method includes acquiring a scan projection image at the end of the target transition duration. Acquiring the scan projection image may include emitting X-ray radiation from an X-ray tube insert through the subject to be imaged and receiving attenuated X-ray radiation at a detector. A controller may generate the scan projection image based on the attenuated X-ray radiation received by the detector. The scan projection image is acquired at the end of the transition duration such that the actual current provided at the X-ray tube insert is equal to the aforementioned target current (e.g., the target current determined at 208).

[0040] As described above, due to the delay associated with transitioning the current to a target current with the desired value (e.g., due to the slow response time of adjusting the current to the target current during the case where the current is directly commanded to be the target current), once the target transition duration has passed, commanding the current to the target current can result in the actual current supplied at the X-ray tube insert differing from the target current. However, by commanding the current to a correction current, the controller ensures that the actual current is approximately equal to the target current at the end of the target transition duration. Therefore, by commanding the current to a correction current instead of the target current, the controller is able to control the actual current to the target current for a relatively short duration (e.g., the target transition duration) compared to conventional imaging systems. (Refer to below) Figures 3 to 5 Describe an example of controlling the actual current by commanding the current as a correction current.

[0041] Because the current can be rapidly adjusted by controlling the current according to this disclosure, the imaging acquisition rate can be increased, which in turn increases the speed of scanning the subject. Increasing the scanning speed may result in a lower likelihood of image artifacts or aberrations caused by the subject's movement during the scan (e.g., breathing or other intentional or unintentional movement). Therefore, image quality can be improved. Furthermore, since the current can be rapidly adjusted, the voltage supplied to the X-ray tube insert can be maintained at a constant voltage (e.g., a voltage with a constant value), which increases the ease of imaging the subject and / or reduces the likelihood of detector oversaturation. For example, the voltage can be maintained at a determined scan voltage throughout the scan duration (e.g., the same constant voltage can be commanded throughout the scan duration, and the command voltage can remain unchanged throughout the scan). The voltage at the X-ray tube can be a scan voltage determined during the acquisition of each image of the subject's scan (e.g., X-ray radiation can be emitted by the X-ray tube, and the command voltage of the X-ray tube is maintained at the same determined scan voltage for each image in the entire sequence of scanned images). In particular, a "constant" voltage as described herein means a voltage value that varies by less than 2% throughout the entire scan duration. Therefore, by maintaining a constant voltage and adjusting the current as described above, it is possible to more clearly image parts of the anatomical structures of subjects with different thicknesses.

[0042] refer to Figure 3 The diagram 300 is shown. Graph 300 includes curve 304, which shows the actual (e.g., measured) current supplied to the X-ray tube insert of the imaging system by commanding the current as a correction current, similar to the example above. The imaging system and the X-ray tube insert are respectively compatible with… Figure 1 The imaging system 100 and X-ray tube insert 109 described above are similar to or identical to those shown. Graph 300 further includes curve 316 showing the corrected current value commanded by the imaging system's controller, curve 306 showing the target current value, and a marker 314 arranged along curve 304 indicating the actual current value at the end of the target transition duration (indicated by a vertical axis 302 arranged 100 milliseconds along a horizontal axis indicating the time). Furthermore, graph 300 includes curve 308, which shows the actual current value provided at the X-ray tube insert in a conventional imaging system during cases where the current is directly commanded as the target current (e.g., not commanded as the corrected current as described in this disclosure). Marker 312 is arranged along curve 308 to indicate the actual current value at the time indicated by the vertical axis 302, where curves 304 and 308 each begin at 0 milliseconds.

[0043] As indicated by curve 308, the current supplied to the X-ray tube insert during the scanning process via a conventional imaging system is from the initial current (in... Figure 3The example shown is 2 mA) directly commanded as the target current (in Figure 3 During the case of 3 mA in the example shown, the transition from the initial current to the target current may be relatively slow compared to the image acquisition rate of the imaging system. In the example shown, the image acquisition rate is one image every 100 milliseconds. At 0 seconds along the horizontal axis, the current supplied at the X-ray tube insert in a conventional imaging system (e.g., the initial current) is directly commanded as the target current. Because the image acquisition rate is one image every 100 milliseconds, a projected image can be acquired along the horizontal axis within 100 milliseconds (e.g., the time indicated by the vertical axis 302). However, due to the relatively slow adjustment rate of the current, at 100 milliseconds along the horizontal axis, the current indicated by curve 308 has a value of approximately 2.35 mA. Therefore, the actual current supplied at the X-ray tube insert will not reach the target current before the image is acquired at 100 milliseconds.

[0044] However, by controlling the operation of the imaging system according to this disclosure, the rate of adjustment of the current from the initial current to the target current is significantly improved. For example, curve 304 shows the current supplied at the X-ray tube insert during the case where the current is commanded from the initial current at 0 seconds to the correction current (indicated by curve 316). Because the correction current is higher than the target current, the actual current transitions from the initial current to the target current much faster (e.g., at a higher rate) compared to a configuration where the actual current is directly commanded from the initial current to the target current. In particular, the actual current transitions from the initial current (at... Figure 3 The example shown transitions between 2 mA at 0 seconds and 100 milliseconds, and reaches the target current at 100 milliseconds. Figure 3 (3 mA in the example shown), as indicated by label 314. The actual current may transition toward the correction current in a logarithmic manner (e.g., the actual current may change at a higher rate toward the beginning of the transition duration than it does toward the end of the transition duration).

[0045] At 100 milliseconds, the imaging system acquires a projected image and can update the target current based on the acquired projected image (e.g., by updating a reference image to identify the acquired projected image as the reference image, as mentioned above). Figure 2(This may be referred to herein as the updated reference image). The controller can determine an updated correction current based on the updated target current and can command the current at 100 milliseconds to transition toward the updated correction current. By transitioning the current toward the updated correction current, the actual current can have the value of the updated target current when acquiring subsequent projected images (e.g., at 200 milliseconds along the horizontal axis). A similar determination can be made for each subsequent projected image scanned such that the actual current provided at the X-ray tube insert used to acquire a given projected image is approximately equal to the target current associated with the given projected image.

[0046] refer to Figure 4 Another graph 400 is shown. Graph 400 includes curve 404, which shows the actual (e.g., measured) current supplied to the X-ray tube insert of the imaging system by commanding the current as a correction current, similar to the example above. The imaging system and the X-ray tube insert are respectively compatible with... Figure 1 The imaging system 100 and X-ray tube insert 109 described above are similar to or identical to those shown. Graph 400 further includes curve 416 showing the corrected current value commanded by the imaging system's controller, curve 406 showing the target current value, and a marker 412 arranged along curve 404 indicating the actual current value at the end of the target transition duration (indicated by a vertical axis 402 arranged 100 milliseconds along a horizontal axis indicating the time). Furthermore, graph 400 includes curve 408, which shows the actual current value provided at the X-ray tube insert in a conventional imaging system during cases where the current is directly commanded as the target current (e.g., not commanded as the corrected current as described in this disclosure). Marker 414 is arranged along curve 408 to indicate the actual current value at the time indicated by the vertical axis 402, where curves 404 and 408 each begin at 0 milliseconds.

[0047] As indicated by curve 408, the current supplied to the X-ray tube insert during the scanning process via a conventional imaging system is from the initial current (in... Figure 4 The example shown is 2 mA) directly commanded as the target current (in Figure 4During the period shown (1 mA in the example), the transition from the initial current to the target current may be relatively slow compared to the image acquisition rate of the imaging system. In the example shown, the image acquisition rate is one image every 100 milliseconds. At 0 seconds along the horizontal axis, the current supplied at the X-ray tube insert (e.g., the initial current) in a conventional imaging system is directly commanded as the target current. Because the image acquisition rate is one image every 100 milliseconds, a projected image can be acquired along the horizontal axis within 100 milliseconds (e.g., the time indicated by the vertical axis 402). However, due to the relatively slow adjustment rate of the current, at 100 milliseconds along the horizontal axis, the current indicated by curve 408 has a value of approximately 1.5 mA. Therefore, the actual current supplied at the X-ray tube insert will not reach the target current before the image is acquired at 100 milliseconds.

[0048] However, by controlling the operation of the imaging system according to this disclosure, the adjustment speed of the current from the initial current to the target current is significantly improved (e.g., similar to the above reference). Figure 3 (The example described above). For example, curve 404 shows the current supplied at the X-ray tube insert during a scenario where the current is commanded from the initial current at 0 seconds to the correction current (indicated by curve 416). Because the difference between the initial current and the correction current is greater than the difference between the initial current and the target current, the initial current transitions toward the target current much faster (e.g., at a higher rate) compared to a configuration where the initial current is directly commanded to the target current. In particular, the actual current transitions from the initial current at 0 seconds to a time of 100 milliseconds, and reaches the target current at 100 milliseconds (e.g., at...). Figure 4 The example shown is 1 mA, as indicated by label 412.

[0049] At 100 milliseconds, the imaging system acquires a projected image and can update the target current based on the acquired projected image (e.g., by updating a reference image to identify the acquired projected image as the reference image, as mentioned above). Figure 2 (This may be referred to herein as the updated reference image). The controller can determine an updated correction current based on the updated target current and can command the current at 100 milliseconds to transition toward the updated correction current. By transitioning the current toward the updated correction current, the actual current can have the value of the updated target current when acquiring subsequent projected images (e.g., at 200 milliseconds along the horizontal axis). A similar determination can be made for each subsequent projected image scanned such that the actual current provided at the X-ray tube insert used to acquire a given projected image is approximately equal to the target current associated with the given projected image.

[0050] In one example Figure 3 The curves shown are 304 and Figure 4 The curve 404 shown can be associated with different scans performed by the imaging system 100 (e.g., Figure 3 Curve 304 illustrates the operating conditions during the first scan, and curve 404 illustrates the operating conditions during a different second scan. In another example, curves 304 and 404 can be associated with a single scan performed by the imaging system (e.g., curve 304 may represent the conditions during the first portion of the scan, and curve 404 may represent the conditions during the second portion of the scan, where the 0-second time along the horizontal axis indicating time in curve 300 is relative to the start of the first portion, and the 0-second time along the horizontal axis indicating time in curve 400 is relative to the start of the second portion). Although in Figures 3 to 4 In the example shown, the image acquisition rate is one image every 100 milliseconds, but in other examples, the image acquisition rate may be different (e.g., one image every 33.3 milliseconds, one image every 66.6 milliseconds, etc.).

[0051] During periods when the target current is higher than the initial current (e.g., the actual current supplied at the X-ray tube insert during the initial transition of current toward the target current), the value of the correction current commanded by the imaging system's controller is higher than the value of the target current (e.g., as...). Figure 3 Curve 316 indicates that the correction current is greater than both the target current and the initial current, as indicated by curve 306 (the initial current being the actual current supplied at the X-ray tube at 0 seconds along the horizontal time axis). Furthermore, during periods where the target current is lower than the initial current, the value of the correction current commanded by the imaging system's controller is lower than the value of the target current (e.g., as indicated by curve 306). Figure 4 Curve 416 indicates that the corrected current is less than both the target current and the initial current, as indicated by curve 406 (the initial current being the actual current supplied at the X-ray tube at 0 seconds along the horizontal time axis). In this configuration, the absolute value of the difference between the initial current and the target current is less than the absolute value of the difference between the initial current and the corrected current. As an example, such as... Figure 3 As shown, the absolute value of the difference 301 between the initial current and the target current is less than the absolute value of the difference 303 between the initial current and the correction current. As another example, such as... Figure 4 As shown, the absolute value of the difference 401 between the initial current and the target current is less than the absolute value of the difference 403 between the initial current and the correction current. During the period when the target current is the same as the initial current, the correction current can be the same as both the target current and the initial current.

[0052] refer to Figure 5The diagram 500 illustrates the current supplied to the X-ray tube of an imaging system (e.g., to an X-ray tube insert housed within the X-ray tube). Figure 1 The C-arm imaging system 100 shown above. Specifically, graph 500 includes curve 502, which shows the target current (e.g., similar to the one described above) throughout the entire duration of the scan of the subject. Figure 2 The target current is stated above, and curve 504, plotted as a dashed line, shows the actual current provided at the X-ray tube insert. The actual current is determined by... Figure 2 The controller shown and described in method 200 above (e.g., Figure 1 The controller 120 shown above controls the current. Specifically, the controller adjusts the actual current to closely match the target current by using a current command as a correction current, wherein the correction current can be as described above. Figure 2 The target current is a function of the X-ray tube. The X-ray tube and the X-ray tube insert can be respectively connected to... Figure 1 The X-ray tube 108 and X-ray tube insert 109 shown are similar to or the same as those described above. Graph 500 is a working example presenting experimental results in an imaging system operated according to the methods described herein.

[0053] In one embodiment, the mobile C-arm system includes: an X-ray tube that generates a two-dimensional X-ray field based on command kVp and mA; an X-ray detector that converts the two-dimensional X-ray field into a two-dimensional digital image; a C-frame that rotates about an isocenter to produce a projected image; a control mechanism that commands the X-ray tube to generate X-rays on each projection, wherein a constant kVp is applied to all projections during a 3D scan, wherein the kVp value varies with an anatomical size determined by a pre-shot taken at the start of the 3D scan, and an initial mA is determined with the same pre-shot as the kVp; and a request for an over-command mA from the X-ray tube such that the desired mA is subsequently achieved from projection to projection, wherein the over-command mA value is determined based on the tube mA model and the image level of the projected image.

[0054] In one embodiment, a method for generating X-rays in a 3D scan of a mobile C-arm system includes: determining an anatomically size-dependent tube kVp value and an initial tube mA value for the 3D scan by taking a pre-shot at the start of the scan; calculating the image level from a projected image in the interactive region; calculating the desired mA based on the target image level of the next projection; and obtaining the command mA for the next projection based on the tube mA model.

[0055] This disclosure also provides support for an imaging system comprising: a C-shaped gantry; an X-ray tube coupled to a first end of the C-shaped gantry; an X-ray detector coupled to a second end of the C-shaped gantry opposite the X-ray tube; and a controller having computer-readable instructions stored in a non-transitory memory, the computer-readable instructions, when executed, causing the controller to: identify a reference image; determine a target current based on the reference image; determine a correction current based on the target current; and transition a current supplied to the X-ray tube to the target current by commanding the current to the correction current while maintaining a constant voltage supplied to the X-ray tube. In a first example of the system, determining the correction current based on the target current includes calculating the correction current according to the target current, wherein the correction current is less than both the target current and the current supplied to the X-ray tube, or greater than both the target current and the current supplied to the X-ray tube. In a second example of the system, optionally including the first example, the system further includes: computer-readable instructions stored in the non-transitory memory, which, when executed, cause the controller to: acquire a series of images in a single scan of the subject while rotating the C-shaped gantry around the subject; and for each image in the series of images, when acquiring each image: identify the most recently acquired image in the series of images as an updated reference image; determine an updated target current based on the updated reference image; determine an updated correction current based on the updated target current; and transition the current supplied to the x-ray tube to the updated target current by commanding the current to the updated correction current while maintaining the constant voltage supplied to the x-ray tube. In a third example of the system, optionally including one or both of the first and second examples, the constant voltage is based on the reference image and is maintained for each image acquired over the entire duration of a scan performed by the imaging system.In a fourth example of the system, optionally including one or more or each of the first to third examples, the system further includes: computer-readable instructions stored in the non-transitory memory, which, when executed, cause the controller to: acquire an image of a subject by: first, performing the identification of the reference image; then performing the determination of the target current based on the reference image; then performing the determination of the correction current based on the target current; then performing a transition of the current supplied to the x-ray tube to the target current by commanding the current to the correction current while maintaining the constant voltage supplied to the x-ray tube; and then emitting x-ray radiation from the x-ray tube and receiving attenuated x-ray radiation at the x-ray detector while maintaining the constant voltage supplied to the x-ray tube and maintaining the current supplied to the x-ray tube at the target current. In a fifth example of the system, optionally including one or more or each of the first to fourth examples, the correction current is a function of the target current, the current supplied to the x-ray tube, and the command duration between the acquisition of continuous images of the subject, and the target current is a function of the image level indicator of the reference image and the initial current supplied to the x-ray tube during the acquisition of the reference image. In a sixth example of the system, optionally including one or more or each of the first to fifth examples, the correction current is defined by: This disclosure also provides support for, wherein the correction current is the target current at time, is the initial current, and is the time constant of the x-ray tube. In a first example of the system, the target current is defined by: wherein the target current is the target current at time, and is a coefficient based on the initial current and the difference between the initial current and the correction current at time = 0. In a second example of the system, optionally including the first example, the target current is defined by: wherein the target current is the target image level indicator, is the image level indicator of the reference image, and is the initial current.

[0056] This disclosure also provides a method for a C-arm imaging system, the method comprising: determining an initial current supplied to an X-ray tube during the acquisition of a reference image; determining an image level of an interactive region within the reference image; determining a target current to be supplied to the X-ray tube based on the image level; determining a correction current based on the target current; and adjusting the actual current supplied to the X-ray tube from the initial current to the target current by commanding the actual current as the correction current. In a first example of the method, the absolute value of the difference between the initial current and the target current is less than the absolute value of the difference between the initial current and the correction current. In a second example of the method, optionally including the first example, the image level of the interactive region is proportional to the initial current. In a third example of the method, optionally including one or both of the first and second examples, the image level is defined by the following formula: where is the image level of the interactive region, is the initial current, and is a scaling factor. In a fourth example of the method, optionally including one or more or each of the first to third examples, the method further includes: maintaining the scan voltage at a constant value throughout the entire duration for which the actual current is adjusted from the initial current to the target current. In a fifth example of the method, optionally including one or more or each of the first to fourth examples, the method further includes: determining the image acquisition rate of the C-arm imaging system based on the rotational speed of the C-arm; and determining the transition duration of the actual current from the initial current to the target current based on the image acquisition rate. In a sixth example of the method, optionally including one or more or each of the first to fifth examples, the correction current is based on the transition duration.

[0057] This disclosure also provides support for an imaging method comprising: identifying a reference projection image and determining an initial current for an x-ray tube based on the reference projection image; determining a target current to be supplied to the x-ray tube based on an image level indicator (VLI) of the reference projection image; determining a correction current for a projection image immediately following the reference projection image in a scanned image sequence based on the target current; and adjusting an actual current at the x-ray tube from the initial current toward the correction current until the actual current equals the target current, and then acquiring the projection image when the actual current equals the target current. In a first example of the method, determining the correction current for the projection image based on the target current includes determining a transition duration between the reference projection image and the projection image based on the image acquisition rate of the scan and adjusting the correction current based on the transition duration. In a second example of the method, optionally including the first example, the duration for adjusting the actual current from the initial current to the target current equals the transition duration is further included, and also includes maintaining a constant voltage at the x-ray tube throughout the transition duration. In a third example of the method, optionally including one or both of the first and second examples, adjusting the actual current toward the correction current includes logarithmically increasing or decreasing the actual current toward the correction current, wherein the target current is between the initial current and the correction current.

[0058] As used herein, unless otherwise specified, the term “approximately” is understood to mean ±5% of the range.

[0059] As used herein, elements or steps listed in the singular and beginning with the word "a" or "an" should be understood to not exclude a plurality of said elements or steps unless such exclusion is explicitly stated. Furthermore, references to "one embodiment" of the invention are not intended to be construed as excluding the existence of additional embodiments that also include the referenced features. Moreover, unless explicitly stated to the contrary, embodiments that "comprise," "include," or "have" elements or multiple elements having a particular characteristic may include additional such elements that do not have that characteristic. The terms "comprise" and "in..." are used as concise linguistic equivalents to the corresponding terms "comprising" and "wherein". Furthermore, the terms "first," "second," and "third," etc., are used merely as notations and are not intended to impose numerical requirements or a particular order of position on their objects.

[0060] This written description uses examples to disclose the invention, including the best mode, and also enables those skilled in the art to practice the invention, including making and using any device or system and performing any included methods. The scope of patentability of the invention is defined by the claims and may include other examples that would occur to those skilled in the art. Such other examples are intended to fall within the scope of the claims if they have structural elements that are not indistinguishable from the literal language of the claims, or if they include equivalent structural elements that have minor differences from the literal language of the claims.

Claims

1. An imaging system (100), the imaging system comprising: C-shaped frame (102); X-ray tube (108), the X-ray tube being connected to the first end (152) of the C-shaped frame (102); An x-ray detector (130) is attached to a second end (150) of the C-frame (102) opposite the x-ray tube (108); and Controller (120), the controller having computer-readable instructions stored in non-transitory memory, the computer-readable instructions causing the controller (120) to: Identify the reference image; The target current (306) is determined based on the reference image. The correction current (316) is determined based on the target current (306); and By maintaining a constant voltage supplied to the x-ray tube (108) while commanding the current (304) supplied to the x-ray tube (108) as the correction current (316), the current (304) supplied to the x-ray tube (108) is transitioned to the target current (306). Determining the correction current (316) based on the target current (306) includes calculating the correction current (316) based on the target current (306), wherein the correction current (316) is less than both the target current (306) and the current (304) supplied to the x-ray tube (108), or greater than both the target current (306) and the current (304) supplied to the x-ray tube (108).

2. The imaging system (100) according to claim 1, further comprising computer-readable instructions stored in the non-transitory memory, the computer-readable instructions causing the controller, when executed, to: While the C-shaped frame (102) rotates around the subject (134), a series of images are acquired in a single scan of the subject (134); and For each image in the series of images, when acquiring each image: The most recently acquired image in the series of images is identified as the updated reference image; The updated target current is determined based on the updated reference image; The updated correction current is determined based on the updated target current; as well as By maintaining the constant voltage supplied to the x-ray tube (108) while commanding the current supplied to the x-ray tube to the updated correction current, the current supplied to the x-ray tube is transitioned to the updated target current.

3. The imaging system (100) of claim 1, wherein the constant voltage is based on the reference image and is maintained for each image acquired over the entire duration of a scan performed by the imaging system (100).

4. The imaging system (100) according to claim 1, further comprising computer-readable instructions stored in the non-transitory memory, the computer-readable instructions causing the controller, when executed, to: Images of the subjects (134) were acquired using the following methods: First, the recognition of the reference image is performed; then The determination of the target current (306) is performed based on the reference image; then The determination of the correction current (316) is performed based on the target current (306); then The transition of the current (304) supplied to the x-ray tube (108) to the target current (306) is performed by commanding the current (304) to the correction current (316) while maintaining the constant voltage supplied to the x-ray tube (108); then While maintaining the constant voltage supplied to the x-ray tube (108) and maintaining the current (304) supplied to the x-ray tube (108) at the target current (306), x-ray radiation is emitted from the x-ray tube (108) and attenuated x-ray radiation is received at the x-ray detector (130).

5. The imaging system (100) according to claim 1, wherein the correction current (316) is a function of the command duration between the target current (306), the current (304) supplied to the x-ray tube (108), and the acquisition of continuous images of the subject (134); and The target current (306) is a function of the image level indicator of the reference image and the initial current supplied to the x-ray tube during the acquisition of the reference image.

6. The imaging system (100) according to claim 1, wherein the correction current (316) is defined by the following formula: in It is the correction current, The target current is located at time t. It is the initial current, and It is the time constant of the X-ray tube.

7. The imaging system (100) according to claim 1, wherein the target current (306) is defined by the following formula: in It is the target current. It is a target image level indicator. It is the image level indicator of the reference image, and It is the initial current.

8. A method for a C-arm imaging system (100), the method comprising: Determine the initial current supplied to the x-ray tube (108) during the acquisition of the reference image; Determine the image level of the interactive region within the reference image; The target current (306) to be supplied to the x-ray tube (108) is determined based on the image level. The correction current (316) is determined based on the target current (306); and By commanding the current (304) supplied to the x-ray tube (108) as the correction current (316), the current (304) supplied to the x-ray tube (108) is adjusted from the initial current to the target current (306). The absolute value of the difference between the initial current and the target current (306) is less than the absolute value of the difference between the initial current and the correction current (316).

9. The method of claim 8, wherein the image level of the interactive region is proportional to the initial current.

10. The method of claim 8, wherein the image level is defined by the following formula: in It is the image level of the interactive area. It is the initial current, and It is the proportionality coefficient.

11. The method according to claim 8, further comprising: The scanning voltage is maintained at a constant value throughout the entire duration during which the current (304) supplied to the x-ray tube (108) is adjusted from the initial current to the target current (306).

12. The method according to claim 8, further comprising: The image acquisition rate of the C-arm imaging system (100) is determined based on the rotational speed of the C-shaped gantry (102) of the C-arm imaging system (100); and The transition duration (302) of the current (304) supplied to the x-ray tube (108) from the initial current to the target current (306) is determined based on the image acquisition rate, wherein the correction current (316) is based on the transition duration.

Images