CN113298903A - Reconstruction method, device, equipment and medium for coarse pitch spiral CT - Google Patents
Reconstruction method, device, equipment and medium for coarse pitch spiral CT Download PDFInfo
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Abstract
The invention discloses a reconstruction method, a device, equipment and a medium of a coarse pitch spiral CT, wherein the method comprises the following steps: calculating the minimum detector row number required for covering a Tam window according to the pitch of the helical scanning system and the row spacing of the multiple rows of detectors; when the actual detector row number is smaller than the required minimum detector row number, performing interpolation based on a v axis of a plane where the detector is located, and performing complementation on missing projection data by using conjugate data weighting; performing cone angle cosine weighting on the completed projection data; performing one-dimensional filtering on the weighted projection data along the u-axis direction of the detector; and carrying out cone beam back projection on the filtered projection data to obtain a CT reconstruction image. According to the method, interpolation is carried out on the v axis of the plane where the spiral detector is located, and the distance on the v axis is the actual distance of the physical detector, so that the weight calculated by interpolation based on the v axis can be closer to the actual weight, the interpolation error is reduced, and the reconstructed image is clearer and more complete.
Description
Technical Field
The invention belongs to the technical field of image reconstruction, and particularly relates to a reconstruction method, a device, equipment and a medium for a coarse pitch spiral CT.
Background
X-ray Computed Tomography (CT) devices are widely used in medicine and industry for diagnosis of disease and non-destructive testing. The principle is that a plurality of groups of projection data are obtained by scanning an object at different angles, and then a tomographic image of the scanned object is obtained through a reconstruction algorithm.
Helical scanning systems are commonly used in the art for CT scanning, which has the advantage that the required projection data can be obtained quickly by continuous scanning without interruption. When in use, the detection speed is generally required to be increased so as to complete object scanning in a short time; in this case, in order to acquire complete projection data required by the reconstruction algorithm, it is usually required to increase the number of rows of the detector or increase the rotation speed. However, increasing the number of rows of detectors can significantly increase the system cost and can introduce cone beam artifacts due to the expanded cone angle; the method for increasing the rotating speed is limited by the stability of the machine and the limit of the rotating speed, and the using effect is often poor.
Therefore, the most effective method is to increase the scanning speed by increasing the helical pitch, but the increase of the helical pitch causes the missing projection data required by the reconstruction algorithm, so the missing projection data needs to be compensated and reconstructed. However, currently, commonly used helical reconstruction algorithms, such as Katsevich type algorithm, BPF type algorithm, FBP type algorithm, and the like, have limitations on the helical pitch factor (generally, the helical pitch factor is not more than 1.5 is required), and when the helical pitch is increased, the projection data is lost, so that the reconstructed image has artifacts and the image quality is poor.
Disclosure of Invention
It is an object of the present invention to provide a reconstruction method, apparatus, device and medium for coarse pitch helical CT to solve at least one of the problems of the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a reconstruction method for a coarse pitch helical CT, including:
calculating the minimum detector row number required for covering a Tam window according to the pitch of the helical scanning system and the row spacing of the multiple rows of detectors;
when the actual detector row number is smaller than the minimum detector row number, performing interpolation based on a v-axis of a plane where the detector is located, and performing complementation on missing projection data by using conjugate data weighting;
performing cone angle cosine weighting on the completed projection data;
performing one-dimensional filtering on the weighted projection data along the u-axis direction of the detector;
and carrying out cone beam back projection on the filtered projection data to obtain a CT reconstruction image.
In one possible design, interpolating based on the v-axis of the plane of the detector, and complementing the missing projection data with conjugate data weighting includes:
when v > vmaxWhen the temperature of the water is higher than the set temperature,
wherein g is projection data, (u, v) are coordinates of a plane of the spiral detector, lambda is an angle parameter of a scanning track of the X-ray source, n is the row number of conjugate projection data used for controlling interpolation, n is more than or equal to 1 and less than or equal to nv, nv is the total row number of the detector, omegajFor the weight of the projection data, vmaxIs the maximum coordinate value, v, of the direction of the spiral detector rowminIs the minimum coordinate value in the direction of the spiral detector row, dv is the detector row spacing,
g(-u，vmin+ j × dv, λ + pi +2 γ) is conjugate projection data of the projection data;
wherein, ω isjThe calculation formula of (a) is as follows:
h is a screw pitch, R is the distance from the X-ray source to the rotation center, and D is the distance from the X-ray source to the spiral detector;
when v < vminWhen the temperature of the water is higher than the set temperature,
wherein, ω isjThe calculation formula of (a) is as follows:
in one possible design, when n is 1, interpolation is performed based on the v-axis of the plane in which the detector is located, and the missing projection data is complemented by conjugate data weighting, including:
when v > vmaxWhen the temperature of the water is higher than the set temperature,
g(u，v，λ)＝(1-ω0)·g(u，vmax，λ)+ω0·g(-u，vmin，λ+π+2γ) (5)
wherein, ω is0The weight of the projection data when n is 1, in this case,
when v < vminWhen the temperature of the water is higher than the set temperature,
g(u，v，λ)＝(1-ω0)·g(u，vmin，λ)+ω0·g(-u，vmax，λ-π+2γ) (7)
at this time, the process of the present invention,
in one possible design, the one-dimensional filtering employs an R-L convolution kernel.
In a second aspect, the present invention provides a reconstruction apparatus for a coarse pitch helical CT, comprising:
the calculation module is used for calculating the minimum detector row number required for covering a Tam window according to the pitch of the helical scanning system and the row spacing of the multiple rows of detectors;
the data completion module is used for performing interpolation based on a v axis of a plane where the detector is positioned and performing completion on missing projection data by utilizing conjugate data weighting when the actual detector row number is smaller than the minimum detector row number;
the weighting module is used for carrying out cone angle cosine weighting on the complemented projection data;
the filtering module is used for carrying out one-dimensional filtering on the weighted projection data along the u-axis direction of the detector;
and the back projection module is used for carrying out cone beam back projection on the filtered projection data to obtain a CT reconstruction image.
In one possible design, when performing interpolation based on a v-axis of a plane in which the detector is located and performing compensation on missing projection data by using conjugate data weighting, the data compensation module is specifically configured to:
when v > vmaxWhen the temperature of the water is higher than the set temperature,
wherein g is projection data, (u, v) are coordinates of a plane of the spiral detector, lambda is an angle parameter of a scanning track of the X-ray source, n is the row number of conjugate projection data used for controlling interpolation, n is more than or equal to 1 and less than or equal to nv, nv is the total row number of the detector, omegajFor the weight of the projection data, vmaxIs the maximum coordinate value, v, of the direction of the spiral detector rowminIs the minimum coordinate value in the row direction of the spiral detector, dv is the detector row spacing, g (-u, v)min+ j × dv, λ + pi +2 γ) is conjugate projection data of the projection data;
wherein, ω isjThe calculation formula of (a) is as follows:
when v < vminWhen the temperature of the water is higher than the set temperature,
wherein, ω isjThe calculation formula of (a) is as follows:
in one possible design, when n is 1, interpolation is performed based on a v-axis of a plane where the detector is located, and missing projection data is compensated by using conjugate data weighting, the data compensation module is specifically configured to:
when v > vmaxWhen the temperature of the water is higher than the set temperature,
g(u，v，λ)＝(1-ω0)·g(u，vmax，λ)+ω0·g(-u，vmin，λ+π+2γ) (5)
wherein, ω is0The weight of the projection data when n is 1, in this case,
when v < vminWhen the temperature of the water is higher than the set temperature,
g(u，v，λ)＝(1-ω0)·g(u，vmin，λ)+ω0·g(-u，vmax，λ-π+2γ) (7)
at this time, the process of the present invention,
in one possible design, the one-dimensional filtering employs an R-L convolution kernel.
In a third aspect, the present invention provides a computer apparatus comprising: a memory, a processor and a transceiver, which are connected in sequence in a communication manner, wherein the memory is used for storing a computer program, the transceiver is used for transceiving a message, and the processor is used for reading the computer program and executing the reconstruction method of the coarse pitch helical CT according to the first aspect.
In a fourth aspect, the present invention provides a computer readable storage medium having stored thereon instructions which, when run on a computer, perform the reconstruction method of a coarse pitch helical CT according to the first aspect.
In a fifth aspect, the present invention provides a computer program product comprising instructions which, when run on a computer, cause the computer to perform the reconstruction method for a coarse pitch helical CT according to the first aspect.
Has the advantages that:
1. according to the invention, interpolation is carried out on the v axis of the plane where the spiral detector is located, and the distance on the v axis is the actual distance of the physical detector, so that the weight calculated by interpolation based on the v axis can be closer to the actual weight, the interpolation error is reduced, and the image quality of the reconstructed CT image is further improved.
2. According to the method, the cone angle effect of different conjugate projection data is fully considered, the row number n of the conjugate projection data used for controlling interpolation is introduced into the interpolation algorithm, and the missing projection data can be weighted and filled up according to different values of n, so that the influence of the cone angle effect on the accuracy of the calculation result of the interpolation algorithm can be overcome, and the calculation accuracy is improved.
3. After the missing projection data are supplemented, the image reconstruction method can be expanded and applied to the situation that the pitch factor is larger than 2, and is wider in application range.
Drawings
FIG. 1 is a schematic diagram of a prior art scanning system;
FIG. 2 is a two-dimensional schematic of conjugate projection data according to the present invention;
FIG. 3 is a flowchart of a reconstruction method of a coarse pitch helical CT according to the present invention;
FIG. 4 is a schematic illustration of the interpolation on the v-axis to complement the weighting of missing projection data according to the present invention;
fig. 5 is a schematic structural diagram of a reconstruction device of a coarse pitch helical CT in the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the drawings in the embodiments of the present disclosure, and it is obvious that the described embodiments are some, but not all embodiments of the present disclosure. All other embodiments, which can be obtained by a person skilled in the art without inventive step based on the embodiments in the present description, belong to the protection scope of the present invention.
Examples
In order to solve the technical problem that the quality of a reconstructed image is not high due to the fact that projection data are missing when an existing helical CT scanning system performs image reconstruction, on the one hand, the embodiment provides a reconstruction method of a coarse pitch helical CT, and clear and complete reconstructed images can be obtained by complementing the missing projection data. The method can be applied to a server, and includes but is not limited to implementation through executing the steps S101 to S105 through python, java, C + + and other languages and tools.
Referring to fig. 1-4, the reconstruction method of the coarse pitch helical CT in the present embodiment will be described in detail.
Therein, fig. 1 shows a schematic view of a typical prior art CT scanning system, wherein the X-ray source and the detector are rotated around a rotational centerline, which is a virtual straight line parallel to the z-axis and passing through a rotational center o. s (lambda) represents the scanning track of the X-ray source, lambda is the rotation angle of the source, (u, v, w) are the rotation coordinates of the detector and the source, (u, v) represent the coordinates of the point on the detector plane, R is the distance from the source to the center of rotation, odThe projection of the ray source on the detector, and D is the distance from the ray source to the detector.
Wherein the scanning track of the ray source is composed of
And showing that lambda is an angle parameter of a scanning track of the ray source. The scan trajectory of the helical scan may be represented as
Wherein z is0Is a rayThe starting z coordinate of the source, H, is the distance the source moves by the scanning bed one revolution, i.e., the pitch. The projection data of the X-ray source through the scanned object can be represented by the following equation:
wherein
Is a unit direction vector, S2The unit spherical surface is expressed,
for projection data, t is an integral variable.
If the projection data is not truncated, the CT image reconstruction problem of the helical scanning system is to reconstruct the internal tomographic structure f (x, y, z) of the scanned object by using the projection data, and the reconstruction algorithm is various, preferably a typical feldkamp (fdk) type reconstruction algorithm, and the mathematical expression is:
wherein the content of the first and second substances,
for reconstructing linear attenuation coefficients, vectors, of the object
Is a point coordinate in three-dimensional space, and Λ (λ) is
The set of covered scan trajectories is then selected,
the weight value of the scanning track based on the angle is represented by l connecting the ray source with the reconstruction point
G is projection data, (u, v) is coordinates of the flat panel detector zoomed to the rotation center, λ is an angle parameter of the X-ray source scanning track, and (u) is a filter function along the u-axis direction.
Based on the above disclosure, as shown in fig. 2 to 4, the reconstruction method of the coarse pitch helical CT in the present embodiment specifically includes:
s101, calculating the minimum detector row number required for covering a Tam window according to the pitch of a helical scanning system and the row spacing of a plurality of rows of detectors;
it should be noted that, in the helical CT reconstruction process, the projection data required for accurate reconstruction is projection data covered by a Tam-Danielsson window (Tam window for short), where the Tam window is a projection of two adjacent helical scanning trajectories on a detector. Thus, for a given pitch, the minimum number of detector rows nv required for an exact reconstructionminComprises the following steps:
where dv is the size of the detector pixel unit in the row number direction (v direction), i.e. the row spacing, D is the distance from the radiation source to the detector, and γ ismaxIs the single-side maximum opening angle of the fan-shaped beam;
wherein u isminAnd umaxRespectively representing the minimum and maximum physical coordinates of the u-axis of the detector plane.
Based on the above equations (c) and (d), the minimum number of detector rows nv required by the helical CT system for accurate reconstruction can be calculatedmin(ii) a When the actual number of detector rows is less than the minimum number of detector rows, then there will be a lack of projection data.
S102, when the actual detector row number is smaller than the minimum detector row number, performing interpolation based on a v axis of a plane where the detector is located, and performing complementation on missing projection data by using conjugate data weighting;
when the actual detector row number is smaller than the minimum detector row number, it indicates that the projection data is incomplete, and the data requirement of the reconstruction algorithm of the helical scanning system cannot be met, so that the missing projection data needs to be reconstructed after being completed.
In the two-dimensional fan beam CT, the conjugate projection data is defined as shown in fig. 2, and the conjugate projection data of the projection data g (u, v, λ ± τ +2 γ) is g (-u, v, λ ± τ +2 ×)
Because there is no cone angle effect, there is a unique co-planar conjugate projection data for each projection data. In the three-dimensional cone beam CT, due to the cone angle and the helical trajectory movement, there is no strictly defined conjugate data, each projection data has a set of conjugate projection data in the front and back directions of the helical scanning trajectory, each conjugate projection data has projection data information in different projection directions due to different cone angles, and the projections of the conjugate projection data on the x-y plane are the same straight line, i.e., the black thin solid lines passing through u and-u shown in fig. 2, so that it is necessary to consider multiple sets of conjugate data under different detector rows to more accurately complement the missing projection data.
In one possible design, interpolation is performed based on the v-axis of the plane of the detector, and the missing projection data is complemented by conjugate data weighting, including:
when v > vmaxWhen the temperature of the water is higher than the set temperature,
wherein g is projection data, (u, v) are coordinates of a plane of the helical detector, λ is an angle parameter of a scanning trajectory of the X-ray source, and n is conjugate projection data for controlling interpolationN is more than or equal to 1 and less than or equal to nv, nv is the total number of rows of the detector, omegajFor the weight of the projection data, vmaxIs the maximum coordinate value, v, of the direction of the spiral detector rowminIs the minimum coordinate value in the row direction of the spiral detector, dv is the detector row spacing, g (-u, v)min+ j × dv, λ + pi +2 γ) is conjugate projection data of the projection data;
wherein, ω isjThe calculation formula of (a) is as follows:
h is a screw pitch, R is the distance from the X-ray source to the rotation center, and D is the distance from the X-ray source to the spiral detector;
when v < Pmin, the value of,
wherein, ω isjThe calculation formula of (a) is as follows:
in one possible design, as shown in fig. 4, when n is 1, interpolation is performed based on the v-axis of the plane of the detector, and the missing projection data is complemented by conjugate data weighting, including:
when v > vmaxWhen the temperature of the water is higher than the set temperature,
g(u，v，λ)＝(1-ω0)·g(u，vmax，λ)+ω0·g(-u，vmin，λ+π+2γ) (5)
wherein, ω is0The weight of the projection data when n is 1, in this case,
when v < vminWhen the temperature of the water is higher than the set temperature,
g(u，v，λ)＝(1-ω0)·g(u，vmin，λ)+ω0·g(-u，vmax，λ-π+2γ) (7)
at this time, the process of the present invention,
s103, cone angle cosine weighting is carried out on the completed projection data;
s104, performing one-dimensional filtering on the weighted projection data along the u-axis direction of the detector;
preferably, the one-dimensional filtering adopts an R-L convolution kernel;
and S105, carrying out cone beam back projection on the filtered projection data to obtain a CT reconstruction image.
Based on the above disclosure, in the embodiment, by performing interpolation on the v-axis of the plane where the spiral detector is located, since the distance on the v-axis is the actual distance of the physical detector, the weight calculated by performing interpolation based on the v-axis can be closer to the actual weight, the interpolation error is reduced, and the image quality of the reconstructed CT image is further improved. In addition, in the embodiment, cone angle effects of different conjugate projection data are fully considered, and the row number n of the conjugate projection data used for controlling interpolation is introduced into the interpolation algorithm, so that the missing projection data can be weighted and filled up according to different values of n for multiple groups of conjugate projection data before and after the v axis, thereby overcoming the influence of the cone angle effects on the accuracy of the calculation result of the interpolation algorithm and improving the accuracy of the calculation. Therefore, after the missing projection data are supplemented, the image reconstruction suitable for the situation that the pitch factor is larger than 2 can be expanded, and the application range is wider.
As shown in fig. 5, in a second aspect, the present invention provides a reconstruction apparatus for a coarse pitch helical CT, including:
the calculation module is used for calculating the minimum detector row number required for covering a Tam window according to the pitch of the helical scanning system and the row spacing of the multiple rows of detectors;
the data completion module is used for performing interpolation based on a v axis of a plane where the detector is positioned and performing completion on missing projection data by utilizing conjugate data weighting when the actual detector row number is smaller than the minimum detector row number;
the weighting module is used for carrying out cone angle cosine weighting on the complemented projection data;
the filtering module is used for carrying out one-dimensional filtering on the weighted projection data along the u-axis direction of the detector;
and the back projection module is used for carrying out cone beam back projection on the filtered projection data to obtain a CT reconstruction image.
In one possible design, when performing interpolation based on a v-axis of a plane in which the detector is located and performing compensation on missing projection data by using conjugate data weighting, the data compensation module is specifically configured to:
when v > vmaxWhen the temperature of the water is higher than the set temperature,
wherein g is projection data, (u, v) is coordinates of a plane of the helical detector, and is an angle parameter of a scanning track of the X-ray source, n is the row number of conjugate projection data used for controlling interpolation, n is more than or equal to 1 and less than or equal to nv, nv is the total row number of the detector, omegajFor the weight of the projection data, vmaxIs the maximum coordinate value, v, of the direction of the spiral detector rowminIs the minimum coordinate value in the row direction of the spiral detector, dv is the detector row spacing, g (-u, v)min+ j × dv, λ + pi +2 γ) is conjugate projection data of the projection data;
wherein, ω isjThe calculation formula of (a) is as follows:
when v < vminWhen the temperature of the water is higher than the set temperature,
wherein, ω isjThe calculation formula of (a) is as follows:
in one possible design, when n is 1, interpolation is performed based on a v-axis of a plane where the detector is located, and missing projection data is compensated by using conjugate data weighting, the data compensation module is specifically configured to:
when v > vmaxWhen the temperature of the water is higher than the set temperature,
g(u，v，λ)＝(1-ω0)·g(u，vmax，λ)+ω0·g(-u，vmin，λ+π+2γ) (5)
wherein, ω is0The weight of the projection data when n is 1, in this case,
wherein AB is the coordinate from point B to point A on the v-axis of the projection datamaxAC is the coordinate of point C to the coordinate of point A on the v-axis of the conjugate projection datamaxA distance of (1) to
Weights calculated at the v-axis;
when v < vminWhen the temperature of the water is higher than the set temperature,
g(u，v，λ)＝(1-ω0)·g(u，vmin，λ)+ω0·g(-u，vmax，λ-π+2γ) (7)
at this time, the process of the present invention,
in one possible design, the one-dimensional filtering employs an R-L convolution kernel.
In a third aspect, the present invention provides a computer apparatus comprising: a memory, a processor and a transceiver, which are connected in sequence in a communication manner, wherein the memory is used for storing a computer program, the transceiver is used for transceiving a message, and the processor is used for reading the computer program and executing the reconstruction method of the coarse pitch helical CT according to the first aspect.
In a fourth aspect, the present invention provides a computer readable storage medium having stored thereon instructions which, when run on a computer, perform the reconstruction method of a coarse pitch helical CT according to the first aspect.
In a fifth aspect, the present invention provides a computer program product comprising instructions which, when run on a computer, cause the computer to perform the reconstruction method for a coarse pitch helical CT according to the first aspect.
Finally, it should be noted that: the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A reconstruction method of a coarse pitch helical CT, comprising:
calculating the minimum detector row number required for covering a Tam window according to the pitch of the helical scanning system and the row spacing of the multiple rows of detectors;
when the actual detector row number is smaller than the minimum detector row number, performing interpolation based on a v-axis of a plane where the detector is located, and performing complementation on missing projection data by using conjugate data weighting;
performing cone angle cosine weighting on the completed projection data;
performing one-dimensional filtering on the weighted projection data along the u-axis direction of the detector;
and carrying out cone beam back projection on the filtered projection data to obtain a CT reconstruction image.
2. The method of claim 1, wherein interpolating based on the v-axis of the plane of the detector and complementing the missing projection data with conjugate data weighting comprises:
when v > vmaxWhen the temperature of the water is higher than the set temperature,
wherein g is projection data, (u, v) is coordinates of a plane of the helical detector, and is an angle parameter of a scanning track of the X-ray source, n is the row number of conjugate projection data used for controlling interpolation, n is more than or equal to 1 and less than or equal to nv, nv is the total row number of the detector, omegajFor the weight of the projection data, vmaxIs the maximum coordinate value, v, of the detector row directionminIs the minimum coordinate value in the detector row direction, dv is the detector row spacing, g (-u, v)min+ j × dv, λ + pi +2 γ) is conjugate projection data of the projection data;
wherein, ω isjThe calculation formula of (a) is as follows:
h is a screw pitch, R is the distance from an X-ray source to a rotation center, and D is the distance from the X-ray source to a detector;
when v < vminWhen the temperature of the water is higher than the set temperature,
at this time, ωjThe calculation formula of (a) is as follows:
3. the method of claim 2, wherein when n is 1, interpolating based on the v-axis of the plane of the detector, and complementing the missing projection data with conjugate data weighting comprises:
when v > vmaxWhen the temperature of the water is higher than the set temperature,
g(u，v，λ)＝(1-ω0)·g(u，vmax，λ)+ω0·g(-u，vmin，λ+π+2γ) (5)
wherein, ω is0The weight of the projection data when n is 1, in this case,
when v < vminWhen the temperature of the water is higher than the set temperature,
g(u，v，λ)＝(1-ω0)·g(u，vmin，λ)+ω0·g(-u，vmax，λ-π+2γ) (7)
at this time, the process of the present invention,
4. the method of claim 1, wherein the one-dimensional filtering employs an R-L convolution kernel.
5. A reconstruction device for a coarse pitch helical CT, comprising:
the calculation module is used for calculating the minimum detector row number required for covering a Tam window according to the pitch of the helical scanning system and the row spacing of the multiple rows of detectors;
the data completion module is used for performing interpolation based on a v axis of a plane where the detector is positioned and performing completion on missing projection data by utilizing conjugate data weighting when the actual detector row number is smaller than the minimum detector row number;
the weighting module is used for carrying out cone angle cosine weighting on the complemented projection data;
the filtering module is used for carrying out one-dimensional filtering on the weighted projection data along the u-axis direction of the detector;
and the back projection module is used for carrying out cone beam back projection on the filtered projection data to obtain a CT reconstruction image.
6. The apparatus of claim 5, wherein when interpolating based on a v-axis of a plane in which the detector is located and compensating missing projection data by weighting conjugate data, the data compensation module is specifically configured to:
when v > vmaxWhen the temperature of the water is higher than the set temperature,
wherein g is projection data, (u, v) are coordinates of a plane of the spiral detector, lambda is an angle parameter of a scanning track of the X-ray source, n is the row number of conjugate projection data used for controlling interpolation, n is more than or equal to 1 and less than or equal to nv, nv is the total row number of the detector, omegajFor the weight of the projection data, vmaxIs the maximum coordinate value, v, of the direction of the spiral detector rowminIs the minimum coordinate value in the row direction of the spiral detector, dv is the detector row spacing, g (-u, v)minConjugate projection data of + j × dv, λ + pi +2 γ);
wherein, ω isjThe calculation formula of (a) is as follows:
when v < vminWhen the temperature of the water is higher than the set temperature,
wherein, ω isjThe calculation formula of (a) is as follows:
7. the apparatus of claim 6, wherein when n-1 is interpolated based on a v-axis of a plane in which the detector is located, and the missing projection data is compensated by conjugate data weighting, the data compensation module is specifically configured to:
when v > vmaxWhen the temperature of the water is higher than the set temperature,
g(u，v，λ)＝(1-ω0)·g(u，vmax，λ)+ω0·g(-u，vmin，λ+π+2γ) (5)
wherein, ω is0The weight of the projection data when n is 1, in this case,
when v < vminWhen the temperature of the water is higher than the set temperature,
g(u，v，λ)＝(1-ω0)·g(u，vmin，λ)+ω0·g(-u，vmax，λ-π+2γ) (7)
at this time, the process of the present invention,
8. the apparatus of claim 5, wherein the one-dimensional filtering employs an R-L convolution kernel.
9. A computer device, comprising: a memory, a processor and a transceiver, communicatively connected in sequence, wherein the memory is configured to store a computer program, the transceiver is configured to transmit and receive messages, and the processor is configured to read the computer program and execute the reconstruction method of the coarse pitch helical CT as claimed in any one of claims 1 to 4.
10. A computer-readable storage medium having stored thereon instructions which, when executed on a computer, perform a reconstruction method of a coarse pitch helical CT as claimed in any one of claims 1 to 4.
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