System and method for X-ray imaging

Abstract

The present invention provides methods and systems for controlling an x-ray imaging system. In one embodiment, the method for an x-ray imaging system includes: acquiring a first image using the x-ray imaging system while an x-ray tube current of the x-ray imaging system is ramped up to a target x-ray tube current; determining a corrected brightness of the first image; the corrected brightness including a measured brightness of the first image, the measured brightness corrected by a feedback x-ray tube current relative to the target x-ray tube current; and updating the target x-ray tube current based on the corrected brightness of the first image.

Description

Technical Field

[0001] Embodiments of the subject matter disclosed herein relate to medical imaging, and more particularly to x-ray fluoroscopic imaging. Background Art

[0002] Non-invasive imaging techniques allow images of internal structures or features of a patient or object to be obtained without performing an invasive procedure on the patient or object. Specifically, such non-invasive imaging techniques rely on various physical principles (such as differential transmission of x-rays through a target volume or reflection of sound waves) to acquire data and construct an image or otherwise represent the observed internal features of a patient or object.

[0003] For example, in fluoroscopy and other x-ray-based imaging techniques, x-ray radiation is directed at a subject, typically a patient in medical diagnostic applications, a package or luggage in security screening applications, or a manufactured component in industrial quality control or inspection applications. A portion of the radiation strikes a detector where image data is collected and used in the image generation process. In the images produced by such systems, it is possible to identify and inspect internal structures and organs within a patient's body, objects within a package or container, or defects (e.g., cracks) within a manufactured component. In some cases, such as in fluoroscopy applications used to support interventional or navigation procedures, low-dose x-rays may be acquired at a high frame rate over an extended period of time to provide real-time image data that can be used to guide or navigate tools within a patient's body. Summary of the invention

[0004] In one embodiment, a method for an x-ray imaging system includes: acquiring a first image with the x-ray imaging system while an x-ray tube current of the x-ray imaging system is ramped up to a target x-ray tube current; determining a corrected brightness of the first image; the corrected brightness comprising a measured brightness of the first image corrected by a feedback x-ray tube current relative to the target x-ray tube current; and updating the target x-ray tube current based on the corrected brightness of the first image.

[0005] It should be understood that the above brief description is provided to introduce in a simplified form selected concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is solely defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present disclosure will be better understood by reading the following description of non-limiting embodiments with reference to the accompanying drawings, in which:

[0007] Figure 1 depicts a block diagram of an embodiment of a digital x-ray imaging system according to aspects of the present disclosure;

[0008] Figure 2 Depicted are implementations of x-ray imaging systems according to aspects of the present disclosure;

[0009] Figure 3 is a flow chart illustrating a method for operating an x-ray imaging system;

[0010] Figure 4 An exemplary index jump lookup table is shown;

[0011] Figure 5 An exemplary index table is shown; and

[0012] Figure 6 An exemplary timeline of image acquisition events, set currents, and measured currents during an automatic brightness stabilization routine is shown. DETAILED DESCRIPTION

[0013] The following description relates to various embodiments that reduce the time from the start of x-ray imaging until an image with stable / target brightness is acquired. During surgical procedures monitored / assisted by fluoroscopic imaging, a continuous real-time x-ray image of the patient can be displayed, allowing the clinician to monitor the movement of anatomical features. During such procedures, it may also be useful to occasionally monitor the patient using a single stationary x-ray image. To initiate fluoroscopic imaging, an exposure control pedal may be depressed, for example, by the clinician's foot. A quick depression and release (e.g., a tap) of the exposure control pedal may indicate that the clinician is requesting a single x-ray image, wherein an extended depression of the exposure control pedal may indicate that the clinician is requesting fluoroscopic imaging.

[0014] Typically, to obtain a high quality x-ray image, a sequence of steps is performed before a stabilized image is acquired and output for display, a sequence referred to as automatic brightness stabilization (ABS). These steps may include preparing the imaging system for exposure; exposing the patient to a radiation beam by activating a radiation source, such as an x-ray tube; and adjusting the voltage and current of the radiation source based on the brightness of the resulting image acquired by the radiation detector. Once the target brightness is reached, further image quality adjustments may be made, such as by applying a temporal noise filter. Once the image reaches a target contrast-to-noise ratio, a stabilized image may be acquired and output for display, and continuous imaging may then be performed as desired.

[0015] The above-described ABS sequence may be relatively long, in part because of system delays caused by the time required to complete the following operations: obtaining an image frame, determining the brightness of the image frame, and then adjusting the radiation source parameters based on the brightness of the image frame. In addition, the radiation source cannot quickly reach the command current using certain types of x-ray tubes. In contrast, although the x-ray tube can reach the command voltage almost instantaneously, the current of the x-ray tube is based on the tube voltage and the temperature of the x-ray tube filament. Therefore, the x-ray tube does not reach the command current until the filament is heated or cooled to a certain temperature, and the time taken to change the filament temperature may be relatively long. During the time when the current is ramped toward the command current, the acquired image may be saturated or otherwise too dark to fully visualize the patient's anatomical features. Therefore, the ABS sequence may wait until the target x-ray tube current (e.g., 3.9 mA) is reached, and then the image can be acquired. Once the image is acquired, the initial command voltage and current are further adjusted (e.g., based on the above-described image brightness), because the actual tube voltage and current required to acquire a high-quality image vary with the patient's anatomical structure, which also prolongs the process.

[0016] According to embodiments disclosed herein, an automatic brightness stabilization sequence of a fluoroscopic imaging system can be shortened by utilizing a predicted brightness of a final stabilized image as an input to determine target x-ray imaging parameters (e.g., current, voltage, and camera gain) as the current ramps toward a target current based on the understanding that the brightness of an image is proportional to the current used to acquire the image. For example, an x-ray system can be activated using initial / default settings (e.g., voltage, current, and gain), and once a first image is acquired, a predicted brightness can be determined based on the relationship between the brightness of the first image and the x-ray tube current used to acquire the first image, rather than using the actual brightness of the first image to determine the predicted brightness. The predicted brightness can be used to obtain a target voltage, current, and gain from a set of indices, and command the system to transmit a radiation beam at the target voltage and current. If the corrected brightness is not within a stabilization window around the target brightness, the process can continue as the tube current ramps from the initial current to the new target current until a stabilized image is achieved.

[0017] Thus, by using the predicted brightness of a future stable image rather than the current brightness of the current image, the time to actually reach a stable brightness can be reduced. In doing so, the amount of radiation to which the patient is exposed can be reduced, and a stable image can be displayed more quickly than during the longer sequence described above, which may be beneficial during time-sensitive procedures. The image stabilization process described herein takes into account the actual x-ray tube current used to acquire the image. For example, an image may be acquired using a preset x-ray technique of 70 kV and 4 mA, but due to the slow response of the x-ray tube filament, the actual current when acquiring the image may be 2 mA. The brightness of the image may be determined (e.g., a video level indication (VLI) of 78). Without the brightness correction described herein, the kV / mA may be adjusted until the measured brightness is within a stable window (e.g., a VLI of ±6% of 110), which may take an excessively long time because the system will need to wait until the current stabilizes to obtain a stable brightness for the examination. For example, an existing method for acquiring an image with a stable target brightness includes waiting until the brightness stabilizes, then determining whether the stable brightness is within a stable window, and adjusting the kV / mA if it is not within the stable window. Another existing method includes adjusting the kV / mA for each frame in a small step-wise manner, regardless of whether the brightness is stable. In either method, the time to reach the target stable brightness is slow.

[0018] In contrast, the stabilization process described herein may correct the brightness based on the actual x-ray tube current at the time the image was acquired (as will be described in more detail below). In the example presented above where the measured brightness of the image was a VLI of 78 and the actual x-ray tube current was 2 mA, the corrected VLI may be 110, within the stabilization window, so the image will be determined to be stable and no additional adjustments will be made to the voltage or current. Although it may take approximately 500 ms for the filament to fully reach a stable target current, the filament may reach 90% of the target current in approximately 200 ms, so after 200 ms, the brightness of the image may be robust enough for measurement, and once corrected, it is predicted that a stable brightness will be reached without further correction of the voltage or current. In doing so, the number of images that may need to be acquired in order to check the brightness may be reduced, thereby reducing the number of adjustments to the x-ray technique to reach a final stable brightness.

[0019] Although a fluoroscopic imaging system is described by way of example, it should be understood that the present technology may also be useful when applied to images acquired using other imaging modalities, such as standard, non-fluoroscopic x-ray imaging, tomosynthesis, etc. The present discussion of the fluoroscopic imaging modality is provided merely as an example of one suitable imaging modality.

[0020] Figure 1An imaging system 10 for acquiring and processing image data is schematically illustrated. In the illustrated embodiment, the system 10 is a digital x-ray system designed to both acquire raw image data and process the image data for display. The imaging system 10 may be a fixed or mobile x-ray system. Figure 1 In the illustrated embodiment, the imaging system 10 includes an x-ray radiation source 12 that emits a radiation beam or stream 16 into an area in which an object or subject 18 is positioned. The x-ray radiation source 12 (which may include an x-ray generator and an x-ray tube) is controlled by a power supply / control circuit 24 that provides power signals and control signals for the inspection sequence. A portion of the radiation 20 passes through or around the subject and strikes a digital x-ray detector, which is generally indicated by the reference numeral 22. The detector 22 may be portable or permanently mounted to the system 10. In certain embodiments, the detector 22 may convert incident x-ray photons into detected lower energy photons. Electrical signals are generated in response to the detected photons, and these signals are processed to reconstruct an image of features within the object or subject.

[0021] The detector array 22 may include one or more CMOS light imager panels, each of which individually defines an array of detector elements (e.g., pixels). Each detector element generates an electrical signal representing the intensity of the x-ray beam incident at the location of the detector element when the beam strikes the detector 22. This signal may be digitized and sent to a monitor / display device for display. In the depicted example, the detector 22 includes or communicates with a detector controller 26 (e.g., a control circuit) that commands the acquisition of signals generated in the detector 22. In the embodiment currently shown, the detector 22 may communicate with the detector controller 26 via any suitable wireless communication standard (R), but it is also contemplated to use a digital x-ray detector 22 that communicates with the detector controller 26 via a cable (T) or some other mechanical connection. Alternatively, in some embodiments, operational aspects of the detector controller 26 may be implemented or otherwise provided on the detector 22 itself. The detector controller 26 may also perform various signal processing and filtering functions, such as initial adjustment for dynamic range, interleaving of digital image data, and the like.

[0022] Both the power / control circuit 24 and the detector controller 26 are responsive to signals from a system controller 28. Generally speaking, the system controller 28 commands the operation of the imaging system to execute the examination protocol and process the acquired image data. In the present case, the system controller 28 may also include signal processing circuitry and one or more data storage structures such as optical memory devices, magnetic memory devices, or solid-state memory devices for storing programs and routines executed by the processor of the system 10 to perform various functions, as well as for storing configuration parameters and image data. In one embodiment, a programmed computer system may be provided with hardware, circuitry, firmware, and / or software for performing the functions attributed to one or more of the power / control circuit 24, the detector controller 26, and / or the system controller 28.

[0023] exist Figure 1 In the illustrated embodiment, the system controller 28 is linked to at least one output device, such as a display or printer as indicated by reference numeral 30. The output device may include a standard monitor or a dedicated monitor and associated processing circuitry. One or more operator workstations 32 may be further linked in the system for outputting system parameters, requesting exams, viewing images, etc. Generally speaking, the displays, printers, workstations, and similar devices provided within the system may be local to the data acquisition components, or may be remote from these components, such as elsewhere within the facility or hospital, or located at an entirely different location, linked to the image acquisition system via one or more configurable networks (such as the Internet, a virtual private network, a cloud-based network, etc.).

[0024] like Figure 1As shown, the x-ray system 10 may also include a variety of alternative embodiments that are generally configured to meet the specific needs of certain applications. For example, the x-ray system 10 may be a fixed system, a mobile system, or a mobile C-arm system, in which the x-ray detector is permanently mounted in one end of the C-arm or can be removed from the system. In addition, the x-ray system 10 may be a table and / or wall bracket system in a fixed x-ray room, in which the x-ray detector 22 is permanently mounted with the system or is portable. Alternatively, the x-ray system 10 may be a mobile x-ray system with a portable x-ray detector. Such a portable x-ray may be further configured to have a detachable tether or cable for connecting the detector readout electronics to the data acquisition system of the scanner. When not in use, the portable x-ray detector may be removed from the scanning station for storage or transfer. In implementation, the imaging system 10 may be any suitable x-ray-based imaging system, including but not limited to conventional x-ray radiography systems, CT imaging systems, tomosynthesis systems, C-arm systems, fluoroscopic fluoroscopy systems, mammography systems, dual-energy or multi-energy systems, navigation or interventional imaging systems, and the like. Furthermore, although the example of a flat panel detector is described above, a digital detector system including an image intensifier and a camera may be used to convert incident x-rays into video signals.

[0025] Although the foregoing schematically describes components of the x-ray based imaging system 10, including the detectors and detector control and readout circuitry as discussed herein, Figure 2 An example of how such an imaging system 10 may be provided in a real-world environment is depicted. As noted above, the x-ray system 10 may be implemented as a mobile x-ray device (e.g., an x-ray device including a C-arm, a mini C-arm, an O-arm, a non-circular arm, etc.) and a fixed x-ray device. By way of example, Figure 2 An x-ray imaging system 10 is shown that includes a C-arm x-ray device 42 that is configured to rotate a detector panel 22 and an x-ray source 12 about a volume to be imaged. In the depicted example, the x-ray system 10 also includes a collimator 48. Any suitable x-ray source 12 may be used, including a standard x-ray source, a rotating anode x-ray source, a stationary or fixed anode x-ray source, a solid state x-ray emission source, or a fluoroscopic x-ray source 54 (e.g., Figure 2 Any suitable x-ray detector 22 may be used, including a digital flat panel detector, an image intensifier, etc.

[0026] Figure 2An embodiment is shown in which the collimator 48 includes an x-ray attenuating material 52 that defines an aperture 56 through which x-rays can pass, and which in turn prevents or limits the emission of x-rays beyond the boundaries of the defined aperture, thereby shaping and limiting the defined beam. The collimator 48 may include any suitable x-ray attenuating material 52 that allows it to collimate the x-ray beam in this manner. Some examples of suitable x-ray attenuating materials include tungsten, lead, gold, copper, tungsten-impregnated substrates (e.g., glass or polymers impregnated with tungsten), coated substrates (e.g., glass or polymers coated with tungsten, lead, gold, etc.), steel, aluminum, bronze, brass, rare earth metals, or combinations thereof.

[0027] Input to system controller 28 may be provided via one or more user input devices. Figure 2 An exemplary user input device in the form of a foot pedal exposure pedal 100 is shown. The exposure pedal 100 may be connected to the system controller 28 via a suitable connection (e.g., wired or wireless). The exposure pedal 100 may have a button that, when depressed, signals the system controller 28 to initiate x-ray imaging. In one example, when the exposure pedal 100 is depressed, a fluoroscopic imaging procedure is initiated. The fluoroscopic imaging procedure may include transmitting a radiation beam toward a patient (e.g., via activation of the x-ray source 12), wherein a portion of the radiation that passes through or bypasses the patient impinges on the detector 22. The signal from the detector 22 is then used to generate an image for display. Once the imaging parameters are adjusted to bring the image to a suitable quality level (e.g., a target contrast-to-noise ratio), fluoroscopic imaging may begin (e.g., wherein the acquired image is displayed at a suitable frame rate, such as 30 fps). If the exposure pedal is released before fluoroscopic imaging begins (e.g., during the series of steps of adjusting the imaging parameters to reach the target contrast-to-noise ratio), a toe tap image may be displayed instead. The toe tap image may be a single non-moving x-ray image.

[0028] In order to acquire an x-ray image of a specific brightness, the x-ray imaging system may be controlled according to an ABS routine, which is executed by an ABS servo mechanism on a system controller (e.g., system controller 28). For example, depending on the type of imaging protocol, the anatomical structure being imaged, etc., the x-ray imaging system may be controlled or commanded to output an image with a specific brightness. Due to variations in patient size, anatomical structure density, etc., the x-ray imaging parameters (such as x-ray source voltage, x-ray source current, and camera / display / image gain) that will achieve a specific brightness are unknown. The ABS routine may be executed to quickly adjust the x-ray imaging parameters so as to output an image with a specific brightness as quickly as possible. The ABS servo mechanism may include a set of index tables that can link specific current, voltage, and gain values. For example, the index table may include a corresponding index table for each of the current, voltage, and gain, wherein each imaging setting is plotted as a function of an index number, for example, in the range of 0 to 250. The index may be selected based on the current image brightness relative to the target brightness. For example, if the current image has a brightness of 50 (defined by the video level indication) and the target brightness is 110, a brightness change of -60 may be determined by subtracting the target brightness from the current brightness (eg, by subtracting 110 from 50).

[0029] This brightness change can be entered into a lookup table that outputs an index jump that defines the amount by which the index should be changed. For example, if an image is acquired at the default system parameters of 70 kV and 3.9 mA, the index at the time the image is acquired may be 188. The lookup table may indicate an index jump of 62 based on a brightness change of -60. Thus, the index may change from 188 to 250. Updated current, voltage, and gain values ​​may be determined by obtaining corresponding values ​​from the index table (e.g., current, voltage, and gain values ​​each corresponding to an index value of 250 may be obtained from the corresponding index table), and the system may be commanded to operate at each of these parameters, and the process may be repeated until the target brightness is reached.

[0030] As will be described in more detail below, the ABS routine can be shortened by determining a predicted brightness of one or more images acquired before the x-ray tube reaches a predefined target current, rather than relying on the actual brightness of the image acquired when the predefined target current is reached. The predicted brightness is determined based on the brightness of the current image and the ratio of the target current to the feedback current (which may be the current used to acquire the current image). By doing so, the ABS servo can determine how much the brightness of the most recently acquired image differs from the target brightness based on the ratio of the currents, and adjust the brightness entered into the lookup table accordingly. In this way, automatic stabilization of image brightness can be performed while the x-ray tube is ramping toward the target current, which can reduce the time to reach the target brightness.

[0031] Go to Figure 3, provides a method for operating an x-ray imaging system (such as Figure 1 to Figure 2 The method 300 of the system 10) will be referred to in this article. Figure 1 to Figure 2 The method 300 is described using the described systems and components, however it should be understood that the method may be implemented using other systems and components without departing from the scope of the present disclosure. The method 300 may be implemented as executable instructions in a non-transitory memory of a computing device such as the system controller 28.

[0032] At 302, method 300 includes determining current imaging conditions. The determined current imaging conditions may include determining whether x-ray imaging is currently being performed, the state of an exposure pedal (e.g., depressed or released), the type of procedure being performed (such as a vascular, cardiac, or spinal procedure), and / or other parameters. At 304, method 300 includes determining whether an exposure pedal depression has been detected. As explained above, an x-ray imaging system (such as system 10) may include one or more user input devices, including an exposure pedal such as exposure pedal 100. The exposure pedal may include a pedal / button that a clinician (such as a surgeon) may depress to initiate x-ray imaging. To facilitate acquisition of x-ray images during surgical procedures, the exposure pedal may be a foot pedal configured to be depressed by a clinician's foot, which may enable control of fluoroscopic imaging in a hands-free manner without interfering with clinical workflow. Thus, determining whether depression of the exposure pedal is detected may include receiving a user input signal from the exposure pedal commanding the start of x-ray imaging. The user input signal may be received continuously or periodically while the exposure pedal is depressed. In other examples, instead of depressing the exposure pedal, a user input signal may be received from another suitable input device such as a keyboard, a touch screen, a voice command, etc.

[0033] If depression of the exposure pedal is not detected, the method 300 proceeds to 306 to maintain the current imaging conditions. The current imaging conditions may include maintaining a radiation source of an x-ray imaging source deactivated (e.g., not providing power to an x-ray generator). In other examples, maintaining the current imaging parameters may include maintaining a current fluoroscopic imaging session. Detecting depression of the exposure pedal may include detecting that the exposure pedal changes from being released (e.g., not depressed) to being depressed. Thus, in examples where the exposure pedal is already depressed when the method 300 is executed, the current fluoroscopic imaging session may continue without interruption.

[0034] If it is detected that the exposure pedal is depressed, the method 300 proceeds to 308 to activate the x-ray source and acquire a first image. For example, upon detecting that the exposure pedal is depressed, the x-ray imaging system may prepare for exposure of radiation, such as by commanding the x-ray generator and the x-ray tube to prepare to generate x-rays having a predetermined tube voltage (e.g., a peak voltage kVp, which is the maximum voltage on the x-ray tube), a predetermined tube current (e.g., the number of electrons jumping from the cathode to the anode of the tube, expressed in mA), and a predetermined pulse width. The system may also command the x-ray detector to prepare to receive x-rays having the commanded predetermined kVp, mA, and pulse width at a predetermined frame rate, etc., and may also command the image processing unit to terminate any current tasks and prepare to process incoming images. In one example, the predetermined kVp and predetermined mA may be default system settings, such as 70 kV and 3.9 mA, but other predetermined voltages and currents are also within the scope of the present disclosure. In some examples, the predetermined kVp and mA may be based on a target brightness, which may be fixed or may vary based on the type of imaging to be performed, the target anatomy to be imaged, etc. For example, the target brightness may include a VLI of 110, and the predetermined kVp and mA may be the kVp and mA that will result in a VLI of 110 for a standard / typical patient (e.g., as determined based on a polymethylmethacrylate (PMMA) sham object).

[0035] In some examples, upon receiving a command to prepare for imaging, the x-ray detector may initiate scrubbing of the detector panel at the requested frame rate. The detector may then generate a synchronization signal when an equilibrium condition is reached and send the synchronization signal back to the system controller. The x-ray generator and x-ray tube may wait for the synchronization signal from the detector and begin generating x-rays at the synchronization signal once the x-ray exposure is enabled. The workstation / image processing unit may stop the current activity, initialize the acquisition and image processing modules, and wait for incoming frames. In addition, in some examples, during the exposure preparation phase, the filament of the x-ray tube may be preheated (e.g., by applying a certain amount of voltage to the filament before the x-ray exposure) in order to reduce the amount of time for the x-ray tube to reach the commanded predefined current. For example, the filament may be heated to a predetermined temperature based on a predefined tube current so that the predefined tube current may be quickly reached once the exposure begins.

[0036] Once the system has commanded the components to prepare for generating / receiving x-rays, once all components are ready, the system proceeds to a subsequent stage in the x-ray imaging sequence (e.g., once the detector begins sending synchronization signals, the x-ray generator sets a generator ready flag, and the workstation sets a workstation ready flag). The subsequent stage includes initiating an x-ray exposure, wherein the x-ray tube is operated at a predefined kVp and mA. This causes x-rays to be generated and transmitted to, through, and around the patient, wherein the x-rays impinge on the detector, and a first image is acquired. The tube voltage may be reached relatively quickly (such as within 3 milliseconds). However, since the tube current depends on the tube filament temperature in addition to the tube voltage, it may take a relatively long time (such as 300 milliseconds or more) to reach the target tube current. After the exposure command is issued, the first image may be acquired relatively quickly (e.g., 10 milliseconds). In some examples, the filament of the x-ray tube may be maintained at an elevated temperature (e.g., relative to room temperature) as described above, which may allow the predefined current to be reached quickly. For example, when an exposure command is sent, it may take 7-8 milliseconds for the x-ray tube current to reach 90% of the predefined / set tube current.

[0037] At 310, a video level indication (VLI) for a first image is determined. The video level indication may be a measurement of image brightness and may include an average brightness of the image in an area of ​​interest (such as an image area corresponding to the center of the detector). At 312, a corrected VLI is determined based on the VLI of the first image, a target current, and a feedback current. The target current may be a predefined current (e.g., 3.9 mA) discussed above, which may be a default current that commands the x-ray system to operate until an updated target current (which is explained in more detail below) is determined. The feedback current may be the x-ray tube current when the first image is acquired. Taking into account the slow filament response, the corrected VLI may be a prediction of the brightness of the image at the target current. The brightness of an x-ray image is proportional to the x-ray tube current at which the image is acquired. When an image (such as the first image) is acquired when the current is ramped up to the target current, the brightness of the image may be defined by the following equation:

[0038] Bright=bright_with_unit_ma*maf (Equation 1)

[0039] In the above equation, ma f is the average (feedback) current of the x-ray source when acquiring the image, and bright_with_unit ma is a conversation factor that relates the current unit (mA) to the brightness unit (e.g., VLI) of a known imaged object (e.g., a false object). Thus, Equation 1 shows that the brightness of an image is proportional to the current used to acquire the image.s In an ideal system (for example, in an ideal system where the current changes instantly when a command to change the current is given), the brightness would be:

[0040] Bright′=Bright*ma s / ma f (Equation 2)

[0041] In the above equation, Bright is the brightness obtained in a real system with a current ramp delay. This means that if Bright*ma s / ma f If the correction is applied to the real brightness, the system with the current ramp delay will "change" to the ideal system. Therefore, if the real brightness is corrected, the constraint of slow current response will no longer be a consideration, and the image brightness prediction and ABS stability prediction will also be achieved.

[0042] Therefore, during the stabilization process, the actual / applied current is monitored in real time and recorded as the feedback current (mA) for each image frame. f ). This feedback current is used to correct VLI because VLI is proportional to the square root of brightness. For example, the corrected VLI (referred to as vli′, )) can be determined based on the measured VLI, the feedback current, and the target current according to the following formula:

[0043]

[0044] In this way, the corrected VLI can be corrected based on a feedback current proportional to a set current (eg, a target current). This corrected brightness, rather than the current brightness, can be used as an input to the ABS system to adjust the x-ray parameters to achieve the target brightness.

[0045] At 312, the method 300 determines whether the corrected VLI is outside a stable VLI window. The stable VLI window may include a threshold range close to the target VLI, such as within 1%-1.5% of the target VLI. In addition, in order to be considered within the stable VLI window, the corrected VLI may be within a threshold of the target VLI for a given number (such as two or three) of consecutive image frames.

[0046] If the corrected VLI is outside the stable VLI window, the method 300 proceeds to 316 to determine an index jump based on the corrected VLI. To determine the index jump, the difference between the target VLI and the corrected VLI (referred to as the VLI change) is calculated and entered into an index jump lookup table, which outputs an index jump based on the VLI change (also referred to as the index change). The index is then changed based on the index jump, for example, according to the following formula:

[0047] f(n)=f(n-1)+LUT(vli n ) (Equation 4)

[0048] In the above equation, f(n-1) is the index of the most recently acquired image (eg, the index corresponding to the imaging parameters applied to acquire the image), and LUT(vli n ) is based on the index change determined by the lookup table based on the correction VLI.

[0049] Figure 4 An exemplary index jump lookup table 400 is shown. Table 400 includes index jumps plotted as a function of VLI change. Because the possible values ​​of both the VLI and index tables are limited (e.g., 0 to 255) and also because the VLI change is relative to a target VLI that can be an intermediate value (e.g., 110), table 400 only includes a limited set of index jump values ​​(e.g., -60 to 80) and VLI change values ​​(e.g., -100 to 150), but other values ​​are possible without departing from the scope of the present disclosure. The relationship between the index jump and the VLI change can be roughly exponential (with negative decay), but other relationships are possible.

[0050] For example, the voltage, current, and gain applied to acquire the first image may be determined, and the index may be determined based on the voltage, current, and gain. The corrected VLI may be determined as described above, and the VLI change may be determined by subtracting the target VLI (e.g., VLI′-target VLI) from the corrected VLI (the target VLI may be a fixed value or may be determined based on the selected imaging protocol, imaging anatomy, user preferences, etc.). If the corrected VLI is 90 and the target VLI is 110, the VLI change may be -20, which may result in an index jump of 15. The index jump may be added to the index, resulting in an increase in the index. The updated index may then be used to obtain an updated target voltage, current, and gain, and the x-ray system may be commanded to operate at the updated target voltage, current, and gain.

[0051] Therefore, at 318 , updated target voltages, currents, and gains are determined from the index table based on the updated index. Figure 5 An exemplary index table 500 for voltage is shown. The index table 500 includes voltage (in kV) plotted as a function of an index, the index including values ​​ranging from 0 to 255. If the previous index (e.g., at which the first image was obtained) was, for example, 135 and the updated index was 150, the previous target voltage may be 58 kV and the updated target voltage may be 62 kV. Similar index tables may be included for current and gain, and the updated index used to determine each of the updated target current and gain.

[0052] At 320, the x-ray system is commanded to operate at the updated target voltage, the updated target current, and the updated target gain. At 322, the next image is acquired. At 324, a corrected VLI for the next image is determined as described above at 312 (e.g., the VLI for the next image is determined, a feedback current for acquiring the next image is determined, and the corrected VLI is determined based on the VLI for the next image, the feedback current, and the target current, wherein the target current is the updated target current determined at 318). The method 300 then loops back to 314 to determine whether the corrected VLI is outside the stable VLI window. If so, the process is repeated (determining an index jump based on the corrected VLI for the next image, determining an updated target voltage, current, and gain based on the index jump, commanding the x-ray imaging system to operate at the updated settings, and acquiring another next image).

[0053] If the corrected VLI is not outside the stable VLI window, the method 300 proceeds to 326 to acquire one or more images at stable settings (e.g., current voltage, current, and gain). Images may be acquired and displayed at a suitable frame rate (e.g., 10 fps to 30 fps) until the exposure pedal is released or until another suitable signal is received commanding termination of imaging. If the exposure pedal has been released, radiation exposure may be terminated by terminating power to the x-ray generator, causing the tube voltage and current to drop to zero and the tube to stop generating x-rays.

[0054] During imaging, the patient may move, a needle or other device may enter the imaging field of view, and / or the position of the x-ray system may change (while moving), each of which may cause a change in the brightness of the output image. Thus, in some examples, if the VLI changes, the imaging settings may be adjusted based on the VLI, as shown at 328. For example, the ABS servo may continue to determine the VLI, and if the VLI moves outside of the stability window, the settings may be adjusted by entering the VLI change into an index table lookup table and adjusting the index, and therefore the imaging settings, until the VLI returns to the stability window. The method 300 then returns.

[0055] Figure 6A timeline 600 of a fluoroscopic imaging process using a measured VLI to adjust imaging settings is shown. The timeline 600 includes a first graph 602 showing a frame acquisition signal (frame sync) indicating when each image frame is acquired, a second graph 604 showing the actual acquired frames, a third graph 606 of a video level indication for each frame, a fourth graph 608 of a target x-ray source current (mA), and a fifth graph 610 of actual mA. For the graphs showing mA, the corresponding mA is depicted along the vertical axis, increasing from a lower value (e.g., 0) to a higher value (e.g., 5). All graphs are shown as a function of time, and all graphs are time-aligned. The third graph 606 showing the VLI does not represent the actual measurement or correction of the VLI, but is merely intended to show when the VLI for the corresponding image is determined.

[0056] Prior to time t1, an operator (e.g., a surgeon) depresses the exposure pedal, and both the tube voltage and current are commanded to predefined values ​​to begin transmitting an x-ray beam to the patient. At time t1, a first image is acquired. Once the first image is acquired, the VLI for the first image is determined. Once the VLI for the first image is determined, the VLI can be used to adjust the current (and voltage and gain) to achieve a target brightness for imaging. Thus, as Figure 6 As shown, there is a delay between when a signal is sent to start acquiring an image (time t1) and when the VLI of the first image is used to adjust the imaging settings (time t2). In the example shown, this delay may be 80ms, but if the x-ray imaging system has a longer frame cycle time (e.g., the time to acquire an image and determine the VLI of the acquired image), the delay may be longer.

[0057] At time t2, the VLI of the first image is used to adjust the x-ray source current. Because the current is lower and ramps up toward the final target current, the VLI of the first image can be lower (e.g., 50) relative to the target VLI (e.g., 110). Using the corrected brightness, the VLI of the first image can be corrected by the target current and the feedback current according to Equation 3 above (50). For example, if the target current is 3.9 mA and the feedback current is 1.2 mA, the corrected VLI can be That is, it will be about 90. The VLI change may be -20, resulting in an index jump of 15.

[0058] The set current may continue to be adjusted as the current ramps toward the target current and as the image brightness ramps toward the target brightness. Around image frame 9, the current begins to stabilize, and is fully stabilized before image frame 14.

[0059] A technical effect of correcting the video level indication of an image based on a set current and a feedback current is to quickly determine a target x-ray tube voltage and a target x-ray tube current, thereby reducing the amount of time required to stabilize image brightness and reducing patient radiation exposure.

[0060] As used herein, the elements or steps listed in the singular and beginning with the word "one" or "a kind of" should be understood as not excluding a plurality of the elements or steps, unless such exclusion is explicitly stated. In addition, the reference to "an embodiment" of the present invention is not intended to be interpreted as excluding the existence of additional embodiments that also include the cited features. In addition, unless explicitly stated to the contrary, the embodiment of "including", "comprising" or "having" an element or multiple elements with a specific characteristic may include additional such elements without the characteristic. The terms "including" and "in..." are used as the concise language equivalents of the corresponding terms "including" and "wherein". In addition, the terms "first", "second" and "third" etc. are only used as marks, and are not intended to impose numerical requirements or specific positional order on their objects.

[0061] This written description uses examples to disclose the invention, including the best mode, and also to enable a person of ordinary skill in the relevant art to practice the invention, including making and using any devices or systems and performing any included methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to a person of ordinary skill in the art. Such other examples are intended to fall within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insignificant differences from the literal language of the claims.

Claims

1. A method for an x-ray imaging system, the method comprising: acquiring a first image using the x-ray imaging system while an x-ray tube current of the x-ray imaging system is ramped up to an initial target x-ray tube current; determining a predicted brightness of a future image to be acquired at the initial target x-ray tube current, the predicted brightness being based on the measured brightness of the first image and a feedback x-ray tube current relative to the initial target x-ray tube current; obtaining a new target x-ray tube current based on the predicted brightness; as well as commanding the x-ray imaging system to deliver a beam at the new target x-ray tube current, wherein obtaining the new target x-ray tube current based on the predicted brightness of the first image comprises obtaining the new target x-ray tube current in response to the predicted brightness being outside a threshold range of target brightness; wherein obtaining the new target x-ray tube current based on the predicted brightness comprises acquiring an index jump value based on the predicted brightness, adjusting an index value based on the index jump value, and obtaining the updated target x-ray tube current according to the adjusted index value; and Wherein obtaining the index jump value based on the predicted brightness includes: determining a brightness change based on the predicted brightness and the target brightness, and obtaining the index jump value by entering the brightness change as an input into an index jump lookup table, wherein the index jump lookup table maps the index jump value to a function of the brightness change.

2. A method for an x-ray imaging system, the method comprising: acquiring a first image using the x-ray imaging system while an x-ray tube current of the x-ray imaging system is ramped up to an initial target x-ray tube current; determining a predicted brightness of a future image to be acquired at the initial target x-ray tube current, the predicted brightness being based on the measured brightness of the first image and a feedback x-ray tube current relative to the initial target x-ray tube current; acquiring a new target x-ray tube current based on the predicted brightness; as well as commanding the x-ray imaging system to deliver a beam at the new target x-ray tube current, wherein obtaining the new target x-ray tube current based on the predicted brightness of the first image comprises obtaining the new target x-ray tube current in response to the predicted brightness being outside a threshold range of target brightness; wherein obtaining the new target x-ray tube current based on the predicted brightness comprises obtaining an index jump value based on the predicted brightness, adjusting an index value based on the index jump value, and obtaining the updated target x-ray tube current according to the adjusted index value; and Wherein obtaining the new target x-ray tube current according to the adjusted index value comprises: entering the adjusted index value as an input into a current index table, wherein the current index table maps the x-ray tube current as a function of the index value.

3. The method of claim 2, further comprising updating the target x-ray tube voltage by entering the adjusted index value as input into a voltage index table, the voltage index table mapping the voltage as a function of the index value.

4. The method according to claim 1, further comprising: One or more additional images are acquired using the x-ray imaging system, a predicted brightness for each additional image is determined, and the new x-ray tube current is adjusted based on the predicted brightness for each additional image until a final additional image having a corrected brightness within the threshold range of the target brightness is acquired. 5 . The method of claim 4 , further comprising, in response to acquiring the final additional image, maintaining an x-ray tube current and acquiring a plurality of images at the x-ray tube current.

6. The method of claim 1 , wherein determining the predicted brightness comprises: A video level indication of the first image is measured and the video level indication is corrected by the feedback x-ray tube current relative to the initial target x-ray tube current.

7. The method of claim 1, wherein the feedback x-ray tube current comprises an x-ray tube current used to acquire the first image.

8. An x-ray imaging system, comprising: a radiation source comprising an x-ray tube configured to project a radiation beam toward a patient; a radiation detector configured to receive the radiation beam projected by the radiation source and impinged by the patient; and A controller, the controller being configured to: acquiring a first image using the radiation source and the radiation detector while an x-ray tube current of the x-ray tube is ramped up to an initial target x-ray tube current; determining a predicted brightness of a future image to be acquired at the initial target x-ray tube current, the predicted brightness being based on the measured brightness of the first image and a feedback x-ray tube current relative to the initial target x-ray tube current; obtaining a new target x-ray tube current based on the predicted brightness; and commanding the x-ray imaging system to transmit a beam at the new target x-ray tube current, wherein obtaining the new target x-ray tube current based on the predicted brightness of the first image comprises obtaining the new target x-ray tube current in response to the predicted brightness being outside a threshold range of target brightness; wherein obtaining the new target x-ray tube current based on the predicted brightness comprises acquiring an index jump value based on the predicted brightness, adjusting an index value based on the index jump value, and obtaining the updated target x-ray tube current according to the adjusted index value; and Wherein obtaining the index jump value based on the predicted brightness includes: determining a brightness change based on the predicted brightness and the target brightness, and obtaining the index jump value by entering the brightness change as an input into an index jump lookup table, wherein the index jump lookup table maps the index jump value to a function of the brightness change.

9. The system of claim 8, wherein the controller is further configured to: acquiring a second image after the first image; determining a predicted brightness of the second image; If the predicted brightness of the second image is within a threshold range of the target brightness, continuing to acquire images at a set x-ray tube current, the set x-ray tube current including an x-ray tube current for acquiring the second image.

10. The system of claim 8, wherein the feedback x-ray tube current comprises an x-ray tube current used to acquire the first image.

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