CN-120019792-B - Scattering correction method, device, digitizing apparatus, and computer readable storage medium

CN120019792BCN 120019792 BCN120019792 BCN 120019792BCN-120019792-B

Abstract

The application provides a scattering correction method, a device, a digitizing device and a computer readable storage medium, wherein the method comprises the steps of acquiring a downsampling response line based on detection data; based on a maximum likelihood-expectation maximization iterative algorithm, an estimated objective function corresponding to each downsampling response line is obtained by utilizing a moment estimation method, the estimated objective function is solved, the scattering coincidence event quantity corresponding to each downsampling response line is obtained, upsampling processing is carried out on the downsampling response lines to obtain upsampling response lines, and the scattering coincidence event quantity corresponding to each upsampling response line is calculated. When the embodiment of the application is used for carrying out scattering correction, the method does not depend on an activity image and an attenuation image, and the method does not need super parameters, so that the super parameters are not required to be set in a determined range, the realization is simple, and the accuracy is high.

Inventors

LI ANG
FANG LEI
LI BINGXUAN
ZHANG BO

Assignees

合肥锐世数字科技有限公司

Dates

Publication Date: 20260512
Application Date: 20231120

Claims (20)

1. A scatter correction method, the scatter correction method comprising: acquiring a downsampling response line based on the detection data; Based on a maximum likelihood-expectation maximization iterative algorithm, acquiring an estimated objective function corresponding to each downsampling response line by using a moment estimation method, wherein the estimated objective function is acquired based on a two-dimensional instantaneous coincidence energy histogram, a two-dimensional delay coincidence energy histogram, a probability density function of scattered photons and a probability density function of unscattered photons corresponding to each downsampling response line; Solving the estimation objective function to obtain the scattering coincidence event number corresponding to each downsampling response line; Up-sampling the down-sampling response line to obtain an up-sampling response line; calculating the number of scattering coincidence events corresponding to each up-sampling response line; The estimated objective function is: , Wherein, the Respectively representing the number of true coincidence events without subsequent processing; representing the number of scattered coincidence events Is the unknown quantity to be calculated, coefficient The calculation mode of (a) is as follows: , , Wherein, the And Is a probability density function of unscattered photons corresponding to two detection modules in the downsampled response line, And Is a scattered photon probability density function corresponding to two detection modules in the downsampling response line; wherein the calculation is acquired The value is the number of scatter coincidence events corresponding to the corresponding downsampled response line.
2. The scatter correction method according to claim 1, wherein the downsampling response line is based on detection data acquisition, comprising: acquiring a coincidence response line based on the detection data; and carrying out downsampling processing on the coincidence response line to obtain a downsampled response line.
3. The scatter correction method according to claim 2, characterized in that the detection data is acquired based on a target object.
4. The scatter correction method according to claim 1, wherein obtaining an estimated objective function corresponding to each downsampled response line using a moment estimation method based on a maximum likelihood-expectation maximization iterative algorithm, comprises: Based on each coincidence event corresponding to each downsampling response line, a two-dimensional instantaneous coincidence energy histogram, a two-dimensional delay coincidence energy histogram and two one-dimensional detection energy spectrums corresponding to each downsampling response line are obtained, and based on the two one-dimensional detection energy spectrums, a probability density function of scattered photons and a probability density function of unscattered photons corresponding to the corresponding downsampling response lines are obtained by adopting a maximum likelihood-expectation maximization iterative algorithm.
5. The scatter correction method of claim 4, wherein obtaining two one-dimensional detection spectra based on respective coincidence events for each downsampled response line comprises: Splitting all coincidence events corresponding to the downsampling response line into single events; dividing the single event into two parts according to the position information of the single event, wherein each part corresponds to one-dimensional detection energy spectrum; based on the divided two parts of single events, two one-dimensional detection energy spectrums are obtained.
6. The scatter correction method of claim 4, wherein obtaining probability density functions of scattered photons and unscattered photons corresponding to respective downsampled response lines using a maximum likelihood-expectation maximization iterative algorithm based on the two one-dimensional detection spectra comprises: Acquiring a corresponding relation function of a one-dimensional detection energy spectrum and a one-dimensional gamma photon energy spectrum; Based on the two acquired one-dimensional detection energy spectrums and a corresponding relation function, acquiring two one-dimensional gamma photon energy spectrums corresponding to the two one-dimensional detection energy spectrums by adopting a maximum likelihood-expectation maximization iterative algorithm and an initial iterative value corresponding to the acquired corresponding downsampling response line; and estimating probability density functions of two scattered photons and probability density functions of two unscattered photons corresponding to the corresponding downsampling response lines based on the two one-dimensional gamma photon energy spectrums.
7. The scatter correction method according to claim 6, wherein the one-dimensional detection energy spectrum and one-dimensional gamma photon energy spectrum correspond to a function of: , Wherein, the Representing an expected value of a one-dimensional detection energy spectrum which corresponds to a single downsampling response line and is obtained based on scanning of a target object; Representing a one-dimensional gamma photon energy spectrum, A fuzzy response matrix corresponding to a single downsampled response line is characterized, Representing a one-dimensional delay profile corresponding to a random coincidence event comprised by a single line of response.
8. The scatter correction method of claim 7, wherein the one-dimensional delay profile corresponding to the random coincidence event is obtained by delaying a coincidence event estimate.
9. The scatter correction method of claim 8, wherein obtaining a one-dimensional delay profile comprises: all delay coincidence events in the downsampling response line are acquired based on the delay coincidence window; dividing the delay single event into two parts according to the position information of the delay single event, wherein each part corresponds to one-dimensional delay energy spectrum; acquiring two one-dimensional delay energy spectrums based on the divided two part delay single events; wherein the position information of the delay single event includes position information of a down-sampling detection module detecting the delay single event.
10. The scatter correction method of claim 7, wherein a fuzzy response matrix is obtained Comprising the following steps: Acquiring prior detection data based on the prosthesis; acquiring an priori down-sampling response line based on priori detection data; dividing all prior coincidence events corresponding to the prior downsampling response line into prior instantaneous coincidence events and prior delay coincidence events; acquiring a priori one-dimensional instantaneous energy spectrum based on a priori instantaneous coincidence event corresponding to the downsampling response line; obtaining a difference value between the prior one-dimensional instantaneous energy spectrum and the prior one-dimensional delay energy spectrum, and carrying out normalization processing on the difference value to obtain a one-dimensional intermediate energy spectrum; and acquiring a fuzzy response matrix based on the one-dimensional intermediate energy spectrum.
11. The scatter correction method according to claim 6, wherein acquiring two one-dimensional gamma photon energy spectra corresponding to the two one-dimensional detection energy spectra comprises: Acquiring a maximum likelihood-expectation maximization iterative algorithm iterative formula based on a corresponding relation function of a one-dimensional detection energy spectrum and a one-dimensional gamma photon energy spectrum; Setting iteration times, and carrying out iteration to the set iteration times through a maximum likelihood-expected maximization iterative algorithm iteration formula based on the obtained initial iteration value to obtain two one-dimensional gamma photon energy spectrums corresponding to the two one-dimensional detection energy spectrums.
12. The scatter correction method according to claim 11, wherein the maximum likelihood-expectation maximization iterative algorithm iteration formula is: , Wherein, the In (a) and (b) A one-dimensional detection energy spectrum corresponding to a single downsampled response line and acquired based on scanning the target object is characterized, Characterization of the first in the energy Spectrum The area of the vertical bar is provided with a plurality of vertical bars, 、 Characterizing the first of the spectra respectively First, second The area of the vertical bar is provided with a plurality of vertical bars, Is the number of iterations that are performed, And In (a) and (b) For the fuzzy response matrix corresponding to the downsampled response line, The first fuzzy response matrix corresponding to the downsampled response line Line 1 The value of the column is used to determine, The first fuzzy response matrix corresponding to the downsampled response line Line 1 Values of columns; Representing a one-dimensional delay energy spectrum corresponding to a random coincidence event included in the downsampling response line; is the first +1 Iteration of the acquired energy spectrum One-dimensional gamma photon energy spectrum corresponding to each vertical bar area; 、 characterization of the first separately The first iteration of obtaining the energy spectrum First, second One-dimensional gamma photon energy spectrum corresponding to each vertical bar area.
13. The scatter correction method of claim 11, wherein obtaining an initial iteration value comprises: acquiring a global initial scattered photon energy spectrum; deblurring the global initial scattered photon energy spectrum to obtain a global intermediate initial iteration value; Stretching the global intermediate initial iteration value to obtain initial iteration values corresponding to the downsampling response lines.
14. The scatter correction method of claim 13, wherein obtaining a global initial scattered photon energy spectrum comprises: acquiring a coincidence response line based on the detection data; dividing all coincidence events corresponding to all coincidence response lines into instant coincidence events and random coincidence events; acquiring a global one-dimensional instantaneous energy spectrum based on the instantaneous coincidence event; Subtracting the global one-dimensional delay energy spectrum corresponding to the delay coincidence event from the global one-dimensional instantaneous energy spectrum corresponding to the instantaneous coincidence event on all the response lines to obtain a global one-dimensional undelayed energy spectrum; and acquiring an objective function of the global initial scattered photon energy spectrum based on the global one-dimensional undelayed energy spectrum.
15. The scatter correction method according to claim 14, wherein the objective function of the global initial scattered photon energy spectrum is: , wherein, among them, In (a) and (b) Is the global initial scattered photon energy spectrum; Characterization of the first in the energy Spectrum The area of the vertical bar is provided with a plurality of vertical bars, In (a) and (b) For a global one-dimensional undelayed spectrum, based on target object acquisition, In (a) and (b) A global one-dimensional intermediate energy spectrum obtained for scanning the whole PET system is obtained based on a prosthesis; And For the lower and upper thresholds of the set high energy window, Is the stretch coefficient.
16. The scatter correction method according to claim 15, wherein the acquisition Comprising the following steps: Acquiring prior detection data based on the prosthesis; acquiring all prior coincidence response lines based on prior detection data; dividing all prior coincidence events corresponding to all prior coincidence response lines into global prior instantaneous coincidence events and global prior delay coincidence events; Acquiring a global priori one-dimensional instantaneous energy spectrum based on the global priori instantaneous coincidence event; Obtaining the difference value between the global priori instantaneous energy spectrum and the global priori delay energy spectrum 。
17. The scatter correction method of claim 13, wherein deblurring the global initial scattered photon energy spectrum to obtain a global intermediate initial iteration value, comprising: Acquiring a deblurring processing iteration formula based on a maximum likelihood-expectation maximization iteration algorithm; Setting a priori initial iteration value and iteration conditions, and iterating through a deblurring processing iteration formula until the iteration conditions are reached, so as to obtain a scattering part of the global initial energy spectrum; estimating an unscattered portion of the global initial energy spectrum based on the scattered portion of the global initial energy spectrum; and acquiring a global intermediate initial iteration value based on the scattered part of the global initial energy spectrum and the unscattered part of the global initial energy spectrum.
18. The scatter correction method of claim 17, wherein the deblurring process iteration formula is: , Wherein, the In (a) and (b) The characterization is based on a global one-dimensional detection spectrum acquired by scanning the target object, Characterization of the first in the energy Spectrum The area of the vertical bar is provided with a plurality of vertical bars, 、 Characterizing the first of the spectra respectively A j-th vertical bar area, Is the number of iterations that are performed, 、 In (a) and (b) In the form of a global fuzzy response matrix, Is the first of the global fuzzy response matrix Line 1 The value of the column is used to determine, Is the first of the global fuzzy response matrix Line 1 Values of columns; Representing global one-dimensional delay energy spectrums corresponding to all random coincidence events; is the first +1 Iteration of the acquired energy spectrum Global one-dimensional gamma photon energy spectrum corresponding to each vertical bar area; 、 characterizing the kth iteration to obtain the energy spectrum First, second Global one-dimensional gamma photon energy spectrum corresponding to each vertical bar area; , Wherein, the The constants are characterized.
19. The scatter correction method of claim 18, wherein a global fuzzy response matrix is obtained Comprising the following steps: Acquiring prior detection data based on the prosthesis; acquiring all prior coincidence response lines based on prior detection data; dividing all prior coincidence events corresponding to all prior coincidence response lines into global prior instantaneous coincidence events and global prior delay coincidence events; Acquiring a global priori one-dimensional instantaneous energy spectrum based on the global priori instantaneous coincidence event; Obtaining a difference value between a global priori instantaneous energy spectrum and a global priori delay energy spectrum; Carrying out normalization processing on the difference value to obtain a global priori intermediate energy spectrum; and acquiring a global fuzzy response matrix based on the global priori intermediate energy spectrum.
20. The scatter correction method according to claim 17, characterized in that estimating the unscattered part of the global initial energy spectrum is performed by an estimation function, the estimation function being: , Wherein, the Is a global fuzzy response matrix; Is a super parameter; Is the ratio of unscattered photons to scattered photons; , Wherein, the The sum is represented by a sum, And Respectively correspond to 、。

Description

Scattering correction method, device, digitizing apparatus, and computer readable storage medium Technical Field The present application relates to the field of signal sampling technologies, and in particular, to a scatter correction method, a scatter correction device, a digitizing apparatus, and a computer readable storage medium. Background Positron emission tomography (Positron Emission Tomography, PET for short) works by labeling a radionuclide onto a compound capable of participating in a blood flow or metabolic process of living tissue, injecting the compound into a living body, and combining a positron emitted by the radionuclide in the living body with a negative electron in the living body, so that an annihilation event of an electron pair occurs, and two gamma photons with equal energy and opposite directions are generated. Since the flight directions of the two gamma photons are different, the times at which the two gamma photons are detected by the detector are also different. If two scintillation crystals located on a Line of Response (LOR) in the detector detect two gamma photons within a specified coincidence time window (e.g., 0-15 nanoseconds), respectively, then the event of detecting the two gamma photons may be referred to as a coincidence event. Coincidence events can generally include true coincidence events, scattered coincidence events, and random coincidence events. Wherein, a true coincidence event refers to an event in which the time difference between two gamma photons generated by the same annihilation event and reaching two scintillation crystals positioned on a line of response is within a coincidence time window. A random coincidence event is a false coincidence event in which two gamma photons detected are from different annihilation events, but are mistaken for two gamma photons occurring "simultaneously" within a coincidence time window. A scatter coincidence event refers to an event in which two gamma photons are generated for the same annihilation event detected, one of which changes the direction of flight due to physical effects such as compton scattering and/or rayleigh scattering occurring during the flight. Of these three coincidence events, this can affect the resolution, contrast, and positioning accuracy of PET imaging, as the data acquired for the random coincidence event and the scattered coincidence event can be erroneous. Therefore, correction of the acquired coincidence events appears to be critical. Currently, the more commonly used scatter correction methods mainly include a multi-energy window technique, a convolution/deconvolution technique, and a simulation-based technique. Among these techniques, the most accurate and most widely used is the simulation-based technique. Simulation-based techniques generally include single-scatter simulation methods, double-scatter simulation methods, and Monte Carlo simulation methods. The single scattering simulation method is to obtain a photon motion path of single scattering (i.e. a pair of gamma photons are scattered once in total) by selecting a scattering point in an input activity image and an attenuation image for each response line, obtain single scattering events on the response line by calculating single scattering events generated on all photon motion paths corresponding to the response line, and finally fit the obtained single scattering events by tail data only comprising scattering events through tail fitting technology (TAIL FITTING, abbreviated as TF) to obtain a stretching factor of a scattering coincidence event, and apply the stretching factor to all data to realize scattering correction. The double scattering simulation method is typically used in combination with the single scattering simulation method, which differs from the single scattering simulation method mainly in that the double scattering simulation method determines the photon motion path by two scattering points. The monte carlo simulation method determines the total scatter distribution mainly by simulating the motion of each gamma photon pair determined based on the input activity image and attenuation image. In carrying out the present application, the inventors have found that simulation-based techniques have at least the following problems: (1) The single scattering simulation method only considers the case of single scattering, however, in practice, the case of multiple scattering occurs, which may result in lower accuracy of the scattering correction result, and thus lower quality of the reconstructed image. Although the double-scattering simulation method and the Monte Carlo simulation method consider the situation of multiple scattering, the calculation process is complex and the calculation amount is large, the image reconstruction process can be dragged, and the efficiency is low. (2) The scattering event needs to be found before the activity image is reconstructed, but the scattering event needs to be known by a simulation-