CN112882081B

CN112882081B - PET detector full-channel gain calibration method

Info

Publication number: CN112882081B
Application number: CN202110041513.7A
Authority: CN
Inventors: 吴国城; 马聪; 叶宏伟; 黄振强
Original assignee: Minfound Medical Systems Co Ltd
Current assignee: Minfound Medical Systems Co Ltd
Priority date: 2021-01-13
Filing date: 2021-01-13
Publication date: 2022-12-23
Anticipated expiration: 2041-01-13
Also published as: CN112882081A

Abstract

The invention provides a full-channel gain calibration method for a PET detector, which relates to the technical field of medical images and comprises the steps of obtaining waveform data of pulse signals of all pixel points in a PET system; calculating the rising edge energy of each pixel point according to the waveform data of the pulse signal; and comparing the obtained rising edge energy with the target energy to obtain the gain calibration coefficient of each pixel. According to the invention, by means of respectively calculating the energy values of the signal rising edges of the pixels, the gain adjustment deviation caused by the difference between signals can be solved, so that the amplitude of the signals is reflected more truly, and finally, the gain adjustment coefficient is reflected more accurately. For a detector system with an SiPM as a photoelectric device, a mode of directly loading a gain table to update a gain coefficient is adopted, and the bias voltage of the corresponding SiPM does not need to be adjusted. For a detector system with an optoelectronic device of SiPM, gain adjustment of all SiPM pixels can be realized.

Description

PET detector full-channel gain calibration method

Technical Field

The invention relates to a full-channel gain calibration method for a PET detector, and belongs to the technical field of medical imaging equipment.

Background

The prior art mainly calibrates the gain of a detector:

1) The photoelectric device is PMT, and gain adjustment coefficient is obtained based on the relation between the energy full energy peak and the target peak position.

2) The photoelectric device is SiPM, and the gain of the corresponding device is adjusted by adjusting the bias voltage of the SiPM array.

The defects of the prior art are as follows:

1) And if the photoelectric device is PMT, acquiring the total energy value of the full energy peaks of all pixel points in the effective area of the corresponding PMT tube, and comparing the energy value with the target energy value to acquire the gain calibration coefficient of the corresponding PMT tube. The disadvantage of this scheme is that energy values are obtained by integrating all points of signals, however, considering the difference between signals, the energy value of the full energy peak cannot completely represent the amplitude of the signal, i.e. the energy value of the full energy peak and the amplitude do not linearly correspond, as shown in fig. 1, therefore, there is a certain deviation when the adjustment of gain is realized by the energy peak;

2) The photoelectric device is the SiPM, and the adjustment of the gain is realized by adjusting the bias value of the whole SiPM array, but the gain of the pixel points in the array cannot be calibrated, so that certain signal assignment difference exists among the pixel points in the array, and finally the counting of the pixel points in the array is not uniform, thereby affecting the final image quality.

The present application was made based on this.

Disclosure of Invention

In order to solve the above defects in the prior art, the invention provides a method for calibrating the gain of a PET detector in a full channel, which can solve the gain adjustment deviation caused by the difference between signals, thereby better realizing the adjustment of the gain without adjusting the bias voltage of the corresponding SiPM.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a full-channel gain calibration method for a PET detector comprises

(1) Acquiring waveform data of pulse signals of all pixel points in a PET system;

(2) Calculating the rising edge energy of each pixel point according to the waveform data of the pulse signal;

(3) And comparing the obtained rising edge energy with the target energy to obtain the gain calibration coefficient of each pixel.

Further, the step (1) is based on the automatic acquisition of background waveform data of the PET system, and specifically, a waveform acquisition flag bit is added on the basis of the existing hardware firmware, so that the automatic acquisition and storage of the system pulse waveform are realized.

Further, the waveform characteristics of the pulse signal include a baseline, a pulse rising edge, and a pulse falling edge.

Further, the step (2) is specifically: according to the rising edge information and the baseline information of the pulse waveform, subtracting the baseline information from the rising edge information of the sampling point to obtain the rising edge energy information of the corresponding pulse waveform; calculating a rising edge energy peak value of the corresponding pixel point according to the rising edge energy information; and the ratio of the rising edge energy peak value of the corresponding pixel point to the target peak value is the gain calibration coefficient of the corresponding pixel.

Further, in the step (3), the PET system is directly loaded and updated with the gain calibration coefficient based on the upper computer, and the gain calibration is completed.

According to the invention, the energy value is obtained by integrating the rising edge part of the signal obtained by each SiPM pixel point, and the gain calibration coefficient of the corresponding SiPM pixel is obtained by comparing the rising edge energy value with the target energy value, so that the gain calibration of all the SiPM pixels is realized.

Compared with the prior art, the invention has the following principle and beneficial technical effects:

(1) According to the invention, by means of respectively calculating the energy values of the signal rising edges of the pixels, the gain adjustment deviation caused by the difference between signals can be solved, so that the amplitude of the signals is reflected more truly, and finally, the gain adjustment coefficient is reflected more accurately.

(2) For a detector system with an optoelectronic device of SiPM, the invention adopts a mode of directly loading a gain table to update the gain coefficient, and does not need to adjust the bias voltage of the corresponding SiPM, thereby not generating the negative effect brought by adjusting the bias voltage value of the SiPM array.

(3) For a detector system with an optoelectronic device of SiPM, the invention can realize the gain adjustment of all SiPM pixels.

Drawings

FIG. 1 is a diagram showing a relationship between a signal amplitude and a full-energy peak value;

FIG. 2 is a schematic view of a PET detector system;

FIG. 3 is a flowchart of a full-channel gain calibration method for a PET detector according to the present embodiment;

FIG. 4 is a schematic diagram of a waveform characteristic of a detector pulse signal;

FIG. 5 is a schematic diagram of an energy-count distribution according to the present embodiment;

FIG. 6 is a schematic diagram of pulse signals according to the present embodiment;

FIG. 7 is a floodmap of a detector module before gain calibration;

FIG. 8 is a graph illustrating a one-dimensional position response function of a detector module before gain calibration;

FIG. 9 is a floodmap of a detector module after gain calibration;

FIG. 10 is a graph illustrating a one-dimensional position response function of a detector module after gain calibration.

Detailed Description

In order to make the technical means and technical effects achieved by the technical means of the present invention more clearly and more perfectly disclosed, the following embodiments are provided, and the following detailed description is made with reference to the accompanying drawings:

as shown in fig. 2, the PET system of this embodiment has 38 large modules, each of which has 24 detector modules, and each of the detector modules has 8 × 8 pixels, that is: the PET system totals 58368 pixels. The waveform characteristics of the detector pulse signal are shown in fig. 4.

As shown in fig. 3, the method for calibrating the gain of the PET detector in the embodiment is specifically implemented by the following steps:

(1) Acquiring background waveform data, and automatically acquiring pulse waveforms of all pixel points;

(2) When pulse waveform data are acquired, acquiring mark positions by waveforms;

(3) Acquiring rising edge information and baseline information of a corresponding pixel point according to the pulse waveform, as shown in fig. 6, wherein 1 is baseline information, 2 is rising edge information, and 3 is falling edge information;

(4) According to the rising edge information and the base line information of the pulse waveform, the rising edge information of the sampling point is adopted to subtract the base line information (the integral value is obtained by subtracting the base line from the amplitude of the rising edge), and the rising edge energy information (integral value) E corresponding to the pulse waveform is obtained _rise，i Wherein i is the number of pixels, namely: i =1 to 58368;

(5) Respectively counting by taking the detector module as a unit according to the rising edge energy informationThe energy-count distribution of the rising edge energy values of all pixels is obtained by using gaussian fitting as shown in fig. 5, and the energy-count distribution peak E of the corresponding pixel point is obtained _peak，i ；

(6) The target peak value (i.e., the experimental reference value) in this embodiment is E _t ＝450；

(7) According to the rising edge energy peak value and the target peak value, gain calibration coefficients of all pixels are obtained

(8) And (3) directly loading a gain calibration coefficient (gain calibration table) to the PET system based on the upper computer, and then completing gain calibration.

The gain calibration table includes at least detector module information and gain calibration coefficient information. The upper computer directly loads the gain calibration, namely gain calibration coefficients are respectively obtained for all pixels of the system, and the gain calibration table is directly loaded through the upper computer without adjusting power supply voltage.

Before gain calibration, a floodmap diagram of a detector module is shown in fig. 7, and a one-dimensional position response function curve thereof is shown in fig. 8, and according to the one-dimensional position response function curve, a corresponding peak-to-valley ratio is obtained as 14;

after gain calibration, the flodmap map of the detector module is shown in FIG. 9, and its one-dimensional position response function is shown in FIG. 10. Obtaining a corresponding peak-to-valley ratio of 18 according to the one-dimensional position response function; the peak-to-valley ratio is improved by about 28 percent.

The above description is provided for the purpose of further elaboration of the technical solutions provided in connection with the preferred embodiments of the present invention, and it should not be understood that the embodiments of the present invention are limited to the above description, and it should be understood that various simple deductions or substitutions can be made by those skilled in the art without departing from the spirit of the present invention, and all such alternatives are included in the scope of the present invention.

Claims

1. A PET detector full-channel gain calibration method is characterized by comprising the following steps: comprises that

(3) Comparing the obtained rising edge energy with the target energy to obtain a gain calibration coefficient of each pixel;

the step (1) is specifically that a waveform acquisition zone bit is added on the basis of the existing hardware firmware to realize automatic acquisition and storage of the system pulse waveform;

the waveform data of the pulse signal comprises a baseline, a pulse rising edge and a pulse falling edge;

the step (2) is specifically as follows: according to the rising edge information and the baseline information of the pulse waveform, subtracting the baseline information from the rising edge information of the sampling point to obtain the rising edge energy information of the corresponding pulse waveform; calculating a rising edge energy peak value of the corresponding pixel point according to the rising edge energy information; the ratio of the rising edge energy peak value of the corresponding pixel point to the target peak value is the gain calibration coefficient of the corresponding pixel;

in the step (3), the PET system is directly loaded with the updated gain calibration coefficient based on the upper computer, and the gain calibration is completed;

the gain calibration method is used for the SiPM detector;

the rising edge energy information is an integral value obtained by subtracting the integral of the baseline from the amplitude of the rising edge.