Method for positive-positron element detection and imaging using time-of-flight positron emission tomography
By measuring the three-photon and two-photon emission count rates and applying scattering correction, the problem of the inability to measure the decay lifetime of o-Ps in the prior art has been solved, enabling tissue health assessment under gamma-ray-free conditions and improving the accuracy and efficiency of the assessment.
Patent Information
- Application Number
- CN202380099529.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-06-20
- Publication Date
- 2026-01-23
AI Technical Summary
Existing technologies make it difficult to measure the decay lifetime of positron-positron (o-Ps) without relying on transient gamma rays, resulting in an inability to accurately assess the health status of tissues.
The decay lifetime of positron-positron elements (o-Ps) is calculated by measuring the count rates of three-photon emission associated with the first positron decay mode and two-photon emission associated with the second positron decay mode, applying a scattering correction factor, and the health status of the tissue is assessed based on this lifetime.
This enables accurate measurement of the decay lifetime of o-Ps under conditions without transient gamma rays, improving the accuracy and efficiency of tissue health assessment.
Smart Images
Figure CN121398748A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present invention relates generally to positron emission tomography (PET), and in particular to a method of imaging tissue by measuring the decay lifetime of ortho-positronium generated from positrons emitted from a radiopharmaceutical injected into a patient. BACKGROUND
[0002] Positron emission tomography can be used to diagnose and characterize cancerous tissue. A radiopharmaceutical, such as fluorodeoxyglucose (FDG) containing positron emitting radionuclide 18 F, is injected into a patient. FDG will be taken up in areas of the body that exhibit a high metabolic rate, which can be an indication of cancer. Once the radiopharmaceutical has been distributed within the body, the emitted positrons can be subsequently imaged to isolate regions of interest (ROIs) with high metabolic uptake. Positrons emitted in a given tissue or ROI either undergo direct annihilation with a free electron or combine with an electron to form positronium (Ps). Ps can either be para-positronium (p-Ps), in which the spins of the positron and electron are antiparallel, or ortho-positronium (o-Ps), in which the spins of the positron and electron are parallel.
[0003] The lifetime of o-Ps depends on the material in which it resides. Current procedures for measuring the lifetime of o-Ps require the emission of prompt gamma rays to mark the start time. However, the vast majority of radiopharmaceuticals, such as FDG, do not emit prompt gamma rays. It is therefore desirable to be able to measure the lifetime of Ps without the need for prompt gamma rays. SUMMARY
[0004] A method of measuring a health condition of a tissue is disclosed. The method includes introducing a radiopharmaceutical radionuclide into the tissue, wherein the radiopharmaceutical radionuclide emits positrons; measuring a first count rate indicative of three-photon emission associated with a first decay mode of the positrons; measuring a second count rate indicative of two-photon emission associated with a second decay mode of the positrons; applying a scatter correction factor to each of the first count rate and the second count rate to account for scattered and attenuated annihilation photons in the tissue; determining a ratio of the first count rate and the second count rate; determining a decay lifetime of ortho-positronium (o-Ps) based on the ratio; and determining the health condition of the tissue based on the decay lifetime of the o-Ps.
[0005] Also disclosed herein are devices for measuring a health condition of a tissue. The device includes a plurality of sensors for detecting events associated with positron decay emitted from a pharmaceutical radionuclide in the tissue, and a processor. The processor is configured to: measure a first count rate indicative of three-photon emission associated with a positron first decay mode; measure a second count rate indicative of two-photon emission associated with a positron second decay mode; apply a scatter correction factor to each of the first count rate and the second count rate to account for scattered and attenuated annihilation photons in the tissue; determine a ratio of the first count rate and the second count rate; determine a decay lifetime of ortho-positronium (o-Ps) based on the ratio; and determine the health condition of the tissue based on the decay lifetime of the o-Ps.
[0006] Also disclosed herein are positron emission tomography (PET) scanners. The PET scanner includes a plurality of sensors for detecting events associated with positron decay emitted from a pharmaceutical radionuclide in a tissue, and a processor. The processor is configured to: measure a first count rate indicative of three-photon emission associated with a positron first decay mode; measure a second count rate indicative of two-photon emission associated with a positron second decay mode; apply a scatter correction factor to each of the first count rate and the second count rate to account for scattered and attenuated annihilation photons in the tissue; determine a ratio of the first count rate and the second count rate; determine a decay lifetime of ortho-positronium (o-Ps) based on the ratio; and determine the health condition of the tissue based on the decay lifetime of the o-Ps. BRIEF DESCRIPTION OF DRAWINGS
[0007] These and other features, aspects, and advantages of the present application will become better understood with reference to the following description and appended claims, taken in conjunction with the accompanying drawings, where: Figure 1 A positron emission tomography scanner is shown in illustrative embodiments; Figure 2 A chart depicting various positron decay modes is shown; Figure 3 Spin states of para-positronium (p-Ps) are shown; Figure 4 Spin states of ortho-positronium (o-Ps) are shown; Figure 5 A three-dimensional grid depicting 3-photon decay of o-Ps is shown in illustrative embodiments; Figure 6 A relationship between measured o-Ps decay lifetime and o-Ps decay rate for a variety of materials is shown; and Figure 7A flowchart showing a method for measuring o-Ps decay due to a pharmaceutical radioactive tracer injected in tissue is shown.
[0008] It should be understood that the various embodiments are not limited to the arrangements and tools shown in the drawings. DETAILED DESCRIPTION
[0009] The present application can be more easily understood with reference to the following detailed description of preferred embodiments of the application and the examples included therein. All numerical values taken in this document are modified by the term "about" unless expressly indicated otherwise. The term "about" generally refers to a numerical range that a person of skill in the art would consider equivalent to the recited value (i.e., having the same function or result). In many instances, the term "about" can include numbers rounded to the nearest significant figure.
[0010] Figure 1 A positron emission tomography scanner (PET scanner 100) in an illustrative embodiment is shown. The PET scanner 100 includes a ring-shaped housing 102 having a plurality of sensors 104a-n disposed circumferentially around a hole 106 formed by the ring-shaped housing 102. A platform 108 can be moved into and out of the hole 106, and a person 110 or another organism lies on the platform 108 to be placed in the PET scanner 100. The person 110 is injected with a positron-emitting pharmaceutical radionuclide, such as fluorodeoxyglucose (FDG). The pharmaceutical radionuclide is absorbed at a higher rate generally in any cancerous tissue in the person 110. The pharmaceutical radionuclide emits positrons, and the sensors 104a-n measure annihilation photons emitted by various decay modes of the positrons. A processor 120 receives data from the sensors 104a-n and calculates various quantities discussed herein that are used to evaluate the health of tissue in the person 110 or to obtain additional diagnostic information about a suspected cancerous lesion (such as whether the lesion is hypoxic).
[0011] Figure 2 A chart 200 depicting various decay modes of positrons is shown. The decay process of the chart 200 begins with a radionuclide 202, which has been injected into a person for illustrative purposes. The radionuclide 202 emits a positron 204. The positron 204 can decay by direct annihilation 206 with a free electron, resulting in a two-photon emission (2-photon emission) that is detected at the PET scanner 100. Alternatively, the positron 204 can combine with a free electron to form a positronium (Ps) 208. The Ps 208 can be either in the form of ortho-positronium (o-Ps) or para-positronium (p-Ps). As Figure 3The p-Ps shown comprise positron 206 and electron 302 with antiparallel spin states (e.g., +1 / 2, -1 / 2). p-Ps have a time span of 125 picoseconds (τ) in vacuum. p =125ps) decay lifetime. For example Figure 4 The o-Ps shown comprise positron 206 and electron 302 with parallel spin states (e.g., +1 / 2, +1 / 2). o-Ps have a time interval of 142 nanoseconds (τ) in vacuum. o The decay lifetime is 142 ns.
[0012] Refer to again Figure 2 p-Ps 208b can be converted to o-Ps 208a via spin exchange interaction 214, and vice versa. o-Ps 208b decays primarily via two-photon emission 210, which is detected by PET scanner 100. o-Ps 208a decays primarily via three-photon emission (three-photon emission 212), which is detected by PET scanner 100.
[0013] Figure 5 A three-dimensional grid 500 depicts the three-photon decay of o-Ps in an illustrative embodiment. o-Ps is located at the source location 502. The decay of o-Ps generates three photons 504, 506, and 508, which are detected as events by a PET scanner 100 (represented by blue cylinders 510). i 1 , i 2 and i 3 .
[0014] Energy conservation and momentum conservation can be applied to events. i 1 , i 2 , i 3 The three-photon events are classified as o-Ps decay. Various criteria are set for events i1, i2, and i3 to identify the presence of o-Ps decay. One criterion is that for each event ( i 1 , i 2 , i 3) have energies less than 550 keV and the sum of the event energies is in the range of 1022 + / - 100 keV. Another criterion is that the plane of the interaction (i.e., plane 512) containing the three photons 504, 506, 508 contains the source location 502. Alternatively, the spherical back-projections of the photons 504, 506, 508 should intersect at the same location (within a chosen criterion). This same location is then identified as the source location 502. Another criterion is that the emission angles between the photons 504, 506, 508 are less than 170° and greater than 10°. Another criterion is that the emission interval of the photons 504, 506, 508 is within 100 ps.
[0015] Figure 6 A relationship 600 between the measured o-Ps decay lifetime and the o-Ps decay rate is shown. The o-Ps decay lifetime is shown along the horizontal axis in nanoseconds (ns). The o-Ps count rate is shown along the vertical axis in counts per second (cps). Data points are shown for aluminum 602, quartz 604, and polycarbonate 606. The relationship 600 shows that the o-Ps decay lifetime varies with the material in which the positron-positron decay resides. Thus, a relationship such as that shown in FIG. 6B can be used with the decay lifetime to determine the type of tissue as well as the health of the tissue. Figure 6
[0016] For example, hypoxic liver tissue has a dissolved oxygen concentration of about 6 mmHg, while healthy liver tissue has a dissolved oxygen concentration of about 40 mmHg. Oxygen that interacts with Ps can cause Ps to undergo spin exchange 214. Due to the spin exchange from the oxygen, hypoxic liver tissue will exhibit a different o-Ps lifetime relative to healthy liver tissue. Thus, the lifetime of the o-Ps decay can be used to determine the concentration of oxygen in the liver tissue and, thus, whether the liver tissue is hypoxic or healthy.
[0017] Figure 7 A flowchart 700 of a method for determining tissue type as well as tissue health from detection of o-Ps decay due to a pharmaceutical radionuclide injected into a patient is shown. The method begins in block 702, where a pharmaceutical radionuclide (e.g., FDG) is introduced into a person and the person is placed in a PET scanner 100. The pharmaceutical radionuclide tends to be absorbed at a higher rate in cancerous tissue and not absorbed (or absorbed to a lesser extent) by non-cancerous tissue. The pharmaceutical radionuclide emits positrons that decay with respect to various modes discussed above. Figure 2
[0018] At block 704, photon emission events are recorded at a PET scanner. At block 706, the recorded events are processed in a processor to determine a first count rate of three-photon emission and a second count rate indicative of a number of two-photon emissions. The first count rate is indicative of decay of o-Ps. The second count rate is indicative of a combination of direct annihilation and decay of p-Ps. At block 708, scatter corrections are applied to the first count rate and the second count rate to account for attenuation and scattering of the annihilating photons due to effects within the body / tissue / patient. At block 710, a ratio of the (corrected) first count rate to the (corrected) second count rate is formed. The ratio provides a normalization of the first count rate from which a decay rate of the ortho-positronium can be determined. At block 712, a decay lifetime of the ortho-positronium is determined from the decay rate. At block 714, a tissue composition is determined from the decay lifetime of the o-Ps. Thus, a health condition of the tissue is determined from the decay lifetime of the o-Ps.
[0019] In various embodiments, the processor 120 can run a machine learning program that determines a health condition, an oxygen concentration, and / or an amount of hypoxic tissue of the tissue based on the decay lifetime of the o-Ps, as disclosed herein. The machine learning program can be a neural network. The program can be trained using known datasets or using one or more tissues with known composition or known hypoxic grade, etc. The trained program can receive decay data related to positron decay at the tissue under test from the scanner sensors and output a health condition of the tissue under test.
[0020] While the application has been described in considerable detail with respect to certain preferred versions thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.
[0021] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which forms a part of the disclosure. All papers and documents are incorporated herein by reference.
[0022] Unless otherwise indicated, all features disclosed in the specification, including any accompanying claims, abstract, and drawings, can be replaced by alternative features that are functionally equivalent. Thus, each feature disclosed in the specification is one example of a generic series of equivalent or similar features.
[0023] No element, act, or instruction used in the description of the present application should be construed as an abandonment of a right to a claim, or a portion thereof, as the existence of multiple elements in a claim is an indication of the existence of multiple claim limitations. No element, act or instruction used in the description of the application should be construed as an abandonment of a right to a claim, or a portion thereof, as the existence of multiple elements in a claim is an indication of the existence of multiple claim limitations. No element, act or instruction used in the description of the application should be construed as an abandonment of a right to a claim, or a portion thereof, as the existence of multiple elements in a claim is an indication of the existence of multiple claim limitations.
Claims
1. A method for measuring the health status of an organization, comprising: Introducing a drug radionuclide into a tissue, wherein the drug radionuclide emits positrons; A first count rate is measured, which indicates three-photon emission associated with a first decay mode of the positron; A second count rate is measured, which indicates two-photon emission associated with the second decay mode of the positron; A scattering correction factor is applied to each of the first count rate and the second count rate to account for scattered and attenuated annihilated photons in the tissue; Determine the ratio of the first count rate to the second count rate; The decay lifetime of the positron-positron (o-Ps) is determined based on the stated ratio; and The health status of the tissue is determined based on the decay lifetime of o-Ps.
2. The method of claim 1, wherein, The pharmaceutical radionuclide is a fluorodeoxyglucose (FDG) comprising 18 F.
3. The method of claim 1, further comprising: The amount of the drug radionuclide in the tissue is determined, and the health status of the tissue is determined based on the decay lifetime of the o-Ps in the tissue.
4. The method of claim 1, further comprising: The oxygen concentration in the tissue is determined from the decay lifetime of the o-Ps.
5. The method of claim 4, further comprising: The amount of hypoxic tissue is determined from the oxygen concentration.
6. The method according to claim 1, further comprising: Three events are detected, and the occurrence of the three-photon emission is determined when the three events meet one or more criteria.
7. The method according to claim 6, wherein, The one or more criteria include at least one of the following: (i) each event is less than 550 keV; (ii) the sum of the event energies is in the range of 1022 + / - 100 keV; (iii) the interaction planes of the photons intersect at the source location; (iv) the emission angle between photons is less than 170º and greater than 10º; and (v) the emission interval between photons is within 100 picoseconds.
8. The method according to claim 1, wherein, The first decay mode is the decay of o-Ps.
9. The method according to claim 1, wherein, The second decay mode includes at least one of p-Ps decay and the direct annihilation of the positron.
10. A device for measuring tissue health status, comprising: Multiple sensors are used to detect events associated with positron decay emitted from drug radionuclides in the tissue; The processor is configured as follows: A first count rate is measured, which indicates three-photon emission associated with a first decay mode of the positron; A second count rate is measured, which indicates two-photon emission associated with the second decay mode of the positron; A scattering correction factor is applied to each of the first count rate and the second count rate to account for scattered and attenuated annihilated photons in the tissue; Determine the ratio of the first count rate to the second count rate; The decay lifetime of the positron-positron (o-Ps) is determined based on the stated ratio; and The health status of the tissue is determined based on the decay lifetime of o-Ps.
11. The device according to claim 10, wherein, The processor is also configured to operate a machine learning program based on o-Ps decay lifetime to determine the health status of the tissue.
12. The device according to claim 10, wherein, The processor is also configured to determine the amount of the drug radionuclide in the tissue and to determine the health status of the tissue based on the decay lifetime of the o-Ps in the tissue.
13. The device according to claim 10, wherein, The processor is also configured to determine the oxygen concentration in the tissue from the decay lifetime of the o-Ps.
14. The device according to claim 13, wherein, The processor is also configured to determine the region of hypoxic tissue from the oxygen concentration.
15. The device according to claim 10, wherein, The plurality of sensors are also configured to detect three events, and the processor is also configured to determine the occurrence of the three-photon emission when the three events meet one or more criteria.
16. The device according to claim 15, wherein, The one or more criteria include at least one of the following: (i) each event is less than 550 keV; (ii) the sum of the event energies is in the range of 1022 + / - 100 keV; (iii) the interaction planes of the photons intersect at the source location; (iv) the emission angle between photons is less than 170º and greater than 10º; and (v) the emission interval between photons is within 100 picoseconds.
17. The device according to claim 10, wherein, The first decay mode is o-Ps decay, and the second decay mode includes at least one of p-Ps decay and direct annihilation of the positron.
18. A positron emission tomography (PET) scanner, comprising: Multiple sensors are used to detect events associated with positron decay emitted from drug radionuclides in the tissue; The processor is configured as follows: A first count rate is measured, which indicates three-photon emission associated with a first decay mode of the positron; A second count rate is measured, which indicates two-photon emission associated with the second decay mode of the positron; A scattering correction factor is applied to each of the first count rate and the second count rate to account for scattered and attenuated annihilated photons in the tissue; Determine the ratio of the first count rate to the second count rate; The decay lifetime of the positron-positron (o-Ps) is determined based on the stated ratio; and The health status of the tissue is determined based on the decay lifetime of o-Ps.
19. The PET scanner according to claim 18, wherein, The processor is also configured to determine the amount of the drug radionuclide in the tissue and to determine the health status of the tissue based on the decay lifetime of the o-Ps in the tissue.
20. The PET scanner of claim 18, wherein, The plurality of sensors are further configured to detect three events, and the processor is further configured to determine the occurrence of the three-photon emission when the three events meet one or more criteria, wherein the one or more criteria include at least one of the following: (i) each event is less than 550 keV; (ii) the sum of the event energies is in the range of 1022 + / - 100 keV; (iii) the interaction planes of the photons intersect at the source location; (iv) the emission angle between the photons is less than 170º and greater than 10º; and (v) the emission interval between the photons is within 100 picoseconds.