System and method for correcting a projected image

Abstract

A method for correcting a projection image, comprising: obtaining at least two projection images of a subject to be examined, the at least two projection images being generated from scan data obtained by a CT scanner at at least two gantry angles, each projection image corresponding to a gantry angle. The method further comprises: correcting a first projection image of the at least two projection images according to a process of generating a corrected projection image. The process of generating the corrected projection image comprises: performing a first correction on the first projection image based on the first projection image and a second projection image of the at least two projection images to generate a preliminarily corrected first projection image; and performing a second correction on the preliminarily corrected first projection image based on at least a part of the preliminarily corrected first projection image to generate a corrected first projection image corresponding to the first gantry angle.

Description

[0001] Cross - reference to related applications

[0002] This application is a divisional application of a Chinese application with an application date of November 05, 2018, an application number of CN201811306943.1, and an invention title of "System and Method for Correcting Projected Images". The parent case claims the priority of a PCT application with an application number of PCT / CN2017 / 110032 filed on November 8, 2017 and a PCT application with an application number of PCT / CN2018 / 087884 filed on May 22, 2018, the content of which is incorporated herein by reference. Technical field

[0003] The present invention relates to computed tomography (CT) technology, and more particularly, to a system and method for correcting projected images in CT image reconstruction. Background art

[0004] In recent years, CT technology has been widely used in clinical examinations and medical diagnoses. During a CT scan, an X - ray imaging source and a detector can rotate around a subject to be examined randomly on a gantry, so as to scan the subject to be examined at multiple gantry angles. Based on the scan data, a plurality of projected images corresponding to the gantry angles can be generated. However, when the gantry rotates, the radiation dose delivered to the subject to be examined may change, which may lead to inconsistencies between the projected images. For example, fluctuations in the X - ray source dose will cause a difference between the actual gray - scale value and the ideal gray - scale value of the projected images at each gantry angle. The imaging quality of the CT image of the subject to be examined reconstructed based on these projected images is poor, which may lead to incorrect medical diagnoses or inaccurate positioning for subsequent treatment. Therefore, it is desirable to correct and / or normalize the projected images to reduce the influence of non - uniform radiation doses at different gantry angles. Summary of the invention

[0005] The object of the present invention is to provide a system and method for correcting projected images, and the corrected projected images reduce the influence of non - uniform radiation doses and improve the image quality of the reconstructed images.

[0006] To achieve the above - mentioned object of the invention, the technical solutions provided by the present invention are as follows:

[0007] According to one aspect of the present application, a system for correcting a projection image is disclosed. The system includes a storage device for storing a set of instruction sets. The system further includes a processor communicatively coupled to the storage device. When the instruction sets are executed, the processor is configured to obtain at least two projection images of a subject. The at least two projection images are generated based on scan data acquired by a CT scanner at at least two gantry angles, and each projection image corresponds to one gantry angle. The processor is further configured to correct a first projection image of the at least two projection images according to a process of generating a corrected projection image. The first projection image corresponds to a first gantry angle of the at least two gantry angles. The process of generating a corrected projection image includes performing a first correction on the first projection image based on the first projection image and a second projection image of the at least two projection images to generate a preliminarily corrected first projection image. The second projection image corresponds to a second gantry angle of the at least two gantry angles. The process of generating a corrected projection image further includes performing a second correction on the preliminarily corrected first projection image based on at least a portion of the preliminarily corrected first projection image to generate a corrected first projection image corresponding to the first gantry angle.

[0008] In the present invention, the processor may further be configured to correct the at least two projection images according to the process of generating a corrected projection image to generate at least two corrected projection images, and reconstruct a CT image of the subject based on the at least two corrected projection images.

[0009] In the present invention, in order to correct the at least two projection images, the processor may perform at least one iteration. Each current iteration of the iteration includes correcting the at least two projection images in the current iteration according to the process of generating a corrected projection image to generate at least two corrected projection images; determining whether the at least two corrected projection images in the current iteration meet a condition; and if the at least two corrected projection images do not meet the condition, designating the at least two corrected projection images in the current iteration as the at least two projection images in the next iteration.

[0010] In the present invention, the second gantry angle is an adjacent gantry angle of the first gantry angle.

[0011] Performing the first correction on the first projection image to generate the preliminarily corrected first projection image includes determining a first correction coefficient of the first projection image based on a difference between the first projection image and the second projection image; and generating the preliminarily corrected first projection image based on the first correction coefficient and the first projection image.

[0012] In the present invention, the difference between the first projection image and the second projection image is the difference between the gray-scale information of the first projection image and the gray-scale information of the second projection image.

[0013] In the present invention, performing the second correction on the preliminarily corrected first projection image to generate a corrected first projection image includes identifying at least one pixel of the preliminarily corrected first projection image, where the identified pixel corresponds to an intermediate channel of the CT scanner at the first gantry angle; for each pixel, identifying an opposite pixel corresponding to each pixel; generating a reference image of the preliminarily corrected first projection image based on at least one opposite pixel of the at least one pixel; determining a second correction coefficient of the preliminarily corrected first projection image based on the difference between the identified at least one pixel and the reference image; and generating the corrected first projection image corresponding to the first gantry angle based on the second correction coefficient and the preliminarily corrected first projection image.

[0014] In the present invention, generating the preliminarily corrected first projection image includes preprocessing the first projection image to generate a preprocessed first projection image, where the preprocessing of the first projection image at least includes beam hardening correction or scatter correction; and performing the first correction on the preprocessed first projection image to generate a preliminarily corrected first projection image.

[0015] In the present invention, the processor can be used to post-process the corrected first projection image, where the post-processing of the corrected first projection image at least includes beam hardening correction or scatter correction.

[0016] According to another aspect of the present application, a method for correcting a projection image is disclosed. The method includes obtaining at least two projection images of a subject. The at least two projection images are generated from scan data obtained by a CT scanner at at least two gantry angles, and each projection image corresponds to one gantry angle. The method further includes correcting a first projection image of the at least two projection images according to a process of generating a corrected projection image. The first projection image corresponds to a first gantry angle of the at least two gantry angles. The process of generating the corrected projection image includes performing a first correction on the first projection image based on the first projection image and a second projection image of the at least two projection images to generate a preliminarily corrected first projection image. The second projection image corresponds to a second gantry angle of the at least two gantry angles. The process of generating the corrected projection image further includes performing a second correction on the preliminarily corrected first projection image based on at least a part of the preliminarily corrected first projection image to generate a corrected first projection image corresponding to the first gantry angle.

[0017] According to another aspect of the present application, a computer-readable storage medium is disclosed. The computer-readable storage medium can store computer instructions, which when executed, can perform the method for correcting a projection image as described in any of the above.

[0018] According to another aspect of the present application, a system for correcting a projection image is disclosed. The system includes an acquisition module and a correction module. The acquisition module can be used to acquire at least two projection images of an object to be examined. The at least two projection images are generated based on scan data obtained by a CT scanner at at least two gantry angles, and each projection image corresponds to one gantry angle. The correction module can be used to correct a first projection image of the at least two projection images according to a process of generating a corrected projection image. The first projection image corresponds to a first gantry angle of the at least two gantry angles. The process of generating a corrected projection image can include performing a first correction on the first projection image based on the first projection image and a second projection image of the at least two projection images to generate a preliminarily corrected first projection image. The second projection image corresponds to a second gantry angle of the at least two gantry angles. The process of generating a corrected projection image can further include performing a second correction on the preliminarily corrected first projection image based on at least a part of the preliminarily corrected first projection image to generate a corrected first projection image corresponding to the first gantry angle.

[0019] Due to the adoption of the above technical solutions, the present invention has the following technical effects:

[0020] First, the corrected projection image reduces the influence of uneven radiation dose and improves the image quality of the reconstructed image;

[0021] Second, the correction method can significantly improve the quality of the reconstructed image at low dose;

[0022] Third, there is no need to introduce a high-precision reference ionization chamber or high-precision radiation source and control system, which can significantly reduce the cost.

[0023] Additional features will be partially described in the following description. For those skilled in the art, the additional features are obvious by studying the following drawings, or can be understood by implementing or operating the embodiments. The features of the present invention can be achieved and obtained through various aspects of the methods, means or combinations thereof described in detail below. Description of the Drawings

[0024] The drawings described herein are used to provide a further understanding of the present application, and constitute a part of the present application. The illustrative embodiments and descriptions thereof of the present application are used to explain the present application, and do not constitute a limitation to the present application. The same reference numerals in each figure represent the same components, where:

[0025] Figure 1 is a schematic diagram of an exemplary CT system according to some embodiments of the present invention;

[0026] Figure 2 is a schematic diagram of exemplary hardware and / or software components of a computing device according to some embodiments of the present invention;

[0027] Figure 3 is a schematic diagram of exemplary hardware and / or software components of a mobile device according to some embodiments of the present invention;

[0028] Figure 4 is a schematic diagram of an exemplary processing device according to some embodiments of the present invention;

[0029] Figure 5 is a flowchart of an exemplary process for reconstructing a CT image according to some embodiments of the present invention;

[0030] Figure 6 is a flowchart of an exemplary process for correcting a projection image according to some embodiments of the present invention;

[0031] Figure 7 is a flowchart of an exemplary process for performing a second correction on a first projection image that has been preliminarily corrected according to some embodiments of the present invention;

[0032] Figure 8 is a flowchart of an exemplary process for reconstructing a CT image according to some embodiments of the present invention;

[0033] Figure 9 is a schematic diagram of the relationship between two exemplary gantry angles according to some embodiments of the present invention;

[0034] Figure 10 is an exemplary CT image of a subject according to some embodiments of the present invention; and

[0035] Figure 11 is the average pixel value of a region in a corrected projection image according to some embodiments of the present invention. Detailed Description

[0036] In the following detailed description, numerous specific details are set forth by way of example in order to provide a thorough understanding of the relevant invention. However, those skilled in the art will appreciate that the invention may be practiced without such specific details. In other instances, well-known methods, procedures, systems, components, and / or circuits have been described at a relatively high level in order to avoid unnecessarily obscuring the main aspects of the invention. Various modifications to the embodiments of the invention will be readily apparent to those skilled in the art, and the general principles defined by the invention may be applied to other embodiments and application scenarios without departing from the spirit and scope of the invention. Accordingly, the invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the claims.

[0037] The terms used in this invention are only for describing specific exemplary embodiments and are not intended to limit it. Unless the context clearly indicates otherwise, the words "a", "an", "one", and "the" used in this invention do not specifically refer to the singular and may also include the plural. It can be further understood that the terms "comprising" and "including" used in the specification mean that there are multiple listed features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or their combinations.

[0038] It can be understood that the terms "system", "module", "unit", and / or "sub-unit" used in this invention are a way to distinguish the hierarchical relationships between different structures. However, these terms may be replaced by other expressions if the same purpose can be achieved.

[0039] Generally, the "module", "unit", and / or "sub-unit" used in this invention refer to the logic or a set of software instructions stored in hardware or firmware. The "module", "unit", and / or "sub-unit" described in this invention can be executed by software and / or hardware modules and can also be stored in any non-transitory computer-readable storage medium or other storage device. In some embodiments, a software module can be compiled and linked to an executable program. Here, the software module can respond to the information passed by itself or other modules and / or can respond when certain events or interrupts are detected. A software module configured to be executable on a computing device (e.g., Figure 2 the processor 210 shown, Figure 3The software modules / units / sub-units for the central processing unit (CPU) 340) to perform operations as shown herein. Here, the computer-readable storage medium can be an optical disc, a digital optical disc, a flash drive, a magnetic disk, or any other type of tangible medium; software modules can also be obtained through digital downloads (here, digital downloads also include data stored in compressed packages or installation packages, which need to be decompressed or decoded before execution). Here, the software code can be partially or fully stored in the storage device of the computing device performing the operations and applied in the operations of the computing device. The software instructions can be implanted in firmware, such as erasable programmable readonly memory (EPROM). It should also be understood that the hardware modules / units / sub-units can include logic units connected together, such as gates, flip-flops, and / or include programmable units, such as programmable gate arrays or processors. The functions of the modules / units / sub-units or computing devices described herein are preferably performed by software modules / units / sub-units, but can also be represented in hardware or firmware. Generally, the modules / units / sub-units mentioned here are logical modules, not limited by their specific physical forms or memories. A module, unit, and / or sub-unit can be combined with other modules, units, and / or sub-units, or be separated into a series of sub-modules and / or sub-units.

[0040] Unless otherwise clearly indicated, it should be understood that when a unit, engine, module, or sub-unit is "located in", "connected to", or "coupled to" another unit, engine, module, or sub-unit, the unit, engine, module, or sub-unit can be directly located in, connected to, or coupled to or communicated with another unit, engine, module, or sub-unit, or there can be intermediate units, engines, modules, or sub-units. The term "and / or" used in the present invention includes any and all combinations of one or more of the related listed terms.

[0041] Considering the following detailed description with reference to the accompanying drawings, these and other features and characteristics of the present invention, the operating methods and functions of the relevant elements of the structure, and the economy of the combination and manufacture of the components will become more obvious, and all of these are part of the present invention. However, it should be clearly understood that the drawings are only for illustrative and descriptive purposes and are not intended to limit the scope of the present invention. It should be understood that all the drawings are not drawn to scale.

[0042] One aspect of the present invention relates to a system and method for correcting at least two projection images of a subject. The at least two projection images may correspond to at least two gantry angles of a CT scanner. To correct the projection images corresponding to the gantry angles, the system may execute the method to perform a first correction on the projection images to generate preliminarily corrected projection images. The first correction may be performed based on another projection image corresponding to another gantry angle. For example, the first correction may be performed based on a neighboring projection image of the projection image described elsewhere in the present invention. The system may also execute the method to perform a second correction on the preliminarily corrected projection images to generate corrected projection images. The second correction may be performed based on at least a portion of the preliminarily corrected projection images, for example, one or more pixels corresponding to an intermediate channel of the CT scanner at the gantry angle. In some embodiments, the system and method may correct at least two projection images corresponding to at least two gantry angles. The system and method may also reconstruct a CT image of the subject based on at least two corrected projection images corresponding to at least two gantry angles.

[0043] Figure 1 is a schematic diagram of an exemplary CT system 100 shown in some embodiments of the present invention. In some embodiments, the CT system 100 may include a conventional CT system, a cone beam CT (CBCT) system, a spiral CT system, a multi-slice CT system, a digital subtraction angiography (DSA) system, etc., or any combination thereof.

[0044] As Figure 1 shown, the CT system 100 may include a CT scanner 110, a network 120, a terminal 130, a processing device 140, and a storage device 150. The components in the CT system 100 may be connected to each other in various ways. For example, the CT scanner 110 may be connected to the processing device 140 via the network 120. For another example, the CT scanner 110 may be directly connected to the processing device 140. For yet another example, the storage device 150 may be directly or via the network 120 connected to the processing device 140. For yet another example, the terminal 130 may be directly or via the network 120 connected to the processing device 140.

[0045] The CT scanner 110 may include a gantry 111, a detector 112, a radiation source 113, and a scan bed 114. The detector 112 and the radiation source 113 may be relatively mounted on the gantry 111. The subject may be placed on the scan bed 114 and moved into the detection channel of the CT scanner 110. For illustrative purposes, a reference coordinate system as Figure 1 shown is introduced. The reference coordinate system may include an X-axis, a Y-axis, and a Z-axis. The Z-axis may refer to the direction in which the subject is moved into and / or out of the detection channel of the CT scanner 110. The X-axis and the Y-axis may form a plane perpendicular to the Z-axis.

[0046] The radiation source 113 can emit X-rays to scan an object to be examined placed on the examination table 114. The object to be examined can be a living organism (e.g., a patient, an animal) or a non-living object (e.g., an artificial object). The detector 112 can detect the radiation (e.g., X-rays) emitted from the radiation source 113. In some embodiments, the detector 112 can include a plurality of detector units. The detector units can include scintillation detectors (e.g., cesium iodide detectors) or gas detectors. The detector units can be arranged in a single row or multiple rows.

[0047] In some embodiments, the CT scanner 110 can include one or more components for blocking or reducing beam hardening and / or radiation scattering during scanning. For example, the CT scanner 110 can include a grid (e.g., an anti-scatter grid) and / or other components that can block or reduce beam hardening. As another example, the CT scanner 110 can include an X-ray collimator, a metal grid, a slit, a beam scatter correction plate (BSA), a beam attenuation grid (BAG), and / or other components that can block or reduce radiation scattering.

[0048] Network 120 can facilitate the exchange of information and / or data. In some embodiments, at least one component in CT system 100 (e.g., CT scanner 110, terminal 130, processing device 140, or storage device 150) can send information and / or data to another component in the CT system 100 via network 120. For example, the processing device 140 can obtain scan data from the CT scanner 110 via the network 120. As another example, the processing device 140 can obtain user instructions from the terminal 130 via the network 120. In some embodiments, network 120 can be any type of wired or wireless network, or a combination thereof. Network 120 can include a public network (e.g., the Internet), a private network (e.g., local area network (LAN), wide area network (WAN)), a wired network (e.g., Ethernet), a wireless network (e.g., 802.11 network, Wi-Fi network), a cellular network (e.g., long term evolution network (LTE)), a frame relay network, a virtual private network (VPN), a satellite network, a telephone network, a router, a hub, a switch, a server computer, or a combination thereof. By way of example only, network 120 can include a cable network, a wireless network, an optical fiber network, a telecommunications network, an intranet, the Internet, a local area network (LAN), a wide area network (WAN), a wireless local area network (WLAN), a metropolitan area network (MAN), a wide area network (WAN), a public switched telephone network (PSTN), a Bluetooth network, a ZigBee network, a near field communication (NFC) network, etc., or any combination thereof. In some embodiments, network 120 can include at least one network access point. For example, network 120 can include a wired or wireless network access point, such as a base station and / or an Internet exchange point, through which the components of the CT system 100 can be connected to network 120 to exchange data and / or information.

[0049] The terminal 130 includes a mobile device 130-1, a tablet computer 130-2, a laptop computer 130-3, etc., or any combination thereof. In some embodiments, the mobile device 130-1 may include a smart home device, a wearable device, a smart mobile device, a virtual reality device, an augmented reality device, etc., or any combination thereof. In some embodiments, the smart home device may include a smart lighting device, a control device for a smart appliance, a smart monitoring device, a smart TV, a smart camera, an intercom, etc., or any combination thereof. In some embodiments, the wearable device may include a smart bracelet, smart shoes and socks, smart glasses, a smart helmet, a smart watch, smart clothing, a smart backpack, smart accessories, etc., or any combination thereof. In some embodiments, the smart mobile device may include a smart phone, a personal digital assistant (PDA), a gaming device, a navigation device, a point of sale (POS) device, etc., or any combination thereof. In some embodiments, the virtual reality device may include a virtual reality helmet, virtual reality glasses, a virtual reality eye mask, an augmented reality helmet, augmented reality glasses, an augmented reality eye mask, etc., or any combination thereof. For example, the virtual reality device and / or the augmented reality device may include Google Glass, Oculus Rift, Hololens, Gear VR, etc. In some embodiments, the terminal 130 may remotely operate the CT scanner 110. For example, the terminal 130 may operate the CT scanner 110 through a wireless connection. In some embodiments, the terminal 130 may receive information and / or instructions input by a user and send the received information and / or instructions to the CT scanner 110 or the processing device 140 via the network 120. In some embodiments, the terminal 130 may receive data and / or information from the processing device 140. In some embodiments, the terminal 130 may be part of the processing device 140. In some embodiments, the terminal 130 may be omitted.

[0050] In some embodiments, the processing device 140 may process data and / or information obtained from the CT scanner 110, the terminal 130, or the storage device 150. For example, the processing device 140 may obtain at least two projection images corresponding to at least two gantry angles. The processing device 140 may also correct the projection images to generate at least two corrected projection images corresponding to the gantry angles.

[0051] The processing device 140 can be a central processing unit (CPU), a digital signal processor (DSP), a system on a chip (SoC), a microcontroller unit (MCU), etc., or any combination thereof. In some embodiments, the processing device 140 can be local or remote. For example, the processing device 140 can access information and / or data stored in the CT scanner 110, the terminal 130, and / or the storage device 150 through the network 120. For another example, the processing device 140 can be directly connected to the CT scanner 110, the terminal 130, and / or the storage device 150 to access the information and / or data stored therein. In some embodiments, the processing device 140 can be implemented on a cloud platform. By way of example only, the cloud platform can include a private cloud, a public cloud, a hybrid cloud, a community cloud, a distributed cloud, an inter-cloud, a multi-cloud, etc., or any combination thereof. In some embodiments, the processing device 140 can be implemented in the present invention Figure 2 on the computing device 200 having at least one component as shown.

[0052] The storage device 150 can store data and / or instructions. In some embodiments, the storage device 150 can store data obtained from the terminal 130 and / or the processing device 140. In some embodiments, the storage device 150 can store the data and / or instructions that the processing device 140 can execute or use to execute the exemplary methods described in the present invention. In some embodiments, the storage device 150 can include a mass storage device, a removable storage device, a volatile read-write memory, a read-only memory (ROM), etc., or any combination thereof. Exemplary mass storage devices can include magnetic disks, optical disks, solid state drives, etc. Exemplary removable storage devices can include flash drives, floppy disks, optical disks, memory cards, compact disks, magnetic tapes, etc. Exemplary volatile read-write memories can include random access memory (RAM). Exemplary RAM can include dynamic RAM (DRAM), double data rate synchronous dynamic RAM (DDR SDRAM), static RAM (SRAM), thyristor RAM (T-RAM), zero capacitor RAM (Z-RAM), etc. Exemplary ROM can include mask ROM (MROM), programmable ROM (PROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), compact disk ROM (CD-ROM), digital versatile disk ROM, etc. In some embodiments, the storage device 150 can be implemented on a cloud platform. By way of example only, the cloud platform can include a private cloud, a public cloud, a hybrid cloud, a community cloud, a distributed cloud, an inter-cloud, a multi-cloud, etc., or any combination thereof.

[0053] In some embodiments, the storage device 150 may be connected to the network 120 to communicate with at least one component of the CT system 100 (e.g., the terminal 130, the processing device 140). At least one component of the CT system 100 may access the data or instructions stored in the storage device 150 through the network 120. In some embodiments, the storage device 150 may be directly connected to or communicate with at least one component of the CT system 100 (e.g., the terminal 130, the processing device 140). In some embodiments, the storage device 150 may be part of the processing device 140.

[0054] Figure 2 is a schematic diagram of exemplary hardware and / or software components of a computing device 200 shown according to some embodiments of the present invention. The computing device 200 may implement the processing device 140. As Figure 2 shown, the computing device 200 may include a processor 210, a memory 220, an input / output (I / O) 230, and a communication port 240.

[0055] The processor 210 may execute computer instructions (program code) according to the techniques described herein and perform the functions of the processing device 140. The computer instructions may include routines, programs, objects, components, data structures, processes, modules, and functions for performing specific functions described herein. For example, the processor 210 may process image data obtained from the CT scanner 110, the terminal 130, the storage device 150, and / or any other component of the CT system 100. For example, the processor 210 may preprocess and / or correct projection images. For another example, the processor 210 may reconstruct a CT image based on at least two corrected projection images and store the CT image in the storage device 150. In some embodiments, the processor 210 may include at least one hardware processor, such as, for example, a microcontroller, a microprocessor, a reduced instruction set computer (RISC), an application specific integrated circuit (ASIC), an application specific instruction set processor (ASIP), a central processing unit (CPU), a graphics processing unit (GPU), a physics processing unit (PPU), a single-chip microcomputer, a digital signal processor (DSP), a field programmable gate array (FPGA), an advanced reduced instruction set system (ARM), a programmable logic device (PLD), any circuit or processor capable of performing at least one function, etc., or any combination thereof.

[0056] For illustration purposes only, only one processor is described in the computing device 200. However, it should be noted that the computing device 200 of the present invention may also include at least two processors. Therefore, the operations and / or method steps performed by one processor described by the present invention may also be performed jointly or separately by at least two processors. For example, if in the present invention, the processor of the computing device 200 performs steps A and B, it should be understood that steps A and B may also be performed jointly or separately by two different processors of the computing device 200 (e.g., the first processor performs step A, the second processor performs step B, or the first and second processors jointly perform steps A and B).

[0057] The memory 220 may store data / information obtained from the CT scanner 110, the terminal 130, the storage device 150, or any other component of the CT system 100. In some embodiments, the memory 220 may include a mass storage device, a removable memory, a volatile read / write memory, a read-only memory (ROM), etc., or any combination thereof. For example, the mass storage device may include a magnetic disk, an optical disk, and a solid state drive, etc. The removable memory may include a flash drive, a floppy disk, an optical disk, a memory card, a compact disk, and a magnetic tape, etc. The volatile read / write memory may include a random access memory (RAM). The RAM may include a dynamic RAM (DRAM), a double data rate synchronous dynamic RAM (DDR SDRAM), a static RAM (SRAM), a thyristor RAM (T-RAM), and a capacitorless RAM (Z-RAM), etc. The ROM may include a mask ROM (MROM), a programmable ROM (PROM), an erasable programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), a CD-ROM, and a digital versatile disk ROM, etc. In some embodiments, the memory 220 may store at least one program and / or instruction to perform the exemplary method described in the present invention. For example, the memory 220 may store a program for correcting a projection image (e.g., in the form of computer-executable instructions) for the processing device 140. As another example, the memory 220 may store a program for reconstructing a CT image based on the projection image (e.g., in the form of computer-executable instructions) for the processing device 140.

[0058] The input / output 230 can input or output signals, data, or information. In some embodiments, the input / output 230 can interact with the processing device 140 for user interaction. In some embodiments, the input / output 230 can include an input device and an output device. Exemplary input devices can include a keyboard, a mouse, a touch screen, a microphone, etc., or a combination thereof. Exemplary output devices can include a display device, a speaker, a printer, a projector, etc., or a combination thereof. Exemplary display devices can include a liquid crystal display (LCD), a light-emitting diode (LED)-based display, a flat panel display, a curved screen, a television device, a cathode ray tube (CRT), etc., or a combination thereof.

[0059] The communication port 240 can be connected to a network (e.g., network 120) to facilitate data communication. The communication port 240 can establish a connection between the processing device 140 and the CT scanner 110, the terminal 130, or the storage device 150. The connection can be a wired connection, a wireless connection, or a combination of both. These connection methods can enable data to be sent and received. The wired connection can include a cable, an optical fiber cable, a telephone line, etc., or any combination thereof. The wireless connection can include Bluetooth, Wi-Fi, WiMax, WLAN, ZigBee, a mobile network (e.g., 3G, 4G, 5G), etc., or a combination thereof. In some embodiments, the communication port 240 can be a standardized communication port such as RS232 and RS485. In some embodiments, the communication port 240 can be a specially designed communication port. For example, the communication port 240 can be designed according to the Digital Imaging and Communications in Medicine (DICOM) protocol.

[0060] Figure 3 is a schematic diagram of exemplary hardware and / or software components of the mobile device 300 shown in some embodiments of the present invention. The mobile device 300 can implement the terminal 130. As Figure 3As shown, the mobile device 300 may include a communication platform 310, a display 320, a graphics processing unit (GPU) 330, a central processing unit (CPU) 340, an input / output 350, a memory 360, and a storage 390. In some embodiments, any other suitable components, including but not limited to a system bus or a controller (not shown in the figure), may also be included in the mobile device 300. In some embodiments, a mobile operating system 370 (e.g., iOS, Android, Windows Phone) and at least one application 380 may be loaded from the storage 390 into the memory 360 for execution by the central processing unit 340. The application 380 may include a browser or any other suitable mobile application for receiving and presenting information related to image processing or other information from the processing device 140. User interaction with the information stream may be achieved through the input / output 350 and provided to the processing device 140 and / or other components of the medical system 100 via the network 120.

[0061] To implement the various modules, units, and their functions described in the present invention, a computer hardware platform may be used as the hardware platform for at least one element described in the present invention. The hardware elements, operating systems, and programming languages of such computers are conventional in nature. Assuming that those skilled in the art are fully familiar with these technologies, such technologies are adapted to the corrected projection images described in the present invention. A computer with user interface elements may be used to implement a personal computer (PC) or other types of workstations or terminal devices. However, if appropriately programmed, the computer may also act as a server. It is believed that those skilled in the art are familiar with the structure, programming, and general operation of such computer devices. Therefore, the drawings should be self-explanatory.

[0062] Figure 4 is a schematic diagram of an exemplary processing device 140 shown according to some embodiments of the present invention. The processing device 140 may be implemented on a computing device 200 (e.g., a processor 210) as shown in Figure 2 or on a CPU 340 as shown in Figure 3 The processing device 140 may include an acquisition module 410, a preprocessing module 420, a correction module 430, and a reconstruction module 440.

[0063] The obtaining module 410 can be used to obtain information related to the CT system 100. The information may include scan data (e.g., one or more gantry angles, radiation dose, parameters related to the collimator or the scanning table, or other parameters), image data (e.g., one or more projection images), etc. For example, the obtaining module 410 can obtain at least two projection images of the subject to be examined. The at least two projection images can be generated based on scan data obtained by a CT scanner (e.g., CT scanner 110) at at least two gantry angles. Each projection image can correspond to one gantry angle. In some embodiments, the gantry angle can be the angle formed by a line connecting the radiation source 113, the rotation center of the gantry 111, and a reference coordinate system (e.g., the X-axis and Y-axis as shown in Figure 1 ). By way of example only, the CT scanner 110 can perform a scan of the subject to be examined by irradiating the subject with X-rays. During the scan, the radiation source 113 and the detector 112 can rotate around the Z-axis with the gantry 111 to scan the subject to be examined at different gantry angles. Thus, at least two sets of scan data corresponding to at least two gantry angles can be obtained. The processing device 140 and / or the CT scanner 110 can generate at least two projection images corresponding to the gantry angles based on the at least two sets of scan data, and transmit the projection images to a storage device (e.g., storage device 150) for storage. The obtaining module 410 can access the storage device and obtain the projection images.

[0064] The preprocessing module 420 can be used to preprocess the projection images. For example, the preprocessing module 420 can preprocess the projection images corresponding to the gantry angles. The preprocessing of the projection images can include dead pixel correction, dark field correction, gain correction, geometric correction, beam hardening correction, scatter correction, etc., or any combination thereof. In some embodiments, the preprocessing of the projection images can include beam hardening correction and / or scatter correction. Details regarding beam hardening correction and / or scatter correction can be found elsewhere in the present invention (e.g., step 520 of process 500 and its related description).

[0065] The correction module 430 can be used to correct the projection images. For example, as described elsewhere in the present invention (e.g., step 530 of process 500, process 600, and their related descriptions), the correction module 430 can correct the projection images corresponding to the gantry angles and / or the preprocessed projection images. In some embodiments, the projection images to be corrected can be two-dimensional (2D) images. In some embodiments, the correction module 430 can correct the (preprocessed) projection images corresponding to the gantry angles by performing a first correction and a second correction on the (preprocessed) projection images. The first correction and the second correction can be used to remove dose variations in the (preprocessed) projection images. Details regarding the first correction and / or the second correction can be found elsewhere in the present invention (e.g., Figure 5 ,Figure 6 and its related descriptions).

[0066] In some embodiments, the correction module 430 can also be used to correct at least two projection images corresponding to at least two gantry angles to generate at least two corrected projection images. The correction of the projection images can include one or more iterations. For example, in each current iteration, the correction module 430 can determine whether the corrected projection images in the current iteration meet the conditions. If the at least two corrected projection images meet the conditions, the correction module 430 can terminate the current iteration. Based on the corrected projection images in the current iteration, a CT image can be reconstructed. If the at least two corrected projection images do not meet the conditions, the correction module 430 can designate the corrected projection images in the current iteration as the projection images in the next iteration. In the next iteration, the projection images can be corrected again (or preprocessed and corrected). The iteration can continue until the correction module 430 determines that in a new iteration, the corrected projection images meet the conditions. Details of the correction iteration can be found elsewhere in the present invention (e.g., Figure 8 and its related descriptions).

[0067] The reconstruction module 440 can be used to reconstruct an image. For example, the reconstruction module 440 can reconstruct a CT image of an object under examination based on at least two (corrected) projection images corresponding to at least two gantry angles. In some embodiments, the reconstruction module 440 can reconstruct an image according to a reconstruction technique. Exemplary reconstruction techniques can include, but are not limited to, algebraic reconstruction technique (ART), simultaneous algebraic reconstruction technique (SART), filtered back projection (FBP) technique, FDK reconstruction technique, etc., or any combination thereof.

[0068] The modules in the processing device 140 can be connected or communicate with each other via wired or wireless means. Wired connections can include metal cables, optical cables, hybrid cables, etc., or any combination thereof. Wireless connections can include local area network (LAN), wide area network (WAN), Bluetooth, ZigBee, near field communication (NFC), etc., or any combination thereof.

[0069] It should be noted that the above description is for illustrative purposes only and is not intended to limit the scope of protection of the present invention. Various changes and modifications can be made by those of ordinary skill in the art under the guidance of the present invention. Nevertheless, these changes and modifications do not depart from the scope of protection of the present invention.

[0070] In some embodiments, two or more modules may be combined into one module, and any one module may be split into two or more units. For example, the preprocessing module 420 and the correction module 430 may be integrated into one module that is configured to perform the functions of the preprocessing module 420 and the correction module 430. As another example, the correction module 430 may be split into two units. The first unit may be configured to perform a first correction on the (preprocessed) projection image to generate a preliminarily corrected projection image. The second unit may be configured to perform a second correction on the preliminarily corrected projection image to generate a corrected projection image.

[0071] In some embodiments, the processing device 140 may include one or more additional modules. For example, the processing device 140 may include a post-processing module (not shown). The post-processing module may be configured to post-process the corrected projection image. For example, beam hardening, scatter correction, image enhancement, etc. may be performed on the corrected projection image. As another example, the processing device 140 may include a storage module (not shown). The storage module may be configured to store data generated by any component of the processing device 140 during any process being executed.

[0072] Figure 5 is a flowchart of an exemplary process for reconstructing a CT image according to some embodiments of the present invention. The process 500 may be implemented in the CT system 100 as shown in Figure 1 For example, the process 500 may be stored in the storage device 150 and / or the memory 220 in the form of instructions (e.g., an application), and invoked and / or executed by the processing device 140 (e.g., the processor 210 as shown in Figure 2 or one or more modules in the processing device 140 as shown in Figure 4 . The operations of the process shown below are exemplary. In some embodiments, the process 500 may be completed with at least one additional operation not mentioned and / or at least one operation discussed omitted. Additionally, Figure 5 the order of operations of the process 500 shown in

[0073] is not intended to limit the present invention.

[0074] Based on the scan data obtained by a CT scanner (e.g., CT scanner 110) at at least two gantry angles, at least two projection images can be generated. Each projection image can correspond to a gantry angle. For example, CT scanner 110 can perform a scan of a subject by irradiating the subject with X-rays. During the scan, the radiation source 113 and the detector 112 can rotate around the Z-axis with the gantry 111 to scan the subject at different gantry angles. The scan data of the subject can include at least two sets of data corresponding to at least two gantry angles. The processing device 140 and / or CT scanner 110 can generate at least two projection images corresponding to at least two gantry angles based on the at least two sets of data, and transmit the projection images to a storage device (e.g., storage device 150) for storage. The acquisition module 410 can access the storage device and obtain the projection images.

[0075] In some embodiments, the gantry angle can be the angle formed by the line connecting the radiation source 113 and the center of rotation of the gantry 111 and a reference coordinate system (e.g., the X-axis, Y-axis as shown Figure 1 ). For example, the gantry angles of the at least two projection images obtained in step 510 can be in the range of 0° to 360°. In some embodiments, when the gantry 111 rotates, the radiation source 113 can continuously emit X-rays to the subject. For example, the gantry angle can be in the range of 0° to 360°, at least two sets of data corresponding to at least two gantry angles (e.g., 1200 or 2400 gantry angles) can be collected by the detector 112, and correspondingly, 1200 projection images corresponding to 1200 gantry angles or 2400 projection images corresponding to 2400 gantry angles can be generated. Optionally, the radiation source 113 can emit X-rays to the subject discontinuously. For example, the gantry angle can be in the range of 0° to 360°, the radiation source 113 can emit X-rays to the subject every time the gantry angle changes by 1°, and correspondingly, 360 projection images can be generated. Another example, the gantry angle can be in the range of 0° to 360°, the radiation source 113 can emit X-rays to the subject every time the gantry angle changes by 0.5°, and correspondingly, 720 projection images can be generated.

[0076] In some embodiments, the gantry angle of the projection image can be obtained from one or more components of the CT system 100 (e.g., the encoder of the gantry angle). In addition, the gantry angle of the projection image can be determined by the processing device 140 based on the data analysis of the gantry angles of other projection images. By way of example only, the processing device 140 can determine the gantry angle of the projection image using an interpolation algorithm based on at least two other projection images corresponding to other gantry angles.

[0077] In some embodiments, at least two projection images may include at least two 2D images. In some embodiments, one projection image may include at least two pixels. A pixel may have a pixel value, e.g., a grayscale value, a luminance value, etc., or any combination thereof. There is a linear relationship between the grayscale value of the projection image of the subject and the radiation dose emitted by the radiation source 113 to the subject. When the gantry 111 rotates, the radiation dose emitted by the radiation source 113 may fluctuate, which results in a difference between the actual grayscale value of the pixels in the projection image at different gantry angles and their ideal grayscale values. In CT image reconstruction, it is assumed that the logarithm of the grayscale value of the projection image is proportional to the attenuation coefficient of the subject. The difference between the actual grayscale value and the ideal pixel value of the projection image affects the quality of the CT image reconstructed based on these projection images, leading to misdiagnosis. Therefore, multiple projection images corresponding to different gantry angles need to be corrected and / or normalized to reduce the impact of the non-uniform radiation dose at different gantry angles.

[0078] In step 520, the preprocessing module 420 may preprocess at least two projection images to generate at least two preprocessed projection images corresponding to at least two gantry angles. The preprocessing of at least two projection images may include dead pixel correction, dark field correction, gain correction, geometric correction, beam hardening correction, scatter correction, etc., or any combination thereof.

[0079] In some embodiments, the preprocessing of at least two projection images may include beam hardening correction and / or scatter correction. The beam hardening correction may be performed based on a beam hardening correction algorithm. Exemplary beam hardening correction algorithms may include polynomial fitting algorithm, Monte Carlo simulation algorithm, iterative correction algorithm, dual energy correction algorithm, single energy correction algorithm, etc., or any combination thereof. The scatter correction may be performed based on a scatter correction algorithm. Exemplary scatter correction algorithms may include convolution algorithm, model evaluation algorithm, deconvolution algorithm, Monte Carlo simulation algorithm, single scatter simulation algorithm, dual energy window technique, scatter correction plate, frequency modulation technique, etc., or any combination thereof.

[0080] In some embodiments, the preprocessing module 420 may preprocess the projection image corresponding to a certain gantry angle based on the radiation dose delivered to the subject at that gantry angle. The radiation dose delivered to the subject at that gantry angle may be the planned dose, or the dose measured by the ionization chamber when the CT scanner 110 scans the subject at that gantry angle. For example, the preprocessing module 420 may determine the X-ray intensity passing through the subject based on the radiation dose delivered to the subject at that gantry angle, and the preprocessing module 420 may perform scatter correction on the projection image based on the X-ray intensity.

[0081] In step 530, the correction module 430 may correct at least two pre-processed projection images corresponding to at least two gantry angles to generate at least two corrected projection images. The corrected projection images may be 2D images.

[0082] In some embodiments, the correction module 430 may correct the first pre-processed projection image corresponding to the first gantry angle by performing a first correction and / or a second correction on the first pre-processed projection image. The first gantry angle may be any one of the gantry angles. The first correction and the second correction may be used to remove dose variations in the first pre-processed projection image. The first correction may be performed on the first pre-processed projection image to generate a preliminarily corrected first projection image. In some embodiments, the first correction may be performed based on the pre-processed projection image corresponding to the second gantry angle. The second gantry angle may be any one of the gantry angles other than the first gantry angle. In some embodiments, the second gantry angle may be a neighboring gantry angle of the first gantry angle. If the angular difference between a gantry angle and the first gantry angle is less than an angle threshold (e.g., 2°), that gantry angle may be considered a neighboring gantry angle of the first gantry angle. For brevity, the projection image corresponding to the neighboring gantry angle of the first gantry angle may be referred to as the neighboring projection image of the first projection image. Details regarding the first correction may be found elsewhere in the present invention (e.g., Figure 6 and its related description).

[0083] The second correction may be performed on the preliminarily corrected first projection image to generate the corrected projection image corresponding to the first gantry angle. In some embodiments, the second correction may be performed based on at least a portion of the preliminarily corrected first projection image. For example, the second correction may be performed based on one or more pixels corresponding to the middle channel of the CT scanner 110 at the first gantry angle. Details regarding the second correction may be found elsewhere in the present invention (e.g., Figure 6 、 Figure 7 and its related description).

[0084] In some embodiments, for each preprocessed projection image, the correction module 430 may perform a first correction and / or a second correction on the preprocessed projection image to generate a corrected projection image. In some embodiments, the first correction may be performed on each preprocessed projection image based on the preprocessed adjacent projection images. Optionally, the correction module 430 may arrange the preprocessed projection images according to the gantry angles of the preprocessed projection images and perform the first correction on at least two preprocessed projection images in sequence. The first correction of the preprocessed projection image corresponding to the gantry angle may be performed based on the preliminarily corrected adjacent projection images. Only by way of example, the correction module 430 may perform the first correction on the first preprocessed projection image corresponding to 0°, the first correction on the second preprocessed projection image corresponding to 1°, …, and the first correction on the 360th preprocessed projection image corresponding to 359°. The correction module 430 may perform the first correction on the first preprocessed projection image based on the 360th preprocessed projection image to generate a preliminarily corrected first projection image, perform the first correction on the second preprocessed projection image based on the preliminarily corrected first projection image, …, and perform the first correction on the 360th preprocessed projection image based on the preliminarily corrected 359th projection image.

[0085] In step 540, the reconstruction module 440 may reconstruct a CT image of the subject based on at least two corrected projection images. In some embodiments, the reconstruction module 440 may reconstruct the CT image according to a reconstruction technique. Exemplary reconstruction techniques may include, but are not limited to, algebraic reconstruction technique (ART), simultaneous algebraic reconstruction technique (SART), filtered back projection (FBP) technique, FDK reconstruction technique, etc., or any combination thereof. In some embodiments, the CT image may be a three-dimensional (3D) CT image. The CT image may include at least two pixels, and the pixel values of the at least two pixels may represent the attenuation coefficients of different parts of the subject.

[0086] It should be noted that the above description of process 500 is for illustrative purposes only and is not intended to limit the scope of the present invention. Various changes and modifications can be made by those of ordinary skill in the art under the guidance of the present invention. Nevertheless, these changes and modifications do not depart from the scope of the present invention.

[0087] In some embodiments, step 520 may be omitted. In step 530, the correction module 430 may correct at least two projection images corresponding to at least two gantry angles to generate at least two corrected projection images. In some embodiments, the order of steps of process 500 may be changed. For example, the partial preprocessing of the projection images as described in step 520 may be performed after step 530. In some embodiments, beam hardening correction and / or scatter correction are not performed in step 520. A processing device 140 (e.g., a post-processing module not shown in the figure) may perform beam hardening and / or scatter correction on the corrected projection images to post-process the corrected projection images after step 530. In step 540, the reconstruction module 440 may reconstruct a CT image of the object under examination based on the post-processed projection images.

[0088] Figure 6 is a flowchart of an exemplary process for correcting projection images according to some embodiments of the present invention. Process 600 may be implemented in the CT system 100 as shown in Figure 1 For example, process 600 may be stored in the storage device 150 and / or the memory 220 in the form of instructions (e.g., an application), and called and / or executed by the processing device 140 (e.g., the processor 210 as shown in Figure 2 or one or more modules in the processing device 140 as shown in Figure 4 . The operations of the process shown below are exemplary. In some embodiments, process 600 may be completed with at least one additional operation mentioned and / or omitting at least one operation discussed. Additionally, Figure 6 the order of operations of process 600 shown in

[0089] In some embodiments, process 600 may be used to correct the first preprocessed projection images obtained in step 520. In step 530, the correction module 430 may repeat process 600 for each preprocessed projection image. Optionally, process 600 may be executed to correct the first projection image of at least two projection images obtained in step 510. In some embodiments, step 520 may be omitted. In step 530, the correction module 430 may correct at least two projection images by repeating process 600 for each projection image. For illustrative purposes, the first projection image of at least two projection images is described as an example in the present invention.

[0090] In step 610, the calibration module 430 can perform a first calibration on the first projection image based on the first projection image and the second projection image of at least two projection images to generate a preliminarily calibrated first projection image. The first calibration image can correspond to a first gantry angle of the gantry angles, and the first gantry angle can be any one of the gantry angles. The second projection image can correspond to a second gantry angle of the gantry angles, and the second gantry angle can be any one of the gantry angles other than the first gantry angle. In some embodiments, the second gantry angle can be an adjacent gantry angle of the first gantry angle. If the angular difference between a gantry angle and the first gantry angle is less than the angle threshold, the gantry angle can be considered an adjacent gantry angle of the first gantry angle. Merely by way of example, the gantry angle can be an integer within the range of 0° to 360°. If the angle threshold is 2°, the adjacent gantry angles of 10° can be 9° or 11°.

[0091] In some embodiments, the calibration module 430 can determine a first calibration coefficient of the first projection image based on the difference between the first projection image and the second projection image, and calibrate the first projection image based on the first calibration coefficient. In some embodiments, the first calibration coefficient can be a multiplication factor applied to the projection image to calibrate the projection image for intensity fluctuations of the radiation source 113 during projection image creation. In some embodiments, the first calibration coefficient can be a scalar applied to the entire projection image. In some embodiments, the first calibration coefficient can be a vector or a matrix that may apply unique factors to different pixels in the projection image. In some embodiments, the difference between the first projection image and the second projection image can be the difference between the gray-level information of the first projection image and the gray-level information of the second projection image. The gray-level information of the first projection image or the second projection image can be represented by an image matrix, an image histogram, etc. In some embodiments, the gray-level information of the projection image can be determined by the intensity of the radiation source 113 and the attenuation characteristics of the object under examination during projection image creation. For example, the logarithm of the gray value of a pixel can be approximated as the attenuation coefficient of the physical point corresponding to the pixel.

[0092] The first calibration coefficient can be a coefficient that minimizes the difference between the first projection image and the second projection image. In some embodiments, the calibration coefficient that minimizes the difference between two images corresponding to two gantry angles can be determined by formula (1):

[0093]

[0094] where i and j respectively represent two gantry angles among a plurality of gantry angles; R represents a set of real number matrices; I i represents the projection image corresponding to the gantry angle i; I j represents the projection image corresponding to the gantry angle j; f(I i ) represents the gray-level information of I i ; f(Ij ) represents I j 's grayscale information; and a ij represents minimizing I i and I j The correction coefficient of the difference between. In some embodiments, f(I i ) can be the image matrix of I i , image histogram, etc., f(I j ) can be the image matrix of I j , image histogram, etc. The norm in formula (1) can be the L2 norm, L1 norm, or other metrics, which increase the similarity between f(I i ) and a ij f(I j ) when being optimized.

[0095] In some embodiments, f(I i ) can represent the attenuation information related to the projection image I i . The attenuation information related to the projection image I i can be determined based on the grayscale information of the projection image I i . For example, the attenuation information can include the cumulative attenuation results of each spatial point on the ray incident on each pixel corresponding to each pixel in the projection image I i . The cumulative attenuation results of each spatial point on the ray corresponding to each pixel in the projection image I i can be obtained by performing a Log transformation on the grayscale value of the corresponding pixel. Similarly, f(I j ) can represent the attenuation information related to the projection image I j .

[0096] In some embodiments, the first correction coefficient of the first projection image can be determined according to formula (1). I i can represent the first projection image, I j can represent the second projection image, a ij can represent the first correction coefficient. Optionally, I j can represent the first projection image, I i can represent the second projection image, a ij can represent the first correction coefficient. After determining the first correction coefficient, the correction module 430 can generate a preliminarily corrected first projection image based on the first correction coefficient and the first projection image. In some embodiments, the preliminarily corrected first projection image can be determined by multiplying the grayscale information of the first projection image by the first correction coefficient, or dividing the grayscale information of the first projection image by the first correction coefficient. For example, when I i represents the first image, I jWhen representing the second image, the correction module 430 can generate a preliminarily corrected first projection image by dividing the grayscale information of the first projection image by a ij j (for example, dividing the grayscale value of a pixel in the first projection image by a ij ). When I j represents the first image and I i represents the second image, the correction module 430 can generate a preliminarily corrected first projection image by multiplying the grayscale information of the first projection image by a ij (for example, multiplying the grayscale value of a pixel in the first projection image by a ij ).

[0097] In some embodiments, the first correction coefficient of the first projection image can be determined based on the attenuation coefficients of the first and second projection images. The correction module 430 can correct the attenuation information of the first projection image by multiplying the attenuation information of the first projection image by the first correction coefficient or by dividing the attenuation information of the first projection image by the first correction coefficient. The correction module 430 can generate a preliminarily corrected first projection image by performing an exponential operation on the corrected attenuation information of the first projection image. The correction process of the first projection image based on the attenuation information of the first and second projection images can be regarded as the preprocessing of the first projection image in CT image reconstruction.

[0098] In step 620, the correction module 430 can perform a second correction on the preliminarily corrected first projection image based on at least a part of the preliminarily corrected first projection image to generate a corrected first projection image. In some embodiments, at least a part of the preliminarily corrected first projection image can include one or more pixels corresponding to the middle channels of the CT scanner 110 at the first gantry angle in the preliminarily corrected first projection image. The second correction coefficient can be determined based on at least a part of the preliminarily corrected first projection image to correct the preliminarily corrected first projection image. In some embodiments, the second correction of the preliminarily corrected first projection image can be performed according to the Figure 7 process 700 shown.

[0099] It should be noted that the description of process 600 is for illustrative purposes only and is not intended to limit the scope of the present invention. Various changes and modifications can be made by those of ordinary skill in the art under the guidance of the present invention. Nevertheless, these changes and modifications do not depart from the scope of the present invention. For example, step 620 can be omitted. In some embodiments, when the number of projection images obtained in step 510 is greater than a threshold, step 620 can be omitted. Also, for example, step 610 can be omitted. In step 620, the correction module 430 can perform a second correction on the first projection image corresponding to the first gantry angle or the preprocessed first projection image to generate a corrected first projection image.

[0100] Figure 7 is a flowchart of an exemplary process for performing a second correction on a preliminarily corrected first projection image according to some embodiments of the present invention. Process 700 may be implemented in a CT system 100 as shown in Figure 1 . For example, process 700 may be stored in a storage device 150 and / or a memory 220 in the form of instructions (e.g., an application), and invoked and / or executed by a processing device 140 (e.g., a processor 210 as shown in Figure 2 , or one or more modules in the processing device 140 as shown in Figure 4 ). The operations for the process shown below are exemplary. In some embodiments, process 700 may be completed with at least one additional operation not mentioned and / or omission of at least one operation discussed. Additionally, Figure 7 the order of operations of process 700 shown in Figure 6 is not intended to limit the present invention. In some embodiments,

[0101] In step 710, a correction module 430 may identify at least one pixel of the preliminarily corrected first projection image. The identified at least one pixel may correspond to an intermediate channel of the CT scanner 110 at a first gantry angle.

[0102] The detector 112 may include at least two detector channels. Each detector channel may correspond to a row of pixels of the preliminarily corrected first projection image. When the CT scanner 110 scans a subject at a first gantry angle, X-rays may pass through the rotation center of the gantry 111 and be detected by the detector channels. The detector channel that detects the X-rays passing through the rotation center of the gantry 111 may be referred to as the intermediate channel of the CT scanner 110 at the first gantry angle. In the case of a fan beam or a cone beam, the X-rays passing through the rotation center of the gantry 111 may undergo substantially equal attenuation of the imaging medium at any pair of angular source positions, where each pair of angular source positions is separated by 180°. For another X-ray passing through a path in a direction substantially opposite to the X-ray, the expected total attenuation of it passing through the rotation center is substantially the same as the expected total attenuation of the X-ray passing through the rotation center of the gantry 111.

[0103] In some embodiments, at least one of the identified pixels corresponding to the intermediate channel may include a row of pixels corresponding to the intermediate channel. Optionally, at least one of the identified pixels may include one or more rows of pixels corresponding to adjacent detector channels of the intermediate channel. If the distance between the detector channel and the intermediate channel is within a predetermined range (e.g., one detector channel, two detector channels), the detector channel may be considered an adjacent detector channel of the intermediate channel. In some embodiments, at least one of the identified pixels may include one or more rows of pixels corresponding to the intermediate channel and its one or more adjacent detector channels. In some embodiments, the correction module 430 may determine the intermediate channel of the CT scanner 110 at the first gantry angle and determine at least one pixel of the first projection image with preliminary correction based on the intermediate channel.

[0104] In step 720, for each pixel of the pixels, the correction module 430 may identify the opposite pixel corresponding to each pixel of the pixels. One pixel of the pixels may correspond to a detector unit of the intermediate channel of the CT scanner 110 at the first gantry angle. The detector unit may detect X-rays or an X-ray beam (collectively referred to as X-rays herein) emitted by the radiation source 113 at the first gantry angle. The opposite pixel may correspond to the opposite X-ray of the X-rays. The opposite X-ray may be emitted by the radiation source 113 at the opposite gantry angle corresponding to the X-rays. In some embodiments, if the X-ray passes through the rotation center of the CT scanner 110 at the first gantry angle, its corresponding opposite X-ray may be emitted by the radiation source 113 at the corresponding opposite gantry angle, and the corresponding opposite gantry angle differs from the first gantry angle by 180°. On the other hand, for an X-ray that does not pass through the rotation center of the CT scanner at the first gantry angle, the corresponding opposite gantry angle may be determined based on the first gantry angle described elsewhere in this application (e.g., Figure 9 and its description).

[0105] In some embodiments, the gantry angle may be in the range of 0° to 360°. The X-rays emitted by the radiation source 113 at a gantry angle may be collinear with another X-ray emitted by the radiation source 113 at another gantry angle. By way of example only, as Figure 9As shown, the X-ray emitted by the radiation source 113 from position A to position B (referred to as X-ray AB) and the X-ray emitted by the radiation source 113 from position B to position A (referred to as X-ray BA) are collinear. X-ray BA can be called the opposite X-ray of X-ray AB. When the radiation source 113 is at position A, the gantry angle of the CT scanner 110 can be β1. When the radiation source 113 is at position B, the gantry angle of the CT scanner 110 can be β2. The gantry angle β2 can be called the opposite gantry angle of the gantry angle β1 corresponding to X-ray AB. X-ray AB can correspond to a pixel of the preliminarily corrected projection image corresponding to the gantry angle β1, and X-ray BA can correspond to a pixel of the preliminarily corrected projection image corresponding to the gantry angle β2. The pixel corresponding to X-ray BA can be called the opposite pixel of the pixel corresponding to X-ray AB. In some embodiments, the opposite gantry angle (e.g., gantry angle β2) of the gantry angle (e.g., gantry angle β1) corresponding to the X-ray can be determined based on this gantry angle. Details regarding the determination of the opposite gantry angle of the gantry angle can be found elsewhere in the present invention (e.g., Figure 9 and its related description).

[0106] For each of the identified at least one pixel in the first preliminarily corrected projection image, the correction module 430 can determine the opposite X-ray and the opposite gantry angle corresponding to this pixel, and identify the opposite pixel of this pixel based on the opposite X-ray and the opposite gantry angle.

[0107] In step 730, the correction module 430 can generate a reference image of the first preliminarily corrected projection image based on the opposite pixel of the pixel.

[0108] In step 740, the correction module 430 can determine the second correction coefficient of the first preliminarily corrected projection image based on the difference between the at least one pixel corresponding to the intermediate channel and the reference image. The difference between the at least one pixel and the reference image can be similar to the difference between the first projection image and the second projection image described in step 610, which will not be repeated here. In some embodiments, the second correction coefficient can be determined based on the difference between the at least one pixel and the corresponding pixel in the reference image.

[0109] The second correction coefficient can be the coefficient that minimizes the difference between the at least one pixel and the reference image. In some embodiments, the second correction coefficient can be determined by formula (2):

[0110]

[0111] where i represents the first gantry angle; C 0i represents the at least one pixel corresponding to the intermediate channel of the CT scanner 110 at the first gantry angle i; C 1i represents C0i Reference image; f(C 0i ) represents the gray information of C 0i ; f(C 1i ) represents the gray information of C 1i ; and b i represents the second correction coefficient for minimizing the difference between C 0i and C 1i . In some embodiments, f(C 0i ) can be the image matrix, image histogram, etc. of C 0i , and f(C 1i ) can be the image matrix, image histogram, etc. of C 1i . In some embodiments, f(C 0i ) can represent the attenuation information related to the identified pixels. The attenuation information related to the identified pixels can be determined based on the gray value of the identified pixels. For example, the attenuation information can include the cumulative attenuation results of each spatial point on the ray incident on the pixel point corresponding to each pixel. The cumulative attenuation results of each spatial point on the ray corresponding to each pixel can be obtained by performing a Log transformation on the gray value of the corresponding pixel. Similarly, f(C 1i ) can represent the attenuation information related to the reference image C 1i .

[0112] In step 750, the correction module 430 can generate a corrected first projection image corresponding to the first gantry angle based on the second correction coefficient and the preliminarily corrected first projection image. In some embodiments, the corrected first projection image can be determined by dividing the gray information of the preliminarily corrected first projection image by the second correction coefficient. In some embodiments, the second correction coefficient can be determined based on the attenuation information of the identified pixels and the reference image. The correction module 430 can correct the attenuation information of the preliminarily corrected first projection image by multiplying the attenuation information of the preliminarily corrected first projection image by the second correction coefficient or dividing the attenuation information of the preliminarily corrected first projection image by the second correction coefficient.

[0113] Figure 8 is a flowchart of an exemplary process for reconstructing a CT image according to some embodiments of the present invention. Process 800 can be implemented in the CT system 100 as shown in Figure 1 . For example, process 800 can be stored in the storage device 150 and / or the memory 220 in the form of instructions (e.g., an application), and can be executed by the processing device 140 (e.g., the processor 210 as shown in Figure 2 , or as shown in Figure 4One or more modules in the processing device 140 shown) are called and / or implemented. The operations for the process shown below are exemplary. In some embodiments, process 800 may be completed with at least one additional operation not mentioned and / or at least one operation discussed omitted. Additionally, Figure 8 The order of operations of the process 800 shown is not intended to limit the present invention. In some embodiments, process 800 may be an embodiment of process 500 that includes one or more iterations.

[0114] In step 810, the acquisition module 410 may acquire at least two projection images of the object to be examined. The at least two projection images are generated based on scan data obtained by a CT scanner (e.g., CT scanner 110) at at least two gantry angles. Each projection image may correspond to one gantry angle. In step 820, the preprocessing module 420 may preprocess the at least two projection images to generate at least two preprocessed projection images corresponding to at least two gantry angles. In step 830, the correction module 430 may correct the at least two preprocessed projection images to generate at least two corrected projection images. Steps 810 to 830 may be performed in a manner similar to steps 510 to 530 and will not be repeated here.

[0115] In step 840, the correction module 430 may determine whether the at least two corrected projection images meet the condition. In some embodiments, the condition may be related to the number of iterations of performing steps 820 to 840 on the at least two projection images acquired in step 810. For example, the number of iterations may be calculated by the correction module 430, and the condition may be that the number of iterations is greater than a first threshold. The correction module 430 may determine whether the number of iterations is greater than the first threshold. If the number of iterations is greater than the first threshold, the correction module 430 may determine that the condition is met. If the number of iterations is less than or equal to the first threshold, the correction module 430 may determine that the condition is not met. In some embodiments, the first threshold may be in the range of 2 - 10. In some embodiments, the first threshold may be defined within a sub - range of 1 - 2, 2 - 4, 1 - 5, or 5 - 10.

[0116] In addition, the condition may be related to the inconsistency between the corrected projection images (or portions thereof). In some embodiments, the inconsistency between the corrected projection images may refer to the inconsistency between the pixel values (e.g., gray values) of the corrected projection images. The pixel values of the corrected projection images may be represented by the average or median pixel value of the corrected projection image, the maximum or minimum pixel value of the corrected projection image, etc., or any combination thereof. For illustrative purposes only, the following description uses the average pixel value of the corrected projection image as an example. The inconsistency between the corrected projection images may be evaluated by the variance of the average pixel value, the standard deviation of the average pixel value, etc., or any combination thereof. The condition may be that the inconsistency between the corrected projection images (or portions thereof) is less than a second threshold. The correction module 430 may determine whether the inconsistency between the corrected projection images (or portions thereof) is less than the second threshold. If the inconsistency between the corrected projection images (or portions thereof) is less than the second threshold, the correction module 430 may determine that the condition is satisfied. If the inconsistency between the corrected projection images (or portions thereof) is greater than or equal to the second threshold, the correction module 430 may determine that the condition is not satisfied.

[0117] In some embodiments, the condition may be that the difference between the corrected CT image in the current iteration and the corrected CT image in the previous iteration is less than a third threshold. For example, for the corrected CT image in the current iteration, the correction module 430 may determine the difference between the gray information (e.g., average gray information) of the corrected CT image and the gray information of the corresponding corrected CT image in the previous iteration. The correction module 430 may determine whether the difference between the gray information is greater than the third threshold (e.g., 5% of the gray information of the corrected CT image in the current iteration). If the gray information is less than or equal to the third threshold, the correction module 430 may determine that the condition is satisfied. If the gray information is greater than the third threshold, the correction module 430 may determine that the condition is not satisfied. In some embodiments, the first threshold, the second threshold, and / or the third threshold may be default values stored in a storage device (e.g., storage device 150), or may be set or adjusted by a user (e.g., a doctor).

[0118] If it is determined that the corrected projection image satisfies the condition, step 850 is executed. In step 850, the reconstruction module 440 may reconstruct a CT image of the subject based on at least two corrected projection images. For the reconstruction technique, refer to Figure 5 the description in, which will not be repeated here.

[0119] Return to step 840. Conversely, if the corrected projection image does not meet the condition, execute step 860. In step 860, the correction module 430 may designate at least two corrected projection images in the current iteration as at least two projection images in the next iteration. In the next iteration, the processing device 140 may execute process 800 and return to step 820. The processing device 140 may preprocess and correct the projection image in the next iteration to generate at least two corrected projection images. Further, if the correction module 430 determines that the corrected projection image in the next iteration meets the condition, the reconstruction module 440 may reconstruct the CT image of the object under examination based on the corrected projection image in the next iteration. If the correction module 430 determines that the corrected projection image does not meet the condition, execute step 860. The iteration from step 820 to 840 may continue until the correction module 430 determines that in a new iteration, the corrected projection image meets the condition.

[0120] It should be noted that the description of process 800 is for illustrative purposes only and is not intended to limit the scope of the present invention. Various changes and modifications can be made by those of ordinary skill in the art under the guidance of the present invention. Nevertheless, these changes and modifications do not depart from the scope of the present invention.

[0121] In some embodiments, in one iteration, the processing device 140 may execute process 800 and return to step 830 after step 860. In some embodiments, step 820 may be omitted. In step 830, the correction module 430 may correct the projection image obtained in step 810 to generate at least two corrected projection images. In some embodiments, the step order of process 800 may be changed. For example, the beam hardening correction and / or scatter correction in step 820 may be performed after step 830 to post-process the corrected projection image. In step 840, the correction module 430 may determine whether the post-processed corrected projection image meets the condition. For another example, the beam hardening correction and / or scatter correction in step 820 may be omitted. If the corrected projection image meets the condition, the processing device 140 may perform beam hardening correction and / or scatter correction on the corrected projection image to post-process the corrected projection image. In step 850, the reconstruction module 440 may reconstruct the CT image of the object under examination based on at least two post-processed projection images.

[0122] Figure 9 is a schematic diagram of the relationship between two exemplary gantry angles shown in some embodiments of the present invention. As Figure 9As shown, the X-ray emitted by the radiation source 113 from position A to position B (e.g., X-ray AB) can be collinear with the X-ray emitted by the radiation source 113 from position B to position A (e.g., X-ray BA). When the radiation source 113 is at position A, the gantry angle of the CT scanner 110 can be β1; when the radiation source 113 is at position B, the gantry angle of the CT scanner 110 can be β2. The gantry angle β2 can be referred to as Figure 7 the opposite gantry angle of the gantry angle β1 corresponding to the X-ray AB described in

[0123] β1 = β2 + 2×γ + π, (3)

[0124] where γ (as Figure 9 shown) represents the crossing angle between the X-ray AB and the line connecting position A and the rotation center O of the CT scanner 110, or the crossing angle between the X-ray BA and the line connecting position B and the rotation center O of the CT scanner 110. The angular unit of formula (3) is radians.

[0125] Figure 10 is an exemplary CT image 1000 of the subject shown according to some embodiments of the present invention. The CT image 1000 can be generated based on a plurality of projection images of the subject. As described elsewhere in the present invention (e.g., step 510 and its related description), the plurality of projection images can correspond to a plurality of gantry angles. The plurality of projection images can be corrected and / or normalized to reduce the influence of uneven radiation doses at different gantry angles. Based on the corrected and / or normalized plurality of projection images, the CT image can be reconstructed.

[0126] In some embodiments, the processing device 140 can correct the projection images by executing the exemplary methods described in the present invention (e.g., process 500 or process 800). Again, for example, the processing device 140 can correct the projection images based on the reported doses delivered to the subject at a plurality of gantry angles. When the CT scanner 110 scans the subject at a certain gantry angle, the reported dose delivered to the subject at the gantry angle can be obtained from the ionization chamber. For illustrative purposes, the corrected projection images generated based on the exemplary methods described in the present invention can be referred to as the third corrected projection images, and the corrected projection images generated based on the reported doses are referred to as the fourth corrected projection images.

[0127] The CT image 1000 includes a region 1010 as Figure 10 shown. For the third and / or fourth corrected projection images, the processing device 140 can determine the average gray value of the pixels in the region 1010. Figure 11is the average pixel value of region 1010 in the corrected projection image shown in some embodiments of the present invention. The horizontal axis represents the gantry angle corresponding to the corrected projection image, and the vertical axis represents the average pixel value of the pixels in region 1010 of the corrected projection image. The points on the dotted line represent the average pixel value of region 1010 in the third corrected projection image. The scattered points represent the average pixel value of region 1010 in the fourth corrected projection image. As Figure 11 shown, the fluctuation amplitude of the average pixel value of region 1010 in the third corrected projection image is smaller than that of the average pixel value of region 1010 in the fourth corrected projection image, which indicates that the third corrected projection image has better consistency than the fourth corrected projection image.

[0128] The basic concepts have been described above. Obviously, for those skilled in the art, the above invention disclosure is only an example and does not constitute a limitation to this application. Although not explicitly stated here, those skilled in the art may make various modifications, improvements, and corrections to this application. Such modifications, improvements, and corrections are proposed in this application, so such modifications, improvements, and corrections still fall within the spirit and scope of the exemplary embodiments of this application.

[0129] Meanwhile, this application uses specific words to describe the embodiments of this application. Such as "one embodiment", "an embodiment", and / or "some embodiments" mean a certain feature, structure, or characteristic related to at least one embodiment of this application. Therefore, it should be emphasized and noted that the "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more at different positions in this specification does not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of this application can be appropriately combined

[0130] In addition, those skilled in the art can understand that various aspects of this application can be illustrated and described by several patentable types or situations, including any new and useful process, machine, product, or combination of substances, or any new and useful improvement to them. Accordingly, various aspects of this application can be executed entirely by hardware, entirely by software (including firmware, resident software, microcode, etc.), or by a combination of hardware and software. The above hardware or software can all be referred to as "data block", "module", "engine", "unit", "component", or "system". In addition, various aspects of this application may be embodied as a computer product located in one or more computer-readable media, and the product includes computer-readable program codes.

[0131] A computer-readable signal medium may include a propagated data signal embodying computer program code thereon, for example, baseband or as part of a carrier wave. The propagated signal may take any of a variety of forms, including electromagnetic, optical, or the like, or any suitable combination thereof. The computer-readable signal medium may be any computer-readable medium other than a computer-readable storage medium that can be connected to an instruction execution system, apparatus, or device to communicate, propagate, or transport the program for use. The program code embodied on the computer-readable signal medium may be propagated via any appropriate medium, including radio, cable, fiber optic cable, RF, or the like, or any combination of the foregoing media.

[0132] The computer program code required for the operation of the various parts of the present application may be written in any one or more programming languages, including object-oriented programming languages such as Java, Scala, Smalltalk, Eiffel, JADE, Emerald, C++, C#, VB.NET, Python, etc., conventional procedural programming languages such as C, Visual Basic, Fortran 2003, Perl, COBOL 2002, PHP, ABAP, dynamic programming languages such as Python, Ruby, and Groovy, or other programming languages. The program code may run entirely on the user's computer, or as a stand-alone software package on the user's computer, or partly on the user's computer and partly on a remote computer, or entirely on the remote computer or server. In the latter case, the remote computer may be connected to the user's computer by any network form, such as a local area network (LAN) or a wide area network (WAN), or connected to an external computer (e.g., via the Internet), or in a cloud computing environment, or used as a service such as software as a service (SaaS).

[0133] Furthermore, unless clearly stated in the claims, the order of the processing elements and sequences, the use of numerical letters, or the use of other names in the present application are not used to limit the order of the processes and methods of the present application. Although some currently useful embodiments of the invention are discussed by way of various examples in the foregoing disclosure, it should be understood that such details are for illustrative purposes only, and the appended claims are not limited to the disclosed embodiments. On the contrary, the claims are intended to cover all modifications and equivalent combinations that conform to the essence and scope of the embodiments of the present application. For example, although the system components described above may be implemented by hardware devices, they may also be implemented only by a software solution, such as installing the described system on an existing server or mobile device.

[0134] Similarly, it should be noted that, in order to simplify the description disclosed in this application and thus help the understanding of one or more embodiments of the invention, in the foregoing description of the embodiments of this application, sometimes multiple features are merged into one embodiment, drawing or description thereof. However, this disclosure method does not mean that the features required by the object of this application are more than those mentioned in the claims. In fact, the features of the embodiment are fewer than all the features of the single embodiment disclosed above.

[0135] In some embodiments, numbers are used to describe components and the quantity of attributes. It should be understood that such numbers used for the description of embodiments are modified by modifiers such as "about", "approximately" or "substantially" in some examples. Unless otherwise specified, "about", "approximately" or "substantially" indicate that the said numbers allow a change of ± as stated. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, and such approximate values may change according to the characteristics required by individual embodiments. In some embodiments, the numerical parameters should consider the specified significant digits and adopt the method of retaining the general number of digits. Although the numerical ranges and parameters used in some embodiments of this application to confirm the breadth of their scope are approximate values, in specific embodiments, such numerical settings are as precise as possible within the feasible range.

[0136] Finally, it should be understood that the embodiments described in this application are only used to illustrate the principles of the embodiments of this application. Other deformations may also fall within the scope of this application. Therefore, by way of example and not limitation, alternative configurations of the embodiments of this application may be considered to be consistent with the teachings of this application. Accordingly, the embodiments of this application are not limited to the embodiments clearly introduced and described in this application.

Claims

1. A system for correcting a projected image, characterized in that, Comprising: A storage device for storing a set of instruction sets; and A processor, the processor communicating with the storage device, wherein, when executing the instruction sets, the processor is configured to: Obtain at least two projection images of an object to be examined, the at least two projection images being generated based on scan data obtained by a CT scanner at at least two gantry angles, each projection image corresponding to one gantry angle; and Correct a first projection image of the at least two projection images according to a process of generating a corrected projection image, the first projection image corresponding to a first gantry angle of the at least two gantry angles, the process of generating the corrected projection image comprising: Performing a second correction on the first projection image based on at least a part of the first projection image to generate a corrected first projection image corresponding to the first gantry angle, wherein at least a part of the first projection image includes one or more pixels corresponding to an intermediate channel of the CT scanner at the first gantry angle.

2. The system for correcting a projected image according to claim 1, wherein The processor is further configured to: Correct the at least two projection images according to the process of generating the corrected projection image to generate at least two corrected projection images; and Reconstruct a CT image of the object to be examined based on the at least two corrected projection images.

3. The system for correcting a projected image according to claim 2, wherein, In order to correct the at least two projection images, the processor is configured to: Perform at least one iteration, each current iteration of the iteration including: Correcting the at least two projection images in the current iteration according to the process of generating the corrected projection image to generate at least two corrected projection images; Determining whether the at least two corrected projection images in the current iteration meet a condition; and If the at least two corrected projection images do not meet the condition, designating the at least two corrected projection images in the current iteration as the at least two projection images in the next iteration.

4. The system for correcting a projected image according to claim 1, wherein Performing the second correction on the first projection image to generate a corrected first projection image includes: Identifying at least one pixel of the first projection image, the identified at least one pixel corresponding to an intermediate channel of the CT scanner at the first gantry angle; For each pixel, identifying the opposite pixel corresponding to each pixel; Generating a reference image of the first projection image based on at least one opposite pixel of the at least one pixel; Determining a second correction coefficient of the first projection image based on a difference between the identified at least one pixel and the reference image; and Generating the corrected first projection image corresponding to the first gantry angle based on the second correction coefficient and the first projection image.

5. The system for correcting a projected image according to claim 1, wherein Generating the first projection image includes: Preprocessing the first projection image to generate a preprocessed first projection image, the preprocessing of the first projection image at least including beam hardening correction or scatter correction.

6. The system for correcting a projected image according to claim 1, wherein, The processor is configured to: Post-process the corrected first projection image, the post-processing of the corrected first projection image at least including beam hardening correction or scatter correction.

7. A method for correcting a projected image, characterized in that, The method includes: Obtain at least two projection images of the object under examination, the at least two projection images being generated based on scan data acquired by a CT scanner at at least two gantry angles, each projection image corresponding to one gantry angle; and Correct a first projection image of the at least two projection images according to a process of generating a corrected projection image, the first projection image corresponding to a first gantry angle of the at least two gantry angles, the process of generating the corrected projection image including: Perform a second correction on the first projection image based on at least a part of the first projection image to generate a corrected first projection image corresponding to the first gantry angle, wherein at least a part of the first projection image includes one or more pixels corresponding to an intermediate channel of the CT scanner at the first gantry angle.

8. The method for correcting a projected image according to claim 7, wherein, The method includes: Correct the at least two projection images according to the process of generating the corrected projection image to generate at least two corrected projection images; and Reconstruct a CT image of the object under examination based on the at least two corrected projection images.

9. The method for correcting a projected image according to claim 8, wherein Correcting the at least two projection images includes: Performing at least one iteration, each current iteration of the iteration including: Correcting the at least two projection images in the current iteration according to the process of generating the corrected projection image to generate a plurality of corrected projection images; Determining whether the at least two corrected projection images in the current iteration satisfy a condition; and If the at least two corrected projection images do not satisfy the condition, designating the at least two corrected projection images in the current iteration as the at least two projection images in the next iteration.

10. The method for correcting a projected image according to claim 7, characterized in that, Performing the second correction on the first projection image to generate a corrected first projection image includes: Identifying at least one pixel of the first projection image, the identified at least one pixel corresponding to an intermediate channel of the CT scanner at the first gantry angle; For each pixel, identifying the opposite pixel corresponding to each pixel; Generating a reference image of the first projection image based on at least one opposite pixel of the at least one pixel; Determining a second correction coefficient of the first projection image based on a difference between the identified at least one pixel and the reference image; and Generating the corrected first projection image corresponding to the first gantry angle based on the second correction coefficient and the first projection image.

Images