CN108030501B - geometric calibration device and method for static cone-beam CT imaging system - Google Patents

Abstract

The invention belongs to the field of X-ray CT imaging, and provides a static cone-beam CT imaging system geometric calibration device, which includes several cold-cathode X-ray tubes arranged in a line or arc to form a multi-beam X-ray source array , where each cold-cathode X-ray tube is used as an X-ray emission source; the support frame reserves adjustment space on the X, Y and Z axes, so that after several cold-cathode X-ray tubes are installed on the support frame, each The position of each cold cathode X-ray tube can be adjusted in the three directions of X, Y or Z axis respectively. By adjusting each cold cathode X-ray tube in the three directions of X, Y or Z axis, the precise calibration of the geometric position of each X-ray source is realized, with extremely high calibration accuracy. At the same time, the present invention also provides a geometric calibration method of the static cone-beam CT imaging system, and the geometric calibration of the static cone-beam CT imaging system is realized by using the above-mentioned device.

Description

A geometrical calibration device and method for a static cone-beam CT imaging system

technical field

The invention belongs to the field of X-ray CT imaging, in particular to a geometric calibration device and method for a static cone-beam CT imaging system.

Background technique

Since the computed tomography (CT) image reconstruction algorithm is based on ideal system geometric parameters, the CT system has very strict requirements on the geometric parameters and installation accuracy of the radiation source, the object to be scanned, and the detector. At present, the existing geometric calibration methods of cone beam CT systems are divided into two types: phantom calibration and algorithm calibration: the phantom-based calibration method adopts a specially designed calibration phantom, obtains the geometric error parameters of the system during the calibration process, and These parameters are used for the hardware adjustment of the system or directly for later image reconstruction; the algorithm-based geometric calibration method directly processes the projection data or projection images, calculates the geometric error parameters of the CT system, and uses them in the reconstruction algorithm. Most of the existing geometric calibration methods for cone-beam CT systems are aimed at a single X-ray source. Among them, the phantom calibration method needs to design and process a high-precision phantom for geometric calibration of the imaging system. Due to the limited precision of the processed phantom, there are certain limitations on the calibration results. The algorithm calibration method usually needs to design a complex algorithm, and then calibrate the imaging geometric parameters through a series of calculations, and the calibrated geometric parameters are limited.

At present, the existing static cone-beam CT system based on an integrally packaged multi-beam X-ray source array also adopts the geometric calibration method of the above-mentioned single-light source cone-beam CT system. However, the static cone-beam CT system that adopts an integrally packaged multi-beam X-ray source array, since multiple X-ray sources are integrally packaged in the same tube, the above-mentioned geometric calibration method cannot be used for each independent multi-beam X-ray source array The geometric position of the emission source is calibrated, the scope of application is limited, and the calibration accuracy is low.

Contents of the invention

The invention provides a geometric calibration device and method for a static cone-beam CT imaging system, aiming at solving the problems of limited application range and low calibration accuracy of the existing static cone-beam CT imaging system geometric calibration methods.

In order to solve the above-mentioned technical problems, the present invention provides a static cone-beam CT imaging system geometric calibration device, the device is placed on an optical table, and the device includes several cold cathode X-ray tubes and a support frame:

Each of the cold cathode X-ray tubes is used as an X-ray emission source, and the support frame is used to install the cold cathode X-ray tubes, and the several cold cathode X-ray tubes are arranged in a line or arc to form Multi-beam X-ray source array; the support frame reserves adjustment space on the X, Y and Z axes, so that after the several cold cathode X-ray tubes are installed on the support frame, each of the cold cathode X-ray tubes The position of the cathode X-ray tube can be adjusted separately in the three directions of X, Y or Z axis.

Further, the device also includes a detector, a two-axis translation platform, a stage and a three-axis translation platform; the detector is mounted on the two-axis translation platform to realize the Y-axis and Z-axis Movement: the stage is used to place the scanning object, and is mounted on the three-axis translation platform, so that the scanning object can move in three directions along the X axis, Y axis and Z axis respectively.

Further, the plurality of cold-cathode X-ray tubes are arranged in a straight line and equidistant on the support frame in turn to form a linear multi-beam X-ray source array; the number of the plurality of cold-cathode X-ray tubes N, N is an odd number, and N>=15; with the (N+1)/2th cold cathode X-ray tube as the center, the cold cathode X-ray tubes on both sides are symmetrically distributed relative to the center .

Further, the angle range of the scanning object covered by the support frame is between 30° and 45°.

Further, the distance between the detector and the focal point of the tube at the center of the multi-beam X-ray source array is 60cm to 70cm; the distance between the center of the scanning object and the detector is 5cm to 10cm .

In order to solve the above-mentioned technical problems, the present invention also provides a geometric calibration method of a static cone-beam CT imaging system, the method adopts the above-mentioned static cone-beam CT imaging system geometric calibration device, and the method includes:

Step 1: Use the geometric calibration device of the static cone beam CT imaging system to control the movement of the three-axis translation stage carrying the block-scale body along the X-axis, Y-axis and Z-axis directions, and control the X-ray source array center X-ray The source is exposed, and according to the position of the block-scale object collected by the detector on the projected image, the position of the two-axis translation stage equipped with the detector in the Y-axis direction and the Z-axis direction is adjusted to complete the calibration of the geometric center position of the imaging;

Step 2: Using the geometric calibration device of the static cone-beam CT imaging system, by controlling the movement of the three-axis translation stage carrying the block-scale body along the X-axis direction, the Y-axis direction and the Z-axis direction, and controlling the movement of the two X-ray sources distributed in the center Each tube on the side is exposed separately, and according to the position of the block-scale body on the projection image acquired by the detector each time, adjust the positions of the tubes distributed on both sides of the central X-ray source along the X, Y, and Z directions. position to complete the calibration of the focus distribution of each X-ray source.

Further, the method also includes step 3:

Step 3: Using the geometric calibration device of the static cone-beam CT imaging system, by adjusting the position of the three-axis translation stage carrying the small ball phantom along the Y-axis direction and the Z-axis direction, the center of the small ball phantom is obtained at the The distance parameter 1 and the distance parameter 2 from the projected position on the detector to the center of the detector, and according to the distance parameter 1 and the distance parameter 2, and the preset formula to calculate the geometric parameters SOD and SID of the imaging system; wherein , SOD represents the distance from the center position of the multi-beam X-ray source to the scanned object, and SID represents the distance from the center position of the multi-beam X-ray source to the detector.

Compared with the prior art, the present invention has the beneficial effects of:

The invention provides a static cone-beam CT imaging system geometric calibration device, which includes several cold cathode X-ray tubes and a support frame. Several cold-cathode X-ray tubes are arranged in a line or arc to form a multi-beam X-ray source array, in which each cold-cathode X-ray tube is used as an X-ray emission source; the support frame is used to install the cold-cathode X-ray ball Tube, and reserve adjustment space on the X, Y and Z axes, so that after the several cold cathode X-ray tubes are installed on the support frame, the position of each cold cathode X-ray tube can be realized in X , Y or Z axis are adjusted in three directions respectively. By adjusting each cold cathode X-ray tube in the three directions of X, Y or Z axis, the precise calibration of the geometric position of each X-ray source is realized, with extremely high calibration accuracy.

Description of drawings

Fig. 1 is a schematic diagram of a static cone-beam CT imaging system geometric calibration device provided by the first embodiment of the present invention;

2 is a schematic diagram of a support frame of a geometric calibration device for a static cone-beam CT imaging system provided by the first embodiment of the present invention;

3 is a schematic diagram of a cold-cathode X-ray tube of a geometric calibration device for a static cone-beam CT imaging system provided by the first embodiment of the present invention;

Fig. 4 is a flow chart of a static cone-beam CT imaging system geometric calibration method provided by the second embodiment of the present invention;

Fig. 5 is a flow chart of step S1 of a static cone beam CT imaging system geometric calibration method provided by the third embodiment of the present invention;

Fig. 6 is a flow chart of step S2 of a static cone beam CT imaging system geometric calibration method provided by the third embodiment of the present invention;

Fig. 7 is a flow chart of step S3 of a static cone-beam CT imaging system geometric calibration method provided by the third embodiment of the present invention;

Fig. 8 is a schematic parameter diagram of a geometric calibration method for a static cone-beam CT imaging system provided by the third embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

As the first embodiment of the present invention, as shown in Figure 1, a static cone beam CT imaging system geometric calibration device provided by the present invention, the device is placed on the optical table, the device includes several cold cathode X-ray spheres Tube 20 and support frame 10:

Each cold cathode X-ray tube 20 is used as an X-ray emission source (hereinafter referred to as X-ray source), and the support frame 10 (as shown in Figure 2, is a schematic diagram of the support frame 10) is used to install the cold cathode X-ray tube, Several cold-cathode X-ray tubes 20 are arranged in a line or in an arc to form a multi-beam X-ray source array (shown as a line in this embodiment). As shown in Figure 2, several cold cathode X-ray tubes 20 are installed on the support frame 10, and the support frame 10 has reserved adjustment space on the X, Y and Z axes respectively, so that several cold cathode X-ray bulbs After the tube 20 is installed on the support frame 10, the position of each cold cathode X-ray tube can be adjusted in three directions of X, Y or Z axis respectively. D shown in FIG. 1 represents a standard Cartesian rectangular coordinate system, and X, Y, and Z are the three axes of the spatial rectangular coordinate system.

In this embodiment, on the basis of designing the support frame 10 and the cold cathode X-ray tube 20, the device also includes a detector 40 for detecting X-rays, a two-axis displacement table 50, a stage 30 and a three-axis displacement Stage 60: The detector 40 is mounted on a two-axis displacement stage 50 (not shown in FIG. 1 ) to move in the Y-axis and Z-axis directions respectively; The axial displacement stage 60 (not shown in FIG. 1 ) enables the scanning object to move in three directions along the X-axis, Y-axis and Z-axis respectively. In this embodiment, the detector 40 is a digital flat panel detector (such as ASX-2430 amorphous selenium digital flat panel detector from Analogic).

Several cold-cathode X-ray tubes 20 are arranged on the support frame 10 in a straight line and equidistant in order to form a linear multi-beam X-ray source array; the number of several cold-cathode X-ray tubes is N, and N is an odd number , and N>=15; with the (N+1)/2th cold-cathode X-ray tube as the center, the cold-cathode X-ray tubes on both sides should be symmetrically distributed relative to the center. As shown in Figure 3, the center 204 is the center of the cold cathode X-ray tube, the tubes 205 and 203 are symmetrical to 204, the tubes 206 and 202 are symmetrical to 204, and the tubes 207 and 201 are symmetrical to 204 .

In addition, in order to make the device have better operability and optimize the calibration process, the angle range of the scanning object covered by the support frame 10 should be controlled between 30° and 45°; the center of the detector 40 and the multi-beam X-ray source array The distance between the focal points of the position tubes (204 in Fig. 3 ) should be 60cm to 70cm; the distance between the center of the scanned object and the detector 40 should be 5cm to 10cm.

In summary, the static cone-beam CT imaging system geometric calibration device provided by the first embodiment of the present invention realizes The precise calibration of the geometric position of each X-ray source has extremely high calibration accuracy.

As the second embodiment of the present invention, as shown in Figure 4, the present invention provides a static cone-beam CT imaging system geometric calibration method, which requires the use of the static cone-beam CT imaging provided by the first embodiment above System geometry calibration device, the method comprises the following steps:

Step S1: Using the geometric calibration device of the above-mentioned static cone beam CT imaging system, by controlling the movement of the three-axis translation stage carrying the block-scale body along the X-axis direction, the Y-axis direction and the Z-axis direction, and controlling the X-ray source in the center of the X-ray source array Perform exposure, and adjust the position of the two-axis translation stage equipped with the detector in the Y-axis direction and the Z-axis direction according to the position of the block-scale body collected by the detector on the projected image, so as to complete the calibration of the geometric center position of the imaging (ie Calibration of the center of the multi-beam X-ray source array and the center of the detector imaging plane).

It should be noted that the static cone-beam CT imaging system geometric calibration device provided by the first embodiment of the present invention has preliminarily assembled the X-ray source tubes of the multi-beam X-ray source array into a linear and equidistant distribution, but due to the There are certain errors in the tube machining accuracy and assembly process, so in the actual use process, it is also necessary to accurately calibrate the focus position along the X-axis, Y-axis and Z-axis directions, so the following step S2 is required.

Step S2: Using the geometric calibration device of the above-mentioned static cone beam CT imaging system, by controlling the movement of the three-axis translation stage carrying the block-scale body along the X-axis direction, the Y-axis direction and the Z-axis direction, and controlling the distribution on both sides of the central X-ray source Each tube is exposed separately, and the position of the tubes distributed on both sides of the central X-ray source along the X, Y, and Z directions is adjusted according to the position of the block-scale body on the projection image acquired by the detector each time. , to complete the calibration of the focus distribution of each X-ray source. After the calibration of the multi-beam X-ray source array is completed, the imaging geometric parameters can also be calculated, and the method provided by this embodiment further includes step S3.

Step S3: Using the geometric calibration device of the above-mentioned static cone beam CT imaging system, by adjusting the position of the three-axis translation stage carrying the small ball phantom in the Y-axis direction and the Z-axis direction, obtain the center of the small ball phantom in the detection The distance parameter 1 and the distance parameter 2 from the projected position on the detector to the center of the detector are calculated according to the distance parameter 1 and distance parameter 2, and preset formulas to obtain the geometric parameters SOD and SID of the imaging system. Wherein, SOD represents the distance from the center position of the multi-beam X-ray source to the scanned object, and SID represents the distance from the center position of the multi-beam X-ray source to the detector.

In summary, the method provided by the second embodiment of the present invention utilizes the geometric calibration device of the static cone beam CT imaging system, and the support frame reserves a certain position for each ball tube installed separately in X, Y, and Z three directions. Axial adjustment, so that the focus distribution of the multi-beam X-ray source, the center of the multi-beam X-ray source array and the center position of the detector imaging plane can be calibrated, and each independent emission source in the packaged X-ray source array can be realized The geometric position is calibrated, the calibration accuracy is high, and the calibration parameters can be obtained through simple calculation.

As the third embodiment of the present invention, as shown in FIG. 4 , this embodiment also provides a geometric calibration method for a static cone-beam CT imaging system. On the basis of the above-mentioned second embodiment, each step Refinement is carried out, the method needs to adopt the static cone-beam CT imaging system geometric calibration device provided by the first embodiment above, and the method includes the following steps:

Step S1: Using the geometric calibration device of the above-mentioned static cone beam CT imaging system, by controlling the movement of the three-axis translation stage carrying the block-scale body along the X-axis direction, the Y-axis direction and the Z-axis direction, and controlling the X-ray source in the center of the X-ray source array Perform exposure, and adjust the position of the two-axis translation stage equipped with the detector in the Y-axis direction and the Z-axis direction according to the position of the block-scale body collected by the detector on the projected image, so as to complete the calibration of the geometric center position of the imaging (ie Calibration of the center of the multi-beam X-ray source array and the center of the detector imaging plane). As shown in Figure 5, step S1 includes the following steps S101 to S118:

Step S101: Determine the height of the focal point of the tube at the center of the multi-beam X-ray source array relative to the height of the optical table, control the two-axis translation stage equipped with the detector to move along the Z-axis direction, and adjust the height of the central row of the detector relative to the height of the optical table It is approximately consistent with the focus height/Z coordinate of the tube at the central position of the multi-beam X-ray source array (that is, adjusted so that the central row of the detector and the central focus of the multi-beam X-ray source array are approximately equal in the Z-axis direction).

Step S102: By measuring and determining the Y coordinate of the focal point of the tube at the center position of the multi-beam X-ray source array, respectively control the three-axis translation stage equipped with a block-scale body and the two-axis translation stage equipped with a detector to move along the Y-axis direction, and adjust the loading The Y coordinate of the center of the stage and the Y coordinate of the detector center column of the block-scale body are approximately consistent with the Y coordinate of the focal point of the tube at the center of the multi-beam X-ray source array.

It should be noted that the stage is used to place the scanning object. In this embodiment, when performing calibration, a standard block-scale body is used as the scanning object and placed on the stage so that the block-scale body can be used for calibration. The present invention can be calibrated by adopting block scale bodies of various standard models, does not need to specially design a calibration model body, and is simpler than the traditional model body calibration method.

The above-mentioned steps S101 and S102 are the process of completing the rough adjustment first, and the processes of the following steps S103 to S118 are fine adjustment processes. Wherein, the precise calibration of the center of the multi-beam X-ray source array and the center column of detectors is completed through the following steps S103 to S110.

Step S103: Control the three-axis translation platform carrying the block-scale body to move along the X-axis direction, and at the same time adjust the position of the block-scale body along the Y-axis direction by controlling the three-axis translation platform.

Step S104: Turn on the X-ray source in the center of the X-ray source array (that is, the (N+1)/2th cold-cathode X-ray tube in the center involved in the first embodiment, the same below) for exposure.

Step S105: collect the exposure image by the detector, and judge (observe) according to the exposure image whether the projected column position of the left edge/right edge (left edge or right edge) of the block scale body on the detector remains constant.

Step S106: If not, return to execute steps S103 to S105 until the position of the projected column of the left edge/right edge of the block-scale body on the detector remains unchanged.

Step S107: Controlling the two-axis translation stage equipped with the detector to move along the Y-axis direction.

Step S108: Turn on the X-ray source at the center of the X-ray source array for exposure.

Step S109: collect an exposure image through the detector, and judge according to the exposure image whether the projection column of the left edge/right edge of the scale body on the detector coincides with the position of the center column of the detector .

Step S110: If not, return to execute steps S107 to S109 until the projection column of the left edge/right edge of the block-scale body on the detector coincides with the center column of the detector to complete the The center of the multi-beam X-ray source array is aligned with the detector center column.

Accurate calibration of the center of the multi-beam X-ray source array and the central row of detectors is completed through the following steps S103 to S110.

Step S111 : controlling the three-axis translation platform carrying the scale body to move along the X-axis direction, and simultaneously adjusting the position of the scale body along the Z-axis direction.

Step S112: Turn on the X-ray source at the center of the X-ray source array for exposure.

Step S113: collecting an exposure image by the detector, and judging according to the exposure image whether the projection line position of the upper surface of the scale body on the detector remains unchanged.

Step S114: If not, return to execute steps S111 to S113 until the projected line position of the upper surface of the block-scale body on the detector remains unchanged.

Step S115: Controlling the two-axis translation stage equipped with the detector to move along the Z-axis direction.

Step S116: Turn on the X-ray source at the center of the X-ray source array for exposure.

Step S117: collecting an exposure image through the detector, and judging according to the exposure image whether the projection line of the upper surface of the scale body on the detector coincides with the central row of the detector.

Step S118: If not, return to execute steps S115 to S117 until the projection line of the upper surface of the block-scale body on the detector coincides with the center line of the detector to complete the multi-beam X The center of the ray source array is aligned with the center of the detector.

The above-mentioned process of S101-S118 first completes the calibration of the imaging geometric center position.

Step S2: Using the geometric calibration device of the above-mentioned static cone beam CT imaging system, by controlling the movement of the three-axis translation stage carrying the block-scale body along the X-axis direction, the Y-axis direction and the Z-axis direction, and controlling the distribution on both sides of the central X-ray source Each tube is exposed separately, and the position of the tubes distributed on both sides of the central X-ray source along the X, Y, and Z directions is adjusted according to the position of the block-scale body on the projection image acquired by the detector each time. , to complete the calibration of the focus distribution of each X-ray source. As shown in Figure 6, step S2 specifically includes the following steps S201 to S219:

First, the following steps S201 to S204 are based on the focus position of the X-ray source at the center of the multi-beam X-ray source array, and adjust the positions of the X-ray sources distributed on both sides of the center along the Z-axis direction.

Step S201: According to the final position of the block size between the center of the multi-beam X-ray source array and the center row of the detector in step S118 (for calibration), turn on the X-ray source at the center of the X-ray source array for exposure, so that the block size The projection line of the upper surface of the body on the detector coincides with the position of the central line of the detector.

Step S202: Turn on a bulb distributed on both sides of the X-ray source at the central position for exposure, collect the exposure image of the block-scale body under the current X-ray source through the detector, and judge the current block according to the exposure image Whether the position of the projection line of the upper surface of the scale body on the detector coincides with the position of the central line of the detector.

Step S203: If they do not overlap, fine-tune the current cold cathode X-ray tube along the Z-axis direction, and repeat Step S202 until the position of the projected line on the detector on the upper surface of the block-scale body is determined to be the same as the The positions of the central rows of the detectors coincide to complete the adjustment of the focus of the current X-ray source along the Z-axis direction.

Step S204: According to the operations of steps S202 to S203, the adjustment of all X-ray source focal points on both sides of the X-ray source at the central position of the X-ray source array along the Z axis direction is completed in sequence, so that the Z of all X-ray source focal points The coordinates are the same (that is, the heights of the focal points of each X-ray source are consistent).

The following steps S205 to S208 are based on the focus position of the X-ray source at the center of the multi-beam X-ray source array, and adjust the positions of the X-ray sources distributed on both sides of the center along the X-axis direction.

Step S205: According to the final position of the block-scale volume between the center of the multi-beam X-ray source array and the center row of the detector in step S118, turn on the ray source at the center position of the X-ray source array for exposure, and record that the lower surface of the block-scale volume is on the detector The location of the projected row.

Step S206: Turn on a bulb distributed on both sides of the X-ray source at the central position for exposure, collect the exposure image of the block-scale body under the current X-ray source through the detector, and judge the current block according to the exposure image Whether the position of the projection line of the lower surface of the scale body on the detector is the same as the position of the projection line of the lower surface of the scale body on the detector recorded in step S205 when the central position of the X-ray source is exposed.

Step S207: If not the same, fine-tune the current cold cathode X-ray tube along the X-axis direction, and repeat step S206 until the position of the projection line of the lower surface of the current scale body on the detector is determined to be the same as that in step S205 The position of the projected line on the lower surface of the block scale body on the detector when the X-ray source at the recorded central position is exposed is the same, so as to complete the adjustment of the focus of the current X-ray source along the X-axis direction.

Step S208: According to the operations of steps S206 to S207, the adjustment of all X-ray source focal points on both sides of the X-ray source at the central position of the X-ray source array along the X-axis direction is completed in sequence, so that the X-ray source focal points of all X-ray source The coordinates are the same (that is, the distances from the focus of each X-ray source to the imaging plane of the detector are the same).

The following steps S209 to S219 are based on the focus position of the X-ray source at the center of the multi-beam X-ray source array, and adjust the equidistant distribution of the tubes distributed on both sides of the central X-ray source along the linear array.

Step S209: Control the three-axis translation stage equipped with a block-scale body and the two-axis translation platform equipped with a detector to move along the positive direction of the Y-axis respectively, and the moving distance is the preset theory between the focus positions of two adjacent X-ray sources distance. The preset theoretical distance refers to a relatively reasonable distance predefined in practical applications, for example, the preset theoretical distance between every two adjacent X-ray source focus positions is set to 5 cm.

Step S210: Turn on the i-th X-ray source to the left of the X-ray source at the central position (along the positive direction of the Y axis, the same below) for exposure, and the initial value of i is 1.

Step S211: collecting an exposure image by the detector, and judging according to the exposure image whether the projection column position of the left edge of the block-scale body on the detector coincides with the central column position of the detector.

Step S212: If there is no coincidence, fine-tune the current cold-cathode X-ray tube along the Y-axis direction, and return to steps S210 to S211 until the projection of the left edge of the block scale on the detector is determined The column position coincides with the detector center column position.

Step S213: Let i=i+1, and according to the operation method of steps S209 to S212, complete the adjustment of all X-ray sources on the left side of the X-ray source at the central position in sequence, so that all X-ray sources on the left side The Y-axis direction is equidistantly distributed. It should be noted that, in this step, when operating the i-th X-ray source on the left side of the X-ray source at the central position, the distance moved in step S209 is i times the theoretical distance of the adjacent focal point, and the X-ray exposure in step S210 is the i-th X-ray source on the current left.

Step S214: (after the calibration of the X-ray tubes distributed on the left side is completed) control the two-axis translation stage equipped with the detector to return to the calibration position corresponding to the cold cathode X-ray tube at the center position (that is, after the multi-beam The position when the center of the X-ray source array is aligned with the center column of the detector).

Step S215: Control the three-axis translation stage equipped with a block-scale body and the two-axis translation platform equipped with a detector to move in the opposite direction of the Y-axis respectively, and the moving distance is the predetermined distance between the focus positions of two adjacent X-ray sources. Set the theoretical distance.

Step S216: Turn on the jth X-ray source on the right side of the X-ray source at the central position (in the opposite direction along the Y axis, the same below) for exposure, and the initial value of j is 1.

Step S217: collecting an exposure image by the detector, and judging according to the exposure image whether the projected column position of the right edge of the scale body on the detector coincides with the central column position of the detector.

Step S218: If there is no coincidence, fine-tune the current cold-cathode X-ray tube along the Y-axis direction, and return to steps S215 to S216 until the projection of the right edge of the block scale on the detector is determined The column position coincides with the detector center column position.

Step S219: set j=j+1, and complete the adjustment of all X-ray sources on the right side of the X-ray source at the central position in sequence according to the operation method of steps S215 to S218, so that all X-ray sources on the right side are adjusted along the The Y-axis direction is equidistantly distributed. It should be noted that when operating on the jth X-ray source on the right, the distance moved in step S216 is j times the theoretical distance of the adjacent focal point, and the X-rays exposed in step S219 are the current j-th X-ray source on the right .

It should be noted that, in the process of adjusting and calibrating the tubes distributed on both sides of the central X-ray source along the equidistant distribution of the linear array in steps S209 to S219, as mentioned above, the tubes on the left side of the central tube can be firstly adjusted. Calibrate one by one (S209 to S214), then control the two-axis translation stage equipped with the detector to return to the center position, and then perform one-by-one calibration on the tubes on the right side of the center tube (S215 to S219); and in the actual application process , you can also calibrate the right side first, and then calibrate the left side, that is, first execute S215 to S219, then control the two-axis translation stage equipped with the detector to return to the center position, and then execute S209 to S214. The calibration sequence does not Not limited by this embodiment, different calibration sequences also belong to the protection scope of the present invention.

Through the above process, the precise calibration of the focus of the multi-beam X-ray source in the X, Y, and Z-axis directions is completed, that is, the calibration of the focus position distribution of the multi-beam X-ray source is realized. The present invention performs geometric calibration on the focus position of each independent emission source in the multi-beam X-ray source array, and has higher precision compared with the traditional method that can only calibrate the entire X-ray source array.

Step S3: Using the geometric calibration device of the above-mentioned static cone beam CT imaging system, by adjusting the position of the three-axis translation stage carrying the small ball phantom in the Y-axis direction and the Z-axis direction, obtain the center of the small ball phantom in the detection The distance parameter 1 and the distance parameter 2 from the projected position on the detector to the center of the detector are calculated according to the distance parameter 1 and distance parameter 2, and preset formulas to obtain the geometric parameters SOD and SID of the imaging system. Wherein, SOD represents the distance from the center position of the multi-beam X-ray source to the scanned object, and SID represents the distance from the center position of the multi-beam X-ray source to the detector. As shown in FIG. 8 , the meanings of the parameters in step S3 are marked. As shown in Figure 7, step 3 specifically includes the following steps S301 to S304:

Step S301: Place the small ball phantom at the center of the stage, and control the three-axis translation stage carrying the small ball phantom to move along the Y-axis and Z-axis directions until the center X-ray source exposure image collected by the detector is small The projection of the center of the spherical phantom on the detector coincides with the center of the imaging plane of the detector.

Step S302: Turn on any X-ray source on the left and right sides of the X-ray source at the central position for exposure, and obtain the distance parameter - l ₁ .

Step S303: Control the three-axis translation stage carrying the ball to move a distance a in the opposite direction of the X-axis, turn on the same X-ray source as in step S302 for exposure, and obtain the projection of the center of the ball phantom on the detector The distance parameter from the position to the center of the detector is l ₂ .

Step S304: Solve the following equations to obtain the distance SID from the center position of the X-ray source array to the detector and the distance SOD to the scanning object.

Wherein, l ₁ represents the distance parameter one from the projected position of the center of the small spherical phantom on the detector to the center of the detector, and l ₂ represents the projected position of the center of the small spherical phantom on the detector Distance parameter 2 to the center of the detector, S represents the distance between the focal point of the X-ray source at the central position and the focal point of the X-ray source selected in step S302 for exposure.

Compared with the algorithm calibration method, the present invention does not need to design an algorithm to obtain the calibration parameters through a large number of calculations, but directly obtains the calibration parameters through simple calculation of the projected displacement of the phantom collected through experiments.

In summary, the method provided by the third embodiment of the present invention uses the geometric calibration device of the static cone-beam CT imaging system, adopts standard block-scale phantoms and small ball phantoms, and can adjust the focus distribution of multi-beam X-ray sources, multi-beam X-ray source The center of the X-ray source array and the center of the detector imaging plane are calibrated, and the geometric position of each independent emission source in the packaged X-ray source array can be calibrated. The calibration accuracy is high, and the calibration parameters can be obtained by simple calculation.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention within.

Claims (7)

1. A static cone-beam CT imaging system geometric calibration device, the device is placed on the optical table, it is characterized in that the device includes several cold cathode X-ray bulbs and a support frame: Each of the cold cathode X-ray tubes is used as an X-ray emission source, and the support frame is used to install the cold cathode X-ray tubes, and the several cold cathode X-ray tubes are arranged in a line or arc to form Multi-beam X-ray source array; The support frame reserves adjustment space on the X, Y and Z axes, so that after the several cold cathode X-ray tubes are installed on the support frame, the position of each cold cathode X-ray tube can be adjusted. Realize adjustments in the three directions of X, Y or Z axis respectively; among them, the X axis direction refers to the left and right direction, the Y axis direction refers to the front and rear direction, and the Z axis direction refers to the up and down direction; The device also includes a detector, a two-axis displacement platform, an object stage and a three-axis displacement platform; The detector is mounted on the two-axis translation platform to realize the movement in the Y-axis and Z-axis directions respectively; The stage is used to place the scanning object, and is mounted on the three-axis translation stage, so that the scanning object can move in three directions along the X axis, Y axis and Z axis respectively; The device is used in particular for: Step 101: Determine the height of the focal point of the tube at the center of the multi-beam X-ray source array relative to the optical table by measuring, control the two-axis translation stage equipped with the detector to move along the Z-axis direction, and adjust the height of the central row of the detector relative to the optical table The height is consistent with the focus height of the tube at the center of the multi-beam X-ray source array; Step 102: Determine the Y coordinate of the focal point of the tube at the center position of the multi-beam X-ray source array by measuring, respectively control the three-axis translation stage equipped with a block-scale body and the two-axis translation stage equipped with a detector to move along the Y-axis direction, and adjust the loading The Y coordinate of the stage center of the block-scale body and the Y coordinate of the center column of the detector are consistent with the focus Y coordinate of the ball tube at the center position of the multi-beam X-ray source array; Step 103: Control the three-axis translation platform carrying the block-scale body to move along the X-axis direction, and at the same time adjust the position of the block-scale body along the Y-axis direction by controlling the three-axis translation platform; Step 104: Turn on the X-ray source at the center of the X-ray source array for exposure; Step 105: collecting an exposure image by the detector, and judging according to the exposure image whether the projected column position of the left edge/right edge of the block-scale body on the detector remains unchanged; Step 106: If not, return to execute steps 103 to 105 until the projected position of the left edge/right edge of the block-scale body on the detector remains unchanged; Step 107: Controlling the two-axis translation platform equipped with the detector to move along the Y-axis direction; Step 108: Turn on the X-ray source at the center of the X-ray source array for exposure; Step 109: collect the exposure image through the detector, and judge according to the exposure image whether the projection column of the left edge/right edge of the scale body on the detector coincides with the position of the center column of the detector ; Step 110: If not, go back and execute steps 107 to 109 until the projection column of the left edge/right edge of the block-scale body on the detector coincides with the position of the center column of the detector, so as to complete the The center of the multi-beam X-ray source array is aligned with the center column of the detector; Step 111: Control the three-axis translation platform carrying the block scale body to move along the X-axis direction, and adjust the position of the block scale body along the Z-axis direction at the same time; Step 112: Turn on the X-ray source at the center of the X-ray source array for exposure; Step 113: collecting an exposure image by the detector, and judging according to the exposure image whether the position of the projection line of the upper surface of the scale body on the detector remains unchanged; Step 114: If not, return to execute steps 111 to 113 until the position of the projection line of the upper surface of the block-scale body on the detector remains unchanged; Step 115: controlling the two-axis translation platform equipped with the detector to move along the Z-axis direction; Step 116: Turn on the X-ray source at the center of the X-ray source array for exposure; Step 117: collecting an exposure image through the detector, and judging according to the exposure image whether the projection line of the upper surface of the scale body on the detector coincides with the central row of the detector; Step 118: If not, return to execute steps 115 to 117 until the projection line of the upper surface of the block-scale body on the detector coincides with the center line of the detector to complete the multi-beam X The center of the ray source array is aligned with the center of the detector. 2. The device according to claim 1, wherein the plurality of cold-cathode X-ray tubes are arranged in a straight line and equidistantly on the support frame to form a linear multi-beam X-ray source array; The number of the cold cathode X-ray tubes is N, N is an odd number, and N 15; With the (N+1)/2th cold-cathode X-ray tube as the center, the cold-cathode X-ray tubes on both sides are symmetrically distributed relative to the center. 3 . The device according to claim 1 , wherein the angle range of the scanning object covered by the support frame is between 30° and 45°. 4. The device according to claim 1, wherein the distance between the detector and the focal point of the tube at the center of the multi-beam X-ray source array is 60cm to 70cm; The distance between the center of the scanning object and the detector is 5cm to 10cm. 5. A static cone-beam CT imaging system geometric calibration method, characterized in that the method uses the static cone-beam CT imaging system geometric calibration device according to any one of claims 1 to 4, the method comprising: Step 1: Use the geometric calibration device of the static cone beam CT imaging system to control the movement of the three-axis translation stage carrying the block-scale body along the X-axis, Y-axis and Z-axis directions, and control the X-ray source array center X-ray The source is exposed, and according to the position of the block-scale object collected by the detector on the projected image, the position of the two-axis translation stage equipped with the detector in the Y-axis direction and the Z-axis direction is adjusted to complete the calibration of the geometric center position of the imaging; Step 2: Using the geometric calibration device of the static cone-beam CT imaging system, by controlling the movement of the three-axis translation stage carrying the block-scale body along the X-axis direction, the Y-axis direction and the Z-axis direction, and controlling the movement of the two X-ray sources distributed in the center Each tube on the side is exposed separately, and according to the position of the block-scale body on the projection image acquired by the detector each time, adjust the positions of the tubes distributed on both sides of the central X-ray source along the X, Y, and Z directions. position, to complete the calibration of the focus distribution of each X-ray source; wherein, the X-axis direction refers to the left-right direction, the Y-axis direction refers to the front-to-back direction, and the Z-axis direction refers to the up-down direction; The step 1 specifically includes the following steps: Step A: Determine the height of the focal point of the tube at the center of the multi-beam X-ray source array relative to the optical table by measuring, control the two-axis translation stage equipped with the detector to move along the Z-axis direction, and adjust the height of the central row of the detector relative to the optical table The height is consistent with the focus height of the tube at the center of the multi-beam X-ray source array; Step B: Determine the Y coordinate of the focal point of the tube at the center of the multi-beam X-ray source array by measuring, respectively control the three-axis translation stage equipped with a block-scale body and the two-axis translation stage equipped with a detector to move along the Y-axis direction, and adjust the loading The Y coordinate of the stage center of the block-scale body and the Y coordinate of the center column of the detector are consistent with the focus Y coordinate of the ball tube at the center position of the multi-beam X-ray source array; Step C1: Control the three-axis translation platform carrying the block-scale body to move along the X-axis direction, and at the same time adjust the position of the block-scale body along the Y-axis direction by controlling the three-axis translation table; Step C2: Turn on the X-ray source at the center of the X-ray source array for exposure; Step C3: collect the exposure image by the detector, and judge whether the projected column position of the left edge/right edge of the block-scale body on the detector remains unchanged according to the exposure image; Step C4: If not, return to execute steps C1 to C3 until the projected position of the left edge/right edge of the block-scale body on the detector remains unchanged; Step C5: controlling the two-axis translation stage equipped with the detector to move along the Y-axis direction; Step C6: Turn on the X-ray source at the center of the X-ray source array for exposure; Step C7: collect the exposure image through the detector, and judge according to the exposure image whether the projection column of the left edge/right edge of the scale body on the detector coincides with the central column position of the detector ; Step C8: If not, go back and execute steps C5 to C7 until the projection column of the left edge/right edge of the block-scale body on the detector coincides with the position of the center column of the detector, so as to complete the The center of the multi-beam X-ray source array is aligned with the center column of the detector; Step D1: Control the three-axis translation platform carrying the block scale body to move along the X-axis direction, and adjust the position of the block scale body along the Z-axis direction at the same time; Step D2: Turn on the X-ray source at the center of the X-ray source array for exposure; Step D3: collecting an exposure image by the detector, and judging according to the exposure image whether the position of the projection line of the upper surface of the scale body on the detector remains unchanged; Step D4: If not, return to execute steps D1 to D3 until the projection line position of the upper surface of the block-scale body on the detector remains unchanged; Step D5: controlling the two-axis translation stage equipped with the detector to move along the Z-axis direction; Step D6: Turn on the X-ray source at the center of the X-ray source array for exposure; Step D7: collecting an exposure image through the detector, and judging according to the exposure image whether the projection line of the upper surface of the scale body on the detector coincides with the central row of the detector; Step D8: If not, go back and execute steps D5 to D7 until the projection line of the upper surface of the block-scale body on the detector coincides with the central row of the detector, so as to complete the multi-beam X The center of the ray source array is aligned with the center of the detector. 6. The method according to claim 5, wherein said step 2 specifically comprises the following steps: Step E1: According to the final position of the multi-beam X-ray source array center and the detector center row in step D8, turn on the X-ray source at the center of the X-ray source array for exposure, so that the upper surface of the block scale body is at The projection line on the detector coincides with the position of the central line of the detector; Step E2: Turn on a bulb distributed on both sides of the X-ray source at the central position for exposure, collect the exposure image of the block-scale body under the current X-ray source through the detector, and judge the current block according to the exposure image Whether the position of the projected row on the detector on the upper surface of the scale coincides with the position of the central row of the detector; Step E3: If there is no coincidence, fine-tune the current cold-cathode X-ray tube along the Z-axis direction, and repeat Step E2 until the position of the projected line on the detector on the upper surface of the block-scale body is determined to be the same as the position on the detector. The positions of the center rows of the detectors coincide to complete the adjustment of the focus of the current X-ray source along the Z-axis direction; Step E4: According to the operations of steps E2 to E3, the adjustment of all X-ray source focal points on both sides of the X-ray source at the central position of the X-ray source array along the Z axis direction is completed in sequence, so that the Z of all X-ray source focal points the same coordinates; Step F1: According to the final position of the block-scale volume between the center of the multi-beam X-ray source array and the center row of the detector in step D8, turn on the radiation source at the center of the X-ray source array for exposure, and record the lower surface of the block-scale volume on the detector the location of the projected row; Step F2: Turn on a bulb distributed on both sides of the X-ray source at the center for exposure, collect the exposure image of the block-scale body under the current X-ray source through the detector, and judge the current block according to the exposure image Whether the position of the projection line of the lower surface of the scale body on the detector is the same as the position of the projection line of the lower surface of the scale body on the detector when the X-ray source at the central position recorded in step F1 is exposed; Step F3: If not the same, fine-tune the current cold-cathode X-ray tube along the X-axis direction, and repeat Step F2 until the position of the projection line of the lower surface of the current block-scale body on the detector is determined to be the same as that in Step F1 The position of the projected line on the lower surface of the block scale body on the detector when the X-ray source at the recorded central position is exposed is the same, so as to complete the adjustment of the focus of the current X-ray source along the X-axis direction; Step F4: According to the operations of steps F2 to F3, the adjustment of all X-ray source focal points on both sides of the X-ray source at the center of the X-ray source array along the X-axis direction is completed in sequence, so that the X-ray source focal points of all X-ray source the same coordinates; Step G1: Control the three-axis translation stage equipped with a block-scale body and the two-axis translation platform equipped with a detector to move along the positive direction of the Y-axis respectively, and the moving distance is the preset theory between the focus positions of two adjacent X-ray sources distance; Step G2: Turn on the i-th X-ray source on the left side of the X-ray source at the central position for exposure, and the initial value of i is 1; Step G3: collecting an exposure image by the detector, and judging according to the exposure image whether the position of the projection column of the left edge of the block-scale body on the detector coincides with the position of the central column of the detector; Step G4: If not coincident, fine-tune the current cold-cathode X-ray tube along the Y-axis direction, and return to steps G2 to G3 until the projection of the left edge of the block-scale body on the detector is determined The column position coincides with the central column position of the detector; Step G5: Let i=i+1, and follow the operation methods of steps G1 to G4, and complete the adjustment of all X-ray sources on the left side of the X-ray source at the central position in order, so that all X-ray sources on the left side Equidistant distribution in the Y-axis direction; Step G6: Controlling the two-axis translation stage equipped with the detector to return to the calibration position corresponding to the cold cathode X-ray tube at the center position; Step G7: Control the three-axis translation stage equipped with a block-scale body and the two-axis translation platform equipped with a detector to move in the opposite direction of the Y-axis respectively, and the moving distance is the predetermined distance between the focus positions of two adjacent X-ray sources. set theoretical distance; Step G8: Turn on the jth X-ray source on the right side of the X-ray source at the central position for exposure, and the initial value of j is 1; Step G9: collecting an exposure image by the detector, and judging according to the exposure image whether the position of the projection column of the right edge of the scale body on the detector coincides with the position of the central column of the detector; Step G10: If not coincident, fine-tune the current cold-cathode X-ray tube along the Y-axis direction, and return to steps G7 to G8 until the projection of the right edge of the block-scale body on the detector is determined The column position coincides with the central column position of the detector; Step G11: set j=j+1, and complete the adjustment of all X-ray sources on the right side of the X-ray source at the central position in sequence according to the operation method of steps G7 to G10, so that all X-ray sources on the right The Y-axis direction is equidistantly distributed. 7. The method of claim 5, further comprising: Step 3: Using the geometric calibration device of the static cone-beam CT imaging system, by adjusting the position of the three-axis translation stage carrying the small ball phantom along the Y-axis direction and the Z-axis direction, the center of the small ball phantom is obtained at the The distance parameter 1 and the distance parameter 2 from the projected position on the detector to the center of the detector, and according to the distance parameter 1 and the distance parameter 2, and the preset formula to calculate the geometric parameters SOD and SID of the imaging system; wherein , SOD represents the distance from the center position of the multi-beam X-ray source to the scanned object, and SID represents the distance from the center position of the multi-beam X-ray source to the detector; The step 3 specifically includes: Step H1: The small ball phantom is placed in the center of the stage, and the three-axis translation stage carrying the small ball phantom is controlled to move along the Y-axis and Z-axis directions until the central X-ray source exposure image collected by the detector Until the projection of the center of the small and medium-sized spherical phantom on the detector coincides with the center of the imaging plane of the detector; Step H2: Turn on any X-ray source on the left and right sides of the X-ray source at the central position for exposure, and obtain the distance parameter from the projected position of the center of the spherical phantom on the detector to the center of the detector. count one; Step H3: Control the movement distance of the three-axis translation stage carrying the small ball in the opposite direction of the X-axis, turn on the same X-ray source as in the step H2 for exposure, and obtain the projected position of the center of the small ball phantom on the detector Distance parameter two to the center of the detector; wherein, the opposite direction of the X axis refers to the left direction; Step H4: Solve the following equations to obtain the distance SID from the center position of the X-ray source array to the detector and the distance SOD to the scanned object; ; in, Represents the distance parameter one from the projected position of the center of the small spherical phantom on the detector to the center of the detector, Representing the distance parameter two from the projected position of the center of the small spherical phantom on the detector to the center of the detector, Indicates the distance between the focal point of the X-ray source at the central position and the focal point of the X-ray source selected in step H2 for exposure.