CN117297634B - CT system air calibration compensation method - Google Patents
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Abstract
The application discloses an air calibration compensation method of a CT system, which comprises the following steps: s10, installing an air calibration reference; s20, acquiring air data and a cold state reference coefficient of a CT system in a cold state; s30, acquiring air data and a thermal state reference coefficient of a CT system in a thermal state; s40, acquiring air data and a normal state reference coefficient of a CT system in a normal state; s50, acquiring data of a patient scanned by a CT system and a reference coefficient when the patient is scanned; s60, compensating the data of the patient scanned by the CT system to obtain final data; according to the CT air calibration method, the air calibration reference object is installed, the air data of the CT system in the cold state, the hot state and the normal state and the corresponding cold state, hot state and normal state reference coefficients are obtained, and the data of the patient scanned by the CT system and the reference coefficients of the patient scanned by the CT system are combined to compensate the data of the patient scanned by the CT system, so that the accuracy and the stability of CT air calibration are improved, the CT image quality is improved, and the CT air calibration method has important practical significance in clinical use.
Description
Technical Field
The invention relates to the technical field related to medical instruments, in particular to an air calibration compensation method of a CT system.
Background
An X-ray computer tomography apparatus, CT (Computed Tomography), uses the characteristic that different substances have different absorption capacities for X-rays to acquire the absorption coefficient data of different scanned object internal tissues for X-rays, uses a computer to process and reconstruct images; the basic process is as follows: x-rays are emitted by an X-ray device, the residual X-rays after the X-rays pass through the scanned object are detected by a CT detector and are subjected to data processing, projection information of the X-ray absorption coefficient inside the scanned object is obtained, and the projection information is subjected to a computer reconstruction algorithm to calculate the distribution information of the X-ray absorption coefficient inside the scanned object, so that a tomographic image is formed.
The CT system needs to acquire the X-ray intensities before and after X-rays pass through the scanned object, namely the incident X-ray photon intensity and the emergent X-ray photon intensity of the X-rays on the scanned object, and then the projection information of the scanned object can be calculated; therefore, CT air calibration is an important quality control means for ensuring that the system and components work in a good state and ensuring stable image quality.
The CT system comprises an X-ray generating device, an X-ray data acquisition detector device and the like, the accuracy and the stability of air calibration are affected by image chain components of the CT system, the conversion efficiency of X-ray photons by a CT detector crystal, the focus drift of the X-ray generating device from a cold state to a hot state and the like are included, therefore, the conventional air calibration cannot be matched with the accurate state of the CT system in each scanning, the quality of CT images is gradually deteriorated along with the prolongation of the interval time from the air calibration, and the air calibration is required to be carried out again.
Based on the problems, a CT system air calibration compensation method is provided.
Disclosure of Invention
The invention aims to provide an air calibration compensation method for a CT system, which can improve the accuracy and stability of CT air calibration and has important practical significance for improving the quality of CT images and clinical application.
In order to solve the technical problems, the invention adopts the following technical scheme:
a CT system air calibration compensation method comprises the following steps:
s10, installing an air calibration reference;
s20, acquiring air data and a cold state reference coefficient of a CT system in a cold state;
s30, acquiring air data and a thermal state reference coefficient of a CT system in a thermal state;
s40, acquiring air data and a normal state reference coefficient of a CT system in a normal state;
s50, acquiring data of a patient scanned by a CT system and a reference coefficient when the patient is scanned;
s60, according to the acquired air data and the reference coefficients of the cold state, the hot state and the normal state of the CT system, and the data of the patient scanned by the CT system and the reference coefficients of the patient scanned by the CT system, compensating the data of the patient scanned by the CT system, and obtaining final data.
Preferably, in step S10, the specific steps of installing the air calibration reference are:
s101, setting a high-density object as a reference object on a propagation path from X-rays emitted by an X-ray tube assembly to X-rays received by a CT detector system, wherein the X-rays pass through the high-density object to form a projection on the CT detector system;
s102, receiving projections of the reference object in a selected area on the CT detector system, and determining that the channel range of the area on the CT detector system is ic1 to ic2 and the row range is ir1 to ir2 through the numerical change generated by the reference object in the process of changing the CT system from a cold state to a hot state.
In a preferred embodiment, in step S20, the specific steps of acquiring the air data and the cold reference coefficient of the CT system in the cold state are as follows:
s201, collecting dark current data offsetdata_low of the CT detector system when the X-ray tube assembly is not exposed;
s202, during the cold state of the CT system, operating the X-ray tube assembly for exposure;
s203, acquiring air original data airdata_low of the CT system in a cold state by using the CT detector system, and converting the air original data airdata_low into projection data airable_low, wherein the formula is as follows:
；
wherein Ref_Low is the reference detector value of the CT system in the cold state;
s204, calculating a detector air calibration reference coefficient R_low in a cold state of the CT system, wherein the calculation method comprises the following steps:
；
wherein temp_low (ic, ir, iv) is an intermediate variable value used in the process of calculating R_low, ic is a channel number of a CT detector system, ir is a number of a CT system detector row, iv is a view angle number of one circle of CT rotation;
the data for all views in the range of rows ir1 to ir2 are averaged for channels ic1 to ic2 of temp_low to obtain the reference coefficient r_low:
；
wherein, ": "refers to all viewing angles in the range of lanes ic1 through ic2, rows ir1 through ir2.
In a preferred embodiment, in step S30, the specific steps of acquiring the air data and the thermal state reference coefficient during the thermal state of the CT system are as follows:
s301, collecting dark current data offsetdata_high of a CT detector system when an X-ray tube assembly is not exposed;
s302, during the thermal state of the CT system, operating the X-ray tube assembly for exposure;
s303, acquiring air raw data airdata_high in a thermal state of the CT system by using the CT detector system, and converting the air raw data into projection data airable_high, wherein the formula is as follows:
；
wherein Ref_high is the reference detector value of the CT system in a thermal state;
s304, calculating a detector air calibration reference coefficient R_high in a thermal state of the CT system, wherein the calculation method is as follows:
；
wherein temp_high (ic, ir, iv) is a median variable value used in the process of calculating R_high, ic is a channel number of the CT detector system, ir is a number of a detector row of the CT system, iv is a view angle number of one circle of CT rotation;
the data for all views in the range of rows ir1 to ir2 are averaged for channels ic1 to ic2 of temp_high to obtain the reference coefficient r_high:
；
wherein, ": "refers to all viewing angles in the range of lanes ic1 through ic2, rows ir1 through ir2.
Preferably, in step S40, the specific steps of acquiring the air data and the normal reference coefficient in the normal state of the CT system are as follows:
s401, collecting detector system dark current data offsetdata_normal when the X-ray tube assembly is not exposed;
s402, operating the X-ray tube assembly for exposure in the normal state of the CT system; s403, acquiring air original data airdata_normal in a normal state of the CT system by using the CT detector system, and converting the air original data airdata_normal into projection data airable_normal, wherein the formula is as follows:
；
wherein Ref_normal is the CT system reference detector value at normal times;
s404, calculating a detector air calibration reference coefficient R_normal in a normal state of the CT system, wherein the calculation method is as follows:
；
wherein temp_normal (ic, ir, iv) is an intermediate variable value used in the process of calculating R_normal, ic is a CT detector system channel number, ir is a CT system detector row number, iv is a view angle number of one revolution of CT;
the data for all views in the range of temp_normal channels ic1 through ic2, rows ir1 through ir2 are averaged to obtain the reference coefficient r_normal:
；
wherein, ": "refers to all viewing angles in the range of lanes ic1 through ic2, rows ir1 through ir2.
Preferably, in step S50, the specific steps of acquiring the data of the patient scanned by the CT system and the reference coefficients when scanning the patient are as follows:
s501, collecting detector system dark current data offsetdata_event when the X-ray tube assembly is not exposed;
s502, during the cold state of the CT system, operating the X-ray tube assembly for exposure;
s503, acquiring original data of a patient scanned by a CT system by using the CT detector system, and calculating a real-time reference coefficient of the patient scanned by the CT system detector, wherein the calculation method comprises the following steps:
；
wherein temp_event (ic, ir, iv) is an intermediate variable value used in the process of calculating R_event, ic is a channel number of a CT detector system, ir is a number of a CT detector row, iv is a view angle number of one circle of CT rotation; ref_parameter is a reference detector value of the CT system when scanning a patient;
the data for all views in the range of rows ir1 to ir2 are averaged for channels ic1 to ic2 of temp_event to obtain the reference coefficient r_event:
；
wherein, ": "refers to all viewing angles in the range of lanes ic1 through ic2, rows ir1 through ir2.
Preferably, in step S60, the data of the patient scanned by the CT system is compensated, and the specific steps for obtaining the final data are as follows:
s601, converting original data patentdata of a patient scanned by a CT system into projection data, and performing air compensation on the projection data to obtain compensated data patentprj_corr, wherein the formula is as follows:
；
here, temp_part is a three-dimensional matrix, and means all elements of the matrix, and temp_part (ic, ir, iv) means one element with coordinates (ic, ir, iv).
Preferably, the reference object is in the shape of a cuboid or sphere, and the material of the reference object includes but is not limited to one of copper, tungsten or lead.
Due to the application of the technical scheme, the application has the beneficial effects compared with the prior art that:
according to the air calibration compensation method for the CT system, the air calibration reference is installed, the air data of the CT system in a cold state, a hot state and a normal state and the corresponding cold state, hot state and normal state reference coefficients are obtained, the data of a patient scanned by the CT system and the reference coefficients of the patient scanned by the CT system are combined, the data of the patient scanned by the CT system are compensated through a series of data, the accuracy and the stability of the air calibration of the CT are improved, the quality of CT images is improved, and the air calibration compensation method has important practical significance in clinical use.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
Fig. 1 is a flow chart of the air calibration compensation method of the CT system according to the present invention.
Detailed Description
In order to make the present application solution better understood by those skilled in the art, the following description will be made in detail and with reference to the accompanying drawings in the embodiments of the present application, it is apparent that the described embodiments are only some embodiments of the present application, not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art based on the embodiments herein without making any inventive effort, shall fall within the scope of the present application.
It should be noted that the terms "first," "second," and the like in the description and claims of the present application and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate in order to describe the embodiments of the present application described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
In the present application, the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate an azimuth or a positional relationship based on that shown in the drawings. These terms are only used to better describe the present invention and its embodiments and are not intended to limit the scope of the indicated devices, elements or components to the particular orientations or to configure and operate in the particular orientations.
Also, some of the terms described above may be used to indicate other meanings in addition to orientation or positional relationships, for example, the term "upper" may also be used to indicate some sort of attachment or connection in some cases. The specific meaning of these terms in the present invention will be understood by those of ordinary skill in the art according to the specific circumstances.
Furthermore, the terms "mounted," "configured," "provided," "connected," "coupled," and "sleeved" are to be construed broadly. For example, it may be a fixed connection, a removable connection, or a unitary construction; may be a mechanical connection, or an electrical connection; may be directly connected, or indirectly connected through intervening media, or may be in internal communication between two devices, elements, or components. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.
It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other. The present application will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
Example 1
Referring to fig. 1, the present application provides an air calibration compensation method for a CT system, which includes the following steps:
s10, installing an air calibration reference;
the method comprises the following specific steps:
s101, setting a high-density object as a reference object on a propagation path from X-rays emitted by an X-ray tube assembly to X-rays received by a CT detector system, wherein the X-rays pass through the high-density object to form a projection on the CT detector system; in order to make the projection easily identifiable, a material with larger attenuation to X-rays, such as copper, tungsten or lead, is selected, and the reference object can be in a cuboid shape or a sphere shape;
s102, receiving projections of the reference object in a selected area on the CT detector system, and determining that the channel range of the area on the CT detector system is ic1 to ic2 and the row range is ir1 to ir2 through obvious numerical value changes generated by the reference object in the process of changing the CT system from a cold state to a hot state;
s20, acquiring air data and a cold state reference coefficient of a CT system in a cold state;
the method comprises the following specific steps:
s201, in order to correct the electronic noise of the CT detector system, collecting dark current data offsetdata_low of the CT detector system when the X-ray tube assembly is not exposed;
s202, during the cold state of the CT system, operating the X-ray tube assembly for exposure;
s203, acquiring air original data airdata_low of the CT system in a cold state by using the CT detector system, and converting the air original data airdata_low into projection data airable_low, wherein the formula is as follows:
；
wherein Ref_Low is the reference detector value of the CT system in the cold state;
s204, calculating a detector air calibration reference coefficient R_low in a cold state of the CT system, wherein the calculation method comprises the following steps:
；
wherein temp_low (ic, ir, iv) is an intermediate variable value used in the process of calculating R_low, ic is a channel number of a CT detector system, ir is a number of a CT system detector row, iv is a view angle number of one circle of CT rotation;
the data for all views in the range of rows ir1 to ir2 are averaged for channels ic1 to ic2 of temp_low to obtain the reference coefficient r_low:
；
wherein, ": "refers to all viewing angles in the range of lanes ic1 through ic2, rows ir1 through ir2.
S30, acquiring air data and a thermal state reference coefficient of a CT system in a thermal state;
the method comprises the following specific steps:
s301, in order to correct the electronic noise of the CT detector system, acquiring dark current data offsetdata_high of the CT detector system when the X-ray tube assembly is not exposed; s302, during the thermal state of the CT system, operating the X-ray tube assembly for exposure;
s303, acquiring air raw data airdata_high in a thermal state of the CT system by using the CT detector system, and converting the air raw data into projection data airable_high, wherein the formula is as follows:
；
wherein Ref_high is the reference detector value of the CT system in a thermal state;
s304, calculating a detector air calibration reference coefficient R_high in a thermal state of the CT system, wherein the calculation method is as follows:
；
wherein temp_high (ic, ir, iv) is a median variable value used in the process of calculating R_high, ic is a channel number of the CT detector system, ir is a number of a detector row of the CT system, iv is a view angle number of one circle of CT rotation;
the data for all views in the range of rows ir1 to ir2 are averaged for channels ic1 to ic2 of temp_high to obtain the reference coefficient r_high:
；
wherein, ": "refers to all viewing angles in the range of lanes ic1 through ic2, rows ir1 through ir2.
S40, acquiring air data and a normal state reference coefficient of a CT system in a normal state;
the method comprises the following specific steps:
s401, in order to correct the electronic noise of the CT detector system, collecting detector system dark current data offsetdata_normal when the X-ray tube assembly is not exposed;
s402, operating the X-ray tube assembly for exposure in the normal state of the CT system;
s403, acquiring air original data airdata_normal in a normal state of the CT system by using the CT detector system, and converting the air original data airdata_normal into projection data airable_normal, wherein the formula is as follows:
；
wherein Ref_normal is the CT system reference detector value at normal times;
s404, calculating a detector air calibration reference coefficient R_normal in a normal state of the CT system, wherein the calculation method is as follows:
；
wherein temp_normal (ic, ir, iv) is an intermediate variable value used in the process of calculating R_normal, ic is a CT detector system channel number, ir is a CT system detector row number, iv is a view angle number of one revolution of CT;
the data for all views in the range of temp_normal channels ic1 through ic2, rows ir1 through ir2 are averaged to obtain the reference coefficient r_normal:
；
wherein, ": "refers to all viewing angles in the range of lanes ic1 through ic2, rows ir1 through ir2.
S50, acquiring data of a patient scanned by a CT system and a reference coefficient when the patient is scanned;
the method comprises the following specific steps:
s501, in order to correct the electronic noise of the CT detector system, collecting dark current data offsetdata_event of the detector system when the X-ray tube assembly is not exposed;
s502, during the cold state of the CT system, operating the X-ray tube assembly for exposure;
s503, acquiring original data of a patient scanned by a CT system by using the CT detector system, and calculating a real-time reference coefficient of the patient scanned by the CT system detector, wherein the calculation method comprises the following steps:
；
wherein temp_event (ic, ir, iv) is an intermediate variable value used in the process of calculating R_event, ic is a channel number of a CT detector system, ir is a number of a CT detector row, iv is a view angle number of one circle of CT rotation; ref_parameter is a reference detector value of the CT system when scanning a patient;
the data for all views in the range of rows ir1 to ir2 are averaged for channels ic1 to ic2 of temp_event to obtain the reference coefficient r_event:
；
wherein, ": "refers to all viewing angles in the range of the channel ic1 to the channel ic2, and the rows ir1 to ir2.
S60, according to the acquired air data of the CT system in the cold state, the hot state and the normal state and the reference coefficients of the cold state, the hot state and the normal state, and by combining the data of the patient scanned by the CT system and the reference coefficients of the patient scanned by the CT system, compensating the data of the patient scanned by the CT system to obtain final data;
the method comprises the following specific steps:
s601, converting original data patentdata of a patient scanned by a CT system into projection data, and performing air compensation on the projection data to obtain final compensated data patentprj_corr, wherein the formula is as follows:
；
here, temp_part is a three-dimensional matrix, and means all elements of the matrix, and temp_part (ic, ir, iv) means one element with coordinates (ic, ir, iv).
The derivation process of the partiprj_corr formula is as follows:
when the existing CT system scans, projection data of the X-ray tube in a cold state, a hot state and a normal state are not considered, and are always directly used, so that a gap in the projection data is not calculated, errors are easily caused, and the result is inaccurate.
The existing CT system does not consider projection data of an X-ray tube in a cold state, a hot state and a normal state, and when scanning is carried out, the formula is as follows:
,
wherein, I_patient is the final scan data obtained when the CT system scans the patient,
wherein, the partial data is the original data of the CT system when scanning the patient, the offset is the dark current data obtained by the detector system when the X-ray tube component is not exposed, and Ref_partial is the reference detector value of the CT system when scanning the patient;
i _ air is the scan data in air at the time of CT system scan,
wherein, airdata is air original data scanned by the CT system when cold state, hot state and normal state of the X-ray tube are not considered, offset is dark current data obtained by the detector system when the X-ray tube component is not exposed, and Ref_air is reference detector value when the cold state, the hot state and the normal state of the X-ray tube are not considered by the CT system;
mu l is the final output projection data;
the derivation is performed according to the above formula to obtain the following formula:
；
；
；
；
obtaining final output projection data mul through the deduction;
the method calibrates log (I_air) by
Log (i_air) is replaced, and compensated final data patentprj_corr is obtained;
；
the final data partial prj_corr is μ l, i.e., the final output projection data, where log (temp_partial) is the same as log (i_partial).
In the above steps, the original data of air refers to that the X-rays reach the detector module after passing through the air, the X-rays are converted into visible light, then are converted into analog electrical signals through the photodiode, and then are converted into digital electrical signals through the analog-to-digital conversion module, so as to become the original data.
The cold state of the CT system refers to the unused state of the X-ray tube for 6 hours, the normal state refers to the state of the X-ray tube during the normal use period, the hot state refers to the state of the X-ray tube during the frequent use period, and the heat quantity is relatively high; the cold state to the hot state actually refer to the tube load of the X-ray tube, which is generally measured as the proportion of the exposure energy in a sliding time window, which is calculated by the exposure power X-exposure time.
The original data of the air comprise three conditions of cold state, hot state and normal state, the stability and accuracy of the scanning condition of the CT system can be affected by different conditions, the original data of the air in different conditions are correspondingly converted into projection data in corresponding conditions, the projection data are recorded, and the data of the patient scanned by the CT system and the reference coefficient when the patient is scanned are combined to compensate the data of the patient scanned by the CT system, so that final data are obtained.
According to the air calibration compensation method for the CT system, the air calibration reference is installed, the air data of the CT system in a cold state, a hot state and a normal state and the corresponding cold state, hot state and normal state reference coefficients are obtained, the data of a patient scanned by the CT system and the reference coefficients of the patient scanned by the CT system are combined, the data of the patient scanned by the CT system are compensated through a series of data, the accuracy and the stability of the air calibration of the CT are improved, the quality of CT images is improved, and the air calibration compensation method has important practical significance in clinical use.
Finally, it should be noted that the foregoing description is only a preferred embodiment of the present invention, and although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications may be made to the technical solutions described in the foregoing embodiments, or equivalents may be substituted for some of the technical features thereof, and any modifications, equivalents, improvements or changes thereof may be made without departing from the spirit and principle of the present invention.
Claims (6)
1. The CT system air calibration compensation method is characterized by comprising the following steps:
s10, installing an air calibration reference;
s20, acquiring air data and a cold state reference coefficient of a CT system in a cold state;
the method comprises the following specific steps:
s201, collecting dark current data offsetdata_low of the CT detector system when the X-ray tube assembly is not exposed;
s202, during the cold state of the CT system, operating the X-ray tube assembly for exposure;
s203, acquiring air original data airdata_low of the CT system in a cold state by using the CT detector system, and converting the air original data airdata_low into projection data airable_low, wherein the formula is as follows:
wherein Ref_Low is the reference detector value of the CT system in the cold state;
s204, calculating a detector air calibration reference coefficient R_low in a cold state of the CT system, wherein the calculation method comprises the following steps:
wherein temp_low (ic, ir, iv) is an intermediate variable value used in the process of calculating R_low, ic is a channel number of a CT detector system, ir is a number of a CT system detector row, iv is a view angle number of one circle of CT rotation;
the data for all views in the range of rows ir1 to ir2 are averaged for channels ic1 to ic2 of temp_low to obtain the reference coefficient r_low:
R_low＝mean(temp_log(ic1：ic2，ir1：ir2，：))，
wherein, ": "refers to all viewing angles in the range of lanes ic1 through ic2, rows ir1 through ir2;
s30, acquiring air data and a thermal state reference coefficient of a CT system in a thermal state, and acquiring projection data available_high and a detector air calibration reference coefficient R_high at the moment;
s40, acquiring air data and a normal reference coefficient in a normal state of the CT system, and acquiring projection data airable_normal and a detector air calibration reference coefficient R_normal at the moment;
s50, acquiring reference coefficient R_parameter and intermediate variable value temp_parameter of a CT system when scanning patient data and scanning the patient;
s60, according to the acquired air data of the CT system in the cold state, the hot state and the normal state and the reference coefficients of the cold state, the hot state and the normal state, and by combining the data of the patient scanned by the CT system and the reference coefficients of the patient scanned by the CT system, compensating the data of the patient scanned by the CT system to obtain final data;
the method comprises the following specific steps:
s601, converting original data of a patient scanned by a CT system into projection data, and performing air compensation on the projection data to obtain compensated data patentprj_corr, wherein the formula is as follows:
here, temp_part is a three-dimensional matrix, and means all elements of the matrix, and temp_part (ic, ir, iv) means one element with coordinates (ic, ir, iv).
2. The method of air calibration compensation for CT systems of claim 1, wherein in step S10, the specific steps of installing an air calibration reference are:
s101, setting a high-density object as a reference object on a propagation path from X-rays emitted by an X-ray tube assembly to X-rays received by a CT detector system, wherein the X-rays pass through the high-density object to form a projection on the CT detector system;
s102, receiving projections of the reference object in a selected area on the CT detector system, and determining that the channel range of the area on the CT detector system is ic1 to ic2 and the row range is ir1 to ir2 through the numerical change generated by the reference object in the process of changing the CT system from a cold state to a hot state.
3. The method for air calibration and compensation of a CT system according to claim 2, wherein in step S30, the specific steps of obtaining the air data and the thermal state reference coefficient of the CT system in the thermal state are as follows:
s301, collecting dark current data offs et data_high of a CT detector system when an X-ray tube assembly is not exposed;
s302, during the thermal state of the CT system, operating the X-ray tube assembly for exposure;
s303, acquiring air raw data airdata_high in a thermal state of the CT system by using the CT detector system, and converting the air raw data into projection data airable_high, wherein the formula is as follows:
wherein Ref_high is the reference detector value of the CT system in a thermal state;
s304, calculating a detector air calibration reference coefficient R_high in a thermal state of the CT system, wherein the calculation method is as follows:
wherein temp_high (ic, ir, iv) is a median variable value used in the process of calculating R_high, ic is a channel number of the CT detector system, ir is a number of a detector row of the CT system, iv is a view angle number of one circle of CT rotation;
the data for all views in the range of rows ir1 to ir2 are averaged for channels ic1 to ic2 of temp_high to obtain the reference coefficient r_high:
r_high=mean (temp_high (ic 1: ic2, ir1: ir2,:)), wherein ": "refers to all viewing angles in the range of lanes ic1 through ic2, rows ir1 through ir2.
4. The method for air calibration and compensation of a CT system as set forth in claim 3, wherein in step S40, the specific steps of acquiring the air data and the normal reference coefficient of the CT system in normal state are as follows:
s401, collecting detector system dark current data offsetdata_normal when the X-ray tube assembly is not exposed;
s402, operating the X-ray tube assembly for exposure in the normal state of the CT system;
s403, acquiring air original data airdata_normal in a normal state of the CT system by using the CT detector system, and converting the air original data airdata_normal into projection data airable_normal, wherein the formula is as follows:
wherein Ref_normal is the CT system reference detector value at normal times;
s404, calculating a detector air calibration reference coefficient R_normal in a normal state of the CT system, wherein the calculation method is as follows:
wherein temp_normal (ic, ir, iv) is an intermediate variable value used in the process of calculating R_normal, ic is a CT detector system channel number, ir is a CT system detector row number, iv is a view angle number of one revolution of CT;
the data for all views in the range of temp_normal channels ic1 through ic2, rows ir1 through ir2 are averaged to obtain the reference coefficient r_normal:
R_normal＝mean(temp_normal(ic1：ic2，ir1：ir2，：))，
wherein, ": "refers to all viewing angles in the range of lanes ic1 through ic2, rows ir1 through ir2.
5. The method of air calibration and compensation for a CT system as set forth in claim 4, wherein in step S50, the steps of obtaining data of a patient scanned by the CT system and reference coefficients of the patient scanned are as follows:
s501, collecting detector system dark current data offsetdata_event when the X-ray tube assembly is not exposed;
s502, during the cold state of the CT system, operating the X-ray tube assembly for exposure;
s503, acquiring original data of a patient scanned by a CT system by using the CT detector system, and calculating a real-time reference coefficient of the patient scanned by the CT system detector, wherein the calculation method comprises the following steps:
wherein temp_event (ic, ir, iv) is an intermediate variable value used in the process of calculating R_event, ic is a channel number of a CT detector system, ir is a number of a CT detector row, iv is a view angle number of one circle of CT rotation; ref_parameter is a reference detector value of the CT system when scanning a patient;
the data for all views in the range of rows ir1 to ir2 are averaged for channels ic1 to ic2 of temp_event to obtain the reference coefficient r_event:
R_patient＝mean(temp_patient(ic1：ic2，ir1：ir2，：))，
wherein, ": "refers to all viewing angles in the range of lanes ic1 through ic2, rows ir1 through ir2.
6. The method of claim 2, wherein the reference object is in the shape of a cuboid or sphere, and the material includes but is not limited to one of copper, tungsten or lead.
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