CT focal point determination method and system

A method for determining a CT focal point includes determining a first intensity of first radiation incident on a first detector unit of a scanner, wherein the scanner may include a non-uniform anti-scatter grid (ASG) and a radiation source, and the non-uniform ASG may be configured according to a first focal point of the radiation source. The method also includes determining a second intensity of second radiation incident on a second detector unit of the scanner, wherein the first radiation and the second radiation are emitted from the radiation source with a second focal point. The method further includes determining a displacement of the second focal point from the first focal point based on the first intensity and the second intensity.

FIELD

The present disclosure generally relates to a technical field of a CT scanner, and more particularly to a focal point determining method and system for determining the focal point of a radiation source of a CT scanner.

BACKGROUND

During a scanning performed by a computed tomography (CT) scanner equipped with anti-scatter grids (ASGs), the displacement of the focal point of the radiation source of the CT scanner may cause a portion of the radiation emitted by the radiation source intended to be received by the detector of the CT scanner blocked by the ASGs, causing a reduction of the quality of the image generated based on the scanning. Various hardware related (e.g., focus point tracing) or software related (e.g., image post-processing) techniques may be adopted for compensating the image quality reduction. However, the displacement of the focal point needs to be determined for most of these techniques. There is a need for a method of low cost and high reliability for determining the displacement of the focal point during the scanning of the CT scanner.

SUMMARY

According to an aspect of the present disclosure, a method may include determining a first intensity of first radiation incident on a first detector unit of a scanner. The scanner may include a non-uniform anti-scatter grids (ASG) and a radiation source, and the non-uniform ASG may be configured according to a first focal point of the radiation source. The method may also include determining a second intensity of second radiation incident on a second detector unit of the scanner, wherein the first radiation and the second radiation are emitted from the radiation source with a second focal point. The method may further include determining a displacement of the second focal point from the first focal point based on the first intensity and the second intensity.

In some embodiments, the determining the displacement may comprise determining a ratio of the first intensity to the second intensity; and determining the displacement based on the ration.

In some embodiments, the method may further comprising determining a correlation between the displacement and the ratio using a pinhole positioned between the radiation source and a detector of the scanner, the detector including the first detector unit and the second detector unit, wherein the displacement is determined further based on the correlation

In some embodiments, the method may further include generating, based on the displacement, a calibration instruction for calibrating the scanner.

In some embodiments, the method may further include obtaining scan data by controlling the scanner to scan a subject, and generating an image based on the scan data and the displacement.

In some embodiments, the first radiation and the second radiation may be emitted during the obtaining the scan data.

In some embodiments, the non-uniform ASG may include at least one first cell. The first detector unit and the second detector unit may be included in the first cell.

In some embodiments, the non-uniform ASG may include at least one second cell and at least one third cell having different structures. The second cell and the third cell may include plates of different heights. The first detector unit may be included in the second cell, and the second detector unit may be included in the third cell.

In some embodiments, the method may further include obtaining at least one parameter relating to the non-uniform ASG, wherein the displacement is determined based at least in part on the at least one parameter.

In some embodiments, the at least one parameter may comprise at least one of a height of at least a portion of the non-uniform ASG and a distance from the second focal point to a top of the at least a portion of the non-uniform ASG.

According to another aspect of the present disclosure, a system may include at least one processor and at least one storage device storing instructions. When executing the instructions, the at least one processor may be configured to cause the system to determine a first intensity of first radiation incident on a first detector unit of a scanner, wherein the scanner may include a non-uniform anti-scatter grids (ASG) and a radiation source, and the non-uniform ASG may be configured according to a first focal point of the radiation source. The at least one processor may also be configured to cause the system to determine a second intensity of second radiation incident on a second detector unit of the scanner, wherein the first radiation and the second radiation may be emitted from the radiation source with a second focal point. The at least one processor may further be configured to cause the system to determine a displacement of the second focal point from the first focal point based on the first intensity and the second intensity.

According to yet another aspect of the present disclosure, an anti-scatter grid for determining a focal point of a radiation source of a scanner may include a plurality of plates defining a plurality of cells. The plurality of cells may include at least one first cell. After the anti-scatter grid being installed on a detector of the scanner, the first cell may include a first detector unit and a second detector unit of the detector.

In some embodiments, the first detector unit and the second detector unit may be adjacent to one another.

In some embodiments, each of the plurality of cells of the anti-scatter grid have a same configuration as the first cell.

According to yet another aspect of the present disclosure, an anti-scatter grid for determining a focal point of a radiation source of a scanner may include a plurality of plates defining a plurality of cells. The plurality of cells may include at least one second cell and at least one third cell. The second cell and the third cell may include plates of different heights. The second cell and the third cell may have different structures. After the anti-scatter grid being installed on a detector of the scanner, the second cell may include a first detector unit of the detector, and the third cell may include a second detector unit of the detector.

In some embodiments, the second cell and the third cell may be adjacent to one another.

DETAILED DESCRIPTION

The present disclosure is directed to determine a focal point of the radiation source of a CT scanner equipped with a non-uniform ASG during the scanning performed by the CT scanner.

Generally, the word “module,” “sub-module,” “unit,” or “block,” as used herein, refers to logic embodied in hardware or firmware, or to a collection of software instructions. A module, a unit, or a block described herein may be implemented as software and/or hardware and may be stored in any type of non-transitory computer-readable medium or other storage device. In some embodiments, a software module/unit/block may be compiled and linked into an executable program. It will be appreciated that software modules can be callable from other modules/units/blocks or from themselves, and/or may be invoked in response to detected events or interrupts.

Software modules/units/blocks configured for execution on computing devices (e.g., processor210as illustrated inFIG. 2-A) may be provided on a computer-readable medium, such as a compact disc, a digital video disc, a flash drive, a magnetic disc, or any other tangible medium, or as a digital download (and can be originally stored in a compressed or installable format that needs installation, decompression, or decryption prior to execution). Such software code may be stored, partially or fully, on a storage device of the executing computing device, for execution by the computing device. Software instructions may be embedded in a firmware, such as an EPROM. It will be further appreciated that hardware modules/units/blocks may be included in connected logic components, such as gates and flip-flops, and/or can be included of programmable units, such as programmable gate arrays or processors. The modules/units/blocks or computing device functionality described herein may be implemented as software modules/units/blocks, but may be represented in hardware or firmware. In general, the modules/units/blocks described herein refer to logical modules/units/blocks that may be combined with other modules/units/blocks or divided into sub-modules/sub-units/sub-blocks despite their physical organization or storage. The description may be applicable to a system, an engine, or a portion thereof.

FIG. 1-A is a schematic diagram illustrating an exemplary CT system according to some embodiments of the present disclosure. As shown, CT system100may include a CT scanner110, a network120, one or more terminals130, a processing engine140, and a storage150.

The CT scanner110may include a gantry111, a detector112, a detecting region113, a table114, and a radiation source115. The gantry111may support the detector112and the radiation source115. A subject may be placed on the table114for scanning. The radiation source115may emit radiation beams (e.g., X-rays) to the subject. The detector112may detect the radiation beams penetrated through at least part of the subject within the detection region113. In some embodiments, the CT scanner110may also be part of a multi-modality system including, for example, PET-CT, SPECT-CT, etc. In some embodiments, a more detailed structure and mechanism of the CT scanner110is illustrated inFIG. 1-B. In some embodiments, one or components in the CT system100may be omitted. Merely by way of example, the CT system100may not include the terminal(s)130.

The connection between the components in the CT system100may be variable. Merely by way of example, as illustrated inFIG. 1-A, the CT scanner110may be connected to the processing engine140through the network120. As another example, the CT scanner110may be connected to the processing engine140directly as illustrated by the dotted double arrow between the CT scanner110and the processing engine140. As a further example, a terminal130may be connected to other portions of the system100through the network120. As still a further example, the CT scanner110may be connected to a portion of the system100, e.g., the processing engine140directly as illustrated by the dotted double arrow between the processing engine140and a terminal130.

For demonstration purposes, a coordinate system as shown inFIG. 1-A may be used to describe direction related issues in the present disclosure.

The network120may include any suitable network that can facilitate exchange of information and/or data for the CT system100. In some embodiments, one or more components of the CT system100(e.g., the CT scanner110, the terminal130, the processing engine140, the storage150) may communicate information and/or data with one or more other components of the CT system100via the network120. For example, the processing engine140may obtain image data from the CT scanner110via the network120. As another example, the processing engine140may obtain user instructions from the terminal130via the network120. The network120may be and/or include a public network (e.g., the Internet), a private network (e.g., a local area network (LAN), a wide area network (WAN))), a wired network (e.g., an Ethernet network), a wireless network (e.g., an 802.11 network, a Wi-Fi network), a cellular network (e.g., a Long Term Evolution (LTE) network), a frame relay network, a virtual private network (“VPN”), a satellite network, a telephone network, routers, hubs, witches, server computers, and/or any combination thereof. Merely by way of example, the network120may include a cable network, a wireline network, a fiber-optic network, a telecommunications network, an intranet, a wireless local area network (WLAN), a metropolitan area network (MAN), a public telephone switched network (PSTN), a Bluetooth™ network, a ZigBee™ network, a near field communication (NFC) network, or the like, or any combination thereof. In some embodiments, the network120may include one or more network access points. For example, the network120may include wired and/or wireless network access points such as base stations and/or internet exchange points through which one or more components of the CT system100may be connected to the network120to exchange data and/or information.

The terminal(s)130may include a mobile device131, a tablet computer132, a laptop computer133, or the like, or any combination thereof. In some embodiments, the mobile device131may include a smart home device, a wearable device, a mobile device, a virtual reality device, an augmented reality device, or the like, or any combination thereof. In some embodiments, the smart home device may include a smart lighting device, a control device of an intelligent electrical apparatus, a smart monitoring device, a smart television, a smart video camera, an interphone, or the like, or any combination thereof. In some embodiments, the wearable device may include a bracelet, a footgear, eyeglasses, a helmet, a watch, clothing, a backpack, a smart accessory, or the like, or any combination thereof. In some embodiments, the mobile device may include a mobile phone, a personal digital assistance (PDA), a gaming device, a navigation device, a point of sale (POS) device, a laptop, a tablet computer, a desktop, or the like, or any combination thereof. In some embodiments, the virtual reality device and/or the augmented reality device may include a virtual reality helmet, virtual reality glasses, a virtual reality patch, an augmented reality helmet, augmented reality glasses, an augmented reality patch, or the like, or any combination thereof. For example, the virtual reality device and/or the augmented reality device may include a Google Glass™, an Oculus Rift™, a Hololens™, a Gear VR™, etc. In some embodiments, the terminal(s)130may be part of the processing engine140.

The processing engine140may process data and/or information obtained from the CT scanner110, the terminal130, and/or the storage150. For example, the processing engine140may generate an image based on data relating to an object obtained from the CT scanner110. The data relating to the object may include projection data corresponding to radiation beams traversing the object. The image may be generated by using an analytical algorithm, an iterative algorithm, and/or other reconstruction techniques. In some embodiments, the processing engine140may include a digital-analog converter (DAC) which may convert the image data into an analog signal. The analog signal may be processed and transmitted to the terminal130for display.

The processing engine140may also determine the focal point or the displacement of the focal point of the radiation source115of the CT scanner110. The processing engine140may further use the obtained focal point or the displacement of the focal point to calibrate the CT scanner110or process the image generated based on the data obtained from the CT scanner110. Detailed descriptions of the processing engine140are provided elsewhere in the present disclosure (e.g., in connection withFIG. 3).

In some embodiments, the processing engine140may be a computer, a user console, a single server or a server group, etc. The server group may be centralized or distributed. In some embodiments, the processing engine140may be local or remote. For example, the processing engine140may access information and/or data stored in the CT scanner110, the terminal130, and/or the storage150via the network120. As another example, the processing engine140may be directly connected to the CT scanner110, the terminal130and/or the storage150to access stored information and/or data. In some embodiments, the processing engine140may be implemented on a cloud platform. Merely by way of example, the cloud platform may include a private cloud, a public cloud, a hybrid cloud, a community cloud, a distributed cloud, an inter-cloud, a multi-cloud, or the like, or any combination thereof. In some embodiments, the processing engine140may be implemented by a computing device200having one or more components as illustrated inFIG. 2-A.

In some embodiments, the storage150may be connected to the network120to communicate with one or more other components in the CT system100(e.g., the processing engine140, the terminal130). One or more components in the CT system100may access the data or instructions stored in the storage150via the network120. In some embodiments, the storage150may be directly connected to or communicate with one or more other components in the CT system100(e.g., the processing engine140, the terminal130). In some embodiments, the storage150may be part of the processing engine140.

FIG. 1-B is a schematic diagram illustrating an exemplary structure and mechanism of a CT scanner according to some embodiments of the present disclosure.FIG. 1-B is a sectional view of the CT scanner110along the Z axis or the X axis within the detection region113. The radiation source115may emit radiation beams190. The radiation beams190may penetrate an object180(e.g., a body, an organ, a tissue, a container) and reach the detector112. The detector112may include a plurality of detector units116(e.g., detector units116-1˜116-4). In response to the incident radiation beams, the plurality of detector units116may generate signals that may be used for generating an image of the object180. The CT scanner110may then transmit the signals to the network120, the processing engine140, and/or other components of the CT system100.

The radiation source115may include a tube, such as a cold cathode ion tube, a high vacuum hot cathode tube, a rotating anode tube, etc. The tube may be powered by a high voltage generator for emitting the radiation beams190. The radiation beams190may be and/or include a particle ray, a photon ray, or the like, or a combination thereof. The radiation source115may be viewed as a point for approximation. The radiation beams190may also be considered as being emitted from this point. The point defined by the radiation source115may be referred to as a focal point (e.g., focal point118). In the present disclosure, the term “focal point” may also relate to the location of the point.

The radiation beams190emitted by the radiation source115may include, for example, a plurality of primary radiation beams (e.g., radiation beam190-1) and a plurality of scattered radiation beams (e.g., radiation beam190-2). The primary radiation beams may propagate along a trajectory path from the focal point118to the detector112. The trajectory path may be, for example, a straight connection between the focal point118and the incident point at the corresponding detector unit116. The scattered radiation beams may include radiation beams emitted by the radiation source115that are scattered or deflected while penetrating the object180. The scattered radiation beams may deviate from their original paths (e.g., trajectory paths). A primary radiation beam may be one that may contribute to the generation of desired imaging data for generating an image of the object180. A scattered radiation beam, when detected by a detector unit, may cause artifacts in the image of the object180.

In some embodiments, for reducing the artifacts in the image of the object180, the detector112may further include one or more anti-scatter grids (ASGs, e.g., ASG117) for limiting the scattered radiation beams received by the detector units116. The ASG117may include a plurality of plates (e.g., plates117-1˜117-5). The plates may include materials that can absorb one or more types of radiation. The radiation absorbing material may include, for example, tungsten, lead, uranium, gold, silver, copper, molybdenum, or the like, or a combination thereof. The interspaces (or cells) enclosed by the plates may be filled with air or a radiolucent material. Exemplary radiolucent materials may include, for example, plastic, carbon fiber, aluminum, inorganic non-metallic material (e.g., paper, ceramic), or the like, or a combination thereof. The ASG117may allow the radiation beams passing through the cells (e.g., cell119) defined by the plates to be received by the detector units116(e.g., detector units116-1˜116-4). The ASG117may block (or absorb) at least a majority of the radiation beams hitting the plates of the ASG117.

The ASG117may be installed or placed between the radiation source115and detector units116. The plates of the ASG117may be aligned toward the focal point118and be distributed along the X direction and/or Z direction. The primary radiation beams (e.g., radiation beam190-1) emitted from the focal point118may pass through the ASG117and be received by the detector units116. The scattered radiation beams (or at least some of them, e.g., radiation beam190-2), as deviated from their original paths, may hit the plates of the ASG117and be absorbed by the ASG117. The scattered radiation beams may then be attenuated, or removed, from the plurality of radiation beams.

In the present disclosure, the X direction and the Z direction, which are perpendicular to each other, are set parallel with the detector112or the tangent plane of the center of the detector112. The X direction and the Z direction are also set parallel with the axis of the detection region113. The Y direction (not shown inFIG. 1-B) is perpendicular to both the X direction and the Z direction.

In the present disclosure, for the determination of the focal point of the radiation source118, one or more ASGs installed on the CT scanner110may be non-uniform ASGs. As one aspect, the term “non-uniform ASG” may indicate that the ASG has non-uniformly arranged plates. For instance, at least two of the plates of the non-uniform ASG may have different shapes, sizes (e.g., heights), and/or be made of different materials (e.g., with different radiation absorbance), etc. The non-uniform ASG of this type may be referred to as Type I non-uniform ASG.FIGS. 4-C and4-D are schematic diagrams illustrating Type I non-uniform ASGs according to this aspect.

Alternatively or additionally, the term “non-uniform” may indicate that the ASG has a structure different from that of a majority of (e.g., more than 50%) the other ASGs installed on the CT scanner110. The “non-uniform” ASG itself may have uniformly (e.g., as illustrated inFIG. 4-B) or non-uniformly (e.g., as illustrated inFIGS. 4-C and4-D) arranged plates. The majority of the other ASGs may share a same structure. Merely for example, the cells of the majority of the other ASGs may each include one detector unit in one direction (e.g., the X direction, the Z direction), while the cells of the non-uniform ASG(s) may each include two or more detector units in the same direction. The non-uniform ASG of this type may be referred to as type II non-uniform ASG.

In some embodiments, the one or more non-uniform ASGs installed on the CT scanner110may only be type I non-uniform ASGs. For instance, all the ASGs (or the only one ASG) installed on the CT scanner110may be the same type I non-uniform ASGs (e.g., ASGs as illustrated inFIGS. 4-C and4-D).

In some embodiments, the one or more non-uniform ASGs installed on the CT scanner110may only be type II non-uniform ASGs. The type II non-uniform ASGs may share a same structure or have different structures.

In some embodiments, the one or more non-uniform ASGs installed on the CT scanner110may be both the type I and type II non-uniform ASGs. These non-uniform ASGs may share a same structure or have different structures.

A detector unit116may detect radiation beams penetrating the object180and then passing through the ASG117(if any). The detector unit116may also be referred to as a detector element or a detector pixel. The detector unit116may convert the incident radiation beams into a signal. The amplitude of the generated signals may correlate with the intensities of the radiation reaching the detector unit116. The detector unit116may include a scintillator and/or a photoelectric sensor, etc. Exemplary materials of the detector unit116may include an inert gas (e.g., Xe), CdWO4, Gd2O2S (GOS), or ceramic (e.g., HiLight™), or the like, or a combination thereof.

The detector units116may be arranged in a single row or multiple rows. For illustration purposes,FIG. 1-B only illustrates one row. The detector units116may be arranged on a flat plane (as shown inFIG. 1-B) or a curved plane (not shown). In some embodiments, the detector units116may be aligned with their normal directions pointing at the focal point118.

When the ASG(s) is installed on the detector116, one or more detector units may be positioned inside a cell of the ASG. A non-uniform ASG (type I and/or type II) may cover an arbitrary portion of the detector116. Merely for example, the installed non-uniform ASG(s) may cover the whole detector116, the central part of the detector116, and/or the edge part of the detector116.

It may be noted that,FIG. 1-B is only provided for demonstration purposes, and is not intend to apply a limitation to the present disclosure. Modification and amendment may be made toFIG. 1-B. The numbers, appearances, and relative locations of the components (e.g., the plates of the ASG117, the detector units, the radiation beams) of the CT scanner110are also for illustration and may not reflect their true states in practical use.

FIG. 2-A is a schematic diagram illustrating exemplary hardware and/or software components of an exemplary computing device on which the processing engine may be implemented according to some embodiments of the present disclosure. As illustrated inFIG. 2-A, the computing device200may include a processor210, a storage220, an input/output (I/O)230, and a communication port240.

The processor210may execute computer instructions (e.g., program code) and perform functions of the processing engine140in accordance with techniques described herein. The computer instructions may include, for example, routines, programs, objects, components, data structures, procedures, modules, and functions, which perform particular functions described herein. For example, the processor210may be configured to perform the functions relating to the determination of the focal point or the displacement of the focal point of the radiation source115of the CT scanner110.

Merely for illustration, only one processor is described in the computing device200. However, it should be noted that the computing device200in the present disclosure may also include multiple processors, thus steps and/or method steps that are performed by one processor as described in the present disclosure may also be jointly or separately performed by the multiple processors. For example, if in the present disclosure the processor of the computing device200executes both step A and step B, it should be understood that step A and step B may also be performed by two or more different processors jointly or separately in the computing device200(e.g., a first processor executes step A and a second processor executes step B, or the first and second processors jointly execute steps A and B).

The storage220may store data/information obtained from the scanner110, the terminal130, the storage150, and/or any other component of the imaging system100. In some embodiments, the storage220may include a mass storage, a removable storage, a volatile read-and-write memory, a read-only memory (ROM), or the like, or any combination thereof. For example, the mass storage may include a magnetic disk, an optical disk, a solid-state drives, etc. The removable storage may include a flash drive, a floppy disk, an optical disk, a memory card, a zip disk, a magnetic tape, etc. The volatile read-and-write memory may include a random access memory (RAM). The RAM may include a dynamic RAM (DRAM), a double date rate synchronous dynamic RAM (DDR SDRAM), a static RAM (SRAM), a thyristor RAM (T-RAM), and a zero-capacitor 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 compact disk ROM (CD-ROM), and a digital versatile disk ROM, etc. In some embodiments, the storage220may store one or more programs and/or instructions to perform exemplary methods described in the present disclosure. For example, the storage220may store a program for the processing engine140for determining a regularization item.

The I/O230may input and/or output signals, data, information, etc. In some embodiments, the I/O230may enable a user interaction with the processing engine140. In some embodiments, the I/O230may include an input device and an output device. Examples of the input device may include a keyboard, a mouse, a touch screen, a microphone, or the like, or a combination thereof. Examples of the output device may include a display device, a loudspeaker, a printer, a projector, or the like, or a combination thereof. Examples of the display device may 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), a touch screen, or the like, or a combination thereof.

The communication port240may be connected to a network (e.g., the network120) to facilitate data communications. The communication port240may establish connections between the processing engine140and the scanner110, the terminal130, and/or the storage150. The connection may be a wired connection, a wireless connection, any other communication connection that can enable data transmission and/or reception, and/or any combination of these connections. The wired connection may include, for example, an electrical cable, an optical cable, a telephone wire, or the like, or any combination thereof. The wireless connection may include, for example, a Bluetooth™ link, a Wi-Fi™ link, a WiMax™ link, a WLAN link, a ZigBee link, a mobile network link (e.g., 3G, 4G, 5G), or the like, or a combination thereof. In some embodiments, the communication port240may be and/or include a standardized communication port, such as RS232, RS485, etc. In some embodiments, the communication port240may be a specially designed communication port. For example, the communication port240may be designed in accordance with the digital imaging and communications in medicine (DICOM) protocol.

FIG. 2-B is a schematic diagram illustrating exemplary hardware and/or software components of an exemplary mobile device on which the terminal may be implemented according to some embodiments of the present disclosure. As illustrated inFIG. 2-B, the mobile device250may include a communication platform260, a display270, a graphic processing unit (GPU)271, a processor272, an I/O273, a memory280, and a storage275. In some embodiments, any other suitable component, including but not limited to a system bus or a controller (not shown), may also be included in the mobile device250. In some embodiments, a mobile operating system281(e.g., iOS™, Android™, Windows Phone™) and one or more applications282may be loaded into the memory280from the storage275in order to be executed by the processor272. The applications282may include a browser or any other suitable mobile apps for receiving and rendering information relating to the determination of the focal point or the displacement of the focal point of the radiation source115of the CT scanner110from the processing engine140. User interactions with the information stream may be achieved via the I/O273and provided to the processing engine140and/or other components of the imaging system100via the network120.

FIG. 3is a schematic diagram illustrating an exemplary processing engine according to some embodiments of the present disclosure. The processing engine140may include an input/output module310, a scanner controlling module320, an image processing module330, and a calibration module340. Other modules may also be included in the processing engine140.

The input/output module310may be configured to communicate (e.g., acquire, receive, send) data for the processing engine140. The data may include data generated by the scanner110, temporary data generated by processing engine140, control signal generated by the processing engine140for controlling the scanner110, instructions for operating processing engine140and/or its modules/units, etc. The data may be communicated with the CT scanner110, the terminal130, the network120, etc.

The scanner controlling module320may be configured to generate control signal for controlling the CT scanner110. The control signal may be generated based on one or more scanning parameters. The scanning parameters may correspond to the type, scanning times, starting time, scanning speed, the scanning region, the scanning condition, etc., of the scanning to be performed or being performed by the scanner110. The generated control signal may be sent to the CT scanner110to control or guide the CT scanner110for performing a scanning on a subject.

One or more of the scanning parameters may be provided by a user through the terminal130, be acquired from a resource via the network120, be acquired from a storage device (e.g., the storage150, the storage220, the memory280), or the like, or a combination thereof. One or more of the scanning parameters may also be determined by one or more modules/units of processing engine140(e.g., calibration module340).

The image processing module330may be configured to generate (or reconstruct) an image based on the scan date acquired by the scanner110. Different image reconstruction techniques or data processing techniques may be adopted by the image processing module330.

In some embodiments, the image processing module330may reconstruct one or more slice images based on the acquired date. A slice image may be a 2D cross-sectional image of the scanned subject. The obtained one or more slice images may be directly used for viewing the inside of the scanned subject. Alternatively or additionally, a plurality of slice images may be used for generating a volume image for enhancing the visual experience. In some embodiments, image processing module330may directly reconstruct a volume image without generating a plurality of slice images first during the reconstruction process.

The calibration module340may be configured to assess the performance of one or more devices, modules and/or units of the CT system100and obtain one or more performance parameters. For example, the one or more performance parameters may relate to the imaging performance of the CT scanner110. The calibration module340may be further configured to adjust (or calibrate) the settings of the one or more devices, modules and/or units (e.g., the CT scanner110) of the CT system100based on the obtained performance parameters.

The calibration module340may include a focal point determination sub-module342. The focal point of the CT scanner110may be displaced (e.g., moved, vibrated, oscillated) during its usage (detailed description are provided in connection withFIG. 4-A). The focal point determination sub-module342may be configured to determine the displaced focal point of the radiation source115. In some embodiments, the focal point determination sub-module342may determine the displacement of the focal point of the radiation source using a non-uniform ASG (type I and/or type II) according to process500described in connection withFIG. 5. The displaced focal point (second focal point) may be expressed in terms of a coordinate or a displacement along the X direction and or the Z direction relative to the original (or intended) focal point (first focal point). In the present disclosure, unless otherwise noted, “displacement” is a vector which includes both the displacement value and the displacement direction.

In some embodiments, during the process500, a parameter (e.g., a ratio of a first radiation intensity to a second radiation intensity of two director units) may be obtained as an intermediate for determining the displaced focal point. The calibration module340may further include a correlation determination sub-module344. The correlation determination sub-module344may be configured to determine the correlation (e.g., in the form of a lookup table, a function) between the parameter obtained in process500and the focal point. The correlation may then be used to determine the displaced focal point in process500.

It may be noted that, the above description about processing engine140is only for illustration purposes, and is not intended to limit the present disclosure. It is understandable that, after learning the major concept and the mechanism of the present disclosure, a person of ordinary skill in the art may alter processing engine140in an uncreative manner. The alteration may include combining and/or splitting modules or sub-modules, adding or removing optional modules or sub-modules, etc. All such modifications are within the protection scope of the present disclosure.

FIG. 4-A is a schematic diagram illustrating the effect of the change of the focal point of the radiation source in the CT scanner. For demonstration purposes, the effect of the change of the focal point is described with a standard ASG (e.g., ASG410). In the present disclosure, the plates (e.g., plates410-1˜410-5) of a standard ASG may have the same or substantially the same shape, size (including length, width, and height), and made of the same material(s). The cells defined by the plates of the standard ASG may also have the same or substantially the same shape and/or size. Cells (e.g., cell411) of the standard ASG may each include only one detector unit (e.g., detector units412-1˜412-4). The plates of the standard ASG410are aligned toward a first focal point (the original or intended focal point, e.g., focal point415) of the radiation source115. Standard ASGs have been widely adopted in the prior art.

During the usage of the CT scanner110, the focal point of the radiation source115may be displaced (e.g., moved, vibrated, oscillated) due to various factors. The various factors may include, for example, the thermal expansion and/or contraction of the radiation source115during the emitting of radiation beams, the gravity, the centrifugal force, the vibration of the radiation source115caused by the running of CT scanner110, the aging of the mechanical structure(s) of CT scanner110, the imaging technique adopted by the CT scanner110(e.g., z-flying focal spot technology), or the like, or a combination thereof. A deviation of the focal point of the radiation source115from its intended position may be expressed in terms of one or more deviation component(s) along the X, Y and/or Z direction. In some embodiments, the deviation component along the Y direction may show a negligible influence and may be omitted.

At a certain time point, the radiation source155may have a second focal point (e.g., focal point416). As the plates of ASG410are aligned toward the focal point415, some primary radiation beams (e.g., radiation beam419) may still find their way passing through the ASG410to the detector units (e.g., detector units412-2), while some of the primary radiation beams (e.g., radiation beam418) may be blocked by the plates (e.g., plate410-2) of the ASG410. As a result, a part (e.g., part413-1) of each of at least some detector units may receive fewer radiation beams compared to the other part (e.g., part413-2), and a shadow may form (e.g., shadow414-1˜414-4). The existence of shadows may cause a reduction of the intensity of radiation received by a detector unit, which may in turn result in a reduction of the quality of an image generated therefrom (e.g., in the form of artifacts or reduced resolution).

When the standard ASG410is used, after the change or displacement of the focal point, the reductions of the radiation intensities occurred on all the detector units may be to the same or similar degree.

The reduction of the image quality caused by shadows may be compensated (e.g., by the calibration module340and/or the Image processing module330) using various hardware related (e.g., focus point tracing) or software related (e.g., image post-processing) techniques. These techniques may involve the determination of the displaced focal point (e.g., the location of a displace focal point (or referred to as a second focal point) relative to the original or intended focal point (or referred to as the first focal point)). Theoretically, the second focal point may be determined based on the reduction of the radiation intensity detected by one (or more for eliminating errors) of the detector units. However, besides the change of the focal point, one or more other factors (e.g., mA modulation, kV ripple, mA ripple, filament establishment) may also cause the reduction of the radiation intensity upon all the detector units. With a standard ASG, it is difficult to differentiate the portion of the reduction of the radiation intensity caused by the displacement of the focal point from the portion of the reduction caused by the one or more other factors.

In the present disclosure, the CT scanner110may be equipped with a non-uniform ASG for identifying the reduction of the radiation intensity caused by the displacement of the focal point. In some embodiments, the focal point determination sub-module342may determine the displaced focal point using the non-uniform ASG according to process500descripted in connection withFIG. 5. The non-uniformity may be effectuated by the arrangements of the plates of an ASG, the sizes of the plates, the materials of the plates, or the like, or a combination thereof. For instance, in a non-uniform ASG, cells formed by the plates enclose different numbers of detector units. As another example, a non-uniform ASG may be formed by plates of different shapes or sizes (e.g., different heights).FIGS. 4-B,4-C, and4-D illustrate exemplary non-uniform ASGs according to some embodiments of the present disclosure. It may be noted that,FIGS. 4-B,4-C, and4-D are only provided for demonstration purposes and not intend to limit the scope of the present disclosure. The illustrated non-uniform ASGs are nonexclusive and may have different forms when applied in practical use.

FIG. 4-B illustrates an exemplary non-uniform ASG according to some embodiments of the present disclosure. ASG420may be installed as a type II non-uniform ASG. ASG420may be equipped on the CT scanner110for facilitating the determination of a displaced or second focal point426relative to an intended or first focal point425according to, for example, process500described in connection withFIG. 5. The plates (e.g., plates420-1˜420-3) of the ASG420may also have the same or substantially the same shape, size, and be made of the same material(s). The cells defined by the plates of the ASG420may also have the same or substantially the same configuration (e.g., shape and size). Distinguished from a standard ASG (e.g., ASG410), a cell (e.g., cell421) of ASG420may include more than one detector units (e.g., detector units422-1˜422-4) along at least one direction (e.g., X direction, Z direction, or both). For instance, each cell of ASG420may include two detector units (four in total) along both the X direction and the Z direction.

The plates of ASG420may be aligned toward the first focal point425(the original or intended focal point) of the radiation source115. When the focal point of the radiation source115changes from the first focal point425to the second focal point426, some detector units (first detector units, e.g., detector units422-1-And422-3) may be covered by the shadows (e.g., shadows424-1and424-2) caused by the displacement of the focal point, while some detector units (second detector units, e.g., detector unit422-2and422-4) may be free of the shadows caused by the same reason. As used herein, a first detector unit may refer to a detector unit that receives or detects a different amount of radiation when the focal point of the radiation source is displaced compared to when the focal point of the radiation source is at its original or intended location, assuming that the radiation source emits the same amount of radiation beams regardless of the location of its focal point. As used herein, a second detector unit may refer to a detector unit that receives the same (or substantially the same) amount radiation when the focal point of the radiation source is displaced from its original or intended location, assuming that the radiation source emits the same amount of radiation beams regardless of the location of its focal point. The reductions of the radiation intensities caused by the change of the focal point detected by the first detector units may be different from the one detected by the second detector units. The difference may be used (e.g., by the focal point determination sub-module342) for determining the second focal point426.

It may be noted that, the first detector units and the second detector units may exchange their roles as a first detector unit at least partially covered by shadow or a second detector unit free of shadow when the focal point is displaced along the direction opposite to that illustrated inFIG. 4-B. For example, the second detector units422-2and422-4may be covered by shadows caused by the displacement of the focal point, while the first detector units422-1and422-3may be free of shadows caused by the same reason. However, the difference between the radiation intensities of the first detector units and the second detector units may still be used for determining the second focal point426.

The radiation intensities of a first-second detector unit pair (e.g., the detector units422-1and422-2, the detector units422-2and422-3, or the detector units422-1and422-4) may be used for determining the second focal point426. In some embodiments, the radiation intensities of at least one arbitrary or predetermined pair of adjacent first detector unit and second detector unit (e.g., the detector units422-2and422-3) may be used for determining the second focal point426.

FIG. 4-C illustrates an exemplary non-uniform ASG according to some embodiments of the present disclosure. ASG430may be equipped on the CT scanner110for facilitating the determination of a displaced or second focal point436relative to an intended or first focal point435according to, for example, process500described in connection withFIG. 5. The plates (e.g., plates440-1˜440-5) of the ASG430may still have same or substantially same shapes, sizes, and the materials. The cells of ASG430, however, may not be uniformly configured. One or more cells (the irregular cells, e.g., cell431-1) of ASG430may include more than one detector units (e.g., detector units432-1and432-2as illustrated inFIG. 4-C) along at least one direction (e.g., the X direction, the Z direction, or both). For instance, ASG430may have one or more irregular cells including two detector units (two in total) along X direction and one or more irregular cells including two detector units (two in total) along Z direction. As another example, ASG430may have one or more irregular cells including two detector units (four in total) along both the X direction and the Z direction. The plates of ASG430may be aligned toward the first focal point435(the original or intended focal point) of the radiation source115. As used herein, a regular cell may refer to one that encloses one detector unit (e.g., cells431-2and431-3as illustrated inFIG. 4-C.). As used herein, an irregular cell may refer to one that encloses more than one detector unit (e.g., the cell431-1as illustrated inFIG. 4-C).

In the ASG430, only a detector unit (e.g., detector units432-1and432-2) enclosed within an irregular cell may be designated as a first detector unit that is at least partially covered by the shadow or a second detector unit that is free of the shadow occurred when the focal point of the radiation source is displaced. Other detector units (e.g., detector units432-3and432-4) enclosed in regular cells may always be covered by shadows (e.g., shadows434-2and434-3) when the focal point is displaced regardless of the direction of the displacement, and are not included in determining the focal point.

When the focal point of the radiation source115is displaced from the first focal point435to the second focal point436, a first detector unit (e.g., the detector unit432-1) within an irregular cell may be covered by the shadow (e.g., shadow434-1) caused by displacement of the focal point, while a second detector unit (e.g., detector unit432-2) within a same irregular cell or different irregular cells may be free of the shadows caused by the same reason. The difference between the radiation intensities received by the first detector unit and the second detector unit may be used (e.g., by the focal point determination sub-module342) for determining the second focal point436. It may also be noted that, the first detector unit(s) and the second detector unit(s) may exchange their roles when the focal point is displaced along the along the direction opposite to that illustrated inFIG. 4-C.

In some embodiments, the radiation intensities of a first detector unit and a second detector unit within an arbitrary or predetermined irregular cell may be used (e.g., by focal point determination sub-module342) for determining the second focal point436. The first detector unit and the second detector unit may be adjacent to one another.

FIG. 4-D illustrates an exemplary non-uniform ASG according to some embodiments of the present disclosure. ASG440may be equipped on the CT scanner110for facilitating the determination of a displaced or second focal point446relative to an intended or first focal point445according to, for example, process500described in connection withFIG. 5. One or more plates (the abnormal plates, e.g., plates440-2) may have different shapes and/or sizes compared to other plates (e.g., plates440-1,440-2,440-3and430-4) of the ASG440. Each cell of the ASG440may enclose one detector unit (e.g., detector units442-1˜442-4). A cell (e.g., cells441-1and441-2as illustrated inFIG. 4-D) surrounded by one or more (along either or both of the X direction and the Z direction) abnormal plates may be referred to as an abnormal cell. One abnormal plate may define a pair of abnormal cells. For instance, the ASG440may include one or more pairs of abnormal cells with one or more abnormal plates along either or both of the X direction and the Z direction. The plates of ASG430may be aligned toward the first focal point435(the original or intended focal point) of the radiation source115. As used herein, a regular cell may refer to one that encloses one detector unit (e.g., the cell enclosing detector unit432-3and the cell enclosing432-4as illustrated inFIG. 4-D.). As used herein, normal plates may refer to the majority of plates included in an ASG which may share a same size (e.g., height). An abnormal plate may refer to one that has a different size compared to the normal plates (e.g., the plate440-2as illustrated inFIG. 4-D). An abnormal cell may refer to one that surrounded by one or more abnormal plates (e.g., the cells441-1and441-2as illustrated inFIG. 4-D).

In the ASG440, only a detector unit (e.g., detector units442-1and442-2) enclosed within an abnormal cell may be designated as a first detector unit that is at least partially covered by the shadow or a second detector unit that is free of the shadow occurred when the focal point of the radiation source is displaced. Other detector units (e.g., detector units442-3and442-4) may always be covered by shadows (e.g., shadows444-2and444-3) when the focal point is displaced regardless of the direction of the displacement, and are not included in determining the focal point.

When the focal point of the radiation source115is displaced from the first focal point445to the second focal point446, a first detector unit (e.g., the detector unit444-1) within an abnormal cell may have a larger part covered by the shadow (e.g., shadow444-1) caused by the displacement of the focal point, while a second detector unit (e.g., detector unit442-2) within another abnormal cell (e.g., an adjacent one which shares a same abnormal plate) may have a smaller part covered by the shadow caused by the same reason. The difference between the radiation intensities received by the first detector unit and the second detector unit may be used (e.g., by the focal point determination sub-module342) for determining the second focal point446. It may also be noted that, the first detector unit(s) and the second detector unit(s) may exchange their roles when the focal point is displaced along the direction opposite to that illustrated inFIG. 4-D.

In some embodiments, the radiation intensities of a first detector unit and a second detector unit within an arbitrary or predetermined pair of abnormal cells may be used (e.g., by focal point determination sub-module342) for determining the second focal point446. The first detector unit and the second detector unit may be adjacent to one another.

It may be noted that, the non-uniform ASG illustrated inFIG. 4-B,FIG. 4-C, andFIG. 4-D are provided only for demonstration purposes, and are not intended to be limiting. Numerous modification may be made to the ASG410,420, or430. For example, the cells of ASG410, the irregular cell(s) of ASG420, or the abnormal cell(s) of ASG430may include more detector units along either or both of the X direction and the Z direction.

In some embodiments, ASG410may also be made as a non-uniform ASG by using different material with different radiation blocking (or absorbing) properties for different plates. For example, one or more of the plates of ASG410(e.g., the plate410-2) may have smaller radiation blocking capacities compared to other plates. When the focal point of radiation115is displaced from the first focal point415to the second focal point416. The shadow region of detector412-2may receive more radiation than other shadow regions. When the focal point of radiation115is displaced along the direction opposite to that illustrated inFIG. 4-A, the shadow region of detector412-1may receive more radiation than other shadow regions. The detector unit412-1may be assigned as the first detector unit receiving reduced radiation, and the detector unit412-2may be assigned as the second detector unit receiving the same amount of radiation when the focal point is displaced compared to when the focal point is located at its original or intended position.

FIG. 5is a schematic diagram illustrating an exemplary process for determining the focal point of the radiation source according to some embodiments of the present disclosure. Process500may be performed by the focal point determination sub-module342for determining the focal point of a radiation source belonging to a CT scanner110equipped with one or more non-uniform ASG (type I and/or type II). The CT scanner110may include only the non-uniform ASG, or include both the standard ASG and the non-uniform ASG. In some embodiments, one or more operations of process500illustrated inFIG. 5for determining the focal point of the radiation source may be implemented in the CT system100illustrated inFIG. 1. For example, the process500illustrated inFIG. 5may be stored in the storage150in the form of instructions, and invoked and/or executed by the processing engine140(e.g., the processor210of the computing device200as illustrated inFIG. 2-A).

The focal point determination sub-module342may determine a displacement of the focal point from a first focal point to a second focal point via process500along the X direction or the Z direction. The displacement may then be used to generate the coordinate of the second focal point, or be directly used (e.g., by the calibration module340and/or the Image processing module330) for compensating the reduction of the image quality caused by the change of focal point via one or more hardware related (e.g., focus point tracing) and/or software (e.g., image post-processing) related techniques. In some embodiments, a calibration instruction for calibrating the CT scanner110may be generated by the calibration module340and/or the scanner controlling module320and sent to the CT scanner for calibration.

In510, the focal point determination sub-module342may determine a first intensity of first radiation incident on a first detector unit of the CT scanner110. In520, the focal point determination sub-module342may determine a second intensity of second radiation incident on a second detector unit of the CT scanner110. The first radiation and the second radiation may be emitted from the radiation source115with the second focal point. The first radiation and the second radiation may be emitted at a same time point or within a same time interval.

The CT scanner110may include a non-uniform ASG as described in connection withFIGS. 4-B to4-D. The first detector unit and the second detector unit may be determined by a user, by the focal point determination sub-module342, or the like, or a combination thereof. The first detector unit and the second detector unit may be determined based on the structure of the non-uniform ASG (see the descriptions ofFIGS. 4-B to4-D). In some embodiments, the first detector unit and the second detector unit adjacent to one another may be determined. In some embodiments, the first detector unit and the second detector unit spaced apart may be determined.

In some embodiments, the ASG420may be the non-uniform ASG installed on the CT scanner110. The first detector unit and the second detector unit may be included in the same cell. For example, the detector units422-1and422-2may be determined as the first detector unit and the second detector units. Alternatively or additionally, the first detector unit and the second detector unit may be included in different cells. The different cells may be adjacent to one another or spaced apart. For example, the detector units422-2and422-3(or the detector units422-1and422-4) may be determined as the first detector unit and the second detector units.

In some embodiments, the ASG430may be the non-uniform ASG installed on the CT scanner110. The first detector unit and the second detector unit may be included in the same cell. For example, the detector units432-1and432-2may be determined as the first detector unit and the second detector units. Alternatively or additionally, the first detector unit and the second detector unit may be included in different cells sharing a same (or substantially same) structure. The different cells may be adjacent to one another or spaced apart.

In some embodiments, the ASG440may be the non-uniform ASG installed on the CT scanner110. The non-uniform ASG440may include abnormal cells (e.g., cells441-1and441-2). The abnormal cells may include plates of different heights. The first detector unit and the second detector unit may be included in different abnormal cells having different structures. The different abnormal cells may be adjacent to one another or be spaced apart. For example, the detector units442-1and442-2may be determined as the first detector unit and the second detector unit.

The focal point determination sub-module342may determine the first intensity and the second intensity based on the signals generated by the first detector unit and the second detector unit in response to the first radiation and the second radiation, respectively. For example, the first intensity and the second intensity may correspond to the amplitudes, average amplitudes, or integrals of the amplitudes of the corresponding signals over a predetermined time interval. Due to the configuration of the non-uniform ASG, after the displacement of the focal point, the first intensity and the second intensity may become different.

The focal point determination sub-module342may determine the first intensity and the second intensity in real time, or based on the scan data (including the information relating to the signals generated by the first detector unit and the second detector unit) stored in a storage device (e.g., storage150, storage220, storage275, memory280) at a later time. Due to the equivalence of510and520, the two operations may be performed in any sequence or be performed simultaneously.

In530, the focal point determination sub-module342may determine the displacement of the focal point based on the first intensity and the second intensity. The direction (e.g., the X direction, the Z direction) along which the first detector unit and the second detector unit are located may define the direction of the displacement determined. For example, to determine the displacement of the focal point along both the X direction and the Z direction, a first pair of a first detector unit and a second detector unit located along the X direction and a second pair of a first detector unit and a second detector unit located along the Z direction may be selected. Process500may then be performed twice for obtaining the displacements along both directions.

In some embodiment, the focal point determination sub-module342may determine the displacement of the focal point based at least in part on at least one parameter relating to the configuration of the ASG. For instance, the at least one parameter may include a height of at least some plates of the ASG and a distance from the second focal point to a top of the at least a portion of the ASG. An exemplary process are described in connection withFIGS. 6, 7-A, and7-B.

Merely by way of example, the focal point determination sub-module342may determine the displacement of the focal point based on a ratio of the first intensity detected by the first detection unit to the second intensity detected by the second detection unit. In some embodiments, the focal point determination sub-module342may obtain a correlation between the displacement and the ratio, then determine the displacement based on the ratio and the correlation. An exemplary process are described in connection withFIGS. 8 and 9.

In some embodiments, a plurality of pairs of first and second detector units may be used for determining the displacement of the focal point along one direction. The focal point determination sub-module342may perform process500upon each of the plurality of detector unit pairs to generate a plurality of results, and determine the displacement along that direction based on the plurality of results. Alternatively, the focal point determination sub-module342may determine the first radiation intensity and second radiation intensity based on (e.g., mean, integral) the signals generated by the first detector units and the second detector units, respectively.

Process500may be performed prior to or during the scanning of a subject using CT scanner100. The subject may be a phantom, or a test object (e.g., patient). Signals detected by the detector units (e.g., the first detector unit and the second detector unit) used for determining the focal point may be included in, or excluded from, the data used for generating an image of the subject.

It may be noted that the above descriptions of the determining of the focal point are only for demonstration purposes, and not intended to limit the scope of the present disclosure. It is understandable that, after learning the major concept and the mechanism of the present disclosure, a person of ordinary skill in the art may alter process500in an uncreative manner. For example, the operations above may be implemented in an order different from that illustrated inFIG. 5. One or more optional operations may be added to the flowcharts. One or more operations may be divided or be combined. All such modifications are within the protection scope of the present disclosure.

FIG. 6is a schematic diagram illustrating an exemplary process for determining the displacement of the focal point based on the first intensity and the second intensity according to some embodiments of the present disclosure. Process600may be performed to achieve530of process500. In some embodiments, process600may be performed by the focal point determination sub-module342. In some embodiments, one or more operations of process600illustrated inFIG. 6for determining the focal point of the radiation source may be implemented in the CT system100illustrated inFIG. 1. For example, the process600illustrated inFIG. 6may be stored in the storage150in the form of instructions, and invoked and/or executed by the processing engine140(e.g., the processor210of the computing device200as illustrated inFIG. 2).

In610, the focal point determination sub-module342may obtain a reference radiation intensity for at least one of the first detector unit and the second detector unit. The reference radiation intensity may correspond to the intensity of the radiation received by the first detector unit or the second detector when the focal point of the radiation source115is at (approximately or precisely) the first focal point. As used herein, “approximately” may indicate that the deviation from the first focal point (the original or intended focal point) is lower than a threshold. In some embodiments, the threshold may be, e.g., 1 micron, 2 microns, 5 microns, 10 microns, 20 microns, 50 microns, 100 microns, etc. In some embodiments, the threshold may be, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, etc., of the range within which the radiation source is allowed to move. The reference radiation intensity may be determined prior to or during the scanning of a subject using CT scanner100. For example, the reference radiation intensity may be retrieved from a storage device (e.g., storage150, storage220, storage275, memory280), determined based on one of the system parameters provided with the CT scanner100. As another example, the reference radiation intensity may be obtained based on one or more signals generated by one or more detector units of the CT scanner100.

In some embodiments, the reference radiation intensity may be obtained by the following process. The scanner control module320may send a control signal to the CT scanner110. The CT scanner110may respond to the control signal, and cause the radiation source115to emit radiation. During the radiation emission process, the temperature of the radiation source115may rise (e.g., by running the radiation source115originally at a sleep mode or a low-load mode), or drop (e.g., by cooling the radiation source115originally at an operative mode or a high-load mode). The focal point of the radiation source115may be displaced due to thermal expansion or contraction accordingly.

The signals generated by the first detector unit and the second detector unit may be extensively collected (e.g., 1˜500 samples per second) during the radiation emission process. A plurality of first intensities and second intensities may be obtained. When the sum of the first intensity and the second intensity collected at a time point (time point A) reaches its maximum compared to other time points, the focal point of the radiation source115at the time point A may be considered as the one (the first focal point) toward which the plates of the ASG are aligned. In some embodiments, the first intensity and the second intensity collected at the time point A may be selected (e.g., by a user or by the focal point determination sub-module342) as reference radiation intensities for the first detector unit and the second detector unit, respectively. In some embodiments, the average value (weighted or not weighted) of the first intensity and the second intensity of the time point A may be determined (e.g., by a user or by the focal point determination sub-module342) as one reference radiation intensity for both the first detector unit and the second detector unit.

In some embodiments, a plurality of pairs of first and second detector units may be used for determining the displacement of the focal point along one direction. The focal point determination sub-module342may obtain one or more reference radiation intensities for each of the plurality of detector unit pairs. Alternatively, the focal point determination sub-module342may determine a common reference radiation intensity set (including one or more reference radiation intensities) for the plurality of detector unit pairs.

The obtained one or more reference radiation intensities may then be stored in a storage device (e.g., storage150, storage220, storage275, memory280) When the focal point determination sub-module342is to determine the displacement of the focal point through process600, the focal point determination sub-module342may obtain at least one of the reference radiation intensities.

In620, the focal point determination sub-module342may obtain at least one ASG parameter relating to the configuration of the non-uniform ASG. The ASG parameter may relate to the height of at least a portion of the ASG, the distance form the second focal point to a top of the at least a portion of the ASG, the length and/or the width of one or more cells of the ASG, or the like, or a combination (e.g., a calculation) thereof. The ASG parameter may be retrieved from a storage device (e.g., storage150, storage220, storage275, memory280), determined based on one of the system parameters provided with the non-uniform ASG, or measured by a user of the ASG or the CT scanner110, or a combination thereof.

In630, the focal point determination sub-module342may determine the displacement of the focal point based on the at least one reference radiation intensity obtained in610, the at least one ASG parameters obtained in620, the first intensity obtained in510, and the second intensity obtained520. The direction (e.g., the X direction, the Z direction) along which the first detector unit and the second detector unit are located may define the direction of the displacement determined in630.

In some embodiments, the focal point determination sub-module342may perform the process600according to the description ofFIGS. 7-A and7-B.

FIGS. 7-A and7-B are schematic diagrams of the process illustrated inFIG. 6according to some embodiments of the present disclosure. It may be noted that, for demonstration purposes,FIGS. 7-A and7-B only illustrate the process600with the non-uniform ASG420as illustrated inFIG. 4-B. However, other non-uniform ASGs (e.g., ASGs430and440illustrated inFIGS. 4-C and4-D) descripted or implied in the present disclosure may also be used for the process600with a similar manner.

The plates (e.g., the plates420-1,420-2, and420-3) of the ASG420are aligned toward a focal point710(first focal point). During the operation of the CT scanner110, the focal point of the radiation source115may be displaced along the X direction or the Z direction (parallel to the detector units). For example, the focal point may be displaced toward one direction to the focal point712(as shown inFIG. 7-A), or toward the opposite direction to the focal point714(as shown inFIG. 7-B). The focal point being at focal point712may cause shadows724-1and724-2on the first director units422-1and422-3. The focal point being at focal point714may cause shadows724-3and724-4on the first director units422-2and422-4.

For the ASG420, any pair of adjacent detector units including a first detector unit and a second detector unit may be identified (e.g., by a user or by the focal point determination sub-module342). InFIGS. 7-A and7-B, detector unit422-2and422-3are determined as the first detector unit and the second detector unit, respectively.

The focal point determination sub-module342may determine the direction of the displacement by comparing the changes of the radiation intensities occurred on the detector units422-2and422-3. For example, when the detector unit422-3has a larger reduction of the radiation intensity (e.g., caused by shadow724-2), the focal point determination sub-module342may determine that the displacement has occurred in a pattern as shown inFIG. 7-A. When the detector unit422-2has a larger reduction of the radiation intensity, the focal point determination sub-module342may determine the displacement has occurred in a pattern as shown inFIG. 7-B.

In some embodiments, the focal point determination sub-module342may directly compare the radiation intensities of the detector units422-2and422-3for determining the direction of the displacement. The one with a smaller intensity may be determined as the one having a larger reduction of the radiation intensity.

In some embodiments, the focal point determination sub-module342may first determine the reductions of the radiation intensities occurred on each of the detector units422-2and422-3with the corresponding reference radiation intensities obtained in610. For example, the focal point determination sub-module342may obtain a ratio of the currently received radiation intensity to the corresponding reference radiation intensity for each of the detector units422-2and422-3. The one with a smaller ratio may be determined as the one having a larger reduction of the radiation intensity.

In some embodiments, when the displacement is determined to have occurred in a pattern as shown inFIG. 7-A, the focal point determination sub-module342may determine the displacement according to Equation (1) in630of process600, which may be expressed as:

D1=(1-I2IR⁢⁢2)⁢L2⁢HF⁢⁢2⁢AHASG,(1)
where D1is the value of the displacement in a pattern as shown inFIG. 7-A, I2is the intensity (second intensity) of the radiation received by the detector unit422-3(second detector unit), IR2is the reference radiation intensity for the detector unit422-3, L2is the length of the detector unit422-3in the X direction or the Z direction, HASGis the height of the plate (e.g., plate420-2) of the ASG420shared by the detector units422-2and422-3, and HF2Ais the distance from the second focal point to the top of the shared plate in a direction perpendicular to the detector422-2and/or422-3(e.g., the Y direction). As the displacement along the Y direction is omitted, HF2Amay be considered as the distance from the first focal point to the top of the shared plate in the Y direction.

In some embodiments, when the displacement is determined to have occurred in a pattern as shown inFIG. 7-B, the focal point determination sub-module342may determine the displacement according to Equation (2) in630of process600, which may be expressed as:

D2=(1-I1IR⁢⁢1)⁢L1⁢HF⁢⁢2⁢AHASG,(2)
where D2is the value of the displacement in a pattern as shown inFIG. 7-B, I1is the intensity (first intensity) of the radiation received by the detector unit422-2(first detector unit), IR1is the reference radiation intensity for the detector unit422-2, L1is the length of the detector unit422-2in the X direction or the Z direction, and HASGand HF2Ahold the same meaning as in Equation (1).

HASGand HF2Amay be obtained as ASG parameters in620of process600. HASGand HF2Amay be provided with CT scanner110or ASG420as system parameters, or be measured directly by a user.

L1and L2may have a same value or different values. In some embodiments, L1and L2may be provided with CT scanner110as system parameters or be measure form the CT scanner110by a user. In some embodiments, L1and L2may be obtained as or determined based on the ASG parameters in620of process600. For example, L1and L2may be considered as half of the length of the cells defined by the plates420-1,420-2, and420-3in the X direction or the Z direction.

In some embodiments, L1and L2may both have a same value L. A parameter with a value of LHF2A/HASGmay be provided with CT scanner110or ASG420, and be obtained as part of the ASG parameter in620of process600.

IR1and/or IR2may be obtained in610of process600. In some embodiments, both of IR1and IR2may be obtained in610. For example, IR1and IR2may be used to determine the pattern of the displacement. In some embodiments, the pattern of the displacement may be determined without using IR1or IR2(e.g., by directly comparing the radiation intensities of the detector units422-2and422-3), and one of IR1or IR2may be obtained in610according to the determined pattern. In some embodiments, IR1and/or IR2may be replaced by the radiation intensity of the detector unit free of shadow caused by the displacement of the focal point. For example, to determine D1, I1may be used to replace IR2in Equation (1); to determine D2, I2may be used to replace IR1in Equation (2).

FIG. 8is a schematic diagram illustrating an exemplary process for determining the displacement of the focal point based on the first intensity and the second intensity according to some embodiments of the present disclosure. Process800may be performed to achieve530of process500. Process800may be performed by the focal point determination sub-module342. In some embodiments, one or more operations of process800illustrated inFIG. 8for determining the focal point of the radiation source may be implemented in the CT system100illustrated inFIG. 1. For example, the process800illustrated inFIG. 8may be stored in the storage150in the form of instructions, and invoked and/or executed by the processing engine140(e.g., the processor210of the computing device200as illustrated inFIG. 2).

In810, the focal point determination sub-module342may determine a ratio of the first intensity to the second intensity. Then in820, the focal point determination sub-module342may obtain a correlation between the ratio and the displacement of the focal point. The correlation may be, for example, a mathematical function (e.g., a polynomial, a piecewise function), or a lookup table (the items of which may each include a ratio and a corresponding displacement), etc. In830, the focal point determination sub-module342may determine the displacement of the focal point based on the ratio and the correlation. For example, the displacement may be obtained by inputting the ratio into the mathematical function, or by searching the item with the same (precisely or approximately) ratio in the lookup table. In some embodiments, an interpolation or extrapolation may be performed to determine a displacement based on the values available in the lookup table.

The correlation between the ratio and the displacement of the focal point may be generated by the correlation determination sub-module344. An exemplary technique for generating the correlation is discussed in connection withFIG. 9.

FIGS. 9-A and9-B are schematic diagrams illustrating exemplary techniques for generating the correlation between the ratio of the first intensity to the second intensity and the displacement of the focal point according to some embodiments of the present disclosure. Detector950may be the same as or similar to the detector112. Detector950may include a plurality of detector units and one or more non-uniform ASGs (not shown inFIG. 9for simplicity). The one or more non-uniform ASGs may be configured according to a focal point901(first focal point) of the radiation source115. A plate910made of radiation absorbing material may be placed between the radiation source115and the detector950for determining the correlation. The plate910may have a pinhole915through which a portion of the radiation emitted by the radiation source115may pass and reach the detector950. A line960linking the center point of the pinhole915and the focal point901may coincide with or parallel to (approximately or precisely) the Y direction. When the focal point of the radiation source115is at the focal point901, a region R1of detector950may be illuminated by the radiation emitted from the radiation source115.

To determine the correlation between the ratio of the first intensity (detected by a first detector unit) to the second intensity (detected by a first detector unit) and the displacement of the focal point of the radiation source, the scanner control module320may send a control signal to the CT scanner110. The CT scanner110may respond to the control signal, and cause the radiation source115to emit radiation. During the radiation emission, the temperature of the radiation source115may rise (e.g., by running the radiation source115originally at a sleep mode or a low-load mode), or drop (e.g., by cooling the radiation source115originally at an operative mode or a high-load mode). The focal point of the radiation source115may be displaced due to thermal expansion or contraction accordingly.

At a time point B, the focal point of the radiation source115may be displaced to the focal point902. A region R2of the detector950may be illuminated by the radiation emitted from the radiation source115at the time point B. The focal point902is an arbitrary focal point of the radiation source115between the focal point901and the farthermost focal point the radiation source115may ever have along the X direction or the Z direction.

In some embodiments, as illustrated inFIG. 9-A, to determine the displacement from the focal point901to the focal point902, the correlation determination sub-module344may determine a distance x between the farther edge (indicated by line961) of region R2(relative to the focal point901) and the intersection point of the surface of the detector950and line960. For example, to determine x, the correlation determination sub-module344may locate an illuminated (or not illuminated) detector unit locating at (approximately or precisely) the farther edge of region R2based on the signals generated by the detector units. The detector unit locating at the farther edge of region R2may be determined as the ith detector unit. The correlation determination sub-module344may also locate the detector unit locating at (approximately or precisely) the intersection point, for example, based on the structure information of the CT scanner110. For instance, the CT scanner110may be configured that the focal point901is right above (approximately or precisely) a certain detector unit (e.g., detector unit locating at the center of the detector950) along the Y direction, and the related structure information may be pre-stored in a storage device (e.g., the storage150, the storage220, the storage275, and memory280). The detector unit locating at the intersection point may be determined as the jth detector unit. The correlation determination sub-module344may obtain x by multiplying the length (or average length) of the detector units with the absolute value of (j−i). Alternatively or additionally, the correlation determination sub-module344may obtain x based on i, j(optional), and a look-up table correlating x, i and j(optional).

The correlation determination sub-module344may then determine the displacement D from the focal point901to the focal point902via Equation (3), which may be express as:

D=(x-d2*(HF⁢⁢2⁢P+HP⁢⁢2⁢D)HF⁢⁢2⁢P)*HF⁢⁢2⁢PHP⁢⁢2⁢D,(3)
where HF2Pis the distance between the focal point902(or focal point901as the displacement along the Y direction is omitted) and the central plane (dashed line) of plate910along the Y direction, HP2Dis the distance between the central plane of the plate910and the detector950along the Y direction, and d is the diameter of the pinhole915. HF2P, HP2Dand d may be provided with the CT scanner110and/or plate910, or be directly measured by a user.

Alternatively or additionally, the correlation determination sub-module344may obtain D based on i, j(optional), and a look-up table correlating D, i and j(optional).

In some embodiments, as illustrated inFIG. 9-B, to determine the displacement from the focal point901to the focal point902, the correlation determination sub-module344may determine a distance x′ between the centroid of region R2and the centroid of region R1. For example, to determine x′, the correlation determination sub-module344may determine the region R2and region R1and their relative position (e.g., the position of one of the region R2and region R1relative to the position of the other) based on the signals generated by the detector units and the structure information of the detector950. The correlation determination sub-module344may then determine the centroids of region R2and region R1and the distance x′. Merely by way of example, the correlation determination sub-module344may then determine the displacement D from the focal point901to the focal point902according to Equation (4), which may be express as:

D=x′*HF⁢⁢2⁢PHP⁢⁢2⁢D,(4)
where HF2Pand HP2Dhold the same meaning as in Equation (3) and may be obtained in a similar way.

Region R3is the common region shared by regions R1and R2. During the displacement of the focal point from the focal point901to the focal point902, region R3may always be illuminated. The non-uniform ASG (not shown inFIG. 9) of the detector950may be configured so that at least a pair of first detector unit and second detector unit may locate within the region R3. The signals generated by the first detector unit and the second detector unit may be extensively collected (e.g., 1˜500 samples per second) during the displacement of the focal point between the focal points901and902. A first intensity and a second intensity may be obtained by the correlation determination sub-module344at each of a plurality of predetermined time points. The correlation determination sub-module344may also determine a displacement from the focal point901to the current focal point at each of the plurality of predetermined time points (e.g., according to the exemplary method described above or in a similar manner). The correlation determination sub-module344may generate a correlation between a ratio of the first intensity to the second intensity and the displacement. The correlation may be in the form of one or more mathematical functions (e.g., by fitting), or a lookup table (e.g., by recording). The generated correlation may be stored in a storage device (e.g., storage150, storage220, storage275, memory280) for further use. In820of process800illustrated inFIG. 8, the focal point determination sub-module342may obtain the correlation from the storage device to determine the displacement of the focal points.

In some embodiments, the determination of the correlation may be performed during the acquisition of scan data by the CT scanner110.