阅读说明：本技术 一种优化多面体探测器中离散晶体布局的方法 (Method for optimizing discrete crystal layout in polyhedral detector ) 是由 许剑锋 叶百合子 张熙 解强强 谢思维 彭旗宇 于 2019-08-29 设计创作，主要内容包括：本发明属于晶体探测器领域,并公开了一种优化多面体探测器中离散晶体布局的方法。该方法包括下列步骤：(a)对于多面体探测器,确定其中最小结构单元的形状和外接圆的半径取值范围；(b)绘制多幅网格图,将最小结构单元放置在每幅网格图中,计算每幅网格图中最小结构单元中包括最多填充单元的数量,以此计算最小结构单元的填充率；(c)所有网格图中填充率的最大值对应的网格图中网格的尺寸大小作为最小结构单元的外接圆尺寸,以此获得最小结构单元的尺寸和该最小结构单元的填充率,实现多面体探测器中离散晶体布局的优化。通过本发明,实现多边形探测器中离散晶体的最优布局,提高探测器的有效覆盖面积。(the invention belongs to the field of crystal detectors and discloses a method for optimizing the layout of discrete crystals in a polyhedral detector. The method comprises the following steps: (a) for a polyhedral detector, determining the shape of a minimum structure unit and the radius value range of a circumscribed circle; (b) drawing a plurality of grid graphs, placing the minimum structural units in each grid graph, and calculating the number of the minimum structural units in each grid graph, wherein the minimum structural units comprise the maximum filling units, so that the filling rate of the minimum structural units is calculated; (c) and the size of the grid in the grid map corresponding to the maximum value of the filling rate in all the grid maps is used as the size of the circumscribed circle of the minimum structure unit, so that the size of the minimum structure unit and the filling rate of the minimum structure unit are obtained, and the optimization of the discrete crystal layout in the polyhedral detector is realized. By the method, the optimal layout of discrete crystals in the polygonal detector is realized, and the effective coverage area of the detector is increased.)

1. A method of optimizing the placement of discrete crystals in a polyhedral detector, the method comprising the steps of:

(a) For a polyhedral detector, determining the shape of a minimum structural unit in the polyhedral detector, and then calculating according to the size of the polyhedral detector to obtain the radius value range of a circumscribed circle of the minimum structural unit;

(b) Drawing a plurality of grid graphs, wherein the size of each grid in each grid graph is set according to the value range of a circumscribed circle of the minimum structure unit, the minimum structure unit is placed in each grid graph, the number of filling units which can be contained in the minimum structure unit in each grid graph at most is calculated, and the filling rate of the minimum structure unit is calculated according to the number of the filling units, so that the filling rate of the minimum structure unit in all the grid graphs is obtained, wherein the filling units are three discrete crystals which are connected in parallel;

(c) and acquiring the maximum value of the filling rate of the minimum structure unit in all the grid graphs, wherein the size of the grid in the grid graph corresponding to the maximum value is taken as the size of the circumscribed circle of the minimum structure unit, so as to acquire the size of the minimum structure unit and the filling rate of the minimum structure unit, and realize the optimization of the discrete crystal layout in the polyhedral detector.

2. A method of optimizing the placement of discrete crystals in a polyhedral detector as recited in claim 1, wherein in step (b), the discrete crystals comprise an array of crystals and an array of sipms, the array of crystals being disposed on and coupled to the array of sipms.

3. A method of optimizing the layout of discrete crystals in a polyhedral detector as recited in claim 2, wherein in step (b), the sipms are 6 x 6 arrays including 36 electron channels for data transmission.

4. A method of optimizing the layout of discrete crystals in a polyhedral detector as recited in claim 1, wherein in step (a), the minimal structural elements are polygons.

5. A method for optimizing the layout of discrete crystals in a polyhedral detector as recited in claim 1, wherein in the step (b), the size of each grid in each grid is set by first setting a step size, then setting the grid size of the initial grid, and finally increasing or decreasing the grid size step by step according to the step size, thereby obtaining the size of the grid in all the grids.

6. A method of optimizing the placement of discrete crystals in a polyhedral detector as recited in claim 1, wherein in step (b), the fill factor is preferably calculated as follows: firstly, the area of the filling units is obtained according to the size of the discrete crystal, then the product of the number of the filling units and the area of the discrete units is calculated, and the ratio of the product to the total area of the grid graph is the filling rate.

7. A method of optimizing the placement of discrete crystals in a polyhedral detector as recited in claim 1, wherein in step (b), the packing elements in the minimal structural unit are preferably distributed in a manner that they are arranged from one side of the minimal structural unit to the opposite side, or from each side of the minimal structural unit to the middle, or from the middle or diagonal of the minimal structural unit to both sides.

Technical Field

The invention belongs to the field of crystal detectors, and particularly relates to a method for optimizing the layout of discrete crystals in a polyhedral detector.

Background

When a brain is imaged by a traditional annular PET system developed by whole-body scanning, most (> 80%) signals are dissipated and not detected, the system has low system sensitivity and low image signal-to-noise ratio, high-performance dynamic imaging is difficult to perform, and the dynamic process of metabolism in the brain is difficult to effectively observe.

the spherical PET system can be used for dynamically monitoring metabolism in the brain, and has higher system sensitivity and spatial resolution due to small radius, large solid space angle, less signal loss and high crystal space filling rate. However, because of the great difficulty in the aspects of detector design, electronic system design and image reconstruction technology, the spherical PET system is difficult to realize in engineering, the system can be designed to be a polyhedral structure and is close to a sphere, and the PET system mainly comprises a gamma-ray detector module, a coincidence discrimination circuit, a data acquisition preprocessing system and a computer image processing system. The positron annihilates in a living body to generate a gamma photon pair, the gamma photon pair is detected by a detector module, a coincidence event is obtained through a coincidence discrimination circuit, a data preprocessing system carries out a series of correction, interpolation and separation on the acquired data, and finally, original projection data for image reconstruction are obtained and transmitted to a computer image processing system for image reconstruction.

System sensitivity, system spatial resolution and signal-to-noise ratio are the most important indicators for evaluating PET technology. The system sensitivity is one of the most important parameters of a medical whole-body PET system, represents the capability of the system for acquiring effective signal data, is an important index for ensuring the spatial resolution of a system reconstruction image, the system spatial resolution is an important index for ensuring the imaging quality of the system, and is influenced by the system spatial resolution and an image reconstruction algorithm, the reduction of the crystal width can improve the image spatial resolution, but the excessive reduction of the crystal size can enlarge the reaction depth effect, increase the parallax, and on the contrary, can cause the reduction of the system spatial resolution. The polyhedral detector is one of spherical PET systems, and how to make the detectable units distributed in the single polygon of the polyhedral detector as much as possible to improve the detection accuracy is closely related to the layout of discrete crystals in the polygonal detector, which is also a problem to be solved at present.

disclosure of Invention

Aiming at the defects or the improvement requirements of the prior art, the invention provides a method for optimizing the layout of discrete crystals in a polyhedral detector, which realizes the layout of the discrete crystals in the polyhedral detector by planning the filling rate of the minimum structural unit in the polyhedral detector, maximizes the detectable region in the polyhedral detector, improves the effective detection region of the polyhedral detector and improves the detection precision.

To achieve the above object, according to the present invention, there is provided a method for optimizing a layout of discrete crystals in a polyhedral detector, the method comprising the steps of:

(a) For a polyhedral detector, determining the shape of a minimum structural unit in the polyhedral detector, and then calculating according to the size of the polyhedral detector to obtain the radius value range of a circumscribed circle of the minimum structural unit;

(b) Drawing a plurality of grid graphs, wherein the size of each grid in each grid graph is set according to the value range of a circumscribed circle of the minimum structure unit, the minimum structure unit is placed in each grid graph, the number of filling units which can be contained in the minimum structure unit in each grid graph at most is calculated, and the filling rate of the minimum structure unit is calculated according to the number of the filling units, so that the filling rate of the minimum structure unit in all the grid graphs is obtained, wherein the filling units are three discrete crystals which are connected in parallel;

(c) and acquiring the maximum value of the filling rate of the minimum structure unit in all the grid graphs, wherein the size of the grid in the grid graph corresponding to the maximum value is taken as the size of the circumscribed circle of the minimum structure unit, so as to acquire the size of the minimum structure unit and the filling rate of the minimum structure unit, and realize the optimization of the discrete crystal layout in the polyhedral detector.

further preferably, in step (b), the discrete crystals comprise an array of crystals and an array of sipms, the array of crystals being disposed on and coupled to the array of sipms.

Further preferably, in step (b), the sipms are 6 × 6 arrays including 36 electronic channels for data transmission.

Further preferably, in step (a), the minimum structural unit is a polygon.

Further preferably, in the step (b), the size of each grid in each grid map is set according to the following manner, firstly setting the step size, then setting the grid size of the initial grid map, and finally gradually increasing or decreasing the grid size according to the step size, thereby obtaining the size of the grid in all grid maps.

Further preferably, in step (b), the filling rate is preferably calculated as follows: firstly, the area of the filling units is obtained according to the size of the discrete crystal, then the product of the number of the filling units and the area of the discrete units is calculated, and the ratio of the product to the total area of the grid graph is the filling rate.

Further preferably, in the step (b), the filling units in the minimum structural unit are preferably distributed in a manner of being arranged from one side of the minimum structural unit to the opposite side, or from each side of the minimum structural unit to the middle, or from the middle part or diagonal line of the minimum structural unit to both sides.

In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:

1. According to the invention, the form of filling the grid diagram by adopting a plurality of filling units is adopted, the filling rate is the largest as the final filling mode, compared with the mode of directly filling the polygonal continuous crystal, the filling units are discrete crystal arrays, the mature decoding and imaging technology is provided, the hidden danger of the complex edge effect is avoided, the resolution ratio of the system can reach a higher level, the DOI decoding capability and the high-performance time measurement potential are provided, meanwhile, the relatively common crystal and the SiPM with the existing model are used, the system forms the polygonal complex form by a simple structure, and the production and processing cost can be greatly reduced on the premise of ensuring the effective area utilization rate of the detector packaging box;

2. the invention has the advantages that the filling unit is three discrete crystals which are connected in parallel, each SiPM is provided with 36 electronic channels, the three discrete crystals comprise 108 electronic channels, the simplicity and systematization of the arrangement of the flat cables can be ensured, compared with the condition that a single polygonal detector module is directly filled with small-size crystal bars in a large area, the FPAG with 108 channels is maximally utilized, the resolution of the imaging position can be facilitated based on the systematization regularity, the inspection, the replacement and the arrangement of a single module are facilitated, and under the condition that the single polygonal detector is filled with the modules, the inconvenience of designing and decoding of the different-type SiPM (silicon photomultiplier) is avoided, the utilization rate and the regularity of the number of reading circuit channels are ensured, and the effective area of the polygonal detector can reach more than 80 percent;

3. According to the invention, the minimum structural unit is filled by the plurality of independent filling units, so that the flat cable arrangement of the polygonal detector is systematized, the regularity of the whole system is excellent, and the imaging position and the inspection, maintenance, replacement and the like of a single module are conveniently distinguished; meanwhile, the invention avoids the inconvenience of designing and decoding the special-shaped SiPM, and the used crystal array has mature decoding and imaging technologies, thereby avoiding the hidden danger of edge effect;

4. The invention maximally utilizes 108-channel FPAG, ensures that the effective area of the polygonal detector can reach more than 80%, greatly reduces the production and processing cost, ensures that the polyhedral PET system approaching to the sphere has higher feasibility, and is expected to obtain a PET brain system with higher system sensitivity and spatial resolution.

drawings

FIG. 1 is a flow chart of a method for optimizing the placement of discrete crystals in a polyhedral detector, constructed in accordance with a preferred embodiment of the present invention;

FIG. 2 is a schematic diagram of a crystal array structure constructed in accordance with a preferred embodiment of the present invention;

FIG. 3 is a schematic diagram of a SiPM array architecture constructed in accordance with a preferred embodiment of the present invention;

FIG. 4 is a schematic diagram of the structure of a discrete crystal constructed in accordance with a preferred embodiment of the present invention;

FIG. 5 is a schematic diagram of the construction of the smallest building block polygon of a polyhedral detector constructed in accordance with a preferred embodiment of the present invention;

FIG. 6 is a schematic diagram of a grid map constructed in accordance with a preferred embodiment of the present invention;

fig. 7 is a graph of fill factor versus circumscribed circle radius constructed in accordance with a preferred embodiment of the present invention.

Detailed Description

in order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

As shown in fig. 1, a method of optimizing the placement of discrete crystals in a polyhedral detector, the method comprising the steps of:

(a) For a polyhedral detector, determining the shape of a minimum structural unit in the polyhedral detector, and then calculating according to the size of the polyhedral detector to obtain the radius value range of a circumscribed circle of the minimum structural unit, wherein the minimum structural unit in the embodiment is a pentagon, but the shape of the minimum structural unit is not limited to the pentagon;

(b) drawing a plurality of grid graphs, setting the size of a polygon in each grid according to the value range of a circumscribed circle of the minimum structure unit, placing the minimum structure unit in each grid graph, calculating the number of the minimum structure units in each grid graph, including the maximum filling units, and calculating the filling rate of the minimum structure units according to the number of the filling units so as to obtain the filling rates of all the grid graphs, wherein the filling units are three discrete crystals connected in parallel;

The invention provides a crystal detector filling and distribution mode based on a fully-wearable polygonal brain PET system packaging box, the polygonal detector packaging box in the mode can basically achieve the optimal crystal filling rate on the premise of ensuring the utilization rate of 108FPGA and the convenience of wire arrangement, and a single discrete crystal comprises a crystal array, an SiPM array and three discrete crystals to form a filling unit. There will be 3 SiPM arrays per filler cell, sharing (3 × 6 × 6)108 channels, i.e. one module can use 100% of a 108-channel FPGA.

In the discrete crystal array, the crystal array and the SiPM array are directly coupled together by a coupling agent (optical glue, air coupling and the like), a light guide exists between the SiPM array and the crystal array, and 6 surfaces of the discrete crystal except the coupling surfaces with the crystal array and the SiPM array are covered by a reflecting material, wherein the reflecting material can be a reflecting film, ESR, Teflon, barium sulfate and the like.

The schematic diagram of a single discrete crystal structure is shown in fig. 4, and is composed of a crystal array and an SiPM array, wherein the crystal array is shown in fig. 2, and the SiPM array is shown in fig. 3. Each individual cubic strip in fig. 2 is a single crystal strip, and the material may be Ce, CsI, NaI, BGO, LYSO, or the like. The plurality of single crystal strips are packed and fixed into a crystal array by various optional substances such as BaSO4 and the like. Each small square in fig. 3 represents a sheet of SiPM (silicon photomultiplier) that is soldered to a circuit board to form an array. The size of the single SiPM is not limited, and the size of the single SiPM can be flexibly changed according to the size of the crystal array on the premise of ensuring the size of the crystal array to be 6 multiplied by 6.

The crystal array and the SiPM can be coupled, the size of a single crystal strip, the size of the crystal array and the size of the SiPM array are not limited, the SiPM is a 6 x 6 array, the size and the area of a single SiPM are not limited, and a single discrete crystal has 36 channels.

The invention is based on the detection of small crystal decoding, using an 8 × 8 array of LYSO discrete crystals with a single stripe size of 0.75 × 0.75 × 10mm³And a single piece size of 3X 3mm²The method comprises the following steps of (1) 10 × 10SiPM array coupling, selecting an energy window of an effective event, respectively using four SiPMs at the coupling center and 9 SiPMs at the coupling center, wherein 4 × 4(16 channels), 2 × 2(4 channels) and 3 × 3(9 channels) are adopted for decoding, and a discrete crystal array formed by small-size crystal bars 3 × 3(9 channels) can be decoded, so that a better decoding effect is achieved, and the decoding feasibility is used as a premise for filling polygons in a polyhedral detector.

(c) And acquiring the maximum value of the filling rate in all the grid graphs, wherein the size of the grid in the grid graph corresponding to the maximum value is taken as the size of the circumscribed circle of the minimum structure unit, so as to acquire the size of the minimum structure unit and the filling rate of the minimum structure unit, and realize the optimization of the discrete crystal layout in the polyhedral detector.

in order to achieve the purposes that the number of modules is an integer, the arrangement of flat cables, the overhaul and the replacement of detectors are convenient, and the utilization rate of FPGA channels is improved, the invention adopts a reverse-thrust thought in the module filling process.

when a single polygonal packaging box of the polyhedral detector is filled, the filling direction is arranged from one side of the polygon to the opposite side, or the filling direction is arranged from each side of the polygon to the middle, or from the middle part or diagonal line to two sides, and the direction and the mode of the filling module are not limited. The manner of filling each module of the cube, either horizontally, vertically, or the rest in combination with the actual requirements, may be all.

On the basis of the arranged modules, the required shape of the polygonal detector is gathered to the maximum extent, the effective filling rate is the ratio of the occupied area of the modules to the area of the polygon, and the data of the size of the side of the polygon with the maximum effective filling area, the inner diameter of a sphere in a polyhedron formed by the polygon and the polygonal detector and the like are reversely deduced.

Specifically, taking a polygonal brain PET system as an example, the inscribed sphere radius range of the target polyhedron is selected according to the average size of the brain, and the corresponding data such as the side length of the polygonal encapsulation box, the radius of the circumscribed circle and the like are calculated. And automatically generating a polygon grid map according to the step length of n in the polygon side length interval by using MATLAB and other compiling programs, obtaining the optimal arrangement and calculating the number of modules required in the arrangement mode and the module filling rate according to the distribution of the grid map and various different module arrangement modes.

And after the calculation of the filling rate in the interval is completed, acquiring a curve corresponding diagram of the theoretical filling rate and the diameter of the inscribed sphere of the polyhedron, and acquiring a theoretical peak value through program fitting to obtain the polyhedron corresponding to the diameter of the inscribed sphere with the optimal size, the polygonal packaging box and a module filling mode of the polygonal packaging box.

the present invention will be further illustrated with reference to specific examples.

For example, a dodecahedron is selected as a target polyhedron structure, and the minimum structural unit of the subelement of the dodecahedron is a pentagonal detector packaging box. The radius of an inscribed sphere of the dodecahedron can be selected to be 12-15 cm according to the size of a brain of a study, the inner size of the pentagonal packaging box and the radius of an circumscribed circle are calculated by considering the machining allowance, the assembly allowance and the like of the packaging box, and the radius range is 9-11 cm.

As shown in fig. 5, the radius R of the internal sphere of the brain system is 12cm to 15cm, R is 1.11351636a, and the external size of the pentagonal packaging box is five-sided. and a is the side length of the pentagonal detector, and after considering the processing allowance, the assembly allowance and the thickness of the packaging box, a 'is the actual side length size inside the packaging box of the pentagonal detector, wherein a is larger than a'. r is the radius of the circumscribed circle of the dodecahedron pentagon which is the minimum structural unit, wherein r is a'/1.1756, and the radius r of the circumscribed sphere of the pentagon packaging box is 9 cm-11 cm;

the program draws a pentagon and a grid graph thereof corresponding to the radius of the circumscribed circle by taking 0.2 as a step length, arranges modules in the pentagon packaging box, obtains the optimal arrangement mode corresponding to the packaging box of each size, and calculates to obtain the corresponding module number N, as shown in FIG. 6, the size of a single grid in the grid graph is the size of a discrete crystal, the pentagon in the grid graph is a polygon generated according to a set step length, and the area occupied by each rectangular color block in the grid graph is the area of a filling unit, namely three discrete crystals connected in parallel. N is the number of the rectangles of the color blocks and is equal to the number of the filling units, and the number of the discrete crystals filled in the pentagonal packaging box is three times of the number of the filling units. The effective filling rate of the pentagonal detector packaging box is the ratio of the occupied area of the modules to the area of the pentagonal detector.

As shown in fig. 7, the abscissa in the figure is the inscribed sphere diameter of the polyhedron detector, and the radius, the margin of the polygonal packaging box of the minimum structural unit, the thickness and the like are calculated according to the inscribed sphere diameter, so as to obtain the size of the polygon and the radius range of the corresponding circumscribed circle of the polygon. And generating polygons according to the set step length, wherein each polygon can obtain the theoretical filling rate in the grid graph. The ordinate in fig. 7 is the theoretical filling rate, and fig. 7 shows the relationship between the theoretical filling rate and the diameter of the inscribed sphere of the polyhedron structure.

and (3) circumcircle: r is 10.15cm

Side length of the pentagon: a' 1.1756r 11.9323cm

Packaging area: s-5 a' (tan54 °) 2/4-244.9612 cm²

the length of the outer side of the pentagonal packaging box is as follows: a > a'

Inscribed sphere radius: r is 1.113516364 × a 13.285cm

Number of submodules: 51 are provided with

the number of modules is as follows: 17 are provided with

Effective filling area: se is 17X 2.016X 3cm²＝207.2771cm²

The filling rate A%

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.