Information processing device, recording medium, and program

Abstract

To provide an information processing device for performing information processing using information on lifetime of a positronium.SOLUTION: An information processing device 1 provided herein is configured to receive a signal indicating detection of a pair of annihilation radiations radiated in opposite directions, and performing analysis and predetermined processing on variation in the number of detections of the annihilation radiations over time that is related to the lifetime of positrons emitted in a subject.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an information processing device, a recording medium, and a program for processing information related to PET (Positron Emission Tomography). [Background technology]

[0002] In the PET device, a pair of gamma rays is generated through the following process: 44 Sc is a positron (e + ) and emit gamma rays (prompt gamma rays) (β + The process includes three processes: the beta decay process (Ps production process), in which a positron interacts with an electron in a nearby molecule to form positronium, and the annihilation process, in which a positron interacts with an electron in a nearby molecule to generate a pair of gamma rays (annihilation radiation). The annihilation process can occur immediately after the beta decay process, or it can occur after the beta decay process, via the Ps production process. In the latter case, the time from beta decay to the annihilation process is delayed by the lifetime of Ps.

[0003] In conventional PET imaging, a pair of gamma rays generated during this annihilation process travels in opposite directions. The pair of annihilation rays is detected by detectors positioned on either side of a subject (such as a human body) containing electrons that generate the annihilation process. The location of the original radioisotope is determined by determining that the positron decay nucleus is located on the line of response (LOR) between the positions of the pair of detectors that detected the annihilation rays. The time-of-flight (TOF) information of the pair of annihilation rays is also used to limit the range of location. The Compton camera technology is also used to detect at least one of the prompt gamma ray and the pair of annihilation rays, thereby limiting the range of location. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Moskal P et al., Feasibility study of the positronium imaging with the J-PET tomograph, Phys. Med. Biol. 64 055017 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, in the information processing using the conventional PET device, information on the lifetime of positronium (Ps) has not been used. On the other hand, in recent years, attempts have been made to obtain medical information by visualizing the lifetime of this positronium (Non-Patent Document 1).

[0006] Under the circumstances described above, one of the objects of the present invention is to provide an information processing device, a recording medium, and a program for performing information processing using information on the lifetime of positronium. [Means for solving the problem]

[0007] One aspect of the present invention that solves the problems of the above-mentioned conventional examples is an information processing device that includes: a signal receiving means that receives a signal indicating that a pair of annihilation radiations emitted in opposite directions has been detected in a subject; a change amount analyzing means that acquires, based on the received signal, information on the change amount of the number of times annihilation radiations have been detected in a time series related to the lifetime of positrons emitted in the subject; and an estimation means that estimates, based on the acquired information on the change amount, the dissolved concentration of radicals near the source of the annihilation radiations.

[0008] In another aspect of the present invention, an information processing device includes: a signal receiving means for receiving a signal indicating that a pair of annihilation radiations emitted in opposite directions has been detected in a subject; a change amount analyzing means for acquiring, based on the received signal, information on the change amount of the number of times the annihilation radiations have been detected in a time series relating to the lifetime of positrons emitted in the subject, for each position where the pair of annihilation radiations are generated; and a component analyzing means for applying an inverse Laplace transform to the acquired change amount information, and acquiring information representing the proportion of the number of times each annihilation radiation is detected, for each annihilation radiation whose change amount with respect to time differs from each other. [Effects of the Invention]

[0009] According to the present invention, it is possible to perform information processing using information on the lifetime of positronium. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a block diagram illustrating an example of the configuration of an information processing device according to an embodiment of the present invention. [Figure 2] FIG. 1 is an explanatory diagram showing the relationship between the dissolved concentration of radical molecules and the amount of annihilation radiation generated. [Figure 3] 1 is a functional block diagram of an information processing device according to an embodiment of the present invention; [Figure 4] FIG. 2 is an explanatory diagram illustrating an example of information acquired by an information processing device according to an embodiment of the present invention. [Figure 5] FIG. 10 is a functional block diagram of another aspect of the information processing device according to the embodiment of the present invention. [Figure 6] 1 is an explanatory diagram illustrating an example of information output by an information processing device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention will be described with reference to the drawings. As shown in Fig. 1, an information processing device 1 according to the embodiment of the present invention includes a control unit 11, a storage unit 12, an operation unit 13, an output unit 14, and an interface unit 15. In one example of the present embodiment, the information processing device 1 is realized as a PET (Positron Emission Tomography) device and is connected to a detector 20.

[0012] That is, the information processing device 1 functions as a general PET device, and performs, for example, 44 Radioactive isotopes such as Sc are + It decays into a positron (e + ) and emits prompt gamma rays, and then the pair of gamma rays (hereinafter referred to as annihilation radiation) generated after the emission is detected by the detector 20. The information processing device 1 then obtains the coordinates of the generation position of the annihilation radiation (information representing the position of the voxel containing the generation position of the pair of annihilation radiation when the space including the subject is divided into virtual cubic voxels) from the position where the pair of annihilation radiations is detected and information on the time of flight (TOF) of each of the pair of annihilation radiations, or the line segment (LOR) connecting the two detection positions of the pair of annihilation radiations, or information on the LOR narrowed down by TOF. Alternatively, if prompt gamma rays or annihilation radiations undergo Compton scattering within the detector, the direction from which the prompt gamma rays or annihilation radiations originated can be detected from the scattering angle using a Compton camera. In this case, too, narrowed down position information (information identifying the position of the voxel or LOR) can be obtained by any combination of information on one or more directions and the LOR. Such a method using a Compton camera and a method using TOF may be used simultaneously.

[0013] The pair of annihilation rays is β + The positrons emitted by the decay interact with the electrons of nearby molecules to form positronium (Ps production process), and the positrons in the formed positronium interact with the electrons of nearby molecules to generate β +In some cases, the positron produced by the decay interacts directly with the electron of a nearby molecule, generating an annihilation radiation pair. In the following, the pair of annihilation radiation generated in these cases is called an annihilation radiation pair.

[0014] Experimentally, the amount of annihilation radiation generated without going through the Ps production process is the largest, and β + It is known that this occurs relatively quickly after decay (i.e., after prompt gamma radiation), and if it goes through the Ps production process, β + After decay, it takes time for the electron to interact with nearby molecules, so the time until annihilation radiation is generated is relatively delayed.

[0015] The control unit 11 is a program-controlled device such as a CPU, and operates according to a program stored in the storage unit 12. In this embodiment, the control unit 11 receives signals, etc., from the detector 20, indicating the time and position at which annihilation radiation pairs emitted in opposite directions were detected. The control unit 11 then generates the generation position of the annihilation radiation pair (information specifying the position of the voxel or the LOR).

[0016] The control unit 11 also controls the time series variation of the number of times annihilation radiation pairs are detected for each voxel or LOR. of Then, the control unit 11 executes a process of acquiring information. Chronological strange of In another example, the control unit 11 may perform a process of estimating the dissolved concentration of radicals near the source of the annihilation radiation pair based on the information. Chronological strange of It is also possible to apply an inverse Laplace transform to the information to obtain information representing the ratio of the number of times annihilation radiation pairs that change over time differently from each other are detected, and to perform processing using the obtained information. The details of these processes performed by the control unit 11 will be described later.

[0017] The storage unit 12 is a memory device, a disk device, or the like, and stores a program executed by the control unit 11. This program may be provided by being stored in a computer-readable, non-transitory recording medium and stored in the storage unit 12. The storage unit 12 also stores various data necessary for the processing of the control unit 11, and also operates as a work memory for the control unit 11.

[0018] The operation unit 13 includes a mouse, a keyboard, etc., and receives instructions from the user and outputs the contents of the instructions to the control unit 11. The output unit 14 is a display device or the like, and outputs information according to instructions input from the control unit 11.

[0019] The interface unit 15 is connected to the detector 20, and receives from the detector 20 a signal indicating that a prompt gamma ray has been detected and a signal indicating the time and position at which an annihilation radiation pair has been detected, and outputs the received signal to the control unit 11.

[0020] [Insights into the interaction between positronium and nearby molecules] Through experiments using a larger number of positronium atoms than in conventional experiments, the inventors have found that positronium atoms easily interact with radicals, and that the rate at which this interaction occurs is proportional to the concentration (dissolved concentration) in the vicinity of the radicals.

[0021] FIG. 2 is an explanatory diagram showing the results of measurements made by the inventors on the amount of annihilation radiation pairs generated per microsecond (positronium annihilation rate) when the abundance ratio of nitrogen N2, a non-radical molecule, and oxygen O2, a radical molecule, was varied.

[0022] As shown in FIG. 2, when the abundance ratio of oxygen O2 is represented by partial pressure pO2 on the horizontal axis and the number of annihilation radiation pairs generated per microsecond is measured and plotted for the cases of only nitrogen N2, air (N2:O2=approximately 8:2), and only oxygen O2, it can be seen that the number of annihilation radiation pairs generated per microsecond is proportional to the abundance ratio of oxygen O2.

[0023] In other words, if the dissolved concentration of oxygen O2 is written as p and the amount of annihilation radiation pairs generated, that is, the annihilation rate of positronium (described later) is written as 1 / τ, then the relationship between these is as follows:

number

[0024] [First example of control unit operation] Based on the above findings, the control unit 11 according to one example of this embodiment executes a program stored in the memory unit 12, thereby realizing a configuration that functionally includes a signal receiving unit 21, a change amount analysis unit 22, an estimation unit 23, and an output unit 24, as illustrated in FIG. 3.

[0025] Here, the signal receiving unit 21 receives a signal indicating that a prompt gamma ray has been detected and a signal indicating the time and position at which an annihilation radiation pair has been detected from the detector 20 connected via the interface unit 15. Furthermore, the signal receiving unit 21 generates information indicating the position at which annihilation radiation pairs have been generated by processing similar to that of a general PET device, and counts and records the number of times annihilation radiation pairs have been detected for each predetermined time and for each position at which annihilation radiation pairs have been generated (voxel or LOR).

[0026] Specifically, the signal receiving unit 21 counts and records the number of times annihilation radiation pairs are detected for each predetermined time period Δt from time t=0, for each position (voxel or LOR) at which annihilation radiation pairs are generated, as shown in Fig. 4. As a result, for each position (P) at which annihilation radiation pairs are generated, count values ​​are recorded such as the total number of times annihilation radiation pairs are detected from t=0 to t=Δt, the total number of times annihilation radiation pairs are detected from time t=Δt to t=2Δt, etc.

[0027] Here, the method for determining the time t=0 may be such that the time when a prompt gamma ray is detected is set as the time t=0.

[0028] The change amount analysis unit 22 refers to the count value of the number of times annihilation radiation pairs are detected in each of the above periods for each position where annihilation radiation pairs are generated, and calculates the change in the number of times annihilation radiation pairs are detected in time series for each position where annihilation radiation pairs are generated. of In this way, the change in the number of annihilation radiation pairs detected in this time series The transformation , in the subject Generate was positronium is related to the lifespan of the

[0029] Specifically, the change amount analysis unit 22 calculates the change in the count value of the number of times annihilation radiation pairs are detected in each of the above periods for each position where annihilation radiation pairs are generated, using a kind of exponential function.

number

[0030] The estimation unit 23 substitutes the calculated annihilation rate 1 / τ into equation (1) to calculate an estimated value of the dissolved concentration p of, for example, oxygen O2, which is a radical. The output unit 24 outputs the calculated estimated value p and presents it to the user as the dissolved concentration of the radical (here, oxygen O2) near the source of the annihilation radiation pair.

[0031] [Second example of control unit operation] Furthermore, the distribution of radicals near the location where positronium is generated within the subject may not be uniform. For example, if there are normal cells and cancerous cells within a human organ, the dissolved concentration of oxygen, which is a radical, within each cell will differ. In such cases, it may not be appropriate to fit the change in the count value of the number of times annihilation radiation pairs are detected with a single exponential function. That is, in such cases, instead of fitting function (2), it may be appropriate to use the sum of multiple types of exponential functions with different annihilation rates 1 / τi (i=1, 2, ...) for the change in the count value of the number of times annihilation radiation pairs are detected. For example,

number

[0032] Here, the necessary information is the value τi relating to the annihilation rate and the number Ii of positronium that reacts with radicals and annihilates at an annihilation rate of 1 / τi.

number

number

[0033] Therefore, the control unit 11 according to another example of the present embodiment executes a program stored in the storage unit 12, thereby realizing a configuration that functionally includes a signal receiving unit 21, a change amount analyzing unit 22′, a component analyzing unit 31, and a component information processing unit 32, as illustrated in Fig. 5. Here, components that are similar to those in the example of Fig. 3 are assigned the same reference numerals, and repeated explanations will be omitted.

[0034] The change amount analysis unit 22' calculates the count value S(t) of the number of times annihilation radiation pairs are detected in each of the above periods for each position where annihilation radiation pairs are generated, output by the signal reception unit 21, as a function of the change in the number of times annihilation radiation pairs are detected in time series for each position where annihilation radiation pairs are generated. of The information is acquired and output to the component analysis unit 31.

[0035] The component analysis unit 31 analyzes the variation of the number of detections of annihilation radiation pairs in the time series output by the variation analysis unit 22'. of The inverse Laplace transform is applied numerically to the information. Specifically, the widely known CONTIN method, which uses Tikhonov regularization, can be used for this numerical inverse Laplace transform. The CONTIN method is widely known, so a detailed explanation of its contents will be omitted.

[0036] That is, the component analysis unit 31

number

[0037] Then, the component analysis unit 31 uses the CONTIN method to find Ii corresponding to τi that minimizes the following J through successive iterative calculations:

number

[0038] The component analysis unit 31 obtains Ii (i=1, 2..., n) that minimizes J by the above-mentioned successive iterative calculation, and outputs them together with the corresponding τi to the component information processing unit 32. Although in this example, the component analysis unit 31 numerically performed the inverse Laplace transform by the CONTIN method using successive iterative calculation, as long as Ii and τi that minimize J can be obtained, the component analysis unit 31 may use any method for the inverse Laplace transform, such as an analytical method or a numerical solution method different from the CONTIN method.

[0039] The component information processing unit 32 substitutes the extinction rate 1 / τi (i=1, 2, ..., n) calculated by a predetermined calculation that minimizes J or by specifying τi into equation (1) to calculate an estimated value of the dissolved concentration pi of the radical (e.g., oxygen O2) corresponding to τi. Here, τi is determined as an ordered number in an arithmetic (or geometric) progression, so if the numbers are arranged in order of magnitude, the values ​​of the dissolved concentration pi proportional to 1 / τi will also be ordered numbers and can be arranged in order of magnitude.

[0040] The component information processor 32 plots the magnitude of the corresponding Ii (Ii corresponding to τi used to estimate pi) with the dissolved concentration pi on the horizontal axis, and outputs the plot. The plot results differ for each part of the subject (i.e., the position where the annihilation radiation pair is generated), and represent the distribution of the dissolved oxygen concentration for each position where the annihilation radiation pair is generated, as shown in FIGS. 6(a) and 6(b).

[0041] The component information processing unit 32 outputs and presents to the user the distribution of dissolved oxygen concentration as shown in FIG. 6 according to the pair of Ii and τi determined for each position where an annihilation radiation pair is generated.

[0042] For example, if the subject is a human body, the area to the left of point X in Figure 6 (the side with a lower dissolved oxygen concentration) indicates that the tissue surrounding the location where the annihilation radiation pair is generated is hypoxic. For example, since cancerous cells are more susceptible to hypoxia than normal cells, the distribution of cancerous cells is shown by the output.

[0043] [Variations] The component analysis unit 31 modifies the second term of equation (4) as follows: The CONTIN method may be implemented using TIFF0007761822000014.tif22170.

[0044] Background It is well known that when the number of prompt gamma rays or annihilation radiation pairs detected by the detector 20 becomes large, non-constant background noise is generated (e.g., Coleman PG, et al., “A method of improving the statistical accuracy in measurements on positrons annihilating in gases”, J. Phys., E5, 376-378, 1972).

[0045] In other words, the time when a prompt gamma ray is detected is set to t=0, and the β + When trying to obtain the time t at which a decay-derived (i.e., corresponding) annihilation radiation pair is detected, if there are a large number of prompt gamma rays and annihilation radiation pairs detected, it may not be possible to match the prompt gamma ray representing time t = 0 with the corresponding annihilation radiation pair. Therefore, the detection rate of annihilation radiation pairs per unit time, η, is used. In this case, the probability of detecting an annihilation radiation pair within a certain time ΔT (where ΔT is sufficiently short so that 0≦ηΔT<<1) is ηΔT, and the probability of not detecting an annihilation radiation pair is 1-ηΔT.

[0046] Therefore, the rate at which annihilation pairs are detected by a certain time t1 (the magnitude of the background noise) is

number

[0047] Therefore, using this result, we take into account the non-constant background noise and rewrite equation (3) as follows:

number

[0048] Furthermore, when equation (5) is used instead of equation (3), equations (4) and (4') become It is transformed into TIFF0007761822000017.tif48170.

[0049] In this example, the component analysis unit 31 executes a sequential iterative calculation (modified CONTIN method) similar to the CONTIN method using equation (6) instead of equations (4) and (4'), and obtains a set of Ii, τi (i = 1, 2..., n) that minimizes J. Note that in the first term of equation (6), The division by TIFF0007761822000018.tif32170 takes into account that the measurement of annihilation radiation pairs is performed by counting, and is intended to normalize the reliability of the data by the uncertainty due to the counting measurement. [Explanation of symbols]

[0050] 1 information processing device, 11 control unit, 12 memory unit, 13 operation unit, 14 output unit, 15 interface unit, 20 detector, 21 signal receiving unit, 22, 22' change amount analysis unit, 23 estimation unit, 24 output unit, 31 component analysis unit, 32 component information processing unit.

Claims

1. signal receiving means for receiving a signal indicating that a pair of annihilation radiation beams emitted in opposite directions have been detected in the subject; an annihilation rate analysis means for acquiring information on the annihilation rate of positronium from the number of detections of time-series annihilation radiation emitted in the subject based on the received signal; an estimation means for estimating a dissolved concentration of radicals in the vicinity of a source of the annihilation radiation based on the acquired information on the annihilation rate of positronium; An information processing device comprising:

2. 2. The information processing device according to claim 1, the annihilation rate analysis means acquires information about the annihilation rate of the positronium by fitting at least one type of exponential function to a change in the time series of detected annihilation radiation emitted in the subject; The estimation means is an information processing device that estimates the dissolved concentration of radicals in the vicinity of the source of the annihilation radiation as an amount proportional to information on the annihilation rate of the positronium.

3. 3. The information processing device according to claim 1, The radical is an oxygen molecule.

4. signal receiving means for receiving a signal indicating that a pair of annihilation radiation beams emitted in opposite directions have been detected in the subject; an annihilation rate analysis means for acquiring information on the annihilation rate of positronium from the number of detections of the time-series annihilation radiations emitted in the subject for each generation position of the pair of annihilation radiations based on the received signal; a component analysis means for applying an inverse Laplace transform to the acquired information on the annihilation rate of positronium, and acquiring information representing the ratio of the number of times each annihilation radiation is detected, for each annihilation radiation having a different annihilation rate with respect to time; An information processing device comprising:

5. 5. The information processing device according to claim 4, an information processing device that estimates the dissolved concentration of radicals in the vicinity of a source of generation of the annihilation radiation as an amount proportional to the annihilation rate of positronium with respect to the time, based on information obtained by the component analysis means that indicates the ratio of the number of times that the annihilation radiation is detected to the dissolved concentration of the radical, and obtains and outputs information that indicates, for each generation position of the pair of annihilation radiations, the ratio of the number of times that the annihilation radiation is detected to the dissolved concentration of the radical.

6. 6. The information processing device according to claim 4, The component analysis means is an information processing device that performs a calculation by applying an inverse Laplace transform to the received signal, assuming time-dependent background noise.

7. Computer, signal receiving means for receiving a signal indicating that a pair of annihilation radiation beams emitted in opposite directions have been detected in the subject; an annihilation rate analysis means for acquiring information on the annihilation rate of positronium from the number of detections of time-series annihilation radiation emitted in the subject based on the received signal; an estimation means for estimating a dissolved concentration of radicals near a source of the annihilation radiation based on the acquired information on the annihilation rate; A computer-readable recording medium storing a program that functions as a

8. Computer, signal receiving means for receiving a signal indicating that a pair of annihilation radiation beams emitted in opposite directions have been detected in the subject; an annihilation rate analysis means for acquiring information on the annihilation rate of positronium from the number of detections of the time-series annihilation radiations emitted in the subject for each generation position of the pair of annihilation radiations based on the received signal; a component analysis means for applying an inverse Laplace transform to the acquired information on the annihilation rate of the positronium, and acquiring information representing the ratio of the number of times each annihilation radiation is detected, for each annihilation radiation having a different annihilation rate of the positronium with respect to time; A computer-readable recording medium storing a program that functions as a

9. Computer, signal receiving means for receiving a signal indicating that a pair of annihilation radiation beams emitted in opposite directions have been detected in the subject; an annihilation rate analysis means for acquiring information on the annihilation rate of positronium from the number of detections of time-series annihilation radiation emitted in the subject based on the received signal; an estimation means for estimating a dissolved concentration of radicals in the vicinity of a source of the annihilation radiation based on the acquired information on the annihilation rate of positronium; A program that functions as a

10. Computer, signal receiving means for receiving a signal indicating that a pair of annihilation radiation beams emitted in opposite directions have been detected in the subject; an annihilation rate analysis means for acquiring information on the annihilation rate of positronium from the number of detections of the time-series annihilation radiations emitted in the subject for each generation position of the pair of annihilation radiations based on the received signal; a component analysis means for applying an inverse Laplace transform to the acquired information on the annihilation rate of the positronium, and acquiring information representing the ratio of the number of times each annihilation radiation is detected, for each annihilation radiation having a different annihilation rate of the positronium with respect to time; A program that functions as a

Images