CN110916705B

CN110916705B - Method and device for calibrating DOI (direction of arrival) scale of double-end detector and PET (positron emission tomography) scanning equipment

Info

Publication number: CN110916705B
Application number: CN201911203792.1A
Authority: CN
Inventors: 邝忠华; 杨永峰; 王晓辉; 任宁; 吴三; 桑子儒; 梁栋; 刘新; 郑海荣
Original assignee: Shenzhen Institute of Advanced Technology of CAS
Current assignee: Shenzhen Institute of Advanced Technology of CAS
Priority date: 2019-11-29
Filing date: 2019-11-29
Publication date: 2023-07-07
Anticipated expiration: 2039-11-29
Also published as: CN110916705A

Abstract

The DOI automatic calibration method and device of the double-end detector comprises the steps of obtaining a DOI ratio through energy ratio of measured detector data, counting the DOI ratio and event information thereof to draw a DOI curve, fitting the DOI curve through a fitting formula to obtain a DOI boundary value, calibrating DOI calibration based on the DOI boundary value, automatically searching the DOI curve boundary value by using a curve fitting method, and obtaining high reliability; in the using process of the PET scanning equipment, the stored DOI scale table is searched, so that the on-line real-time calculation is facilitated.

Description

Method and device for calibrating DOI (direction of arrival) scale of double-end detector and PET (positron emission tomography) scanning equipment

Technical Field

The application belongs to the technical field of medical imaging equipment, and particularly relates to a method and a device for calibrating DOI (direction of arrival) scales of a double-end detector and PET (positron emission tomography) scanning equipment.

Background

At present, positron emission tomography (Positron Emission Tomography, PET) is a molecular imaging technology with high sensitivity for tumor imaging, brain science disease research and the like. Depth of action (Depth Of Interaction, DOI) is a major factor impeding the realization of PET imaging systems simultaneously with uniform high spatial resolution and high efficiency. The traditional PET detector based on double-end reading can provide very high depth resolution and continuous depth information, and is an effective solution for simultaneously realizing high spatial resolution and high sensitivity.

However, at present, a traditional double-end readout PET detector does not have a referenceable depth automatic calibration method, and a depth lookup table (DOI lookup table) is obtained by manually searching for a boundary and then linearly calibrating, however, for a PET imaging system, the number of used crystals is usually large (more than 5000 scintillation crystals), the manual calibration becomes difficult, and the workload is also large.

Disclosure of Invention

The application aims to provide a DOI automatic calibration method and device of a double-end detector and PET scanning equipment, and aims to solve the problems of high difficulty and large workload of the DOI automatic method of the traditional PET detector.

A first aspect of an embodiment of the present application provides a DOI automatic calibration method for a double-ended detector, including:

carrying out energy ratio calculation on the acquired data of the double-end detector to obtain a DOI ratio of the action depth;

acquiring event information corresponding to each DOI ratio, and drawing a DOI curve based on the DOI ratio and the corresponding event information;

performing approximate fitting on the DOI curve, and determining a DOI boundary value based on the fitted DOI curve;

and calibrating the DOI scale based on the DOI boundary value.

A second aspect of embodiments of the present application provides a DOI automatic calibration device for a double-ended detector, including:

the first calculation module is used for calculating the energy ratio of the acquired data of the double-end detector to obtain the DOI ratio of the action depth;

the curve drawing module is used for obtaining the event information corresponding to each DOI ratio and drawing a DOI curve based on the DOI ratio and the corresponding event information;

the second calculation module is used for performing approximate fitting on the DOI curve and determining a DOI boundary value based on the fitted DOI curve;

and the scale module is used for calibrating the DOI scale based on the DOI boundary value.

A third aspect of the embodiments of the present application provides a PET scanning device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, the processor implementing the steps of the method as described above when executing the computer program.

A fourth aspect of the embodiments of the present application provides a computer readable storage medium storing a computer program which, when executed by a processor, implements the steps of the DOI auto-scaling method as described above.

Compared with the prior art, the embodiment of the application has the beneficial effects that:

according to the DOI automatic calibration method and device for the double-end detector, the DOI ratio is obtained through the energy ratio of the detected detector data, the DOI ratio and event information thereof are counted to draw a DOI curve, then the DOI curve is fitted through a fitting formula to obtain a DOI boundary value, the DOI scale is calibrated based on the DOI boundary value, the DOI curve boundary value is automatically searched by using a curve fitting method, and the reliability of the result is high; in the using process of the PET scanning equipment, the stored DOI scale table is searched, so that the on-line real-time calculation is facilitated.

Drawings

FIG. 1 is a specific flowchart of a DOI automatic calibration method of a double-ended detector according to an embodiment of the present application;

FIG. 2 is a schematic diagram of a dual-end detector according to an embodiment of the present disclosure;

FIG. 3 is a DOI curve and fitted graph provided in the examples of the application;

FIG. 4 is a block diagram of a DOI automatic calibration device for a double-ended detector according to an embodiment of the present application;

fig. 5 is a schematic diagram of a PET scanning device provided in an embodiment of the present invention.

Detailed Description

In order to make the technical problems, technical schemes and beneficial effects to be solved by the present application more clear, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application.

According to the embodiment of the application, the DOI ratio data is obtained through the energy ratio of the measured detector data to draw the DOI curve, then the DOI curve is fitted through the fitting formula to obtain the DOI boundary value, the DOI scale is calibrated based on the DOI boundary value to obtain the DOI lookup table, the DOI curve boundary value is automatically searched by using the curve fitting method, and the result reliability is high.

Referring to fig. 1, a DOI automatic calibration method of a double-ended detector in an embodiment of the present application includes the following steps:

step S110, energy ratio calculation is carried out on the acquired data of the double-end detector, and the DOI ratio of the action depth is obtained.

Referring to fig. 2, the dual end readout PET detector includes a first PET detector 210 and a second PET detector 220, and the acquired data of the dual end readout PET detector includes a first energy value acquired by the first PET detector 210 and a second energy value acquired by the second PET detector 220.

In this embodiment, the first PET detector 210 and the second PET detector 220 are disposed opposite to each other, and the first PET detector 210 and the second PET detector 220 are both silicon photomultiplier (Silicon Photomultiplier, siPM) arrays, and the double-end detector using the silicon photomultiplier can effectively measure the interaction depth, and has good magnetic field compatibility. The dual end readout PET detector also includes a scintillation crystal array 230 disposed between the first PET detector 210 and the second PET detector 220. The scintillation crystal can be any one of Lutetium Yttrium Silicate (LYSO), lutetium Silicate (LSO), bismuth Germanate (BGO) and the like, and the length of the crystal is 10 mm-30 mm. In this embodiment, the material of the scintillation crystal is lutetium yttrium silicate, and the crystal length is 20mm.

In one embodiment, the radiation source is positioned on the side of the dual-end readout PET detector adjacent to the second PET detector 220, and then measurements are taken and data acquired by the first PET detector 210 and the second PET detector 220. The DOI ratio is calculated by substituting the first and second energy values acquired by the first and

second PET detectors

210 and 220 into the following formula.

E1 is a first energy value and E2 is a second energy value.

And step S120, obtaining event information corresponding to each DOI ratio, and drawing a DOI curve based on the DOI ratio and the corresponding event information.

Specifically, after each DOI ratio is obtained, event information corresponding to each DOI ratio is counted based on each DOI ratio, and in the embodiment of the present application, a visible light is converted into an electrical signal by a silicon photomultiplier to be referred to as event information. Then, the DOI ratio and the corresponding event information quantity are formed into a coordinate data: [ DOI ratio, event information count ], and then plotted as DOI curve 11 (see FIG. 3) based on the coordinate data.

And step S130, performing approximate fitting on the DOI curve, and determining a DOI (ratio) boundary value based on the fitted DOI curve.

In this embodiment, a fitting formula is adopted to perform approximate fitting on the DOI curve, and a DOI boundary value is obtained according to the fitted DOI curve (fitting formula).

The fitting formula is constructed for Erf (x) based on an error function,

the DOI curve (i.e., the coordinate data based on the DOI ratio) is approximately fitted using the fitting formula to obtain a fitted curve 12 (refer to fig. 3), and the boundary value of the DOI curve is obtained through the fitting result.

In this embodiment, the fitting formula is:

wherein A is an amplitude coefficient, and the fitting initial value of A is about the maximum count value; alpha is an exponential decay coefficient, and the fitting initial value of alpha is smaller than 0.1; erf (x) is the error function,

delta is root mean square error, and the fitting initial value of delta is generally selected as0.1 to 1, such as 0.5; x is DOI ratio; a is the left boundary value of the DOI curve after fitting, the fitting initial value of a is 0-0.5, which can be selected according to practical situations, 0.3 is selected in the embodiment, b is the right boundary value of the DOI curve after fitting, the fitting initial value of b is 0.5-1, and 0.7 is selected in the embodiment. And then fitting is carried out based on a fitting formula according to the initial value of each parameter and the DOI curve, and the boundary value of the DOI curve is obtained through the fitting result.

And step S140, calibrating the DOI (ratio) scale based on the DOI (ratio) boundary value.

Specifically, according to a linear scale method, equally dividing the DOI ratio between boundary values of the DOI curve into N parts to obtain a DOI scale table, wherein N is a positive integer greater than or equal to 2.

The DOI ratio is equally divided into N parts (e.g., a=0.3, b=0.7, n=8) to obtain the DOI scale (7 demarcation points per section doi_12 to doi_78) as follows:

DOI_12	DOI_23	DOI_34	DOI_45	DOI_56	DOI_67	DOI_78
							0.35	0.40	0.45	0.50	0.55	0.60	0.65

in the table, DOI_12 represents the demarcation point for DOI_1 and DOI_2, and so on.

Referring to fig. 4, a DOI automatic calibration device of a double-ended detector according to an embodiment of the present application includes:

a first calculation module 410, configured to perform an energy ratio calculation on the data collected by the double-end detector, so as to obtain a DOI ratio of the depth of action;

the curve drawing module 420 is configured to obtain event information corresponding to each DOI ratio, and draw a DOI curve based on the DOI ratios and the respective corresponding event information;

a second calculation module 430, configured to perform approximate fitting on the DOI curve, and determine a DOI boundary value based on the DOI curve after fitting;

a scale module 440 for calibrating the DOI scale based on the DOI boundary value.

In one embodiment, the second calculation module 410 is specifically configured to approximately fit the DOI curve using the following fitting formula, and calculate the DOI boundary value according to the fitting formula:

wherein A is an amplitude coefficient, alpha is an exponential decay coefficient, erf (x) is an error function,

delta is root mean square error, x is DOI ratio, a is left boundary value of the DOI curve after fitting, and b is right boundary value of the DOI curve after fitting.

In one embodiment, a dual end detector includes a first PET detector and a second PET detector, the acquired data of the dual end detector including a first energy value acquired by the first PET detector and a second energy value acquired by the second PET detector;

the first calculation module is specifically configured to calculate a DOI ratio by substituting the first energy value and the second energy value into the following formula; the method comprises the steps of carrying out a first treatment on the surface of the

Wherein E1 is a first energy value and E2 is a second energy value.

In one embodiment, the first PET detector and the second PET detector are silicon photomultiplier arrays, and the double-ended detector further includes a scintillation crystal array disposed between the first PET detector and the second PET detector, where the scintillation crystal is any one of Lutetium Yttrium Silicate (LYSO), lutetium Silicate (LSO), bismuth Germanate (BGO), and the like.

In one embodiment, the scaling module 440 is configured to divide the DOI ratio between the boundary values of the DOI curve into N parts according to a linear scaling method, to obtain a DOI (scale) lookup table, where N is a positive integer greater than or equal to 2.

Fig. 5 is a schematic diagram of a PET scanning device according to an embodiment of the present application. As shown in fig. 5, the PET scanning device 5 of this embodiment includes: a processor 50, a memory 51 and a computer program 52 stored in said memory 51 and executable on said processor 50. The processor 50, when executing the computer program 52, implements the steps of the DOI automatic calibration method embodiment of each double-ended detector described above, such as steps S110 to 140 shown in fig. 1. Alternatively, the processor 50, when executing the computer program 52, performs the functions of the modules/units of the apparatus embodiments described above, such as the functions of the modules 410-440 shown in fig. 4.

By way of example, the computer program 52 may be partitioned into one or more modules/units that are stored in the memory 51 and executed by the processor 50 to complete the present application. The one or more modules/units may be a series of computer program instruction segments capable of performing specific functions for describing the execution of the computer program 52 in the PET scanning device 5. For example, the computer program 52 may be divided into a first calculation module, a curve drawing module, a second calculation module, and a scale module.

The console in the PET scanning device 5 may be a computing device such as a desktop computer, a notebook computer, a palm computer, and a cloud server. The PET scanning device may include, but is not limited to, a processor 50, a memory 51. It will be appreciated by those skilled in the art that fig. 5 is merely an example of a PET scanning device 5 and is not meant to be limiting as to the PET scanning device 5, and may include more or fewer components than shown, or may combine certain components, or different components, e.g., the PET scanning device may also include input and output devices, network access devices, buses, etc.

The processor 50 may be a central processing unit (Central Processing Unit, CPU), other general purpose processors, digital signal processors (Digital Signal Processor, DSP), application specific integrated circuits (Application Specific Integrated Circuit, ASIC), off-the-shelf programmable gate arrays (Field-Programmable Gate Array, FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or the like. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.

The memory 51 may be an internal storage unit of the PET scanning device 5, such as a hard disk or a memory of the PET scanning device 5. The memory 51 may also be an external storage device of the PET scanning device 5, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card) or the like, which are provided on the PET scanning device 5. Further, the memory 51 may also include both an internal storage unit and an external storage device of the PET scanning device 5. The memory 51 is used for storing the computer program as well as other programs and data required by the PET scanning device 5. The memory 51 may also be used to temporarily store data that has been output or is to be output.

The above embodiments are only for illustrating the technical solution of the present application, and are not limiting; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present application, and are intended to be included in the scope of the present application.

Claims

1. A method of calibrating DOI scale for a double ended detector, comprising:

calibrating a DOI scale based on the DOI boundary value;

the approximately fitting the DOI curve, and determining the DOI boundary value based on the fitted DOI curve comprises:

performing approximate fitting on the DOI curve by adopting the following fitting formula, and fitting according to the fitting formula to obtain a DOI boundary value;

2. A method as in claim 1, wherein said calibrating the DOI scale based on the DOI boundary value comprises:

equally dividing the DOI ratio between the DOI boundary values into N parts to obtain a DOI scale, wherein N is an integer greater than or equal to 2.

3. The method of claim 1, wherein the double ended detector comprises a first PET detector and a second PET detector, the data acquired by the double ended detector comprising a first energy value acquired by the first PET detector and a second energy value acquired by the second PET detector;

the energy ratio calculation is performed on the collected data of the double-end detector to obtain a DOI ratio of action depth, and the method comprises the following steps: substituting the first energy value and the second energy value into the following formula to calculate DOI ratio;

wherein E1 is the first energy value and E2 is the second energy value.

4. The method of claim 3, wherein the first PET detector and the second PET detector are each a silicon photomultiplier array, the double ended detector further comprising a scintillation crystal array disposed between the first PET detector and the second PET detector.

5. An apparatus for calibrating DOI scale of a double ended detector, comprising:

the scale module is used for calibrating DOI scales based on the DOI boundary values;

the second calculation module is specifically configured to perform approximate fitting on the DOI curve by using the following fitting formula, and obtain a DOI boundary value by fitting according to the fitting formula:

6. The apparatus of claim 5, wherein the double ended detector comprises a first PET detector and a second PET detector, the data acquired by the double ended detector comprising a first energy value acquired by the first PET detector and a second energy value acquired by the second PET detector;

the first calculation module is specifically configured to calculate a DOI ratio by substituting the first energy value and the second energy value into the following formula;

wherein E1 is the first energy value and E2 is the second energy value.

7. A PET scanning device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that the processor implements the steps of the method according to any one of claims 1 to 4 when the computer program is executed.

8. A computer readable storage medium storing a computer program, characterized in that the computer program when executed by a processor implements the steps of the method according to any one of claims 1 to 4.