Attenuation correction method and system and storage medium

Abstract

The embodiment of the invention provides an attenuation correction method and system and a storage medium. The method comprises the following steps: acquiring transmission data; acquiring radiation coincidence event data of the target object; and based on the transmission data and the radiation coincidence event data, performing attenuation correction reconstruction on the radiation image of the target object to obtain a radiation image after attenuation correction. The attenuation correction system is used for realizing the attenuation correction method and comprises a first acquisition module used for acquiring transmission data; the second acquisition module is used for acquiring radiation coincidence event data of the target object; and the reconstruction module is used for performing attenuation correction reconstruction on the radiation image of the target object based on the transmission data and the radiation coincidence event data to obtain the radiation image after attenuation correction.

Description

Technical Field

[0001] The present invention relates to the field of positron emission tomography technology, and in particular to an attenuation correction method, system, and storage medium. Background Art

[0002] Attenuation correction is an important factor that needs to be compensated for in quantitative positron emission tomography (PET). Attenuation correction is usually achieved by fusing PET data with computed tomography (CT) data. CT data provides tissue density information, which can be used to calculate the attenuation coefficient of photons. These attenuation coefficients are then applied to the PET data to eliminate the attenuation effect of photons in tissue. However, the attenuation map (μ-map) derived from CT data has certain limitations. For example, high radiation dose, metal artifacts, beam hardening artifacts, truncation of large patients, and patient motion between PET / CT scans can affect the derivation results.

[0003] Therefore, there is a need for an attenuation correction method, system and storage medium to provide accurate attenuation correction results. Summary of the Invention

[0004] One or more embodiments of the present specification provide an attenuation correction method, the method comprising: acquiring transmission data; acquiring radiation coincidence event data of a target object; performing attenuation correction and reconstruction on a radiation image of the target object based on the transmission data and the radiation coincidence event data to obtain an attenuation-corrected radiation image; wherein the transmission data includes backscatter coincidence event data of the target object.

[0005] In some embodiments, acquiring transmission data includes: acquiring single event data of the target object; determining whether the energy and arrival time of the single event data meet a first preset rule; and in response to the single event data meeting the first preset rule, determining that the single event data meeting the first preset rule is the transmission data.

[0006] In some embodiments, acquiring radiation compliance event data of the target object includes: acquiring single event data of the target object; determining whether the energy and arrival time of the single event data comply with a second preset rule; and in response to the single event data complying with the second preset rule, determining that the single event data complying with the second preset rule is the radiation compliance event data.

[0007] In some embodiments, the attenuation-corrected reconstruction of the target object's radiographic image based on the transmission data and the radiographic coincidence event data to obtain the attenuation-corrected radiographic image includes: performing attenuation image initialization to obtain an initial attenuation image; performing radiographic image initialization to obtain an initial radiographic image; and iteratively reconstructing based on the initial attenuation image, the initial radiographic image, the transmission data, and the radiographic coincidence event data to obtain the attenuation-corrected radiographic image.

[0008] In some embodiments, the iteration includes: obtaining a scattering estimate of backscattering, a blank scan estimate of backscattering, and a scattering estimate of radiation based on the attenuation image of the previous iteration and the radiation image of the previous iteration; the attenuation image of the first iteration is the initial attenuation image, and the radiation image of the first iteration is the initial radiation image; obtaining an attenuation image of the current iteration based on the scattering estimate of backscattering, the blank scan estimate of backscattering, and the transmission data; obtaining a radiation image of the current iteration based on the attenuation image of the current iteration, the scattering estimate of radiation, and the radiation coincidence event data; judging whether the iteration termination condition is met, and if not, performing the next iteration; and if so, determining the radiation image of the current iteration as the radiation image after attenuation correction.

[0009] In some embodiments, obtaining the backscattered scattering estimate, the backscattered blank scan estimate, and the radiation scattering estimate based on the attenuation image of the previous iteration and the radiation image of the previous iteration includes: processing the attenuation image of the previous iteration and the radiation image of the previous iteration by a first processing method to obtain the backscattered scattering estimate and the radiation scattering estimate; processing the attenuation image of the previous iteration and the radiation image of the previous iteration by a second processing method to obtain the backscattered blank scan estimate; the second processing method includes at least one of a Monte Carlo method and a lookup table method.

[0010] In some embodiments, the backscatter coincidence event data is acquired by a positron emission tomography system, and the lookup table includes a probability distribution of backscattering events on each response line of the positron emission tomography system being detected on the remaining response lines. The lookup table method includes: acquiring a lookup table; simplifying the lookup table based on the symmetry of the positron emission tomography system and / or the merging of the response lines; and determining a blank scan estimate of the backscatter based on the simplified lookup table and scan data.

[0011] In some embodiments, the transmission data further includes lutetium background event data.

[0012] One or more embodiments of the present specification provide an attenuation correction system, which is used to implement an attenuation correction method. The system includes: a first acquisition module for acquiring transmission data; a second acquisition module for acquiring radiation coincidence event data of a target object; and a reconstruction module for performing attenuation correction and reconstruction on a radiation image of the target object based on the transmission data and the radiation coincidence event data to obtain an attenuation-corrected radiation image; wherein the transmission data includes backscatter coincidence event data of the target object.

[0013] One or more embodiments of the present specification provide a computer-readable storage medium, wherein the storage medium stores computer instructions. When a computer reads the computer instructions in the storage medium, the computer executes the attenuation correction method. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] This specification will be further described in the form of exemplary embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are not limiting, and in these embodiments, like numbers represent like structures, wherein:

[0015] Figure 1 is a schematic diagram of an application scenario of the attenuation correction system according to some embodiments of this specification;

[0016] Figure 2 is an exemplary schematic diagram of an attenuation correction system according to some embodiments of this specification;

[0017] Figure 3 is an exemplary flow chart of an attenuation correction method according to some embodiments of this specification;

[0018] Figure 4 is an exemplary schematic diagram of obtaining radiation coincidence event data of a target object according to some embodiments of this specification;

[0019] Figure 5 is an exemplary schematic diagram of a backscatter event according to some embodiments of the present specification;

[0020] Figure 6 is an exemplary schematic diagram of lutetium background events according to some embodiments of the present specification;

[0021] Figure 7 is an exemplary schematic diagram of symmetry according to some embodiments of this specification;

[0022] Figure 8 is an exemplary schematic diagram of an attenuation image according to some embodiments of this specification;

[0023] Figure 9Ais an exemplary flow chart for determining an attenuation-corrected radiographic image according to some embodiments of the present specification;

[0024] Figure 9B is an exemplary flow chart of determining a radiological image after attenuation correction according to other embodiments of the present specification;

[0025] Figure 9C is an exemplary flow chart of determining a radiological image after attenuation correction according to some other embodiments of the present specification. DETAILED DESCRIPTION

[0026] To more clearly illustrate the technical solutions of the embodiments of this specification, the following briefly describes the drawings required for describing the embodiments. Obviously, the drawings described below are merely examples or embodiments of this specification. Those skilled in the art can apply this specification to other similar scenarios based on these drawings without inventive effort. Unless otherwise apparent from the context or otherwise noted, the same reference numerals in the figures represent the same structure or operation.

[0027] It should be understood that the terms "system," "device," "unit," and / or "module" used herein are a method for distinguishing different components, elements, parts, portions, or assemblies at different levels. However, if other terms can achieve the same purpose, the terms may be replaced by other expressions.

[0028] As used in this specification and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" do not refer to the singular but also include the plural. Generally speaking, the terms "comprises" and "include" only indicate the inclusion of the steps and elements specifically identified, and these steps and elements do not constitute an exclusive list. A method or apparatus may also include other steps or elements.

[0029] Flowcharts are used throughout this specification to illustrate the operations performed by systems according to embodiments of this specification. It should be understood that preceding or following operations do not necessarily need to be performed in exact order. Instead, the steps may be processed in reverse order or simultaneously. Furthermore, other operations may be added to these processes, or one or more operations may be removed from these processes.

[0030] Attenuation correction (AC) is a crucial step in PET imaging. During PET imaging, emitted positrons interact with surrounding tissues, generating 511keV photons. These photons experience varying degrees of attenuation as they pass through human tissue, so correction for these attenuations is necessary to obtain more accurate PET images.

[0031] In PET / CT imaging, attenuation correction is typically achieved by fusing PET and CT data. The CT data provides information about tissue density, which can be used to calculate photon attenuation coefficients. These attenuation coefficients are then applied to the PET data to eliminate the effects of photon attenuation in tissue.

[0032] However, the attenuation map (μ-map) derived from CT data has certain limitations, such as high radiation dose, metal artifacts, beam hardening artifacts, truncation of large patients, and patient motion between PET / CT scans.

[0033] Existing techniques perform attenuation correction by jointly reconstructing attenuation and activity maps. This method can directly extract attenuation coefficient information from radiological data. First, a maximum likelihood estimate (MLAA) of the attenuation and activity maps is calculated. PET and attenuation image reconstruction is then iterated sequentially using the maximum likelihood expectation maximization (MLEM) and maximum likelihood transmission tomography (MLTR) algorithms. Similar to MLAA, some studies have proposed a maximum likelihood estimate (MLACF) of the activity map and attenuation correction factor, in which the attenuation factor is estimated after or during each activity image update.

[0034] Potential problems with this type of algorithm are that, on the one hand, if the initial values ​​are not good enough, MLAA or MLACF may converge to a local optimum. On the other hand, MLAA and MLACF use the same set of radiometric data to estimate activity and attenuation maps, and crosstalk may affect convergence speed and estimated image quality.

[0035] To address the above issues, some studies have used external rotating sources to reconstruct attenuation maps, which are directly used for attenuation correction or as the initial value of the attenuation map in MLAA. The disadvantage of external source scanning is that it requires additional equipment, increases the complexity of system design and user operation, and also increases the radiation dose received by the patient.

[0036] In some embodiments of this specification, a method for attenuation correction is provided. By acquiring transmission data and radiation coincidence event data of a target object, an attenuation-corrected radiographic image of the target object is reconstructed, resulting in an attenuation-corrected radiographic image. The transmission data includes backscatter coincidence event data of the target object. This method estimates an attenuation image or attenuation factor and performs correction without requiring CT data, increasing system complexity, scanning time, or patient radiation dose.

[0037] Figure 1 This is a schematic diagram of an application scenario of the attenuation correction system according to some embodiments of this specification.

[0038] like Figure 1 As shown, in some embodiments, an application scenario 100 of the attenuation correction system may include a scanning device 110 , a processing device 120 , a storage device 130 , a terminal 140 , and a network 150 .

[0039] The scanning device 110 refers to a medical device that uses different media to reproduce the internal structure of the human body as an image. In some embodiments, the scanning device 110 can be any medical device that uses radioactive nuclides to image or treat a designated part of the patient's body, such as a positron emission tomography (PET) device, a computed tomography (CT) device, a PET-CT device, etc. The scanning device 110 provided above is for illustrative purposes only and is not intended to limit its scope. The detector in the scanning device 110 can receive radiation from a radiation source and measure the received radiation. The detector is a plurality of detection units arranged into one or more ring structures. In some embodiments, the scanning device 110 can send data and information related to the detector, such as the energy value of the radiation photons received by the detector, the output value of the detector, etc., to the processing device 120. In some embodiments, the scanning device 110 can collect transmission data, radiation coincidence event data of the scanned target object, etc., and send them to the processing device 120. For more information about transmission data, target objects, and radiation coincidence event data, please refer to Figure 3 and its related description. In some embodiments, the scanning device 110 can receive instructions sent by the doctor through the terminal 140, and perform relevant operations according to the instructions, such as irradiation imaging, etc. In some embodiments, the scanning device 110 can exchange data and / or information with other components in the system 100 (e.g., the processing device 120, the storage device 130, the terminal 140) through the network 150. In some embodiments, the scanning device 110 can be directly connected to other components in the application scenario 100 of the attenuation correction system. In some embodiments, one or more components in the application scenario 100 of the attenuation correction system (e.g., the processing device 120, the storage device 130) can be included in the scanning device 110.

[0040] The processing device 120 can process data and / or information obtained from other devices or system components and, based on this data, information, and / or processing results, execute the methods for correcting scanned images described in some embodiments of this specification to accomplish one or more functions described in some embodiments of this specification. For example, the processing device 120 can perform attenuation correction and reconstruction on a radiographic image of a target object based on the transmission data and radiographic coincidence event data acquired by the scanning device 110 to obtain an attenuation-corrected radiographic image. In some embodiments, the processing device 120 can retrieve pre-stored data and / or information, such as transmission data, radiographic coincidence event data, various calculation formulas, etc., from the storage device 130 to execute the attenuation correction methods described in some embodiments of this specification.

[0041] In some embodiments, the processing device 120 may include one or more sub-processing devices (e.g., a single-core processing device or a multi-core multi-core processing device). By way of example only, the processing device 120 may include a central processing unit (CPU), an application-specific integrated circuit (ASIC), a graphics processing unit (GPU), a digital signal processor (DSP), a field-programmable gate array (FPGA), a microcontroller unit (MCU), a reduced instruction set computer (RISC), a microprocessor, or any combination thereof.

[0042] The storage device 130 can store data or information generated by other devices. In some embodiments, the storage device 130 can store data and / or information collected by the scanning device 110, such as transmission data, radiation coincidence event data, etc. The storage device 130 may include one or more storage components, each of which may be a standalone device or part of another device. The storage device may be local or implemented via the cloud. In some embodiments, one or more components of the system 100 (e.g., the scanning device 110, the processing device 120, the terminal 140) may include their own storage components.

[0043] The terminal 140 can control the operation of the scanning device 110. The doctor can issue operating instructions to the scanning device 110 through the terminal 140 to enable the scanning device 110 to complete the specified operation, for example, irradiate and image the patient's specified body part. In some embodiments, the terminal 140 can instruct the processing device 120 to execute the attenuation correction method as described in some embodiments of this specification. In some embodiments, the terminal 140 can receive attenuation-corrected radiological images, etc. from the processing device 120, so that the doctor can accurately judge the patient's condition and perform effective and targeted examinations and / or treatments on the patient. In some embodiments, the terminal 140 can be one of the mobile devices 140-1, tablet computers 140-2, laptop computers 140-3, desktop computers, and other devices with input and / or output functions, or any combination thereof.

[0044] Network 150 can connect the various components of the system and / or connect the system to external resources. Network 150 enables communication between the various components and with other components outside the system, facilitating the exchange of data and / or information. In some embodiments, one or more components in system 100 (e.g., scanning device 110, processing device 120, storage device 130, terminal 140) can send data and / or information to other components via network 150. In some embodiments, network 150 can be any one or more of a wired network and a wireless network.

[0045] It should be noted that the above description is provided for illustrative purposes only and is not intended to limit the scope of this specification. For those skilled in the art, various changes and modifications can be made under the guidance of the contents of this specification. The features, structures, methods and other features of the exemplary embodiments described in this specification can be combined in various ways to obtain additional and / or alternative exemplary embodiments. For example, the processing device 120 can be based on a cloud computing platform, such as a public cloud, a private cloud, a community and a hybrid cloud. However, these changes and modifications do not deviate from the scope of this specification.

[0046] Figure 2 is an exemplary schematic diagram of an attenuation correction system according to some embodiments of the present specification.

[0047] In some embodiments, the attenuation correction system 200 may include a first acquisition module 210 , a second acquisition module 220 , and a reconstruction module 230 .

[0048] In some embodiments, the first acquisition module 210 may be used to acquire transmission data.

[0049] In some embodiments, the second acquisition module 220 may be configured to acquire radiation coincidence event data of the target object.

[0050] In some embodiments, the reconstruction module 230 can be used to perform attenuation correction reconstruction on the radiographic image of the target object based on the transmission data and the radiographic coincidence event data to obtain an attenuation-corrected radiographic image; wherein the transmission data may include the backscattered coincidence event data of the target object.

[0051] For more information on transmission data, target objects, radiographic coincidence data, radiographic images, attenuation correction, and backscatter coincidence data, see Figure 3 、 Figure 4 and its related descriptions.

[0052] It should be noted that the above description of the attenuation correction system and its modules is for convenience only and does not limit this specification to the scope of the embodiments. It is understood that after understanding the principles of the system, those skilled in the art may arbitrarily combine the modules or form subsystems connected to other modules without departing from the principles. In some embodiments, Figure 2 The first acquisition module 210, second acquisition module 220, and reconstruction module 230 disclosed herein may be separate modules within a system, or a single module may implement the functions of two or more of the aforementioned modules. For example, the modules may share a storage module, or each module may have its own storage module. Such variations are within the scope of protection of this specification.

[0053] Figure 3 FIG. 1 is an exemplary flow chart of an attenuation correction method according to some embodiments of this specification. Figure 3 As shown, the process 300 includes the following steps: In some embodiments, the process 300 may be executed by the processing device 120 .

[0054] Step 310: Acquire transmission data.

[0055] Transmission data refers to data transmitted through a target object. For example, backscattered coincident event data and lutetium background event data are collected from the target object. The target object is the object to be scanned, such as a living organism or a phantom. The living organism can be a human or an animal, and the phantom can be made of various materials and shapes, such as water phantoms, gel phantoms, cylinders, and rectangular blocks.

[0056] Before a PET scan is performed, a tracer is introduced into the subject's body. During the PET scan, the tracer emits positrons. The subject's body naturally contains a large number of negatively charged electrons. Positrons have the same mass as electrons but the opposite charge. When positrons collide with electrons, annihilation occurs (also known as an "annihilation event" or "coincidence event"). This annihilation produces two gamma photons (or radiation rays) with an energy of 511 keV traveling in opposite directions. The line connecting the two gamma photons is called the Line of Response (LOR).

[0057] In a PET detector, two 511keV gamma rays interact with matter, producing the photoelectric effect and Compton scattering. The photoelectric effect occurs when a gamma ray interacts with an electron in matter and transfers all of its energy to an electron, freeing the electron from the atom. Compton scattering occurs when a gamma ray interacts with an electron in matter but only partially transfers its energy to the electron, causing the gamma ray to change direction.

[0058] In this application, we focus on the physical process of Compton scattering of gamma rays in PET detectors. One or two gamma rays are Compton scattered in the first crystal ( Figure 5 The gamma ray is then backscattered (backscatter refers to the phenomenon that waves, particles or signals are reflected back from the direction they came from) and penetrates back into the target object. Finally, the gamma ray is detected by another crystal on the other side (as shown in the dashed line). Figure 5 Detecting backscattered events can form a transmission response line, which is used for transmission image estimation.

[0059] Backscatter coincidence event data refers to data related to backscatter coincidence events, such as counts and trajectories of backscatter coincidence events.

[0060] In some embodiments, the transmission data may further include lutetium background event data.

[0061] like Figure 6 As shown, common PET systems use LSO or LYSO crystals as scintillation crystals, which contain the isotope Lu-176, which can produce spontaneous background radiation.

[0062] Lutetium background event data is coincident event data generated by the spontaneous background radiation of lutetium from the crystal in the scanning device. For example, lutetium background event counts and traces are included.

[0063] In some embodiments, the processing device 120 can acquire transmission data via the scanning device 110. For example, the processing device 120 can collect background radiation signals from the scanning device to acquire lutetium background event data. For another example, the processing device 120 can scan a target object via the scanning device 110 to acquire backscatter coincidence event data.

[0064] In some embodiments, the processing device 120 can obtain single event data of the target object; determine whether the energy and arrival time of the single event data meet the first preset rule; in response to the single event data meeting the first preset rule, determine that the single event data meeting the first preset rule is transmission data.

[0065] Single event data refers to data related to a single event. For example, single event data can include counts or traces of multiple single events.

[0066] The processing device 120 may scan and acquire single event data through the scanning device 110 .

[0067] Arrival time refers to the time when a detector detects a single event.

[0068] The processing device 120 may scan and obtain the energy and arrival time of single event data through the scanning device 110 .

[0069] The first preset rule can be set based on experience or demand. In some embodiments, the first preset rule may include: if the energies of two different single events in the single event data are respectively within a first preset energy window and a second preset energy window, and the difference in arrival time of the two different single events is within a first preset time window, then the data corresponding to the two different single events are transmission data.

[0070] As you can understand, the energy and arrival times of transmission data exhibit certain characteristics. For example, backscatter coincidence events are signal events reflected from an object, and their arrival times tend to be longer than those of directly transmitted signals. Therefore, by setting an appropriate arrival time threshold, it is possible to distinguish directly transmitted signal events from backscatter coincidence events. Accordingly, due to energy loss during reflection, backscatter coincidence events are typically weaker than directly transmitted signal events. Therefore, by setting an appropriate energy threshold, backscatter coincidence events can be screened out. The same principle applies to lutetium background event data.

[0071] The first preset energy window is an energy range used to determine whether the later-occurring single event data is transmission data. The second preset energy window is an energy range used to determine whether the earlier-occurring single event data is transmission data. The first and second preset energy windows can be set based on experience or needs.

[0072] The first preset time window refers to a preset time interval for distinguishing whether single event data is transmission data. The first preset time window can be set based on experience or demand.

[0073] In some embodiments, the processing device 120 may pre-set parameters in a first preset rule (a first preset energy window, a second preset energy window, a first preset time window, etc.), compare the single event data with the first preset rule, and determine the single event data as transmission data if the single event data meets the first preset rule. By setting different parameters in the first preset rule (the first preset energy window, the second preset energy window, the first preset time window, etc.), different transmission data (e.g., backscattered matching event data, lutetium background event data, etc.) may be screened.

[0074] For example, the processing device 120 may set the first preset energy window to 250keV-380keV, the second preset energy window to 140keV-250keV, and the first preset time window to the theoretical arrival time ±3σ, wherein the theoretical arrival time is the time when a single event arrives at the detector, which is obtained based on the ratio of the flight distance of the single event (the distance between the annihilation position of the single event and the detection position) to the speed of light, σ is the standard deviation of the system Gaussian time distribution, σ=FWHM / 2.355, FWHM represents the full width at half maximum of the Gaussian function; two single event data are selected. different single events, single event 2 occurs before single event 1, the energy of single event 1 is compared with the first preset energy window, the energy of single event 2 is compared with the second preset energy window, and the difference in arrival time between single event 1 and single event 2 is compared with the first preset time window. If the energy of single event 1 is within the first preset energy window, the energy of single event 2 is within the second preset energy window, and the difference in arrival time between single event 1 and single event 2 is within the first preset time window, then it is determined that the data corresponding to single event 1 and single event 2 belong to the backscattering coincident event data in the transmission data.

[0075] For another example, the processing device 120 can set the first preset energy window to 0keV-1000keV, the second preset energy window to 100keV-350keV, and the first preset time window to the theoretical arrival time ±3σ; two different single events are selected in the single event data, single event 4 occurs before single event 3, the energy of single event 3 is compared with the first preset energy window, the energy of single event 4 is compared with the second preset energy window, and the difference in arrival time between single event 3 and single event 4 is compared with the first preset time window. If the energy of single event 3 is within the first preset energy window, the energy of single event 4 is within the second preset energy window, and the difference in arrival time between single event 3 and single event 4 is within the first preset time window, then it is determined that the data corresponding to single event 3 and single event 4 belong to lutetium background event data in the transmission data.

[0076] In some embodiments, the processing device 120 can simultaneously collect single event data and apply them to the judgment of backscattered coincident event data and lutetium background event data in the transmission data, or it can collect single event data separately and apply them to the judgment of backscattered coincident event data and lutetium background event data in the transmission data respectively.

[0077] In some embodiments of the present specification, by acquiring single-event data of a target object and determining the single-event data that meets a first preset rule as transmission data, the single-event data can be comprehensively screened from two dimensions, namely, energy and arrival time, to eliminate noise and interference signals, thereby improving the accuracy and reliability of projection data identification.

[0078] Step 320: Acquire radiation coincidence event data of the target object.

[0079] Radioactive coincidence event data refers to data related to radioactive coincidence events. For example, the count and trajectory of radioactive coincidence events for a target object. A radioactive coincidence event, also known as an electron-positron annihilation coincidence event, occurs when an electron and a positron collide and annihilate within the target object, producing a pair of gamma photons.

[0080] In some embodiments, the processing device 120 may acquire radiation coincidence event data of the target object through the scanning device 110 .

[0081] In some embodiments, processing device 120 may acquire single-event data from a target object; determine whether the energy and arrival time of the single-event data meet a second preset rule; and, in response to the single-event data meeting the second preset rule, determine that the single-event data meeting the second preset rule is radiation coincident event data. For more information about target objects, single-event data, energy, and arrival time, please refer to the aforementioned related description.

[0082] The second preset rule can be set based on experience or needs. In some embodiments, the second preset rule may include: if the energies of two different single events in the single event data are both within a third preset energy window, and the difference in arrival time of the two different single events is within a second preset time window, then the data corresponding to the two different single events are considered radiation coincident event data.

[0083] The third preset energy window is an energy interval used to determine whether two single events are radiation coincidence events.

[0084] The second preset time window refers to a preset time interval for distinguishing whether a single event is a radiation coincidence event.

[0085] In some embodiments, the third preset energy window and the second preset time window can be determined in a variety of ways. For example, they can be determined based on experience or demand. Another example is that they can be set based on scanning device parameters. Scanning device parameters can refer to data related to the scanning device, such as the axial length and energy resolution of the scanning device. The processing device 120 can obtain the third preset energy window and the second preset time window by looking up a table. The table includes different scanning device parameters and their corresponding third preset energy windows and second preset time windows. The table can be obtained through presets, historical data, etc.

[0086] In some embodiments, the processing device 120 can pre-set the parameters in the second preset rules (third preset energy window, second preset time window, etc.), compare the single event data with the second preset rules, and if the single event data meets the second preset rules, it is determined as radiation compliance event data.

[0087] For example, the processing device 120 can set the third preset energy window to 425keV-800keV and the second preset time window to 4.4ns based on the PET scanning equipment, select two different single events in the single event data, single event 6 occurs before single event 5, compare the energy of single event 5 and the energy of single event 6 with the third preset energy window, and compare the difference in arrival time between single event 5 and single event 6 with the second preset time window. If the energy of single event 5 and the energy of single event 6 are within the third preset energy window, and the difference in arrival time between single event 5 and single event 6 is within the second preset time window, then it is determined that the data corresponding to single event 5 and single event 6 are radiation coincident event data.

[0088] In some embodiments, single-event data can be collected simultaneously, discriminated using different preset energy windows and preset time windows, to obtain transmission data and coincident event data. In some embodiments, the scanning device 110 can use an extended energy window for single-event acquisition. As will be appreciated, the extended energy window has a larger window size, enabling detection of multiple types of events (e.g., lutetium background radiation events, object scattering events, inter-crystal scattering events, etc.). The parameters of the extended energy window can be set based on experience or needs. For example, the parameters of the extended energy window can be set to 100 keV for the low-level discriminator (LLD) and 1024 keV for the upper-level discriminator (ULD).

[0089] In some embodiments of the present specification, by acquiring single event data of the target object, the single event data that meets the second preset rule is determined to be radiation coincidence event data. The single event data can be comprehensively screened from two dimensions, energy and arrival time, to eliminate noise and interference signals, thereby improving the accuracy and reliability of radiation coincidence event data identification.

[0090] Step 330 : Based on the transmission data and the radiation coincidence event data, attenuation correction and reconstruction are performed on the radiographic image of the target object to obtain an attenuation-corrected radiographic image.

[0091] Radiological images are images obtained through medical radiology technology and used for diagnosis and evaluation of diseases, such as PET images.

[0092] Attenuation correction refers to the correction of errors in medical images caused by photon attenuation.

[0093] As you can understand, during the radiographic imaging process, emitted positrons interact with surrounding tissue, generating photons. These photons experience varying degrees of attenuation as they pass through human tissue, necessitating correction for this attenuation to obtain more accurate radiographic images. Attenuation correction eliminates the attenuation effects of different tissues on photons, resulting in more accurate radiographic images.

[0094] In some embodiments, the processing device may reconstruct the radiographic image of the target object using a preset attenuation correction method based on the transmission data and the radiographic coincidence event data to obtain an attenuation-corrected radiographic image. The preset attenuation correction method may be set based on experience or demand.

[0095] In some embodiments, the processing device 120 can perform attenuation image initialization to obtain an initial attenuation image; perform radiological image initialization to obtain an initial radiological image; and iteratively reconstruct based on the initial attenuation image, the initial radiological image, the transmission data, and the radiological coincidence event data to obtain an attenuation-corrected radiological image.

[0096] The attenuation image refers to an image reflecting the attenuation characteristics of the target object. The initial attenuation image refers to the initially obtained attenuation image.

[0097] In some embodiments, the processing device 120 may assign an average value to each pixel value in a preset image (e.g., a mask image) to initialize the attenuation image and obtain an initial attenuation image. The average value may be preset based on experience or needs. For example, the processing device 120 may assign a water attenuation value to each pixel value in the preset image to initialize the attenuation image and obtain an initial attenuation image.

[0098] In some embodiments, processing device 120 may determine a boundary of a target object in a predetermined image based on the transmission data, and then assign an average value to each pixel value within the boundary. For example, processing device 120 may determine multiple data points associated with the boundary based on the transmission data, and then assign an attenuation coefficient of water to each pixel value within the boundary.

[0099] The initial radiographic image refers to the radiographic image initially obtained. For more information about the radiographic image, please refer to the aforementioned related description.

[0100] In some embodiments, the processing device 120 may assign an average value to each pixel value in a preset image to perform radiological image initialization and obtain an initial radiological image. The average value may be preset based on experience or needs. In some embodiments, the processing device 120 may determine the boundary of the target object in the preset image based on the radiological coincidence event data and then assign an average value to each pixel value within the boundary. For specific methods, please refer to the aforementioned section on attenuation image initialization.

[0101] In some embodiments, the processing device 120 may perform iterative reconstruction based on the initial attenuation image, the initial radiological image, the transmission data, and the radiological coincidence event data using a preset algorithm to obtain an attenuation-corrected radiological image. The preset algorithm may be preset based on experience or needs, and may include, for example, a Monte Carlo method.

[0102] Iteration refers to a process of multiple repetitions, in which at least a portion of the output of each round is used as a portion of the input of the next round.

[0103] For example, in iterative reconstruction of radiographic images after attenuation correction, the initial attenuation image and initial radiographic image are first obtained based on attenuation image initialization and radiographic image initialization as the iterative input for the first round of iteration; in each round of iteration, the iterative input is subjected to parameter analysis and reconstruction to obtain iterative attenuation image and iterative radiographic image, which can be used to update the iterative input for the next round of iteration. For detailed instructions on iteration, see Figure 4 Related content.

[0104] In some embodiments of the present specification, by acquiring transmission data and radiation coincidence event data, attenuation correction and reconstruction are performed on the radiation image of the target object to obtain an attenuation-corrected radiation image. Accurate attenuation-corrected radiation images can be obtained without the aid of CT images, thus avoiding the influence of errors such as artifacts of CT images on the correction results. This process does not increase the complexity of the system, the scanning time, or the radiation dose of the patient, and takes into account both the system design and the convenience of user operation, thus avoiding affecting the health of the patient.

[0105] Figure 4 is an exemplary schematic diagram of obtaining radiation coincidence event data of a target object according to some embodiments of this specification.

[0106] In some embodiments, the iteration includes: obtaining a backscattered scattering estimate 461, a backscattered blank scan estimate 463, and a radiation scattering estimate 472 based on the attenuation image 430 of the previous iteration and the radiation image 440 of the previous iteration; the attenuation image of the first iteration is the initial attenuation image 410, and the radiation image of the first iteration is the initial radiation image 420; obtaining an attenuation image 470 of the current iteration based on the backscattered scattering estimate 461, the backscattered blank scan estimate 463, and the transmission data 464; obtaining a radiation image 480 of the current iteration based on the attenuation image 470 of the current iteration, the radiation scattering estimate 472, and the radiation coincidence event data 471; determining whether the iteration termination condition 490 is met, and if not, proceeding to the next iteration; and if so, determining the radiation image 480 of the current iteration as the attenuation-corrected radiation image 4100.

[0107] Backscatter scatter estimate 461 refers to an estimate of the distribution of scatter events present in the backscatter coincident event data.

[0108] Scan data refers to the data acquired in real time by the scanning device and used to reconstruct attenuation-corrected radiological images. For example, the count of all events obtained during the scan of the target object.

[0109] The backscatter blank scan estimate 463 refers to the estimation of the distribution of backscatter events assuming that there is no target object in the backscatter process.

[0110] Radiation scatter estimate 472 refers to an estimate of the distribution of coincident events present in the scan data of the target object.

[0111] Backscattered scatter estimate 461, backscattered blank scan estimate 463, and radioactive scatter estimate 472 are represented in the form of chord diagrams.

[0112] In some embodiments, the processing device 120 may obtain a backscatter estimation 461 using a preset algorithm based on the attenuation image 430 and the radiological image 440 of the previous iteration. The preset algorithm may be preset based on experience or demand, for example, the preset algorithm may include a Monte Carlo method.

[0113] In some embodiments, the processing device 120 can process the attenuation image 430 of the previous iteration and the radiological image 440 of the previous iteration through a first processing method 451 to obtain a backscattered scattering estimate 461 and a radiological scattering estimate 472; and can process the attenuation image 430 of the previous iteration and the radiological image 440 of the previous iteration through a second processing method 452 to obtain a backscattered blank scan estimate 463; the second processing method 452 includes at least one of a Monte Carlo method and a lookup table method.

[0114] The first processing method 451 is a processing method for obtaining scatter estimation. In some embodiments, the first processing method 451 may include a Monte Carlo method, a traditional single scattering simulation (SSS) method, an energy-based scatter estimation (EBS) method, etc.

[0115] The second processing method 452 refers to a processing method for obtaining a blank scan estimate. In some embodiments, the second processing method 452 may include at least one of a Monte Carlo method and a lookup table method.

[0116] The lookup table refers to a data table that reflects the probability distribution of backscattering on a response line. In some embodiments, the lookup table includes the probability distribution of backscattering on each response line being detected on the remaining response lines. For more information about response lines, see Figure 3 and its related descriptions.

[0117] A lookup table can be represented as a matrix. For example, if there are M response lines, each corresponding to an M*1 chord diagram. The chord diagram reflects the probability distribution of backscattering from an event on one response line being detected on the remaining response lines. In this case, the lookup table is an M*M matrix consisting of M M*1 chord diagrams, where M is an integer.

[0118] In some embodiments, the processing device 120 can obtain a lookup table method; simplify the lookup table based on the symmetry of the PET system and / or the merging of response lines; and determine a backscattered blank scan estimate 463 based on the simplified lookup table and scan data.

[0119] In some embodiments, the processing device 120 may obtain the lookup table using a physical model, Monte Carlo method, or other mathematical modeling techniques. For example, the processing device 120 may simulate, using a physical model (model parameters need to be independently set based on the actual scenario), Monte Carlo method, etc., all probabilities of a transmission event incident along a certain response line being detected by other response lines, fill the data into a column of the lookup table, and then traverse all response lines to construct the lookup table.

[0120] It is understood that the PET system has symmetry, which may include the reflection symmetry of the cross section of the detector (e.g. Figure 7 (a) in the figure), the cross section is rotationally symmetrical (as shown in Figure 7 (b)), axially parallel and symmetrical (as shown in Figure 7 (c)), axial reflection symmetry (as shown in Figure 7 (as shown in (d)).

[0121] In some embodiments, the processing device 120 can, based on the symmetry of the positron emission tomography system, retain only the data of any one response line among multiple response lines with a symmetrical relationship (i.e., the probability distribution data of the backscattering of an event on the response line being detected on the remaining response lines) in the lookup table, delete the data of other response lines, and simplify the lookup table.

[0122] Response lines can be merged by merging the detection units of the corresponding detectors. For example, response lines can be merged by merging four adjacent detection units, that is, merging the response lines detected by the four adjacent detection units into a single line. The specific merging rules can be preset based on experience or needs.

[0123] In some embodiments, the processing device 120 may merge multiple response lines into one response line based on the merging of the response lines, and only retain the data of the response line in the lookup table, thereby simplifying the lookup table.

[0124] In some embodiments, the processing device 120 may calculate and determine a backscatter blank scan estimate 463 based on the simplified lookup table and the scan data. For example, the processing device 120 may calculate the sum of the event count on each response line in the scan data and the product of the probability distribution of the corresponding response line on other response lines in the simplified lookup table (i.e., the aforementioned chord diagram of the response line) to determine the backscatter blank scan estimate.

[0125] In some embodiments of the present specification, by constructing and simplifying a lookup table to determine the backscatter blank scan estimate 463, the probability distribution of backscattering of an event on a response line being detected on the remaining response lines can be obtained through simulation, thereby obtaining an accurate backscatter blank scan estimate.

[0126] In some embodiments of the present specification, the attenuation image 430 of the previous iteration and the radiological image 440 of the previous iteration are processed by the first processing method 451 and the second processing method 452 to obtain a backscattered scattering estimate 461, a radiological scattering estimate 472, and a backscattered blank scan estimate 463. This can make the determination process of the scattering estimate and the blank scan estimate efficient, accurate, and convenient, and facilitate the subsequent updating and reconstruction of the corresponding images.

[0127] In some embodiments, the processing device 120 may obtain an attenuation image 470 for the current iteration based on the backscattered scatter estimate 461 , the backscattered blank scan estimate 463 , and the transmission data 464 .

[0128] In some embodiments, as Figure 8As shown in (a), when the attenuation image is iterated based only on the backscattered coincident event data in the transmission data, the attenuation image can be iteratively calculated based on formula (1):

[0129] in, represents the attenuation image of this iteration, represents the attenuation image of the previous iteration, represents the backscatter blank scan estimate, H represents the system matrix, and y bs represents backscattered events in the transmission data, represents the scattering estimate of backscatter, r bs Represents the backscattered chance event estimate, which estimates the distribution of chance events in the backscattered coincident event data. This can be obtained using methods such as the Delay Window Method and the Singles Rate. k represents the current iteration number.

[0130] In some embodiments, as Figure 8 As shown in (b), when the attenuation image iteration is performed based only on the lutetium background event data in the transmission data, the attenuation image can be iteratively calculated based on formula (2):

[0131] in, represents the attenuation image of this iteration, represents the attenuation image of the previous iteration, B Lu represents the blank scan of the lutetium background event, H represents the system matrix, and y Lu represents the lutetium background event in the transmission data, represents the scattering estimate of the lutetium background event. The scattering estimate of the lutetium background event refers to the distribution estimate of the scattering events existing in the lutetium background event data. r Lu represents the random event estimate of the lutetium background event. The random event estimate of the lutetium background event refers to the distribution estimate of the random events present in the lutetium background event data, which can be obtained through the delay window method (Delay Window Method), single rate (Singles Rate), etc. k represents the current iteration number. A blank scan of the lutetium background event can be obtained by performing an empty scan by the scanning device 110. An empty scan refers to scanning the air directly without a target object such as a human body or a phantom. In this case, the target object can be regarded as air.

[0132] In some embodiments, as Figure 8As shown in (c), when the attenuation image is iterated based on the backscatter coincident event data and the lutetium background event data in the transmission data, the attenuation image can be iteratively calculated based on formula (3):

[0133] in, represents the attenuation image of this iteration, represents the attenuation image of the previous iteration, y all =y bs +y Lu , r all =r bs +r Lu .

[0134] In some embodiments, the processing device 120 may obtain a radiological image 480 of this iteration based on the attenuation image 470 of this iteration, the radiation scatter estimate 472, and the radiation coincidence event data 471. In some embodiments, the radiological image may be iteratively calculated based on formula (4):

[0135] Among them, λ k+1 represents the radiographic image of this iteration, λ k Shows the radiological image of the last iteration, y emission represents the radiation coincidence event data, ss represents the scattering estimate of the radiation event, which refers to the distribution estimate of the scattering events existing in the radiation coincidence event data, and rr represents the random event estimate of the radiation event, which refers to the distribution estimate of the random events existing in the radiation coincidence event data, and can be obtained through the Delay Window Method (DTM), Singles Rate (SR), etc. for or or

[0136] The iterations are stopped and the attenuation correction ends when the iterations meet preset conditions. These conditions can include convergence, reaching a pre-specified number of iterations, the difference between the radiographic images between two consecutive iterations being less than a certain threshold, or the difference between the attenuation effect chordograms between two consecutive iterations being less than a certain threshold. The attenuation effect chordogram refers to the forward projection of the attenuation image.

[0137] The attenuation-corrected radiographic image 4100 refers to a radiographic image that has undergone attenuation correction and is the radiographic image output from the final round of iterations.

[0138] In some embodiments of the present specification, a scattering estimate of backscattering, a blank scan estimate of backscattering, and a scattering estimate of radiation are obtained based on the attenuation image of the previous iteration and the radiation image of the previous iteration; and then the attenuation image and the radiation image of the current iteration are obtained; the iteration is terminated after the iteration termination condition is met, and the attenuation image and the radiation image can be updated and reconstructed based on real-time data, making the attenuation correction process more accurate and efficient.

[0139] Figure 9A FIG. 1 is an exemplary flow chart of determining a radiographic image after attenuation correction according to some embodiments of the present specification. Figure 9A As shown, the process 900A includes the following steps: In some embodiments, the process 900A may be executed by the processing device 120 .

[0140] Step 910A: Acquire backscatter coincidence event data. In some embodiments, processing device 120 may acquire backscatter coincidence event data through various methods, such as scanning device 110. For more information on how to acquire backscatter coincidence event data, please refer to the description of step 310.

[0141] Step 920A: Initialize the attenuation image to obtain the initial attenuation image. For more information on how to initialize the attenuation image, please refer to Figure 4 Related description.

[0142] Step 930A: Acquire radiation coincidence event data. In some embodiments, the processing device 120 may acquire radiation coincidence event data through various methods, such as the scanning device 110. For more information on how to acquire radiation coincidence event data, please refer to the description of step 320.

[0143] Step 940A: Initialize the radiographic image to obtain an initial radiographic image. For more information on how to initialize the radiographic image, see Figure 4 Related description.

[0144] Step 950A, obtaining a backscattered scattering estimate and a backscattered blank scan estimate. In some embodiments, the processing device 120 may process the attenuation image and the radiological image of the previous iteration using a first processing method to obtain a backscattered scattering estimate; and may process the attenuation image and the radiological image of the previous iteration using a second processing method to obtain a backscattered blank scan estimate. For details, see Figure 4 Related description.

[0145] Step 960A, update the attenuation image. In some embodiments, the processing device 120 can obtain the attenuation image of this iteration based on the backscattered scattering estimate, the backscattered blank scan estimate, and the transmission data. For details, see Figure 4 Related description.

[0146] Step 970A, obtaining a radiation scatter estimation. In some embodiments, the processing device 120 may process the radiation scatter estimation based on the attenuation image of the previous iteration and the radiation image of the previous iteration using a first processing method. For details, see Figure 4 Related description.

[0147] Step 980A: Update the radiological image. In some embodiments, the processing device 120 may obtain the radiological image of this iteration based on the attenuation image, radiation scatter estimation, and radiation coincidence event data of this iteration. For details, see Figure 4 Related description.

[0148] Step 990A: Determine whether the iteration termination condition is met. For more information on the iteration termination condition and its determination, please refer to Figure 4 Related description.

[0149] If yes, step 9100A determines the attenuation-corrected radiographic image; if no, repeat steps 950A to 990A. For more information on attenuation-corrected radiographic images and their determination, see Figure 4 Related description.

[0150] Figure 9B FIG. 1 is an exemplary flow chart of determining a radiological image after attenuation correction according to other embodiments of the present specification. Figure 9B As shown, the process 900B includes the following steps: In some embodiments, the process 900B may be executed by the processing device 120 .

[0151] Step 910B: Obtain lutetium background event data. In some embodiments, the processing device 120 may obtain lutetium background event data through various methods, such as the scanning device 110. For more information on how to obtain lutetium background event data, please refer to the description of step 310.

[0152] Step 920B: Initialize the attenuation image to obtain the initial attenuation image. For more information on how to initialize the attenuation image, please refer to Figure 4 Related description.

[0153] Step 930B: Acquire radiation coincidence event data. In some embodiments, the processing device 120 may acquire radiation coincidence event data through various methods, such as the scanning device 110. For more information on how to acquire radiation coincidence event data, please refer to the description of step 320.

[0154] Step 940B: Initialize the radiographic image to obtain an initial radiographic image. For more information on how to initialize the radiographic image, see Figure 4 Related description.

[0155] Step 950B, obtaining a scattering estimate of the lutetium background event. In some embodiments, the processing device 120 can process the attenuation image and the radiological image of the previous iteration using a first processing method to obtain a scattering estimate of the lutetium background event. The specific method can be referred to Figure 4 Get the backscattered scattering estimate as described in .

[0156] Step 960B, obtain a blank scan of the lutetium background event. In some embodiments, the processing device 120 can obtain a blank scan of the lutetium background event by various means such as the scanning device 110. For details, see Figure 4 Related description.

[0157] Step 970B, update the attenuation image. In some embodiments, the processing device 120 can obtain the attenuation image of this iteration based on the scattering estimate of the lutetium background event, the blank scan of the lutetium background event, and the transmission data. For details, see Figure 4 Related description.

[0158] Step 980B, obtain radiation scatter estimation. In some embodiments, the processing device 120 can process the attenuation image of the previous iteration and the radiation image of the previous iteration using the first processing method to obtain the radiation scatter estimation. For details, see Figure 4 Related description.

[0159] Step 990B: Update the radiological image. In some embodiments, the processing device 120 may obtain the radiological image of this iteration based on the attenuation image of this iteration, the radiation scatter estimation, and the radiation coincidence event data. For details, see Figure 4 Related description.

[0160] Step 9100B: Determine whether the iteration termination condition is met. For more information on the iteration termination condition and its determination, please refer to Figure 4 Related description.

[0161] If yes, step 9110B determines the attenuation-corrected radiographic image; if no, repeat steps 950B to 9100B. For more information on attenuation-corrected radiographic images and their determination, see Figure 4 Related description.

[0162] Figure 9C FIG. 1 is an exemplary flow chart of determining a radiological image after attenuation correction according to some other embodiments of the present specification. Figure 9C As shown, the process 900C includes the following steps: In some embodiments, the process 900C may be executed by the processing device 120 .

[0163] Step 910C: Obtain backscatter coincidence event data and lutetium background event data. For more information on how to obtain backscatter coincidence event data and lutetium background event data, please refer to Figure 9A 、 Figure 9B Related description.

[0164] Step 920C: Initialize the attenuation image to obtain the initial attenuation image. For more information on how to initialize the attenuation image, please refer to Figure 4 Related description.

[0165] Step 930C: Acquire radiation coincidence event data. In some embodiments, the processing device 120 may acquire radiation coincidence event data through various methods, such as the scanning device 110. For more information on how to acquire radiation coincidence event data, please refer to the description of step 320.

[0166] Step 940C: Initialize the radiographic image to obtain an initial radiographic image. For more information on how to initialize the radiographic image, see Figure 4 Related description.

[0167] Step 950C: Obtain backscattered scattering estimates, lutetium background event scattering estimates, and backscattered blank scan estimates. Figure 9A 、 Figure 9B Related description.

[0168] Step 960C: Obtain a blank scan of the lutetium background event. In some embodiments, the processing device 120 can obtain a blank scan of the lutetium background event by various means such as the scanning device 110. For details, see Figure 4 Related description.

[0169] Step 970C: Update the attenuation image. In some embodiments, the processing device 120 may obtain the attenuation image of this iteration based on the backscattered scattering estimate, the scattering estimate of the lutetium background event, the backscattered blank scan estimate, the blank scan of the lutetium background event, and the transmission data. For details, see Figure 4 Related description.

[0170] Step 980C: Obtain radiation scatter estimation. In some embodiments, the processing device 120 may process the attenuation image and the radiation image of the previous iteration using a first processing method to obtain radiation scatter estimation. For details, see Figure 4 Related description.

[0171] Step 990C: Update the radiological image. In some embodiments, the processing device 120 may obtain the radiological image of this iteration based on the attenuation image of this iteration, the radiation scatter estimation, and the radiation coincidence event data. For details, see Figure 4 Related description.

[0172] Step 9100C: Determine whether the iteration termination condition is met. For more information on the iteration termination condition and its determination, please refer to Figure 4 Related description.

[0173] If yes, step 9110C determines the attenuation-corrected radiographic image; if no, repeat steps 950C to 9100C. For more information on attenuation-corrected radiographic images and their determination, see Figure 4 Related description.

[0174] One or more embodiments of this specification further provide a computer-readable storage medium that stores computer instructions. When a computer reads the computer instructions in the storage medium, the computer executes the attenuation correction method as described in any one of the above embodiments.

[0175] While the basic concepts have been described above, it will be apparent to those skilled in the art that the detailed disclosure is merely illustrative and does not limit this specification. Although not explicitly stated herein, various modifications, improvements, and revisions to this specification may be made by those skilled in the art. Such modifications, improvements, and revisions are suggested in this specification and remain within the spirit and scope of the exemplary embodiments of this specification.

[0176] This specification also uses specific terms to describe the embodiments of this specification. For example, "one embodiment," "an embodiment," and / or "some embodiments" refer to a feature, structure, or characteristic associated with at least one embodiment of this specification. Therefore, it should be emphasized and noted that references to "one embodiment," "an embodiment," or "an alternative embodiment" two or more times in different locations in this specification do not necessarily refer to the same embodiment. Furthermore, certain features, structures, or characteristics of one or more embodiments of this specification may be appropriately combined.

[0177] In addition, unless expressly stated in the claims, the order of the processing elements and sequences, the use of alphanumeric characters, or the use of other names described in this specification are not intended to limit the order of the processes and methods of this specification. Although the above disclosure discusses some of the invention embodiments currently considered useful through various examples, 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 are consistent with the spirit and scope of the embodiments of this specification. For example, although the system components described above can be implemented by hardware devices, they can also be implemented only by software solutions, such as installing the described system on an existing server or mobile device.

[0178] Similarly, it should be noted that, in order to simplify the presentation of this specification and thus facilitate understanding of one or more embodiments of the invention, the foregoing descriptions of the embodiments of this specification sometimes combine multiple features into a single embodiment, figure, or description thereof. However, this disclosure method does not imply that the subject matter of this specification requires more features than those recited in the claims. In fact, an embodiment may have fewer features than all of the features of a single disclosed embodiment.

[0179] In some embodiments, numbers are used to describe the quantity of components and attributes. It should be understood that such numbers used in the description of the embodiments are modified by the modifiers "about", "approximately" or "substantially" in some examples. Unless otherwise stated, "about", "approximately" or "substantially" indicate that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the description and claims are approximate values, which may change according to the required characteristics of individual embodiments. In some embodiments, the numerical parameters should take into account the specified significant digits and adopt the general method of retaining digits. Although the numerical domains and parameters used to confirm the breadth of their range in some embodiments of this specification are approximate values, in specific embodiments, the settings of such numerical values ​​are as accurate as possible within the feasible range.

[0180] Each patent, patent application, patent application publication, and other materials, such as articles, books, specifications, publications, and documents, cited in this specification is hereby incorporated by reference in its entirety. This includes application history documents that are inconsistent with or conflict with the content of this specification, as well as documents (currently or subsequently attached to this specification) that limit the broadest scope of the claims of this specification. It should be noted that if the descriptions, definitions, and / or terminology used in the accompanying materials are inconsistent or conflicting with the content of this specification, the descriptions, definitions, and / or terminology used in this specification will control.

[0181] Finally, it should be understood that the embodiments described in this specification are intended only to illustrate the principles of the embodiments of this specification. Other variations may also fall within the scope of this specification. Therefore, by way of example and not limitation, alternative configurations of the embodiments of this specification may be considered consistent with the teachings of this specification. Accordingly, the embodiments of this specification are not limited to the embodiments explicitly described and illustrated in this specification.

Claims

1. A method for attenuation correction, characterized in that: The method comprises: Obtain transmission data; Acquiring radiation coincidence event data of a target object; Based on the transmission data and the radiation coincidence event data, attenuation correction and reconstruction are performed on the radiation image of the target object to obtain an attenuation-corrected radiation image; wherein the transmission data includes backscatter coincidence event data of the target object.

2. The method according to claim 1, characterized in that The obtaining of transmission data comprises: Acquire single event data of the target object; Determining whether the energy and arrival time of the single event data meet a first preset rule; In response to the single event data meeting the first preset rule, the single event data meeting the first preset rule is determined to be the transmission data.

3. The method according to claim 1, characterized in that The obtaining of radiation coincidence event data of the target object includes: Acquire single event data of the target object; Determining whether the energy and arrival time of the single event data meet a second preset rule; In response to the single event data meeting the second preset rule, the single event data meeting the second preset rule is determined to be the radiation coincidence event data.

4. The method according to claim 1, wherein The attenuation-corrected reconstruction of the radiographic image of the target object based on the transmission data and the radiographic coincidence event data to obtain the attenuation-corrected radiographic image comprises: Initialize the attenuation image and obtain the initial attenuation image; Perform radiographic image initialization to obtain an initial radiographic image; Based on the initial attenuation image, the initial radiological image, the transmission data, and the radiological coincidence event data, iterative reconstruction is performed to obtain the radiological image after attenuation correction.

5. The method according to claim 4, characterized in that The iterations include: Based on the attenuation image of the previous iteration and the radiological image of the previous iteration, a backscattering estimation, a blank scan estimation of the backscattering, and a radiological scattering estimation are obtained; the attenuation image of the first iteration is the initial attenuation image, and the radiological image of the first iteration is the initial radiological image; obtaining an attenuation image for this iteration based on the backscattered scatter estimate, the backscattered blank scan estimate, and the transmission data; Obtaining a radiological image of this iteration based on the attenuation image of this iteration, the radiation scatter estimate, and the radiation coincidence event data; Determine whether an iteration termination condition is met, and if not, proceed to the next round of iteration; if so, determine the radiographic image of the current round of iteration as the radiographic image after attenuation correction.

6. The method according to claim 5, characterized in that The step of obtaining a backscattered scattering estimate, a backscattered blank scan estimate, and a radiation scattering estimate based on the attenuation image of the previous iteration and the radiation image of the previous iteration includes: Based on the attenuation image of the previous iteration and the radiological image of the previous iteration, performing processing by a first processing method to obtain the backscattering scattering estimate and the radiological scattering estimate; Based on the attenuation image of the previous iteration and the radiological image of the previous iteration, a second processing method is used to obtain the backscatter blank scan estimation; the second processing method includes at least one of a Monte Carlo method and a lookup table method.

7. The method according to claim 6, characterized in that The backscatter coincidence event data is acquired by a positron emission tomography system, and the lookup table includes a probability distribution of backscattering events occurring on each response line of the positron emission tomography system being detected on other response lines. The lookup table method includes: Obtaining a lookup table; simplifying the lookup table based on the symmetry of the PET system and / or the merging of the response lines; Based on the simplified lookup table and scan data, a blank scan estimate of the backscatter is determined.

8. The method according to claim 1, characterized in that The transmission data further includes lutetium background event data.

9. An attenuation correction system, characterized in that: The system is used to implement an attenuation correction method, and the system includes: A first acquisition module, configured to acquire transmission data; a second acquisition module, configured to acquire radiation coincidence event data of a target object; A reconstruction module is used to perform attenuation correction reconstruction on the radiographic image of the target object based on the transmission data and the radiographic coincidence event data to obtain an attenuation-corrected radiographic image; wherein the transmission data includes backscattered coincidence event data of the target object. 10 . A computer-readable storage medium storing computer instructions, wherein when a computer reads the computer instructions in the storage medium, the computer executes the attenuation correction method according to claim 1 .

Images