CN113962922B - Tomographic imaging method and system based on planar array radiation source - Google Patents

Abstract

The invention discloses a tomographic imaging method and a tomographic imaging system based on a planar array radiation source. According to the invention, the emergent angle of the cold cathode flat-panel ray source is researched through simulation, the beam light efficiency is researched, the beam light device is used for restraining the divergent cold cathode flat-panel ray source, and the aliasing of measurement data is reduced while the dose is ensured; the radiation is encoded by a radiation source addressing control circuit. Decoupling the aliased measurement data by using correlation between projections through different irradiation modes; and solving an imaging object through a reconstruction system to realize tomographic imaging based on the planar array radiation source. The invention covers the imaging object by combining the light beams under the condition of ensuring the imaging dosage, decouples the aliasing data by utilizing different irradiation modes, and finally obtains the internal structure information of the object.

Description

A tomographic imaging method and system based on a planar array ray source

technical field

The invention belongs to the field of tomographic imaging, and in particular relates to a tomographic imaging method and system based on a plane array ray source.

Background technique

Due to its non-destructive properties, X-rays are widely used in industrial, medical and other fields. The traditional X-ray planar imaging system mainly uses hot cathodes as the single-focus electron source. During imaging, it is necessary to adjust the relative positions of the ray source, the detector and the object to be detected to realize the scanning of the region of interest (ROI). Influenced by the size of the X-ray cone angle, the distance between the tube and the object to be detected must be far enough to cover the area to be detected during scanning, resulting in an imaging system that is much larger than the object to be detected and requires a larger space. In this case, areas of the scanned object that are not of interest increase the radiation risk. In addition, thermionic emission in traditional light sources has a time delay, which makes it difficult to achieve high time resolution and programmable emission.

Different from the traditional single light source X-ray planar imaging, the planar array ray source based on cold cathode technology has the characteristics of fast response, long service life and programmable control. In addition, the cold cathode flat-panel ray source can integrate thousands of ray sources in the device, and emit light through programming. Each light source covers a part of the imaging object, and finally can completely cover the region of interest of the imaging object, which can achieve high density. The low-power imaging system design, as shown in Figure 1, can greatly reduce the volume of the imaging system to achieve close-range imaging, overcome the limitations of traditional ray source site applications, and make the imaging system miniaturized and portable.

At present, the luminous intensity of a single pixel of a cold-cathode flat-panel ray source is lower than the detection lower limit of a flat-panel detector, and single-pixel imaging cannot be realized yet. Therefore, some sources and all point sources need to emit light at the same time to achieve detector response. At the same time, the beam angle of the cold-cathode flat-panel ray source is too divergent, so that the detector cannot receive all of them, which reduces the photon utilization rate and increases the radiation dose.

During the data acquisition process, the imaging of the flat-panel X-ray array light source caused measurement data aliasing due to multi-source lighting. Different from the one-to-one correspondence between the attenuation coefficient and the measured value in the traditional X-ray imaging path, this irradiation method will cause the details of the measured data to be blurred.

Contents of the invention

The object of the present invention is to overcome the above-mentioned deficiencies and provide a tomographic imaging method and system based on a planar array ray source. The method is designed for a cold cathode planar array ray source imaging system and is also suitable for other possible planar array X-ray sources. The imaging system can realize close-range tomographic imaging and obtain internal information of objects while ensuring imaging resolution.

In order to achieve the above object, a tomographic imaging method based on a planar array ray source comprises the following steps:

S1, using a beamer to shape the beam;

S2, using the control circuit to perform addressable lighting on the radiation source;

S3, using the reconstruction system to finally obtain the internal structure information of the object.

In S1, the shape and angle of the beam aperture are designed according to the photon utilization angle, so that each light source only covers a part of the imaging target, and all light sources will completely cover the imaging target.

In S2, use the control circuit to light up the ray source addressably, where Pattern={P ₁ , P ₂ ,...,P _i ...,P _N } is the sequence of N designed irradiation schemes, and the specific The number of illuminated flat-panel X-ray arrays under the irradiation situation P _i is denoted as S _i , and the number of detector units is denoted as D. Under specific irradiation, the measured data on detector d is denoted as I _d,Pi . The ideal The collection process is expressed as:

in, is the measurement data on the d-th detector under one kind of irradiation P _i , a _sd represents the system matrix of the s-th ray source corresponding to the d-th detector, I ₀ is the light source intensity, and x is to be reconstructed image.

The method of addressable lighting is to design different illumination sequences, and deal with the aliasing measurement data through the combination of a series of illumination sequences.

In S3, the reconstruction system uses the method of establishing an objective function to optimize and solve the reconstruction image, and obtain the internal structure information of the imaging object.

The specific method for the reconstruction system to obtain the internal structure information of the object is as follows:

Establish the Lagrangian optimization equation to optimize and solve the reconstructed image;

in, is the measurement data on the d-th detector under one kind of irradiation, a _sd represents the system matrix of the s-th ray source corresponding to the d-th detector, S _i is the lighted plate under a specific irradiation scheme P _i The total number of ray sources, I ₀ is the light source intensity, D is the total number of detectors, x is the reconstructed image, β _i is the regularization parameter, R _i (x) is the regularization item, and M is the number of regularization items.

In the Lagrangian optimization equation, the regularization term can be selected, but not limited to the total variational regularization. The optimization equation is specifically:

The solution process of the optimization equation is solved using the POCS convex set projection method. The specific solution process is as follows:

The first step is to load the measurement data and update x:

make Indicates the error between the reconstructed projections of N illumination schemes and the actual measured data, where:

Iterative update using Newton's gradient method:

Among them, n-1 and n represent the number of iterations, λ is the update interval, and Taylor expansion is used to optimize and solve the formula. I ₀ exp(-a _sd x) is expanded by Taylor at x ₀ as:

Into the formula get:

and The first derivative is:

The second derivative is:

Will Substitute into f'(x _n-1 ), f"(x _n-1 ), update and reconstruct the image to get x _n ;

In the second step, the image is positively constrained as

The third step, TV gradient descent for image update:

Among them, M is the number of gradient descents, β _TV is the step size, and d _A is the residual error.

A tomographic imaging system based on a planar array ray source, comprising a planar array ray source, a light beam device, a ray source addressing control circuit, a detector and a reconstruction system;

The light beam device is fixed on the plane array radiation source, and the radiation source is controlled by the circuit to generate different irradiation sequences, which constitute the radiation source part of the system;

The detector is arranged on the opposite side of the ray source for receiving measurement signals, the detector is connected to the reconstruction system, and the detector is used to transmit the received data to the reconstruction system through the detector acquisition software.

The flat panel array ray source can be, but not limited to, select a column-addressable coplanar focus nano-cold cathode electron source array.

Compared with the prior art, the present invention studies the exit angle and beam efficiency of the flat-panel array ray source through simulation, and designs the beam device to constrain the divergent flat-panel ray source so that each light source only covers a part of the imaging target. It improves photon utilization, reduces unnecessary aliasing, and can adapt to the design of high-density light sources and low power consumption requirements; decouples aliasing data through different illumination methods, and realizes close-range imaging while ensuring imaging resolution , to obtain the internal structure information of the object. By controlling the circuit to design the sequential light emission mode, under the condition of ensuring the dose, the correlation between the projections is used to decouple the aliased measurement data; finally, the reconstruction system of the present invention is used to finally solve the imaging object, and realize the imaging based on the planar array X-ray source tomography system. The system of the present invention has the characteristics of miniaturization, portability and long life, and makes up for the defect that the traditional single-point source ray source imaging system is bulky and cannot be used in unconventional conditions.

Description of drawings

Fig. 1 is a schematic diagram of cold cathode planar array ray source and luminous angle;

Fig. 2 is a schematic diagram of changing a cold cathode planar array ray source into a parallel beam;

Fig. 3 is a schematic diagram of the angular distribution of the cold cathode planar array ray source according to the Monte Carlo simulation;

Fig. 4 is a schematic diagram of a light beam device;

Fig. 5 is a schematic diagram of the irradiation angle of the light source, wherein (a) is a schematic diagram of a vertical light exit, and (b) is a schematic diagram of a side oblique light exit angle;

Fig. 6 is a schematic diagram of the irradiation scheme of P _N = 36 groups, wherein the solid represents the radiation source lit by the control circuit;

7 is a schematic diagram of a tomography system based on a planar array ray source;

Fig. 8 is a flow chart of image reconstruction;

Figure 9 is a schematic diagram of the simulation results;

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

A tomographic imaging method based on a plane array ray source, comprising the following steps:

S1, the planar array ray source can be selected, but not limited to, column-addressable coplanar focusing nano-cold cathode electron source array (patent number: 201711063201.6), and the beam is shaped by the beam device.

First of all, consider adding beam optics to shape the beam to suppress the aliasing of measurement data. If the cold cathode planar array ray source is directly transformed into a parallel beam through the beam device, as shown in Figure 2. The following problems exist:

1. Considering the light beam device, the resolution of the light source is much larger than that of the detector, and the imaging resolution will depend on the resolution of the light source;

2. Referring to Figure 3, it can be seen from the Monte Carlo simulation that the number of direct photons is very small, as shown in Figure 1. Assuming that the beam beam distance is 1mm and the opening size is 0.035mm, only 1.04% of the photons pass through after beaming, and 99% of the photons will be wasted, and the utilization efficiency of the light source is extremely low. In order to reduce the aliasing of measurement data at the detector end while ensuring the utilization efficiency of the light source, it is necessary to perform beam shaping on the cold cathode flat panel ray source, that is, to place a beamer in front of the cold cathode planar array ray source.

Referring to Fig. 4, a simulation experiment is performed on the shape of the opening of the light beam, the distance between the openings, and the size of the angle of the light beam. From the perspective of photon utilization efficiency, the plan of the beam beam device is finally determined as a copper plate beam beam device with a cylindrical opening, a spacing of 3mm, a hole radius of 0.5mm, and a size of 60mm×60mm×2mm, as shown in Figure 4. It shows that the design of the number of light sources is not unique. This system adopts the number density of 15x15 light sources for system design. In addition, the irradiation angle of the flat panel source can be changed by changing the opening method of the light beam device. For example, the oblique light exiting from the side can increase more Z-axis resolution information. The following shows two light source irradiation methods after the beam device is opened , as shown in Figure 5.

S2, using the control circuit to perform addressable lighting on the radiation source, and completing data collection in a sequential lighting manner.

The function of controllable light emission of the cold cathode planar array ray source is realized through the programming of the control circuit. In the case of ensuring the dose, the measured projection data is encoded through different irradiation methods. Using correlations between projections, aliasing is further disentangled. Theoretically speaking, there are enough combinations of irradiation schemes, and linear equations can be directly used to solve the projection values corresponding to each ray source. However, due to dose considerations, the design of the irradiation scheme should follow the principle of simplicity and efficiency. The design of the illumination scheme is not unique. This design proposes several efficient illumination combination methods, through which the object can be reconstructed efficiently. The designed illumination scheme is shown in Figure 6, where the black represents the point source controlled by the circuit.

Use the control circuit to light up the ray source addressably, where Pattern={P ₁ ,P ₂ ,...,P _i ...,P _N } is a sequence of N designed irradiation schemes, and the specific irradiation situation P The number of flat-panel X-ray arrays illuminated under _i is denoted as S _i , the number of detector units is denoted as D, and the measured data on detector d is denoted as The ideal acquisition process is expressed as:

in, is the measurement data on the d-th detector under one kind of irradiation P _i , a _sd represents the system matrix of the s-th ray source corresponding to the d-th detector, I ₀ is the light source intensity, and x is to be reconstructed image.

The method of addressable lighting is to design different illumination sequences, and deal with the aliasing measurement data through the combination of a series of illumination sequences.

Through the reconstruction system, the method of establishing the objective function is used to optimize and solve the reconstruction image, and obtain the internal structure information of the imaging object. The specific method for the reconstruction system to obtain the internal structure information of the object is as follows:

Establish the Lagrangian optimization equation to optimize and solve the reconstructed image;

in, is the measurement data on the d-th detector under one kind of irradiation, a _sd represents the system matrix of the s-th ray source corresponding to the d-th detector, S _i is the light-up panel under a specific irradiation scheme P _i The total number of ray sources, I ₀ is the light source intensity, D is the total number of detectors, x is the reconstructed image, β _i is the regularization parameter, R _i (x) is the regularization item, and M is the number of regularization items.

S3, use the reconstruction system to reconstruct, and finally obtain the internal structure information of the object.

Referring to Fig. 7, a tomographic imaging system based on a planar array radiation source, wherein the system includes a cold cathode planar array radiation source, a light beam device, a radiation source addressing control circuit, a detector, and a reconstruction system, wherein the size of the beam light device is as shown in the figure As shown in Figure 4, the light emitting mode can use the two modes in Figure 5. In the acquisition process, the encoding of the irradiation mode is completed through circuit control, as shown in Figure 6. On the detector side, place the object directly on the detector. The following describes in detail the data acquisition process and reconstruction process of the tomography system based on the cold cathode flat-panel ray source in conjunction with Figures 4-8:

(a) Assuming that the shape of the beam passing through each beam aperture is consistent with the output light intensity, that is, the beam constraint is carried out in the manner shown in Figure 5(a).

(b) An imaging object is placed at the detector end, and a control circuit is used to generate different irradiation code combinations, P _N =36.

(c) In the image reconstruction process, there are two loops, as shown in Figure 8, each time the index information of an irradiation scheme is loaded, and the following optimization equation is used for optimization:

For example, in the case of TV regularization, the solution process can use POCS (Projection on Convex Sets) to solve. The main solution process can be divided into the following steps:

S1. Load measurement data and update x:

make Indicates the error between the reconstructed projections of the N illumination schemes and the actual measured data. in:

The update method is not limited to Newton gradient descent, and the Newton gradient method is used for iterative update:

where n-1 and n represent the number of iterations, and λ is the update interval. Using Taylor expansion to optimize and solve the formula, I ₀ exp(-a _sd x) is expanded by Taylor at x ₀ as:

Into the formula get:

and The first derivative is:

The second derivative is:

Will Substitute into f'(x _n-1 ), f"(x _n-1 ), and update the reconstructed image to obtain x _n .

S2. Image positive constraints,

S3.TV gradient descent for image update

Among them, M is the number of gradient descents, β _TV is the step size, d _A is the residual error, and enters the next iteration.

Using the model and reconstruction method described above, build a tomography system based on a cold cathode planar array ray source. The parameters used are consistent with those in Figure 4-7. The distance between the source and the detector is 190mm, and the size of the detector is 0.2mm. The simulation experiment result is shown in Fig. 9 . It can be seen from the experimental results that the tomographic imaging system based on the planar array ray source of the present invention can decouple aliased data through different irradiation methods, realize close-range imaging while ensuring imaging resolution, and obtain internal structure information of objects.

The invention realizes the first tomographic imaging system based on the planar array ray source. Referring to Figure 7, the beam shaper is designed to shape the beam to improve the photon utilization rate, and the control circuit is used to combine the irradiation methods and decouple the aliasing measurement data, so that the system has the characteristics of close-range imaging and has no site application restrictions , with a wide range of application scenarios.

Claims (6)

1. A tomography method based on a planar array ray source, characterized in that, comprising the following steps: S1, using a beamer to shape the beam; Among them, the opening shape and angle of the beam light device are designed according to the angle of photon utilization, so that each light source only covers a part of the imaging target, and all light sources will completely cover the imaging target; S2, using the control circuit to perform addressable lighting on the radiation source; Wherein, the control circuit is used to addressably light up the ray source, where Pattern={P ₁ , P ₂ ,...,P _i ...,P _N } is a sequence of N designed irradiation schemes, and the specific irradiation The number of illuminated flat-panel X-ray arrays under the situation P _i is denoted as S _i , the number of detector units is denoted as D, and the measured data on the detector d is denoted as The ideal acquisition process is expressed as: Among them, I _d,Pi is the measurement data on the dth detector under a kind of irradiation _Pi , a _sd represents the system matrix of the sth ray source corresponding to the dth detector, and I ₀ is the light source Intensity, x is the image to be reconstructed; S3, using the reconstruction system to finally obtain the internal structure information of the object; Among them, the reconstruction system uses the method of establishing an objective function to optimize and solve the reconstruction image, and obtain the internal structure information of the imaging object; The specific method for the reconstruction system to obtain the internal structure information of the object is as follows: Establish the Lagrangian optimization equation to optimize and solve the reconstructed image; in, is the measurement data on the d-th detector under one kind of irradiation, a _sd represents the system matrix of the s-th ray source corresponding to the d-th detector, S _i is the light-up panel under a specific irradiation scheme P _i The total number of ray sources, I ₀ is the light source intensity, D is the total number of detectors, x is the reconstructed image, β _i is the regularization parameter, R _i (x) is the regularization item, and M is the number of regularization items. 2. A tomographic imaging method based on a planar array ray source according to claim 1, wherein the method of addressable lighting is to design different irradiation sequences, and to measure the aliasing by a combination of a series of irradiation sequences Data unaliasing. 3. a kind of tomographic imaging method based on planar array ray source according to claim 1, it is characterized in that, in the Lagrangian optimization equation, regularization term can be selected, but not limited to total variation regularity, optimization equation is specifically : 4. a kind of tomography method based on planar array ray source according to claim 1, it is characterized in that, the solving process of optimization equation uses POCS convex set projection method to solve, and concrete solving process is as follows: The first step is to load the measurement data and update x: make Indicates the error between the reconstructed projections of N illumination schemes and the actual measured data, where: Iterative update using Newton's gradient method: Among them, n-1 and n represent the number of iterations, λ is the update interval, and the formula is optimized and solved by Taylor expansion, I ₀ exp(-a _sd x) is expanded by Taylor at x ₀ as: Into the formula get: and The first derivative is: The second derivative is: Will Substitute into f'(x _n-1 ), f"(x _n-1 ), update and reconstruct the image to get x _n ; In the second step, the image is positively constrained as The third step, TV gradient descent for image update: Among them, M is the number of gradient descents, β _TV is the step size, and d _A is the residual error. 5. An imaging system based on the tomographic imaging method of the planar array ray source according to claim 1, characterized in that it comprises a planar array ray source, a light beam device, a ray source addressing control circuit, a detector, and a reconstruction system; The light beam device is fixed on the plane array radiation source, and the radiation source is controlled by the circuit to generate different irradiation sequences, which constitute the radiation source part of the system; The detector is arranged on the opposite side of the ray source for receiving measurement signals, the detector is connected to the reconstruction system, and the detector is used to transmit the received data to the reconstruction system through the detector acquisition software. 6 . The imaging system of a tomographic imaging method based on a planar array ray source according to claim 5 , wherein the planar array ray source is a column-addressable coplanar focusing nano-cold cathode electron source array. 7 .