PET (positron emission tomography) acquisition method and system dynamically conforming to time window

Abstract

The invention relates to a PET (positron emission tomography) acquisition method and system dynamically conforming to a time window. The method comprises the following steps: acquiring contour information of a measured target; generating a contour cylinder of each scanning bed according to the contour information; respectively determining a coincidence time window of each bed according to the distance between two farthest points on the surface of each profile cylinder in the PET view; pET data acquisition is carried out on each bed based on the coincidence time window of each bed; and performing PET data reconstruction on each bed based on the coincidence time window of each bed. The method has the beneficial effects that a corresponding coincidence time window is set for image scanning of each bed, so that the noise influence of random events on an imaging result is reduced, the signal-to-noise ratio of data is improved, and the imaging quality is improved.

Description

Technical Field

[0001] The present invention relates to the field of PET technology, and in particular to a PET acquisition method and system that dynamically matches a time window. Background Art

[0002] PET (Positron Emission Tomography) is a clinical diagnostic imaging technology in the field of nuclear medicine. Its basic principle is to inject a tracer with positron-emitting radionuclides into the body, and then detect the energy information, time information and position information of the 511keV gamma rays emitted in the opposite direction when the positrons are annihilated in vitro. Finally, the three-dimensional imaging technology is used to determine the enrichment position of the tracer nuclide by statistically reconstructing the location of the annihilation event. It has the characteristics of high sensitivity, good accuracy, and functional imaging, and is widely used in the diagnosis of tumors, cardiovascular and neurological diseases. Small animal PET is also widely used in pathological research, new drug metabolism dynamics and other research fields.

[0003] The data collected by the PET system can be divided into true events, scattered events and random events according to their relationship with imaging. A true event refers to an event in which two gamma photons after positron annihilation are directly detected by the detector of the PET system and recorded as a coincidence event. It is a "good" event that can normally reflect the annihilation point and has a positive effect on the imaging quality. A scattered event refers to an event in which one or both of the two gamma photons after positron annihilation are scattered in the detection field of the PET system and then detected by the detector of the PET system and recorded as a coincidence event. Its imaging exists as a "slow" variable around the annihilation point, which has a blurring effect on the imaging. The influence on the image must be removed by scattering correction. A random event is an event in which two unrelated gamma photons are detected within the time window instead of a gamma photon after positron annihilation in the PET field of view and recorded as a coincidence event. Random events exist as background noise in imaging and need to be corrected by random coincidence. The main influencing factor of random coincidence is the setting of the coincidence time window. The larger the coincidence time window, the more random coincidence events there are. Figure 1 This is a schematic diagram of true coincidence, scattered coincidence and random coincidence counting. Summary of the invention

[0004] Technical issues to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a PET acquisition method and system with dynamic time window compliance, which solves the technical problem of how to reduce the noise impact of random events on imaging results.

[0006] Technical Solution

[0007] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0008] In a first aspect, the present invention provides a PET acquisition method that is dynamically consistent with a time window, comprising:

[0009] Obtain the contour information of the target being measured;

[0010] Generate a contour cylinder of each scanning bed position according to the contour information;

[0011] The compliance time window for each bed is determined based on the distance between the two farthest points on the surface of each contour cylinder in the PET field of view;

[0012] PET data is collected for each bed based on the coincident time window of each bed;

[0013] The PET data of each bed is reconstructed based on the coincident time window of each bed.

[0014] Optionally, obtaining contour information of the target to be measured includes:

[0015] Before performing a PET scan, contour information of the target is obtained through CT reconstructed images in a PET / CT system, magnetic resonance reconstructed images in a PET / MR system, images acquired by an optical camera on a PET rack, images acquired by a surveillance camera in a scanning room, images acquired by a scanning radar, contour images acquired by other external detectors, or images after fusion processing of the above images.

[0016] Optionally, generating a contour cylinder of each scanning bed position according to the contour information includes:

[0017] The farthest distance from the center axis of the PET system in the contour information is taken as the radius, and the longest distance of the target to be measured in the PET scanning field of view of the current bed is taken as the length to generate a contour cylinder.

[0018] Optionally, the compliance time window is determined according to the following formula:

[0019] CW ij =2L ijmax / c+t e , among which CW ij is the matching time window of this scan, L ijmax is the distance between the two farthest points on the surface of the contour cylinder in the PET field of view, c is the speed of light, t e Extended time for protection.

[0020] Optionally, t e It is a fixed value or n times of the system time resolution, 1≤n≤10.

[0021] Optionally, the method further comprises:

[0022] In the case where the contour information of the measured target cannot be obtained, the time window is released for a short period of time to collect the corresponding data before the formal data collection of each bed;

[0023] Analyze the temporal spectrum distribution of short-term coincidence data;

[0024] The eligible time window for each bed was confirmed by removing the random count threshold method.

[0025] Optionally, the compliance time window for each bed is confirmed based on the random count threshold removal method, including:

[0026] The counting threshold N for removing random coincidences is calculated according to the following formula:

[0027] N=k×(PB)+B, where k is the threshold coefficient, P is the peak count of the short-term data time spectrum distribution, and B is the reference count of the mean of the short-term data time spectrum edge count;

[0028] The coincidence time window is determined according to the range of the short-time coincidence data time spectrum that reaches a count threshold N for removing random coincidences.

[0029] In a second aspect, the present invention provides a PET acquisition system that dynamically matches a time window, comprising:

[0030] An acquisition module is used to acquire the contour information of the target being measured;

[0031] A generation module generates a contour cylinder of each scanning bed according to the contour information;

[0032] A determination module determines the compliance time window for each bed according to the distance between the two farthest points on the surface of each contour cylinder in the PET field of view;

[0033] The acquisition module collects PET data for each bed based on the matching time window of each bed;

[0034] The reconstruction module reconstructs the PET data of each bed based on the matching time window of each bed.

[0035] In a third aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein when the program is executed, the dynamic time-windowed PET acquisition method described in any one of the first aspects above is implemented.

[0036] In a fourth aspect, the present invention provides a storage device, including a storage medium and a processor, wherein the storage medium stores a computer program, and when the program is executed by the processor, the PET acquisition method of dynamic time window compliance as described in any one of the first aspects above is implemented.

[0037] Beneficial Effects

[0038] The beneficial effects of the present invention are as follows: a PET acquisition method of the present invention dynamically conforms to a time window, designs a scanning mode that dynamically sets a conforming time window, evaluates the contour range of the measured target through a CT image or an image of an optical probe, and then plans the scanning contour range of each bed, and sets a corresponding conforming time window for the image scan of each bed, thereby reducing the noise impact of random events on the imaging results, improving the signal-to-noise ratio of the data, and improving the imaging quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of true coincidence, scattered coincidence and random coincidence counting provided by the present invention;

[0040] Figure 2 A schematic diagram of a flow chart of a PET acquisition method that dynamically complies with a time window provided by an embodiment of the present invention;

[0041] Figure 3 A schematic diagram of a dynamic time window acquisition mode flow chart provided by an embodiment of the present invention;

[0042] Figure 4 Comparison of NECR results between the dynamic time window acquisition mode provided by the embodiment of the present invention and the traditional acquisition mode;

[0043] Figure 5 The embodiment of the present invention provides a conforming time window confirmed according to the time spectrum distribution.

[0044] Description of Reference Numerals

[0045] 1: True coincidence count; 2: Scattered coincidence count; 3: Random coincidence count. DETAILED DESCRIPTION

[0046] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below in conjunction with the accompanying drawings through specific embodiments. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a clearer and more thorough understanding of the present invention and to be able to fully convey the scope of the present invention to those skilled in the art.

[0047] First, refer to Figure 2 This embodiment provides a PET acquisition method that dynamically complies with a time window, including:

[0048] S1, obtain the contour information of the target to be measured.

[0049] S2, generating a contour cylinder of each scanning bed position according to the contour information.

[0050] S3, determining the compliance time window for each bed according to the distance between the two farthest points on the surface of each contour cylinder in the PET field of view.

[0051] S4, collecting PET data for each bed based on the matching time window of each bed.

[0052] S5, reconstructing PET data for each bed based on the matching time window of each bed.

[0053] Data acquisition and reconstruction are performed in the planned time window, and the random coincidence correction of the image reconstruction of each bed is performed according to the corresponding time window setting.

[0054] Optionally, obtaining contour information of the target to be measured includes:

[0055] Before performing a PET scan, contour information of the target is obtained through CT reconstructed images in a PET / CT system, magnetic resonance reconstructed images in a PET / MR system, images acquired by an optical camera on a PET rack, images acquired by a surveillance camera in a scanning room, images acquired by a scanning radar, contour images acquired by other external detectors, or images after fusion processing of the above images.

[0056] Optionally, generating a contour cylinder of each scanning bed position according to the contour information includes:

[0057] The farthest distance from the center axis of the PET system in the contour information is taken as the radius, and the longest distance of the target to be measured in the PET scanning field of view of the current bed is taken as the length to generate a contour cylinder.

[0058] Attached is the cross section diagram of the cylinder Figure 3 ,In the figure, the middle black line is the central axis of the system, the black shaded block is the ,overall contour section of the target to be measured, and the rectangle is the ,section of the obtained cylindrical contour.

[0059] Optionally, the compliance time window is determined according to the following formula:

[0060] CW ij =2L ijmax / c+t e , among which CW ij is the matching time window of this scan, L ijmax is the distance between the two farthest points on the surface of the contour cylinder in the PET field of view, c is the speed of light, t e Extended time for protection.

[0061] Optionally, t eIt is a fixed value or n times of the system time resolution, 1≤n≤10.

[0062] Optionally, the method further comprises:

[0063] In the case where the contour information of the measured target cannot be obtained, the time window is released for a short period of time to collect the corresponding data before the formal data collection of each bed;

[0064] Analyze the temporal spectrum distribution of short-term coincidence data;

[0065] The eligible time window for each bed was confirmed by removing the random count threshold method.

[0066] Optionally, the compliance time window for each bed is confirmed based on the random count threshold removal method, including:

[0067] The counting threshold N for removing random coincidences is calculated according to the following formula:

[0068] N=k×(PB)+B, where k is a threshold coefficient, the range of k is 0.01-0.5, P is a peak count based on a short-term compliance with the data time spectrum distribution, and B is a reference count based on a short-term compliance with the data time spectrum edge count mean;

[0069] The coincidence time window is determined according to the range of the short-time coincidence data time spectrum that reaches a count threshold N for removing random coincidences.

[0070] For PET systems that are not easy to process the contour information of the scanned object, the range adjustment of the coincident time window can also be carried out by collecting coincident data for a short period of time under the setting of a larger time window, analyzing the coincident time distribution, and blocking the random coincident part according to the shape of the coincident time spectrum distribution.

[0071] By dynamically setting the coincidence time window, the coincidence time window is reduced as much as possible, and the noise disturbance of random coincidence on the image is reduced without reducing the true coincidence and scattered coincidence, thereby improving the image quality. The improvement effect is more obvious in the image scanning of small detection objects such as the head.

[0072] Random coincidence counts are noise components in the PET system. Reducing the coincidence time window setting of the system can improve the system's image signal-to-noise ratio and image quality. However, in order to ensure the detection field of view of the system, the traditional PET system sets the coincidence time window to a fixed value, which will introduce unnecessary random coincidence noise when scanning smaller targets. The present invention designs a PET data acquisition mode with a dynamic time window setting, which not only ensures that the acquisition results of the real coincidence data of the measured object are not lost, but also reduces the noise counts caused by random coincidence counts, improves the signal-to-noise ratio of the coincidence data, and improves the image quality.

[0073] The following takes a system noise equivalent count rate (NECR) evaluation as an example to further introduce a dynamic PET acquisition method of the present application that conforms to the time window:

[0074] The noise equivalent count rate reflects the ratio of the absolute number of photons acquired by the PET device to the square of the true coincidence event T, and reflects the proportional relationship between the system's "useful" signal and the total signal. It also reflects the system's ability to identify true coincidence events T and exclude "dirty" data such as scattering events S and accidental coincidence events R. The NECR capability will ultimately be reflected in the image's signal-to-noise ratio, and the PET system is a low signal-to-noise ratio system. The quality of the signal-to-noise ratio is more important than the quality of the resolution. Therefore, the system signal-to-noise ratio is the most important determining factor in the quality of PET imaging, and the NECR most directly reflects the quality of the system's signal-to-noise ratio.

[0075] The test model of the noise equivalent count rate is a plastic cylinder with a diameter of 20cm and a length of 70cm. During the test, the cylinder is placed in the PET system with its central axis coinciding with the central axis of the PET system. A line source is inserted into the through hole at the lower part of the inside, and the entire plastic cylinder acts as a scattering model.

[0076] Under the fixed time window system acquisition setting, the time window is set to 4ns, and then the data acquisition for the NECR test is performed.

[0077] In the dynamic time window PET acquisition system, a CT scan of the phantom is first performed to confirm that the maximum distance of the cylindrical contour surface in the PET field of view is 22 cm. Combined with the system time resolution of 300 ps, ​​using twice the system time resolution as the protective expansion time, the system time window can be set to:

[0078] CW ij =2L ijmax / c+t e =2×22 / 30+0.3×2≈2.10(ns)

[0079] Conduct NECR testing under the new time window setting.

[0080] Comparing the NECR results under the two time window settings, it can be seen that the system NECR result under the dynamic time window setting is better, and a better image signal-to-noise ratio can be obtained, especially under high activity conditions. Figure 4 .

[0081] In the second aspect, this embodiment provides a PET acquisition system that dynamically matches the time window, including: an acquisition module, which acquires the contour information of the measured target; a generation module, which generates the contour cylinder of each scanning bed according to the contour information; a determination module, which determines the matching time window of each bed according to the distance between the two points on the surface of each contour cylinder that are farthest apart in the PET field of view; an acquisition module, which performs PET data acquisition on each bed based on the matching time window of each bed; and a reconstruction module, which performs PET data reconstruction on each bed based on the matching time window of each bed. According to the PET acquisition system that dynamically matches the time window provided by this embodiment, since it is used to implement the steps of a PET acquisition method that dynamically matches the time window provided by the embodiment of the first aspect of the present invention, the PET acquisition system that dynamically matches the time window has all the technical effects of the PET acquisition method that dynamically matches the time window, which will not be repeated here.

[0082] In a third aspect, an embodiment of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein when the program is executed, the dynamic time-windowed PET acquisition method described in any one of the first aspects above is implemented.

[0083] In a fourth aspect, an embodiment of the present invention provides a storage device, including a storage medium and a processor, wherein the storage medium stores a computer program, and when the program is executed by the processor, the PET acquisition method of dynamic time window compliance as described in any one of the first aspects above is implemented.

[0084] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0085] Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention should also include these modifications and variations.

[0086] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may alter, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A dynamic PET acquisition method in accordance with a time window, characterized in that: include: Obtain the contour information of the target being measured; Generate a contour cylinder of each scanning bed position according to the contour information; The compliance time window for each bed is determined based on the distance between the two farthest points on the surface of each contour cylinder in the PET field of view; PET data is collected for each bed based on the coincident time window of each bed; The PET data of each bed is reconstructed based on the coincident time window of each bed.

2. A dynamic PET acquisition method with a time window according to claim 1, characterized in that: Obtain the contour information of the measured target, including: Before performing a PET scan, contour information of the target is obtained through CT reconstructed images in a PET / CT system, magnetic resonance reconstructed images in a PET / MR system, images acquired by an optical camera on a PET rack, images acquired by a surveillance camera in a scanning room, images acquired by a scanning radar, contour images acquired by other external detectors, or images after fusion processing of the above images.

3. A dynamic PET acquisition method with a time window according to claim 2, characterized in that: Generate the contour cylinder of each scanning bed according to the contour information, including: The farthest distance from the center axis of the PET system in the contour information is taken as the radius, and the longest distance of the target to be measured in the PET scanning field of view of the current bed is taken as the length to generate a contour cylinder.

4. A dynamic time-windowed PET acquisition method according to claim 3, characterized in that: The compliance time window is determined according to the following formula: CW ij =2L ijmax / c+t e , among which CW ij is the matching time window of this scan, L ijmax is the distance between the two farthest points on the surface of the contour cylinder in the PET field of view, c is the speed of light, t e Extended time for protection.

5. A dynamic time-windowed PET acquisition method according to claim 4, characterized in that: t e It is a fixed value or n times of the system time resolution, 1≤n≤10.

6. A dynamic time-windowed PET acquisition method according to claim 5, characterized in that: The method further comprises: In the case where the contour information of the measured target cannot be obtained, the time window is released for a short period of time to collect the corresponding data before the formal data collection of each bed; Analyze the temporal spectrum distribution of short-term coincidence data; The eligible time window for each bed was confirmed by removing the random count threshold method.

7. A dynamic time-windowed PET acquisition method according to claim 6, characterized in that: The eligible time window for each bed is confirmed by removing the random count threshold method, including: The counting threshold N for removing random coincidences is calculated according to the following formula: N=k×(PB)+B, where k is the threshold coefficient, P is the peak count of the short-term data time spectrum distribution, and B is the reference count of the mean of the short-term data time spectrum edge count; The coincidence time window is determined according to the range of the short-time coincidence data time spectrum that reaches a count threshold N for removing random coincidences.

8. A PET acquisition system with dynamic time window, characterized in that: include: An acquisition module is used to acquire the contour information of the target being measured; A generation module generates a contour cylinder of each scanning bed according to the contour information; A determination module determines the compliance time window for each bed according to the distance between the two farthest points on the surface of each contour cylinder in the PET field of view; The acquisition module collects PET data for each bed based on the matching time window of each bed; The reconstruction module reconstructs the PET data of each bed based on the matching time window of each bed.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the dynamic PET acquisition method with a time window as described in any one of claims 1 to 7 is implemented.

10. A storage device comprising a storage medium and a processor, wherein the storage medium stores a computer program, wherein: When the processor executes the computer program, the dynamic PET acquisition method consistent with the time window described in any one of claims 1 to 7 is implemented.

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