CN113017665B - CT detector Gap _ Size calibration plate and calibration method and calibration assembly thereof - Google Patents
CT detector Gap _ Size calibration plate and calibration method and calibration assembly thereof Download PDFInfo
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- CN113017665B CN113017665B CN202110148046.8A CN202110148046A CN113017665B CN 113017665 B CN113017665 B CN 113017665B CN 202110148046 A CN202110148046 A CN 202110148046A CN 113017665 B CN113017665 B CN 113017665B
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/58—Testing, adjusting or calibrating apparatus or devices for radiation diagnosis
- A61B6/582—Calibration
- A61B6/585—Calibration of detector units
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/02—Devices for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
- A61B6/03—Computerised tomographs
- A61B6/032—Transmission computed tomography [CT]
Abstract
The invention belongs to the technical field of CT, and particularly relates to a CT detector Gap _ Size calibration plate, a calibration method and a calibration assembly thereof. The calibration plate comprises a plate body, wherein the plate body is provided with array type crevice gaps distributed along the length direction of the plate body, and each Gap crevice is at least covered on two rows of detector modules in a projection area of the CT detector to the CT detector; the first side of the crevice gap is a bevel structure extending in the Z-direction such that a projection of the crevice gap onto the corresponding row of detector modules is from completely covering to completely uncovering the respective scintillation crystal blade. The invention does not need the rotation of the CT scanning frame, and completely removes the influences generated by the focus drift and the mechanical deformation of the frame and the detector; and non-linear optimization solution is not needed, and the problem of difficult solution does not exist.
Description
Technical Field
The invention belongs to the technical field of CT, and particularly relates to a CT detector Gap _ Size calibration plate, a calibration method and a calibration assembly thereof.
Background
A Computed Tomography (CT) scanner is a device that rotationally irradiates an object to be measured with X-rays and then obtains a tomographic image of the object by computer processing. In the CT scanning imaging, in order to obtain better image quality, the actual geometric optical dimension is required to be ensured to be consistent with the theoretical geometric optical dimension, the geometric optical dimension relates to a plurality of geometric parameters, wherein the X-direction position of a detector scintillator, particularly the air Gap Size (Gap _ Size) between adjacent detector modules at the X-direction position, is most sensitive to the influence of the detector imaging, cannot be self-calibrated, and is required to be ensured by depending on machining; however, machining errors exist in machining, and if geometric accuracy is guaranteed by completely depending on machining, difficulty in manufacturing and machining is greatly improved.
In the prior art, the Gap _ Size calibration uses an elongated cylindrical metal phantom, which is placed at a position deviated from the rotation center of the CT scan, and the Gap _ Size is calculated by a plurality of scans through the projection coordinates of the elongated cylindrical metal phantom on a detector. For example, patent document CN103969269B discloses a method for geometrically calibrating a CT scanner, comprising for each detector cell of at least one row of detector cells the steps of: establishing a complete geometric description of the CT scanner, wherein the complete geometric description includes at least one unknown geometric parameter; establishing a description of the forward projection function using the complete geometric description; acquiring actual projection coordinates of a calibration model placed in a scanning field of view SFOV on a current row of detector units corresponding to a plurality of angles; acquiring calculated projection coordinates of a calibration mode on the detector units of the current row corresponding to a plurality of angles by using the description of the forward projection function; solving the at least one unknown geometric parameter based on the acquired actual projection coordinates and the calculated projection coordinates by a nonlinear least squares fitting algorithm, thereby obtaining a calibration value of the at least one unknown geometric parameter. However, in the calibration process, the CT gantry needs to rotate, and the influence caused by the focus drift and the mechanical deformation of the gantry and the detector cannot be removed; in addition, a nonlinear optimization problem needs to be solved, and when the number of Gap _ Size between adjacent detector modules to be solved is too large, numerical values are unstable, so that the solution is difficult to solve, and even the solution cannot be solved.
Therefore, if the geometric dimension calibration in the algorithm can be carried out by means of the tool, the machining cost is greatly reduced, and the image quality is improved.
Disclosure of Invention
Based on the above disadvantages and shortcomings of the prior art, an object of the present invention is to solve at least one or more of the above problems of the prior art, in other words, to provide a calibration plate for CT detector Gap _ Size, a calibration method thereof, and a calibration assembly thereof, which satisfy one or more of the above requirements.
In order to achieve the purpose, the invention adopts the following technical scheme:
a CT detector Gap _ Size calibration plate, the CT detector comprises a plurality of rows of detector modules arranged along an X direction, each row of detector modules comprises a plurality of scintillation crystal plates arranged along a Z direction, the calibration plate comprises a plate body, the plate body is provided with array type crevice gaps distributed along the length direction of the plate body, and the projection area of each crevice to the CT detector at least covers two rows of detector modules; the first side of the crevice gap is a bevel structure extending in the Z-direction such that a projection of the crevice gap onto the corresponding row of detector modules is from completely covering to completely uncovering the respective scintillation crystal blade.
Preferably, the projection area of each crevice to the CT detector covers three columns of detector modules.
Preferably, the secondary side of the crevice gap is a planar structure extending in the Z-direction, the secondary side being opposite to the primary side.
Preferably, the calibration plate further comprises a mounting bracket, and the plate body is mounted on the CT detector through the mounting bracket.
Preferably, the plate body has a mounting hole, and is mounted to the mounting hole by a fastener to fix the plate body to the mounting bracket.
Preferably, the plate body has lugs at both ends in the length direction thereof, and each lug has at least one mounting hole.
The invention also provides a method for calibrating Gap _ Size of a CT detector, which adopts the calibration plate according to any scheme, and comprises the following steps:
(1) the calibration plate is arranged between the CT detector and the radiation source, and the X-ray absorption I of each scintillation crystal slice of the same row of detector modules in the CT detector is acquirediI is sequentially valued as 1, 2, …, n, n is the number of the scintillation crystal slices in the same row of detector modules; obtaining a theoretical area S of the uncovered area of each scintillation crystal piece according to a linear function z ═ f (x) corresponding to the slope structure of the crevice gapi(ii) a According to the X-ray absorption amount I of each scintillation crystal sliceiAnd theoretical area SiFitting to obtain I ═ f(s); obtaining S ═ S (x) according to an area calculation formula of an uncovered area of each scintillation crystal slice; determining a theoretical X-direction central position and a theoretical Z-direction central position of a target scintillation crystal piece according to Z ═ f (X), I ═ F (S) and S ═ S (X);
(2) if the scintillation crystal slices are offset from the calibration plate, acquiring the X-ray absorption I 'of each scintillation crystal slice of the detector module in the same row under the actual position of the CT detector'iObtaining the actual area S 'of the uncovered region of each scintillation crystal piece from I' ═ F (S ')'i(ii) a According to the uncommitted of each scintillation crystal pieceAn area calculation formula of the coverage area is obtained, and S '═ S' (x) is obtained; obtaining Z ═ f' (X) according to the one-to-one correspondence between the Z-direction position and the X-direction position of each scintillation crystal piece, and obtaining the actual X-direction central position of the target scintillation crystal piece based on the theoretical Z-direction central position of the target scintillation crystal piece;
(3) calculating the distance between the actual X-direction central position of the target scintillation crystal wafer and the theoretical X-direction central position to obtain an X-direction position deviation delta X, wherein the sum of the theoretical Gap _ Size and the X-direction position deviation delta X of the CT detector is the actual Gap _ Size of the CT detector; calibration was performed using the actual Gap Size.
Preferably, in the step (1), the X-ray absorption amount I is determined according to each scintillation crystal pieceiAnd theoretical area SiFitting results in I ═ f(s), including:
obtaining the area S of each scintillation crystal slice which is not covered completely0And X-ray absorption amount is I ″)i；
According to
Fitting to obtain I ═ f(s); where δ is a correction coefficient.
Preferably, the target scintillation crystal slice is a central scintillation crystal slice of the same row of detector modules.
The invention also provides a CT detector Gap _ Size calibration assembly which is characterized by comprising a plurality of calibration plates which are arranged in parallel or at an angle according to any scheme.
Compared with the prior art, the invention has the beneficial effects that:
according to the CT detector Gap _ Size calibration plate, the calibration method and the calibration assembly thereof, the CT scanning frame does not need to rotate, and the influences caused by focus drift and mechanical deformation of the frame and the detector are completely eliminated; non-linear optimization solution is not needed, and the problem of difficult solution is avoided; can be used for testing multi-module detectors.
Drawings
FIG. 1 is a schematic structural diagram of a calibration plate of Gap _ Size of a CT detector according to embodiment 1 of the present invention;
FIG. 2 is a schematic view of the installation structure of a Gap _ Size calibration plate of a CT detector according to embodiment 1 of the present invention;
FIG. 3 is a schematic view of an alternative view angle of the installation structure of the calibration plate of the CT detector Gap _ Size according to embodiment 1 of the present invention;
FIG. 4 is a schematic view of an alternative view angle of the installation structure of the calibration plate of the CT detector Gap _ Size according to embodiment 1 of the present invention;
FIG. 5 is a schematic diagram of the installation position of a Gap _ Size calibration plate of a CT detector according to embodiment 1 of the present invention;
fig. 6 is a schematic calibration principle diagram of a CT detector Gap _ Size calibration method according to embodiment 1 of the present invention.
Detailed Description
In order to more clearly illustrate the embodiments of the present invention, the following description will explain the embodiments of the present invention with reference to the accompanying drawings. It is obvious that the drawings in the following description are only some examples of the invention, and that for a person skilled in the art, other drawings and embodiments can be derived from them without inventive effort.
Example 1:
the CT detector Gap _ Size calibration board of the present embodiment is applied to the Gap _ Size calibration of the adjacent detector modules of the CT detector.
Specifically, the CT detector includes a plurality of rows of detector modules arranged along the X direction, and each row of channel detector modules includes a plurality of scintillation crystal slices arranged along the Z direction.
As shown in FIG. 1, the calibration plate comprises a plate body 1, wherein the plate body 1 is provided with array-type crevice gap 10 distributed along the length direction thereof, and the projection area of each crevice gap to the CT detector covers three-row detector modules; the left side of the crevice gap 10 is a bevel structure extending in the Z-direction such that the projection of the crevice gap onto the corresponding row of detector modules in turn completely covers the respective scintillation crystal blades to completely uncover the crevice gap; the right side of the crevice gap 10 is a planar structure extending in the Z-direction, i.e. in the width direction of the calibration plate.
As shown in fig. 2 to 4, the calibration board of the present embodiment further includes a mounting bracket 2, and the board body 1 is mounted on the CT detector through the mounting bracket 2. Specifically, as shown in fig. 1, the plate body 1 has lugs 11 at both ends thereof in the longitudinal direction thereof, each of the lugs having two mounting holes 110, and is mounted to the mounting holes 110 of the plate body by fasteners (e.g., screws, bolts, etc.), thereby fixing the plate body 1 to the mounting bracket 2. The position of the calibration plate relative to the mounting bracket can be positioned by the positioning pin, the mounting bracket is mounted on the CT detector, and the position of the mounting bracket relative to the CT detector can also be positioned by the positioning pin.
As shown in fig. 5, a calibration plate a is mounted between the radiation source O and the CT detector B to calibrate the CT detector Gap _ Size.
The calibration method for the CT detector Gap _ Size of the present embodiment adopts the calibration plate of the present embodiment to perform calibration. Specifically, the calibration method comprises the following steps:
(1) collecting X-ray absorption I ″' of each scintillation crystal wafer of the same row of detector modules in the CT detector under the condition of no calibration plateiAnd obtaining the area S of each scintillation crystal slice which is not covered completely0(ii) a Obtaining theoretical Gap _ Size of the CT detector; wherein, i is sequentially valued as 1, 2, …, n, n is the number of the scintillation crystal slices in the same row of detector modules;
(2) installing a calibration plate between the CT detector and the radiation source, wherein X-rays of the radiation source penetrate through the array crevice of the calibration plate and are projected onto the CT detector, different scintillation crystal pieces of the detector modules in the same row are completely shielded from being completely shielded, and the amount of rays received by the different scintillation crystal pieces is gradually changed from maximum to minimum;
the calibration plate is arranged between the CT detector and the radiation source, and the X-ray absorption I of each scintillation crystal slice of the same row of detector modules in the CT detector is acquiredi(ii) a Obtaining a theoretical area S of the uncovered area of each scintillation crystal piece according to a linear function z ═ f (x) corresponding to the slope structure of the crevice gapi(ii) a According to the X-ray absorption amount I of each scintillation crystal sliceiAnd theoretical area SiFitting to obtain I ═ f(s); obtaining S ═ S (x) according to an area calculation formula of an uncovered area of each scintillation crystal slice; according to z ═ f (x), I ═ f(s)And S ═ S (X) determining the theoretical X-direction central position and the theoretical Z-direction central position of the target scintillation crystal wafer;
wherein, the uncovered area of each scintillation crystal plate has a trapezoid structure and a square structure (is not shielded at all), and the theoretical area S of the uncovered area of each scintillation crystal plate can be calculated according to the area formula of the trapezoidi。
Wherein, according to
Fitting to obtain I ═ F (S), which is beneficial to avoiding errors caused by differences among the scintillation crystal slices; wherein, δ is a correction coefficient, which can be obtained by experimental test, a shielding plate with the same inclination angle as the inclined plane structure (namely helical teeth) of the calibration plate is covered on the position corresponding to the theoretical Gap _ Size of the CT detector, and the irradiation area mean value of each scintillation crystal piece is obtained by multiple scanning, and the irradiation area mean value and S of each scintillation crystal piece are obtained according to the irradiation area mean value of each scintillation crystal piece0Obtaining δ.
(3) If the scintillation crystal slices are offset from the calibration plate, acquiring the X-ray absorption I 'of each scintillation crystal slice of the detector module in the same row under the actual position of the CT detector'iObtaining the actual area S 'of the uncovered region of each scintillation crystal piece from I' ═ F (S ')'i(ii) a Obtaining S '═ S' (x) according to a formula for calculating the area of the uncovered region of each scintillator crystal piece; obtaining Z ═ f' (X) according to the one-to-one correspondence between the Z-direction position and the X-direction position of each scintillation crystal piece, and obtaining the actual X-direction central position of the target scintillation crystal piece based on the theoretical Z-direction central position of the target scintillation crystal piece;
(4) calculating the distance between the actual X-direction central position of the target scintillation crystal wafer and the theoretical X-direction central position to obtain an X-direction position deviation delta X, wherein the sum of the theoretical Gap _ Size and the X-direction position deviation delta X of the CT detector is the actual Gap _ Size of the CT detector; calibration was performed using the actual Gap Size.
As shown in fig. 6, the abscissa is a row of detector modules (channels for short), the ordinate is a scintillation crystal plate (slice for short), and the median of the receiving values of the theoretical detector and the median of the central offset displacement are obtained through calculation, so as to obtain the median of the receiving values of the actual offset detector.
The calibration assembly for the CT detector Gap _ Size of the present embodiment includes a plurality of calibration plates of the present embodiment arranged in parallel or at an angle, so as to facilitate calibration of all detector modules.
Example 2:
the difference between the CT detector Gap _ Size calibration method of the present embodiment and embodiment 1 is that:
need not according to
Fitting to obtain I ═ F (S), and directly according to X-ray absorption quantity I of each scintillation crystal sliceiAnd theoretical area SiThe fitting precision is relatively reduced, and the requirements of different application occasions can be met.
Accordingly, step (1)' collecting X-ray absorption I of each scintillation crystal slice of the same row of detector modules in the CT detectoriAnd obtaining the area S of each scintillation crystal slice which is not covered completely0", other steps can refer to example 1;
the corresponding calibration plate and calibration assembly can be referred to in example 1.
Example 3:
the difference between the CT detector Gap _ Size calibration method of the present embodiment and embodiment 1 is that:
the actual CT detector Gap _ Size is an average of actual Gap _ Size of CT detectors corresponding to three rows of detector modules corresponding to the crevices, and further improves the calibration accuracy of the CT detector Gap _ Size.
Other procedures can be referred to example 1;
the corresponding calibration plate and calibration assembly can be referred to in example 1.
Example 4:
the CT detector Gap _ Size calibration plate of the present embodiment is different from that of embodiment 1 in that:
the number of rows of detector modules covered by each crevice to the projection area of the CT detector is not limited to three rows as in embodiment 1, but may be two rows, four rows, five rows, etc., and may be specifically designed according to practical requirements to meet the requirements of different applications.
Other structures can refer to embodiment 1;
the corresponding calibration method and calibration assembly can be referred to in example 1.
The foregoing has outlined rather broadly the preferred embodiments and principles of the present invention and it will be appreciated that those skilled in the art may devise variations of the present invention that are within the spirit and scope of the appended claims.
Claims (9)
1. A CT detector Gap _ Size calibration plate, the CT detector comprising a plurality of rows of detector modules arranged along an X direction, each row of detector modules comprising a plurality of scintillation crystal slices arranged along a Z direction, the calibration plate comprising a plate body having array crevices distributed along a length thereof, a projection area of each crevice to the CT detector at least covering two rows of detector modules; a first side of the crevice gap is a beveled structure extending in a Z-direction such that a projection of the crevice gap onto a corresponding column of detector modules is from completely covering to completely uncovering the respective scintillation crystal slab;
the CT detector Gap _ Size calibration method corresponding to the CT detector Gap _ Size calibration plate comprises the following steps:
(1) the calibration plate is arranged between the CT detector and the radiation source, and the X-ray absorption I of each scintillation crystal piece of the detector module in the same column in the CT detector is collectediI is sequentially valued as 1, 2, …, n, n is the number of the scintillation crystal slices in the same row of detector modules; obtaining a theoretical area S of the uncovered area of each scintillation crystal piece according to a linear function z ═ f (x) corresponding to the slope structure of the crevice gapi(ii) a According to the X-ray absorption amount I of each scintillation crystal sliceiAnd theoretical area SiFitting to obtain the relation I ═ F (S) between the X-ray absorption amount and the area of the scintillation crystal plate; obtaining S ═ S (x) according to an area calculation formula of an uncovered area of each scintillation crystal slice; determining the theoretical X-direction central position and theory of the target scintillation crystal piece according to z ═ f (X), I ═ F (S) and S ═ S (X)The center position in the Z direction;
(2) if the scintillation crystal slices are offset from the calibration plate, acquiring the X-ray absorption I 'of each scintillation crystal slice of the detector module in the same row under the actual position of the CT detector'iObtaining the actual area S 'of the uncovered region of each scintillation crystal piece from I' ═ F (S ')'i(ii) a Obtaining S '═ S' (x) according to a formula for calculating the area of the uncovered region of each scintillator crystal piece; obtaining Z ═ f' (X) according to the one-to-one correspondence between the Z-direction position and the X-direction position of each scintillation crystal piece, and obtaining the actual X-direction central position of the target scintillation crystal piece based on the theoretical Z-direction central position of the target scintillation crystal piece;
(3) calculating the distance between the actual X-direction central position of the target scintillation crystal wafer and the theoretical X-direction central position to obtain an X-direction position deviation delta X, wherein the sum of the theoretical Gap _ Size and the X-direction position deviation delta X of the CT detector is the actual Gap _ Size of the CT detector; calibration was performed using the actual Gap Size.
2. The CT detector Gap _ Size calibration plate of claim 1, wherein each crevice to projection region of the CT detector covers three columns of detector modules.
3. The CT detector Gap _ Size calibration plate as claimed in claim 1, wherein the second side of the crevice Gap is a planar structure extending in the Z direction, the second side being opposite to the first side.
4. The Gap _ Size calibration plate for a CT detector of claim 1, wherein the calibration plate further comprises a mounting bracket, and the plate body is mounted on the CT detector through the mounting bracket.
5. The Gap _ Size calibration plate of CT detector of claim 4, wherein the plate body has mounting holes, and the plate body is mounted to the mounting holes by fasteners to fix the plate body to the mounting bracket.
6. The Gap _ Size calibration plate for a CT detector of claim 5, wherein the plate body has two ends along the length direction thereof respectively having a lug, each lug having at least one mounting hole.
7. The CT detector Gap _ Size calibration plate as claimed in claim 1, wherein in step (1), the X-ray absorption amount I of each scintillation crystal slice is determined according to the X-ray absorption amount IiAnd theoretical area SiFitting results in I ═ f(s), including:
under the condition of not installing the calibration plate, obtaining the area S of each scintillation crystal slice which is not covered completely0And X-ray absorption amount is I ″)i；
According to
Fitting to obtain I ═ f(s); where δ is a correction coefficient.
8. The CT detector Gap _ Size calibration plate of claim 1, wherein the target scintillation crystal piece is a central scintillation crystal piece of a same row of detector modules.
9. A CT detector Gap Size calibration assembly comprising a plurality of calibration plates according to any of claims 1-6 arranged in parallel or at an angle.
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| WO2006109148A2 (en) * | 2005-04-13 | 2006-10-19 | Lodox Systems (Proprietary) Limited | A calibration tool and a method of calibrating an imaging system |
| CN102802531B (en) * | 2009-06-23 | 2014-12-03 | 株式会社日立医疗器械 | X-ray ct device |
| US9389320B2 (en) * | 2010-12-21 | 2016-07-12 | Takara Telesystems Corp. | Radiation detector, and radiation imaging apparatus provided with detector |
| US9826944B2 (en) * | 2013-03-07 | 2017-11-28 | Hitachi, Ltd. | Radiation detector and X-ray CT apparatus provided therewith |
| EP3250909B1 (en) * | 2015-01-26 | 2020-11-25 | Illinois Tool Works Inc. | Gap resolution for linear detector array |
| US9947116B2 (en) * | 2015-03-13 | 2018-04-17 | General Electric Company | Methods and systems for detector gap corrections |
| CN106447637B (en) * | 2016-09-30 | 2019-03-15 | 北京纳米维景科技有限公司 | A kind of splicing detector geometric correction body mould and bearing calibration |
| WO2019240645A1 (en) * | 2018-06-13 | 2019-12-19 | Prismatic Sensors Ab | X-ray detector design |
| CN109549661B (en) * | 2018-12-29 | 2022-11-15 | 北京纳米维景科技有限公司 | Detector geometric correction phantom and correction method |
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Inventor after: Wang Bin Inventor after: Xu Qin Inventor after: Chen Wei Inventor after: Liu Jianhong Inventor before: Wang Bin Inventor before: Xu Qin Inventor before: Chen Wei Inventor before: Liu Jianhong |