CN111736203A - Three-dimensional position calibration method, device and equipment for continuous crystal gamma detector - Google Patents

Abstract

The invention discloses a three-dimensional position calibration method, device and equipment of a continuous crystal gamma detector. The method includes: collecting the detector output signal of each gamma event under the irradiation condition of a non-collimated source; Irradiation conditions, determine the real three-dimensional action position distribution of gamma events in the detector; according to the detector output signal of each gamma event, initial partition of all gamma events; according to the partition results of all gamma events, determine the corresponding The initial detector output response of the gamma event of each partition; according to the current detector output response and the three-dimensional action position distribution of the gamma event in the detector, a cost function for optimizing the detector output response is constructed; The minimum value iterative optimization solution is performed, the detector output response of each 3D position partition is updated, and the 3D position scale of the detector is completed. The method simplifies the three-dimensional position calibration process and improves the accuracy of the position calibration.

Description

Three-dimensional position calibration method, device and equipment for continuous crystal gamma detector

technical field

The present invention generally relates to the field of radiation detectors, and in particular relates to a three-dimensional position calibration method, device and equipment for a continuous crystal gamma detector.

Background technique

At present, nuclear technology has penetrated into all fields of human production and life, and has been widely used in industry, agriculture, environment and medicine. Gamma photon is one of the main messenger particles in the application of nuclear technology. Accurate and effective detection of its energy, position and time information is the key to quantitatively understand the type, intensity and distribution of nuclear radiation and then obtain nuclear information. Therefore, gamma detectors are indispensable for the effective utilization of nuclear technology.

The continuous crystal gamma detector is a new detector design that has gradually emerged in recent years. Different from the traditional discrete crystal detector design in which the crystal is cut into small units for assembly, it couples a whole crystal to the optoelectronic device array, and realizes gamma through the readout signal of the optoelectronic device array at the back end. The acquisition of position, time and energy information of the interaction between photons and detectors. Compared with the traditional discrete crystal detector design, it has higher detection efficiency, lower processing and assembly costs, better time and energy measurement performance, and direct 3D position information acquisition capability. significant application prospects.

The position calibration of the continuous crystal gamma detector, especially the three-dimensional position calibration, is to obtain the output response of the detector when the gamma rays act on different three-dimensional positions in the detector, which is the position where the continuous crystal gamma detector performs gamma events. The basis of positioning. Traditional position calibration methods often use a collimated source for calibration. The basic idea is to use a pencil-shaped collimated beam, and the action position of the gamma ray and the detector can be precisely controlled and known, so that the output response of the detector when the gamma ray acts on different known positions in the detector can be obtained, and then the detector can be realized. position scale. This method is cumbersome and time-consuming due to the introduction of a collimation source, and it is difficult to implement in system-level applications. On the other hand, using a collimated gamma source can only precisely control the two-dimensional interaction position between the ray and the detector, so it is difficult to directly obtain the detector response when the ray acts on different three-dimensional positions. Third, the application of the collimation source is easy to introduce the deviation of the collimation position, which leads to systematic errors and affects the calibration accuracy. Some methods simplify the calibration process of the collimation source on this basis, and propose a calibration method based on a fan-shaped collimated beam, which can reduce the time consumption of calibration to a certain extent, but there is still the problem of reducing calibration accuracy due to the introduction of collimation deviation. Still not practical in system-level applications.

In order to eliminate the use of collimation sources and simplify the detection calibration process, one of the common methods is to use Monte Carlo simulation to simulate the scintillation light transport process in the detector, so as to obtain the response of the detector at different three-dimensional positions. This method does not require experimental measurements, the process is simplified, and it is easy to operate and execute. However, the light transport process in the detector, especially the behavior of scintillation photons on the crystal surface is often difficult to accurately model, and there is usually a deviation between the simulation results and the actual results, which affects the calibration accuracy. On the other hand, this method cannot Consider the individual differences between different detectors in practical applications.

There are also some continuous crystal detector calibration methods using non-collimated sources. The basic idea is to use a radioactive source to illuminate the detector nearly uniformly, record the detector output of each particle event, and use a self-organizing map. The detector output data is learned to obtain detector output responses at different positions. However, the obtained detector output response often requires complex distortion correction in the later stage, which is easy to introduce systematic errors. On the other hand, this method can only apply two-dimensional position scale at present, and when it is extended to three-dimensional position scale, it will be due to the excessive calculation amount. rather than practical.

SUMMARY OF THE INVENTION

In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a three-dimensional position calibration method, apparatus, device and storage medium for a continuous crystal gamma detector.

In a first aspect, the present invention provides a three-dimensional position calibration method for a continuous crystal gamma detector, comprising:

Collect the detector output signal of each gamma event under the illumination condition of the non-collimated source, and record the corresponding illumination condition of the non-collimated source;

Based on the illumination condition of the non-collimated source, determine the real three-dimensional action position distribution of the gamma event in the detector;

Initial partitioning of all gamma events based on the detector output signal for each gamma event;

According to the partition results of all gamma events, determine the initial detector output response corresponding to the gamma event of each partition;

According to the current detector output response and the real three-dimensional action position distribution of the gamma event in the detector, the three-dimensional action position of each gamma event and the three-dimensional action position distribution of the measured gamma event in the detector are calculated. Optimize the cost function of the detector output response;

The minimum iterative optimization solution is performed on the cost function, the detector output response of each three-dimensional position partition is updated, and the three-dimensional position scale of the detector is completed.

In one of the embodiments, the minimum value iterative optimization solution is performed on the cost function, and the detector output response of each three-dimensional position partition is updated, including:

The value of the cost function is iteratively optimized by the gradient descent algorithm, and the detector output response of each three-dimensional position partition is determined according to the optimization result.

In one of the embodiments, the minimum value iterative optimization of the cost function is performed through a gradient descent algorithm, including:

The detector output response is iteratively updated according to the iterative formula determined by the detector output response, and the iteration is terminated when the set number of iterations or the iteration termination condition is reached.

In one of the embodiments, the iteration termination condition is that the difference between the function values of the cost functions of adjacent iterations does not exceed a preset value.

In one embodiment, according to the current detector output response and the three-dimensional action position distribution of the gamma event in the detector, a cost function for optimizing the detector output response is constructed, including:

Determine the first function according to the difference between the three-dimensional position distribution of all gamma events determined by the maximum likelihood estimation algorithm and the currently estimated three-dimensional action position distribution of all gamma events according to the current detector output response;

According to the current detector output response using the maximum likelihood estimation method to determine the three-dimensional position partition positions of all gamma events, and using the sum of the optimal likelihood functions for the three-dimensional position positioning of the gamma events to determine the second function;

A cost function is determined according to the first function and the second function.

In one embodiment, the estimated three-dimensional action position distribution of all gamma events is used to convolve a Gaussian convolution kernel that represents the spatial resolution of the detector at different positions by using the calculated real three-dimensional action position distribution of all gamma events. obtained, where the spatial resolution of the detector at different positions is estimated from the current detector output response.

In one embodiment, the irradiation conditions include the type of radiation source irradiating the continuous crystal gamma detector, the relative positional relationship between the radiation source and the continuous crystal gamma detector, and the material and geometry of the continuous crystal gamma detector.

In one embodiment, all gamma events are initially partitioned according to the detector output signal of each gamma event, including:

According to the detector output signal of each gamma event, calculate the position measurement factors in the X, Y and Z directions corresponding to each gamma event;

Gamma events are initially partitioned based on location metric factors in X, Y and Z directions and a k-d tree partitioning strategy.

In a second aspect, the present application provides a three-dimensional position calibration device for a continuous crystal gamma detector, comprising:

The acquisition and recording module is used to acquire the detector output signal of each gamma event under the illumination condition of the non-collimated source, and record the corresponding illumination condition of the non-collimated source;

a first determination module, configured to determine the three-dimensional action position distribution of the gamma event in the detector based on the illumination condition of the non-collimated source;

A partition module for initially partitioning all gamma events according to the detector output signal of each gamma event;

The second determination module is used to determine the initial detector output response of the gamma event corresponding to each partition according to the partition results of all the gamma events;

The building block is used to calculate the three-dimensional action position of each gamma event and measure the three-dimensional action position distribution of the gamma event in the detector according to the current detector output response and the three-dimensional action position distribution of the gamma event in the detector. , constructing a cost function for optimizing the detector output response;

The update module is used to perform a minimum iterative optimization solution on the cost function, update the detector output response of each three-dimensional position partition, and complete the three-dimensional position scale of the detector.

In a third aspect, the present application provides a device, including a memory, a processor, and a computer program stored in the memory and running on the processor, where any of the above three-dimensional position calibration methods are implemented when the processor executes the program.

In a fourth aspect, the present application provides a readable storage medium on which a computer program is stored, and when the program is executed by a processor, implements any of the above three-dimensional position calibration methods.

The present application provides a three-dimensional position calibration method, device, equipment and storage medium for a continuous crystal gamma detector. The method is based on the real three-dimensional action position distribution of a gamma event in the detector determined under the irradiation condition of a non-collimated source. , construct the cost function for optimizing the detector output response, and then solve the minimum value of the cost function to realize the three-dimensional position scale of the detector. The method simplifies the three-dimensional position calibration process of the continuous crystal gamma detector, improves the accuracy of the three-dimensional position calibration, and enhances the engineering practicability of the detector.

Description of drawings

Other features, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

1 is a schematic flowchart of a three-dimensional position calibration method provided by an embodiment of the present invention;

2 is a schematic flowchart of performing initial partitioning on all gamma events provided by an embodiment of the present invention;

3 is a k-d tree partition strategy provided by an embodiment of the present invention;

4 is a schematic flowchart of constructing a cost function according to an embodiment of the present invention;

5 is a schematic structural diagram of a continuous crystal gamma detector for implementing the three-dimensional position calibration method of the present invention;

FIG. 6 is a schematic diagram of the three-dimensional action position distribution of gamma events in the detector;

Fig. 7- _Fig . 9 are the distribution diagrams of the position measurement factors X _n , Y _n and Zn in the X, Y and Z directions respectively;

Figures 10-12 show the output responses of the SiPM unit in the lower left corner corresponding to different x and y action positions when the z positions of the gamma photon events are 0.5mm, 6.5mm and 12.5mm, respectively;

Figures 13-15 show the output response of a certain SiPM unit in the central area corresponding to different x and y action positions when the z positions of the gamma photon events are 0.5mm, 6.5mm and 12.5mm respectively;

16 is a schematic structural diagram of a three-dimensional position calibration device provided by an embodiment of the present invention;

FIG. 17 is a schematic structural diagram of a computer device according to an embodiment of the present invention.

Detailed ways

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 herein are only used to explain the related invention, but not to limit the invention. In addition, it should be noted that, for the convenience of description, only the parts related to the invention are shown in the drawings.

It should be noted that the embodiments of the present invention and the features of the embodiments may be combined with each other under the condition of no conflict. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

The basic idea of the existing continuous crystal detector calibration method is to use the radioactive source to irradiate the detector nearly uniformly, record the detector output of each particle event, and use self-organization mapping (self-organization mapping). organizing map) to learn the detector output data to obtain detector output responses at different locations. However, the obtained detector output response often requires complex distortion correction in the later stage, which is easy to introduce systematic errors. On the other hand, this method can only apply two-dimensional position scale at present, and when it is extended to three-dimensional position scale, it will be due to the excessive calculation amount. rather than practical.

Aiming at the above-mentioned defects of the existing continuous crystal detector calibration method when using non-collimated source irradiation conditions, the present application proposes a three-dimensional position calibration method for a continuous crystal gamma detector.

Referring to FIG. 1 , it shows a schematic flowchart of a three-dimensional position calibration method for a continuous crystal gamma detector according to an embodiment of the present application.

As shown in Figure 1, a three-dimensional position calibration method for a continuous crystal gamma detector may include:

S110. Collect the detector output signal of each gamma event under the irradiation condition of the non-collimated source, and record the corresponding irradiation condition.

Specifically, the radiation source irradiated by the non-collimated source can be a surface source or a point source; the relative positional relationship between the radiation source and the detector is adjusted according to the actual experimental requirements. Here, the type of the radiation source, the radiation source and the detector are adjusted. There is no restriction on the relative positional relationship of , as long as the irradiation conditions are accurately known.

The irradiation conditions include the type of radiation source irradiating the continuous crystal gamma detector, the relative positional relationship between the radiation source and the continuous crystal gamma detector, the material and geometric structure of the continuous crystal gamma detector, and the like. The type of radioactive source can be gamma radioactive source such as ¹⁸ F point source, and can also be background radiation ¹⁷⁶ Lu of LYSO crystal, etc., and other types of radioactive sources can also be used, which are not limited here.

Collect the output signal of each channel of the detector of each gamma event under the illumination condition of the non-collimated source, and record the normalized output signal of the detector of each gamma event after the main peak energy window is taken, which is recorded as:

Among them, an _ns is the normalized output signal of the s-th output channel of the detector of the n-th gamma event collected, n is the gamma event number, s is the output channel number of the detector, and S is the detector's output channel number. The total number of output channels, and N is the total number of gamma events collected.

The detector is irradiated with a non-collimated radiation source under known illumination conditions, and the detector output of each gamma event is recorded as scale data; under known illumination conditions, although the precise The three-dimensional effect position is unknown, but the three-dimensional effect position distribution of a large number of gamma events in the detector can be accurately calculated.

Using a non-collimated radiation source, since the use of a collimated source is eliminated, the calibration process of the detector is greatly simplified, and the measurement deviation of the detector response characteristics caused by the collimation error is avoided. The count of collected ray particle events can also be greatly improved, thereby reducing the impact of statistical noise on the calculation of detector response characteristics. In addition, compared with the existing non-collimated source calibration method, this method does not require nearly uniform irradiation conditions, but is relaxed to basically any irradiation conditions, which greatly reduces the constraints on irradiation conditions, so it has stronger application flexibility and practical applicability.

S120. Determine the true three-dimensional action position distribution of the gamma event in the detector based on the illumination condition of the non-collimated source.

Specifically, based on the illumination condition of the non-collimated source, Monte Carlo simulation or analytical calculation can be used to calculate the real three-dimensional action position distribution of the gamma event in the detector under the illumination condition, which is recorded as:

Among them, pi is the ratio of the number of gamma events in the _i -th three-dimensional position partition, I is the total number of three-dimensional position partitions of the detector, and I=I _x ·I _y ·I _z , where I _x , I _y and I _z are the number of partitions in the X, Y and Z directions of the detector, respectively. The lengths of the three directions of each three-dimensional position partition are _{Dx/Ix , Dy} / _Iy and _Dz / _Iz , respectively, where _Dx , _Dy and _Dz are the dimensions of the detector in the three directions, respectively , I _x , I _y and I _z are selected to ensure that D _x /I _x , D _y /I _y and D _z /I _z are all less than half of the spatial resolution of the corresponding direction. The length may be about 0.5 to 1 mm. It should be noted that, for the non-cube-shaped continuous crystal gamma detector, the partition mode can be adjusted accordingly.

S130. Perform initial partitioning on all gamma events according to the detector output signal of each gamma event.

In one embodiment, as shown in FIG. 2 , it shows a schematic flowchart of initial partitioning of all gamma events in S130 according to the detector output signal of each gamma event, including:

S210 , according to the detector output signal of each gamma event, calculate the position measurement factors in the X, Y and Z directions corresponding to each gamma event.

Specifically, for the detector output signal of each gamma event collected in S110, calculate its position measurement factors in the X, Y and Z directions respectively:

Among them, x _s and y _s are the coordinates of the detector unit corresponding to the s-th output channel in the x and y directions, respectively.

S220, based on the position measurement factors in the X, Y and Z directions and the k-d tree partition strategy, perform an initial partition on the gamma event.

Specifically, as shown in Figure 3, the kd tree partition strategy is: first find the median x ₁ of the position measurement factor in the X direction in all gamma events, and put the position measurement factor in the X direction less than or equal to x ₁ to the left partition , those greater than x ₁ are placed in the right partition. Then, for the gamma event of the left partition, the position measurement factor in the Y direction less than or equal to y ₁ is placed in the left partition, and the one greater than y ₁ is placed in the right partition, for the gamma event of the right partition and the subsequent partitions of each layer are And so on. Finally, a total of 1 three-dimensional position partitions are formed. Wherein, in the figure, x ₁ , y ₁ , y ₂ , z ₁ , z ₂ , z ₃ and z ₄ are the medians of the position measurement factors corresponding to the corresponding directions of the partition gamma events, respectively.

Through the kd tree formed above, all gamma events in S110 are classified into a specific partition, and the three-dimensional position partition to which the _nth event belongs is denoted as I _n , where 1≤In ≤I. Complete initial partitioning of gamma events.

S140. Determine the output response of the detector corresponding to the gamma event of each partition according to the partition results of all the gamma events.

Specifically, the output response of the detector includes the mean _μis and the standard deviation _σis of each output channel of the detector when the gamma event acts on each three-dimensional position partition.

The output response of the detector corresponding to the gamma event for each partition is:

和

上标中的0代表当前是第0次迭代。in,

and

The 0 in the superscript means that the current iteration is the 0th iteration.

S150. Determine the three-dimensional position partition to which each gamma event belongs according to the output response of the detector.

Specifically, according to the output response of the detector, the three-dimensional position partition to which each gamma event belongs can be determined according to the maximum likelihood estimation algorithm. The three-dimensional position partition of the nth event is:

where k is the current number of iterations.

S160. According to the current detector output response and the real three-dimensional action position distribution of the gamma event in the detector, construct a cost function for optimizing the detector output response.

Specifically, FIG. 4 is a schematic flowchart of constructing a cost function. In Figure 4:

S410. The three-dimensional position distribution of all gamma events calculated by the maximum likelihood estimation algorithm according to the output response of the current detector should be as consistent as possible with the currently estimated three-dimensional action position distribution of all gamma events, and a corresponding first function is determined (characterizing function) is:

为根据当前的探测器的输出响应利用公式(5)计算的第i个三维位置分区的事件比例，

为根据当前的探测器输出响应和S120中确定的伽马事件的真实三维作用位置分布预估的第i个三维位置分区的事件比例。

由步骤S120中得到的伽马事件的真实三维作用位置分布和当前计算的表征探测器不同三维位置分区的空间分辨率的高斯卷积核卷积获得。Among them, k is the current iteration number,

is the event proportion of the i-th three-dimensional location partition calculated according to the current detector output response using formula (5),

The event ratio of the i-th three-dimensional position partition estimated according to the current detector output response and the true three-dimensional action position distribution of the gamma event determined in S120.

It is obtained by convolving the real three-dimensional action position distribution of the gamma event obtained in step S120 with the currently calculated Gaussian convolution kernel representing the spatial resolution of the different three-dimensional position partitions of the detector.

in:

Among them, R ^(k) is the Gaussian convolution kernel that characterizes the spatial resolution of different three-dimensional positions of the detector calculated according to the response of the current detector (the full width at half maximum of the Gaussian convolution kernel in the corresponding direction is equal to the space in the corresponding direction of the position Resolution), estimated according to the current detector response by the Cramer-Rao criterion, P is the three-dimensional action position distribution of the real gamma event, see the definition in formula (2).

The method of calculating the spatial resolution of the detector according to the response of the current detector using the Cramer-Rao criterion is as follows:

①When gamma photons act on different three-dimensional position partitions in the detector, the output of the detector can be characterized as S joint Gaussian probability density functions, namely:

和

分别代表当伽马光子作用于三维位置

时探测器的第s个输出通道的归一化输出信号的均值和标准差。where m _s represents the normalized output signal of the s-th output channel of the detector,

and

respectively represent when the gamma photon acts on the three-dimensional position

The mean and standard deviation of the normalized output signal of the sth output channel of the detector.

②The spatial resolution of different three-dimensional position partitions in the detector can be characterized as:

表示探测器内

位置处x，y和z三个方向的空间分辨率，

代表每一个三维位置分区的中心位置(相当于对连续晶体做离散化处理)，diag(g)算符表示求矩阵的对角线元素，

表示探测器内

位置处的费雪信息矩阵(Fisher Information Matrix)，为3×3的矩阵，矩阵元素表示为：in,

Indicates the detector

the spatial resolution in the x, y and z directions at the location,

Represents the center position of each three-dimensional position partition (equivalent to discretizing continuous crystals), the diag(g) operator represents the diagonal elements of the matrix,

Indicates the detector

The Fisher Information Matrix at the location is a 3×3 matrix, and the matrix elements are expressed as:

The E(g) operator represents the mathematical expectation of the parameters in parentheses, and r ₁ , r ₂ and r ₃ represent the three directions of x, y and z, respectively.

S420, all gamma events, according to the current output response of the detector, use the maximum likelihood estimation method to calculate the three-dimensional position partition position to which they belong, and use the sum of the optimal likelihood functions for the three-dimensional position positioning of the gamma events, Determine the _second function f2:

所属三维位置分区的似然函数表征为：Among them, the gamma event

The likelihood function of the three-dimensional position partition to which it belongs is characterized as:

In order to facilitate the calculation, the log-likelihood function is used, that is:

Find a three-dimensional position partition i so that the value of lnL is the largest, which is the process of determining the three-dimensional position zone to which the gamma photon event belongs. After determining the three-dimensional position zone to which it belongs, substitute μ and σ of the three-dimensional position zone to which it belongs into the above formula (13) , the calculated value of lnL should be as large as possible, that is, the sum of the optimal likelihood function values should be as large as possible, and f ₂ should be as small as possible.

The constructed cost function for optimizing the detector output response is:

f=f ₁ +f ₂ (14)

S170. Perform a minimum iterative optimization solution on the cost function, update the detector output response of each three-dimensional position partition, and complete the three-dimensional position calibration of the detector.

Optionally, the value of the cost function is iteratively optimized by a minimum value through a gradient descent algorithm, and the detector output response of each three-dimensional position partition is determined according to the optimization result.

Specifically, the minimum iterative optimization of the value of f is carried out through optimization algorithms such as gradient descent method, so as to realize the solution of the detector output response, update the detector output response of each three-dimensional position partition, and complete the three-dimensional position scale of the detector. .

Optionally, the minimum value iterative optimization of the cost function is performed through a gradient descent algorithm, including: iteratively updating the detector output response according to an iterative formula determined by the detector output response, when the set number of iterations or the iteration termination condition is reached, Terminate the iteration. When the set number of iterations or the iteration termination condition is not reached, return to step S150 to continue execution.

Specifically, the iterative formula for determining the output response of the detector is:

W ^k+1 =W ^k -α▽f(W ^k ) (15)

Among them, α is the iteration step term, where α can be taken as: 0.001/max(|▽f(W ^k )|), ▽(g) is the gradient operator, and W ^k represents the output response of the current detector:

The number of iterations can be set according to actual requirements, for example, the number of iterations can be 2000 and so on. Optionally, the iteration termination condition may be that the difference between the function values of the cost functions of adjacent iterations does not exceed a preset value. The preset value can be set according to actual requirements, for example, the preset value can be 1×10 ^-4 .

FIG. 5 is a schematic diagram of a continuous crystal gamma detector for implementing the three-dimensional position calibration method of the continuous crystal gamma detector of the present invention. Among them, the continuous LYSO crystal 1 in the figure can be 26mm×26mm×13mm in size, that is, the lengths in the x, y, and z directions are 26mm, 26mm, and 13mm, respectively. The silicon photomultiplier (SiPM) array 2 can use the SensLFC30035 series, wherein the effective detection area of a single SiPM unit is about 3mm×3mm, and the size of the array is 6×6. The data acquisition and transmission module 3 is used to acquire the output signal of the SiPM array 2 and transmit the acquired signal to the computer terminal 4 for subsequent detector calibration. Except for the bottom surface, the other surfaces of the continuous LYSO crystal 1 can be wrapped with Teflon to reduce light loss, while the bottom surface of the LYSO crystal 1 is coupled with the SiPM array, and the gamma photons act in the LYSO crystal 1. 1. The propagating transport to the bottom surface is detected by the SiPM array 2. The output signal of each SiPM unit in the SiPM array 2 is read out independently, that is, each gamma photon event has 6×6=36 signals recorded by the computer terminal 4 .

The following embodiments illustrate the three-dimensional position calibration method of the continuous crystal gamma detector of the present invention by using the background radiation ¹⁷⁶ Lu of LYSO crystal as an example of a non-collimated source. It should be noted that other types of radiation sources can also be used to irradiate the continuous crystal gamma detector.

S1. For each event, collect and record the normalized output signal of each SiPM unit in the SiPM array, eg, collect about 2M gamma events in total.

S2. According to the irradiation conditions, the Monte Carlo simulation method is used to calculate the three-dimensional action position distribution of the ¹⁷⁶ Lu background radiation event of the LYSO crystal in the continuous LYSO crystal. The continuous LYSO crystal is discretely divided with a small cube of 1mm×1mm×1mm as a three-dimensional position unit. The number of division units in the x, y, and z directions are 26, 26, and 13 respectively, and the total division is 26×26×13=8788 three-dimensional location unit. Figure 6 shows the relative count ratio of ¹⁷⁶ Lu background radiation events in all three-dimensional position cells calculated by Monte Carlo simulation, that is, the three-dimensional action position distribution of gamma events in the detector (in formula (2) P).

S3. Use the kd tree to initially partition the gamma events collected in S1. Figures 7-9 show the distributions of X _n , Y _n and _Zn calculated according to the collected ¹⁷⁶ Lu background radiation events and formula (3). Based on the distribution and the partition strategy of the kd tree, the above Acquisition events were assigned to a total of 8788 three-dimensional position cells, enabling initial partitioning of gamma events.

S4. According to the gamma event partition result in S3, formula (4) is used to calculate the gamma event corresponding to each partition and the output response of the detector (mean and standard deviation of the output signal of each SiPM detection unit).

S5. According to the output response of the detector, the maximum likelihood estimation algorithm is used to calculate the three-dimensional position partition of each gamma event according to formula (5).

S6. Construct a cost function for optimizing the detector output response, and use formulas (6), (11) and (14) to construct a cost function f for optimizing the detector output response.

S7. Use the gradient descent algorithm to optimize the minimum value of the cost function f of the output response of the detector, and realize the iterative update of the output response of the detector according to formula (15), where α in the iterative process can be taken as:

α=0.001/max(|▽f(W ^k )|)

The number of iterations can be set to T=2000, and the termination condition of the iteration can be that the relative change of the cost function of the two iterations before and after does not exceed β=1×10 ⁻⁴ . When the iteration termination condition or the set number of iterations is reached, the iteration is terminated, the detector output response for each three-dimensional position partition is output, and the three-dimensional position calibration of the detector is completed.

10-15 show the detector output responses obtained by the three-dimensional position calibration method of the continuous crystal gamma detector of the present invention. Among them, Fig. 10-Fig. 12 are the output responses (μ _is ) of the SiPM unit in the lower left corner of the three-dimensional action position, Fig. 10-Fig. 12 are the z-positions where the action of the gamma photon event is 0.5mm (close to the SiPM unit), respectively, 6.5mm (the position of the center layer of the crystal) and 12.5mm (the position near the upper surface of the crystal). Among them, Fig. 13-Fig. 15 are the output responses (μ _is ) of the SiPM unit at the center of the three-dimensional action position, Fig. 13-Fig. 15 are the z-positions where the action of the gamma photon event is 0.5mm (close to the SiPM unit), 6.5mm mm (position of the crystal center layer) and 12.5 mm (position close to the upper surface of the crystal).

FIG. 16 is a schematic structural diagram of a three-dimensional position calibration device 1600 of a continuous crystal gamma detector according to an embodiment of the present invention. As shown in FIG. 16, the apparatus can implement the method shown in FIG. 1, and the apparatus can include:

The acquisition and recording module 1610 is configured to acquire the detector output signal of each gamma event under the irradiation condition of the non-collimated source, and record the corresponding irradiation condition of the non-collimated source;

a first determining module 1620, configured to determine the true three-dimensional action position distribution of the gamma event in the detector based on the illumination condition of the non-collimated source;

Partitioning module 1630, configured to initially partition all gamma events according to the detector output signal of each gamma event;

The second determination module 1640 is configured to determine the initial detector output response of the gamma event corresponding to each partition according to the partition results of all the gamma events;

The building module 1650 is used to calculate the three-dimensional effect position of each gamma event and measure the three-dimensional effect of the gamma event in the detector according to the current detector output response and the real three-dimensional effect position distribution of the gamma event in the detector Location distribution, constructing a cost function for optimizing the detector output response;

The updating module 1660 is configured to perform a minimum iterative optimization solution on the cost function, update the detector output response of each three-dimensional position partition, and complete the three-dimensional position calibration of the detector.

Optionally, the updating module 1660 is further configured to: perform a minimum value optimization on the value of the cost function through a gradient descent algorithm, and determine the detector output response of each three-dimensional position partition according to the optimization result.

Optionally, the updating module 1660 is further configured to: iteratively update the detector output response according to an iterative formula determined by the detector output response, and terminate the iteration when the set number of iterations or the iteration termination condition is reached.

Optionally, the iteration termination condition is that the difference between the function values of the cost functions of adjacent iterations does not exceed a preset value.

Optionally, building block 1650 is also used to:

Determine the first function according to the difference between the three-dimensional position distribution of all gamma events determined by the maximum likelihood estimation algorithm and the currently estimated three-dimensional action position distribution of all gamma events according to the current detector output response;

According to the current detector output response using the maximum likelihood estimation method to determine the three-dimensional position partition positions of all gamma events, and using the sum of the optimal likelihood functions for the three-dimensional position positioning of the gamma events to determine the second function;

A cost function is determined according to the first function and the second function.

Optionally, building block 1650 is also used to:

Obtained by convolving a Gaussian convolution kernel that characterizes the spatial resolution of the detector at different positions using the calculated real three-dimensional action position distribution of all gamma events, where the spatial resolution of the detector at different positions is estimated from the current detector output response .

Optionally, the irradiation conditions include the type of the radiation source irradiating the continuous crystal gamma detector, and the relative positional relationship between the radiation source and the continuous crystal gamma detector.

Optionally, the partition module 1630 is also used to:

According to the detector output signal of each gamma event, calculate the position measurement factors in the X, Y and Z directions corresponding to each gamma event;

Gamma events are initially partitioned based on location metric factors in X, Y and Z directions and a k-d tree partitioning strategy.

The three-dimensional position calibration device of the continuous crystal gamma detector provided in this embodiment can implement the embodiments of the above method, and the implementation principle and technical effect thereof are similar, and are not repeated here.

FIG. 17 is a schematic structural diagram of a device according to an embodiment of the present invention. As shown in FIG. 17 , it shows a schematic structural diagram of a computer system 1700 suitable for implementing the terminal device or server according to the embodiment of the present application.

As shown in FIG. 17, a computer system 1700 includes a central processing unit (CPU) 1701, which can be loaded into a random access memory (RAM) 1703 according to a program stored in a read only memory (ROM) 1702 or a program from a storage section 1708 Instead, various appropriate actions and processes are performed. In the RAM 1703, various programs and data necessary for the operation of the system 1700 are also stored. The CPU 1701 , the ROM 1702 , and the RAM 1703 are connected to each other through a bus 1704 . An input/output (I/O) interface 1706 is also connected to bus 1704 .

The following components are connected to the I/O interface 1705: an input section 1706 including a keyboard, a mouse, etc.; an output section 1707 including a cathode ray tube (CRT), a liquid crystal display (LCD), etc., and a speaker, etc.; a storage section 1708 including a hard disk, etc. ; and a communication section 1709 including a network interface card such as a LAN card, a modem, and the like. The communication section 1709 performs communication processing via a network such as the Internet. Drivers 1710 are also connected to I/O interface 1706 as needed. A removable medium 1711, such as a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory, etc., is mounted on the drive 1710 as needed, so that a computer program read therefrom is installed into the storage section 1708 as needed.

In particular, according to an embodiment of the present disclosure, the process described above with reference to FIG. 1 may be implemented as a computer software program. For example, embodiments of the present disclosure include a computer program product comprising a computer program tangibly embodied on a machine-readable medium, the computer program comprising program code for performing the above-described method of three-dimensional position calibration of a continuous crystal gamma detector . In such an embodiment, the computer program may be downloaded and installed from the network via the communication portion 1709, and/or installed from the removable medium 1711.

The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code that contains one or more functions for implementing the specified logical function(s) executable instructions. It should also be noted that, in some alternative implementations, the functions noted in the blocks may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It is also noted that each block of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, can be implemented in dedicated hardware-based systems that perform the specified functions or operations , or can be implemented in a combination of dedicated hardware and computer instructions.

The units or modules involved in the embodiments of the present application may be implemented in a software manner, and may also be implemented in a hardware manner. The described units or modules may also be provided in a processor. The names of these units or modules do not, in any case, qualify the units or modules themselves.

As another aspect, the present application also provides a computer-readable storage medium, and the computer-readable storage medium may be the computer-readable storage medium included in the aforementioned apparatus in the foregoing embodiment; computer-readable storage medium in the device. The computer-readable storage medium stores one or more programs used by one or more processors to execute the three-dimensional position calibration method for a continuous crystal gamma detector described in this application.

The above description is only a preferred embodiment of the present invention and an illustration of the applied technical principles. Those skilled in the art should understand that the scope of the invention involved in the present invention is not limited to the technical solution formed by the specific combination of the above-mentioned technical features, and should also cover the above-mentioned technical features without departing from the inventive concept. Other technical solutions formed by any combination of its equivalent features. For example, a technical solution is formed by replacing the above features with the technical features disclosed in the present invention (but not limited to) having similar functions.

Claims (10)

1. A method for calibrating the three-dimensional position of a continuous crystal gamma detector is characterized by comprising the following steps:

acquiring a detector output signal of each gamma event under the irradiation condition of a non-collimated source, and recording the corresponding irradiation condition of the non-collimated source;

determining a true three-dimensional effect position distribution of the gamma events within the detector based on the non-collimated source illumination conditions;

initially partitioning all of the gamma events according to the detector output signal for each gamma event;

determining an initial detector output response of the gamma event corresponding to each partition according to the partition results of all the gamma events;

calculating the three-dimensional action position of each gamma event and measuring the three-dimensional action position distribution of the acquired gamma event in the detector according to the current detector output response and the real three-dimensional action position distribution of the gamma event in the detector, and constructing a cost function for optimizing the detector output response;

and carrying out minimum value iterative optimization solution on the cost function, updating the output response of the detector of each three-dimensional position partition, and finishing the three-dimensional position scale of the detector.

2. The method of claim 1, wherein performing a minimal iterative optimization solution on the cost function to update the detector output response for each of the three-dimensional location partitions comprises:

and carrying out minimum value iterative optimization on the value of the cost function through a gradient descent algorithm, and determining the output response of the detector of each three-dimensional position partition according to an optimization result.

3. The method of claim 2, wherein the performing a minimum iterative optimization of the cost function by a gradient descent algorithm comprises:

and carrying out iterative updating on the output response of the detector according to an iterative formula determined by the output response of the detector, and terminating iteration when a set iteration number or an iteration termination condition is reached.

4. The method according to claim 3, wherein the iteration termination condition is that a difference between function values of the cost functions of adjacent iterations does not exceed a preset value.

5. The method of claim 1, wherein constructing a cost function for optimizing the detector output response based on the current detector output response and a three-dimensional effect location distribution of the gamma events within the detector comprises:

determining a first function according to the difference between the three-dimensional position distribution of all the gamma events determined by the current output response of the detector by utilizing a maximum likelihood estimation algorithm and the currently estimated three-dimensional action position distribution of all the gamma events;

determining a second function by using the sum of optimal likelihood functions for carrying out three-dimensional position positioning on the gamma events according to the three-dimensional position subarea positions of all the gamma events determined by the maximum likelihood estimation method in response to the current output of the detector;

and determining the cost function according to the first function and the second function.

6. The method of claim 5, wherein said predicted three-dimensional effect position distribution of all said gamma events is obtained by convolving a Gaussian convolution kernel characterizing spatial resolutions at different locations of a detector with a calculated true three-dimensional effect position distribution of all said gamma events, wherein the spatial resolutions at different locations of said detector are predicted from a current said detector output response.

7. The method of any one of claims 1-6, wherein the irradiation conditions include a type of radiation source irradiating the continuous crystal gamma detector, a relative positional relationship of the radiation source to the continuous crystal gamma detector, a material and a geometry of the continuous crystal gamma detector.

8. The method of any one of claims 1-6, wherein said initially binning all of said gamma events according to the detector output signal of each of said gamma events comprises:

calculating X, Y and a Z-direction position metric factor corresponding to each said gamma event based on the detector output signal of each said gamma event;

initially partitioning the gamma events based on the X, Y and the Z-direction position metric factor and a k-d tree partitioning strategy.

9. A three-dimensional position calibration apparatus for a continuous crystal gamma detector, comprising:

the acquisition and recording module is used for acquiring the detector output signal of each gamma event under the irradiation condition of the non-collimated source and recording the corresponding irradiation condition of the non-collimated source;

a first determining module for determining a true three-dimensional effect position distribution of the gamma events within the detector based on the non-collimated source illumination condition;

a partitioning module for initially partitioning all of the gamma events according to the detector output signal of each gamma event;

the second determination module is used for determining the initial detector output response of the gamma event corresponding to each subarea according to the subarea results of all the gamma events;

the construction module is used for calculating the three-dimensional action position of each gamma event and measuring the three-dimensional action position distribution of the acquired gamma event in the detector according to the current detector output response and the real three-dimensional action position distribution of the gamma event in the detector, and constructing a cost function for optimizing the detector output response;

and the updating module is used for carrying out minimum value iterative optimization solution on the cost function, updating the output response of the detector of each three-dimensional position partition and finishing the three-dimensional position scale of the detector.

10. An apparatus comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the three-dimensional position scaling method of any of claims 1-8 when executing the program.

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